check if sig already computed in S3

wort/blueprints/compute/views.py

@@ -1,5 +1,6 @@
 import csv
 import os
+from pathlib import Path
 
 from flask import Blueprint, current_app, jsonify, render_template, url_for
 import requests
@@ -29,10 +30,45 @@ def compute_sra(sra_id, recompute=False):
         db.session.add(dataset)
         db.session.commit()
 
-    if not recompute and dataset.computed is not None:
+    up_to_date = False
+    if not recompute:
+        if dataset.computed is not None:
+            up_to_date = True
+
+        if dataset.computed is None:
+            # check on S3 to see if it was computed and not updated in DB
+            import boto3
+            import botocore
+            conn = boto3.client("s3")
+            s3 = boto3.resource("s3")
+
+            key_path = Path("sigs") / f"{sra_id}.sig"
+            try:
+                obj = s3.Object("wort-sra", key_path)
+                obj.load()
+            except botocore.exceptions.ClientError as e:
+                if e.response["Error"]["Code"] == "404":
+                    pass  # Object does not exist yet
+                else:
+                    # Something else has gone wrong
+                    raise
+            else:
+                # The key already exists, update compute field in DB
+                dataset.computed = obj.last_modified
+                db.session.add(dataset)
+                db.session.commit()
+                # Remove from cache, will be refreshed from DB next time
+                # there is a view request for it
+                current_app.cache.delete(f"sra/{sra_id}")
+
+                up_to_date = True
+
+    if up_to_date:
         return jsonify({"status": "Signature already calculated"}), 202
 
     if recompute:
+        # Force recomputation of sketch,
+        # clean status from DB and remove from cache
         dataset.computed = None
         db.session.add(dataset)
         db.session.commit()