font-patcher: Fix: Use WIN metrics in all conflicting cases

[why]
With commit
  6210087  font-patcher: Use WIN metrics in all conflicting cases
we intended to use the WIN metrics for the baseline to baseline
calculations for fonts that have contradicting (i.e. broken) metrices.

But we use the TYPO metrics instead.

[how]
This is obviously a typo in the code. To prevent such errors and improve
the readability we use Enums now. I believe we silently dropped support
for Python 2 some time back. And if not we drop it today :-}

[note]
Many thanks to Nathaniel Evan for again finding this bug!

Mentioned in: #1116

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

font-patcher

@@ -6,7 +6,7 @@
 from __future__ import absolute_import, print_function, unicode_literals
 
 # Change the script version when you edit this script:
-script_version = "3.5.6"
+script_version = "3.5.7"
 
 version = "2.3.3"
 projectName = "Nerd Fonts"
@@ -21,6 +21,7 @@ from argparse import RawTextHelpFormatter
 import errno
 import subprocess
 import json
+from enum import Enum
 try:
     import configparser
 except ImportError:
@@ -996,30 +997,34 @@ class font_patcher:
         (hhea_btb, typo_btb, win_btb, win_gap) = get_btb_metrics(self.sourceFont)
         use_typo = self.sourceFont.os2_use_typo_metrics != 0
 
+        Metric = Enum('Metric', ['HHEA', 'TYPO', 'WIN'])
+
         # We use either TYPO (1) or WIN (2) and compare with HHEA
         # and use HHEA (0) if the fonts seems broken - no WIN, see #1056
         our_btb = typo_btb if use_typo else win_btb
         if our_btb == hhea_btb:
-            metrics = 1 if use_typo else 2 # conforming font
+            metrics = Metric.TYPO if use_typo else Metric.WIN # conforming font
         else:
             # We trust the WIN metric more, see experiments in #1056
             print("{}: WARNING Font vertical metrics inconsistent (HHEA {} / TYPO {} / WIN {}), using WIN".format(projectName, hhea_btb, typo_btb, win_btb))
             our_btb = win_btb
-            metrics = 1
+            metrics = Metric.WIN
 
         # print("FINI hhea {} typo {} win {} use {}     {}      {}".format(hhea_btb, typo_btb, win_btb, use_typo, our_btb != hhea_btb, self.sourceFont.fontname))
 
         self.font_dim = {'xmin': 0, 'ymin': 0, 'xmax': 0, 'ymax': 0, 'width' : 0, 'height': 0}
 
-        if metrics == 0:
+        if metrics == Metric.HHEA:
             self.font_dim['ymin'] = self.sourceFont.hhea_descent - half_gap(self.sourceFont.hhea_linegap, False)
             self.font_dim['ymax'] = self.sourceFont.hhea_ascent + half_gap(self.sourceFont.hhea_linegap, True)
-        elif metrics == 1:
+        elif metrics == Metric.TYPO:
             self.font_dim['ymin'] = self.sourceFont.os2_typodescent - half_gap(self.sourceFont.os2_typolinegap, False)
             self.font_dim['ymax'] = self.sourceFont.os2_typoascent + half_gap(self.sourceFont.os2_typolinegap, True)
-        else:
+        elif metrics == Metric.WIN:
             self.font_dim['ymin'] = -self.sourceFont.os2_windescent - half_gap(win_gap, False)
             self.font_dim['ymax'] = self.sourceFont.os2_winascent + half_gap(win_gap, True)
+        else:
+            pass # Will fail the metrics check some line later
 
         # Calculate font height
         self.font_dim['height'] = -self.font_dim['ymin'] + self.font_dim['ymax']