using System.Text;
using NubLang.Ast;
using NubLang.Syntax;

namespace NubLang.Generation;

public class Generator
{
    private readonly CompilationUnit _compilationUnit;
    private readonly IndentedTextWriter _writer;
    private readonly Stack<List<DeferNode>> _deferStack = [];
    private int _tmpIndex;

    public Generator(CompilationUnit compilationUnit)
    {
        _compilationUnit = compilationUnit;
        _writer = new IndentedTextWriter();
    }

    // todo(nub31): Handle name collisions
    private string NewTmp()
    {
        return $"_t{++_tmpIndex}";
    }

    private static string FuncName(string module, string name, string? externSymbol)
    {
        return externSymbol ?? $"{module}_{name}";
    }

    private static string StructName(string module, string name)
    {
        return $"{module}_{name}";
    }

    public string Emit()
    {
        _writer.WriteLine("#include <stdint.h>");
        _writer.WriteLine("#include <stdarg.h>");
        _writer.WriteLine("#include <stddef.h>");
        _writer.WriteLine();

        _writer.WriteLine("""
                          typedef struct
                          {
                              size_t length;
                              uint8_t *data;
                          } string;

                          typedef struct
                          {
                              size_t length;
                              void *data;
                          } slice;

                          """);

        foreach (var structType in _compilationUnit.ImportedStructTypes)
        {
            _writer.WriteLine("typedef struct");
            _writer.WriteLine("{");
            using (_writer.Indent())
            {
                foreach (var field in structType.Fields)
                {
                    _writer.WriteLine($"{CType.Create(field.Type, field.Name)};");
                }
            }

            _writer.WriteLine($"}} {StructName(structType.Module, structType.Name)};");
            _writer.WriteLine();
        }

        // note(nub31): Forward declarations
        foreach (var prototype in _compilationUnit.ImportedFunctions)
        {
            EmitLine(prototype.Tokens.FirstOrDefault());
            var parameters = prototype.Parameters.Count != 0
                ? string.Join(", ", prototype.Parameters.Select(x => CType.Create(x.Type, x.Name)))
                : "void";

            var name = FuncName(prototype.Module, prototype.Name, prototype.ExternSymbol);
            _writer.WriteLine($"{CType.Create(prototype.ReturnType, name)}({parameters});");
            _writer.WriteLine();
        }

        // note(nub31): Normal functions
        foreach (var funcNode in _compilationUnit.Functions)
        {
            if (funcNode.Body == null) continue;

            EmitLine(funcNode.Tokens.FirstOrDefault());
            var parameters = funcNode.Prototype.Parameters.Count != 0
                ? string.Join(", ", funcNode.Prototype.Parameters.Select(x => CType.Create(x.Type, x.Name)))
                : "void";

            var name = FuncName(funcNode.Module, funcNode.Name, funcNode.Prototype.ExternSymbol);
            _writer.WriteLine($"{CType.Create(funcNode.Prototype.ReturnType, name)}({parameters})");
            EmitBlock(funcNode.Body);
            _writer.WriteLine();
        }

        return _writer.ToString();
    }

    private void EmitStatement(StatementNode statementNode)
    {
        EmitLine(statementNode.Tokens.FirstOrDefault());
        switch (statementNode)
        {
            case AssignmentNode assignmentNode:
                EmitAssignment(assignmentNode);
                break;
            case BlockNode blockNode:
                EmitBlock(blockNode);
                break;
            case BreakNode breakNode:
                EmitBreak(breakNode);
                break;
            case ContinueNode continueNode:
                EmitContinue(continueNode);
                break;
            case DeferNode deferNode:
                EmitDefer(deferNode);
                break;
            case IfNode ifNode:
                EmitIf(ifNode);
                break;
            case ReturnNode returnNode:
                EmitReturn(returnNode);
                break;
            case StatementFuncCallNode statementFuncCallNode:
                EmitStatementFuncCall(statementFuncCallNode);
                break;
            case VariableDeclarationNode variableDeclarationNode:
                EmitVariableDeclaration(variableDeclarationNode);
                break;
            case WhileNode whileNode:
                EmitWhile(whileNode);
                break;
            default:
                throw new ArgumentOutOfRangeException(nameof(statementNode));
        }
    }

    private void EmitLine(Token? token)
    {
        if (token == null) return;
        var file = token.Span.FilePath;
        var line = token.Span.Start.Line;
        _writer.WriteLine($"#line {line} \"{file}\"");
    }

    private void EmitAssignment(AssignmentNode assignmentNode)
    {
        var target = EmitExpression(assignmentNode.Target);
        var value = EmitExpression(assignmentNode.Value);
        _writer.WriteLine($"{target} = {value};");
    }

    private void EmitBreak(BreakNode _)
    {
        // todo(nub31): Emit deferred statements
        _writer.WriteLine("break;");
    }

    private void EmitContinue(ContinueNode _)
    {
        // todo(nub31): Emit deferred statements
        _writer.WriteLine("continue;");
    }

    private void EmitDefer(DeferNode deferNode)
    {
        _deferStack.Peek().Add(deferNode);
    }

    private void EmitIf(IfNode ifNode, bool elseIf = false)
    {
        var condition = EmitExpression(ifNode.Condition);
        _writer.WriteLine($"{(elseIf ? "else " : "")}if ({condition})");
        EmitBlock(ifNode.Body);
        ifNode.Else?.Match
        (
            elseIfNode => EmitIf(elseIfNode, true),
            elseNode =>
            {
                _writer.WriteLine("else");
                EmitBlock(elseNode);
            }
        );
    }

    private void EmitReturn(ReturnNode returnNode)
    {
        if (returnNode.Value == null)
        {
            var blockDefers = _deferStack.Peek();
            for (var i = blockDefers.Count - 1; i >= 0; i--)
            {
                EmitStatement(blockDefers[i].Statement);
            }

            _writer.WriteLine("return;");
        }
        else
        {
            var returnValue = EmitExpression(returnNode.Value);

            if (_deferStack.Peek().Count != 0)
            {
                var tmp = NewTmp();
                _writer.WriteLine($"{CType.Create(returnNode.Value.Type, tmp)} = {returnValue};");

                var blockDefers = _deferStack.Peek();
                for (var i = blockDefers.Count - 1; i >= 0; i--)
                {
                    EmitStatement(blockDefers[i].Statement);
                }

                EmitLine(returnNode.Tokens.FirstOrDefault());
                _writer.WriteLine($"return {tmp};");
            }
            else
            {
                EmitLine(returnNode.Tokens.FirstOrDefault());
                _writer.WriteLine($"return {returnValue};");
            }
        }
    }

    private void EmitStatementFuncCall(StatementFuncCallNode statementFuncCallNode)
    {
        var funcCall = EmitFuncCall(statementFuncCallNode.FuncCall);
        _writer.WriteLine($"{funcCall};");
    }

    private void EmitVariableDeclaration(VariableDeclarationNode variableDeclarationNode)
    {
        if (variableDeclarationNode.Assignment != null)
        {
            var value = EmitExpression(variableDeclarationNode.Assignment);
            _writer.WriteLine($"{CType.Create(variableDeclarationNode.Type, variableDeclarationNode.Name)} = {value};");
        }
        else
        {
            _writer.WriteLine($"{CType.Create(variableDeclarationNode.Type, variableDeclarationNode.Name)};");
        }
    }

    private void EmitWhile(WhileNode whileNode)
    {
        var condition = EmitExpression(whileNode.Condition);
        _writer.WriteLine($"while ({condition})");
        EmitBlock(whileNode.Body);
    }

    private string EmitExpression(ExpressionNode expressionNode)
    {
        var expr = expressionNode switch
        {
            ArrayIndexAccessNode arrayIndexAccessNode => EmitArrayIndexAccess(arrayIndexAccessNode),
            ArrayInitializerNode arrayInitializerNode => EmitArrayInitializer(arrayInitializerNode),
            BinaryExpressionNode binaryExpressionNode => EmitBinaryExpression(binaryExpressionNode),
            BoolLiteralNode boolLiteralNode => boolLiteralNode.Value ? "true" : "false",
            ConvertCStringToStringNode convertCStringToStringNode => EmitConvertCStringToString(convertCStringToStringNode),
            ConvertFloatNode convertFloatNode => EmitConvertFloat(convertFloatNode),
            ConvertIntNode convertIntNode => EmitConvertInt(convertIntNode),
            ConvertStringToCStringNode convertStringToCStringNode => EmitConvertStringToCString(convertStringToCStringNode),
            CStringLiteralNode cStringLiteralNode => $"\"{cStringLiteralNode.Value}\"",
            DereferenceNode dereferenceNode => EmitDereference(dereferenceNode),
            Float32LiteralNode float32LiteralNode => EmitFloat32Literal(float32LiteralNode),
            Float64LiteralNode float64LiteralNode => EmitFloat64Literal(float64LiteralNode),
            FloatToIntBuiltinNode floatToIntBuiltinNode => EmitFloatToIntBuiltin(floatToIntBuiltinNode),
            FuncCallNode funcCallNode => EmitFuncCall(funcCallNode),
            FuncIdentifierNode funcIdentifierNode => FuncName(funcIdentifierNode.Module, funcIdentifierNode.Name, funcIdentifierNode.ExternSymbol),
            IntLiteralNode intLiteralNode => EmitIntLiteral(intLiteralNode),
            AddressOfNode addressOfNode => EmitAddressOf(addressOfNode),
            SizeBuiltinNode sizeBuiltinNode => $"sizeof({CType.Create(sizeBuiltinNode.TargetType)})",
            SliceIndexAccessNode sliceIndexAccessNode => EmitSliceArrayIndexAccess(sliceIndexAccessNode),
            StringLiteralNode stringLiteralNode => EmitStringLiteral(stringLiteralNode),
            StructFieldAccessNode structFieldAccessNode => EmitStructFieldAccess(structFieldAccessNode),
            StructInitializerNode structInitializerNode => EmitStructInitializer(structInitializerNode),
            UIntLiteralNode uIntLiteralNode => EmitUIntLiteral(uIntLiteralNode),
            UnaryExpressionNode unaryExpressionNode => EmitUnaryExpression(unaryExpressionNode),
            VariableIdentifierNode variableIdentifierNode => variableIdentifierNode.Name,
            _ => throw new ArgumentOutOfRangeException(nameof(expressionNode))
        };

        return $"({expr})";
    }

    private string EmitArrayIndexAccess(ArrayIndexAccessNode arrayIndexAccessNode)
    {
        var array = EmitExpression(arrayIndexAccessNode.Target);
        var index = EmitExpression(arrayIndexAccessNode.Index);
        return $"{array}[{index}]";
    }

    private string EmitArrayInitializer(ArrayInitializerNode arrayInitializerNode)
    {
        var capacity = EmitExpression(arrayInitializerNode.Capacity);
        var tmp = NewTmp();
        _writer.WriteLine($"{CType.Create(arrayInitializerNode.ElementType)} {tmp}[{capacity}];");
        return tmp;
    }

    private string EmitBinaryExpression(BinaryExpressionNode binaryExpressionNode)
    {
        var left = EmitExpression(binaryExpressionNode.Left);
        var right = EmitExpression(binaryExpressionNode.Right);

        var op = binaryExpressionNode.Operator switch
        {
            BinaryOperator.Plus => "+",
            BinaryOperator.Minus => "-",
            BinaryOperator.Multiply => "*",
            BinaryOperator.Divide => "/",
            BinaryOperator.Modulo => "%",
            BinaryOperator.Equal => "==",
            BinaryOperator.NotEqual => "!=",
            BinaryOperator.LessThan => "<",
            BinaryOperator.LessThanOrEqual => "<=",
            BinaryOperator.GreaterThan => ">",
            BinaryOperator.GreaterThanOrEqual => ">=",
            BinaryOperator.LogicalAnd => "&&",
            BinaryOperator.LogicalOr => "||",
            BinaryOperator.BitwiseAnd => "&",
            BinaryOperator.BitwiseOr => "|",
            BinaryOperator.BitwiseXor => "^",
            BinaryOperator.LeftShift => "<<",
            BinaryOperator.RightShift => ">>",
            _ => throw new ArgumentOutOfRangeException()
        };

        return $"{left} {op} {right}";
    }

    private string EmitConvertCStringToString(ConvertCStringToStringNode convertCStringToStringNode)
    {
        var value = EmitExpression(convertCStringToStringNode.Value);
        return $"(string){{.length = strlen({value}), .data = {value}}}";
    }

    private string EmitConvertFloat(ConvertFloatNode convertFloatNode)
    {
        var value = EmitExpression(convertFloatNode.Value);
        var targetCast = convertFloatNode.TargetType.Width switch
        {
            32 => "f32",
            64 => "f64",
            _ => throw new ArgumentOutOfRangeException()
        };

        return $"({targetCast}){value}";
    }

    private string EmitConvertInt(ConvertIntNode convertIntNode)
    {
        var value = EmitExpression(convertIntNode.Value);
        var targetType = convertIntNode.TargetType.Width switch
        {
            8 => convertIntNode.TargetType.Signed ? "int8_t" : "uint8_t",
            16 => convertIntNode.TargetType.Signed ? "int16_t" : "uint16_t",
            32 => convertIntNode.TargetType.Signed ? "int32_t" : "uint32_t",
            64 => convertIntNode.TargetType.Signed ? "int64_t" : "uint64_t",
            _ => throw new ArgumentOutOfRangeException()
        };
        return $"({targetType}){value}";
    }

    private string EmitConvertStringToCString(ConvertStringToCStringNode convertStringToCStringNode)
    {
        var value = EmitExpression(convertStringToCStringNode.Value);
        return $"(char*){value}.data";
    }

    private string EmitDereference(DereferenceNode dereferenceNode)
    {
        var pointer = EmitExpression(dereferenceNode.Target);
        return $"*{pointer}";
    }

    private string EmitFloat32Literal(Float32LiteralNode float32LiteralNode)
    {
        var str = float32LiteralNode.Value.ToString("G9", System.Globalization.CultureInfo.InvariantCulture);
        if (!str.Contains('.') && !str.Contains('e') && !str.Contains('E'))
        {
            str += ".0";
        }

        return str + "f";
    }

    private string EmitFloat64Literal(Float64LiteralNode float64LiteralNode)
    {
        var str = float64LiteralNode.Value.ToString("G17", System.Globalization.CultureInfo.InvariantCulture);
        if (!str.Contains('.') && !str.Contains('e') && !str.Contains('E'))
        {
            str += ".0";
        }

        return str;
    }

    private string EmitFloatToIntBuiltin(FloatToIntBuiltinNode floatToIntBuiltinNode)
    {
        var value = EmitExpression(floatToIntBuiltinNode.Value);
        var targetType = floatToIntBuiltinNode.TargetType.Width switch
        {
            8 => floatToIntBuiltinNode.TargetType.Signed ? "int8_t" : "uint8_t",
            16 => floatToIntBuiltinNode.TargetType.Signed ? "int16_t" : "uint16_t",
            32 => floatToIntBuiltinNode.TargetType.Signed ? "int32_t" : "uint32_t",
            64 => floatToIntBuiltinNode.TargetType.Signed ? "int64_t" : "uint64_t",
            _ => throw new ArgumentOutOfRangeException()
        };
        return $"({targetType}){value}";
    }

    private string EmitFuncCall(FuncCallNode funcCallNode)
    {
        var name = EmitExpression(funcCallNode.Expression);
        var parameterNames = funcCallNode.Parameters.Select(x => EmitExpression(x)).ToList();
        return $"{name}({string.Join(", ", parameterNames)})";
    }

    private string EmitIntLiteral(IntLiteralNode intLiteralNode)
    {
        var type = (NubIntType)intLiteralNode.Type;
        return type.Width switch
        {
            8 or 16 or 32 => intLiteralNode.Value.ToString(),
            64 => intLiteralNode.Value + "LL",
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private string EmitAddressOf(AddressOfNode addressOfNode)
    {
        var value = EmitExpression(addressOfNode.LValue);
        return $"&{value}";
    }

    private string EmitSliceArrayIndexAccess(SliceIndexAccessNode sliceIndexAccessNode)
    {
        var value = EmitExpression(sliceIndexAccessNode.Target);
        var index = EmitExpression(sliceIndexAccessNode.Index);
        // todo(nub31): We can emit bounds checking here
        return $"(({CType.Create(sliceIndexAccessNode.Target.Type)}){value}.data)[{index}]";
    }

    private string EmitStringLiteral(StringLiteralNode stringLiteralNode)
    {
        var length = Encoding.UTF8.GetByteCount(stringLiteralNode.Value);
        return $"(string){{.length = {length}, .data = \"{stringLiteralNode.Value}\"}}";
    }

    private string EmitStructFieldAccess(StructFieldAccessNode structFieldAccessNode)
    {
        var structExpr = EmitExpression(structFieldAccessNode.Target);
        return $"{structExpr}.{structFieldAccessNode.Field}";
    }

    private string EmitStructInitializer(StructInitializerNode structInitializerNode)
    {
        var initValues = new List<string>();
        foreach (var initializer in structInitializerNode.Initializers)
        {
            var value = EmitExpression(initializer.Value);
            initValues.Add($".{initializer.Key} = {value}");
        }

        var initString = initValues.Count == 0
            ? "0"
            : string.Join(", ", initValues);

        return $"({CType.Create(structInitializerNode.Type)}){{{initString}}}";
    }

    private string EmitUIntLiteral(UIntLiteralNode uIntLiteralNode)
    {
        var type = (NubIntType)uIntLiteralNode.Type;
        return type.Width switch
        {
            8 or 16 or 32 => uIntLiteralNode.Value + "U",
            64 => uIntLiteralNode.Value + "ULL",
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private string EmitUnaryExpression(UnaryExpressionNode unaryExpressionNode)
    {
        var value = EmitExpression(unaryExpressionNode.Operand);

        return unaryExpressionNode.Operator switch
        {
            UnaryOperator.Negate => $"-{value}",
            UnaryOperator.Invert => $"!{value}",
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private void EmitBlock(BlockNode blockNode)
    {
        EmitLine(blockNode.Tokens.FirstOrDefault());
        _writer.WriteLine("{");
        using (_writer.Indent())
        {
            _deferStack.Push([]);

            foreach (var statementNode in blockNode.Statements)
            {
                EmitStatement(statementNode);
            }

            var blockDefers = _deferStack.Pop();
            for (var i = blockDefers.Count - 1; i >= 0; i--)
            {
                EmitStatement(blockDefers[i].Statement);
            }
        }

        EmitLine(blockNode.Tokens.LastOrDefault());
        _writer.WriteLine("}");
    }
}