// 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.
 
#if NET

#pragma warning disable RS0016 // Add public types and members to the declared API (this is a supporting forwarder for an internal polyfill API)
[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Range))]
#pragma warning restore RS0016 // Add public types and members to the declared API

#else
using System.Runtime.CompilerServices;
 
namespace System
{
    /// <summary>Represent a range has start and end indexes.</summary>
    /// <remarks>
    /// Range is used by the C# compiler to support the range syntax.
    /// <code>
    /// int[] someArray = new int[5] { 1, 2, 3, 4, 5 };
    /// int[] subArray1 = someArray[0..2]; // { 1, 2 }
    /// int[] subArray2 = someArray[1..^0]; // { 2, 3, 4, 5 }
    /// </code>
    /// </remarks>
    internal readonly struct Range : IEquatable<Range>
    {
        /// <summary>Represent the inclusive start index of the Range.</summary>
        public Index Start { get; }
 
        /// <summary>Represent the exclusive end index of the Range.</summary>
        public Index End { get; }
 
        /// <summary>Construct a Range object using the start and end indexes.</summary>
        /// <param name="start">Represent the inclusive start index of the range.</param>
        /// <param name="end">Represent the exclusive end index of the range.</param>
        public Range(Index start, Index end)
        {
            Start = start;
            End = end;
        }
 
        /// <summary>Indicates whether the current Range object is equal to another object of the same type.</summary>
        /// <param name="value">An object to compare with this object</param>
        public override bool Equals(object? value) =>
            value is Range r &&
            r.Start.Equals(Start) &&
            r.End.Equals(End);
 
        /// <summary>Indicates whether the current Range object is equal to another Range object.</summary>
        /// <param name="other">An object to compare with this object</param>
        public bool Equals(Range other) => other.Start.Equals(Start) && other.End.Equals(End);
 
        /// <summary>Returns the hash code for this instance.</summary>
        public override int GetHashCode()
            => unchecked(Start.GetHashCode() * (int)0xA5555529 + End.GetHashCode());
 
        /// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
        public override string ToString()
        {
            return $"{getFromEndSpecifier(Start)}{toString(Start)}..{getFromEndSpecifier(End)}{toString(End)}";
 
            static string getFromEndSpecifier(Index index) => index.IsFromEnd ? "^" : string.Empty;
            static string toString(Index index) => ((uint)index.Value).ToString();
        }
 
        /// <summary>Create a Range object starting from start index to the end of the collection.</summary>
        public static Range StartAt(Index start) => new Range(start, Index.End);
 
        /// <summary>Create a Range object starting from first element in the collection to the end Index.</summary>
        public static Range EndAt(Index end) => new Range(Index.Start, end);
 
        /// <summary>Create a Range object starting from first element to the end.</summary>
        public static Range All => new Range(Index.Start, Index.End);
 
#if !NO_VALUE_TUPLE // workaround for https://github.com/dotnet/roslyn/issues/78392
 
        /// <summary>Calculate the start offset and length of range object using a collection length.</summary>
        /// <param name="length">The length of the collection that the range will be used with. length has to be a positive value.</param>
        /// <remarks>
        /// For performance reason, we don't validate the input length parameter against negative values.
        /// It is expected Range will be used with collections which always have non negative length/count.
        /// We validate the range is inside the length scope though.
        /// </remarks>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public (int Offset, int Length) GetOffsetAndLength(int length)
        {
            int start;
            Index startIndex = Start;
            if (startIndex.IsFromEnd)
                start = length - startIndex.Value;
            else
                start = startIndex.Value;
 
            int end;
            Index endIndex = End;
            if (endIndex.IsFromEnd)
                end = length - endIndex.Value;
            else
                end = endIndex.Value;
 
            if ((uint)end > (uint)length || (uint)start > (uint)end)
            {
                throw new ArgumentOutOfRangeException(nameof(length));
            }
 
            return (start, end - start);
        }
#endif
    }
}
#endif