[FEAT] Mod installer (aka Blue Shift support part 1)

[Alienmario]

In order to support overhaul mods that come with their own game folder + gameinfo.txt (such as Blue Shift) we should devise an automated mod install + launch process for servers.

Mod registry

There should be a central registry file that we can ship, which for each of supported mods includes:

• workshop id
• short name
• sequence of commands needed for installation. These can be generic - create link, copy .. or os specific commands
• first map

Plugin commands

All commands take workshop id or short name for mod resolution.

Install mod

• Adds the specified mod to subscribed_file_ids.txt if missing.
• Prints a message telling the user to restart, so mods can start to download.
• Prints error message for unsupported mods.
• sc_install bshift

Launch mod

This is where it gets tricky since overhaul mods require launching with custom -game parameter, which we have no direct way to affect.

As a workaround we can use a static game name scmodlauncher as a dynamically updating symlink pointing to the active mod directory. We then instruct users to launch with -game scmodlauncher.

We'll most likely need to do the same with the +map parameter, since server won't fully start with launch map missing.
We can ship an empty placeholder map.

The final file structure would look like this:

• Black Mesa Dedicated Server
  • bms
  • bshift [symlink to workshop content (./bms/addons/workshop/content/362890/2424633574/bshift)]
  • scmodlauncher [symlink to active mod (bms, bshift, ..)]

sc_launch would do the following (approximately):

• checks that the mod has downloaded
• runs post-download install commands, creating mod symlink in server root
• creates symlinks for addons, maps, server.cfg and other req files inside the mod folder
• updates scmodlauncher symlink
• configures Sourcemod
  • replacing all "bms" references in gamedata
• kicks clients with instructions
• quits server

After the restart, we can detect our placeholder map and change to the first map of the mod.

Implementation

• Can be a part of srccoop_addon_workshop_manager.sp
• We can use System2 for running commands or archiving functionality.