dead fucking simple forge installer automation shim

ForgeHax.java

// dead fucking simple forge installer automation shim.

// compile  : javac -cp forge-${version}-installer.jar ForgeHax.java
// run      : java -cp .:forge-${version}-installer.jar ForgeHax -client FloraverseCommunityPack ~/.minecraft

import java.io.File;
import java.lang.reflect.Field;

// he he :3c
import net.minecraftforge.installer.actions.Action;
import net.minecraftforge.installer.actions.ActionCanceledException;
import net.minecraftforge.installer.actions.ClientInstall;
import net.minecraftforge.installer.actions.ProgressCallback;
import net.minecraftforge.installer.actions.ServerInstall;
import net.minecraftforge.installer.json.Install;
import net.minecraftforge.installer.json.Util;

class ForgeHax {
    public static void main(String[] args) {
        boolean serverInstall = false;
        String profileName = null;
        File installPath = null;

        // absolute bare minimum naive command line option handling here lmao. of note is the fact that passing multiple -client and -server options is accepted, but only the last affects the outcome. also quietly ignore any excess arguments... it's fine because this isn't a user-facing tool
        int i = 0;
        while (i < args.length) {
            String arg = args[i++];
            if (arg.equals("-client"))
                serverInstall = false;
            else if (arg.equals("-server"))
                serverInstall = true;
            else if (profileName == null)
                profileName = arg;
            else if (installPath == null)
                installPath = new File(arg);
            else break;
        }

        if (profileName == null)
            die("Missing profile name and install path");
        if (installPath == null)
            die("Missing install path");

        // this call loads the installation instructions from the forge installer jar
        Install installProfile = Util.loadInstallProfile();

        // we want to change this to something modpack specific so we don't accidentally replace an existing forge install's profile. we don't bother with the icon or display name though because that stuff can be done by the launcher updater. this is literally the quickest, dirtiest hack there is.
        setPrivate(Install.class, installProfile, "profile", profileName);

        Action installer;
        if (serverInstall)
            installer = new ServerInstall(installProfile, ProgressCallback.TO_STD_OUT);
        else
            installer = new ClientInstall(installProfile, ProgressCallback.TO_STD_OUT);


        // it pays to check this stuff ourselves because calling run with an invalid install path results in an ugly swing(?) dialog box and an apparent success from the caller's perspective.
        if (!installer.isPathValid(installPath)) {
            String errorMessage = installer.getFileError(installPath);
            die(errorMessage);
        }

        try {
            // run the installation process
            installer.run(installPath, a -> true);
            System.err.println(installer.getSuccessMessage());
        }
        catch (ActionCanceledException err) {
            // i'm not sure this can even happen
            die("Installation was canceled");
        }
    }


    // just a convenience wrapper to print an error message and exit with a nonzero return code.
    static void die(String message) {
        System.err.println(message);
        System.exit(1);
    }


    // hoo boy this is nasty, but it works!!
    static <T> void setPrivate(Class cls, Object instance, String fieldName, T value) {
        try {
            Field field = cls.getDeclaredField(fieldName);
            field.setAccessible(true); // ← right here                  ← this way
            field.set(instance, value); // boom, fuck encapsulation
        }
        // i promise the one field i am using this for actually exists
        catch (NoSuchFieldException fuckYourCheckedExceptions) {}
        // I PROMISE I DID THE MAGIC INVOCATION TO MAKE THIS NOT HAPPEN, LOOK ↑
        catch (IllegalAccessException why) {}
    }
}