using System.Diagnostics;
using System.Text;

namespace Compiler;

public class Generator
{
    public static string Emit(List<TypedNodeDefinitionFunc> functions, ModuleGraph moduleGraph, string? entryPoint)
    {
        return new Generator(functions, moduleGraph, entryPoint).Emit();
    }

    private Generator(List<TypedNodeDefinitionFunc> functions, ModuleGraph moduleGraph, string? entryPoint)
    {
        this.functions = functions;
        this.moduleGraph = moduleGraph;
        this.entryPoint = entryPoint;
    }

    private readonly List<TypedNodeDefinitionFunc> functions;
    private readonly ModuleGraph moduleGraph;
    private readonly string? entryPoint;
    private IndentedTextWriter writer = new();
    private HashSet<NubType> referencedTypes = new();
    private readonly HashSet<NubType> emittedTypes = new();
    private readonly Stack<Scope> scopes = new();
    private int tmpNameIndex = 0;

    private string Emit()
    {
        if (entryPoint != null)
        {
            writer.WriteLine($$"""
                             int main(int argc, char *argv[])
                             {
                                return {{entryPoint}}();
                             }
                             """);

            writer.WriteLine();
        }

        foreach (var function in functions)
        {
            if (!moduleGraph.TryResolveIdentifier(function.Module, function.Name.Ident, true, out var info))
                throw new UnreachableException($"Module graph does not have info about the function {function.Module}::{function.Name.Ident}. This should have been caught earlier");

            if (info.Source == Module.DefinitionSource.Imported || info.Extern)
                writer.Write("extern ");
            else if (info.Source == Module.DefinitionSource.Internal && !info.Extern && !info.Exported)
                writer.Write("static ");

            var parameters = function.Parameters.Select(x => CType(x.Type, x.Name.Ident));

            writer.WriteLine($"{CType(function.ReturnType, info.MangledName)}({string.Join(", ", parameters)})");
            writer.WriteLine("{");
            using (writer.Indent())
            {
                PushScope();
                EmitStatement(function.Body);
                PopScope();
            }
            writer.WriteLine("}");
            writer.WriteLine();
        }

        var implementations = writer.ToString();

        writer = new IndentedTextWriter();

        foreach (var module in moduleGraph.GetModules())
        {
            foreach (var (name, info) in module.GetIdentifiers())
            {
                if (info.Source == Module.DefinitionSource.Internal || info.Exported)
                {
                    if (info.Source == Module.DefinitionSource.Imported || info.Extern)
                        writer.Write("extern ");
                    else if (info.Source == Module.DefinitionSource.Internal && !info.Extern && !info.Exported)
                        writer.Write("static ");

                    if (info.Type is NubTypeFunc fn)
                        writer.WriteLine($"{CType(fn.ReturnType, info.MangledName)}({string.Join(", ", fn.Parameters.Select(p => CType(p)))});");
                    else
                        writer.WriteLine($"{CType(info.Type, info.MangledName)};");
                }
            }
        }

        var declarations = writer.ToString();

        writer = new IndentedTextWriter();

        writer.WriteLine("""
                         #include <float.h>
                         #include <stdarg.h>
                         #include <stddef.h>
                         #include <stdbool.h>
                         #include <stdint.h>
                         #include <stdlib.h>

                         """);

        while (referencedTypes.Count != 0)
        {
            var type = referencedTypes.ElementAt(0);
            EmitTypeDefinitionIfNotEmitted(type);
            referencedTypes.Remove(type);
        }

        var header = writer.ToString();

        return $"{header}\n{declarations}\n{implementations}";
    }

    private void EmitTypeDefinitionIfNotEmitted(NubType type)
    {
        if (emittedTypes.Contains(type))
            return;

        emittedTypes.Add(type);

        switch (type)
        {
            case NubTypeString stringType:
            {
                writer.WriteLine($"struct {NameMangler.Mangle("core", "string", stringType)}");
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    writer.WriteLine("char *data;");
                    writer.WriteLine("size_t length;");
                    writer.WriteLine("uint32_t ref;");
                }
                writer.WriteLine("};");
                writer.WriteLine();
                break;
            }
            case NubTypeStruct structType:
            {
                if (!moduleGraph.TryResolveType(structType.Module, structType.Name, true, out var info) || info is not Module.TypeInfoStruct structInfo)
                    throw new UnreachableException();

                foreach (var field in structInfo.Fields)
                    EmitTypeDefinitionIfNotEmitted(field.Type);

                writer.Write("struct ");

                if (structInfo.Packed)
                    writer.Write("__attribute__((__packed__)) ");

                writer.WriteLine(NameMangler.Mangle(structType.Module, structType.Name, structType));
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    foreach (var field in structInfo.Fields)
                    {
                        writer.WriteLine($"{CType(field.Type, field.Name)};");
                    }
                }
                writer.WriteLine("};");
                writer.WriteLine();

                break;
            }
            case NubTypeAnonymousStruct anonymousStructType:
            {
                foreach (var field in anonymousStructType.Fields)
                    EmitTypeDefinitionIfNotEmitted(field.Type);

                writer.WriteLine($"struct {NameMangler.Mangle("anonymous", "struct", anonymousStructType)}");
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    foreach (var field in anonymousStructType.Fields)
                    {
                        writer.WriteLine($"{CType(field.Type, field.Name)};");
                    }
                }
                writer.WriteLine("};");
                writer.WriteLine();

                break;
            }
            case NubTypeEnum enumType:
            {
                if (!moduleGraph.TryResolveType(enumType.Module, enumType.Name, true, out var info) || info is not Module.TypeInfoEnum enumInfo)
                    throw new UnreachableException();

                foreach (var variant in enumInfo.Variants)
                    EmitTypeDefinitionIfNotEmitted(variant.Type);

                writer.WriteLine($"struct {NameMangler.Mangle(enumType.Module, enumType.Name, enumType)}");
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    writer.WriteLine("uint32_t tag;");
                    writer.WriteLine("union");
                    writer.WriteLine("{");
                    using (writer.Indent())
                    {
                        foreach (var variant in enumInfo.Variants)
                        {
                            writer.WriteLine($"{CType(variant.Type, variant.Name)};");
                        }
                    }
                    writer.WriteLine("};");
                }
                writer.WriteLine("};");
                writer.WriteLine();

                break;
            }
            case NubTypeEnumVariant variantType:
            {
                EmitTypeDefinitionIfNotEmitted(variantType.EnumType);
                break;
            }
        }
    }

    private void EmitStatement(TypedNodeStatement node)
    {
        if (scopes.Peek().Unreachable)
            return;

        switch (node)
        {
            case TypedNodeStatementBlock statement:
                EmitStatementBlock(statement);
                break;
            case TypedNodeStatementFuncCall statement:
                EmitStatementFuncCall(statement);
                break;
            case TypedNodeStatementReturn statement:
                EmitStatementReturn(statement);
                break;
            case TypedNodeStatementVariableDeclaration statement:
                EmitStatementVariableDeclaration(statement);
                break;
            case TypedNodeStatementAssignment statement:
                EmitStatementAssignment(statement);
                break;
            case TypedNodeStatementIf statement:
                EmitStatementIf(statement);
                break;
            case TypedNodeStatementWhile statement:
                EmitStatementWhile(statement);
                break;
            case TypedNodeStatementMatch statement:
                EmitStatementMatch(statement);
                break;
            default:
                throw new ArgumentOutOfRangeException(nameof(node), node, null);
        }
    }

    private void EmitStatementBlock(TypedNodeStatementBlock node)
    {
        writer.WriteLine("{");
        using (writer.Indent())
        {
            PushScope();
            foreach (var statement in node.Statements)
                EmitStatement(statement);
            PopScope();
        }
        writer.WriteLine("}");
    }

    private void EmitStatementFuncCall(TypedNodeStatementFuncCall node)
    {
        var name = EmitExpression(node.Target);
        var parameterValues = node.Parameters.Select(EmitExpression).ToList();
        writer.WriteLine($"{name}({string.Join(", ", parameterValues)});");
    }

    private void EmitStatementReturn(TypedNodeStatementReturn statement)
    {
        if (statement.Value != null)
        {
            var value = EmitExpression(statement.Value);
            var variableName = TmpName();
            writer.WriteLine($"{CType(statement.Value.Type, variableName)} = {value};");
            EmitCleanupAllScopes();
            writer.WriteLine($"return {variableName};");
        }
        else
        {
            EmitCleanupAllScopes();
            writer.WriteLine($"return;");
        }

        scopes.Peek().Unreachable = true;
    }

    private void EmitStatementVariableDeclaration(TypedNodeStatementVariableDeclaration statement)
    {
        var value = EmitExpression(statement.Value);
        EmitCopyConstructor(value, statement.Value.Type);
        writer.WriteLine($"{CType(statement.Type, statement.Name.Ident)} = {value};");
        scopes.Peek().Locals.Add((statement.Name.Ident, statement.Type));
    }

    private void EmitStatementAssignment(TypedNodeStatementAssignment statement)
    {
        var target = EmitExpression(statement.Target);
        EmitCopyDestructor(target, statement.Target.Type);
        var value = EmitExpression(statement.Value);
        EmitCopyConstructor(value, statement.Value.Type);
        writer.WriteLine($"{target} = {value};");
    }

    private void EmitStatementIf(TypedNodeStatementIf statement)
    {
        var condition = EmitExpression(statement.Condition);
        writer.WriteLine($"if ({condition})");
        writer.WriteLine("{");
        using (writer.Indent())
        {
            PushScope();
            EmitStatement(statement.ThenBlock);
            PopScope();
        }
        writer.WriteLine("}");

        if (statement.ElseBlock != null)
        {
            writer.Write("else");
            if (statement.ElseBlock is TypedNodeStatementIf)
                writer.Write(" ");
            else
                writer.WriteLine();

            writer.WriteLine("{");
            using (writer.Indent())
            {
                PushScope();
                EmitStatement(statement.ElseBlock);
                PopScope();
            }
            writer.WriteLine("}");
        }
    }

    private void EmitStatementWhile(TypedNodeStatementWhile statement)
    {
        var condition = EmitExpression(statement.Condition);
        writer.WriteLine($"while ({condition})");
        writer.WriteLine("{");
        using (writer.Indent())
        {
            PushScope();
            EmitStatement(statement.Body);
            PopScope();
        }
        writer.WriteLine("}");
    }

    private void EmitStatementMatch(TypedNodeStatementMatch statement)
    {
        var target = EmitExpression(statement.Target);
        var enumType = (NubTypeEnum)statement.Target.Type;

        if (!moduleGraph.TryResolveType(enumType.Module, enumType.Name, true, out var info))
            throw new UnreachableException();

        var enumInfo = (Module.TypeInfoEnum)info;

        writer.WriteLine($"switch ({target}.tag)");
        writer.WriteLine("{");
        using (writer.Indent())
        {
            foreach (var @case in statement.Cases)
            {
                var variantInfo = enumInfo.Variants.First(x => x.Name == @case.Variant.Ident);
                var tag = enumInfo.Variants.ToList().FindIndex(x => x.Name == @case.Variant.Ident);

                writer.WriteLine($"case {tag}:");
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    PushScope();
                    writer.WriteLine($"{CType(variantInfo.Type, @case.VariableName.Ident)} = {target}.{@case.Variant.Ident};");
                    EmitStatement(@case.Body);
                    PopScope();
                    writer.WriteLine("break;");
                }
                writer.WriteLine("}");
            }
        }
        writer.WriteLine("}");
    }

    private string EmitExpression(TypedNodeExpression node)
    {
        return node switch
        {
            TypedNodeExpressionBinary expression => EmitExpressionBinary(expression),
            TypedNodeExpressionUnary expression => EmitExpressionUnary(expression),
            TypedNodeExpressionBoolLiteral expression => expression.Value.Value ? "true" : "false",
            TypedNodeExpressionIntLiteral expression => expression.Value.Value.ToString(),
            TypedNodeExpressionStringLiteral expression => EmitExpressionStringLiteral(expression),
            TypedNodeExpressionStructLiteral expression => EmitExpressionStructLiteral(expression),
            TypedNodeExpressionEnumLiteral expression => EmitExpressionEnumLiteral(expression),
            TypedNodeExpressionStructMemberAccess expression => EmitExpressionMemberAccess(expression),
            TypedNodeExpressionStringLength expression => EmitExpressionStringLength(expression),
            TypedNodeExpressionStringPointer expression => EmitExpressionStringPointer(expression),
            TypedNodeExpressionLocalIdent expression => expression.Name,
            TypedNodeExpressionGlobalIdent expression => EmitNodeExpressionGlobalIdent(expression),
            TypedNodeExpressionFuncCall expression => EmitExpressionFuncCall(expression),
            _ => throw new ArgumentOutOfRangeException(nameof(node), node, null)
        };
    }

    private string EmitExpressionBinary(TypedNodeExpressionBinary expression)
    {
        var left = EmitExpression(expression.Left);
        var right = EmitExpression(expression.Right);

        return expression.Operation switch
        {
            TypedNodeExpressionBinary.Op.Add => $"({left} + {right})",
            TypedNodeExpressionBinary.Op.Subtract => $"({left} - {right})",
            TypedNodeExpressionBinary.Op.Multiply => $"({left} * {right})",
            TypedNodeExpressionBinary.Op.Divide => $"({left} / {right})",
            TypedNodeExpressionBinary.Op.Modulo => $"({left} % {right})",
            TypedNodeExpressionBinary.Op.Equal => $"({left} == {right})",
            TypedNodeExpressionBinary.Op.NotEqual => $"({left} != {right})",
            TypedNodeExpressionBinary.Op.LessThan => $"({left} < {right})",
            TypedNodeExpressionBinary.Op.LessThanOrEqual => $"({left} <= {right})",
            TypedNodeExpressionBinary.Op.GreaterThan => $"({left} > {right})",
            TypedNodeExpressionBinary.Op.GreaterThanOrEqual => $"({left} >= {right})",
            TypedNodeExpressionBinary.Op.LeftShift => $"({left} << {right})",
            TypedNodeExpressionBinary.Op.RightShift => $"({left} >> {right})",
            TypedNodeExpressionBinary.Op.LogicalAnd => $"({left} && {right})",
            TypedNodeExpressionBinary.Op.LogicalOr => $"({left} || {right})",
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private string EmitExpressionUnary(TypedNodeExpressionUnary expression)
    {
        var target = EmitExpression(expression.Target);

        return expression.Operation switch
        {
            TypedNodeExpressionUnary.Op.Negate => $"(-{target})",
            TypedNodeExpressionUnary.Op.Invert => $"(!{target})",
            _ => throw new ArgumentOutOfRangeException()
        };
    }

    private string EmitExpressionStringLiteral(TypedNodeExpressionStringLiteral expression)
    {
        var name = TmpName();
        scopes.Peek().Locals.Add((name, expression.Type));

        var variable = CType(expression.Type, name);

        writer.WriteLine($"{variable} = malloc(sizeof(struct {NameMangler.Mangle("core", "string", expression.Type)}));");
        writer.WriteLine($"{name}->data = \"{expression.Value.Value}\";");
        writer.WriteLine($"{name}->length = {expression.Value.Value.Length};");
        writer.WriteLine($"{name}->ref = 1;");

        return name;
    }

    private string EmitExpressionStructLiteral(TypedNodeExpressionStructLiteral expression)
    {
        var initializerValues = new Dictionary<string, string>();

        foreach (var initializer in expression.Initializers)
        {
            var values = EmitExpression(initializer.Value);
            initializerValues[initializer.Name.Ident] = values;
        }

        var initializerStrings = initializerValues.Select(x => $".{x.Key} = {x.Value}");

        return $"({CType(expression.Type)}){{ {string.Join(", ", initializerStrings)} }}";
    }

    private string EmitExpressionEnumLiteral(TypedNodeExpressionEnumLiteral expression)
    {
        var enumVariantType = (NubTypeEnumVariant)expression.Type;

        if (!moduleGraph.TryResolveType(enumVariantType.EnumType.Module, enumVariantType.EnumType.Name, true, out var info))
            throw new UnreachableException();

        var enumInfo = (Module.TypeInfoEnum)info;
        var tag = enumInfo.Variants.ToList().FindIndex(x => x.Name == enumVariantType.Variant);

        var value = EmitExpression(expression.Value);

        return $"({CType(expression.Type)}){{ .tag = {tag}, .{enumVariantType.Variant} = {value} }}";
    }

    private string EmitExpressionMemberAccess(TypedNodeExpressionStructMemberAccess expression)
    {
        var target = EmitExpression(expression.Target);
        return $"{target}.{expression.Name.Ident}";
    }

    private string EmitExpressionStringLength(TypedNodeExpressionStringLength expression)
    {
        var target = EmitExpression(expression.Target);
        return $"{target}->length";
    }

    private string EmitExpressionStringPointer(TypedNodeExpressionStringPointer expression)
    {
        var target = EmitExpression(expression.Target);
        return $"{target}->data";
    }

    private string EmitNodeExpressionGlobalIdent(TypedNodeExpressionGlobalIdent expression)
    {
        if (!moduleGraph.TryResolveIdentifier(expression.Module, expression.Name, true, out var info))
            throw new UnreachableException($"Module graph does not have info about identifier {expression.Module}::{expression.Name}. This should have been caught earlier");

        return info.MangledName;
    }

    private string EmitExpressionFuncCall(TypedNodeExpressionFuncCall expression)
    {
        var name = EmitExpression(expression.Target);
        var parameterValues = expression.Parameters.Select(EmitExpression).ToList();
        return $"{name}({string.Join(", ", parameterValues)})";
    }

    public string CType(NubType node, string? varName = null)
    {
        referencedTypes.Add(node);

        return node switch
        {
            NubTypeVoid => "void" + (varName != null ? $" {varName}" : ""),
            NubTypeBool => "bool" + (varName != null ? $" {varName}" : ""),
            NubTypeStruct type => $"struct {NameMangler.Mangle(type.Module, type.Name, type)}" + (varName != null ? $" {varName}" : ""),
            NubTypeAnonymousStruct type => CTypeAnonymousStruct(type, varName),
            NubTypeEnum type => $"struct {NameMangler.Mangle(type.Module, type.Name, type)}" + (varName != null ? $" {varName}" : ""),
            NubTypeEnumVariant type => CType(type.EnumType, varName),
            NubTypeSInt type => $"int{type.Width}_t" + (varName != null ? $" {varName}" : ""),
            NubTypeUInt type => $"uint{type.Width}_t" + (varName != null ? $" {varName}" : ""),
            NubTypePointer type => CType(type.To) + (varName != null ? $" *{varName}" : "*"),
            NubTypeString type => $"struct {NameMangler.Mangle("core", "string", type)}" + (varName != null ? $" *{varName}" : "*"),
            NubTypeFunc type => $"{CType(type.ReturnType)} (*{varName})({string.Join(", ", type.Parameters.Select(p => CType(p)))})",
            _ => throw new ArgumentOutOfRangeException(nameof(node), node, null)
        };
    }

    private static string CTypeAnonymousStruct(NubTypeAnonymousStruct type, string? varName)
    {
        return $"struct {NameMangler.Mangle("anonymous", "struct", type)}{(varName != null ? $" {varName}" : "")}";
    }

    private string TmpName()
    {
        return $"_tmp{tmpNameIndex++}";
    }

    private void EmitCleanupAllScopes()
    {
        foreach (var scope in scopes.Reverse())
        {
            for (int i = scope.Locals.Count - 1; i >= 0; i--)
            {
                var (name, type) = scope.Locals[i];
                EmitCopyDestructor(name, type);
            }
        }
    }

    private void EmitCleanupCurrentScope(Scope scope)
    {
        for (int i = scope.Locals.Count - 1; i >= 0; i--)
        {
            var (name, type) = scope.Locals[i];
            EmitCopyDestructor(name, type);
        }
    }

    private void EmitCopyConstructor(string value, NubType type)
    {
        switch (type)
        {
            case NubTypeString:
                writer.WriteLine($"{value}->ref += 1;");
                break;
        }
    }

    private void EmitCopyDestructor(string value, NubType type)
    {
        switch (type)
        {
            case NubTypeString:
                writer.WriteLine($"{value}->ref -= 1;");
                writer.WriteLine($"if ({value}->ref == 0)");
                writer.WriteLine("{");
                using (writer.Indent())
                {
                    writer.WriteLine($"free({value});");
                }
                writer.WriteLine("}");
                break;
        }
    }

    private void PushScope()
    {
        scopes.Push(new Scope());
    }

    private void PopScope()
    {
        var scope = scopes.Pop();
        if (!scope.Unreachable)
            EmitCleanupCurrentScope(scope);
    }

    private class Scope
    {
        public List<(string Name, NubType Type)> Locals { get; } = [];
        public bool Unreachable { get; set; }
    }
}

internal class IndentedTextWriter
{
    private readonly StringBuilder builder = new();
    private int indentLevel;

    public IDisposable Indent()
    {
        indentLevel++;
        return new IndentScope(this);
    }

    public void WriteLine(string text)
    {
        WriteIndent();
        builder.AppendLine(text);
    }

    public void Write(string text)
    {
        WriteIndent();
        builder.Append(text);
    }

    public void WriteLine()
    {
        builder.AppendLine();
    }

    public override string ToString()
    {
        return builder.ToString();
    }

    private void WriteIndent()
    {
        if (builder.Length > 0)
        {
            var lastChar = builder[^1];
            if (lastChar != '\n' && lastChar != '\r')
                return;
        }

        for (var i = 0; i < indentLevel; i++)
        {
            builder.Append("    ");
        }
    }

    private class IndentScope(IndentedTextWriter writer) : IDisposable
    {
        private bool disposed;

        public void Dispose()
        {
            if (disposed) return;
            writer.indentLevel--;
            disposed = true;
        }
    }
}