unit Myc.Ast.Script;

interface

uses
    System.SysUtils,
    Myc.Ast.Nodes;

type
    // Provides a high-level facade for parsing and printing the AST.
    TAstScript = record
    public
        class function Parse(const ASource: string): IAstNode; static;
        class function Print(const ANode: IAstNode): string; static;
    end;

implementation

uses
    System.Classes,
    System.Generics.Collections,
    System.Character,
    System.Math,
    Myc.Data.Scalar,
    Myc.Data.Value,
    Myc.Ast;

type

    // --- Internal Parser Implementation ---

    TTokenKind = (
        tkLeftParen, // (
        tkRightParen, // )
        tkLeftBracket, // [
        tkRightBracket, // ]
        tkIdentifier,
        tkNumber,
        tkString,
        tkEOF,
        tkError
    );

    TTokenKindHelper = record helper for TTokenKind
        function ToString: String;
    end;

    TToken = record
        Kind: TTokenKind;
        Text: string;
    end;

    TLexer = class
    private
        FSource: string;
        FCurrentPos: Integer;
        function Peek: Char;
        procedure Advance;
        function ReadNumber: string;
        function ReadString: string;
        function ReadIdentifier: string;
    public
        constructor Create(const ASource: string);
        function GetNextToken: TToken;
    end;

    TExpr = record
        Token: TToken;
        Node: IAstNode;
        Params: TArray<IIdentifierNode>;
    end;

    TParser = class
    private
        FLexer: TLexer;
        FCurrentToken: TToken;
        procedure Consume(AExpectedKind: TTokenKind);
        procedure NextToken;
        function ParseList: IAstNode;
        function ParseParameterList: TArray<IIdentifierNode>;
        function ParseExpression: TExpr;
    public
        constructor Create(const ASource: string);
        destructor Destroy; override;
        function Parse: IAstNode;
    end;

    // --- Internal Printer Implementation ---

    TPrettyPrintVisitor = class(TInterfacedObject, IAstVisitor)
    private
        FBuilder: TStringBuilder;
        FIndentLevel: Integer;
        procedure Indent;
        procedure Unindent;
        procedure Append(const S: string);
        procedure NewLine;
    public
        constructor Create;
        destructor Destroy; override;
        function GetResult: string;
        // IAstVisitor
        function Execute(const RootNode: IAstNode): TDataValue;
        function VisitConstant(const Node: IConstantNode): TDataValue;
        function VisitIdentifier(const Node: IIdentifierNode): TDataValue;
        function VisitBinaryExpression(const Node: IBinaryExpressionNode): TDataValue;
        function VisitUnaryExpression(const Node: IUnaryExpressionNode): TDataValue;
        function VisitIfExpression(const Node: IIfExpressionNode): TDataValue;
        function VisitTernaryExpression(const Node: ITernaryExpressionNode): TDataValue;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): TDataValue;
        function VisitFunctionCall(const Node: IFunctionCallNode): TDataValue;
        function VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): TDataValue;
        function VisitAssignment(const Node: IAssignmentNode): TDataValue;
        function VisitIndexer(const Node: IIndexerNode): TDataValue;
        function VisitMemberAccess(const Node: IMemberAccessNode): TDataValue;
        function VisitCreateSeries(const Node: ICreateSeriesNode): TDataValue;
        function VisitAddSeriesItem(const Node: IAddSeriesItemNode): TDataValue;
        function VisitSeriesLength(const Node: ISeriesLengthNode): TDataValue;
        function VisitRecurNode(const Node: IRecurNode): TDataValue;
    end;

{ TLexer }

constructor TLexer.Create(const ASource: string);
begin
    inherited Create;
    FSource := ASource;
    FCurrentPos := 1;
end;

function TLexer.Peek: Char;
begin
    if FCurrentPos > Length(FSource) then
        Result := #0
    else
        Result := FSource[FCurrentPos];
end;

procedure TLexer.Advance;
begin
    inc(FCurrentPos);
end;

function TLexer.ReadIdentifier: string;
var
    startPos: Integer;
begin
    startPos := FCurrentPos;
    // Corrected W1050: Use CharInSet for robust unicode support.
    while (Peek <> #0) and (not (Peek.IsWhiteSpace or CharInSet(Peek, ['(', ')', '[', ']']))) do
        Advance;
    Result := Copy(FSource, startPos, FCurrentPos - startPos);
end;

function TLexer.ReadNumber: string;
var
    startPos: Integer;
begin
    startPos := FCurrentPos;
    while (Peek <> #0) and (Peek.IsDigit or (Peek = '.')) do
        Advance;
    Result := Copy(FSource, startPos, FCurrentPos - startPos);
end;

function TLexer.ReadString: string;
var
    startPos: Integer;
begin
    Advance; // Skip opening "
    startPos := FCurrentPos;
    while (Peek <> #0) and (Peek <> '"') do
        Advance;
    Result := Copy(FSource, startPos, FCurrentPos - startPos);
    if Peek = '"' then
        Advance; // Skip closing "
end;

function TLexer.GetNextToken: TToken;
begin
    while (FCurrentPos <= Length(FSource)) and FSource[FCurrentPos].IsWhiteSpace do
        Advance;

    if FCurrentPos > Length(FSource) then
    begin
        Result.Kind := tkEOF;
        exit;
    end;

    var c := Peek;
    case c of
        '(':
        begin
            Result.Kind := tkLeftParen;
            Advance;
        end;
        ')':
        begin
            Result.Kind := tkRightParen;
            Advance;
        end;
        '[':
        begin
            Result.Kind := tkLeftBracket;
            Advance;
        end;
        ']':
        begin
            Result.Kind := tkRightBracket;
            Advance;
        end;
        '"':
        begin
            Result.Kind := tkString;
            Result.Text := ReadString;
        end;
    else
        if c.IsDigit or ((c = '-') and (FCurrentPos < Length(FSource)) and FSource[FCurrentPos + 1].IsDigit) then
        begin
            Result.Kind := tkNumber;
            Result.Text := ReadNumber;
        end
        else
        begin
            Result.Kind := tkIdentifier;
            Result.Text := ReadIdentifier;
        end;
    end;
end;

{ TParser }

constructor TParser.Create(const ASource: string);
begin
    inherited Create;
    FLexer := TLexer.Create(ASource);
    NextToken; // Load the first token
end;

destructor TParser.Destroy;
begin
    FLexer.Free;
    inherited;
end;

procedure TParser.NextToken;
begin
    FCurrentToken := FLexer.GetNextToken;
end;

procedure TParser.Consume(AExpectedKind: TTokenKind);
begin
    if FCurrentToken.Kind <> AExpectedKind then
        raise Exception.CreateFmt('Syntax Error: Expected token %s, but found %s', [AExpectedKind.ToString, FCurrentToken.Kind.ToString]);
    NextToken;
end;

function TParser.ParseParameterList: TArray<IIdentifierNode>;
var
    params: TList<IIdentifierNode>;
begin
    Consume(tkLeftBracket);
    params := TList<IIdentifierNode>.Create;
    try
        while FCurrentToken.Kind <> tkRightBracket do
        begin
            if FCurrentToken.Kind = tkEOF then
                raise Exception.Create('Syntax Error: Unexpected end of file.');
            if FCurrentToken.Kind <> tkIdentifier then
                raise Exception.Create('Syntax Error: Expected identifier in parameter list.');
            params.Add(TAst.Identifier(FCurrentToken.Text));
            NextToken;
        end;
        Result := params.ToArray;
    finally
        params.Free;
    end;
    Consume(tkRightBracket);
end;

function TParser.ParseList: IAstNode;

    function IfThen(cond: Boolean; const TrueBranch, FalseBranch: IAstNode): IAstNode;
    begin
        if cond then
            exit(TrueBranch)
        else
            exit(FalseBranch);
    end;

var
    elements: TList<TExpr>;
    head: TExpr;
    tailTokens: TArray<TToken>;
    tailNodes: TArray<IAstNode>;
begin
    Consume(tkLeftParen);
    if FCurrentToken.Kind = tkRightParen then
        raise Exception.Create('Syntax Error: Empty list () is not a valid expression.');

    elements := TList<TExpr>.Create;
    try
        while FCurrentToken.Kind <> tkRightParen do
        begin
            if FCurrentToken.Kind = tkEOF then
                raise Exception.Create('Syntax Error: Unexpected end of file.');
            elements.Add(ParseExpression);
        end;

        head := elements[0];

        // Convert the rest of the list to an array for the factory functions
        SetLength(tailTokens, elements.Count - 1);
        SetLength(tailNodes, elements.Count - 1);
        for var i := 0 to High(tailNodes) do
        begin
            tailTokens[i] := elements[i + 1].Token;
            tailNodes[i] := elements[i + 1].Node;
        end;

        if head.Token.Kind = tkIdentifier then
        begin
            // Handle special forms
            if SameText(head.Token.Text, 'if') then
            begin
                if not (Length(tailNodes) in [2, 3]) then
                    raise Exception.Create('Syntax Error in if statement.');

                Result := TAst.IfExpr(tailNodes[0], tailNodes[1], IfThen(Length(tailNodes) > 2, tailNodes[2], nil))
            end
            else if SameText(head.Token.Text, '?') then
            begin
                if Length(tailNodes) <> 3 then
                    raise Exception.Create('Syntax Error in ternary statement.');

                Result := TAst.TernaryExpr(tailNodes[0], tailNodes[1], tailNodes[2]);
            end
            else if SameText(head.Token.Text, 'def') then
            begin
                if tailTokens[0].Kind <> tkIdentifier then
                    raise Exception.Create('Syntax Error: Expected an identifier for def statement.');
                Result := TAst.VarDecl(IIdentifierNode(tailNodes[0]), IfThen(Length(tailNodes) > 1, tailNodes[1], nil));
            end
            else if SameText(head.Token.Text, 'assign') then
            begin
                if tailTokens[0].Kind <> tkIdentifier then
                    raise Exception.Create('Syntax Error: Expected an identifier for assignment.');
                Result := TAst.Assign(IIdentifierNode(tailNodes[0]), tailNodes[1]);
            end
            else if SameText(head.Token.Text, 'fn') then
                Result := TAst.LambdaExpr(elements[High(tailNodes)].Params, tailNodes[1])
            else if SameText(head.Token.Text, 'do') then
                Result := TAst.Block(tailNodes)
            else if SameText(head.Token.Text, 'recur') then
                Result := TAst.Recur(tailNodes)
            else if SameText(head.Token.Text, 'get') then
                Result := TAst.Indexer(tailNodes[0], tailNodes[1])
            else if (Length(head.Token.Text) > 1) and (head.Token.Text.StartsWith('.')) then
                Result := TAst.MemberAccess(tailNodes[0], TAst.Identifier(head.Token.Text.Substring(1)))
            else
            begin
                if Length(tailNodes) = 1 then
                begin
                    for var op := Low(TScalar.TUnaryOp) to High(TScalar.TUnaryOp) do
                    begin
                        if head.Token.Text = op.ToString then
                        begin
                            Result := TAst.UnaryExpr(op, tailNodes[0]);
                            break
                        end;
                    end;
                end
                else if Length(tailNodes) = 2 then
                begin
                    for var op := Low(TScalar.TBinaryOp) to High(TScalar.TBinaryOp) do
                    begin
                        if head.Token.Text = op.ToString then
                        begin
                            Result := TAst.BinaryExpr(tailNodes[0], op, tailNodes[1]);
                            break
                        end;
                    end;
                end;
            end;
        end;

        if Result = nil then
            Result := TAst.FunctionCall(head.Node, tailNodes);

    finally
        elements.Free;
    end;

    Consume(tkRightParen);
end;

function TParser.ParseExpression: TExpr;
var
    i64: Int64;
    dbl: Double;
begin
    Result.Token := FCurrentToken;
    case FCurrentToken.Kind of
        tkNumber:
        begin
            if TryStrToInt64(FCurrentToken.Text, i64) then
                Result.Node := TAst.Constant(i64)
            else if TryStrToFloat(FCurrentToken.Text, dbl) then
                Result.Node := TAst.Constant(dbl)
            else
                raise Exception.CreateFmt('Syntax Error: Invalid number format "%s"', [FCurrentToken.Text]);
            NextToken;
        end;
        tkString:
        begin
            Result.Node := TAst.Constant(FCurrentToken.Text);
            NextToken;
        end;
        tkIdentifier:
        begin
            Result.Node := TAst.Identifier(FCurrentToken.Text);
            NextToken;
        end;
        tkLeftParen: Result.Node := ParseList;
        tkLeftBracket: Result.Params := ParseParameterList;
        tkEOF: {nop};
    else
        raise Exception.CreateFmt('Syntax Error: Unexpected token %s', [FCurrentToken.Kind.ToString]);
    end;
end;

function TParser.Parse: IAstNode;
begin
    var expr := ParseExpression;
    if FCurrentToken.Kind <> tkEOF then
        raise Exception.Create('Syntax Error: Unexpected characters after end of expression.');
    Result := expr.Node;
end;

{ TPrettyPrintVisitor }
// ... (Implementation of TPrettyPrintVisitor is unchanged and correct) ...
constructor TPrettyPrintVisitor.Create;
begin
    inherited Create;
    FBuilder := TStringBuilder.Create;
    FIndentLevel := 0;
end;

destructor TPrettyPrintVisitor.Destroy;
begin
    FBuilder.Free;
    inherited Destroy;
end;

function TPrettyPrintVisitor.GetResult: string;
begin
    Result := FBuilder.ToString;
end;

procedure TPrettyPrintVisitor.Indent;
begin
    inc(FIndentLevel, 2);
end;

procedure TPrettyPrintVisitor.Unindent;
begin
    dec(FIndentLevel, 2);
end;

procedure TPrettyPrintVisitor.Append(const S: string);
begin
    FBuilder.Append(S);
end;

procedure TPrettyPrintVisitor.NewLine;
begin
    FBuilder.AppendLine;
    FBuilder.Append(''.PadLeft(FIndentLevel));
end;

function TPrettyPrintVisitor.Execute(const RootNode: IAstNode): TDataValue;
begin
    if Assigned(RootNode) then
        RootNode.Accept(Self);
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitConstant(const Node: IConstantNode): TDataValue;
var
    val: TDataValue;
begin
    val := Node.Value;
    if val.Kind = vkText then
        Append('"' + val.AsText + '"')
    else
        Append(val.ToString);
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitIdentifier(const Node: IIdentifierNode): TDataValue;
begin
    Append(Node.Name);
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitBinaryExpression(const Node: IBinaryExpressionNode): TDataValue;
begin
    Append('(' + Node.Operator.ToString);
    Append(' ');
    Node.Left.Accept(Self);
    Append(' ');
    Node.Right.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitUnaryExpression(const Node: IUnaryExpressionNode): TDataValue;
begin
    Append('(' + Node.Operator.ToString);
    Append(' ');
    Node.Right.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitIfExpression(const Node: IIfExpressionNode): TDataValue;
begin
    Append('(if ');
    Node.Condition.Accept(Self);
    Indent;
    NewLine;
    Node.ThenBranch.Accept(Self);
    if Assigned(Node.ElseBranch) then
    begin
        NewLine;
        Node.ElseBranch.Accept(Self);
    end;
    Unindent;
    NewLine;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitTernaryExpression(const Node: ITernaryExpressionNode): TDataValue;
begin
    Append('(? ');
    Node.Condition.Accept(Self);
    Indent;
    NewLine;
    Node.ThenBranch.Accept(Self);
    NewLine;
    Node.ElseBranch.Accept(Self);
    Unindent;
    NewLine;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitLambdaExpression(const Node: ILambdaExpressionNode): TDataValue;
var
    param: IIdentifierNode;
    sb: TStringBuilder;
begin
    sb := TStringBuilder.Create;
    try
        for param in Node.Parameters do
            sb.Append(param.Name + ' ');
        if sb.Length > 0 then
            sb.Remove(sb.Length - 1, 1); // remove trailing space

        Append('(fn [' + sb.ToString + ']');
    finally
        sb.Free;
    end;

    Indent;
    NewLine;
    Node.Body.Accept(Self);
    Unindent;
    NewLine;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitFunctionCall(const Node: IFunctionCallNode): TDataValue;
var
    arg: IAstNode;
begin
    Append('(');
    Node.Callee.Accept(Self);

    Indent;
    for arg in Node.Arguments do
    begin
        NewLine;
        arg.Accept(Self);
    end;
    Unindent;

    if Length(Node.Arguments) > 0 then
        NewLine;

    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitRecurNode(const Node: IRecurNode): TDataValue;
var
    arg: IAstNode;
begin
    Append('(recur');
    Indent;
    for arg in Node.Arguments do
    begin
        NewLine;
        arg.Accept(Self);
    end;
    Unindent;
    if Length(Node.Arguments) > 0 then
        NewLine;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitBlockExpression(const Node: IBlockExpressionNode): TDataValue;
var
    expr: IAstNode;
begin
    Append('(do');
    Indent;
    for expr in Node.Expressions do
    begin
        NewLine;
        expr.Accept(Self);
    end;
    Unindent;
    NewLine;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitVariableDeclaration(const Node: IVariableDeclarationNode): TDataValue;
begin
    Append('(def ');
    Node.Identifier.Accept(Self);
    if Assigned(Node.Initializer) then
    begin
        Append(' ');
        Node.Initializer.Accept(Self);
    end;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitAssignment(const Node: IAssignmentNode): TDataValue;
begin
    Append('(assign ');
    Node.Identifier.Accept(Self);
    Append(' ');
    Node.Value.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitIndexer(const Node: IIndexerNode): TDataValue;
begin
    Append('(get ');
    Node.Base.Accept(Self);
    Append(' ');
    Node.Index.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitMemberAccess(const Node: IMemberAccessNode): TDataValue;
begin
    Append('(.');
    Node.Member.Accept(Self);
    Append(' ');
    Node.Base.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitCreateSeries(const Node: ICreateSeriesNode): TDataValue;
begin
    Append(Format('(new-series "%s")', [Node.Definition]));
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitAddSeriesItem(const Node: IAddSeriesItemNode): TDataValue;
begin
    Append('(add-item ');
    Node.Series.Accept(Self);
    Append(' ');
    Node.Value.Accept(Self);
    if Assigned(Node.Lookback) then
    begin
        Append(' ');
        Node.Lookback.Accept(Self);
    end;
    Append(')');
    Result := TDataValue.Void;
end;

function TPrettyPrintVisitor.VisitSeriesLength(const Node: ISeriesLengthNode): TDataValue;
begin
    Append('(count ');
    Node.Series.Accept(Self);
    Append(')');
    Result := TDataValue.Void;
end;

{ TAstScript }

class function TAstScript.Parse(const ASource: string): IAstNode;
var
    p: TParser;
begin
    if ASource.Trim.IsEmpty then
        exit(nil);
    p := TParser.Create(ASource);
    try
        Result := p.Parse;
    finally
        p.Free;
    end;
end;

class function TAstScript.Print(const ANode: IAstNode): string;
var
    visitor: TPrettyPrintVisitor;
begin
    if not Assigned(ANode) then
        exit('');
    visitor := TPrettyPrintVisitor.Create;
    try
        visitor.Execute(ANode);
        Result := visitor.GetResult;
    finally
        visitor.Free;
    end;
end;

function TTokenKindHelper.ToString: String;
begin
    case Self of
        tkLeftParen: Result := '(';
        tkRightParen: Result := ')';
        tkLeftBracket: Result := '[';
        tkRightBracket: Result := ']';
        tkIdentifier: Result := '<identifier>';
        tkNumber: Result := '<number>';
        tkString: Result := '<string>';
        tkEOF: Result := '<EOF>';
    else
        Result := '<error>';
    end;
end;

end.