// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CodeGeneration;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Editing;
using Microsoft.CodeAnalysis.Shared.Utilities;
 
using static Microsoft.CodeAnalysis.CodeGeneration.CodeGenerationHelpers;
using static Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpCodeGenerationHelpers;
 
namespace Microsoft.CodeAnalysis.CSharp.CodeGeneration
{
    internal static class EnumMemberGenerator
    {
        internal static EnumDeclarationSyntax AddEnumMemberTo(EnumDeclarationSyntax destination, IFieldSymbol enumMember, CSharpCodeGenerationContextInfo info, CancellationToken cancellationToken)
        {
            var members = new List<SyntaxNodeOrToken>();
            members.AddRange(destination.Members.GetWithSeparators());
 
            var member = GenerateEnumMemberDeclaration(enumMember, destination, info, cancellationToken);
 
            if (members.Count == 0)
            {
                members.Add(member);
            }
            else if (members.LastOrDefault().Kind() == SyntaxKind.CommaToken)
            {
                members.Add(member);
                members.Add(SyntaxFactory.Token(SyntaxKind.CommaToken));
            }
            else
            {
                var lastMember = members.Last();
                var trailingTrivia = lastMember.GetTrailingTrivia();
                members[members.Count - 1] = lastMember.WithTrailingTrivia();
                members.Add(SyntaxFactory.Token(SyntaxKind.CommaToken).WithTrailingTrivia(trailingTrivia));
                members.Add(member);
            }
 
            return destination.EnsureOpenAndCloseBraceTokens()
                .WithMembers(SyntaxFactory.SeparatedList<EnumMemberDeclarationSyntax>(members));
        }
 
        public static EnumMemberDeclarationSyntax GenerateEnumMemberDeclaration(
            IFieldSymbol enumMember,
            EnumDeclarationSyntax? destination,
            CSharpCodeGenerationContextInfo info,
            CancellationToken cancellationToken)
        {
            var reusableSyntax = GetReuseableSyntaxNodeForSymbol<EnumMemberDeclarationSyntax>(enumMember, info);
            if (reusableSyntax != null)
            {
                return reusableSyntax;
            }
 
            var value = CreateEnumMemberValue(info.Generator, destination, enumMember);
            var member = SyntaxFactory.EnumMemberDeclaration(enumMember.Name.ToIdentifierToken())
                .WithEqualsValue(value == null ? null : SyntaxFactory.EqualsValueClause(value: value));
 
            return AddFormatterAndCodeGeneratorAnnotationsTo(
                ConditionallyAddDocumentationCommentTo(member, enumMember, info, cancellationToken));
        }
 
        private static ExpressionSyntax? CreateEnumMemberValue(
            SyntaxGenerator generator, EnumDeclarationSyntax? destination, IFieldSymbol enumMember)
        {
            if (!enumMember.HasConstantValue)
            {
                return null;
            }
 
            if (enumMember.ConstantValue is not byte and
                not sbyte and
                not ushort and
                not short and
                not int and
                not uint and
                not long and
                not ulong)
            {
                return null;
            }
 
            var value = IntegerUtilities.ToInt64(enumMember.ConstantValue);
 
            if (destination != null)
            {
                if (destination.Members.Count == 0)
                {
                    if (value == 0)
                    {
                        return null;
                    }
                }
                else
                {
                    // Don't generate an initializer if no other members have them, and our value
                    // would be correctly inferred from our position.
                    if (destination.Members.Count == value &&
                        destination.Members.All(m => m.EqualsValue == null))
                    {
                        return null;
                    }
 
                    // Existing members, try to stay consistent with their style.
                    var lastMember = destination.Members.LastOrDefault(m => m.EqualsValue != null);
                    if (lastMember != null)
                    {
                        var lastExpression = lastMember.EqualsValue!.Value;
                        if (lastExpression.Kind() == SyntaxKind.LeftShiftExpression &&
                            IntegerUtilities.HasOneBitSet(value))
                        {
                            var binaryExpression = (BinaryExpressionSyntax)lastExpression;
                            if (binaryExpression.Left.Kind() == SyntaxKind.NumericLiteralExpression)
                            {
                                var numericLiteral = (LiteralExpressionSyntax)binaryExpression.Left;
                                if (numericLiteral.Token.ValueText == "1")
                                {
                                    // The user is left shifting ones, stick with that pattern
                                    var shiftValue = IntegerUtilities.LogBase2(value);
 
                                    // Re-use the numericLiteral text so type suffixes match too
                                    return SyntaxFactory.BinaryExpression(
                                        SyntaxKind.LeftShiftExpression,
                                        SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal(numericLiteral.Token.Text, 1)),
                                        SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression, SyntaxFactory.Literal(shiftValue.ToString(), shiftValue)));
                                }
                            }
                        }
                        else if (lastExpression is LiteralExpressionSyntax(SyntaxKind.NumericLiteralExpression) numericLiteral)
                        {
                            var numericToken = numericLiteral.Token;
                            var numericText = numericToken.ToString();
 
                            if (numericText.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
                            {
                                // Hex
                                return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression,
                                    SyntaxFactory.Literal(numericText[..2] + value.ToString("X"), value));
                            }
                            else if (numericText.StartsWith("0b", StringComparison.OrdinalIgnoreCase))
                            {
                                return SyntaxFactory.LiteralExpression(SyntaxKind.NumericLiteralExpression,
                                    SyntaxFactory.Literal(numericText[..2] + Convert.ToString(value, 2), value));
                            }
                        }
                    }
                }
            }
 
            var namedType = enumMember.Type as INamedTypeSymbol;
            var underlyingType = namedType?.EnumUnderlyingType;
 
            return ExpressionGenerator.GenerateNonEnumValueExpression(
                generator,
                underlyingType,
                enumMember.ConstantValue,
                canUseFieldReference: true);
        }
    }
}