// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Text;
 
namespace Microsoft.DotNet.RemoteExecutor
{
    internal static class PasteArguments
    {
        private const char Quote = '\"';
        private const char Backslash = '\\';
 
        /// <summary>
        /// Repastes a set of arguments into a linear string that parses back into the originals under pre- or post-2008 VC parsing rules.
        /// The rules for parsing the executable name (argv[0]) are special, so you must indicate whether the first argument actually is argv[0].
        /// </summary>
        public static string Paste(IEnumerable<string> arguments, bool pasteFirstArgumentUsingArgV0Rules)
        {
            var stringBuilder = new StringBuilder();
 
            foreach (string argument in arguments)
            {
                if (pasteFirstArgumentUsingArgV0Rules && RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                {
                    pasteFirstArgumentUsingArgV0Rules = false;
 
                    // Special rules for argv[0]
                    //   - Backslash is a normal character.
                    //   - Quotes used to include whitespace characters.
                    //   - Parsing ends at first whitespace outside quoted region.
                    //   - No way to get a literal quote past the parser.
 
                    bool hasWhitespace = false;
                    foreach (char c in argument)
                    {
                        if (c == Quote)
                        {
                            throw new ApplicationException("The argv[0] argument cannot include a double quote.");
                        }
                        if (char.IsWhiteSpace(c))
                        {
                            hasWhitespace = true;
                        }
                    }
                    if (argument.Length == 0 || hasWhitespace)
                    {
                        stringBuilder.Append(Quote);
                        stringBuilder.Append(argument);
                        stringBuilder.Append(Quote);
                    }
                    else
                    {
                        stringBuilder.Append(argument);
                    }
                }
                else
                {
                    AppendArgument(stringBuilder, argument);
                }
            }
 
            return stringBuilder.ToString();
        }
 
        public static void AppendArgument(StringBuilder stringBuilder, string argument)
        {
            if (stringBuilder.Length != 0)
            {
                stringBuilder.Append(' ');
            }
 
            // Parsing rules for non-argv[0] arguments:
            //   - Backslash is a normal character except followed by a quote.
            //   - 2N backslashes followed by a quote ==> N literal backslashes followed by unescaped quote
            //   - 2N+1 backslashes followed by a quote ==> N literal backslashes followed by a literal quote
            //   - Parsing stops at first whitespace outside of quoted region.
            //   - (post 2008 rule): A closing quote followed by another quote ==> literal quote, and parsing remains in quoting mode.
            if (argument.Length != 0 && ContainsNoWhitespaceOrQuotes(argument))
            {
                // Simple case - no quoting or changes needed.
                stringBuilder.Append(argument);
            }
            else
            {
                stringBuilder.Append(Quote);
                int idx = 0;
                while (idx < argument.Length)
                {
                    char c = argument[idx++];
                    if (c == Backslash)
                    {
                        int numBackSlash = 1;
                        while (idx < argument.Length && argument[idx] == Backslash)
                        {
                            idx++;
                            numBackSlash++;
                        }
 
                        if (idx == argument.Length)
                        {
                            // We'll emit an end quote after this so must double the number of backslashes.
                            stringBuilder.Append(Backslash, numBackSlash * 2);
                        }
                        else if (argument[idx] == Quote)
                        {
                            // Backslashes will be followed by a quote. Must double the number of backslashes.
                            stringBuilder.Append(Backslash, numBackSlash * 2 + 1);
                            stringBuilder.Append(Quote);
                            idx++;
                        }
                        else
                        {
                            // Backslash will not be followed by a quote, so emit as normal characters.
                            stringBuilder.Append(Backslash, numBackSlash);
                        }
 
                        continue;
                    }
 
                    if (c == Quote)
                    {
                        // Escape the quote so it appears as a literal. This also guarantees that we won't end up generating a closing quote followed
                        // by another quote (which parses differently pre-2008 vs. post-2008.)
                        stringBuilder.Append(Backslash);
                        stringBuilder.Append(Quote);
                        continue;
                    }
 
                    stringBuilder.Append(c);
                }
 
                stringBuilder.Append(Quote);
            }
        }
 
        private static bool ContainsNoWhitespaceOrQuotes(string s)
        {
            for (int i = 0; i < s.Length; i++)
            {
                char c = s[i];
                if (char.IsWhiteSpace(c) || c == Quote)
                {
                    return false;
                }
            }
 
            return true;
        }
    }
}