4 files changed, 55 insertions, 43 deletions
diff --git a/vk/tracking/db/backend/csv.py b/vk/tracking/db/backend/csv.py
index f20c617..e607774 100644
--- a/vk/tracking/db/backend/csv.py
+++ b/vk/tracking/db/backend/csv.py
@@ -14,12 +14,6 @@ class Writer:
         self._fd = fd
         self._writer = csv.writer(fd, lineterminator='\n')
 
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *args):
-        pass
-
     def on_initial_status(self, user):
         self._write_record(user)
         self._fd.flush()
@@ -47,12 +41,6 @@ class Reader(Iterable):
     def __init__(self, fd):
         self._reader = csv.reader(fd)
 
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *args):
-        pass
-
     def __iter__(self):
         return map(Reader._record_from_row, self._reader)
 
diff --git a/vk/tracking/db/backend/log.py b/vk/tracking/db/backend/log.py
index 6eebc35..f248d65 100644
--- a/vk/tracking/db/backend/log.py
+++ b/vk/tracking/db/backend/log.py
@@ -15,12 +15,6 @@ class Writer:
             datefmt='%Y-%m-%d %H:%M:%S'))
         self._logger.addHandler(handler)
 
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *args):
-        pass
-
     def info(self, msg):
         self._logger.info(msg)
 
diff --git a/vk/tracking/db/backend/null.py b/vk/tracking/db/backend/null.py
index 6454f84..3cdb41e 100644
--- a/vk/tracking/db/backend/null.py
+++ b/vk/tracking/db/backend/null.py
@@ -6,13 +6,7 @@
 from collections.abc import Iterable
 
 class Writer:
-    def __init__(self, fd):
-        pass
-
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *args):
+    def __init__(self):
         pass
 
     def on_initial_status(self, user):
@@ -25,13 +19,7 @@ class Writer:
         pass
 
 class Reader(Iterable):
-    def __init__(self, fd):
-        pass
-
-    def __enter__(self):
-        return self
-
-    def __exit__(self, *args):
+    def __init__(self):
         pass
 
     def __iter__(self):
diff --git a/vk/tracking/db/format.py b/vk/tracking/db/format.py
index 9d5c6e4..e1b34a1 100644
--- a/vk/tracking/db/format.py
+++ b/vk/tracking/db/format.py
@@ -3,7 +3,9 @@
 # For details, see https://github.com/egor-tensin/vk-scripts.
 # Distributed under the MIT License.
 
+from contextlib import contextmanager
 from enum import Enum
+import sys
 
 from . import backend
 
@@ -12,25 +14,65 @@ class Format(Enum):
     LOG = 'log'
     NULL = 'null'
 
-    def create_writer(self, fd):
-        if self is Format.CSV:
-            return backend.csv.Writer(fd)
-        elif self is Format.LOG:
-            return backend.log.Writer(fd)
+    @contextmanager
+    def create_writer(self, path=None):
+        with self._open_output_file(path) as fd:
+            if self is Format.CSV:
+                yield backend.csv.Writer(fd)
+            elif self is Format.LOG:
+                yield backend.log.Writer(fd)
+            elif self is Format.NULL:
+                yield backend.null.Writer()
+            else:
+                raise NotImplementedError('unsupported database format: ' + str(self))
+
+    @contextmanager
+    def _open_output_file(self, path=None):
+        fd = sys.stdout
+        if path is None:
+            pass
+        elif self is Format.CSV or self is Format.LOG:
+            fd = open(path, 'w', encoding='utf-8')
         elif self is Format.NULL:
-            return backend.null.Writer(fd)
+            pass
         else:
             raise NotImplementedError('unsupported database format: ' + str(self))
+        try:
+            yield fd
+        finally:
+            if fd is not sys.stdout:
+                fd.close()
+
+    @contextmanager
+    def create_reader(self, path=None):
+        with self._open_input_file(path) as fd:
+            if self is Format.CSV:
+                yield backend.csv.Reader(fd)
+            elif self is Format.LOG:
+                raise NotImplementedError('cannot read from a log file')
+            elif self is Format.NULL:
+                yield backend.null.Reader()
+            else:
+                raise NotImplementedError('unsupported database format: ' + str(self))
 
-    def create_reader(self, fd):
-        if self is Format.CSV:
-            return backend.csv.Reader(fd)
+    @contextmanager
+    def _open_input_file(self, path=None):
+        fd = sys.stdin
+        if path is None:
+            pass
+        elif self is Format.CSV:
+            fd = open(path, encoding='utf-8')
         elif self is Format.LOG:
-            raise NotImplementedError()
+            raise NotImplementedError('cannot read from a log file')
         elif self is Format.NULL:
-            return backend.null.Reader(fd)
+            pass
         else:
             raise NotImplementedError('unsupported database format: ' + str(self))
+        try:
+            yield fd
+        finally:
+            if fd is not sys.stdin:
+                fd.close()
 
     def __str__(self):
         return self.value