PoC for script update event

composer.json

{
    "prefer-stable": true,
    "autoload": {
        "psr-4": {
            "DrupalComposer\\DrupalProject\\": "."
        }
    },
    "scripts": {
        "post-package-install": [
          "DrupalComposer\\DrupalProject\\Scripts::hook"
        ],
        "post-package-update": [
          "DrupalComposer\\DrupalProject\\Scripts::hook"
        ]
    },
    "require": {
        "monolog/monolog": "1.17.0",
        "composer/composer": "dev-master"
    }
}

Scripts.php

<?php

namespace DrupalComposer\DrupalProject;

use Composer\DependencyResolver\Operation\InstallOperation;
use Composer\DependencyResolver\Operation\UninstallOperation;
use Composer\DependencyResolver\Operation\UpdateOperation;
use Composer\Package\PackageInterface;

class Scripts {
  public static function hook(\Composer\Installer\PackageEvent $event){
    $operation = $event->getOperation();
    if ($operation instanceof InstallOperation) {
      $package = $operation->getPackage();
    }
    elseif ($operation instanceof UpdateOperation) {
      $package = $operation->getTargetPackage();
    }
    elseif ($operation instanceof UninstallOperation) {
      $package = $operation->getPackage();
    }
    if ($package && $package instanceof PackageInterface) {
      /** @var \Composer\Installer\InstallationManager $installationManager */
      $installationManager = $event->getComposer()->getInstallationManager();
      $path = $installationManager->getInstallPath($package);
      $event->getIO()->write(sprintf('Event called: %s, Package: %s (%s), Path: %s',
        $event->getName(),
        $package->getName(),
        $package->getVersion(),
        $path
      ), TRUE);
    }
  }
}