feat: Add WaniKani lessons fetcher to retrieve unlocked lesson datetimes

personal_data/fetchers/wanikani_lessons.py

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+import datetime
+import logging
+import requests
+import dataclasses
+from typing import Iterator, Mapping
+# Import the base Scraper class; adjust the import if your code structure differs.
+from personal_data.data import Scraper
+
+logger = logging.getLogger(__name__)
+
+@dataclasses.dataclass(frozen=True)
+class WaniKaniLessonsFetcher(Scraper):
+    api_token: str
+
+    @staticmethod
+    def dataset_name() -> str:
+        return "wanikani_lessons"
+
+    def scrape(self) -> Iterator[Mapping[str, object]]:
+        """
+        Fetch assignments from the WaniKani API and yield a dict for each assignment
+        with a non-null unlocked_at timestamp.
+        """
+        url = "https://api.wanikani.com/v2/assignments"
+        headers = {
+            "Authorization": f"Bearer {self.api_token}",
+            "Wanikani-Revision": "20170710"
+        }
+        response = requests.get(url, headers=headers)
+        if response.status_code != 200:
+            logger.error("Error retrieving assignments: %s", response.text)
+            return
+        data = response.json()
+        # Check that 'data' key exists in the JSON response.
+        assignments = data.get("data", [])
+        for assignment in assignments:
+            assignment_data = assignment.get("data", {})
+            # Only yield if unlocked_at is available.
+            unlocked_at = assignment_data.get("unlocked_at")
+            if unlocked_at:
+                # Convert unlocked_at ISO8601 string (assume 'Z' for UTC) to a datetime object.
+                try:
+                    dt = datetime.datetime.fromisoformat(unlocked_at.replace("Z", "+00:00"))
+                except Exception as e:
+                    logger.error("Error parsing unlocked_at '%s': %s", unlocked_at, e)
+                    continue
+                yield {
+                    "subject_id": assignment_data.get("subject_id"),
+                    "unlocked_at": dt
+                }