Add "jackson" script

jackson

@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+from subprocess import call, check_output
+import argparse
+import os
+import sys
+
+ADD_PACKAGE_PREFIX = " + "
+
+def log (message, *args):
+    print(message.format(*args), file=sys.stderr)
+
+def get_all_package_generations ():
+    package_generations = {}
+    for line in check_output(["guix", "package", "--list-generations"]).decode().split("\n"):
+        if not line.startswith(ADD_PACKAGE_PREFIX):
+            continue
+            
+        (package, version, output, path) = line[len(ADD_PACKAGE_PREFIX):].split("\t")
+        if not package in package_generations:
+            package_generations[package] = []
+        
+        package_generations[package].append({
+            "path": path,
+            "version": version,
+            "output": output,
+            "package": package
+        })
+        
+    return package_generations
+
+def run_with_packages (packages, command):
+    env = {}
+    env.update(os.environ)
+    env.update({
+        "PATH": ":".join(["{}/bin".format(package['path']) for package in packages] + [env.get("PATH", "")]),
+        "LD_LIBRARY_PATH": ":".join(["{}/lib".format(package['path']) for package in packages] + [env.get("PATH", "")])
+    })
+    call(args.run, env=env)    
+    
+parser = argparse.ArgumentParser()
+parser.add_argument("--package", help="package name", required=True)
+parser.add_argument("--version", help="package version")
+parser.add_argument("--index", help="", type=int, default=0)
+parser.add_argument("--run", nargs="*", help="run command")
+args = parser.parse_args()
+
+all_package_generations = get_all_package_generations()
+package_generations_for_package = all_package_generations[args.package]
+package_generations_for_package.reverse()
+
+log("Found {} generations for package {}", len(package_generations_for_package), args.package)
+
+if args.version:
+    package_generations_for_package = [generation for generation in package_generations_for_package if generation['version'] == args.version]
+    log("Found {} generations for version {}", len(package_generations_for_package), args.version)
+
+selected_package = package_generations_for_package[args.index]
+
+log("Selected package: {}", selected_package)
+
+if args.run:
+    run_with_packages([selected_package], args.run)
+else:
+    print(selected_package)