unit Myc.Ast.Compiler.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 Layout: IScopeLayout): IAstNode;
    end;

    TTypeChecker = class(TAstTransformer, IAstTypeChecker)
    private
        type
            // Helper to track types per scope during traversal (The "Scratchpad")
            TTypeContext = class
            private
                FParent: TTypeContext;
                FLayout: IScopeLayout;
                FSlotTypes: TArray<IStaticType>;
                FUpvalueTypes: TArray<IStaticType>; // Types of captured variables
            public
                constructor Create(AParent: TTypeContext; ALayout: IScopeLayout; const AUpvalueTypes: TArray<IStaticType>);
                function LookupType(const Address: TResolvedAddress): IStaticType;
                procedure SetType(SlotIndex: Integer; AType: IStaticType);
                property Types: TArray<IStaticType> read FSlotTypes;
            end;

    private
        FCurrentContext: TTypeContext;

        // Helper to recursively rebuild the context stack from the layout hierarchy
        function CreateContextChain(L: IScopeLayout): TTypeContext;

    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 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;
        function VisitNop(const Node: INopNode): IAstNode; override;

        // Base cases (types are now set here)
        function VisitConstant(const Node: IConstantNode): IAstNode; override;
        function VisitKeyword(const Node: IKeywordNode): IAstNode; override;

    public
        constructor Create(const RootLayout: IScopeLayout);
        destructor Destroy; override;

        function Execute(const RootNode: IAstNode; const Layout: IScopeLayout): IAstNode;

        class function CheckTypes(const RootNode: IAstNode; const Layout: IScopeLayout): IAstNode; static;
    end;

implementation

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

{ TTypeChecker.TTypeContext }

constructor TTypeChecker.TTypeContext.Create(AParent: TTypeContext; ALayout: IScopeLayout; const AUpvalueTypes: TArray<IStaticType>);
begin
    inherited Create;
    FParent := AParent;
    FLayout := ALayout;
    FUpvalueTypes := AUpvalueTypes;

    // Initialize slot types with Unknown
    if Assigned(FLayout) then
    begin
        SetLength(FSlotTypes, FLayout.SlotCount);
        for var i := 0 to High(FSlotTypes) do
            FSlotTypes[i] := TTypes.Unknown;
    end;
end;

function TTypeChecker.TTypeContext.LookupType(const Address: TResolvedAddress): IStaticType;
var
    ctx: TTypeContext;
    i: Integer;
begin
    case Address.Kind of
        akLocalOrParent:
        begin
            ctx := Self;
            for i := 1 to Address.ScopeDepth do
            begin
                if not Assigned(ctx.FParent) then
                    raise Exception.CreateFmt('Scope depth mismatch during type lookup. Requested Depth: %d.', [Address.ScopeDepth]);
                ctx := ctx.FParent;
            end;

            if (Address.SlotIndex >= 0) and (Address.SlotIndex < Length(ctx.FSlotTypes)) then
                Result := ctx.FSlotTypes[Address.SlotIndex]
            else
                Result := TTypes.Unknown;
        end;
        akUpvalue:
        begin
            // Look up type in our local upvalue type cache
            if (Address.SlotIndex >= 0) and (Address.SlotIndex < Length(FUpvalueTypes)) then
                Result := FUpvalueTypes[Address.SlotIndex]
            else
                Result := TTypes.Unknown;
        end;
    else
        Result := TTypes.Unknown;
    end;
end;

procedure TTypeChecker.TTypeContext.SetType(SlotIndex: Integer; AType: IStaticType);
begin
    if (SlotIndex >= 0) and (SlotIndex < Length(FSlotTypes)) then
        FSlotTypes[SlotIndex] := AType;
end;

{ TTypeChecker }

function TTypeChecker.CreateContextChain(L: IScopeLayout): TTypeContext;
var
    p: TTypeContext;
begin
    if L = nil then
        exit(nil);

    // Recursively build parent context
    p := CreateContextChain(L.Parent);

    // Create context for current layout level
    // Note: We don't know UpvalueTypes for these static/parent layouts here, so [] is passed.
    // Also: Slot types will be initialized to Unknown.
    Result := TTypeContext.Create(p, L, []);
end;

constructor TTypeChecker.Create(const RootLayout: IScopeLayout);
begin
    inherited Create;
    // Build the full context chain based on the Layout's parent hierarchy
    // This ensures that ScopeDepth lookups can traverse up to the root.
    FCurrentContext := CreateContextChain(RootLayout);

    // Fallback if RootLayout is nil (should not happen in valid pipeline)
    if FCurrentContext = nil then
        FCurrentContext := TTypeContext.Create(nil, nil, []);
end;

destructor TTypeChecker.Destroy;
begin
    // Cleanup context stack
    while Assigned(FCurrentContext) do
    begin
        var temp := FCurrentContext;
        FCurrentContext := FCurrentContext.FParent;
        temp.Free;
    end;
    inherited;
end;

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

function TTypeChecker.Execute(const RootNode: IAstNode; const Layout: IScopeLayout): IAstNode;
begin
    // Note: Layout passed here matches what was passed to Create/Constructor (via recursed ContextChain)
    Result := Accept(RootNode);
    if not Assigned(Result) then
        Result := TAst.Block([]);
end;

function TTypeChecker.VisitConstant(const Node: IConstantNode): IAstNode;
begin
    Assert(Node.StaticType.Kind <> stUnknown);
    Result := Node;
end;

function TTypeChecker.VisitKeyword(const Node: IKeywordNode): IAstNode;
begin
    Assert(Node.StaticType.Kind = stKeyword);
    Result := Node;
end;

function TTypeChecker.VisitIdentifier(const Node: IIdentifierNode): IAstNode;
var
    typ: IStaticType;
    adr: TResolvedAddress;
begin
    adr := Node.Address;
    // Lookup type in our scratchpad context using the address resolved by Binder
    typ := FCurrentContext.LookupType(adr);

    // Create a new node with the inferred type
    Result := TAst.Identifier(Node.Name, adr, typ);
end;

function TTypeChecker.VisitRecurNode(const Node: IRecurNode): IAstNode;
var
    newArgs: TArray<IAstNode>;
    i: Integer;
begin
    SetLength(newArgs, Length(Node.Arguments));
    for i := 0 to High(Node.Arguments) do
        newArgs[i] := Accept(Node.Arguments[i]);

    Result := TAst.Recur(newArgs, TTypes.Void);
end;

function TTypeChecker.VisitVariableDeclaration(const Node: IVariableDeclarationNode): IAstNode;
var
    initType: IStaticType;
    newInitializer, newIdent: IAstNode;
    adr: TResolvedAddress;
    lambdaNode: ILambdaExpressionNode;
    placeholderType: IStaticType;
    i: Integer;
begin
    adr := Node.Identifier.Address;
    initType := TTypes.Unknown;

    // Recursive lambda bootstrap logic
    placeholderType := nil;
    if (Node.Initializer <> nil) and (Node.Initializer.Kind = akLambdaExpression) then
    begin
        lambdaNode := Node.Initializer.AsLambdaExpression;
        var paramTypes: TArray<IStaticType>;
        SetLength(paramTypes, Length(lambdaNode.Parameters));
        for i := 0 to High(paramTypes) do
            paramTypes[i] := TTypes.Unknown;

        placeholderType := TTypes.CreateMethod(paramTypes, TTypes.Unknown);

        // Update Context (Scratchpad)
        FCurrentContext.SetType(adr.SlotIndex, placeholderType);
        initType := placeholderType;
    end;

    if Assigned(Node.Initializer) then
        newInitializer := Accept(Node.Initializer)
    else
        newInitializer := nil;

    if Assigned(newInitializer) then
        initType := newInitializer.AsTypedNode.StaticType
    else if not Assigned(placeholderType) then
        initType := TTypes.Unknown;

    // Update Context with final type
    if initType.Kind <> stUnknown then
        FCurrentContext.SetType(adr.SlotIndex, initType);

    newIdent := TAst.Identifier(Node.Identifier.Name, adr, initType);

    Result := TAst.VarDecl(newIdent.AsIdentifier, newInitializer, initType, Node.IsBoxed);
end;

function TTypeChecker.VisitAssignment(const Node: IAssignmentNode): IAstNode;
var
    targetType, sourceType: IStaticType;
    newIdent, newValue: IAstNode;
    adr: TResolvedAddress;
    lambdaNode: ILambdaExpressionNode;
    placeholderType: IStaticType;
    i: Integer;
begin
    newIdent := Accept(Node.Identifier);
    targetType := newIdent.AsTypedNode.StaticType;
    adr := newIdent.AsIdentifier.Address;

    // Recursive lambda assignment check
    placeholderType := nil;
    if (Node.Value <> nil) and (Node.Value.Kind = akLambdaExpression) then
    begin
        lambdaNode := Node.Value.AsLambdaExpression;
        if (targetType.Kind <> stMethod) then
        begin
            var paramTypes: TArray<IStaticType>;
            SetLength(paramTypes, Length(lambdaNode.Parameters));
            for i := 0 to High(paramTypes) do
                paramTypes[i] := TTypes.Unknown;

            placeholderType := TTypes.CreateMethod(paramTypes, TTypes.Unknown);
            FCurrentContext.SetType(adr.SlotIndex, placeholderType);
            targetType := placeholderType;
        end;
    end;

    newValue := Accept(Node.Value);
    sourceType := newValue.AsTypedNode.StaticType;

    if not TTypeRules.CanAssign(targetType, sourceType) then
    begin
        if (targetType.Kind = stUnknown) then
        begin
            if not TTypeRules.CanAssign(sourceType, targetType) then
                raise ETypeException.CreateFmt('Cannot assign type %s to %s', [sourceType.ToString, targetType.ToString]);
        end
        else
            raise ETypeException.CreateFmt('Cannot assign type %s to %s', [sourceType.ToString, targetType.ToString]);
    end;

    if ((targetType.Kind = stUnknown) or Assigned(placeholderType)) and (sourceType.Kind <> stUnknown) then
    begin
        FCurrentContext.SetType(adr.SlotIndex, sourceType);
        newIdent := TAst.Identifier(newIdent.AsIdentifier.Name, adr, sourceType);
        targetType := sourceType;
    end;

    Result := TAst.Assign(newIdent.AsIdentifier, newValue, targetType);
end;

function TTypeChecker.VisitLambdaExpression(const Node: ILambdaExpressionNode): IAstNode;
var
    newParams: TArray<IIdentifierNode>;
    newBody: IAstNode;
    bodyType, methodType: IStaticType;
    paramTypes: TArray<IStaticType>;

    // Upvalue Type Resolution
    upvalueTypes: TArray<IStaticType>;
    upvalueAddrs: TArray<TResolvedAddress>;

    i: Integer;
    finalDescriptor: IScopeDescriptor;
begin
    // 1. Resolve Upvalue Types *in the current (parent) context*
    upvalueAddrs := Node.Upvalues;
    SetLength(upvalueTypes, Length(upvalueAddrs));
    for i := 0 to High(upvalueAddrs) do
    begin
        // We look up the physical address (from Binder) in the current context chain
        upvalueTypes[i] := FCurrentContext.LookupType(upvalueAddrs[i]);
    end;

    // 2. Create new TypeContext for this lambda scope, PASSING the upvalue types
    // We use the layout from the Binder-Result-Node
    FCurrentContext := TTypeContext.Create(FCurrentContext, Node.Layout, upvalueTypes);
    try
        // 3. Set parameter types in the context
        SetLength(newParams, Length(Node.Parameters));
        SetLength(paramTypes, Length(Node.Parameters));

        for i := 0 to High(Node.Parameters) do
        begin
            var paramIdent := Node.Parameters[i];
            var paramAdr := paramIdent.Address;

            // Here we could infer types if we had type annotations. For now, parameters are Unknown.
            paramTypes[i] := TTypes.Unknown;

            // Update context so body can resolve params
            FCurrentContext.SetType(paramAdr.SlotIndex, paramTypes[i]);

            newParams[i] := TAst.Identifier(paramIdent.Name, paramAdr, paramTypes[i]);
        end;

        // 4. Visit body
        newBody := Accept(Node.Body);
        bodyType := newBody.AsTypedNode.StaticType;

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

        // 6. Update <self> type in context (Slot 0)
        FCurrentContext.SetType(0, methodType);

        // 7. FINALIZE: Bake the Descriptor
        finalDescriptor := TScope.CreateDescriptor(Node.Layout, FCurrentContext.Types);

    finally
        // 8. Pop Context
        var temp := FCurrentContext;
        FCurrentContext := FCurrentContext.FParent;
        temp.Free;
    end;

    // 9. Create new node with the Descriptor attached!
    Result := TAst.LambdaExpr(newParams, newBody, Node.Layout, finalDescriptor, Node.Upvalues, Node.HasNestedLambdas, methodType);
end;

function TTypeChecker.VisitFunctionCall(const Node: IFunctionCallNode): IAstNode;
var
    calleeType, retType: IStaticType;
    i, j: Integer;
    newCallee: IAstNode;
    newArgs: TArray<IAstNode>;
    argTypes: TArray<IStaticType>;
    hasUnknownArgs: Boolean;
    bestSig: IMethodSignature;
    sig: IMethodSignature;
    match: Boolean;
begin
    newCallee := Accept(Node.Callee);
    SetLength(newArgs, Length(Node.Arguments));
    SetLength(argTypes, Length(Node.Arguments));

    hasUnknownArgs := False;
    for i := 0 to High(Node.Arguments) do
    begin
        newArgs[i] := Accept(Node.Arguments[i]);
        argTypes[i] := newArgs[i].AsTypedNode.StaticType;
        if argTypes[i].Kind = stUnknown then
            hasUnknownArgs := True;
    end;

    calleeType := newCallee.AsTypedNode.StaticType;
    retType := TTypes.Unknown;

    if calleeType.Kind = TStaticTypeKind.stMethod then
    begin
        if not hasUnknownArgs then
        begin
            bestSig := nil;
            for sig in calleeType.Signatures do
            begin
                if Length(sig.ParamTypes) <> Length(argTypes) then
                    continue;

                match := True;
                for j := 0 to High(argTypes) do
                begin
                    if not TTypeRules.CanAssign(sig.ParamTypes[j], argTypes[j]) then
                    begin
                        match := False;
                        break;
                    end;
                end;

                if match then
                begin
                    bestSig := sig;
                    break;
                end;
            end;

            if Assigned(bestSig) then
                retType := bestSig.ReturnType
            else
            begin
                var argsStr: string := '';
                for i := 0 to High(argTypes) do
                    argsStr := argsStr + argTypes[i].ToString + ' ';
                raise ETypeException
                    .CreateFmt('No matching signature for call with args (%s) found on method %s', [argsStr, calleeType.ToString]);
            end;
        end;
    end
    else if calleeType.Kind <> TStaticTypeKind.stUnknown then
        raise ETypeException.CreateFmt('Cannot invoke type %s as a function.', [calleeType.ToString]);

    Result := TAst.FunctionCall(newCallee, newArgs, retType, Node.IsTailCall);
end;

function TTypeChecker.VisitBlockExpression(const Node: IBlockExpressionNode): IAstNode;
var
    blockType: IStaticType;
    newExprs: TArray<IAstNode>;
    i: Integer;
begin
    SetLength(newExprs, Length(Node.Expressions));
    for i := 0 to High(Node.Expressions) do
        newExprs[i] := Accept(Node.Expressions[i]);

    if Length(newExprs) > 0 then
        blockType := newExprs[High(newExprs)].AsTypedNode.StaticType
    else
        blockType := TTypes.Void;

    Result := TAst.Block(newExprs, blockType);
end;

function TTypeChecker.VisitIfExpression(const Node: IIfExpressionNode): IAstNode;
var
    conditionType, thenType, elseType, resultType: IStaticType;
    newCond, newThen, newElse: IAstNode;
begin
    newCond := Accept(Node.Condition);
    newThen := Accept(Node.ThenBranch);
    newElse := Accept(Node.ElseBranch);

    conditionType := newCond.AsTypedNode.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]);

    thenType := newThen.AsTypedNode.StaticType;
    elseType :=
        if newElse <> nil then newElse.AsTypedNode.StaticType
        else TTypes.Void;

    resultType := TTypeRules.Promote(thenType, elseType);

    Result := TAst.IfExpr(newCond, newThen, newElse, resultType);
end;

function TTypeChecker.VisitTernaryExpression(const Node: ITernaryExpressionNode): IAstNode;
var
    conditionType, thenType, elseType, resultType: IStaticType;
    newCond, newThen, newElse: IAstNode;
begin
    newCond := Accept(Node.Condition);
    newThen := Accept(Node.ThenBranch);
    newElse := Accept(Node.ElseBranch);

    conditionType := newCond.AsTypedNode.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]);

    thenType := newThen.AsTypedNode.StaticType;
    elseType := newElse.AsTypedNode.StaticType;

    resultType := TTypeRules.Promote(thenType, elseType);

    Result := TAst.TernaryExpr(newCond, newThen, newElse, resultType);
end;

function TTypeChecker.VisitMemberAccess(const Node: IMemberAccessNode): IAstNode;
var
    baseType, elemType: IStaticType;
    fieldIndex: Integer;
    newBase, newMember: IAstNode;
begin
    newBase := Accept(Node.Base);
    newMember := Accept(Node.Member);

    baseType := newBase.AsTypedNode.StaticType;
    elemType := TTypes.Unknown;

    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
                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
            raise ETypeException.CreateFmt('Member access requires a record type, but got %s', [baseType.ToString]);
    end;

    Result := TAst.MemberAccess(newBase, newMember.AsKeyword, elemType);
end;

function TTypeChecker.VisitIndexer(const Node: IIndexerNode): IAstNode;
var
    baseType, indexType, elemType: IStaticType;
    newBase, newIndex: IAstNode;
begin
    newBase := Accept(Node.Base);
    newIndex := Accept(Node.Index);

    baseType := newBase.AsTypedNode.StaticType;
    indexType := newIndex.AsTypedNode.StaticType;
    elemType := TTypes.Unknown;

    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
            elemType := TTypes.CreateRecord(baseType.Definition);
    end;

    Result := TAst.Indexer(newBase, newIndex, elemType);
end;

function TTypeChecker.VisitRecordLiteral(const Node: IRecordLiteralNode): IAstNode;
var
    i: Integer;
    scalarDefFields: TArray<TScalarRecordField>;
    def: IScalarRecordDefinition;
    staticType: IStaticType;
    valType: IStaticType;
    scalarKind: TScalar.TKind;
    allScalar: Boolean;
    newFields: TArray<TRecordFieldLiteral>;
begin
    SetLength(newFields, Length(Node.Fields));
    for i := 0 to High(Node.Fields) do
    begin
        newFields[i].Key := Accept(Node.Fields[i].Key).AsKeyword;
        newFields[i].Value := Accept(Node.Fields[i].Value);
    end;

    SetLength(scalarDefFields, Length(newFields));
    allScalar := True;

    for i := 0 to High(newFields) do
    begin
        valType := newFields[i].Value.AsTypedNode.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;
        end;

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

    if allScalar then
    begin
        def := TScalarRecordRegistry.Intern(scalarDefFields);
        staticType := TTypes.CreateRecord(def);
        Result := TAst.RecordLiteral(newFields, def, nil, staticType);
    end
    else
    begin
        var genDefFields: TArray<TPair<IKeyword, IStaticType>>;
        SetLength(genDefFields, Length(newFields));
        for i := 0 to High(newFields) do
            genDefFields[i] := TPair<IKeyword, IStaticType>.Create(newFields[i].Key.Value, newFields[i].Value.AsTypedNode.StaticType);

        var genDef := TGenericRecordRegistry.Intern(genDefFields);
        staticType := TTypes.CreateGenericRecord(genDef);
        Result := TAst.RecordLiteral(newFields, nil, genDef, staticType);
    end;
end;

function TTypeChecker.VisitCreateSeries(const Node: ICreateSeriesNode): IAstNode;
var
    elemType: IStaticType;
begin
    try
        elemType := TTypes.FromScalarKind(TScalar.StringToKind(Node.Definition));
    except
        on E: Exception do
            elemType := TTypes.Unknown;
    end;

    Result := TAst.CreateSeries(Node.Definition, TTypes.CreateSeries(elemType));
end;

function TTypeChecker.VisitAddSeriesItem(const Node: IAddSeriesItemNode): IAstNode;
var
    seriesType, valueType: IStaticType;
    newSeries, newValue, newLookback: IAstNode;
begin
    newSeries := Accept(Node.Series);
    newValue := Accept(Node.Value);
    newLookback := Accept(Node.Lookback);

    seriesType := newSeries.AsTypedNode.StaticType;
    valueType := newValue.AsTypedNode.StaticType;

    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 (newLookback <> nil) then
    begin
        var lookbackType := newLookback.AsTypedNode.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 := TAst.AddSeriesItem(newSeries.AsIdentifier, newValue, newLookback, TTypes.Void);
end;

function TTypeChecker.VisitNop(const Node: INopNode): IAstNode;
begin
    Result := TAst.Nop(TTypes.Void);
end;

function TTypeChecker.VisitSeriesLength(const Node: ISeriesLengthNode): IAstNode;
var
    seriesType: IStaticType;
    newSeries: IAstNode;
begin
    newSeries := Accept(Node.Series);
    seriesType := newSeries.AsTypedNode.StaticType;

    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 := TAst.SeriesLength(newSeries.AsIdentifier, TTypes.Ordinal);
end;

end.