// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.

#if !NETCOREAPP

using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using Analyzer.Utilities;

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>
    [SuppressMessage("Performance", "CA1815:Override equals and operator equals on value types", Justification = "Matches implementation from dotnet/runtime")]
    [SuppressMessage("Usage", "CA2231:Overload operator equals on overriding value type Equals", Justification = "Matches implementation from dotnet/runtime")]
    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()
        {
            return HashUtilities.Combine(Start.GetHashCode(), End.GetHashCode());
        }

        /// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
        public override string ToString()
        {
            return Start.ToString() + ".." + End.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);

        /// <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
