namespace BitBadger.Documents

open System.Security.Cryptography

/// The types of logical operations available for JSON fields
[<Struct>]
type Op =
    /// Equals (=)
    | EQ
    /// Greater Than (>)
    | GT
    /// Greater Than or Equal To (>=)
    | GE
    /// Less Than (<)
    | LT
    /// Less Than or Equal To (<=)
    | LE
    /// Not Equal to (<>)
    | NE
    /// Between (BETWEEN)
    | BT
    /// In (IN)
    | IN
    // Array Contains/Exists (PostgreSQL: |? SQLite: EXISTS / json_each / IN)
    //| AEX
    /// Exists (IS NOT NULL)
    | EX
    /// Does Not Exist (IS NULL)
    | NEX
    
    override this.ToString() =
        match this with
        | EQ -> "="
        | GT -> ">"
        | GE -> ">="
        | LT -> "<"
        | LE -> "<="
        | NE -> "<>"
        | BT -> "BETWEEN"
        | IN -> "IN"
        | EX -> "IS NOT NULL"
        | NEX -> "IS NULL"


/// The dialect in which a command should be rendered
[<Struct>]
type Dialect =
    | PostgreSQL
    | SQLite

/// Criteria for a field WHERE clause
type Field = {
    /// The name of the field
    Name: string
    
    /// The operation by which the field will be compared
    Op: Op
    
    /// The value of the field
    Value: obj
    
    /// The name of the parameter for this field
    ParameterName: string option
    
    /// The table qualifier for this field
    Qualifier: string option
} with
    
    /// Create an equals (=) field criterion
    static member EQ name (value: obj) =
        { Name = name; Op = EQ; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a greater than (>) field criterion
    static member GT name (value: obj) =
        { Name = name; Op = GT; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a greater than or equal to (>=) field criterion
    static member GE name (value: obj) =
        { Name = name; Op = GE; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a less than (<) field criterion
    static member LT name (value: obj) =
        { Name = name; Op = LT; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a less than or equal to (<=) field criterion
    static member LE name (value: obj) =
        { Name = name; Op = LE; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a not equals (<>) field criterion
    static member NE name (value: obj) =
        { Name = name; Op = NE; Value = value; ParameterName = None; Qualifier = None }
    
    /// Create a BETWEEN field criterion
    static member BT name (min: obj) (max: obj) =
        { Name = name; Op = BT; Value = [ min; max ]; ParameterName = None; Qualifier = None }
    
    /// Create an IN field criterion
    static member IN name (values: obj seq) =
        { Name = name; Op = IN; Value = values; ParameterName = None; Qualifier = None }
        
    /// Create an exists (IS NOT NULL) field criterion
    static member EX name =
        { Name = name; Op = EX; Value = obj (); ParameterName = None; Qualifier = None }
    
    /// Create a not exists (IS NULL) field criterion
    static member NEX name =
        { Name = name; Op = NEX; Value = obj (); ParameterName = None; Qualifier = None }
    
    /// Transform a field name (a.b.c) to a path for the given SQL dialect
    static member NameToPath (name: string) dialect =
        let path =
            if name.Contains '.' then
                match dialect with
                | PostgreSQL -> "#>>'{" + String.concat "," (name.Split '.') + "}'"
                | SQLite -> "->>'" + String.concat "'->>'" (name.Split '.') + "'"
            else $"->>'{name}'"
        $"data{path}"
    
    /// Create a field with a given name, but no other properties filled (op will be EQ, value will be "")
    static member Named name =
        { Name = name; Op = EQ; Value = ""; ParameterName = None; Qualifier = None }
    
    /// Specify the name of the parameter for this field
    member this.WithParameterName name =
        { this with ParameterName = Some name }
    
    /// Specify a qualifier (alias) for the table from which this field will be referenced
    member this.WithQualifier alias =
        { this with Qualifier = Some alias }

    /// Get the qualified path to the field
    member this.Path dialect =
        (this.Qualifier |> Option.map (fun q -> $"{q}.") |> Option.defaultValue "") + Field.NameToPath this.Name dialect


/// How fields should be matched
[<Struct>]
type FieldMatch =
    /// Any field matches (OR)
    | Any
    /// All fields match (AND)
    | All
    
    /// The SQL value implementing each matching strategy
    override this.ToString() =
        match this with Any -> "OR" | All -> "AND"


/// Derive parameter names (each instance wraps a counter to uniquely name anonymous fields)
type ParameterName() =
    /// The counter for the next field value
    let mutable currentIdx = -1
    
    /// Return the specified name for the parameter, or an anonymous parameter name if none is specified
    member this.Derive paramName =
        match paramName with
        | Some it -> it
        | None ->
            currentIdx <- currentIdx + 1
            $"@field{currentIdx}"

#if NET6_0
open System.Text
#endif

/// Automatically-generated document ID strategies
[<Struct>]
type AutoId =
    /// No automatic IDs will be generated
    | Disabled
    /// Generate a MAX-plus-1 numeric value for documents
    | Number
    /// Generate a GUID for each document (as a lowercase, no-dashes, 32-character string)
    | Guid
    /// Generate a random string of hexadecimal characters for each document
    | RandomString
with
    /// Generate a GUID string
    static member GenerateGuid () =
        System.Guid.NewGuid().ToString "N"
    
    /// Generate a string of random hexadecimal characters
    static member GenerateRandomString (length: int) =
#if NET8_0_OR_GREATER
        RandomNumberGenerator.GetHexString(length, lowercase = true)
#else
        RandomNumberGenerator.GetBytes((length / 2) + 1)
        |> Array.fold (fun (str: StringBuilder) byt -> str.Append(byt.ToString "x2")) (StringBuilder length)
        |> function it -> it.Length <- length; it.ToString()
#endif
    
    /// Does the given document need an automatic ID generated?
    static member NeedsAutoId<'T> strategy (document: 'T) idProp =
        match strategy with
        | Disabled -> false
        | _ ->
            let prop = document.GetType().GetProperty idProp
            if isNull prop then invalidOp $"{idProp} not found in document"
            else
                match strategy with
                | Number ->
                    if prop.PropertyType = typeof<int8> then
                        let value = prop.GetValue document :?> int8
                        value = int8 0
                    elif prop.PropertyType = typeof<int16> then
                        let value = prop.GetValue document :?> int16
                        value = int16 0
                    elif prop.PropertyType = typeof<int> then
                        let value = prop.GetValue document :?> int
                        value = 0
                    elif prop.PropertyType = typeof<int64> then
                        let value = prop.GetValue document :?> int64
                        value = int64 0
                    else invalidOp "Document ID was not a number; cannot auto-generate a Number ID"
                | Guid | RandomString ->
                    if prop.PropertyType = typeof<string> then
                        let value =
                            prop.GetValue document
                            |> Option.ofObj
                            |> Option.map (fun it -> it :?> string)
                            |> Option.defaultValue ""
                        value = ""
                    else invalidOp "Document ID was not a string; cannot auto-generate GUID or random string"
                | Disabled -> false


/// The required document serialization implementation
type IDocumentSerializer =
    
    /// Serialize an object to a JSON string
    abstract Serialize<'T> : 'T -> string
    
    /// Deserialize a JSON string into an object
    abstract Deserialize<'T> : string -> 'T


/// Document serializer defaults 
module DocumentSerializer =
    
    open System.Text.Json
    open System.Text.Json.Serialization
    
    /// The default JSON serializer options to use with the stock serializer
    let private jsonDefaultOpts =
        let o = JsonSerializerOptions()
        o.Converters.Add(JsonFSharpConverter())
        o
    
    /// The default JSON serializer
    [<CompiledName "Default">]
    let ``default`` =
        { new IDocumentSerializer with
            member _.Serialize<'T>(it: 'T) : string =
                JsonSerializer.Serialize(it, jsonDefaultOpts)
            member _.Deserialize<'T>(it: string) : 'T =
                JsonSerializer.Deserialize<'T>(it, jsonDefaultOpts)
        }


/// Configuration for document handling
[<RequireQualifiedAccess>]
module Configuration =

    /// The serializer to use for document manipulation
    let mutable private serializerValue = DocumentSerializer.``default``
    
    /// Register a serializer to use for translating documents to domain types
    [<CompiledName "UseSerializer">]
    let useSerializer ser =
        serializerValue <- ser

    /// Retrieve the currently configured serializer
    [<CompiledName "Serializer">]
    let serializer () =
        serializerValue
    
    /// The serialized name of the ID field for documents
    let mutable private idFieldValue = "Id"
    
    /// Specify the name of the ID field for documents
    [<CompiledName "UseIdField">]
    let useIdField it =
        idFieldValue <- it
    
    /// Retrieve the currently configured ID field for documents
    [<CompiledName "IdField">]
    let idField () =
        idFieldValue
    
    /// The automatic ID strategy used by the library
    let mutable private autoIdValue = Disabled
    
    /// Specify the automatic ID generation strategy used by the library
    [<CompiledName "UseAutoIdStrategy">]
    let useAutoIdStrategy it =
        autoIdValue <- it
    
    /// Retrieve the currently configured automatic ID generation strategy
    [<CompiledName "AutoIdStrategy">]
    let autoIdStrategy () =
        autoIdValue
    
    /// The length of automatically generated random strings
    let mutable private idStringLengthValue = 16
    
    /// Specify the length of automatically generated random strings
    [<CompiledName "UseIdStringLength">]
    let useIdStringLength length =
        idStringLengthValue <- length
    
    /// Retrieve the currently configured length of automatically generated random strings
    [<CompiledName "IdStringLength">]
    let idStringLength () =
        idStringLengthValue


/// Query construction functions
[<RequireQualifiedAccess>]
module Query =
    
    /// Combine a query (select, update, etc.) and a WHERE clause 
    [<CompiledName "StatementWhere">]
    let statementWhere statement where =
        $"%s{statement} WHERE %s{where}"
    
    /// Queries to define tables and indexes
    module Definition =
        
        /// SQL statement to create a document table
        [<CompiledName "EnsureTableFor">]
        let ensureTableFor name dataType =
            $"CREATE TABLE IF NOT EXISTS %s{name} (data %s{dataType} NOT NULL)"
        
        /// Split a schema and table name
        let private splitSchemaAndTable (tableName: string) =
            let parts = tableName.Split '.'
            if Array.length parts = 1 then "", tableName else parts[0], parts[1]
        
        /// SQL statement to create an index on one or more fields in a JSON document
        [<CompiledName "EnsureIndexOn">]
        let ensureIndexOn tableName indexName (fields: string seq) dialect =
            let _, tbl = splitSchemaAndTable tableName
            let jsonFields =
                fields
                |> Seq.map (fun it ->
                    let parts = it.Split ' '
                    let fieldName = if Array.length parts = 1 then it else parts[0]
                    let direction = if Array.length parts < 2 then "" else $" {parts[1]}"
                    $"({Field.NameToPath fieldName dialect}){direction}")
                |> String.concat ", "
            $"CREATE INDEX IF NOT EXISTS idx_{tbl}_%s{indexName} ON {tableName} ({jsonFields})"

        /// SQL statement to create a key index for a document table
        [<CompiledName "EnsureKey">]
        let ensureKey tableName dialect =
            (ensureIndexOn tableName "key" [ Configuration.idField () ] dialect).Replace("INDEX", "UNIQUE INDEX")
        
    /// Query to insert a document
    [<CompiledName "Insert">]
    let insert tableName =
        $"INSERT INTO %s{tableName} VALUES (@data)"

    /// Query to save a document, inserting it if it does not exist and updating it if it does (AKA "upsert")
    [<CompiledName "Save">]
    let save tableName =
        sprintf
            "INSERT INTO %s VALUES (@data) ON CONFLICT ((data->>'%s')) DO UPDATE SET data = EXCLUDED.data"
            tableName (Configuration.idField ()) 
    
    /// Query to count documents in a table (no WHERE clause)
    [<CompiledName "Count">]
    let count tableName =
        $"SELECT COUNT(*) AS it FROM %s{tableName}"
    
    /// Query to check for document existence in a table
    [<CompiledName "Exists">]
    let exists tableName where =
        $"SELECT EXISTS (SELECT 1 FROM %s{tableName} WHERE %s{where}) AS it"
    
    /// Query to select documents from a table (no WHERE clause)
    [<CompiledName "Find">]
    let find tableName =
        $"SELECT data FROM %s{tableName}"
    
    /// Query to update a document (no WHERE clause)
    [<CompiledName "Update">]
    let update tableName =
        $"UPDATE %s{tableName} SET data = @data"
    
    /// Query to delete documents from a table (no WHERE clause)
    [<CompiledName "Delete">]
    let delete tableName =
        $"DELETE FROM %s{tableName}"
    
    /// Create a SELECT clause to retrieve the document data from the given table
    [<CompiledName "SelectFromTable">]
    [<System.Obsolete "Use Find instead">]
    let selectFromTable tableName =
        find tableName
    
    /// Create an ORDER BY clause for the given fields
    [<CompiledName "OrderBy">]
    let orderBy fields dialect =
        if Seq.isEmpty fields then ""
        else
            fields
            |> Seq.map (fun it ->
                if it.Name.Contains ' ' then
                    let parts = it.Name.Split ' '
                    { it with Name = parts[0] }, Some $""" {parts |> Array.skip 1 |> String.concat " "}"""
                else it, None)
            |> Seq.map (fun (field, direction) ->
                if field.Name.StartsWith "n:" then
                    let f = { field with Name = field.Name[2..] }
                    match dialect with PostgreSQL -> $"({f.Path PostgreSQL})::numeric" | SQLite -> f.Path SQLite
                elif field.Name.StartsWith "i:" then
                    let p = { field with Name = field.Name[2..] }.Path dialect
                    match dialect with PostgreSQL ->  $"LOWER({p})" | SQLite -> $"{p} COLLATE NOCASE"
                else field.Path dialect
                |> function path -> path + defaultArg direction "")
            |> String.concat ", "
            |> function it -> $" ORDER BY {it}"