get_imports: Make it fetch the latest bundle data when run

.. and also optionally get the learn guide repo's location from the
environment

The bundle-data-fetching code is adapted from Circup.

Author: jepler

python_generator/get_imports.py

@@ -1,11 +1,102 @@
-import findimports
+import requests
 import json
 import os
+import findimports
 
-LEARN_GUIDE_REPO = "../../Adafruit_Learning_System_Guides/"
+BUNDLE_DATA = "latest_bundle_data.json"
+BUNDLE_TAG = "latest_bundle_tag.json"
+
+LEARN_GUIDE_REPO = os.environ.get('LEARN_GUIDE_REPO', "../../Adafruit_Learning_System_Guides/")
 
 SHOWN_FILETYPES = ["py", "mpy", "bmp", "pcf", "bdf", "wav", "mp3", "json", "txt"]
 
+def get_bundle(tag):
+    url = f"https://adafruit-circuit-python.s3.amazonaws.com/bundles/adafruit/adafruit-circuitpython-bundle-{tag}.json"
+    print("get bundle metadata from {url}")
+    r = requests.get(url)
+    with open(BUNDLE_DATA, "wb") as f:
+        f.write(r.content)
+
+LATEST_BUNDLE_VERSION = ""
+def get_latest_tag():
+    """
+    Find the value of the latest tag for the Adafruit CircuitPython library
+    bundle.
+    :return: The most recent tag value for the project.
+    """
+    global LATEST_BUNDLE_VERSION
+    if not LATEST_BUNDLE_VERSION:
+        LATEST_BUNDLE_VERSION = get_latest_release_from_url(
+            "https://github.com/adafruit/Adafruit_CircuitPython_Bundle/releases/latest"
+        )
+    return LATEST_BUNDLE_VERSION
+
+def get_latest_release_from_url(url):
+    """
+    Find the tag name of the latest release by using HTTP HEAD and decoding the redirect.
+
+    :return: The most recent tag value for the release.
+    """
+
+    print(f"Requesting redirect information: {url}")
+    response = requests.head(url)
+    responseurl = response.url
+    if response.is_redirect:
+        responseurl = response.headers["Location"]
+    tag = responseurl.rsplit("/", 1)[-1]
+    print(f"Tag: {tag!r}")
+    return tag
+
+
+def get_latest_tag():
+    """
+    Find the value of the latest tag for the Adafruit CircuitPython library
+    bundle.
+    :return: The most recent tag value for the project.
+    """
+    global LATEST_BUNDLE_VERSION
+    if LATEST_BUNDLE_VERSION == "":
+        LATEST_BUNDLE_VERSION = get_latest_release_from_url(
+            "https://github.com/adafruit/Adafruit_CircuitPython_Bundle/releases/latest"
+        )
+    return LATEST_BUNDLE_VERSION
+
+def ensure_latest_bundle():
+    """
+    Ensure that there's a copy of the latest library bundle available so circup
+    can check the metadata contained therein.
+    """
+    print("Checking for library updates.")
+    tag = get_latest_tag()
+    old_tag = "0"
+    if os.path.isfile(BUNDLE_TAG):
+        with open(BUNDLE_TAG, encoding="utf-8") as data:
+            try:
+                old_tag = json.load(data)["tag"]
+            except json.decoder.JSONDecodeError as ex:
+                # Sometimes (why?) the JSON file becomes corrupt. In which case
+                # log it and carry on as if setting up for first time.
+                print(f"Could not parse {BUNDLE_TAG:r}")
+    if tag > old_tag:
+        print(f"New version available {tag}.")
+        try:
+            get_bundle(tag)
+            with open(BUNDLE_TAG, "w", encoding="utf-8") as data:
+                json.dump({"tag": tag}, data)
+        except requests.exceptions.HTTPError as ex:
+            # See #20 for reason this this
+            print(
+                (
+                    "There was a problem downloading the bundle. "
+                    "Please try again in a moment."
+                ),
+            )
+            raise
+    else:
+        print(f"Current library bundle up to date {tag}")
+
+ensure_latest_bundle()
+
 with open("latest_bundle_data.json", "r") as f:
     bundle_data = json.load(f)