trap_transformer.py

#!/usr/bin/env python3
"""Trap Style MIDI Transformer"""

import pretty_midi as pm
import numpy as np
import random
from pathlib import Path

class TrapTransformer:
    def __init__(self, bpm=140):
        self.bpm = bpm
        self.beat_duration = 60.0 / bpm

    def extract_bass_notes(self, midi_data):
        """Pull low notes that can become 808s"""
        bass_notes = []
        for track in midi_data.instruments:
            if track.is_drum:
                continue
            for note in track.notes:
                if note.pitch < 48:  # Below C3
                    bass_notes.append(note)
        return bass_notes

    def create_808_bass(self, bass_notes, duration_seconds):
        """Longer sustain + louder = 808 feel"""
        enhanced = []
        for note in bass_notes:
            new_note = pm.Note(
                velocity=min(note.velocity + 20, 127),
                pitch=note.pitch,
                start=note.start,
                end=min(note.end + 0.3, duration_seconds),
            )
            enhanced.append(new_note)
        return enhanced

    def add_hi_hats(self, duration_seconds):
        """Fast hi-hat rolls (trap signature)"""
        hat_track = pm.Instrument(program=0, is_drum=True, name="HiHats")
        t = 0.0
        while t < duration_seconds:
            step = self.beat_duration / 4  # 1/16 notes
            if random.random() < 0.3:  # 30% chance → roll
                rolls = random.choice([4, 8])
                for i in range(rolls):
                    hat_track.notes.append(
                        pm.Note(
                            velocity=random.randint(80, 120),
                            pitch=42,
                            start=t + (i * step / rolls),
                            end=t + ((i + 1) * step / rolls),
                        )
                    )
            else:
                hat_track.notes.append(
                    pm.Note(
                        velocity=random.randint(90, 115),
                        pitch=42,
                        start=t,
                        end=t + step * 0.5,
                    )
                )
            t += step
        return hat_track

    def add_trap_drums(self, duration_seconds):
        """Half-time kicks + snares"""
        drum_track = pm.Instrument(program=0, is_drum=True, name="TrapDrums")
        bar = self.beat_duration * 2  # Half-time bar
        num_bars = int(duration_seconds / bar)

        for b in range(num_bars):
            kick_t = b * bar
            snare_t = b * bar + self.beat_duration  # Snare on beat 3 (half-time)

            drum_track.notes.append(
                pm.Note(velocity=120, pitch=36, start=kick_t, end=kick_t + 0.1)
            )
            drum_track.notes.append(
                pm.Note(velocity=110, pitch=38, start=snare_t, end=snare_t + 0.08)
            )
        return drum_track

    def apply_sidechain(self, midi_data, kick_times):
        """Simulate sidechain pump — duck melody before kicks"""
        for instrument in midi_data.instruments:
            if instrument.is_drum:
                continue
            for note in instrument.notes:
                for kt in kick_times:
                    if note.start <= kt <= note.end:
                        note.velocity = max(1, note.velocity - 10)
        return midi_data

    def transform_to_trap(self, input_midi_path, output_midi_path=None):
        """Main: transform any MIDI → Trap"""
        midi_data = pm.PrettyMIDI(str(input_midi_path))
        duration = midi_data.get_end_time()

        # Enhance existing bass
        bass_notes = self.extract_bass_notes(midi_data)
        enhanced_bass = self.create_808_bass(bass_notes, duration)

        # Add new drum + hat tracks
        hat_track = self.add_hi_hats(duration)
        drum_track = self.add_trap_drums(duration)

        # Sidechain
        kick_times = [n.start for n in drum_track.notes if n.pitch == 36]
        midi_data = self.apply_sidechain(midi_data, kick_times)

        # Append trap layers
        midi_data.instruments.append(hat_track)
        midi_data.instruments.append(drum_track)

        # Set tempo
        try:
            for tempo_change in midi_data._tempo_changes:
                tempo_change.tempo = self.bpm
        except Exception:
            pass

        if output_midi_path:
            midi_data.write(str(output_midi_path))

        return midi_data