SabreTools/SabreTools.Skippers/SkipperMatch.cs

using System.Collections.Generic;
using System.IO;

namespace SabreTools.Skippers
{
    /// <summary>
    /// Class for matching existing Skippers
    /// <summary>
    /// <remarks>
    /// Skippers, in general, are distributed as XML files by some projects
    /// in order to denote a way of transforming a file so that it will match
    /// the hashes included in their DATs. Each skipper file can contain multiple
    /// skipper rules, each of which denote a type of header/transformation. In
    /// turn, each of those rules can contain multiple tests that denote that
    /// a file should be processed using that rule. Transformations can include
    /// simply skipping over a portion of the file all the way to byteswapping
    /// the entire file. For the purposes of this library, Skippers also denote
    /// a way of changing files directly in order to produce a file whose external
    /// hash would match those same DATs.
    /// </remarks>
    public static class SkipperMatch
    {
        /// <summary>
        /// Header detectors represented by a list of detector objects
        /// </summary>
        private static List<Detector>? Skippers = null;

        /// <summary>
        /// Initialize static fields
        /// </summary>
        public static void Init()
        {
            // If the list is populated, don't add to it
            if (Skippers != null)
                return;

            // Generate header skippers internally
            PopulateSkippers();
        }

        /// <summary>
        /// Populate the entire list of header skippers from generated objects
        /// </summary>
        /// <remarks>
        /// http://mamedev.emulab.it/clrmamepro/docs/xmlheaders.txt
        /// http://www.emulab.it/forum/index.php?topic=127.0
        /// </remarks>
        private static void PopulateSkippers()
        {
            // Ensure the list exists
            Skippers ??= [];

            // Get skippers for each known header type
            Skippers.Add(new Detectors.Atari7800());
            Skippers.Add(new Detectors.AtariLynx());
            Skippers.Add(new Detectors.CommodorePSID());
            Skippers.Add(new Detectors.NECPCEngine());
            Skippers.Add(new Detectors.Nintendo64());
            Skippers.Add(new Detectors.NintendoEntertainmentSystem());
            Skippers.Add(new Detectors.NintendoFamicomDiskSystem());
            Skippers.Add(new Detectors.SuperNintendoEntertainmentSystem());
            Skippers.Add(new Detectors.SuperFamicomSPC());
        }

        /// <summary>
        /// Get the Rule associated with a given file
        /// </summary>
        /// <param name="input">Name of the file to be checked</param>
        /// <param name="skipperName">Name of the skipper to be used, blank to find a matching skipper</param>
        /// <param name="logger">Logger object for file and console output</param>
        /// <returns>The Rule that matched the file</returns>
        public static Rule GetMatchingRule(string input, string skipperName)
        {
            // If the file doesn't exist, return a blank skipper rule
            if (!File.Exists(input))
                return new Rule(null, null, HeaderSkipOperation.None, null, null);

            return GetMatchingRule(File.OpenRead(input), skipperName);
        }

        /// <summary>
        /// Get the Rule associated with a given stream
        /// </summary>
        /// <param name="input">Name of the file to be checked</param>
        /// <param name="skipperName">Name of the skipper to be used, blank to find a matching skipper</param>
        /// <param name="keepOpen">True if the underlying stream should be kept open, false otherwise</param>
        /// <returns>The Rule that matched the file</returns>
        public static Rule GetMatchingRule(Stream? input, string skipperName, bool keepOpen = false)
        {
            var skipperRule = new Rule(null, null, HeaderSkipOperation.None, null, null);

            // If we have an invalid input
            if (input == null || !input.CanRead)
                return skipperRule;

            // If we have an invalid set of skippers or skipper name
            if (Skippers == null || skipperName == null)
                return skipperRule;

            // Loop through all known Detectors
            foreach (Detector? skipper in Skippers)
            {
                // This should not happen
                if (skipper == null)
                    continue;

                skipperRule = skipper.GetMatchingRule(input, skipperName);
                if (skipperRule != null)
                    break;
            }

            // If we're not keeping the stream open, dispose of the binary reader
            if (!keepOpen)
                input?.Dispose();

            // If the Rule is null, make it empty
            skipperRule ??= new Rule(null, null, HeaderSkipOperation.None, null, null);
            return skipperRule;
        }
    }
}