1 files changed, 84 insertions, 0 deletions
diff --git a/modules/hashes.py b/modules/hashes.py
new file mode 100644
index 00000000..14231771
--- /dev/null
+++ b/modules/hashes.py
@@ -0,0 +1,84 @@
+import hashlib
+import json
+import os.path
+
+import filelock
+
+
+cache_filename = "cache.json"
+cache_data = None
+
+
+def dump_cache():
+    with filelock.FileLock(cache_filename+".lock"):
+        with open(cache_filename, "w", encoding="utf8") as file:
+            json.dump(cache_data, file, indent=4)
+
+
+def cache(subsection):
+    global cache_data
+
+    if cache_data is None:
+        with filelock.FileLock(cache_filename+".lock"):
+            if not os.path.isfile(cache_filename):
+                cache_data = {}
+            else:
+                with open(cache_filename, "r", encoding="utf8") as file:
+                    cache_data = json.load(file)
+
+    s = cache_data.get(subsection, {})
+    cache_data[subsection] = s
+
+    return s
+
+
+def calculate_sha256(filename):
+    hash_sha256 = hashlib.sha256()
+
+    with open(filename, "rb") as f:
+        for chunk in iter(lambda: f.read(4096), b""):
+            hash_sha256.update(chunk)
+
+    return hash_sha256.hexdigest()
+
+
+def sha256_from_cache(filename, title):
+    hashes = cache("hashes")
+    ondisk_mtime = os.path.getmtime(filename)
+
+    if title not in hashes:
+        return None
+
+    cached_sha256 = hashes[title].get("sha256", None)
+    cached_mtime = hashes[title].get("mtime", 0)
+
+    if ondisk_mtime > cached_mtime or cached_sha256 is None:
+        return None
+
+    return cached_sha256
+
+
+def sha256(filename, title):
+    hashes = cache("hashes")
+
+    sha256_value = sha256_from_cache(filename, title)
+    if sha256_value is not None:
+        return sha256_value
+
+    print(f"Calculating sha256 for {filename}: ", end='')
+    sha256_value = calculate_sha256(filename)
+    print(f"{sha256_value}")
+
+    hashes[title] = {
+        "mtime": os.path.getmtime(filename),
+        "sha256": sha256_value,
+    }
+
+    dump_cache()
+
+    return sha256_value
+
+
+
+
+