CodeString.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rubberduck.VBEditor
{
    public class TestCodeString : CodeString
    {
        public static readonly char PseudoCaret = '|';

        public TestCodeString(CodeString codeString)
            : this(codeString.Code, codeString.CaretPosition, codeString.SnippetPosition)
        { }

        public TestCodeString(string code, Selection zPosition, Selection pPosition = default)
            : base(code, zPosition, pPosition)
        { }

        public override string ToString()
        {
            return InsertPseudoCaret();
        }

        private string InsertPseudoCaret()
        {
            if (string.IsNullOrEmpty(Code))
            {
                return string.Empty;
            }

            var lines = Lines;
            var line = lines[CaretPosition.StartLine];
            lines[CaretPosition.StartLine] = line.Insert(Math.Min(CaretPosition.StartColumn, line.Length), PseudoCaret.ToString());
            return string.Join("\r\n", lines);
        }
    }

    /// <summary>
    /// Represents a code string that includes caret position.
    /// </summary>
    public class CodeString : IEquatable<CodeString>
    {
        /// <summary>
        /// Creates a new <c>CodeString</c>
        /// </summary>
        /// <param name="code">Code string</param>
        /// <param name="zPosition">Zero-based caret position in the code string.</param>
        /// <param name="pPosition">One-based selection span of the code string in the containing module.</param>
        public CodeString(string code, Selection zPosition, Selection pPosition = default)
        {
            Code = code ?? throw new ArgumentNullException(nameof(code));
            CaretPosition = zPosition;

            var lines = Lines;
            SnippetPosition = pPosition == default
                ? new Selection(1, 1, lines.Length, lines[lines.Length-1].Length)
                : pPosition;
        }

        /// <summary>
        /// The code string.
        /// </summary>
        public string Code { get; }
        /// <summary>
        /// Zero-based caret position in the code string.
        /// </summary>
        public Selection CaretPosition { get; }
        /// <summary>
        /// Gets the 0-based index of the caret position in the flattened <see cref="Code"/> string.
        /// </summary>
        public int CaretCharIndex
        {
            get
            {
                var i = 0;
                for (var line = 0; line <= CaretPosition.StartLine; line++)
                {
                    if (line < CaretPosition.StartLine)
                    {
                        i += Lines[line].Length;
                    }
                    else
                    {
                        i += CaretPosition.StartColumn;
                        return i;
                    }

                    i += 2; // "\r\n"
                }

                return i;
            }
        }
        /// <summary>
        /// One-based position of the code string in the containing module.
        /// </summary>
        public Selection SnippetPosition { get; }
        /// <summary>
        /// Gets the individual <see cref="Code"/> string lines.
        /// </summary>
        public string[] Lines => Code?.Replace("\r", string.Empty).Split('\n') ?? new string[] { };
        /// <summary>
        /// Gets the contents of the line that is immediately before the line that contains the caret.
        /// </summary>
        public string PreviousLine => CaretPosition.StartLine == 0 ? null : Lines[CaretPosition.StartLine - 1];
        /// <summary>
        /// Gets the contents of the line that is immediately after the line that contains the caret.
        /// </summary>
        public string NextLine => CaretPosition.StartLine == Lines.Length ? null : Lines[CaretPosition.StartLine + 1];

        /// <summary>
        /// Gets the contents of the line that contains the caret.
        /// </summary>
        public string CaretLine => Lines[CaretPosition.StartLine];

        public CodeString ReplaceLine(int index, string content)
        {
            var lines = Lines;
            Debug.Assert(index >= 0 && index < lines.Length);

            lines[index] = content;
            var code = string.Join("\r\n", lines);
            return new CodeString(code, CaretPosition, SnippetPosition);
        }

        private static readonly IReadOnlyList<string> ValidRemCommentMarkers =
            new []
            {
                "Rem" + ' ',
                "Rem" + '?',
                "Rem" + '<',
                "Rem" + '>',
                "Rem" + '{',
                "Rem" + '}',
                "Rem" + '~',
                "Rem" + '`',
                "Rem" + '!',
                "Rem" + '/',
                "Rem" + '*',
                "Rem" + '(',
                "Rem" + ')',
                "Rem" + '-',
                "Rem" + '=',
                "Rem" + '+',
                "Rem" + '\\',
                "Rem" + '|',
                "Rem" + ';',
                "Rem" + ':',
                "Rem" + '\'',
                "Rem" + '"',
                "Rem" + ',',
                "Rem" + '.',
            };

        public bool IsComment
        {
            get
            {
                var noIndent = CaretLine.TrimStart();
                if (noIndent.StartsWith("'") || noIndent.StartsWith("rem ", StringComparison.InvariantCultureIgnoreCase))
                {
                    // no-brainer comment
                    return true;
                }

                var stripped = StripBracketedExpressions(StripStringLiterals(Code));
                var length = stripped.Length;
                var leftOfCaret = stripped.Substring(0, Math.Max(0, Math.Min(length - 1, CaretCharIndex)));
                if (leftOfCaret.IndexOf('\'') >= 0)
                {
                    // single-quote comment
                    return true;
                }
                else
                {
                    // Rem comment
                    var instructions = leftOfCaret.Split(':');
                    return ValidRemCommentMarkers.Any(marker => instructions.Any(instruction => instruction.TrimStart().StartsWith(marker)));
                }
                    
            }
        }

        private string StripStringLiterals(string line)
        {
            return Regex.Replace(line, "\"[^\"]*\"", match => new string(' ', match.Length));
        }

        private string StripBracketedExpressions(string line)
        {
            return Regex.Replace(line, "\\[[^\\]]*\\]", match => new string(' ', match.Length));
        }

        public bool IsInsideStringLiteral
        {
            get
            {
                if (string.IsNullOrWhiteSpace(CaretLine) || !CaretLine.Substring(0, CaretPosition.StartColumn).Contains('"') || IsComment)
                {
                    return false;
                }

                var stringStart = CaretLine.IndexOf('"');
                var escaped = CaretLine.Substring(0, stringStart + 1) + 
                              CaretLine.Substring(stringStart + 1).Replace("\"\"", "__");

                var leftOfCaret = escaped.Substring(0, CaretPosition.StartColumn);
                var rightOfCaret = escaped.Substring(Math.Min(CaretPosition.StartColumn + 1, CaretLine.Length - 1));
                if (!rightOfCaret.Contains('"') || CaretPosition.StartColumn + 1 > CaretLine.Length)
                {
                    // the string isn't terminated, but VBE would terminate it here.
                    rightOfCaret += '"';
                }

                // odd number of double quotes on either side of the caret means we're inside a string literal:
                return (leftOfCaret.Count(c => c.Equals('"')) % 2) != 0 && 
                       (rightOfCaret.Count(c => c.Equals('"')) % 2) != 0;
            }
        }

        public override bool Equals(object obj)
        {
            if (obj == null)
            {
                return false;
            }

            var other = (CodeString)obj;
            return Equals(other);
        }

        public override int GetHashCode()
        {
            return HashCode.Compute(Code, CaretPosition);
        }

        public override string ToString()
        {
            return Code;
        }

        public bool Equals(CodeString other)
        {
            if (other == null)
            {
                return false;
            }
            return (Code == null && other.Code == null) 
                || (Code != null && Code.Equals(other.Code) && CaretPosition.Equals(other.CaretPosition));
        }
    }
}