From 20320f539f7ddd2d68c1a6bbe71aed6c231377b8 Mon Sep 17 00:00:00 2001
From: Virgil Dupras <hsoft@hardcoded.net>
Date: Fri, 10 Aug 2012 15:58:37 -0400
Subject: [PATCH] [#199 state:fixed] Added a mtime column to PE's cache DB so
 that we can purge outdated caches.

---
 core_pe/cache.py            | 54 +++++++++++++++++++++++++++----------
 core_pe/matchblock.py       |  1 +
 core_pe/tests/cache_test.py |  2 +-
 3 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/core_pe/cache.py b/core_pe/cache.py
index 0bbe4b15..01421f01 100644
--- a/core_pe/cache.py
+++ b/core_pe/cache.py
@@ -7,6 +7,7 @@
 # http://www.hardcoded.net/licenses/bsd_license
 
 import os
+import os.path as op
 import logging
 import sqlite3 as sqlite
 
@@ -30,7 +31,7 @@ def colors_to_string(colors):
 #         result.append((number >> 16, (number >> 8) & 0xff, number & 0xff))
 #     return result
 
-class Cache(object):
+class Cache:
     """A class to cache picture blocks.
     """
     def __init__(self, db=':memory:'):
@@ -72,29 +73,34 @@ class Cache(object):
         result = self.con.execute(sql).fetchall()
         return result[0][0]
     
-    def __setitem__(self, key, value):
-        value = colors_to_string(value)
-        if key in self:
-            sql = "update pictures set blocks = ? where path = ?"
+    def __setitem__(self, path_str, blocks):
+        blocks = colors_to_string(blocks)
+        if op.exists(path_str):
+            mtime = int(os.stat(path_str).st_mtime)
         else:
-            sql = "insert into pictures(blocks,path) values(?,?)"
+            mtime = 0
+        if path_str in self:
+            sql = "update pictures set blocks = ?, mtime = ? where path = ?"
+        else:
+            sql = "insert into pictures(blocks,mtime,path) values(?,?,?)"
         try:
-            self.con.execute(sql, [value, key])
+            self.con.execute(sql, [blocks, mtime, path_str])
         except sqlite.OperationalError:
-            logging.warning('Picture cache could not set value for key %r', key)
+            logging.warning('Picture cache could not set value for key %r', path_str)
         except sqlite.DatabaseError as e:
-            logging.warning('DatabaseError while setting value for key %r: %s', key, str(e))
+            logging.warning('DatabaseError while setting value for key %r: %s', path_str, str(e))
     
     def _create_con(self, second_try=False):
         def create_tables():
-            sql = "create table pictures(path TEXT, blocks TEXT)"
-            self.con.execute(sql);
-            sql = "create index idx_path on pictures (path)"
-            self.con.execute(sql)
+            logging.debug("Creating picture cache tables.")
+            self.con.execute("drop table if exists pictures");
+            self.con.execute("drop index if exists idx_path");
+            self.con.execute("create table pictures(path TEXT, mtime INTEGER, blocks TEXT)");
+            self.con.execute("create index idx_path on pictures (path)")
         
         self.con = sqlite.connect(self.dbname, isolation_level=None)
         try:
-            self.con.execute("select * from pictures where 1=2")
+            self.con.execute("select path, mtime, blocks from pictures where 1=2")
         except sqlite.OperationalError: # new db
             create_tables()
         except sqlite.DatabaseError as e: # corrupted db
@@ -134,3 +140,23 @@ class Cache(object):
         cur = self.con.execute(sql)
         return ((rowid, string_to_colors(blocks)) for rowid, blocks in cur)
     
+    def purge_outdated(self):
+        """Go through the cache and purge outdated records.
+        
+        A record is outdated if the picture doesn't exist or if its mtime is greater than the one in
+        the db.
+        """
+        todelete = []
+        sql = "select rowid, path, mtime from pictures"
+        cur = self.con.execute(sql)
+        for rowid, path_str, mtime in cur:
+            if mtime and op.exists(path_str):
+                picture_mtime = os.stat(path_str).st_mtime
+                if int(picture_mtime) <= mtime:
+                    # not outdated
+                    continue
+            todelete.append(rowid)
+        if todelete:
+            sql = "delete from pictures where rowid in (%s)" % ','.join(map(str, todelete))
+            self.con.execute(sql)
+    
diff --git a/core_pe/matchblock.py b/core_pe/matchblock.py
index 583efba4..4ab88762 100644
--- a/core_pe/matchblock.py
+++ b/core_pe/matchblock.py
@@ -55,6 +55,7 @@ def prepare_pictures(pictures, cache_path, with_dimensions, j=job.nulljob):
     # MemoryError happens when trying to read an image file, which is freed from memory by the
     # time that MemoryError is raised.
     cache = Cache(cache_path)
+    cache.purge_outdated()
     prepared = [] # only pictures for which there was no error getting blocks
     try:
         for picture in j.iter_with_progress(pictures, tr("Analyzed %d/%d pictures")):
diff --git a/core_pe/tests/cache_test.py b/core_pe/tests/cache_test.py
index 49b51712..3b45fd95 100644
--- a/core_pe/tests/cache_test.py
+++ b/core_pe/tests/cache_test.py
@@ -141,5 +141,5 @@ class TestCaseCacheSQLEscape:
         try:
             del c["foo'bar"]
         except KeyError:
-            self.fail()
+            assert False