using System;
using System.ComponentModel;
using System.Runtime.InteropServices;

namespace MeloongCore {

    /// <summary>
    /// 使用 Windows MsDelta API 生成、应用增量补丁文件。
    /// </summary>
    public static class MsDelta {

        /// <summary>
        /// 生成增量补丁文件：比较 <paramref name="oldFilePath"/> 和 <paramref name="newFilePath"/>，将补丁写入 <paramref name="deltaFilePath"/>。
        /// </summary>
        public static void Create(string oldFilePath, string newFilePath, string deltaFilePath) {
            // fileTypeSet：https://learn.microsoft.com/en-us/previous-versions/bb417345(v=msdn.10)?redirectedfrom=MSDN#file-type-sets (15L: DELTA_FILE_TYPE_SET_EXECUTABLES)
            // 131072L: IgnoreFileSizeLimit, 32u: Crc32
            if (!CreateDelta(15L, 131072L, 0L, 
                PathUtils.Shorten(oldFilePath), PathUtils.Shorten(newFilePath), null, null, new DeltaInput(), IntPtr.Zero, 32u, PathUtils.Shorten(deltaFilePath)))
                throw new Win32Exception();
        }

        /// <summary>
        /// 应用增量补丁文件：将 <paramref name="deltaFilePath"/> 补丁应用到 <paramref name="oldFilePath"/>，将结果写入 <paramref name="newFilePath"/>。
        /// </summary>
        public static void Apply(string oldFilePath, string deltaFilePath, string newFilePath) {
            // 1L: AllowLegacy
            if (!ApplyDelta(1L, PathUtils.Shorten(oldFilePath), PathUtils.Shorten(deltaFilePath), PathUtils.Shorten(newFilePath)))
                throw new Win32Exception();
        }


        [StructLayout(LayoutKind.Sequential)]
        private struct DeltaInput {
            public IntPtr Start;
            public IntPtr Size;
            [MarshalAs(UnmanagedType.Bool)] public bool Editable;
        }
        [DllImport("msdelta.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool CreateDelta(
            long fileTypeSet, long setFlags, long resetFlags,
            string sourceName, string targetName, string sourceOptionsName,
            string targetOptionsName, DeltaInput globalOptions,
            IntPtr targetFileTime, uint hashAlgId, string deltaName);
        [DllImport("msdelta.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool ApplyDelta(long applyFlags, string sourceName, string deltaName, string targetName);

    }

}