Chord Families

generator/chord_families.py

@@ -0,0 +1,49 @@
+"""Transposable guitar families, derived from the written chord and legal grips."""
+import generator.harmony
+import generator.model
+import generator.vocabulary
+
+def acoustic(chord, grip):
+  degrees = generator.harmony.degrees(chord)
+  root = int(generator.model.NATURAL[chord['root']['letter']] + generator.model.alteration(chord['root']['alter']))
+  classes = {d: (root + generator.harmony.degree_semitones(d, a)) % 12 for d, a in degrees.items()}
+  guide = next((d for d in (3, 4, 2) if d in degrees), None)
+  terminal = next((d for d in (7, 6) if d in degrees), None)
+  color = max((d for d in degrees if d > 7), default=None)
+  kind = 'extended' if terminal and color else 'tetrad' if terminal else 'triad'
+  bass = next((d for d in (1, 5, 3) if classes.get(d) == grip[0].midi % 12), None)
+  slots = {'root': 1, 'fifth': 5, 'guide': guide, 'terminal': terminal, 'color': color}
+  policy = generator.vocabulary.accompaniment('acoustic')['voicing_families']
+  orders = policy[kind].get(f'{grip[0].string_number}/{bass}', ())
+  upper = tuple(p.midi % 12 for p in grip[1:])
+  preferred = any(all(slots[s] in classes for s in order) and tuple(classes[slots[s]] for s in order) == upper for order in orders)
+  # The physical/harmonic enumerator remains authoritative: an explicit bass
+  # or an unrepresented extension can use another valid compact voicing.
+  return {'id': f'{kind}/s{grip[0].string_number}/bass{bass or "written"}/' + '-'.join(str(next((d for d in sorted(classes) if pc == classes[d]), 'bass')) for pc in upper),
+    'preferred': preferred, 'bass_degree': bass, 'bass_string': grip[0].string_number,
+    'relative_frets': [p.fret - grip[0].fret for p in grip]}
+
+def electric(grip):
+  """Classify actual voicing geometry, without inventing chord permissions."""
+  pitches = sorted(p.midi for p in grip)
+  if len(grip) == 3:
+    return 'three-note-shell'
+  if len(set(p % 12 for p in pitches)) < len(pitches):
+    return 'compact-doubled'
+  if len(pitches) == 4:
+    lifted = sorted([pitches[0] + 12, *pitches[1:]])
+    if lifted[-1] - lifted[0] < 12 and lifted[2] == pitches[0] + 12:
+      return 'drop-two'
+  return 'close-position' if pitches and pitches[-1] - pitches[0] < 12 else 'compact-open'
+
+def coverage(chord, options, part):
+  if part == 'electric':
+    return {name: sum(electric(v) == name for v in options) for name in generator.vocabulary.accompaniment('electric')['voicing_families']['rank']}
+  families = [acoustic(chord, v) for v in options]
+  result = []
+  for string in (5, 6):
+    for degree in (1, 5):
+      found = [f for f in families if f['bass_degree'] == degree and f['bass_string'] == string]
+      result.append({'bass_string': string, 'bass_degree': degree, 'candidates': len(found), 'preferred': sum(f['preferred'] for f in found),
+        'reason': '' if found else 'no legal grip for this bass under written harmony and current fret/span limits'})
+  return result