// 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.Diagnostics;

namespace System
{
    public readonly struct Range : IEquatable<Range>
    {
        public Index Start { get; }
        public Index End { get; }

        private Range(Index start, Index end)
        {
            Start = start;
            End = end;
        }

        public override bool Equals(object value)
        {
            if (value is Range)
            {
                Range r = (Range)value;
                return r.Start.Equals(Start) && r.End.Equals(End);
            }

            return false;
        }

        public bool Equals (Range other) => other.Start.Equals(Start) && other.End.Equals(End);

        public override int GetHashCode()
        {
            return HashCode.Combine(Start.GetHashCode(), End.GetHashCode());
        }

        public override string ToString()
        {
            Span<char> span = stackalloc char[2 + (2 * 11)]; // 2 for "..", then for each index 1 for '^' and 10 for longest possible uint
            int charsWritten;
            int pos = 0;

            if (Start.FromEnd)
            {
                span[0] = '^';
                pos = 1;
            }
            bool formatted = ((uint)Start.Value).TryFormat(span.Slice(pos), out charsWritten);
            Debug.Assert(formatted);
            pos += charsWritten;

            span[pos++] = '.';
            span[pos++] = '.';

            if (End.FromEnd)
            {
                span[pos++] = '^';
            }
            formatted = ((uint)End.Value).TryFormat(span.Slice(pos), out charsWritten);
            Debug.Assert(formatted);
            pos += charsWritten;

            return new string(span.Slice(0, pos));
        }

        public static Range Create(Index start, Index end) => new Range(start, end);
        public static Range FromStart(Index start) => new Range(start, new Index(0, fromEnd: true));
        public static Range ToEnd(Index end) => new Range(new Index(0, fromEnd: false), end);
        public static Range All() => new Range(new Index(0, fromEnd: false), new Index(0, fromEnd: true));
    }
}