using System;
using Microsoft.CodeAnalysis;

namespace Svrnty.CQRS.Grpc.Generators;

/// <summary>
/// Maps C# types to Protocol Buffer types for proto file generation
/// </summary>
internal static class ProtoFileTypeMapper
{
    public static string MapType(ITypeSymbol typeSymbol, out bool needsImport, out string? importPath)
    {
        needsImport = false;
        importPath = null;

        // Handle special name (fully qualified name)
        var fullTypeName = typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);
        var typeName = typeSymbol.Name;

        // Note: NullableAnnotation.Annotated is for reference type nullability (List<T>?, string?, etc.)
        // We don't unwrap these - just use the underlying type. Nullable<T> value types are handled later.

        // Basic types
        switch (typeName)
        {
            case "String":
                return "string";
            case "Int32":
                return "int32";
            case "UInt32":
                return "uint32";
            case "Int64":
                return "int64";
            case "UInt64":
                return "uint64";
            case "Int16":
                return "int32"; // Proto has no int16
            case "UInt16":
                return "uint32"; // Proto has no uint16
            case "Byte":
                return "uint32"; // Proto has no byte
            case "SByte":
                return "int32"; // Proto has no sbyte
            case "Boolean":
                return "bool";
            case "Single":
                return "float";
            case "Double":
                return "double";
            case "Byte[]":
                return "bytes";
        }

        // Special types that need imports
        if (fullTypeName.Contains("System.DateTime"))
        {
            needsImport = true;
            importPath = "google/protobuf/timestamp.proto";
            return "google.protobuf.Timestamp";
        }

        if (fullTypeName.Contains("System.TimeSpan"))
        {
            needsImport = true;
            importPath = "google/protobuf/duration.proto";
            return "google.protobuf.Duration";
        }

        if (fullTypeName.Contains("System.Guid"))
        {
            // Guid serialized as string
            return "string";
        }

        if (fullTypeName.Contains("System.Decimal") || typeName == "Decimal" || fullTypeName == "decimal")
        {
            // Decimal serialized as string (no native decimal in proto)
            return "string";
        }

        // Handle Nullable<T> value types (e.g., int?, decimal?, enum?)
        if (typeSymbol is INamedTypeSymbol nullableType &&
            nullableType.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T &&
            nullableType.TypeArguments.Length == 1)
        {
            // Unwrap the nullable and map the inner type
            return MapType(nullableType.TypeArguments[0], out needsImport, out importPath);
        }

        // Collections
        if (typeSymbol is INamedTypeSymbol collectionType)
        {
            // List, IEnumerable, Array, ICollection etc. (but not Nullable<T>)
            var typeName2 = collectionType.Name;
            if (collectionType.TypeArguments.Length == 1 &&
                (typeName2.Contains("List") || typeName2.Contains("Collection") ||
                 typeName2.Contains("Enumerable") || typeName2.Contains("Array") ||
                 typeName2.Contains("Set") || typeName2.Contains("IList") ||
                 typeName2.Contains("ICollection") || typeName2.Contains("IEnumerable")))
            {
                var elementType = collectionType.TypeArguments[0];
                var protoElementType = MapType(elementType, out needsImport, out importPath);
                return $"repeated {protoElementType}";
            }

            // Dictionary<K, V>
            if (collectionType.TypeArguments.Length == 2 &&
                (typeName.Contains("Dictionary") || typeName.Contains("IDictionary")))
            {
                var keyType = MapType(collectionType.TypeArguments[0], out var keyNeedsImport, out var keyImportPath);
                var valueType = MapType(collectionType.TypeArguments[1], out var valueNeedsImport, out var valueImportPath);

                // Set import flags if either key or value needs imports
                if (keyNeedsImport)
                {
                    needsImport = true;
                    importPath = keyImportPath;
                }
                if (valueNeedsImport)
                {
                    needsImport = true;
                    importPath = valueImportPath; // Note: This only captures last import, may need improvement
                }

                return $"map<{keyType}, {valueType}>";
            }
        }

        // Enums
        if (typeSymbol.TypeKind == TypeKind.Enum)
        {
            return typeName; // Use the enum name directly
        }

        // Complex types (classes/records) become message types
        if (typeSymbol.TypeKind == TypeKind.Class || typeSymbol.TypeKind == TypeKind.Struct)
        {
            return typeName; // Reference the message type by name
        }

        // Fallback
        return "string"; // Default to string for unknown types
    }

    /// <summary>
    /// Converts C# PascalCase property name to proto snake_case field name
    /// </summary>
    public static string ToSnakeCase(string pascalCase)
    {
        if (string.IsNullOrEmpty(pascalCase))
            return pascalCase;

        var result = new System.Text.StringBuilder();
        result.Append(char.ToLowerInvariant(pascalCase[0]));

        for (int i = 1; i < pascalCase.Length; i++)
        {
            var c = pascalCase[i];
            if (char.IsUpper(c))
            {
                // Handle sequences of uppercase letters (e.g., "APIKey" -> "api_key")
                if (i + 1 < pascalCase.Length && char.IsUpper(pascalCase[i + 1]))
                {
                    result.Append(char.ToLowerInvariant(c));
                }
                else
                {
                    result.Append('_');
                    result.Append(char.ToLowerInvariant(c));
                }
            }
            else
            {
                result.Append(c);
            }
        }

        return result.ToString();
    }

    /// <summary>
    /// Checks if a type should be skipped/ignored for proto generation
    /// </summary>
    public static bool IsUnsupportedType(ITypeSymbol typeSymbol)
    {
        var fullTypeName = typeSymbol.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat);

        // Skip these types - they should trigger a warning/error
        if (fullTypeName.Contains("System.IO.Stream") ||
            fullTypeName.Contains("System.Threading.CancellationToken") ||
            fullTypeName.Contains("System.Threading.Tasks.Task") ||
            fullTypeName.Contains("System.Collections.Generic.IAsyncEnumerable") ||
            fullTypeName.Contains("System.Func") ||
            fullTypeName.Contains("System.Action") ||
            fullTypeName.Contains("System.Delegate"))
        {
            return true;
        }

        return false;
    }

    /// <summary>
    /// Gets the element type from a collection type, or returns the type itself if not a collection.
    /// Also unwraps Nullable types.
    /// </summary>
    public static ITypeSymbol GetElementOrUnderlyingType(ITypeSymbol typeSymbol)
    {
        // Unwrap Nullable<T>
        if (typeSymbol is INamedTypeSymbol nullableType &&
            nullableType.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T &&
            nullableType.TypeArguments.Length == 1)
        {
            return GetElementOrUnderlyingType(nullableType.TypeArguments[0]);
        }

        // Extract element type from collections
        if (typeSymbol is INamedTypeSymbol collectionType && collectionType.TypeArguments.Length == 1)
        {
            var typeName = collectionType.Name;
            if (typeName.Contains("List") || typeName.Contains("Collection") ||
                typeName.Contains("Enumerable") || typeName.Contains("Array") ||
                typeName.Contains("Set") || typeName.Contains("IList") ||
                typeName.Contains("ICollection") || typeName.Contains("IEnumerable"))
            {
                return GetElementOrUnderlyingType(collectionType.TypeArguments[0]);
            }
        }

        return typeSymbol;
    }

    /// <summary>
    /// Checks if the type is an enum (including nullable enums)
    /// </summary>
    public static bool IsEnumType(ITypeSymbol typeSymbol)
    {
        var underlying = GetElementOrUnderlyingType(typeSymbol);
        return underlying.TypeKind == TypeKind.Enum;
    }

    /// <summary>
    /// Gets the enum type symbol if this is an enum or nullable enum, otherwise null
    /// </summary>
    public static INamedTypeSymbol? GetEnumType(ITypeSymbol typeSymbol)
    {
        var underlying = GetElementOrUnderlyingType(typeSymbol);
        if (underlying.TypeKind == TypeKind.Enum && underlying is INamedTypeSymbol enumType)
        {
            return enumType;
        }
        return null;
    }
}