// 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;
using System.Collections.Generic;
 
namespace Microsoft.CodeAnalysis.Syntax
{
    internal class SyntaxTriviaListBuilder
    {
        private SyntaxTrivia[] _nodes;
        private int _count;
 
        public SyntaxTriviaListBuilder(int size)
        {
            _nodes = new SyntaxTrivia[size];
        }
 
        public static SyntaxTriviaListBuilder Create()
        {
            return new SyntaxTriviaListBuilder(4);
        }
 
        public static SyntaxTriviaList Create(IEnumerable<SyntaxTrivia>? trivia)
        {
            if (trivia == null)
            {
                return new SyntaxTriviaList();
            }
 
            var builder = SyntaxTriviaListBuilder.Create();
            builder.AddRange(trivia);
            return builder.ToList();
        }
 
        public int Count
        {
            get { return _count; }
        }
 
        public void Clear()
        {
            _count = 0;
        }
 
        public SyntaxTrivia this[int index]
        {
            get
            {
                if (index < 0 || index >= _count)
                {
                    throw new IndexOutOfRangeException();
                }
 
                return _nodes[index];
            }
        }
 
        public void AddRange(IEnumerable<SyntaxTrivia>? items)
        {
            if (items != null)
            {
                foreach (var item in items)
                {
                    this.Add(item);
                }
            }
        }
 
        public SyntaxTriviaListBuilder Add(SyntaxTrivia item)
        {
            if (_count >= _nodes.Length)
            {
                this.Grow(_count == 0 ? 8 : _nodes.Length * 2);
            }
 
            _nodes[_count++] = item;
            return this;
        }
 
        public void Add(SyntaxTrivia[] items)
            => Add(items.AsSpan());
 
        public void Add(ReadOnlySpan<SyntaxTrivia> items)
        {
            this.Add(items, 0, items.Length);
        }
 
        public void Add(SyntaxTrivia[] items, int offset, int length)
            => Add(items.AsSpan(), offset, length);
 
        public void Add(ReadOnlySpan<SyntaxTrivia> items, int offset, int length)
        {
            if (_count + length > _nodes.Length)
            {
                this.Grow(_count + length);
            }
 
            items.Slice(offset, length).CopyTo(_nodes.AsSpan().Slice(_count, length));
            _count += length;
        }
 
        public void Add(in SyntaxTriviaList list)
        {
            this.Add(list, 0, list.Count);
        }
 
        public void Add(in SyntaxTriviaList list, int offset, int length)
        {
            if (_count + length > _nodes.Length)
            {
                this.Grow(_count + length);
            }
 
            list.CopyTo(offset, _nodes, _count, length);
            _count += length;
        }
 
        private void Grow(int size)
        {
            var tmp = new SyntaxTrivia[size];
            Array.Copy(_nodes, tmp, _nodes.Length);
            _nodes = tmp;
        }
 
        public static implicit operator SyntaxTriviaList(SyntaxTriviaListBuilder builder)
        {
            return builder.ToList();
        }
 
        public SyntaxTriviaList ToList()
        {
            if (_count > 0)
            {
                switch (_count)
                {
                    case 1:
                        return new SyntaxTriviaList(default(SyntaxToken), _nodes[0].UnderlyingNode, position: 0, index: 0);
                    case 2:
                        return new SyntaxTriviaList(default(SyntaxToken),
                            InternalSyntax.SyntaxList.List(
                            _nodes[0].UnderlyingNode!,
                            _nodes[1].UnderlyingNode!), position: 0, index: 0);
                    case 3:
                        return new SyntaxTriviaList(default(SyntaxToken),
                            InternalSyntax.SyntaxList.List(
                                _nodes[0].UnderlyingNode!,
                                _nodes[1].UnderlyingNode!,
                                _nodes[2].UnderlyingNode!),
                            position: 0, index: 0);
                    default:
                        {
                            var tmp = new ArrayElement<GreenNode>[_count];
                            for (int i = 0; i < _count; i++)
                            {
                                tmp[i].Value = _nodes[i].UnderlyingNode!;
                            }
 
                            return new SyntaxTriviaList(default(SyntaxToken),
                                InternalSyntax.SyntaxList.List(tmp), position: 0, index: 0);
                        }
                }
            }
            else
            {
                return default(SyntaxTriviaList);
            }
        }
    }
}