#region CPL License
/*
Nuclex.NAnt.Tasks
Copyright (C) 2009 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

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

using Microsoft.Win32;

namespace Nuclex.NAnt.Tasks.Helpers {

  /// <summary>Helper class that tries to locate the 7-Zip executable</summary>
  internal static class SevenZipLocator {

    /// <summary>Tries to locate the 7-Zip executable on the current system</summary>
    /// <remarks>
    ///   You do not need to call this normally. The 'Location' property will
    ///   automatically initiate a search the first time it is called. Only call
    ///   this method if you suspect the system might have changed and wish to
    ///   rescan for the 7-Zip executable.
    /// </remarks>
    public static void Locate() {
      if(OsHelper.IsWindows) {
        location = findUsingRegistry();
        if(location == null) {
          location = findOnWindows();
        }
      } else {
        location = findOnUnix();
      }

      locationAttempted = true;
    }

    /// <summary>The location of the 7-Zip executable or null if not found</summary>
    /// <remarks>
    ///   Will search for 7-Zip on the system the first time it is called, so it
    ///   may block for a moment before returning.
    /// </remarks>
    public static string Location {
      get {
        if(!locationAttempted) {
          Locate();
        }

        return location;
      }
    }

    /// <summary>Tries to locate 7-Zip using its registry path</summary>
    /// <returns>The path to the 7-Zip executable or null if not found</returns>
    private static string findUsingRegistry() {
      Debug.Assert(OsHelper.IsWindows);

      // This has a major issue on x64 systems because NAnt runs in x86 mode,
      // so it will look in the Wow6432Node whereas 7-Zip's registry key
      // (assuming the x64 version is being used) is in the normal SOFTWARE node.

      using(
        RegistryKey sevenZipKey = Registry.LocalMachine.OpenSubKey(
          @"SOFTWARE\7-Zip"
        )
      ) {
        if(sevenZipKey == null) {
          return null;
        }
      
        string location = (string)sevenZipKey.GetValue("Path");
        if(Directory.Exists(location)) {
          location = Path.Combine(location, "7z.exe");
          if(File.Exists(location)) {
            return location;
          }
        }
      }

      return null;
    }

    /// <summary>Tries to locate 7-Zip in its default path on a windows system</summary>
    /// <returns>The path to the 7-Zip executable or null if not found</returns>
    private static string findOnWindows() {
      Debug.Assert(OsHelper.IsWindows);

      // If we're running on a 64 bit OS, search the 64 bit program files folder, too.
      // 7-Zip provides 64 bit executables, so it might very well be in this folder.
      if(EnvironmentHelper.RunningOn64BitOS) {
        string location = searchWindowsProgramFilesFolder(KnownFolders.ProgramFiles64Path);
        if(location != null) {
          return location;
        }
      }

      return searchWindowsProgramFilesFolder(KnownFolders.ProgramFiles32Path);
    }

    /// <summary>Searches the program files folder for a 7-Zip executable</summary>
    /// <returns>The path to the 7-Zip executable or null if not found</returns>
    private static string searchWindowsProgramFilesFolder(string programFilesFolder) {
      string[] sevenZipFolders = Directory.GetDirectories(
        programFilesFolder, "7-Zip*"
      );
      for(int index = 0; index < sevenZipFolders.Length; ++index) {
        string potentialLocation = Path.Combine(sevenZipFolders[index], "7z.exe");
        if(File.Exists(potentialLocation)) {
          return potentialLocation;
        }
      }

      return null;
    }

    /// <summary>Tries to locate 7-Zip in its default path on a unix system</summary>
    /// <returns>The path to the 7-Zip executable or null if not found</returns>
    private static string findOnUnix() {
      Debug.Assert(OsHelper.IsUnix);

      string sevenZipPath = "/usr/local/bin/7za";
      if(File.Exists(sevenZipPath)) {
        return sevenZipPath;
      }

      sevenZipPath = "/usr/bin/7za";
      if(File.Exists(sevenZipPath)) {
        return sevenZipPath;
      }

      sevenZipPath = "/bin/7za";
      if(File.Exists(sevenZipPath)) {
        return sevenZipPath;
      }

      return null;
    }

    /// <summary>Whether we attempted to locate 7-Zip already</summary>
    private static volatile bool locationAttempted;
    /// <summary>The location of the 7-Zip executable or null</summary>
    private static string location;

  }

} // namespace Nuclex.NAnt.Tasks.Helpers