using System.Diagnostics;
using System.Globalization;
using System.Text;
using Nub.Lang.Frontend.Lexing;
using Nub.Lang.Frontend.Parsing;
using Nub.Lang.Frontend.Parsing.Definitions;
using Nub.Lang.Frontend.Parsing.Expressions;
using Nub.Lang.Frontend.Parsing.Statements;
using Nub.Lang.Frontend.Typing;

namespace Nub.Lang.Frontend.Generation;

public class QBEGenerator
{
    private const string OutOfBoundsMessage = "Index is out of bounds\\n";

    private List<SourceFile> _sourceFiles = [];
    private StringBuilder _builder = new();
    private Dictionary<string, string> _variables = [];
    private List<string> _strings = [];
    private Stack<string> _breakLabels = [];
    private Stack<string> _continueLabels = [];
    private int _variableIndex;
    private int _labelIndex;
    private bool _codeIsReachable = true;
    private Dictionary<IFuncSignature, string> _funcNames = [];

    public string Generate(List<SourceFile> sourceFiles)
    {
        _sourceFiles = sourceFiles;
        _builder = new StringBuilder();
        _variables = new Dictionary<string, string>();
        _strings = [];
        _funcNames = [];
        _breakLabels = [];
        _continueLabels = [];
        _variableIndex = 0;
        _labelIndex = 0;
        _codeIsReachable = true;

        foreach (var structDef in _sourceFiles.SelectMany(f => f.Definitions).OfType<StructDefinitionNode>())
        {
            GenerateStructDefinition(structDef);
            _builder.AppendLine();
        }

        foreach (var funcSignature in _sourceFiles.SelectMany(f => f.Definitions).OfType<IFuncSignature>())
        {
            switch (funcSignature)
            {
                case ExternFuncDefinitionNode externFuncDefinitionNode:
                    _funcNames[funcSignature] = "$" + externFuncDefinitionNode.CallName;
                    break;
                case LocalFuncDefinitionNode localFuncDefinitionNode:
                    if (localFuncDefinitionNode.Exported)
                    {
                        _funcNames[funcSignature] = "$" + localFuncDefinitionNode.Name;
                    }
                    else
                    {
                        _funcNames[funcSignature] = "$" + localFuncDefinitionNode.Namespace + "_" + localFuncDefinitionNode.Name;
                    }

                    break;
                default:
                    throw new ArgumentOutOfRangeException(nameof(funcSignature));
            }
        }

        foreach (var funcDef in _sourceFiles.SelectMany(f => f.Definitions).OfType<LocalFuncDefinitionNode>())
        {
            GenerateFuncDefinition(funcDef);
            _builder.AppendLine();
        }

        _builder.AppendLine($"data $oob_message = {{ b \"{OutOfBoundsMessage}\" }}");

        for (var i = 0; i < _strings.Count; i++)
        {
            var str = _strings[i];
            _builder.AppendLine($"data $string{i + 1} = {{ b \"{str}\", b 0 }}");
        }

        return _builder.ToString();
    }

    private static string QBEStore(NubType type)
    {
        return $"store{type switch
        {
            NubArrayType => "l",
            NubPointerType => "l",
            NubPrimitiveType primitiveType => primitiveType.Kind switch
            {
                PrimitiveTypeKind.I64 => "l",
                PrimitiveTypeKind.I32 => "w",
                PrimitiveTypeKind.I16 => "h",
                PrimitiveTypeKind.I8 => "b",
                PrimitiveTypeKind.U64 => "l",
                PrimitiveTypeKind.U32 => "w",
                PrimitiveTypeKind.U16 => "h",
                PrimitiveTypeKind.U8 => "b",
                PrimitiveTypeKind.F64 => "d",
                PrimitiveTypeKind.F32 => "s",
                PrimitiveTypeKind.Bool => "w",
                _ => throw new UnreachableException()
            },
            NubStructType => "l",
            NubFixedArrayType => "l",
            _ => throw new NotSupportedException($"'{type}' type cannot be used in store instructions")
        }}";
    }
    
    private static string QBELoad(NubType type)
    {
        return $"load{type switch
        {
            NubArrayType => "l",
            NubPointerType => "l",
            NubPrimitiveType primitiveType => primitiveType.Kind switch
            {
                PrimitiveTypeKind.I64 => "l",
                PrimitiveTypeKind.I32 => "w",
                PrimitiveTypeKind.I16 => "sh",
                PrimitiveTypeKind.I8 => "sb",
                PrimitiveTypeKind.U64 => "l",
                PrimitiveTypeKind.U32 => "w",
                PrimitiveTypeKind.U16 => "uh",
                PrimitiveTypeKind.U8 => "ub",
                PrimitiveTypeKind.F64 => "d",
                PrimitiveTypeKind.F32 => "s",
                PrimitiveTypeKind.Bool => "w",
                _ => throw new UnreachableException()
            },
            NubStructType => "l",
            NubFixedArrayType => "l",
            _ => throw new NotSupportedException($"'{type}' type cannot be used in load instructions")
        }}";
    }
    
    private static string QBEAssign(NubType type)
    {
        return $"={type switch
        {
            NubArrayType => "l",
            NubPointerType => "l",
            NubPrimitiveType primitiveType => primitiveType.Kind switch
            {
                PrimitiveTypeKind.I64 => "l",
                PrimitiveTypeKind.I32 => "w",
                PrimitiveTypeKind.I16 => "w",
                PrimitiveTypeKind.I8 => "w",
                PrimitiveTypeKind.U64 => "l",
                PrimitiveTypeKind.U32 => "w",
                PrimitiveTypeKind.U16 => "w",
                PrimitiveTypeKind.U8 => "w",
                PrimitiveTypeKind.F64 => "d",
                PrimitiveTypeKind.F32 => "s",
                PrimitiveTypeKind.Bool => "w",
                _ => throw new UnreachableException()
            },
            NubStructType => "l",
            NubFixedArrayType => "l",
            _ => throw new NotSupportedException($"'{type}' type cannot be used in variables")
        }}";
    }

    private int SizeOf(NubType type)
    {
        switch (type)
        {
            case NubPrimitiveType primitiveType:
            {
                switch (primitiveType.Kind)
                {
                    case PrimitiveTypeKind.I64:
                    case PrimitiveTypeKind.U64:
                        return 8;
                    case PrimitiveTypeKind.I32:
                    case PrimitiveTypeKind.U32:
                        return 4;
                    case PrimitiveTypeKind.I16:
                    case PrimitiveTypeKind.U16:
                        return 2;
                    case PrimitiveTypeKind.I8:
                    case PrimitiveTypeKind.U8:
                    case PrimitiveTypeKind.Bool:
                        return 1;
                    case PrimitiveTypeKind.F64:
                        return 8;
                    case PrimitiveTypeKind.F32:
                        return 4;
                    default:
                        throw new ArgumentOutOfRangeException();
                }
            }
            case NubStructType nubStructType:
            {
                var definition = LookupStructDefinition(nubStructType.Namespace, nubStructType.Name);
                return definition.Fields.Sum(f => SizeOf(f.Type));
            }
            case NubPointerType:
            case NubArrayType:
            {
                return 8;
            }
            case NubFixedArrayType nubFixedArrayType:
            {
                return SizeOf(nubFixedArrayType.ElementType) * nubFixedArrayType.Capacity;
            }
            default:
            {
                throw new UnreachableException();
            }
        }
    }

    private bool IsLargeType(NubType type)
    {
        return type switch
        {
            NubArrayType => false,
            NubPointerType => false,
            NubPrimitiveType => false,
            NubStructType => true,
            NubFixedArrayType => true,
            _ => throw new ArgumentOutOfRangeException(nameof(type))
        };
    }

    private void GenerateFuncDefinition(LocalFuncDefinitionNode node)
    {
        _variables.Clear();

        if (node.Exported)
        {
            _builder.Append("export ");
        }

        _builder.Append("function ");
        if (node.ReturnType is not NubVoidType)
        {
            _builder.Append(node.ReturnType switch
            {
                NubArrayType => "l",
                NubPointerType => "l",
                NubPrimitiveType primitiveType => primitiveType.Kind switch
                {
                    PrimitiveTypeKind.I64 => "l",
                    PrimitiveTypeKind.I32 => "w",
                    PrimitiveTypeKind.I16 => "sh",
                    PrimitiveTypeKind.I8 => "sb",
                    PrimitiveTypeKind.U64 => "l",
                    PrimitiveTypeKind.U32 => "w",
                    PrimitiveTypeKind.U16 => "uh",
                    PrimitiveTypeKind.U8 => "ub",
                    PrimitiveTypeKind.F64 => "d",
                    PrimitiveTypeKind.F32 => "s",
                    PrimitiveTypeKind.Bool => "w",
                    _ => throw new UnreachableException()
                },
                NubStructType structType => $":{structType.Namespace}_{structType.Name}",
                NubFixedArrayType => "l",
                _ => throw new NotSupportedException($"'{node.ReturnType}' type cannot be used as a function return type")
            });
            _builder.Append(' ');
        }

        _builder.Append(_funcNames[node]);

        var parameterStrings = node.Parameters.Select(parameter => parameter.Variadic ? "..." : $"{parameter.Type switch
        {
            NubArrayType => "l",
            NubPointerType => "l",
            NubPrimitiveType primitiveType => primitiveType.Kind switch
            {
                PrimitiveTypeKind.I64 => "l",
                PrimitiveTypeKind.I32 => "w",
                PrimitiveTypeKind.I16 => "sh",
                PrimitiveTypeKind.I8 => "sb",
                PrimitiveTypeKind.U64 => "l",
                PrimitiveTypeKind.U32 => "w",
                PrimitiveTypeKind.U16 => "uh",
                PrimitiveTypeKind.U8 => "ub",
                PrimitiveTypeKind.F64 => "d",
                PrimitiveTypeKind.F32 => "s",
                PrimitiveTypeKind.Bool => "w",
                _ => throw new UnreachableException()
            },
            NubStructType structType => $":{structType.Namespace}_{structType.Name}", 
            NubFixedArrayType => "l",
            _ => throw new NotSupportedException($"'{parameter.Type}' type cannot be used as a function parameter type")
        }} %{parameter.Name}");

        _builder.AppendLine($"({string.Join(", ", parameterStrings)}) {{");
        _builder.AppendLine("@start");

        foreach (var parameter in node.Parameters)
        {
            var parameterName = "%" + parameter.Name;

            if (parameter.Type is NubPrimitiveType primitiveType)
            {
                switch (primitiveType.Kind)
                {
                    case PrimitiveTypeKind.I16:
                        parameterName = GenVarName();
                        _builder.AppendLine($"    {parameterName} =w extsh %{parameter.Name}");
                        break;
                    case PrimitiveTypeKind.I8:
                        parameterName = GenVarName();
                        _builder.AppendLine($"    {parameterName} =w extsb %{parameter.Name}");
                        break;
                    case PrimitiveTypeKind.U16:
                        parameterName = GenVarName();
                        _builder.AppendLine($"    {parameterName} =w extuh %{parameter.Name}");
                        break;
                    case PrimitiveTypeKind.U8:
                        parameterName = GenVarName();
                        _builder.AppendLine($"    {parameterName} =w extub %{parameter.Name}");
                        break;
                }
            }
            
            _variables[parameter.Name] = parameterName;
        }

        GenerateBlock(node.Body);

        if (node.Body.Statements.LastOrDefault() is not ReturnNode)
        {
            if (node.ReturnType is NubVoidType)
            {
                _builder.AppendLine("    ret");
            }
        }

        _builder.AppendLine("}");
    }

    private void GenerateStructDefinition(StructDefinitionNode structDefinition)
    {
        _builder.Append($"type :{structDefinition.Namespace}_{structDefinition.Name} = {{ ");
        foreach (var structDefinitionField in structDefinition.Fields)
        {
            var fieldQbeType = structDefinitionField.Type switch
            {
                NubArrayType => "l",
                NubPointerType => "l",
                NubPrimitiveType primitiveType => primitiveType.Kind switch
                {
                    PrimitiveTypeKind.I64 => "l",
                    PrimitiveTypeKind.I32 => "w",
                    PrimitiveTypeKind.I16 => "h",
                    PrimitiveTypeKind.I8 => "b",
                    PrimitiveTypeKind.U64 => "l",
                    PrimitiveTypeKind.U32 => "w",
                    PrimitiveTypeKind.U16 => "h",
                    PrimitiveTypeKind.U8 => "b",
                    PrimitiveTypeKind.F64 => "d",
                    PrimitiveTypeKind.F32 => "s",
                    PrimitiveTypeKind.Bool => "w",
                    _ => throw new UnreachableException()
                },
                NubStructType structType => $":{structType.Namespace}_{structType.Name}",
                NubFixedArrayType fixedArrayType => $"b {SizeOf(fixedArrayType)}",
                _ => throw new NotSupportedException($"'{structDefinitionField.Type}' type cannot be used in structs")
            };
            _builder.Append(fieldQbeType + ", ");
        }
        _builder.AppendLine("}");
    }

    private void GenerateStatement(StatementNode statement)
    {
        switch (statement)
        {
            case ArrayIndexAssignmentNode arrayIndexAssignment:
                GenerateArrayIndexAssignment(arrayIndexAssignment);
                break;
            case BreakNode:
                GenerateBreak();
                break;
            case ContinueNode:
                GenerateContinue();
                break;
            case DereferenceAssignmentNode dereferenceAssignment:
                GenerateDereferenceAssignment(dereferenceAssignment);
                break;
            case IfNode ifStatement:
                GenerateIf(ifStatement);
                break;
            case MemberAssignmentNode memberAssignment:
                GenerateMemberAssignment(memberAssignment);
                break;
            case ReturnNode @return:
                GenerateReturn(@return);
                break;
            case StatementExpressionNode statementExpression:
                GenerateExpression(statementExpression.Expression);
                break;
            case VariableAssignmentNode variableAssignment:
                GenerateVariableAssignment(variableAssignment);
                break;
            case VariableDeclarationNode variableDeclaration:
                GenerateVariableDeclaration(variableDeclaration);
                break;
            case WhileNode whileStatement:
                GenerateWhile(whileStatement);
                break;
            default:
                throw new ArgumentOutOfRangeException(nameof(statement));
        }
    }

    private void GenerateArrayIndexAssignment(ArrayIndexAssignmentNode arrayIndexAssignment)
    {
        var array = GenerateExpression(arrayIndexAssignment.ArrayIndexAccess.Array);
        var index = GenerateExpression(arrayIndexAssignment.ArrayIndexAccess.Index);
        GenerateArrayBoundsCheck(array, index);
        var value = GenerateExpression(arrayIndexAssignment.Value);

        switch (arrayIndexAssignment.ArrayIndexAccess.Array.Type)
        {
            case NubArrayType arrayType:
            {
                var startName = GenVarName();
                _builder.AppendLine($"    {startName} =l add {array}, 8");
                
                var adjustedIndex = GenVarName();
                _builder.AppendLine($"    {adjustedIndex} =l mul {index}, {SizeOf(arrayType.ElementType)}");

                var pointer = GenVarName();
                _builder.AppendLine($"    {pointer} =l add {startName}, {adjustedIndex}");

                GenerateCopy(arrayType.ElementType, value, pointer);
                break;
            }
            case NubFixedArrayType fixedArrayType:
            {
                var startName = GenVarName();
                _builder.AppendLine($"    {startName} =l add {array}, 8");
                
                var adjustedIndex = GenVarName();
                _builder.AppendLine($"    {adjustedIndex} =l mul {index}, {SizeOf(fixedArrayType.ElementType)}");

                var pointer = GenVarName();
                _builder.AppendLine($"    {pointer} =l add {startName}, {adjustedIndex}");

                GenerateCopy(fixedArrayType.ElementType, value, pointer);
                break;
            }
            default:
            {
                throw new UnreachableException();
            }
        }
    }

    private void GenerateBlock(BlockNode block)
    {
        foreach (var statement in block.Statements.Where(_ => _codeIsReachable))
        {
            GenerateStatement(statement);
        }

        _codeIsReachable = true;
    }

    private void GenerateBreak()
    {
        _builder.AppendLine($"    jmp {_breakLabels.Peek()}");
        _codeIsReachable = false;
    }

    private void GenerateContinue()
    {
        _builder.AppendLine($"    jmp {_continueLabels.Peek()}");
        _codeIsReachable = false;
    }

    private void GenerateDereferenceAssignment(DereferenceAssignmentNode dereferenceAssignment)
    {
        var pointer = GenerateExpression(dereferenceAssignment.Dereference.Expression);
        var value = GenerateExpression(dereferenceAssignment.Value);
        GenerateCopy(dereferenceAssignment.Value.Type, value, pointer);
    }

    private void GenerateIf(IfNode ifStatement)
    {
        var trueLabel = GenLabelName();
        var falseLabel = GenLabelName();
        var endLabel = GenLabelName();

        var result = GenerateExpression(ifStatement.Condition);
        _builder.AppendLine($"    jnz {result}, {trueLabel}, {falseLabel}");
        _builder.AppendLine(trueLabel);
        GenerateBlock(ifStatement.Body);
        _builder.AppendLine($"    jmp {endLabel}");
        _builder.AppendLine(falseLabel);
        if (ifStatement.Else.HasValue)
        {
            ifStatement.Else.Value.Match
            (
                GenerateIf,
                GenerateBlock
            );
        }

        _builder.AppendLine(endLabel);
    }

    private void GenerateMemberAssignment(MemberAssignmentNode memberAssignment)
    {
        var structType = memberAssignment.MemberAccess.Expression.Type as NubStructType;
        Debug.Assert(structType != null);
        
        var structDefinition = LookupStructDefinition(structType.Namespace, structType.Name);
        var offset = LookupMemberOffset(structDefinition, memberAssignment.MemberAccess.Member);

        var item = GenerateExpression(memberAssignment.MemberAccess.Expression);
        var pointer = GenVarName();
        
        _builder.AppendLine($"    {pointer} =l add {item}, {offset}");

        var value = GenerateExpression(memberAssignment.Value);

        GenerateCopy(memberAssignment.Value.Type, value, pointer);
    }

    private void GenerateReturn(ReturnNode @return)
    {
        if (@return.Value.HasValue)
        {
            var result = GenerateExpression(@return.Value.Value);
            _builder.AppendLine($"    ret {result}");
        }
        else
        {
            _builder.AppendLine("    ret");
        }
    }
    
    private void GenerateVariableAssignment(VariableAssignmentNode variableAssignment)
    {
        var value = GenerateExpression(variableAssignment.Value);
        var pointer = _variables[variableAssignment.Identifier.Identifier];
        GenerateCopy(variableAssignment.Value.Type, value, pointer);
    }

    private void GenerateVariableDeclaration(VariableDeclarationNode variableDeclaration)
    {
        var type = variableDeclaration.ExplicitType.Value ?? variableDeclaration.Value.Value!.Type;
        var pointer = GenVarName();
        _builder.AppendLine($"    {pointer} =l alloc8 {SizeOf(type)}");
        
        if (variableDeclaration.Value.HasValue)
        {
            var value = GenerateExpression(variableDeclaration.Value.Value);
            GenerateCopy(variableDeclaration.Value.Value.Type, value, pointer);
        }
        else
        {
            var pointerName = GenVarName();
            _variables[variableDeclaration.Name] = pointerName;
        }
        
        _variables[variableDeclaration.Name] = pointer;
    }

    private void GenerateWhile(WhileNode whileStatement)
    {
        var conditionLabel = GenLabelName();
        var iterationLabel = GenLabelName();
        var endLabel = GenLabelName();

        _breakLabels.Push(endLabel);
        _continueLabels.Push(conditionLabel);

        _builder.AppendLine($"    jmp {conditionLabel}");
        _builder.AppendLine(iterationLabel);
        GenerateBlock(whileStatement.Body);
        _builder.AppendLine(conditionLabel);
        var result = GenerateExpression(whileStatement.Condition);
        _builder.AppendLine($"    jnz {result}, {iterationLabel}, {endLabel}");
        _builder.AppendLine(endLabel);

        _continueLabels.Pop();
        _breakLabels.Pop();
    }

    private string GenerateExpression(ExpressionNode expression)
    {
        return expression switch
        {
            AddressOfNode addressOf => GenerateAddressOf(addressOf),
            ArrayIndexAccessNode arrayIndex => GenerateArrayAccessIndex(arrayIndex),
            ArrayInitializerNode arrayInitializer => GenerateArrayInitializer(arrayInitializer),
            BinaryExpressionNode binaryExpression => GenerateBinaryExpression(binaryExpression),
            DereferenceNode dereference => GenerateDereference(dereference),
            FixedArrayInitializerNode fixedArrayInitializer => GenerateFixedArrayInitializer(fixedArrayInitializer),
            FuncCallNode funcCallExpression => GenerateFuncCall(funcCallExpression),
            IdentifierNode identifier => GenerateIdentifier(identifier),
            LiteralNode literal => GenerateLiteral(literal),
            StructInitializerNode structInitializer => GenerateStructInitializer(structInitializer),
            UnaryExpressionNode unaryExpression => GenerateUnaryExpression(unaryExpression),
            MemberAccessNode memberAccess => GenerateMemberAccess(memberAccess),
            _ => throw new ArgumentOutOfRangeException(nameof(expression))
        };
    }

    private string GenerateArrayIndexPointer(ArrayIndexAccessNode arrayIndexAccess)
    {
        var array = GenerateExpression(arrayIndexAccess.Array);
        var index = GenerateExpression(arrayIndexAccess.Index);
        GenerateArrayBoundsCheck(array, index);
        
        switch (arrayIndexAccess.Array.Type)
        {
            case NubArrayType arrayType:
            {
                var firstItemPointerName = GenVarName();
                _builder.AppendLine($"    {firstItemPointerName} =l add {array}, 8");
                var offsetPointerName = GenVarName();
                _builder.AppendLine($"    {offsetPointerName} =l mul {index}, {SizeOf(arrayType.ElementType)}");
                var resultPointerName = GenVarName();
                _builder.AppendLine($"    {resultPointerName} =l add {firstItemPointerName}, {offsetPointerName}");
                return resultPointerName;
            }
            case NubFixedArrayType fixedArrayType:
            {
                var firstItemPointerName = GenVarName();
                _builder.AppendLine($"    {firstItemPointerName} =l add {array}, 8");
                var offsetPointerName = GenVarName();
                _builder.AppendLine($"    {offsetPointerName} =l mul {index}, {SizeOf(fixedArrayType.ElementType)}");
                var resultPointerName = GenVarName();
                _builder.AppendLine($"    {resultPointerName} =l add {firstItemPointerName}, {offsetPointerName}");
                return resultPointerName;
            }
            default:
            {
                throw new UnreachableException();
            }
        }
    }
    
    private string GenerateArrayAccessIndex(ArrayIndexAccessNode arrayIndexAccess)
    {
        var pointerName = GenerateArrayIndexPointer(arrayIndexAccess);

        if (IsLargeType(arrayIndexAccess.Type))
        {
            return pointerName;
        }
        else
        {
            var outputName = GenVarName();
            _builder.AppendLine($"    {outputName} {QBEAssign(arrayIndexAccess.Type)} {QBELoad(arrayIndexAccess.Type)} {pointerName}");
            return outputName;   
        }
    }

    private void GenerateArrayBoundsCheck(string array, string index)
    {
        var countName = GenVarName();
        _builder.AppendLine($"    {countName} =l loadl {array}");
        
        var isNegativeName = GenVarName();
        _builder.AppendLine($"    {isNegativeName} =w csltl {index}, 0");
        
        var isOobName = GenVarName();
        _builder.AppendLine($"    {isOobName} =w csgel {index}, {countName}");
        
        var anyOobName = GenVarName();
        _builder.AppendLine($"    {anyOobName} =w or {isNegativeName}, {isOobName}");
        
        var oobLabel = GenLabelName();
        var notOobLabel = GenLabelName();
        _builder.AppendLine($"    jnz {anyOobName}, {oobLabel}, {notOobLabel}");
        
        _builder.AppendLine(oobLabel);
        _builder.AppendLine($"    call $nub_panic(l $oob_message, l {OutOfBoundsMessage.Length})");
        
        _builder.AppendLine(notOobLabel);
    }

    private string GenerateArrayInitializer(ArrayInitializerNode arrayInitializer)
    {
        var capacity = GenerateExpression(arrayInitializer.Capacity);
        var capacityInBytes = GenVarName();
        _builder.AppendLine($"    {capacityInBytes} =l mul {capacity}, {SizeOf(arrayInitializer.ElementType)}");
        var totalArraySize = GenVarName();
        _builder.AppendLine($"    {totalArraySize} =l add {capacityInBytes}, 8");
        var outputName = GenVarName();
        _builder.AppendLine($"    {outputName} =l alloc8 {totalArraySize}");
        _builder.AppendLine($"    storel {capacity}, {outputName}");

        var dataPtr = GenVarName();
        _builder.AppendLine($"    {dataPtr} =l add {outputName}, 8");
        _builder.AppendLine($"    call $nub_memset(l {dataPtr}, w 0, l {capacityInBytes})");

        return outputName;
    }

    private string GenerateDereference(DereferenceNode dereference)
    {
        var result = GenerateExpression(dereference.Expression);
        var outputName = GenVarName();
        _builder.AppendLine($"    {outputName} {QBEAssign(dereference.Type)} {QBELoad(dereference.Type)} {result}");
        return outputName;
    }

    private string GenerateAddressOf(AddressOfNode addressOf)
    {
        switch (addressOf.Expression)
        {
            case ArrayIndexAccessNode arrayIndexAccess:
                return GenerateArrayIndexPointer(arrayIndexAccess);
            case DereferenceNode dereference:
                return GenerateExpression(dereference.Expression);
            case IdentifierNode identifier:
                return _variables[identifier.Identifier];
            case MemberAccessNode memberAccess:
                return GenerateMemberAccessPointer(memberAccess);
            default:
                throw new UnreachableException();
        }
    }

    private string GenerateBinaryExpression(BinaryExpressionNode binaryExpression)
    {
        var left = GenerateExpression(binaryExpression.Left);
        var right = GenerateExpression(binaryExpression.Right);
        var outputName = GenVarName();

        switch (binaryExpression.Operator)
        {
            case BinaryExpressionOperator.Equal:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w ceql {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w ceqw {left}, {right}");
                    return outputName;
                }

                // if (binaryExpression.Left.Type.Equals(NubPrimitiveType.String))
                // {
                //     _builder.AppendLine($"    {outputName} =w call $nub_strcmp(l {left}, l {right})");
                //     return outputName;
                // }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w ceqw {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.NotEqual:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w cnel {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w cnew {left}, {right}");
                    return outputName;
                }

                // if (binaryExpression.Left.Type.Equals(NubPrimitiveType.String))
                // {
                //     _builder.AppendLine($"    {outputName} =w call $nub_strcmp(l {left}, l {right})");
                //     _builder.AppendLine($"    {outputName} =w xor {outputName}, 1");
                //     return outputName;
                // }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w cnew {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.GreaterThan:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w csgtl {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w csgtw {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w csgtw {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.GreaterThanOrEqual:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w csgel {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w csgew {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w csgew {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.LessThan:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w csltl {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w csltw {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w csltw {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.LessThanOrEqual:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =w cslel {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w cslew {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.Bool))
                {
                    _builder.AppendLine($"    {outputName} =w cslew {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.Plus:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =l add {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w add {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.Minus:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =l sub {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w sub {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.Multiply:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =l mul {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w mul {left}, {right}");
                    return outputName;
                }

                break;
            }
            case BinaryExpressionOperator.Divide:
            {
                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I64))
                {
                    _builder.AppendLine($"    {outputName} =l div {left}, {right}");
                    return outputName;
                }

                if (binaryExpression.Left.Type.Equals(NubPrimitiveType.I32))
                {
                    _builder.AppendLine($"    {outputName} =w div {left}, {right}");
                    return outputName;
                }

                break;
            }
            default:
            {
                throw new ArgumentOutOfRangeException();
            }
        }

        throw new NotSupportedException($"Binary operator {binaryExpression.Operator} for types {binaryExpression.Left.Type} and {binaryExpression.Right.Type} not supported");
    }

    private string GenerateIdentifier(IdentifierNode identifier)
    {
        return _variables[identifier.Identifier];
    }

    private string GenerateLiteral(LiteralNode literal)
    {
        if (literal.Type.IsInteger)
        {
            switch (literal.Kind)
            {
                case LiteralKind.Integer:
                    return literal.Literal;
                case LiteralKind.Float:
                    return literal.Literal.Split(".").First();
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }

        if (literal.Type.IsFloat64)
        {
            var value = double.Parse(literal.Literal, CultureInfo.InvariantCulture);
            var bits = BitConverter.DoubleToInt64Bits(value);
            return bits.ToString();
        }
        
        if (literal.Type.IsFloat32)
        {
            var value = float.Parse(literal.Literal, CultureInfo.InvariantCulture);
            var bits = BitConverter.SingleToInt32Bits(value);
            return bits.ToString();
        }

        switch (literal.Kind)
        {
            case LiteralKind.String:
                _strings.Add(literal.Literal);
                return $"$string{_strings.Count}";
            case LiteralKind.Bool:
                return bool.Parse(literal.Literal) ? "1" : "0";
            default:
                throw new ArgumentOutOfRangeException();
        }
    }

    private string GenerateStructInitializer(StructInitializerNode structInitializer)
    {
        var structDefinition = LookupStructDefinition(structInitializer.StructType.Namespace, structInitializer.StructType.Name);
        
        var structVar = GenVarName();
        var size = structDefinition.Fields.Sum(x => SizeOf(x.Type));
        _builder.AppendLine($"    {structVar} =l alloc8 {size}");

        foreach (var field in structDefinition.Fields)
        {
            var offset = LookupMemberOffset(structDefinition, field.Name);

            if (structInitializer.Initializers.TryGetValue(field.Name, out var fieldValue))
            {
                var value = GenerateExpression(fieldValue);
                var pointer = GenVarName();
                _builder.AppendLine($"    {pointer} =l add {structVar}, {offset}");
                GenerateCopy(field.Type, value, pointer);
            }
            else if (field.Value.HasValue)
            {
                var value = GenerateExpression(field.Value.Value);
                var pointer = GenVarName();
                _builder.AppendLine($"    {pointer} =l add {structVar}, {offset}");
                GenerateCopy(field.Type, value, pointer);
            }
            else
            {
                Debug.Assert(false);
            }
        }

        return structVar;
    }

    private string GenerateUnaryExpression(UnaryExpressionNode unaryExpression)
    {
        var operand = GenerateExpression(unaryExpression.Operand);
        var outputName = GenVarName();

        switch (unaryExpression.Operator)
        {
            case UnaryExpressionOperator.Negate:
            {
                switch (unaryExpression.Operand.Type)
                {
                    case NubPrimitiveType { Kind: PrimitiveTypeKind.I64 }:
                        _builder.AppendLine($"    {outputName} =l neg {operand}");
                        return outputName;
                    case NubPrimitiveType { Kind: PrimitiveTypeKind.I32 or PrimitiveTypeKind.I16 or PrimitiveTypeKind.I8 }:
                        _builder.AppendLine($"    {outputName} =w neg {operand}");
                        return outputName;
                    case NubPrimitiveType { Kind: PrimitiveTypeKind.F64 }:
                        _builder.AppendLine($"    {outputName} =d neg {operand}");
                        return outputName;
                    case NubPrimitiveType { Kind: PrimitiveTypeKind.F32 }:
                        _builder.AppendLine($"    {outputName} =s neg {operand}");
                        return outputName;
                }

                break;
            }
            case UnaryExpressionOperator.Invert:
            {
                switch (unaryExpression.Operand.Type)
                {
                    case NubPrimitiveType { Kind: PrimitiveTypeKind.Bool }:
                        _builder.AppendLine($"    {outputName} =w xor {operand}, 1");
                        return outputName;
                }

                break;
            }
            default:
            {
                throw new ArgumentOutOfRangeException();
            }
        }

        throw new NotSupportedException($"Unary operator {unaryExpression.Operator} for type {unaryExpression.Operand.Type} not supported");
    }

    private string GenerateMemberAccessPointer(MemberAccessNode memberAccess)
    {
        var item = GenerateExpression(memberAccess.Expression);
        switch (memberAccess.Expression.Type)
        {
            case NubArrayType:
            {
                if (memberAccess.Member == "count")
                {
                    return item;
                }

                throw new UnreachableException(nameof(memberAccess.Member));
            }
            case NubStructType structType:
            {
                var structDefinition = LookupStructDefinition(structType.Namespace, structType.Name);
                var offset = LookupMemberOffset(structDefinition, memberAccess.Member);

                var offsetName = GenVarName();
                _builder.AppendLine($"    {offsetName} =l add {item}, {offset}");
                return offsetName;
            }
            default:
            {
                throw new UnreachableException(nameof(memberAccess.Expression.Type));
            }
        }
    }

    private string GenerateMemberAccess(MemberAccessNode memberAccess)
    {
        var pointer = GenerateMemberAccessPointer(memberAccess);
        
        if (IsLargeType(memberAccess.Type))
        {
            return pointer;
        }
        else
        {
            var outputName = GenVarName();
            _builder.AppendLine($"    {outputName} {QBEAssign(memberAccess.Type)} {QBELoad(memberAccess.Type)} {pointer}");
            return outputName;
        }
    }

    private string GenerateFixedArrayInitializer(FixedArrayInitializerNode fixedArrayInitializer)
    {
        var capacityInBytes = SizeOf(fixedArrayInitializer.Type);
        var outputName = GenVarName();
        _builder.AppendLine($"    {outputName} =l alloc8 {capacityInBytes + 8}");
        _builder.AppendLine($"    storel {fixedArrayInitializer.Capacity}, {outputName}");

        var dataPtr = GenVarName();
        _builder.AppendLine($"    {dataPtr} =l add {outputName}, 8");
        _builder.AppendLine($"    call $nub_memset(l {dataPtr}, w 0, l {capacityInBytes})");

        return outputName;
    }

    private string GenerateFuncCall(FuncCallNode funcCall)
    {
        var funcDefinition = LookupFuncSignature(funcCall.Namespace, funcCall.Name);
        if (funcDefinition == null)
        {
            throw new Exception($"Unknown function {funcCall}");
        }

        var parameterStrings = new List<string>();

        for (var i = 0; i < funcCall.Parameters.Count; i++)
        {
            if (i < funcDefinition.Parameters.Count && funcDefinition.Parameters[i].Variadic)
            {
                parameterStrings.Add("...");
            }

            var parameter = funcCall.Parameters[i];
            var result = GenerateExpression(parameter);

            var qbeParameterType = parameter.Type switch
            {
                NubArrayType => "l",
                NubPointerType => "l",
                NubPrimitiveType pointerType => pointerType.Kind switch
                {
                    PrimitiveTypeKind.I64 => "l",
                    PrimitiveTypeKind.I32 => "w",
                    PrimitiveTypeKind.I16 => "sh",
                    PrimitiveTypeKind.I8 => "sb",
                    PrimitiveTypeKind.U64 => "l",
                    PrimitiveTypeKind.U32 => "w",
                    PrimitiveTypeKind.U16 => "uh",
                    PrimitiveTypeKind.U8 => "ub",
                    PrimitiveTypeKind.F64 => "d",
                    PrimitiveTypeKind.F32 => "s",
                    PrimitiveTypeKind.Bool => "w",
                    _ => throw new ArgumentOutOfRangeException()
                },
                NubStructType structType => $":{structType.Namespace}_{structType.Name}",
                NubFixedArrayType => "l",
                _ => throw new NotSupportedException($"'{parameter.Type}' type cannot be used in function calls")
            };
            parameterStrings.Add($"{qbeParameterType} {result}");
        }

        var funcName = _funcNames[funcDefinition];

        if (funcDefinition.ReturnType is not NubVoidType)
        {
            var outputName = GenVarName();
            _builder.AppendLine($"    {outputName} {QBEAssign(funcCall.Type)} call {funcName}({string.Join(", ", parameterStrings)})");
            return outputName;
        }
        else
        {
            _builder.AppendLine($"    call {funcName}({string.Join(", ", parameterStrings)})");
            return "this should never show up!";
        }
    }

    private void GenerateCopy(NubType type, string value, string destinationPointer)
    {
        if (IsLargeType(type))
        {
            _builder.AppendLine($"    blit {value}, {destinationPointer}, {SizeOf(type)}");
        }
        else
        {
            _builder.AppendLine($"    {QBEStore(type)} {value}, {destinationPointer}");
        }
    }

    private string GenVarName()
    {
        return $"%v{++_variableIndex}";
    }

    private string GenLabelName()
    {
        return $"@l{++_labelIndex}";
    }

    private IFuncSignature LookupFuncSignature(string @namespace, string name)
    {
        return _sourceFiles
            .Where(f => f.Namespace == @namespace)
            .SelectMany(f => f.Definitions)
            .OfType<IFuncSignature>()
            .Single(f => f.Name == name);
    }

    private StructDefinitionNode LookupStructDefinition(string @namespace, string name)
    {
        return _sourceFiles
            .Where(f => f.Namespace == @namespace)
            .SelectMany(f => f.Definitions)
            .OfType<StructDefinitionNode>()
            .Single(s => s.Name == name);
    }

    private int LookupMemberOffset(StructDefinitionNode structDefinition, string member)
    {
        return structDefinition.Fields.TakeWhile(f => f.Name != member).Sum(f => SizeOf(f.Type));
    }
}