unit Myc.Ast;

interface

uses
    System.SysUtils,
    System.Generics.Collections,
    Myc.Data.Types;

type
    // Operators are now type-safe enums
    TBinaryOperator = (boAdd, boSubtract, boMultiply, boDivide, boEqual, boNotEqual, boLess, boGreater, boLessOrEqual, boGreaterOrEqual);
    TUnaryOperator = (uoNegate, uoNot);

    // Helper to convert operators to string
    TBinaryOperatorHelper = record helper for TBinaryOperator
        function ToString: string;
    end;

    TUnaryOperatorHelper = record helper for TUnaryOperator
        function ToString: string;
    end;

    // Forward declarations for interfaces
    IAstVisitor = interface;
    IAstNode = interface;
    IExpressionNode = interface;
    IConstantNode = interface;
    IIdentifierNode = interface;
    IBinaryExpressionNode = interface;
    IUnaryExpressionNode = interface;
    IIfExpressionNode = interface;
    ILambdaExpressionNode = interface;
    IFunctionCallNode = interface;
    IBlockExpressionNode = interface;
    IVariableDeclarationNode = interface;

    // --- Abstract Node Interfaces ---

    // Base interface for all AST nodes
    IAstNode = interface(IInterface)
        // Accept is a function that returns the result of the visit.
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    // Abstract interface for all nodes that evaluate to a value.
    // In this paradigm, all nodes are expressions.
    IExpressionNode = interface(IAstNode)
    end;

    // --- Concrete Expression Node Interfaces ---

    IConstantNode = interface(IExpressionNode)
        {$region 'private'}
        function GetValue: IDataValue;
        {$endregion}
        property Value: IDataValue read GetValue;
    end;

    IIdentifierNode = interface(IExpressionNode)
        {$region 'private'}
        function GetName: string;
        {$endregion}
        property Name: string read GetName;
    end;

    IBinaryExpressionNode = interface(IExpressionNode)
        {$region 'private'}
        function GetLeft: IExpressionNode;
        function GetOperator: TBinaryOperator;
        function GetRight: IExpressionNode;
        {$endregion}
        property Left: IExpressionNode read GetLeft;
        property Operator: TBinaryOperator read GetOperator;
        property Right: IExpressionNode read GetRight;
    end;

    IUnaryExpressionNode = interface(IExpressionNode)
        {$region 'private'}
        function GetOperator: TUnaryOperator;
        function GetRight: IExpressionNode;
        {$endregion}
        property Operator: TUnaryOperator read GetOperator;
        property Right: IExpressionNode read GetRight;
    end;

    IIfExpressionNode = interface(IExpressionNode)
        {$region 'private'}
        function GetCondition: IExpressionNode;
        function GetThenBranch: IExpressionNode;
        function GetElseBranch: IExpressionNode;
        {$endregion}
        property Condition: IExpressionNode read GetCondition;
        property ThenBranch: IExpressionNode read GetThenBranch;
        property ElseBranch: IExpressionNode read GetElseBranch;
    end;

    ILambdaExpressionNode = interface(IExpressionNode)
        {$region 'private'}
        function GetParameters: TList<IIdentifierNode>;
        function GetBody: IExpressionNode; // Body is now always an expression
        {$endregion}
        property Parameters: TList<IIdentifierNode> read GetParameters;
        property Body: IExpressionNode read GetBody;
    end;

    IFunctionCallNode = interface(IExpressionNode)
        {$region 'private'}
        function GetCallee: IExpressionNode;
        function GetArguments: TList<IExpressionNode>;
        {$endregion}
        property Callee: IExpressionNode read GetCallee;
        property Arguments: TList<IExpressionNode> read GetArguments;
    end;

    // A block is an expression that returns the value of its last expression.
    IBlockExpressionNode = interface(IExpressionNode)
        {$region 'private'}
        function GetExpressions: TList<IExpressionNode>;
        {$endregion}
        property Expressions: TList<IExpressionNode> read GetExpressions;
    end;

    // A variable declaration is an expression that returns a void value.
    IVariableDeclarationNode = interface(IExpressionNode)
        {$region 'private'}
        function GetIdentifier: IIdentifierNode;
        function GetInitializer: IExpressionNode; // Can be nil
        {$endregion}
        property Identifier: IIdentifierNode read GetIdentifier;
        property Initializer: IExpressionNode read GetInitializer;
    end;

    // All visitor methods are functions returning a value.
    IAstVisitor = interface
        ['{5F4110E9-0158-41E9-A512-E57A843E8A5A}']
        function VisitConstant(const Node: IConstantNode): IDataValue;
        function VisitIdentifier(const Node: IIdentifierNode): IDataValue;
        function VisitBinaryExpression(const Node: IBinaryExpressionNode): IDataValue;
        function VisitUnaryExpression(const Node: IUnaryExpressionNode): IDataValue;
        function VisitIfExpression(const Node: IIfExpressionNode): IDataValue;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): IDataValue;
        function VisitFunctionCall(const Node: IFunctionCallNode): IDataValue;
        function VisitBlockExpression(const Node: IBlockExpressionNode): IDataValue;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): IDataValue;
    end;

    // Record acting as a namespace for the factory functions.
    TAst = record
        class function Constant(AValue: IDataValue): IConstantNode; static;
        class function Identifier(AName: string): IIdentifierNode; static;
        class function BinaryExpr(
            ALeft: IExpressionNode;
            AOperator: TBinaryOperator;
            ARight: IExpressionNode
        ): IBinaryExpressionNode; static;
        class function UnaryExpr(const AOperator: TUnaryOperator; const ARight: IExpressionNode): IUnaryExpressionNode; static;
        class function IfExpr(
            const ACondition: IExpressionNode;
            const AThenBranch, AElseBranch: IExpressionNode
        ): IIfExpressionNode; static;
        class function LambdaExpr(const AParameters: array of IIdentifierNode; const ABody: IExpressionNode): ILambdaExpressionNode; static;
        class function FunctionCall(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode): IFunctionCallNode; static;
        class function Block(const AExpressions: array of IExpressionNode): IBlockExpressionNode; static;
        class function VarDecl(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode): IVariableDeclarationNode; static;
    end;

implementation

{ TBinaryOperatorHelper }

function TBinaryOperatorHelper.ToString: string;
begin
    case Self of
        boAdd: Result := '+';
        boSubtract: Result := '-';
        boMultiply: Result := '*';
        boDivide: Result := '/';
        boEqual: Result := '==';
        boNotEqual: Result := '!=';
        boLess: Result := '<';
        boGreater: Result := '>';
        boLessOrEqual: Result := '<=';
        boGreaterOrEqual: Result := '>=';
    else
        Result := '?';
    end;
end;

{ TUnaryOperatorHelper }

function TUnaryOperatorHelper.ToString: string;
begin
    case Self of
        uoNegate: Result := '-';
        uoNot: Result := 'not';
    else
        Result := '?';
    end;
end;

type
    TConstantNodeImpl = class(TInterfacedObject, IConstantNode)
    private
        FValue: IDataValue;
        function GetValue: IDataValue;
    public
        constructor Create(AValue: IDataValue);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TIdentifierNodeImpl = class(TInterfacedObject, IIdentifierNode)
    private
        FName: string;
        function GetName: string;
    public
        constructor Create(AName: string);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TBinaryExpressionNodeImpl = class(TInterfacedObject, IBinaryExpressionNode)
    private
        FLeft: IExpressionNode;
        FOperator: TBinaryOperator;
        FRight: IExpressionNode;
        function GetLeft: IExpressionNode;
        function GetOperator: TBinaryOperator;
        function GetRight: IExpressionNode;
    public
        constructor Create(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TUnaryExpressionNodeImpl = class(TInterfacedObject, IUnaryExpressionNode)
    private
        FOperator: TUnaryOperator;
        FRight: IExpressionNode;
        function GetOperator: TUnaryOperator;
        function GetRight: IExpressionNode;
    public
        constructor Create(AOperator: TUnaryOperator; ARight: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TIfExpressionNodeImpl = class(TInterfacedObject, IIfExpressionNode)
    private
        FCondition: IExpressionNode;
        FThenBranch: IExpressionNode;
        FElseBranch: IExpressionNode;
        function GetCondition: IExpressionNode;
        function GetThenBranch: IExpressionNode;
        function GetElseBranch: IExpressionNode;
    public
        constructor Create(ACondition, AThenBranch, AElseBranch: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TLambdaExpressionNodeImpl = class(TInterfacedObject, ILambdaExpressionNode)
    private
        FParameters: TList<IIdentifierNode>;
        FBody: IExpressionNode;
        function GetParameters: TList<IIdentifierNode>;
        function GetBody: IExpressionNode;
    public
        constructor Create(AParameters: TList<IIdentifierNode>; ABody: IExpressionNode);
        destructor Destroy; override;
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TFunctionCallNodeImpl = class(TInterfacedObject, IFunctionCallNode)
    private
        FCallee: IExpressionNode;
        FArguments: TList<IExpressionNode>;
        function GetCallee: IExpressionNode;
        function GetArguments: TList<IExpressionNode>;
    public
        constructor Create(ACallee: IExpressionNode; AArguments: TList<IExpressionNode>);
        destructor Destroy; override;
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TBlockExpressionNodeImpl = class(TInterfacedObject, IBlockExpressionNode)
    private
        FExpressions: TList<IExpressionNode>;
        function GetExpressions: TList<IExpressionNode>;
    public
        constructor Create(AExpressions: TList<IExpressionNode>);
        destructor Destroy; override;
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

    TVariableDeclarationNodeImpl = class(TInterfacedObject, IVariableDeclarationNode)
    private
        FIdentifier: IIdentifierNode;
        FInitializer: IExpressionNode;
        function GetIdentifier: IIdentifierNode;
        function GetInitializer: IExpressionNode;
    public
        constructor Create(AIdentifier: IIdentifierNode; AInitializer: IExpressionNode);
        function Accept(const Visitor: IAstVisitor): IDataValue;
    end;

{ TAst - Factory Function Implementations }

class function TAst.Constant(AValue: IDataValue): IConstantNode;
begin
    Result := TConstantNodeImpl.Create(AValue);
end;

class function TAst.Identifier(AName: string): IIdentifierNode;
begin
    Result := TIdentifierNodeImpl.Create(AName);
end;

class function TAst.BinaryExpr(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode): IBinaryExpressionNode;
begin
    Result := TBinaryExpressionNodeImpl.Create(ALeft, AOperator, ARight);
end;

class function TAst.UnaryExpr(const AOperator: TUnaryOperator; const ARight: IExpressionNode): IUnaryExpressionNode;
begin
    Result := TUnaryExpressionNodeImpl.Create(AOperator, ARight);
end;

class function TAst.IfExpr(const ACondition: IExpressionNode; const AThenBranch, AElseBranch: IExpressionNode): IIfExpressionNode;
begin
    Result := TIfExpressionNodeImpl.Create(ACondition, AThenBranch, AElseBranch);
end;

class function TAst.LambdaExpr(const AParameters: array of IIdentifierNode; const ABody: IExpressionNode): ILambdaExpressionNode;
var
    paramList: TList<IIdentifierNode>;
    param: IIdentifierNode;
begin
    paramList := TList<IIdentifierNode>.Create;
    for param in AParameters do
        paramList.Add(param);
    Result := TLambdaExpressionNodeImpl.Create(paramList, ABody);
end;

class function TAst.FunctionCall(const ACallee: IExpressionNode; const AArguments: array of IExpressionNode): IFunctionCallNode;
var
    argList: TList<IExpressionNode>;
    arg: IExpressionNode;
begin
    argList := TList<IExpressionNode>.Create;
    for arg in AArguments do
        argList.Add(arg);
    Result := TFunctionCallNodeImpl.Create(ACallee, argList);
end;

class function TAst.Block(const AExpressions: array of IExpressionNode): IBlockExpressionNode;
var
    exprList: TList<IExpressionNode>;
    expr: IExpressionNode;
begin
    exprList := TList<IExpressionNode>.Create;
    for expr in AExpressions do
        exprList.Add(expr);
    Result := TBlockExpressionNodeImpl.Create(exprList);
end;

class function TAst.VarDecl(const AIdentifier: IIdentifierNode; AInitializer: IExpressionNode): IVariableDeclarationNode;
begin
    Result := TVariableDeclarationNodeImpl.Create(AIdentifier, AInitializer);
end;

{ TConstantNodeImpl }

constructor TConstantNodeImpl.Create(AValue: IDataValue);
begin
    inherited Create;
    FValue := AValue;
end;

function TConstantNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitConstant(Self);
end;

function TConstantNodeImpl.GetValue: IDataValue;
begin
    Result := FValue;
end;

{ TIdentifierNodeImpl }

constructor TIdentifierNodeImpl.Create(AName: string);
begin
    inherited Create;
    FName := AName;
end;

function TIdentifierNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitIdentifier(Self);
end;

function TIdentifierNodeImpl.GetName: string;
begin
    Result := FName;
end;

{ TBinaryExpressionNodeImpl }

constructor TBinaryExpressionNodeImpl.Create(ALeft: IExpressionNode; AOperator: TBinaryOperator; ARight: IExpressionNode);
begin
    inherited Create;
    FLeft := ALeft;
    FOperator := AOperator;
    FRight := ARight;
end;

function TBinaryExpressionNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitBinaryExpression(Self);
end;

function TBinaryExpressionNodeImpl.GetLeft: IExpressionNode;
begin
    Result := FLeft;
end;

function TBinaryExpressionNodeImpl.GetOperator: TBinaryOperator;
begin
    Result := FOperator;
end;

function TBinaryExpressionNodeImpl.GetRight: IExpressionNode;
begin
    Result := FRight;
end;

{ TUnaryExpressionNodeImpl }

constructor TUnaryExpressionNodeImpl.Create(AOperator: TUnaryOperator; ARight: IExpressionNode);
begin
    inherited Create;
    FOperator := AOperator;
    FRight := ARight;
end;

function TUnaryExpressionNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitUnaryExpression(Self);
end;

function TUnaryExpressionNodeImpl.GetOperator: TUnaryOperator;
begin
    Result := FOperator;
end;

function TUnaryExpressionNodeImpl.GetRight: IExpressionNode;
begin
    Result := FRight;
end;

{ TIfExpressionNodeImpl }

constructor TIfExpressionNodeImpl.Create(ACondition, AThenBranch, AElseBranch: IExpressionNode);
begin
    inherited Create;
    FCondition := ACondition;
    FThenBranch := AThenBranch;
    FElseBranch := AElseBranch;
end;

function TIfExpressionNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitIfExpression(Self);
end;

function TIfExpressionNodeImpl.GetCondition: IExpressionNode;
begin
    Result := FCondition;
end;

function TIfExpressionNodeImpl.GetElseBranch: IExpressionNode;
begin
    Result := FElseBranch;
end;

function TIfExpressionNodeImpl.GetThenBranch: IExpressionNode;
begin
    Result := FThenBranch;
end;

{ TLambdaExpressionNodeImpl }

constructor TLambdaExpressionNodeImpl.Create(AParameters: TList<IIdentifierNode>; ABody: IExpressionNode);
begin
    inherited Create;
    FParameters := AParameters;
    FBody := ABody;
end;

destructor TLambdaExpressionNodeImpl.Destroy;
begin
    FParameters.Free;
    inherited Destroy;
end;

function TLambdaExpressionNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitLambdaExpression(Self);
end;

function TLambdaExpressionNodeImpl.GetBody: IExpressionNode;
begin
    Result := FBody;
end;

function TLambdaExpressionNodeImpl.GetParameters: TList<IIdentifierNode>;
begin
    Result := FParameters;
end;

{ TFunctionCallNodeImpl }

constructor TFunctionCallNodeImpl.Create(ACallee: IExpressionNode; AArguments: TList<IExpressionNode>);
begin
    inherited Create;
    FCallee := ACallee;
    FArguments := AArguments;
end;

destructor TFunctionCallNodeImpl.Destroy;
begin
    FArguments.Free;
    inherited Destroy;
end;

function TFunctionCallNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitFunctionCall(Self);
end;

function TFunctionCallNodeImpl.GetArguments: TList<IExpressionNode>;
begin
    Result := FArguments;
end;

function TFunctionCallNodeImpl.GetCallee: IExpressionNode;
begin
    Result := FCallee;
end;

{ TBlockExpressionNodeImpl }

constructor TBlockExpressionNodeImpl.Create(AExpressions: TList<IExpressionNode>);
begin
    inherited Create;
    FExpressions := AExpressions;
end;

destructor TBlockExpressionNodeImpl.Destroy;
begin
    FExpressions.Free;
    inherited Destroy;
end;

function TBlockExpressionNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitBlockExpression(Self);
end;

function TBlockExpressionNodeImpl.GetExpressions: TList<IExpressionNode>;
begin
    Result := FExpressions;
end;

{ TVariableDeclarationNodeImpl }

constructor TVariableDeclarationNodeImpl.Create(AIdentifier: IIdentifierNode; AInitializer: IExpressionNode);
begin
    inherited Create;
    FIdentifier := AIdentifier;
    FInitializer := AInitializer;
end;

function TVariableDeclarationNodeImpl.Accept(const Visitor: IAstVisitor): IDataValue;
begin
    Result := Visitor.VisitVariableDeclaration(Self);
end;

function TVariableDeclarationNodeImpl.GetIdentifier: IIdentifierNode;
begin
    Result := FIdentifier;
end;

function TVariableDeclarationNodeImpl.GetInitializer: IExpressionNode;
begin
    Result := FInitializer;
end;

end.