fix off-by-one issues in pyosmium-get-changes

When a start date is given, then start at the change that contains
the date, not the one after.

When writing out end sequences without downloading data, use the
sequence ID **before** the computed start ID, i.e. the of the previous
run. Note that this might result in negative state IDs.

Author: lonvia

test/test_pyosmium_get_changes.py

@@ -67,7 +67,7 @@ def test_init_id(self, capsys):
 
         output = capsys.readouterr().out.strip()
 
-        assert output == '454'
+        assert output == '453'
 
 
     def test_init_date(self, capsys, mock_requests):
@@ -85,22 +85,22 @@ def test_init_date(self, capsys, mock_requests):
 
         output = capsys.readouterr().out.strip()
 
-        assert output == '1'
+        assert output == '-1'
 
 
     def test_init_to_file(self, tmp_path):
         fname = tmp_path / 'db.seq'
 
         assert 0 == self.main('-I', '453', '-f', str(fname))
-        assert fname.read_text() == '454'
+        assert fname.read_text() == '453'
 
 
     def test_init_from_seq_file(self, tmp_path):
         fname = tmp_path / 'db.seq'
         fname.write_text('453')
 
         assert 0 == self.main('-f', str(fname))
-        assert fname.read_text() == '454'
+        assert fname.read_text() == '453'
 
 
     def test_init_date_with_cookie(self, capsys, tmp_path, mock_urllib):
@@ -123,4 +123,4 @@ def test_init_date_with_cookie(self, capsys, tmp_path, mock_urllib):
 
         output = capsys.readouterr().out.strip()
 
-        assert output == '1'
+        assert output == '-1'

tools/pyosmium-get-changes

@@ -62,18 +62,16 @@ class ReplicationStart(object):
             return self.seq_id + 1
 
         log.debug("Looking up sequence ID for timestamp %s" % self.date)
-        seq = svr.timestamp_to_sequence(self.date)
-
-        return seq + 1 if seq is not None else None
+        return svr.timestamp_to_sequence(self.date)
 
     @staticmethod
     def from_id(idstr):
         try:
-            seq_id=int(idstr)
+            seq_id = int(idstr)
         except ValueError:
             raise ArgumentTypeError("Sequence id '%s' is not a number" % idstr)
 
-        if seq_id < 0:
+        if seq_id < -1:
             raise ArgumentTypeError("Sequence id '%s' is negative" % idstr)
 
         return ReplicationStart(seq_id=seq_id)
@@ -229,7 +227,7 @@ def main(args):
             return 1
 
         if options.outfile is None:
-            write_end_sequence(options.seq_file, startseq)
+            write_end_sequence(options.seq_file, startseq - 1)
             return 0
 
         log.debug("Starting download at ID %d (max %d MB)" % (startseq, options.outsize))