// 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.Diagnostics;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Text
{
    /// <summary>
    /// Information about the character boundaries of a single line of text.
    /// </summary>
    public readonly struct TextLine : IEquatable<TextLine>
    {
        private readonly SourceText? _text;
        private readonly int _start;
        private readonly int _endIncludingBreaks;
 
        private TextLine(SourceText text, int start, int endIncludingBreaks)
        {
            _text = text;
            _start = start;
            _endIncludingBreaks = endIncludingBreaks;
        }
 
        /// <summary>
        /// Creates a <see cref="TextLine"/> instance.
        /// </summary>
        /// <param name="text">The source text.</param>
        /// <param name="span">The span of the line.</param>
        /// <returns>An instance of <see cref="TextLine"/>.</returns>
        /// <exception cref="ArgumentOutOfRangeException">The span does not represent a text line.</exception>
        public static TextLine FromSpan(SourceText text, TextSpan span)
        {
            if (text == null)
            {
                throw new ArgumentNullException(nameof(text));
            }
 
            if (span.Start > text.Length || span.Start < 0 || span.End > text.Length)
            {
                throw new ArgumentOutOfRangeException(nameof(span));
            }
 
            if (text.Length > 0)
            {
                // check span is start of line
                if (span.Start > 0 && !TextUtilities.IsAnyLineBreakCharacter(text[span.Start - 1]))
                {
                    throw new ArgumentOutOfRangeException(nameof(span), CodeAnalysisResources.SpanDoesNotIncludeStartOfLine);
                }
 
                bool endIncludesLineBreak = false;
                if (span.End > span.Start)
                {
                    endIncludesLineBreak = TextUtilities.IsAnyLineBreakCharacter(text[span.End - 1]);
                }
 
                if (!endIncludesLineBreak && span.End < text.Length)
                {
                    var lineBreakLen = TextUtilities.GetLengthOfLineBreak(text, span.End);
                    if (lineBreakLen > 0)
                    {
                        // adjust span to include line breaks
                        endIncludesLineBreak = true;
                        span = new TextSpan(span.Start, span.Length + lineBreakLen);
                    }
                }
 
                // check end of span is at end of line
                if (span.End < text.Length && !endIncludesLineBreak)
                {
                    throw new ArgumentOutOfRangeException(nameof(span), CodeAnalysisResources.SpanDoesNotIncludeEndOfLine);
                }
 
                return new TextLine(text, span.Start, span.End);
            }
            else
            {
                return new TextLine(text, 0, 0);
            }
        }
 
        // Do not use unless you are certain the span you are passing in is valid!
        // This was added to allow SourceText.LineInfo's indexer to directly create TextLines
        // without the performance implications of calling FromSpan.
        internal static TextLine FromSpanUnsafe(SourceText text, TextSpan span)
        {
            Debug.Assert(span.Start == 0 || TextUtilities.IsAnyLineBreakCharacter(text[span.Start - 1]));
            Debug.Assert(span.End == text.Length || TextUtilities.IsAnyLineBreakCharacter(text[span.End - 1]));
 
            return new TextLine(text, span.Start, span.End);
        }
 
        /// <summary>
        /// Gets the source text.
        /// </summary>
        public SourceText? Text
        {
            get { return _text; }
        }
 
        /// <summary>
        /// Gets the zero-based line number.
        /// </summary>
        public int LineNumber
        {
            get
            {
                return _text?.Lines.IndexOf(_start) ?? 0;
            }
        }
 
        /// <summary>
        /// Gets the start position of the line.
        /// </summary>
        public int Start
        {
            get { return _start; }
        }
 
        /// <summary>
        /// Gets the end position of the line not including the line break.
        /// </summary>
        public int End
        {
            get { return _endIncludingBreaks - this.LineBreakLength; }
        }
 
        private int LineBreakLength
        {
            get
            {
                if (_text == null || _text.Length == 0 || _endIncludingBreaks == _start)
                {
                    return 0;
                }
 
                int startLineBreak;
                int lineBreakLength;
                TextUtilities.GetStartAndLengthOfLineBreakEndingAt(_text, _endIncludingBreaks - 1, out startLineBreak, out lineBreakLength);
                return lineBreakLength;
            }
        }
 
        /// <summary>
        /// Gets the end position of the line including the line break.
        /// </summary>
        public int EndIncludingLineBreak
        {
            get { return _endIncludingBreaks; }
        }
 
        /// <summary>
        /// Gets the line span not including the line break.
        /// </summary>
        public TextSpan Span
        {
            get { return TextSpan.FromBounds(this.Start, this.End); }
        }
 
        /// <summary>
        /// Gets the line span including the line break.
        /// </summary>
        public TextSpan SpanIncludingLineBreak
        {
            get { return TextSpan.FromBounds(this.Start, this.EndIncludingLineBreak); }
        }
 
        public override string ToString()
        {
            if (_text == null || _text.Length == 0)
            {
                return string.Empty;
            }
            else
            {
                return _text.ToString(this.Span);
            }
        }
 
        public static bool operator ==(TextLine left, TextLine right)
        {
            return left.Equals(right);
        }
 
        public static bool operator !=(TextLine left, TextLine right)
        {
            return !left.Equals(right);
        }
 
        public bool Equals(TextLine other)
        {
            return other._text == _text
                && other._start == _start
                && other._endIncludingBreaks == _endIncludingBreaks;
        }
 
        public override bool Equals(object? obj)
        {
            if (obj is TextLine)
            {
                return Equals((TextLine)obj);
            }
 
            return false;
        }
 
        public override int GetHashCode()
        {
            return Hash.Combine(_text, Hash.Combine(_start, _endIncludingBreaks));
        }
    }
}