"""
Scythe MCP - Chord Progressions
Common progressions, genre-specific patterns, and modulation helpers.
"""
from typing import List, Dict, Tuple, Optional
from dataclasses import dataclass
from .chords import Chord, parse_chord, voice_lead
# Roman numeral to scale degree mapping
ROMAN_NUMERALS = {
'I': 1, 'II': 2, 'III': 3, 'IV': 4, 'V': 5, 'VI': 6, 'VII': 7,
'i': 1, 'ii': 2, 'iii': 3, 'iv': 4, 'v': 5, 'vi': 6, 'vii': 7,
}
# Scale degree to chord quality in major key
MAJOR_KEY_CHORDS = {
1: "major", 2: "minor", 3: "minor", 4: "major",
5: "major", 6: "minor", 7: "diminished"
}
# Scale degree to chord quality in minor key
MINOR_KEY_CHORDS = {
1: "minor", 2: "diminished", 3: "major", 4: "minor",
5: "minor", 6: "major", 7: "major"
}
# Common progressions by genre (in Roman numerals for transposition)
COMMON_PROGRESSIONS: Dict[str, Dict[str, List[str]]] = {
"pop": {
"axis": ["I", "V", "vi", "IV"], # Axis of Awesome
"classic": ["I", "IV", "V", "I"],
"sensitive": ["vi", "IV", "I", "V"],
"doo_wop": ["I", "vi", "IV", "V"],
},
"jazz": {
"ii_v_i": ["ii7", "V7", "Imaj7"],
"ii_v_i_vi": ["ii7", "V7", "Imaj7", "vi7"],
"rhythm_changes_a": ["Imaj7", "vi7", "ii7", "V7"],
"minor_ii_v_i": ["iiø7", "V7b9", "i7"],
"turnaround": ["Imaj7", "vi7", "ii7", "V7"],
"backdoor": ["Imaj7", "bVII7", "Imaj7"],
"coltrane": ["Imaj7", "bIIImaj7", "Vmaj7"], # Giant Steps
},
"blues": {
"12_bar": ["I7", "I7", "I7", "I7", "IV7", "IV7", "I7", "I7", "V7", "IV7", "I7", "V7"],
"quick_change": ["I7", "IV7", "I7", "I7", "IV7", "IV7", "I7", "I7", "V7", "IV7", "I7", "V7"],
"minor_blues": ["i7", "i7", "i7", "i7", "iv7", "iv7", "i7", "i7", "VI7", "V7", "i7", "V7"],
},
"rock": {
"classic": ["I", "IV", "V", "I"],
"power": ["I5", "bVII5", "IV5", "I5"],
"grunge": ["I", "IV", "bVI", "bVII"],
"modal": ["i", "bVII", "bVI", "bVII"],
},
"lofi": {
"chill": ["ii7", "V7", "Imaj7", "vi7"],
"melancholic": ["i9", "bVI9", "III9", "bVII9"],
"jazzy": ["IVmaj7", "iii7", "vi7", "ii7"],
"dreamy": ["Imaj7", "ii7", "iii7", "IVmaj7"],
},
"electronic": {
"trance": ["i", "bVI", "bVII", "i"],
"house": ["i", "i", "bVI", "bVII"],
"edm_drop": ["vi", "IV", "I", "V"],
"techno": ["i", "bVII", "bVI", "V"],
},
"shoegaze": {
"wall": ["I", "iii", "IV", "ii"],
"ethereal": ["Iadd9", "IVadd9", "vi", "V"],
"dreamy": ["I", "bVII", "IV", "I"],
},
"dreampop": {
"lush": ["Imaj7", "IVmaj7add9", "vi7", "IV"],
"nostalgic": ["I", "vi", "IV", "iii"],
},
"emo": {
"classic": ["I", "vi", "IV", "V"],
"midwest": ["I", "V", "vi", "IV"],
"post": ["i", "III", "bVII", "IV"],
},
"folk": {
"simple": ["I", "IV", "V", "I"],
"storytelling": ["I", "V", "vi", "IV"],
"modal": ["i", "bVII", "i", "iv"],
},
"chiptune": {
"heroic": ["I", "IV", "V", "I"],
"boss_battle": ["i", "bVI", "bVII", "i"],
"victory": ["I", "IV", "I", "V", "I"],
},
"ambient": {
"drone": ["I", "I", "I", "I"], # Static harmony
"evolving": ["Imaj7", "IVmaj7", "Imaj7", "Vmaj7"],
"cinematic": ["i", "bVI", "IV", "i"],
},
}
@dataclass
class Progression:
"""Represents a chord progression."""
key: str
mode: str # "major" or "minor"
chords: List[str] # Roman numerals or chord names
bars_per_chord: int = 1
def to_chords(self, octave: int = 4) -> List[Chord]:
"""Convert Roman numerals to actual Chord objects."""
from .scales import NOTE_NAMES, ENHARMONIC
result = []
key_idx = NOTE_NAMES.index(
self.key.upper() if self.key.upper() in NOTE_NAMES
else ENHARMONIC.get(self.key.upper(), 'C')
)
scale_intervals = [0, 2, 4, 5, 7, 9, 11] if self.mode == "major" else [0, 2, 3, 5, 7, 8, 10]
chord_qualities = MAJOR_KEY_CHORDS if self.mode == "major" else MINOR_KEY_CHORDS
for numeral in self.chords:
chord = self._parse_roman_numeral(numeral, key_idx, scale_intervals, chord_qualities, octave)
result.append(chord)
return result
def _parse_roman_numeral(
self,
numeral: str,
key_idx: int,
scale_intervals: List[int],
chord_qualities: Dict[int, str],
octave: int
) -> Chord:
"""Parse a Roman numeral chord symbol."""
from .scales import NOTE_NAMES
# Handle flats/sharps
modifier = 0
if numeral.startswith('b'):
modifier = -1
numeral = numeral[1:]
elif numeral.startswith('#'):
modifier = 1
numeral = numeral[1:]
# Extract base numeral
base_numeral = ""
for char in numeral:
if char.upper() in "IVX":
base_numeral += char
else:
break
remainder = numeral[len(base_numeral):]
# Get scale degree
degree = ROMAN_NUMERALS.get(base_numeral.upper(), 1)
is_minor = base_numeral.islower()
# Calculate root note
interval = scale_intervals[degree - 1] + modifier
root_idx = (key_idx + interval) % 12
root = NOTE_NAMES[root_idx]
# Determine chord quality
if remainder:
# Explicit chord type in Roman numeral
chord_type = remainder.replace("ø", "m7b5").lower()
if chord_type == "7" and is_minor:
chord_type = "min7"
elif chord_type == "7":
chord_type = "7" # Dominant
elif chord_type == "maj7":
chord_type = "maj7"
else:
# Infer from numeral case
chord_type = "minor" if is_minor else "major"
return Chord(root=root, chord_type=chord_type, octave=octave)
def with_voice_leading(self, octave: int = 4) -> List[Chord]:
"""Get chords with optimized voice leading."""
raw_chords = self.to_chords(octave)
if len(raw_chords) < 2:
return raw_chords
result = [raw_chords[0]]
for chord in raw_chords[1:]:
voiced = voice_lead(result[-1], chord)
result.append(voiced)
return result
def get_progression(
key: str,
genre: str,
style: str = None,
mode: str = "major"
) -> Progression:
"""Get a chord progression for a genre/style."""
genre_progs = COMMON_PROGRESSIONS.get(genre.lower(), COMMON_PROGRESSIONS["pop"])
if style:
chords = genre_progs.get(style, list(genre_progs.values())[0])
else:
# Get first progression for genre
chords = list(genre_progs.values())[0]
return Progression(key=key, mode=mode, chords=chords)
# Modulation helpers
def modulate_up_half_step(key: str) -> str:
"""Modulate up by a half step."""
from .scales import NOTE_NAMES
key_idx = NOTE_NAMES.index(key.upper() if key.upper() in NOTE_NAMES else 'C')
return NOTE_NAMES[(key_idx + 1) % 12]
def modulate_to_relative_minor(major_key: str) -> str:
"""Get the relative minor of a major key."""
from .scales import NOTE_NAMES
key_idx = NOTE_NAMES.index(major_key.upper() if major_key.upper() in NOTE_NAMES else 'C')
return NOTE_NAMES[(key_idx - 3) % 12]
def modulate_to_relative_major(minor_key: str) -> str:
"""Get the relative major of a minor key."""
from .scales import NOTE_NAMES
key_idx = NOTE_NAMES.index(minor_key.upper() if minor_key.upper() in NOTE_NAMES else 'A')
return NOTE_NAMES[(key_idx + 3) % 12]
def modulate_circle_of_fifths(key: str, steps: int = 1) -> str:
"""Move around the circle of fifths."""
from .scales import NOTE_NAMES
key_idx = NOTE_NAMES.index(key.upper() if key.upper() in NOTE_NAMES else 'C')
# Each step is 7 semitones up (fifth) or 5 semitones down (fourth)
return NOTE_NAMES[(key_idx + (7 * steps)) % 12]
