unit Myc.Ast.TypeChecker;

interface

uses
    System.SysUtils,
    System.Classes,
    System.Generics.Collections,
    Myc.Data.Scalar,
    Myc.Data.Value,
    Myc.Ast.Nodes,
    Myc.Ast.Visitor,
    Myc.Ast.Scope,
    Myc.Ast.Types,
    Myc.Ast;

type
    IAstTypeChecker = interface(IAstVisitor)
        function Execute(const RootNode: IAstNode; const ADecriptor: IScopeDescriptor): IAstNode;
    end;

    // This transformer runs *after* the TAstBinder.
    // It takes the "Bound AST" (which has addresses but mostly TTypes.Unknown)
    // and traverses it bottom-up to infer and check all static types.
    // It modifies the node.StaticType property and updates the IScopeDescriptor.
    TTypeChecker = class(TAstTransformer, IAstTypeChecker)
    private
        FCurrentDescriptor: IScopeDescriptor;
        function SetType(const Node: IAstNode; const AType: IStaticType): IAstNode;
    protected
        // Override all visit methods to perform type checking
        function VisitIdentifier(const Node: IIdentifierNode): IAstNode; override;
        function VisitVariableDeclaration(const Node: IVariableDeclarationNode): IAstNode; override;
        function VisitAssignment(const Node: IAssignmentNode): IAstNode; override;
        function VisitLambdaExpression(const Node: ILambdaExpressionNode): IAstNode; override;
        function VisitFunctionCall(const Node: IFunctionCallNode): IAstNode; override;
        function VisitBlockExpression(const Node: IBlockExpressionNode): IAstNode; override;
        function VisitIfExpression(const Node: IIfExpressionNode): IAstNode; override;
        function VisitTernaryExpression(const Node: ITernaryExpressionNode): IAstNode; override;
        function VisitBinaryExpression(const Node: IBinaryExpressionNode): IAstNode; override;
        function VisitUnaryExpression(const Node: IUnaryExpressionNode): IAstNode; override;
        function VisitMemberAccess(const Node: IMemberAccessNode): IAstNode; override;
        function VisitIndexer(const Node: IIndexerNode): IAstNode; override;
        function VisitRecordLiteral(const Node: IRecordLiteralNode): IAstNode; override;
        function VisitCreateSeries(const Node: ICreateSeriesNode): IAstNode; override;
        function VisitAddSeriesItem(const Node: IAddSeriesItemNode): IAstNode; override;
        function VisitSeriesLength(const Node: ISeriesLengthNode): IAstNode; override;
        function VisitRecurNode(const Node: IRecurNode): IAstNode; override;

        // Base cases (types are already set by Binder)
        function VisitConstant(const Node: IConstantNode): IAstNode; override;
        function VisitKeyword(const Node: IKeywordNode): IAstNode; override;

        // Compile-time nodes (should not be present)
        function VisitMacroExpansionNode(const Node: IMacroExpansionNode): IAstNode; override;
        function VisitMacroDefinition(const Node: IMacroDefinitionNode): IAstNode; override;
    public
        constructor Create(const ADescriptor: IScopeDescriptor);
        function Execute(const RootNode: IAstNode; const ADescriptor: IScopeDescriptor): IAstNode;

        class function CheckTypes(const RootNode: IAstNode; const ADescriptor: IScopeDescriptor): IAstNode; static;
    end;

implementation

uses
    System.Generics.Defaults,
    Myc.Data.Keyword;

{ TTypeChecker }

constructor TTypeChecker.Create(const ADescriptor: IScopeDescriptor);
begin
    inherited Create;
    Assert(Assigned(ADescriptor));
    FCurrentDescriptor := ADescriptor;
end;

class function TTypeChecker.CheckTypes(const RootNode: IAstNode; const ADescriptor: IScopeDescriptor): IAstNode;
begin
    var checker := TTypeChecker.Create(ADescriptor) as IAstTypeChecker;
    Result := checker.Execute(RootNode, ADescriptor);
end;

function TTypeChecker.Execute(const RootNode: IAstNode; const ADescriptor: IScopeDescriptor): IAstNode;
begin
    FCurrentDescriptor := ADescriptor;
    Result := Accept(RootNode); // Use IAstNode-returning Accept
    if not Assigned(Result) then
        Result := TAst.Block([]);

    // (Result as TAstNode).StaticType is set by the last Visit call
end;

function TTypeChecker.SetType(const Node: IAstNode; const AType: IStaticType): IAstNode;
begin
    if Assigned(Node) then
        (Node as TAstNode).StaticType := AType;
    Result := Node;
end;

function TTypeChecker.VisitConstant(const Node: IConstantNode): IAstNode;
begin
    // Type was set by Binder, just propagate it up.
    Result := inherited VisitConstant(Node);
end;

function TTypeChecker.VisitKeyword(const Node: IKeywordNode): IAstNode;
begin
    // Type was set by Binder, just propagate it up.
    Result := inherited VisitKeyword(Node);
end;

function TTypeChecker.VisitIdentifier(const Node: IIdentifierNode): IAstNode;
begin
    // Type was set by Binder (read from scope), just propagate it up.
    Result := inherited VisitIdentifier(Node);
end;

function TTypeChecker.VisitRecurNode(const Node: IRecurNode): IAstNode;
begin
    // Type was set by Binder (TTypes.Void), just propagate it up.
    Result := inherited VisitRecurNode(Node);
end;

function TTypeChecker.VisitMacroDefinition(const Node: IMacroDefinitionNode): IAstNode;
begin
    raise Exception.Create('TTypeChecker: MacroDefinition node encountered.');
end;

function TTypeChecker.VisitMacroExpansionNode(const Node: IMacroExpansionNode): IAstNode;
begin
    // TypeChecker runs *after* expansion, so we just visit the body.
    Result := Accept(Node.ExpandedBody);
end;

function TTypeChecker.VisitVariableDeclaration(const Node: IVariableDeclarationNode): IAstNode;
var
    initType: IStaticType;
    boundIdent: IIdentifierNode;
    adr: TResolvedAddress;
begin
    // 1. Visit children first (Identifier is leaf, Initializer is traversed)
    inherited;

    // 2. Get initializer type
    if Assigned(Node.Initializer) then
        initType := (Node.Initializer as TAstNode).StaticType
    else
        initType := TTypes.Void;

    // 3. Get the address from the bound identifier (SAFE CAST)
    boundIdent := Node.Identifier;
    adr := boundIdent.AsBoundIdentifierNode.Address;

    // 4. Update the type in the scope descriptor (which was set to Unknown by the binder).
    FCurrentDescriptor.UpdateType(adr.SlotIndex, initType);

    // 5. Update the static types of the nodes themselves.
    (boundIdent as TAstNode).StaticType := initType;
    Result := SetType(Node, initType);
end;

function TTypeChecker.VisitAssignment(const Node: IAssignmentNode): IAstNode;
var
    targetType, sourceType: IStaticType;
begin
    // 1. Visit children first (Identifier, Value)
    inherited;

    // 2. Get types
    targetType := (Node.Identifier as TAstNode).StaticType;
    sourceType := (Node.Value as TAstNode).StaticType;

    // 3. Check assignment
    if not TTypeRules.CanAssign(targetType, sourceType) then
        raise ETypeException.CreateFmt('Cannot assign type %s to %s', [sourceType.ToString, targetType.ToString]);

    Result := SetType(Node, targetType);
end;

function TTypeChecker.VisitLambdaExpression(const Node: ILambdaExpressionNode): IAstNode;
var
    boundNode: TLambdaExpressionNode;
    bodyType, methodType: IStaticType;
    paramTypes: TArray<IStaticType>;
    i: Integer;
    savedDescriptor: IScopeDescriptor;
begin
    boundNode := (Node as TLambdaExpressionNode);

    // 1. Enter the lambda's scope (which Binder already created)
    savedDescriptor := FCurrentDescriptor;
    FCurrentDescriptor := boundNode.ScopeDescriptor;
    try
        // 2. Parameters are leaves, so we don't try to evaluate them

        // 3. Get parameter types (currently Unknown, but required for signature)
        SetLength(paramTypes, Length(boundNode.Parameters));
        for i := 0 to High(boundNode.Parameters) do
            paramTypes[i] := (boundNode.Parameters[i] as TAstNode).StaticType; // Propagates Unknown

        // 4. Visit the body to infer its return type
        Accept(boundNode.Body);
        bodyType := (boundNode.Body as TAstNode).StaticType;

        // 5. Create the final method type
        methodType := TTypes.CreateMethod(paramTypes, bodyType);

        // 6. Update the type for <self> (Slot 0) in the descriptor
        FCurrentDescriptor.UpdateType(0, methodType);

    finally
        // 7. Restore parent descriptor
        FCurrentDescriptor := savedDescriptor;
    end;

    // 8. Set the type of the lambda node itself
    Result := SetType(boundNode, methodType);
end;

function TTypeChecker.VisitFunctionCall(const Node: IFunctionCallNode): IAstNode;
var
    calleeType, retType: IStaticType;
    i: Integer;
begin
    // 1. Visit children first (bottom-up)
    inherited;

    // 2. Get callee type (now inferred)
    calleeType := (Node.Callee as TAstNode).StaticType;
    retType := TTypes.Unknown; // Default if not a method

    // 3. Perform type checking
    if calleeType.Kind = TStaticTypeKind.stMethod then
    begin
        var signature := calleeType.Signature;
        if Length(Node.Arguments) <> Length(signature.ParamTypes) then
            raise ETypeException
                .CreateFmt('Function expects %d arguments, but got %d', [Length(signature.ParamTypes), Length(Node.Arguments)]);

        retType := signature.ReturnType;

        // Check argument types
        for i := 0 to High(Node.Arguments) do
        begin
            var argType := (Node.Arguments[i] as TAstNode).StaticType;
            var paramType := signature.ParamTypes[i];
            if not TTypeRules.CanAssign(paramType, argType) then
                raise ETypeException
                    .CreateFmt('Cannot assign argument %d (type %s) to parameter (type %s)', [i, argType.ToString, paramType.ToString]);
        end;
    end
    else if calleeType.Kind <> TStaticTypeKind.stUnknown then
        raise ETypeException.CreateFmt('Cannot invoke type %s as a function.', [calleeType.ToString]);

    // 4. Set the type for this call node
    Result := SetType(Node, retType);
end;

function TTypeChecker.VisitBlockExpression(const Node: IBlockExpressionNode): IAstNode;
var
    blockType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Type is type of last expression
    if Length(Node.Expressions) > 0 then
        blockType := (Node.Expressions[High(Node.Expressions)] as TAstNode).StaticType
    else
        blockType := TTypes.Void;

    Result := SetType(Node, blockType);
end;

function TTypeChecker.VisitIfExpression(const Node: IIfExpressionNode): IAstNode;
var
    conditionType, thenType, elseType, resultType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Check condition
    conditionType := (Node.Condition as TAstNode).StaticType;
    if (conditionType.Kind <> stUnknown) and not TTypeRules.CanAssign(TTypes.Ordinal, conditionType) then
        raise ETypeException.CreateFmt('If condition must be Ordinal, but got %s', [conditionType.ToString]);

    // 3. Promote branch types
    thenType := (Node.ThenBranch as TAstNode).StaticType;
    elseType :=
        if Node.ElseBranch <> nil then (Node.ElseBranch as TAstNode).StaticType
        else TTypes.Void;

    resultType := TTypeRules.Promote(thenType, elseType);
    Result := SetType(Node, resultType);
end;

function TTypeChecker.VisitTernaryExpression(const Node: ITernaryExpressionNode): IAstNode;
var
    conditionType, thenType, elseType, resultType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Check condition
    conditionType := (Node.Condition as TAstNode).StaticType;
    if (conditionType.Kind <> stUnknown) and not TTypeRules.CanAssign(TTypes.Ordinal, conditionType) then
        raise ETypeException.CreateFmt('Ternary condition must be Ordinal, but got %s', [conditionType.ToString]);

    // 3. Promote branch types
    thenType := (Node.ThenBranch as TAstNode).StaticType;
    elseType := (Node.ElseBranch as TAstNode).StaticType;

    resultType := TTypeRules.Promote(thenType, elseType);
    Result := SetType(Node, resultType);
end;

function TTypeChecker.VisitBinaryExpression(const Node: IBinaryExpressionNode): IAstNode;
var
    leftType, rightType, resultType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Get types
    leftType := (Node.Left as TAstNode).StaticType;
    rightType := (Node.Right as TAstNode).StaticType;

    // 3. Resolve
    resultType := TTypeRules.ResolveBinaryOp(Node.Operator, leftType, rightType);
    Result := SetType(Node, resultType);
end;

function TTypeChecker.VisitUnaryExpression(const Node: IUnaryExpressionNode): IAstNode;
var
    rightType, resultType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Get types
    rightType := (Node.Right as TAstNode).StaticType;

    // 3. Resolve
    resultType := TTypeRules.ResolveUnaryOp(Node.Operator, rightType);
    Result := SetType(Node, resultType);
end;

function TTypeChecker.VisitMemberAccess(const Node: IMemberAccessNode): IAstNode;
var
    baseType, elemType: IStaticType;
    fieldIndex: Integer;
begin
    // 1. Visit children
    inherited;

    // 2. Get types
    baseType := (Node.Base as TAstNode).StaticType;
    elemType := TTypes.Unknown;

    // 3. Resolve
    if (baseType.Kind <> TStaticTypeKind.stUnknown) then
    begin
        if (baseType.Kind = TStaticTypeKind.stRecord) or (baseType.Kind = TStaticTypeKind.stRecordSeries) then
        begin
            fieldIndex := baseType.Definition.IndexOf(Node.Member.Value);
            if fieldIndex < 0 then
                raise ETypeException.CreateFmt('Member "%s" not found in type %s', [Node.Member.Value.Name, baseType.ToString]);

            var fieldType := TTypes.FromScalarKind(baseType.Definition.Fields[fieldIndex].Value);

            if baseType.Kind = TStaticTypeKind.stRecord then
                elemType := fieldType
            else // stRecordSeries
                elemType := TTypes.CreateSeries(fieldType);
        end
        else if (baseType.Kind = TStaticTypeKind.stGenericRecord) then
        begin
            var genDef := baseType.GenericDefinition;
            fieldIndex := genDef.IndexOf(Node.Member.Value);
            if fieldIndex < 0 then
                raise ETypeException.CreateFmt('Member "%s" not found in type %s', [Node.Member.Value.Name, baseType.ToString]);
            elemType := genDef.Fields[fieldIndex].Value;
        end
        else
        begin
            raise ETypeException.CreateFmt('Member access requires a record type, but got %s', [baseType.ToString]);
        end;
    end;

    Result := SetType(Node, elemType);
end;

function TTypeChecker.VisitIndexer(const Node: IIndexerNode): IAstNode;
var
    baseType, indexType, elemType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Get types
    baseType := (Node.Base as TAstNode).StaticType;
    indexType := (Node.Index as TAstNode).StaticType;
    elemType := TTypes.Unknown;

    // 3. Resolve
    if (baseType.Kind <> TStaticTypeKind.stUnknown) then
    begin
        if (baseType.Kind <> TStaticTypeKind.stSeries) and (baseType.Kind <> TStaticTypeKind.stRecordSeries) then
            raise ETypeException.CreateFmt('Indexer `[]` can only be applied to series types, but got %s', [baseType.ToString]);

        if (indexType.Kind <> stUnknown) and not TTypeRules.CanAssign(TTypes.Ordinal, indexType) then
            raise ETypeException.CreateFmt('Indexer `[]` requires an Ordinal index, but got %s', [indexType.ToString]);

        if baseType.Kind = TStaticTypeKind.stSeries then
            elemType := baseType.ElementType
        else // stRecordSeries
            elemType := TTypes.CreateRecord(baseType.Definition);
    end;

    Result := SetType(Node, elemType);
end;

function TTypeChecker.VisitRecordLiteral(const Node: IRecordLiteralNode): IAstNode;
var
    i: Integer;
    scalarDefFields: TArray<TScalarRecordField>;
    def: IScalarRecordDefinition;
    staticType: IStaticType;
    valNode: IAstNode;
    valType: IStaticType;
    scalarKind: TScalar.TKind;
    allScalar: Boolean;
    N: TGenericRecordLiteralNode; // Parser creates this type
begin
    // 1. Visit all child nodes first to infer their types
    inherited;

    N := (Node as TGenericRecordLiteralNode);

    SetLength(scalarDefFields, Length(N.Fields));
    allScalar := True;

    // 2. Check if this record literal can be a TScalarRecord
    for i := 0 to High(N.Fields) do
    begin
        valNode := N.Fields[i].Value;
        valType := (valNode as TAstNode).StaticType;

        if (valType.Kind = stOrdinal) then
            scalarKind := TScalar.TKind.Ordinal
        else if (valType.Kind = stFloat) then
            scalarKind := TScalar.TKind.Float
        else if (valType.Kind = stKeyword) then
            scalarKind := TScalar.TKind.Keyword
        else
        begin
            allScalar := False;
            scalarKind := TScalar.TKind.Ordinal; // Dummy
        end;

        if allScalar then
            scalarDefFields[i] := TScalarRecordField.Create(N.Fields[i].Key.Value, scalarKind);
    end;

    // 3. Create the appropriate record type (Scalar or Generic) and mutate the node
    if allScalar then
    begin
        def := TScalarRecordRegistry.Intern(scalarDefFields);
        staticType := TTypes.CreateRecord(def);
        N.Definition := def; // Mutate
        N.GenericDefinition := nil; // Mutate
    end
    else
    begin
        var genDefFields: TArray<TPair<IKeyword, IStaticType>>;
        SetLength(genDefFields, Length(N.Fields));
        for i := 0 to High(N.Fields) do
            genDefFields[i] := TPair<IKeyword, IStaticType>.Create(N.Fields[i].Key.Value, (N.Fields[i].Value as TAstNode).StaticType);

        var genDef := TGenericRecordRegistry.Intern(genDefFields);
        staticType := TTypes.CreateGenericRecord(genDef);
        N.GenericDefinition := genDef; // Mutate
        N.Definition := nil; // Mutate
    end;

    Result := SetType(N, staticType);
end;

function TTypeChecker.VisitCreateSeries(const Node: ICreateSeriesNode): IAstNode;
begin
    // Type was set by Binder, just propagate it up.
    Result := inherited VisitCreateSeries(Node);
end;

function TTypeChecker.VisitAddSeriesItem(const Node: IAddSeriesItemNode): IAstNode;
var
    seriesType, valueType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Get types
    seriesType := (Node.Series as TAstNode).StaticType;
    valueType := (Node.Value as TAstNode).StaticType;

    // 3. Check types
    if (seriesType.Kind <> stUnknown) then
    begin
        if (seriesType.Kind <> TStaticTypeKind.stSeries) then
            raise ETypeException.CreateFmt('"add" requires a series as its first argument, but got %s', [seriesType.ToString]);

        if not TTypeRules.CanAssign(seriesType.ElementType, valueType) then
            raise ETypeException
                .CreateFmt('Cannot add item of type %s to series of type %s', [valueType.ToString, seriesType.ElementType.ToString]);
    end;

    if (Node.Lookback <> nil) then
    begin
        var lookbackType := (Node.Lookback as TAstNode).StaticType;
        if (lookbackType.Kind <> stUnknown) and not (lookbackType.Kind = TStaticTypeKind.stOrdinal) then
            raise ETypeException.Create('Lookback parameter for "add" must be an ordinal value.');
    end;

    Result := SetType(Node, TTypes.Void);
end;

function TTypeChecker.VisitSeriesLength(const Node: ISeriesLengthNode): IAstNode;
var
    seriesType: IStaticType;
begin
    // 1. Visit children
    inherited;

    // 2. Get type
    seriesType := (Node.Series as TAstNode).StaticType;

    // 3. Check type
    if (seriesType.Kind <> stUnknown)
        and (seriesType.Kind <> TStaticTypeKind.stSeries)
        and (seriesType.Kind <> TStaticTypeKind.stRecordSeries) then
        raise ETypeException.CreateFmt('"length" requires a series, but got %s', [seriesType.ToString]);

    Result := SetType(Node, TTypes.Ordinal);
end;

end.