// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

// Copied from dotnet/runtime/src/libraries/System.Private.CoreLib/src/System/PasteArguments.cs
namespace Microsoft.DotNet.Watcher;

internal static class CommandLineUtilities
{
    public static string JoinArguments(IEnumerable<string> arguments)
    {
        var builder = new StringBuilder();
        AppendArguments(builder, arguments);
        return builder.ToString();
    }

    public static void AppendArguments(StringBuilder builder, IEnumerable<string> arguments)
    {
        foreach (var arg in arguments)
        {
            AppendArgument(builder, arg);
        }
    }

    private 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;
    }

    private const char Quote = '\"';
    private const char Backslash = '\\';
}
