WIP: conversion to Fluid (#47)

src/MyWebLog/Caches.fs

@@ -180,70 +180,6 @@ module CategoryCache =
     }
 
 
-/// Cache for parsed templates
-module TemplateCache =
-    
-    open System
-    open System.Text.RegularExpressions
-    open DotLiquid
-    
-    /// Cache of parsed templates
-    let private _cache = ConcurrentDictionary<string, Template> ()
-    
-    /// Custom include parameter pattern
-    let private hasInclude = Regex("""{% include_template \"(.*)\" %}""", RegexOptions.None, TimeSpan.FromSeconds 2)
-    
-    /// Get a template for the given theme and template name
-    let get (themeId: ThemeId) (templateName: string) (data: IData) = backgroundTask {
-        let templatePath = $"{themeId}/{templateName}"
-        match _cache.ContainsKey templatePath with
-        | true -> return Ok _cache[templatePath]
-        | false ->
-            match! data.Theme.FindById themeId with
-            | Some theme ->
-                match theme.Templates |> List.tryFind (fun t -> t.Name = templateName) with
-                | Some template ->
-                    let mutable text = template.Text
-                    let mutable childNotFound = ""
-                    while hasInclude.IsMatch text do
-                        let child = hasInclude.Match text
-                        let childText =
-                            match theme.Templates |> List.tryFind (fun t -> t.Name = child.Groups[1].Value) with
-                            | Some childTemplate -> childTemplate.Text
-                            | None ->
-                                childNotFound <-
-                                    if childNotFound = "" then child.Groups[1].Value
-                                    else $"{childNotFound}; {child.Groups[1].Value}"
-                                ""
-                        text <- text.Replace(child.Value, childText)
-                    if childNotFound <> "" then
-                        let s = if childNotFound.IndexOf ";" >= 0 then "s" else ""
-                        return Error $"Could not find the child template{s} {childNotFound} required by {templateName}"
-                    else
-                        _cache[templatePath] <- Template.Parse(text, SyntaxCompatibility.DotLiquid22)
-                        return Ok _cache[templatePath]
-                | None ->
-                    return Error $"Theme ID {themeId} does not have a template named {templateName}"
-            | None -> return Error $"Theme ID {themeId} does not exist"
-    }
-    
-    /// Get all theme/template names currently cached
-    let allNames () =
-        _cache.Keys |> Seq.sort |> Seq.toList
-    
-    /// Invalidate all template cache entries for the given theme ID
-    let invalidateTheme (themeId: ThemeId) =
-        let keyPrefix = string themeId
-        _cache.Keys
-        |> Seq.filter _.StartsWith(keyPrefix)
-        |> List.ofSeq
-        |> List.iter (fun key -> match _cache.TryRemove key with _, _ -> ())
-    
-    /// Remove all entries from the template cache
-    let empty () =
-        _cache.Clear()
-
-
 /// A cache of asset names by themes
 module ThemeAssetCache =
     

src/MyWebLog/Handlers/Admin.fs

@@ -28,13 +28,13 @@ module Dashboard =
               ListedPages        = listed
               Categories         = cats
               TopLevelCategories = topCats }
-        return! adminPage "Dashboard" false next ctx (Views.WebLog.dashboard model)
+        return! adminPage "Dashboard" next ctx (Views.WebLog.dashboard model)
     }
 
     // GET /admin/administration
     let admin : HttpHandler = requireAccess Administrator >=> fun next ctx -> task {
         let! themes = ctx.Data.Theme.All()
-        return! adminPage "myWebLog Administration" true next ctx (Views.Admin.dashboard themes)
+        return! adminPage "myWebLog Administration" next ctx (Views.Admin.dashboard themes)
     }
 
 /// Redirect the user to the admin dashboard
@@ -71,7 +71,7 @@ module Cache =
     let refreshTheme themeId : HttpHandler = requireAccess Administrator >=> fun next ctx -> task {
         let data = ctx.Data
         if themeId = "all" then
-            TemplateCache.empty ()
+            Template.Cache.empty ()
             do! ThemeAssetCache.fill data
             do! addMessage ctx
                     { UserMessage.Success with
@@ -79,7 +79,7 @@ module Cache =
         else
             match! data.Theme.FindById(ThemeId themeId) with
             | Some theme ->
-                TemplateCache.invalidateTheme    theme.Id
+                Template.Cache.invalidateTheme    theme.Id
                 do! ThemeAssetCache.refreshTheme theme.Id data
                 do! addMessage ctx
                         { UserMessage.Success with
@@ -98,7 +98,7 @@ module Category =
     // GET /admin/categories
     let all : HttpHandler = fun next ctx ->
         let response = fun next ctx ->
-            adminPage "Categories" true next ctx (Views.WebLog.categoryList (ctx.Request.Query.ContainsKey "new"))
+            adminPage "Categories" next ctx (Views.WebLog.categoryList (ctx.Request.Query.ContainsKey "new"))
         (withHxPushUrl (ctx.WebLog.RelativeUrl (Permalink "admin/categories")) >=> response) next ctx
 
     // GET /admin/category/{id}/edit
@@ -115,7 +115,7 @@ module Category =
         | Some (title, cat) ->
             return!
                 Views.WebLog.categoryEdit (EditCategoryModel.FromCategory cat)
-                |> adminBarePage title true next ctx
+                |> adminBarePage title next ctx
         | None -> return! Error.notFound next ctx
     }
 
@@ -167,7 +167,7 @@ module RedirectRules =
 
     // GET /admin/settings/redirect-rules
     let all : HttpHandler = fun next ctx ->
-        adminPage "Redirect Rules" true next ctx (Views.WebLog.redirectList ctx.WebLog.RedirectRules)
+        adminPage "Redirect Rules" next ctx (Views.WebLog.redirectList ctx.WebLog.RedirectRules)
 
     // GET /admin/settings/redirect-rules/[index]
     let edit idx : HttpHandler = fun next ctx ->
@@ -182,7 +182,7 @@ module RedirectRules =
                     Some
                         ("Edit", (Views.WebLog.redirectEdit (EditRedirectRuleModel.FromRule idx (List.item idx rules))))
         match titleAndView with
-        | Some (title, view) -> adminBarePage $"{title} Redirect Rule" true next ctx view
+        | Some (title, view) -> adminBarePage $"{title} Redirect Rule" next ctx view
         | None -> Error.notFound next ctx
         
     /// Update the web log's redirect rules in the database, the request web log, and the web log cache
@@ -247,7 +247,7 @@ module TagMapping =
     // GET /admin/settings/tag-mappings
     let all : HttpHandler = fun next ctx -> task {
         let! mappings = ctx.Data.TagMap.FindByWebLog ctx.WebLog.Id
-        return! adminBarePage "Tag Mapping List" true next ctx (Views.WebLog.tagMapList mappings)
+        return! adminBarePage "Tag Mapping List" next ctx (Views.WebLog.tagMapList mappings)
     }
 
     // GET /admin/settings/tag-mapping/{id}/edit
@@ -260,7 +260,7 @@ module TagMapping =
         | Some tm ->
             return!
                 Views.WebLog.tagMapEdit (EditTagMapModel.FromMapping tm)
-                |> adminBarePage (if isNew then "Add Tag Mapping" else $"Mapping for {tm.Tag} Tag") true next ctx
+                |> adminBarePage (if isNew then "Add Tag Mapping" else $"Mapping for {tm.Tag} Tag") next ctx
         | None -> return! Error.notFound next ctx
     }
 
@@ -302,12 +302,12 @@ module Theme =
         let! themes = ctx.Data.Theme.All ()
         return!
             Views.Admin.themeList (List.map (DisplayTheme.FromTheme WebLogCache.isThemeInUse) themes)
-            |> adminBarePage "Themes" true next ctx
+            |> adminBarePage "Themes" next ctx
     }
 
     // GET /admin/theme/new
     let add : HttpHandler = requireAccess Administrator >=> fun next ctx ->
-        adminBarePage "Upload a Theme File" true next ctx Views.Admin.themeUpload
+        adminBarePage "Upload a Theme File" next ctx Views.Admin.themeUpload
 
     /// Update the name and version for a theme based on the version.txt file, if present
     let private updateNameAndVersion (theme: Theme) (zip: ZipArchive) = backgroundTask {
@@ -398,7 +398,7 @@ module Theme =
                     do! themeFile.CopyToAsync stream
                     let! _ = loadFromZip themeId stream data
                     do! ThemeAssetCache.refreshTheme themeId data
-                    TemplateCache.invalidateTheme themeId
+                    Template.Cache.invalidateTheme themeId
                     // Ensure the themes directory exists
                     let themeDir = Path.Combine(".", "themes")
                     if not (Directory.Exists themeDir) then Directory.CreateDirectory themeDir |> ignore
@@ -464,7 +464,7 @@ module WebLog =
         return!
             Views.WebLog.webLogSettings
                 (SettingsModel.FromWebLog ctx.WebLog) themes pages uploads (EditRssModel.FromRssOptions ctx.WebLog.Rss)
-            |> adminPage "Web Log Settings" true next ctx
+            |> adminPage "Web Log Settings" next ctx
     }
 
     // POST /admin/settings

src/MyWebLog/Handlers/Feed.fs

@@ -453,7 +453,7 @@ let editCustomFeed feedId : HttpHandler = requireAccess WebLogAdmin >=> fun next
             { Name = string Blog;       Value = "Blog" }
         ]
         Views.WebLog.feedEdit (EditCustomFeedModel.FromFeed f) ratings mediums
-        |> adminPage $"""{if feedId = "new" then "Add" else "Edit"} Custom RSS Feed""" true next ctx
+        |> adminPage $"""{if feedId = "new" then "Add" else "Edit"} Custom RSS Feed""" next ctx
     | None -> Error.notFound next ctx
 
 // POST /admin/settings/rss/save

src/MyWebLog/Handlers/Helpers.fs

@@ -19,112 +19,9 @@ type ISession with
         | item -> Some (JsonSerializer.Deserialize<'T> item)
 
 
-/// Keys used in the myWebLog-standard DotLiquid hash
-module ViewContext =
-    
-    /// The anti cross-site request forgery (CSRF) token set to use for form submissions
-    [<Literal>]
-    let AntiCsrfTokens = "csrf"
-    
-    /// The unified application view context
-    [<Literal>]
-    let AppViewContext = "app"
-    
-    /// The categories for this web log
-    [<Literal>]
-    let Categories = "categories"
-    
-    /// The main content of the view
-    [<Literal>]
-    let Content = "content"
-    
-    /// The current page URL
-    [<Literal>]
-    let CurrentPage = "current_page"
-    
-    /// The generator string for the current version of myWebLog
-    [<Literal>]
-    let Generator = "generator"
-    
-    /// The HTML to load htmx from the unpkg CDN
-    [<Literal>]
-    let HtmxScript = "htmx_script"
-    
-    /// Whether the current user has Administrator privileges
-    [<Literal>]
-    let IsAdministrator = "is_administrator"
-    
-    /// Whether the current user has Author (or above) privileges
-    [<Literal>]
-    let IsAuthor = "is_author"
-    
-    /// Whether the current view is displaying a category archive page
-    [<Literal>]
-    let IsCategory = "is_category"
-    
-    /// Whether the current view is displaying the first page of a category archive
-    [<Literal>]
-    let IsCategoryHome = "is_category_home"
-    
-    /// Whether the current user has Editor (or above) privileges
-    [<Literal>]
-    let IsEditor = "is_editor"
-    
-    /// Whether the current view is the home page for the web log
-    [<Literal>]
-    let IsHome = "is_home"
-    
-    /// Whether there is a user logged on
-    [<Literal>]
-    let IsLoggedOn = "is_logged_on"
-    
-    /// Whether the current view is displaying a page
-    [<Literal>]
-    let IsPage = "is_page"
-    
-    /// Whether the current view is displaying a post
-    [<Literal>]
-    let IsPost = "is_post"
-    
-    /// Whether the current view is a tag archive page
-    [<Literal>]
-    let IsTag = "is_tag"
-    
-    /// Whether the current view is the first page of a tag archive
-    [<Literal>]
-    let IsTagHome = "is_tag_home"
-    
-    /// Whether the current user has Web Log Admin (or above) privileges
-    [<Literal>]
-    let IsWebLogAdmin = "is_web_log_admin"
-    
 /// Messages to be displayed to the user
 [<Literal>]
-    let Messages = "messages"
+let MESSAGES = "messages"
-    
-    /// The view model / form for the page
-    [<Literal>]
-    let Model = "model"
-    
-    /// The listed pages for the web log
-    [<Literal>]
-    let PageList = "page_list"
-    
-    /// The title of the page being displayed
-    [<Literal>]
-    let PageTitle = "page_title"
-    
-    /// The slug for category or tag archive pages
-    [<Literal>]
-    let Slug = "slug"
-    
-    /// The ID of the current user
-    [<Literal>]
-    let UserId = "user_id"
-    
-    /// The current web log
-    [<Literal>]
-    let WebLog = "web_log"
 
 
 /// The HTTP item key for loading the session
@@ -147,36 +44,25 @@ open MyWebLog.ViewModels
 /// Add a message to the user's session
 let addMessage (ctx: HttpContext) message = task {
     do! loadSession ctx
-    let msg = match ctx.Session.TryGet<UserMessage list> ViewContext.Messages with Some it -> it | None -> []
+    let msg = match ctx.Session.TryGet<UserMessage list> MESSAGES with Some it -> it | None -> []
-    ctx.Session.Set(ViewContext.Messages, message :: msg)
+    ctx.Session.Set(MESSAGES, message :: msg)
 }
 
 /// Get any messages from the user's session, removing them in the process
 let messages (ctx: HttpContext) = task {
     do! loadSession ctx
-    match ctx.Session.TryGet<UserMessage list> ViewContext.Messages with
+    match ctx.Session.TryGet<UserMessage list> MESSAGES with
     | Some msg ->
-        ctx.Session.Remove ViewContext.Messages
+        ctx.Session.Remove MESSAGES
         return msg |> (List.rev >> Array.ofList)
     | None -> return [||]
 }
 
 open MyWebLog
-open DotLiquid
 
-/// Shorthand for creating a DotLiquid hash from an anonymous object
+/// Create a view context with the page title filled
-let makeHash (values: obj) =
+let viewCtxForPage title =
-    Hash.FromAnonymousObject values
+    { AppViewContext.Empty with PageTitle = title }
-
-/// Create a hash with the page title filled
-let hashForPage (title: string) =
-    makeHash {| page_title = title |}
-
-/// Add a key to the hash, returning the modified hash
-//    (note that the hash itself is mutated; this is only used to make it pipeable)
-let addToHash key (value: obj) (hash: Hash) =
-    if hash.ContainsKey key then hash[key] <- value else hash.Add(key, value)
-    hash
 
 open System.Security.Claims
 open Giraffe
@@ -194,13 +80,13 @@ let private getCurrentMessages ctx = task {
 }
 
 /// Generate the view context for a response
-let private generateViewContext pageTitle messages includeCsrf (ctx: HttpContext) =
+let private generateViewContext messages viewCtx (ctx: HttpContext) =
-    { WebLog          = ctx.WebLog
+    { viewCtx with
+        WebLog          = ctx.WebLog
         UserId          = ctx.User.Claims
                           |> Seq.tryFind (fun claim -> claim.Type = ClaimTypes.NameIdentifier)
                           |> Option.map (fun claim -> WebLogUserId claim.Value)
-      PageTitle       = pageTitle
+        Csrf            = Some ctx.CsrfTokenSet
-      Csrf            = if includeCsrf then Some ctx.CsrfTokenSet else None
         PageList        = PageListCache.get ctx
         Categories      = CategoryCache.get ctx
         CurrentPage     = ctx.Request.Path.Value[1..]
@@ -212,36 +98,13 @@ let private generateViewContext pageTitle messages includeCsrf (ctx: HttpContext
         IsWebLogAdmin   = ctx.HasAccessLevel WebLogAdmin
         IsAdministrator = ctx.HasAccessLevel Administrator }
 
-
+/// Update the view context with standard information (if it has not been done yet) or updated messages
-/// Populate the DotLiquid hash with standard information
+let updateViewContext ctx viewCtx = task {
-let addViewContext ctx (hash: Hash) = task {
     let! messages = getCurrentMessages ctx
-    if hash.ContainsKey ViewContext.AppViewContext then
+    if viewCtx.Generator = "" then
-        let oldApp = hash[ViewContext.AppViewContext] :?> AppViewContext
+        return generateViewContext messages viewCtx ctx
-        let newApp = { oldApp with Messages = Array.concat [ oldApp.Messages; messages ] }
-        return
-            hash
-            |> addToHash ViewContext.AppViewContext newApp
-            |> addToHash ViewContext.Messages       newApp.Messages
     else
-        let app =
+        return { viewCtx with Messages = Array.concat [ viewCtx.Messages; messages ] }
-            generateViewContext (string hash[ViewContext.PageTitle]) messages
-                                (hash.ContainsKey ViewContext.AntiCsrfTokens) ctx
-        return
-            hash
-            |> addToHash ViewContext.UserId          (app.UserId |> Option.map string |> Option.defaultValue "")
-            |> addToHash ViewContext.WebLog          app.WebLog
-            |> addToHash ViewContext.PageList        app.PageList
-            |> addToHash ViewContext.Categories      app.Categories
-            |> addToHash ViewContext.CurrentPage     app.CurrentPage
-            |> addToHash ViewContext.Messages        app.Messages
-            |> addToHash ViewContext.Generator       app.Generator
-            |> addToHash ViewContext.HtmxScript      app.HtmxScript
-            |> addToHash ViewContext.IsLoggedOn      app.IsLoggedOn
-            |> addToHash ViewContext.IsAuthor        app.IsAuthor
-            |> addToHash ViewContext.IsEditor        app.IsEditor
-            |> addToHash ViewContext.IsWebLogAdmin   app.IsWebLogAdmin
-            |> addToHash ViewContext.IsAdministrator app.IsAdministrator
 }
 
 /// Is the request from htmx?
@@ -311,65 +174,65 @@ module Error =
             else ServerErrors.INTERNAL_ERROR message earlyReturn ctx)
 
 
-/// Render a view for the specified theme, using the specified template, layout, and hash
+/// Render a view for the specified theme, using the specified template, layout, and context
-let viewForTheme themeId template next ctx (hash: Hash) = task {
+let viewForTheme themeId template next ctx (viewCtx: AppViewContext) = task {
-    let! hash = addViewContext ctx hash
+    let! updated = updateViewContext ctx viewCtx
     
-    // NOTE: DotLiquid does not support {% render %} or {% include %} in its templates, so we will do a 2-pass render;
+    // NOTE: Although Fluid's view engine support implements layouts and sections, it also relies on the filesystem.
-    //       the net effect is a "layout" capability similar to Razor or Pug
+    //       As we are loading templates from memory or a database, we do a 2-pass render; the first for the content,
+    //       the second for the overall page.
     
     // Render view content...
-    match! TemplateCache.get themeId template ctx.Data with
+    match! Template.Cache.get themeId template ctx.Data with
     | Ok contentTemplate ->
-        let _ = addToHash ViewContext.Content (contentTemplate.Render hash) hash
+        let forLayout = { updated with Content = Template.render contentTemplate updated }
         // ...then render that content with its layout
-        match! TemplateCache.get themeId (if isHtmx ctx then "layout-partial" else "layout") ctx.Data with
+        match! Template.Cache.get themeId (if isHtmx ctx then "layout-partial" else "layout") ctx.Data with
-        | Ok layoutTemplate ->  return! htmlString (layoutTemplate.Render hash) next ctx
+        | Ok layoutTemplate ->  return! htmlString (Template.render layoutTemplate forLayout) next ctx
         | Error message -> return! Error.server message next ctx
     | Error message -> return! Error.server message next ctx
 }
 
-/// Render a bare view for the specified theme, using the specified template and hash
+/// Render a bare view for the specified theme, using the specified template and context
-let bareForTheme themeId template next ctx (hash: Hash) = task {
+let bareForTheme themeId template next ctx viewCtx = task {
-    let! hash        = addViewContext ctx hash
+    let! updated     = updateViewContext ctx viewCtx
     let  withContent = task {
-        if hash.ContainsKey ViewContext.Content then return Ok hash
+        if updated.Content = "" then 
-        else
+            match! Template.Cache.get themeId template ctx.Data with
-            match! TemplateCache.get themeId template ctx.Data with
+            | Ok contentTemplate -> return Ok { updated with Content = Template.render contentTemplate updated }
-            | Ok contentTemplate -> return Ok(addToHash ViewContext.Content (contentTemplate.Render hash) hash)
             | Error message -> return Error message
+        else
+            return Ok viewCtx 
     }
     match! withContent with
-    | Ok completeHash ->
+    | Ok completeCtx ->
         // Bare templates are rendered with layout-bare
-        match! TemplateCache.get themeId "layout-bare" ctx.Data with
+        match! Template.Cache.get themeId "layout-bare" ctx.Data with
         | Ok layoutTemplate ->
             return!
-                (messagesToHeaders (hash[ViewContext.Messages] :?> UserMessage array)
+                (messagesToHeaders completeCtx.Messages >=> htmlString (Template.render layoutTemplate completeCtx))
-                 >=> htmlString (layoutTemplate.Render completeHash))
                     next ctx
         | Error message -> return! Error.server message next ctx
     | Error message -> return! Error.server message next ctx
 }
 
 /// Return a view for the web log's default theme
-let themedView template next ctx hash = task {
+let themedView template next (ctx: HttpContext) viewCtx = task {
-    let! hash = addViewContext ctx hash
+    return! viewForTheme ctx.WebLog.ThemeId template next ctx viewCtx
-    return! viewForTheme (hash[ViewContext.WebLog] :?> WebLog).ThemeId template next ctx hash
 }
 
 /// Display a page for an admin endpoint
-let adminPage pageTitle includeCsrf next ctx (content: AppViewContext -> XmlNode list) = task {
+let adminPage pageTitle next ctx (content: AppViewContext -> XmlNode list) = task {
     let! messages = getCurrentMessages ctx
-    let  appCtx   = generateViewContext pageTitle messages includeCsrf ctx
+    let  appCtx   = generateViewContext messages (viewCtxForPage pageTitle) ctx
     let  layout   = if isHtmx ctx then Layout.partial else Layout.full
     return! htmlString (layout content appCtx |> RenderView.AsString.htmlDocument) next ctx
 }
 
 /// Display a bare page for an admin endpoint
-let adminBarePage pageTitle includeCsrf next ctx (content: AppViewContext -> XmlNode list) = task {
+let adminBarePage pageTitle next ctx (content: AppViewContext -> XmlNode list) = task {
     let! messages = getCurrentMessages ctx
-    let  appCtx   = generateViewContext pageTitle messages includeCsrf ctx
+    let  appCtx   = generateViewContext messages (viewCtxForPage pageTitle) ctx
     return!
         (    messagesToHeaders appCtx.Messages
          >=> htmlString (Layout.bare content appCtx |> RenderView.AsString.htmlDocument)) next ctx

src/MyWebLog/Handlers/Page.fs

@@ -17,7 +17,7 @@ let all pageNbr : HttpHandler = requireAccess Author >=> fun next ctx -> task {
         |> List.ofSeq
     return!
         Views.Page.pageList displayPages pageNbr (pages.Length > 25)
-        |> adminPage "Pages" true next ctx
+        |> adminPage "Pages" next ctx
 }
 
 // GET /admin/page/{id}/edit
@@ -34,7 +34,7 @@ let edit pgId : HttpHandler = requireAccess Author >=> fun next ctx -> task {
     | Some (title, page) when canEdit page.AuthorId ctx ->
         let  model     = EditPageModel.FromPage page
         let! templates = templatesForTheme ctx "page"
-        return! adminPage title true next ctx (Views.Page.pageEdit model templates)
+        return! adminPage title next ctx (Views.Page.pageEdit model templates)
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -56,7 +56,7 @@ let editPermalinks pgId : HttpHandler = requireAccess Author >=> fun next ctx ->
         return!
             ManagePermalinksModel.FromPage pg
             |> Views.Helpers.managePermalinks
-            |> adminPage "Manage Prior Permalinks" true next ctx
+            |> adminPage "Manage Prior Permalinks" next ctx
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -84,7 +84,7 @@ let editRevisions pgId : HttpHandler = requireAccess Author >=> fun next ctx ->
         return!
             ManageRevisionsModel.FromPage pg
             |> Views.Helpers.manageRevisions
-            |> adminPage "Manage Page Revisions" true next ctx
+            |> adminPage "Manage Page Revisions" next ctx
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -115,7 +115,7 @@ let private findPageRevision pgId revDate (ctx: HttpContext) = task {
 let previewRevision (pgId, revDate) : HttpHandler = requireAccess Author >=> fun next ctx -> task {
     match! findPageRevision pgId revDate ctx with
     | Some pg, Some rev when canEdit pg.AuthorId ctx ->
-        return! adminBarePage "" false next ctx (Views.Helpers.commonPreview rev)
+        return! adminBarePage "" next ctx (Views.Helpers.commonPreview rev)
     | Some _, Some _ -> return! Error.notAuthorized next ctx
     | None, _ | _, None -> return! Error.notFound next ctx
 }
@@ -141,7 +141,7 @@ let deleteRevision (pgId, revDate) : HttpHandler = requireAccess Author >=> fun
     | Some pg, Some rev when canEdit pg.AuthorId ctx ->
         do! ctx.Data.Page.Update { pg with Revisions = pg.Revisions |> List.filter (fun r -> r.AsOf <> rev.AsOf) }
         do! addMessage ctx { UserMessage.Success with Message = "Revision deleted successfully" }
-        return! adminBarePage "" false next ctx (fun _ -> [])
+        return! adminBarePage "" next ctx (fun _ -> [])
     | Some _, Some _ -> return! Error.notAuthorized next ctx
     | None, _
     | _, None -> return! Error.notFound next ctx

src/MyWebLog/Handlers/Post.fs

@@ -4,6 +4,7 @@ module MyWebLog.Handlers.Post
 open System
 open System.Collections.Generic
 open MyWebLog
+open MyWebLog.Views
 
 /// Parse a slug and page number from an "everything else" URL
 let private parseSlugAndPage webLog (slugAndPage: string seq) =
@@ -87,10 +88,10 @@ let preparePostList webLog posts listType (url: string) pageNbr perPage (data: I
           OlderName  = olderPost |> Option.map _.Title
         }
     return
-        makeHash {||}
+        { AppViewContext.Empty with
-        |> addToHash ViewContext.Model  model
+            Payload     = model
-        |> addToHash "tag_mappings"     tagMappings
+            TagMappings = Array.ofList tagMappings
-        |> addToHash ViewContext.IsPost (match listType with SinglePost -> true | _ -> false)
+            IsPost = (match listType with SinglePost -> true | _ -> false) }
 }
 
 open Giraffe
@@ -100,17 +101,16 @@ let pageOfPosts pageNbr : HttpHandler = fun next ctx -> task {
     let  count   = ctx.WebLog.PostsPerPage
     let  data    = ctx.Data
     let! posts   = data.Post.FindPageOfPublishedPosts ctx.WebLog.Id pageNbr count
-    let! hash  = preparePostList ctx.WebLog posts PostList "" pageNbr count data
+    let! viewCtx = preparePostList ctx.WebLog posts PostList "" pageNbr count data
     let  title   =
         match pageNbr, ctx.WebLog.DefaultPage with
         | 1, "posts" -> None
         | _, "posts" -> Some $"Page {pageNbr}"
         | _,  _      -> Some $"Page {pageNbr} « Posts"
     return!
-        match title with Some ttl -> addToHash ViewContext.PageTitle ttl hash | None -> hash
+        { viewCtx with
-        |> function
+            PageTitle = defaultArg title viewCtx.PageTitle
-        | hash ->
+            IsHome    = pageNbr = 1 && ctx.WebLog.DefaultPage = "posts" }
-            if pageNbr = 1 && ctx.WebLog.DefaultPage = "posts" then addToHash ViewContext.IsHome true hash else hash
         |> themedView "index" next ctx
 }
 
@@ -134,14 +134,15 @@ let pageOfCategorizedPosts slugAndPage : HttpHandler = fun next ctx -> task {
             match! data.Post.FindPageOfCategorizedPosts webLog.Id (getCategoryIds slug ctx) pageNbr webLog.PostsPerPage
                 with
             | posts when List.length posts > 0 ->
-                let! hash = preparePostList webLog posts CategoryList cat.Slug pageNbr webLog.PostsPerPage data
+                let! viewCtx = preparePostList webLog posts CategoryList cat.Slug pageNbr webLog.PostsPerPage data
                 let pgTitle = if pageNbr = 1 then "" else $""" <small class="archive-pg-nbr">(Page {pageNbr})</small>"""
                 return!
-                       addToHash ViewContext.PageTitle      $"{cat.Name}: Category Archive{pgTitle}" hash
+                    { viewCtx with
-                    |> addToHash "subtitle"                 (defaultArg cat.Description "")
+                        PageTitle      = $"{cat.Name}: Category Archive{pgTitle}"
-                    |> addToHash ViewContext.IsCategory     true
+                        Subtitle       = cat.Description
-                    |> addToHash ViewContext.IsCategoryHome (pageNbr = 1)
+                        IsCategory     = true
-                    |> addToHash ViewContext.Slug           slug
+                        IsCategoryHome = (pageNbr = 1)
+                        Slug           = Some slug }
                     |> themedView "index" next ctx
             | _ -> return! Error.notFound next ctx
         | None -> return! Error.notFound next ctx
@@ -169,13 +170,14 @@ let pageOfTaggedPosts slugAndPage : HttpHandler = fun next ctx -> task {
         else
             match! data.Post.FindPageOfTaggedPosts webLog.Id tag pageNbr webLog.PostsPerPage with
             | posts when List.length posts > 0 ->
-                let! hash    = preparePostList webLog posts TagList rawTag pageNbr webLog.PostsPerPage data
+                let! viewCtx = preparePostList webLog posts TagList rawTag pageNbr webLog.PostsPerPage data
-                let  pgTitle = if pageNbr = 1 then "" else $""" <small class="archive-pg-nbr">(Page {pageNbr})</small>"""
+                let  pgTitle = if pageNbr = 1 then "" else $" <small class=\"archive-pg-nbr\">(Page {pageNbr})</small>"
                 return!
-                       addToHash ViewContext.PageTitle $"Posts Tagged &ldquo;{tag}&rdquo;{pgTitle}" hash
+                    { viewCtx with
-                    |> addToHash ViewContext.IsTag     true
+                        PageTitle = $"Posts Tagged &ldquo;{tag}&rdquo;{pgTitle}"
-                    |> addToHash ViewContext.IsTagHome (pageNbr = 1)
+                        IsTag     = true
-                    |> addToHash ViewContext.Slug      rawTag
+                        IsTagHome = (pageNbr = 1)
+                        Slug      = Some rawTag }
                     |> themedView "index" next ctx
             // Other systems use hyphens for spaces; redirect if this is an old tag link
             | _ ->
@@ -200,9 +202,9 @@ let home : HttpHandler = fun next ctx -> task {
         match! ctx.Data.Page.FindById (PageId pageId) webLog.Id with
         | Some page ->
             return!
-                hashForPage page.Title
+                { viewCtxForPage page.Title with
-                |> addToHash "page" (DisplayPage.FromPage webLog page)
+                    Payload = DisplayPage.FromPage webLog page
-                |> addToHash ViewContext.IsHome true
+                    IsHome  = true }
                 |> themedView (defaultArg page.Template "single-page") next ctx
         | None -> return! Error.notFound next ctx
 }
@@ -253,8 +255,8 @@ let chapters (post: Post) : HttpHandler = fun next ctx ->
 let all pageNbr : HttpHandler = requireAccess Author >=> fun next ctx -> task {
     let  data    = ctx.Data
     let! posts   = data.Post.FindPageOfPosts ctx.WebLog.Id pageNbr 25
-    let! hash  = preparePostList ctx.WebLog posts AdminList "" pageNbr 25 data
+    let! viewCtx = preparePostList ctx.WebLog posts AdminList "" pageNbr 25 data
-    return! adminPage "Posts" true next ctx (Views.Post.list (hash[ViewContext.Model] :?> PostDisplay))
+    return! adminPage "Posts" next ctx (Post.list viewCtx.Posts)
 }
 
 // GET /admin/post/{id}/edit
@@ -278,7 +280,7 @@ let edit postId : HttpHandler = requireAccess Author >=> fun next ctx -> task {
             { Name = string No;    Value = "No" }
             { Name = string Clean; Value = "Clean" }
         ]
-        return! adminPage title true next ctx (Views.Post.postEdit model templates ratings)
+        return! adminPage title next ctx (Post.postEdit model templates ratings)
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -298,8 +300,8 @@ let editPermalinks postId : HttpHandler = requireAccess Author >=> fun next ctx
     | Some post when canEdit post.AuthorId ctx ->
         return!
             ManagePermalinksModel.FromPost post
-            |> Views.Helpers.managePermalinks
+            |> managePermalinks
-            |> adminPage "Manage Prior Permalinks" true next ctx
+            |> adminPage "Manage Prior Permalinks" next ctx
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -326,8 +328,8 @@ let editRevisions postId : HttpHandler = requireAccess Author >=> fun next ctx -
     | Some post when canEdit post.AuthorId ctx ->
         return!
             ManageRevisionsModel.FromPost post
-            |> Views.Helpers.manageRevisions
+            |> manageRevisions
-            |> adminPage "Manage Post Revisions" true next ctx
+            |> adminPage "Manage Post Revisions" next ctx
     | Some _ -> return! Error.notAuthorized next ctx
     | None -> return! Error.notFound next ctx
 }
@@ -359,7 +361,7 @@ let private findPostRevision postId revDate (ctx: HttpContext) = task {
 let previewRevision (postId, revDate) : HttpHandler = requireAccess Author >=> fun next ctx -> task {
     match! findPostRevision postId revDate ctx with
     | Some post, Some rev when canEdit post.AuthorId ctx ->
-        return! adminBarePage "" false next ctx (Views.Helpers.commonPreview rev)
+        return! adminBarePage "" next ctx (commonPreview rev)
     | Some _, Some _ -> return! Error.notAuthorized next ctx
     | None, _ | _, None -> return! Error.notFound next ctx
 }
@@ -385,7 +387,7 @@ let deleteRevision (postId, revDate) : HttpHandler = requireAccess Author >=> fu
     | Some post, Some rev when canEdit post.AuthorId ctx ->
         do! ctx.Data.Post.Update { post with Revisions = post.Revisions |> List.filter (fun r -> r.AsOf <> rev.AsOf) }
         do! addMessage ctx { UserMessage.Success with Message = "Revision deleted successfully" }
-        return! adminBarePage "" false next ctx (fun _ -> [])
+        return! adminBarePage "" next ctx (fun _ -> [])
     | Some _, Some _ -> return! Error.notAuthorized next ctx
     | None, _
     | _, None -> return! Error.notFound next ctx
@@ -399,8 +401,8 @@ let manageChapters postId : HttpHandler = requireAccess Author >=> fun next ctx
              && Option.isSome post.Episode.Value.Chapters
              && canEdit post.AuthorId ctx ->
         return!
-            Views.Post.chapters false (ManageChaptersModel.Create post)
+            Post.chapters false (ManageChaptersModel.Create post)
-            |> adminPage "Manage Chapters" true next ctx
+            |> adminPage "Manage Chapters" next ctx
     | Some _ | None -> return! Error.notFound next ctx
 }
 
@@ -419,8 +421,8 @@ let editChapter (postId, index) : HttpHandler = requireAccess Author >=> fun nex
         match chapter with
         | Some chap ->
             return!
-                Views.Post.chapterEdit (EditChapterModel.FromChapter post.Id index chap)
+                Post.chapterEdit (EditChapterModel.FromChapter post.Id index chap)
-                |> adminBarePage (if index = -1 then "Add a Chapter" else "Edit Chapter") true next ctx
+                |> adminBarePage (if index = -1 then "Add a Chapter" else "Edit Chapter") next ctx
         | None -> return! Error.notFound next ctx
     | Some _ | None -> return! Error.notFound next ctx
 }
@@ -447,8 +449,8 @@ let saveChapter (postId, index) : HttpHandler = requireAccess Author >=> fun nex
                 do! data.Post.Update updatedPost
                 do! addMessage ctx { UserMessage.Success with Message = "Chapter saved successfully" }
                 return!
-                    Views.Post.chapterList form.AddAnother (ManageChaptersModel.Create updatedPost)
+                    Post.chapterList form.AddAnother (ManageChaptersModel.Create updatedPost)
-                    |> adminBarePage "Manage Chapters" true next ctx
+                    |> adminBarePage "Manage Chapters" next ctx
             with
             | ex -> return! Error.server ex.Message next ctx
         else return! Error.notFound next ctx
@@ -471,8 +473,8 @@ let deleteChapter (postId, index) : HttpHandler = requireAccess Author >=> fun n
             do! data.Post.Update updatedPost
             do! addMessage ctx { UserMessage.Success with Message = "Chapter deleted successfully" }
             return!
-                Views.Post.chapterList false (ManageChaptersModel.Create updatedPost)
+                Post.chapterList false (ManageChaptersModel.Create updatedPost)
-                |> adminPage "Manage Chapters" true next ctx
+                |> adminPage "Manage Chapters" next ctx
         else return! Error.notFound next ctx
     | Some _ | None -> return! Error.notFound next ctx
 }

src/MyWebLog/Handlers/Routes.fs

@@ -34,9 +34,8 @@ module CatchAll =
                         yield Post.chapters post
                     else
                         yield fun next ctx ->
-                            Post.preparePostList webLog [ post ] Post.ListType.SinglePost "" 1 1 data
+                            { await (Post.preparePostList webLog [ post ] Post.ListType.SinglePost "" 1 1 data) with
-                            |> await
+                                PageTitle = post.Title }
-                            |> addToHash ViewContext.PageTitle post.Title
                             |> themedView (defaultArg post.Template "single-post") next ctx
             | None -> ()
             // Current page
@@ -44,9 +43,9 @@ module CatchAll =
             | Some page ->
                 debug (fun () -> "Found page by permalink")
                 yield fun next ctx ->
-                    hashForPage page.Title
+                    { viewCtxForPage page.Title with
-                    |> addToHash "page"             (DisplayPage.FromPage webLog page)
+                        Payload = DisplayPage.FromPage webLog page
-                    |> addToHash ViewContext.IsPage true
+                        IsPage  = true }
                     |> themedView (defaultArg page.Template "single-page") next ctx
             | None -> ()
             // RSS feed

src/MyWebLog/Handlers/Upload.fs

@@ -120,12 +120,12 @@ let list : HttpHandler = requireAccess Author >=> fun next ctx -> task {
         |> Seq.append diskUploads
         |> Seq.sortByDescending (fun file -> file.UpdatedOn, file.Path)
         |> Views.WebLog.uploadList
-        |> adminPage "Uploaded Files" true next ctx
+        |> adminPage "Uploaded Files" next ctx
 }
 
 // GET /admin/upload/new
 let showNew : HttpHandler = requireAccess Author >=> fun next ctx ->
-    adminPage "Upload a File" true next ctx Views.WebLog.uploadNew
+    adminPage "Upload a File" next ctx Views.WebLog.uploadNew
 
 // POST /admin/upload/save
 let save : HttpHandler = requireAccess Author >=> fun next ctx -> task {

src/MyWebLog/Handlers/User.fs

@@ -35,7 +35,7 @@ let logOn returnUrl : HttpHandler = fun next ctx ->
         match returnUrl with
         | Some _ -> returnUrl
         | None -> if ctx.Request.Query.ContainsKey "returnUrl" then Some ctx.Request.Query["returnUrl"].[0] else None
-    adminPage "Log On" true next ctx (Views.User.logOn { LogOnModel.Empty with ReturnTo = returnTo })
+    adminPage "Log On" next ctx (Views.User.logOn { LogOnModel.Empty with ReturnTo = returnTo })
 
 
 open System.Security.Claims
@@ -91,12 +91,12 @@ let private goAway : HttpHandler = RequestErrors.BAD_REQUEST "really?"
 // GET /admin/settings/users
 let all : HttpHandler = fun next ctx -> task {
     let! users = ctx.Data.WebLogUser.FindByWebLog ctx.WebLog.Id
-    return! adminBarePage "User Administration" true next ctx (Views.User.userList users)
+    return! adminBarePage "User Administration" next ctx (Views.User.userList users)
 }
 
 /// Show the edit user page
 let private showEdit (model: EditUserModel) : HttpHandler = fun next ctx ->
-    adminBarePage (if model.IsNew then "Add a New User" else "Edit User") true next ctx (Views.User.edit model)
+    adminBarePage (if model.IsNew then "Add a New User" else "Edit User") next ctx (Views.User.edit model)
     
 // GET /admin/settings/user/{id}/edit
 let edit usrId : HttpHandler = fun next ctx -> task {
@@ -139,7 +139,7 @@ let myInfo : HttpHandler = requireAccess Author >=> fun next ctx -> task {
     | Some user ->
         return!
             Views.User.myInfo (EditMyInfoModel.FromUser user) user
-            |> adminPage "Edit Your Information" true next ctx
+            |> adminPage "Edit Your Information" next ctx
     | None -> return! Error.notFound next ctx
 }
 
@@ -164,7 +164,7 @@ let saveMyInfo : HttpHandler = requireAccess Author >=> fun next ctx -> task {
         do! addMessage ctx { UserMessage.Error with Message = "Passwords did not match; no updates made" }
         return!
             Views.User.myInfo { model with NewPassword = ""; NewPasswordConfirm = "" } user
-            |> adminPage "Edit Your Information" true next ctx
+            |> adminPage "Edit Your Information" next ctx
     | None -> return! Error.notFound next ctx
 }
 

src/MyWebLog/MyWebLog.fsproj

@@ -9,6 +9,8 @@
   <ItemGroup>
     <Content Include="appsettings*.json" CopyToOutputDirectory="Always" />
     <Compile Include="Caches.fs" />
+    <Compile Include="ViewContext.fs" />
+    <Compile Include="Template.fs" />
     <Compile Include="Views\Helpers.fs" />
     <Compile Include="Views\Admin.fs" />
     <Compile Include="Views\Page.fs" />
@@ -31,6 +33,7 @@
   <ItemGroup>
     <PackageReference Include="BitBadger.AspNetCore.CanonicalDomains" Version="1.0.0" />
     <PackageReference Include="DotLiquid" Version="2.2.692" />
+    <PackageReference Include="Fluid.Core" Version="2.11.1" />
     <PackageReference Include="Giraffe" Version="6.4.0" />
     <PackageReference Include="Giraffe.Htmx" Version="2.0.2" />
     <PackageReference Include="Giraffe.ViewEngine.Htmx" Version="2.0.2" />

src/MyWebLog/Template.fs

@@ -0,0 +1,282 @@
+module MyWebLog.Template
+
+open Fluid
+open Fluid.Values
+open Giraffe.ViewEngine
+open MyWebLog
+open MyWebLog.ViewModels
+
+/// Alias for ValueTask
+type VTask<'T> = System.Threading.Tasks.ValueTask<'T>
+
+
+/// Extensions on Fluid's TemplateContext object
+type TemplateContext with
+    
+    /// Get the model of the context as an AppViewContext instance
+    member this.App =
+        this.Model.ToObjectValue() :?> AppViewContext
+
+
+/// Helper functions for filters and tags
+[<AutoOpen>]
+module private Helpers =
+    
+    /// Does an asset exist for the current theme?
+    let assetExists fileName (webLog: WebLog) =
+        ThemeAssetCache.get webLog.ThemeId |> List.exists (fun it -> it = fileName)
+
+    /// Obtain the link from known types
+    let permalink (item: FluidValue) (linkFunc: Permalink -> string) =
+        match item.Type with
+        | FluidValues.String -> Some (item.ToStringValue())
+        | FluidValues.Object ->
+            match item.ToObjectValue() with
+            | :? DisplayPage  as page -> Some page.Permalink
+            | :? PostListItem as post -> Some post.Permalink
+            | :? Permalink    as link -> Some (string link)
+            | _ -> None
+        | _ -> None
+        |> function
+        | Some link -> linkFunc (Permalink link)
+        | None      -> $"alert('unknown item type {item.Type}')"
+
+    /// Generate a link for theme asset (image, stylesheet, script, etc.)
+    let themeAsset (input: FluidValue) (ctx: TemplateContext) =
+        let app = ctx.App
+        app.WebLog.RelativeUrl(Permalink $"themes/{app.WebLog.ThemeId}/{input.ToStringValue()}")
+
+
+/// Fluid template options customized with myWebLog filters
+let options =
+    let sValue = StringValue >> VTask<FluidValue>
+    let it = TemplateOptions.Default
+    it.MemberAccessStrategy.MemberNameStrategy <- MemberNameStrategies.SnakeCase
+    
+    // A filter to generate an absolute link
+    it.Filters.AddFilter("absolute_link", fun input _ ctx -> sValue (permalink input ctx.App.WebLog.AbsoluteUrl))
+    
+    // A filter to generate a link with posts categorized under the given category
+    it.Filters.AddFilter("category_link",
+        fun input _ ctx ->
+            match input.ToObjectValue() with
+            | :? DisplayCategory as cat  -> Some cat.Slug
+            | :? string          as slug -> Some slug
+            | _ -> None
+            |> function
+            | Some slug -> ctx.App.WebLog.RelativeUrl(Permalink $"category/{slug}/")
+            | None      -> $"alert('unknown category object type {input.Type}')"
+            |> sValue)
+    
+    // A filter to generate a link that will edit a page
+    it.Filters.AddFilter("edit_page_link",
+        fun input _ ctx ->
+            match input.ToObjectValue() with
+            | :? DisplayPage as page  -> Some page.Id
+            | :? string      as theId -> Some theId
+            | _ -> None
+            |> function
+            | Some pageId -> ctx.App.WebLog.RelativeUrl(Permalink $"admin/page/{pageId}/edit")
+            | None        -> $"alert('unknown page object type {input.Type}')"
+            |> sValue)
+    
+    // A filter to generate a link that will edit a post
+    it.Filters.AddFilter("edit_post_link",
+        fun input _ ctx ->
+            match input.ToObjectValue() with
+            | :? PostListItem as post  -> Some post.Id
+            | :? string       as theId -> Some theId
+            | _ -> None
+            |> function
+            | Some postId -> ctx.App.WebLog.RelativeUrl(Permalink $"admin/post/{postId}/edit")
+            | None        -> $"alert('unknown post object type {input.Type}')"
+            |> sValue)
+    
+    // A filter to generate nav links, highlighting the active link (starts-with match)
+    it.Filters.AddFilter("nav_link",
+        fun input args ctx ->
+            let app       = ctx.App
+            let extraPath = app.WebLog.ExtraPath
+            let path      = if extraPath = "" then "" else $"{extraPath[1..]}/"
+            let url       = input.ToStringValue()
+            seq {
+                "<li class=nav-item><a class=\"nav-link"
+                if app.CurrentPage.StartsWith $"{path}{url}" then " active"
+                "\" href=\""
+                app.WebLog.RelativeUrl(Permalink url)
+                "\">"
+                args.At(0).ToStringValue()
+                "</a>"
+            }
+            |> String.concat ""
+            |> sValue)
+    
+    // A filter to generate a relative link
+    it.Filters.AddFilter("relative_link", fun input _ ctx -> sValue (permalink input ctx.App.WebLog.RelativeUrl))
+    
+    // A filter to generate a link with posts tagged with the given tag
+    it.Filters.AddFilter("tag_link",
+        fun input _ ctx ->
+            let tag = input.ToStringValue()
+            ctx.App.TagMappings
+            |> Array.tryFind (fun it -> it.Tag = tag)
+            |> function
+            | Some tagMap -> tagMap.UrlValue
+            | None        -> tag.Replace(" ", "+")
+            |> function tagUrl -> ctx.App.WebLog.RelativeUrl(Permalink $"tag/{tagUrl}/")
+            |> sValue)
+    
+    // A filter to generate a link for theme asset (image, stylesheet, script, etc.)
+    it.Filters.AddFilter("theme_asset", fun input _ ctx -> sValue (themeAsset input ctx))
+    
+    // A filter to retrieve the value of a meta item from a list
+    //   (shorter than `{% assign item = list | where: "Name", [name] | first %}{{ item.value }}`)
+    it.Filters.AddFilter("value",
+        fun input args _ ->
+            let items = input.ToObjectValue() :?> MetaItem list
+            let name  = args.At(0).ToStringValue()
+            match items |> List.tryFind (fun it -> it.Name = name) with
+            | Some item -> item.Value
+            | None -> $"-- {name} not found --"
+            |> sValue)
+    
+    it
+    
+
+/// Fluid parser customized with myWebLog filters and tags
+let parser =
+    // spacer
+    let s = "    "
+    // Required return for tag delegates
+    let ok () =
+        VTask<Fluid.Ast.Completion> Fluid.Ast.Completion.Normal
+    
+    let it = FluidParser()
+    
+    // Create various items in the page header based on the state of the page being generated
+    it.RegisterEmptyTag("page_head",
+        fun writer encoder context ->
+            let app = context.App
+            // let getBool name =
+            //     defaultArg (context.Environments[0].[name] |> Option.ofObj |> Option.map Convert.ToBoolean) false
+            
+            writer.WriteLine $"""{s}<meta name=generator content="{app.Generator}">"""
+            
+            // Theme assets
+            if assetExists "style.css" app.WebLog then
+                themeAsset (StringValue "style.css") context
+                |> sprintf "%s<link rel=stylesheet href=\"%s\">" s
+                |> writer.WriteLine
+            if assetExists "favicon.ico" app.WebLog then
+                themeAsset (StringValue "favicon.ico") context
+                |> sprintf "%s<link rel=icon href=\"%s\">" s
+                |> writer.WriteLine
+            
+            // RSS feeds and canonical URLs
+            let feedLink title url =
+                let escTitle = System.Web.HttpUtility.HtmlAttributeEncode title
+                let relUrl   = app.WebLog.RelativeUrl(Permalink url)
+                $"""{s}<link rel=alternate type="application/rss+xml" title="{escTitle}" href="{relUrl}">"""
+            
+            if app.WebLog.Rss.IsFeedEnabled && app.IsHome then
+                writer.WriteLine(feedLink app.WebLog.Name app.WebLog.Rss.FeedName)
+                writer.WriteLine $"""{s}<link rel=canonical href="{app.WebLog.AbsoluteUrl Permalink.Empty}">"""
+            
+            if app.WebLog.Rss.IsCategoryEnabled && app.IsCategoryHome then
+                let slug = context.AmbientValues["slug"] :?> string
+                writer.WriteLine(feedLink app.WebLog.Name $"category/{slug}/{app.WebLog.Rss.FeedName}")
+                
+            if app.WebLog.Rss.IsTagEnabled && app.IsTagHome then
+                let slug = context.AmbientValues["slug"] :?> string
+                writer.WriteLine(feedLink app.WebLog.Name $"tag/{slug}/{app.WebLog.Rss.FeedName}")
+                
+            if app.IsPost then
+                let post = (* context.Environments[0].["model"] *) obj() :?> PostDisplay
+                let url  = app.WebLog.AbsoluteUrl(Permalink post.Posts[0].Permalink)
+                writer.WriteLine $"""{s}<link rel=canonical href="{url}">"""
+            
+            if app.IsPage then
+                let page = (* context.Environments[0].["page"] *) obj() :?> DisplayPage
+                let url  = app.WebLog.AbsoluteUrl(Permalink page.Permalink)
+                writer.WriteLine $"""{s}<link rel=canonical href="{url}">"""
+            
+            ok ())
+    
+    // Create various items in the page footer based on the state of the page being generated
+    it.RegisterEmptyTag("page_foot",
+        fun writer encoder context ->
+            let webLog = context.App.WebLog
+            if webLog.AutoHtmx then
+                writer.WriteLine $"{s}{RenderView.AsString.htmlNode Htmx.Script.minified}"
+            if assetExists "script.js" webLog then
+                themeAsset (StringValue "script.js") context
+                |> sprintf "%s<script src=\"%s\"></script>" s
+                |> writer.WriteLine
+            ok ())
+    
+    // Create links for a user to log on or off, and a dashboard link if they are logged off
+    it.RegisterEmptyTag("user_links",
+        fun writer encoder ctx ->
+            let app = ctx.App
+            let link it = app.WebLog.RelativeUrl(Permalink it)
+            seq {
+                """<ul class="navbar-nav flex-grow-1 justify-content-end">"""
+                match app.IsLoggedOn with
+                | true ->
+                    $"""<li class=nav-item><a class=nav-link href="{link "admin/dashboard"}">Dashboard</a>"""
+                    $"""<li class=nav-item><a class=nav-link href="{link "user/log-off"}">Log Off</a>"""
+                | false ->
+                    $"""<li class=nav-item><a class=nav-link href="{link "user/log-on"}">Log On</a>"""
+                "</ul>"
+            }
+            |> Seq.iter writer.WriteLine
+            ok())
+    
+    it
+
+/// Cache for parsed templates
+module Cache =
+    
+    open System.Collections.Concurrent
+    open MyWebLog.Data
+    
+    /// Cache of parsed templates
+    let private _cache = ConcurrentDictionary<string, IFluidTemplate> ()
+    
+    /// Get a template for the given theme and template name
+    let get (themeId: ThemeId) (templateName: string) (data: IData) = backgroundTask {
+        let templatePath = $"{themeId}/{templateName}"
+        match _cache.ContainsKey templatePath with
+        | true -> return Ok _cache[templatePath]
+        | false ->
+            match! data.Theme.FindById themeId with
+            | Some theme ->
+                match theme.Templates |> List.tryFind (fun t -> t.Name = templateName) with
+                | Some template ->
+                    _cache[templatePath] <- parser.Parse(template.Text)
+                    return Ok _cache[templatePath]
+                | None ->
+                    return Error $"Theme ID {themeId} does not have a template named {templateName}"
+            | None -> return Error $"Theme ID {themeId} does not exist"
+    }
+    
+    /// Get all theme/template names currently cached
+    let allNames () =
+        _cache.Keys |> Seq.sort |> Seq.toList
+    
+    /// Invalidate all template cache entries for the given theme ID
+    let invalidateTheme (themeId: ThemeId) =
+        let keyPrefix = string themeId
+        _cache.Keys
+        |> Seq.filter _.StartsWith(keyPrefix)
+        |> List.ofSeq
+        |> List.iter (fun key -> match _cache.TryRemove key with _, _ -> ())
+    
+    /// Remove all entries from the template cache
+    let empty () =
+        _cache.Clear()
+
+
+/// Render a template to a string
+let render (template: IFluidTemplate) (viewCtx: AppViewContext) =
+    template.Render(TemplateContext(viewCtx, options, true))

src/MyWebLog/ViewContext.fs

@@ -0,0 +1,126 @@
+/// View rendering context for myWebLog
+[<AutoOpen>]
+module MyWebLog.ViewContext
+
+open Microsoft.AspNetCore.Antiforgery
+open MyWebLog.ViewModels
+
+/// The rendering context for this application
+[<NoComparison; NoEquality>]
+type AppViewContext = {
+    /// The web log for this request
+    WebLog: WebLog
+    
+    /// The ID of the current user
+    UserId: WebLogUserId option
+    
+    /// The title of the page being rendered
+    PageTitle: string
+    
+    /// The subtitle for the page
+    Subtitle: string option
+    
+    /// The anti-Cross Site Request Forgery (CSRF) token set to use when rendering a form
+    Csrf: AntiforgeryTokenSet option
+    
+    /// The page list for the web log
+    PageList: DisplayPage array
+    
+    /// Categories and post counts for the web log
+    Categories: DisplayCategory array
+    
+    /// Tag mappings
+    TagMappings: TagMap array
+    
+    /// The URL of the page being rendered
+    CurrentPage: string
+    
+    /// User messages
+    Messages: UserMessage array
+    
+    /// The generator string for the rendered page
+    Generator: string
+    
+    /// The payload for this page (see other properties that wrap this one)
+    Payload: obj
+    
+    /// The content of a page (wrapped when rendering the layout)
+    Content: string
+    
+    /// A string to load the minified htmx script
+    HtmxScript: string
+    
+    /// Whether the current user is an author
+    IsAuthor: bool
+    
+    /// Whether the current user is an editor (implies author)
+    IsEditor: bool
+    
+    /// Whether the current user is a web log administrator (implies author and editor)
+    IsWebLogAdmin: bool
+    
+    /// Whether the current user is an installation administrator (implies all web log rights)
+    IsAdministrator: bool
+    
+    /// Whether the current page is the home page of the web log
+    IsHome: bool
+    
+    /// Whether the current page is a category archive page
+    IsCategory: bool
+    
+    /// Whether the current page is a category archive home page
+    IsCategoryHome: bool
+    
+    /// Whether the current page is a tag archive page
+    IsTag: bool
+    
+    /// Whether the current page is a tag archive home page
+    IsTagHome: bool
+    
+    /// Whether the current page is a single post
+    IsPost: bool
+    
+    /// Whether the current page is a static page
+    IsPage: bool
+    
+    /// The slug for a category or tag
+    Slug: string option }
+with
+    
+    /// Whether there is a user logged on
+    member this.IsLoggedOn = Option.isSome this.UserId
+    
+    member this.Page =
+        this.Payload :?> DisplayPage
+    
+    member this.Posts =
+        this.Payload :?> PostDisplay
+    
+    /// An empty view context
+    static member Empty =
+        { WebLog          = WebLog.Empty
+          UserId          = None
+          PageTitle       = ""
+          Subtitle        = None
+          Csrf            = None
+          PageList        = [||]
+          Categories      = [||]
+          TagMappings     = [||] 
+          CurrentPage     = ""
+          Messages        = [||]
+          Generator       = ""
+          Payload         = obj () 
+          Content         = "" 
+          HtmxScript      = ""
+          IsAuthor        = false
+          IsEditor        = false
+          IsWebLogAdmin   = false
+          IsAdministrator = false
+          IsHome          = false
+          IsCategory      = false 
+          IsCategoryHome  = false
+          IsTag           = false 
+          IsTagHome       = false
+          IsPost          = false
+          IsPage          = false
+          Slug            = None }

src/MyWebLog/Views/Admin.fs

@@ -8,7 +8,7 @@ open MyWebLog.ViewModels
 
 /// The administrator dashboard
 let dashboard (themes: Theme list) app = [
-    let templates      = TemplateCache.allNames ()
+    let templates      = Template.Cache.allNames ()
     let cacheBaseUrl   = relUrl app "admin/cache/"
     let webLogCacheUrl = $"{cacheBaseUrl}web-log/"
     let themeCacheUrl  = $"{cacheBaseUrl}theme/"

src/MyWebLog/Views/Helpers.fs

@@ -1,7 +1,6 @@
 [<AutoOpen>]
 module MyWebLog.Views.Helpers
 
-open Microsoft.AspNetCore.Antiforgery
 open Giraffe.ViewEngine
 open Giraffe.ViewEngine.Accessibility
 open Giraffe.ViewEngine.Htmx
@@ -10,56 +9,6 @@ open MyWebLog.ViewModels
 open NodaTime
 open NodaTime.Text
 
-/// The rendering context for this application
-[<NoComparison; NoEquality>]
-type AppViewContext = {
-    /// The web log for this request
-    WebLog: WebLog
-    
-    /// The ID of the current user
-    UserId: WebLogUserId option
-    
-    /// The title of the page being rendered
-    PageTitle: string
-    
-    /// The anti-Cross Site Request Forgery (CSRF) token set to use when rendering a form
-    Csrf: AntiforgeryTokenSet option
-    
-    /// The page list for the web log
-    PageList: DisplayPage array
-    
-    /// Categories and post counts for the web log
-    Categories: DisplayCategory array
-    
-    /// The URL of the page being rendered
-    CurrentPage: string
-    
-    /// User messages
-    Messages: UserMessage array
-    
-    /// The generator string for the rendered page
-    Generator: string
-    
-    /// A string to load the minified htmx script
-    HtmxScript: string
-    
-    /// Whether the current user is an author
-    IsAuthor: bool
-    
-    /// Whether the current user is an editor (implies author)
-    IsEditor: bool
-    
-    /// Whether the current user is a web log administrator (implies author and editor)
-    IsWebLogAdmin: bool
-    
-    /// Whether the current user is an installation administrator (implies all web log rights)
-    IsAdministrator: bool
-} with
-    
-    /// Whether there is a user logged on
-    member this.IsLoggedOn = Option.isSome this.UserId
-
-
 /// Create a relative URL for the current web log
 let relUrl app =
     Permalink >> app.WebLog.RelativeUrl