[Android] Refactor md5_check + add tests

build/android/gyp/util/md5_check.py

Index: build/android/gyp/util/md5_check.py
diff --git a/build/android/gyp/util/md5_check.py b/build/android/gyp/util/md5_check.py
index 47f1ec941544d97c8ec5500013537a0a3ac05691..acf707c283c30f1289a5ea0cf5b71fa15d0562c1 100644
--- a/build/android/gyp/util/md5_check.py
+++ b/build/android/gyp/util/md5_check.py
@@ -6,7 +6,24 @@ import hashlib
 import os
 
 
-def UpdateMd5ForFile(md5, path, block_size=2**16):
+def CallAndRecordIfStale(
+    function, record_path=None, input_paths=[], input_strings=[]):
+  """Calls function if the md5sum of the input paths/strings has changed.
+
+  The md5sum of the inputs is compared with the one stored in record_path. If
+  this has changed (or the record doesn't exist), function will be called and
+  the new md5sum will be recorded.
+  """
+  md5_checker = _Md5Checker(
+      record_path=record_path,
+      input_paths=input_paths,
+      input_strings=input_strings)
+  if md5_checker.IsStale():
+    function()
+    md5_checker.Write()
+
+
+def _UpdateMd5ForFile(md5, path, block_size=2**16):
   with open(path, 'rb') as infile:
     while True:
       data = infile.read(block_size)
@@ -15,38 +32,42 @@ def UpdateMd5ForFile(md5, path, block_size=2**16):
       md5.update(data)
 
 
-def UpdateMd5ForDirectory(md5, dir_path):
+def _UpdateMd5ForDirectory(md5, dir_path):
   for root, _, files in os.walk(dir_path):
     for f in files:
-      UpdateMd5ForFile(md5, os.path.join(root, f))
+      _UpdateMd5ForFile(md5, os.path.join(root, f))
 
 
-def UpdateMd5ForPath(md5, path):
+def _UpdateMd5ForPath(md5, path):
   if os.path.isdir(path):
-    UpdateMd5ForDirectory(md5, path)
+    _UpdateMd5ForDirectory(md5, path)
   else:
-    UpdateMd5ForFile(md5, path)
+    _UpdateMd5ForFile(md5, path)
+
 
+class _Md5Checker(object):
+  def __init__(self, record_path=None, input_paths=[], input_strings=[]):
+    assert record_path.endswith('.stamp'), (
+        'record paths must end in \'.stamp\' so that they are easy to find '
+        'and delete')
 
-class Md5Checker(object):
-  def __init__(self, stamp=None, inputs=[], command=[]):
-    self.stamp = stamp
+    self.record_path = record_path
 
     md5 = hashlib.md5()
-    for i in inputs:
-      UpdateMd5ForPath(md5, i)
-    for s in command:
+    for i in sorted(input_paths):
+      _UpdateMd5ForPath(md5, i)
+    for s in input_strings:
       md5.update(s)
     self.new_digest = md5.hexdigest()
 
     self.old_digest = ''
-    if os.path.exists(stamp):
-      with open(stamp, 'r') as old_stamp:
-        self.old_digest = old_stamp.read()
+    if os.path.exists(self.record_path):
+      with open(self.record_path, 'r') as old_record:
+        self.old_digest = old_record.read()
 
   def IsStale(self):
     return self.old_digest != self.new_digest
 
   def Write(self):
-    with open(self.stamp, 'w') as new_stamp:
-      new_stamp.write(self.new_digest)
+    with open(self.record_path, 'w') as new_record:
+      new_record.write(self.new_digest)