// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
 
namespace System.Collections.Frozen
{
    internal sealed partial class LengthBucketsFrozenDictionary<TValue>
    {
        [MethodImpl(MethodImplOptions.NoInlining)]
        private protected override ref readonly TValue GetValueRefOrNullRefCore<TAlternateKey>(TAlternateKey alternate)
        {
            Debug.Assert(typeof(TAlternateKey) == typeof(ReadOnlySpan<char>));
            ReadOnlySpan<char> key = Unsafe.As<TAlternateKey, ReadOnlySpan<char>>(ref alternate);
 
            IAlternateEqualityComparer<ReadOnlySpan<char>, string> comparer = GetAlternateEqualityComparer<ReadOnlySpan<char>>();
 
            // If the length doesn't have an associated bucket, the key isn't in the dictionary.
            int bucketIndex = (key.Length - _minLength) * LengthBuckets.MaxPerLength;
            int bucketEndIndex = bucketIndex + LengthBuckets.MaxPerLength;
            int[] lengthBuckets = _lengthBuckets;
            if (bucketIndex >= 0 && bucketEndIndex <= lengthBuckets.Length)
            {
                string[] keys = _keys;
                TValue[] values = _values;
 
                for (; bucketIndex < bucketEndIndex; bucketIndex++)
                {
                    int index = lengthBuckets[bucketIndex];
                    if ((uint)index < (uint)keys.Length)
                    {
                        if (comparer.Equals(key, keys[index]))
                        {
                            return ref values[index];
                        }
                    }
                    else
                    {
                        // -1 is used to indicate a null, when it's casted to unit it becomes > keys.Length
                        break;
                    }
                }
            }
 
            return ref Unsafe.NullRef<TValue>();
        }
    }
}