#!/usr/bin/env python3
"""Encode GPS phrases, sharing their identical encoded prefix without loss."""
import argparse
from pathlib import Path
import struct
import wave

STEPS = (7,8,9,10,11,12,13,14,16,17,19,21,23,25,28,31,34,37,41,45,50,55,
    60,66,73,80,88,97,107,118,130,143,157,173,190,209,230,253,279,307,
    337,371,408,449,494,544,598,658,724,796,876,963,1060,1166,1282,1411,
    1552,1707,1878,2066,2272,2499,2749,3024,3327,3660,4026,4428,4871,
    5358,5894,6484,7132,7845,8630,9493,10442,11487,12635,13899,15289,
    16818,18500,20350,22385,24623,27086,29794,32767)
ADJUST = (-1,-1,-1,-1,2,4,6,8)

def encode(samples):
    predictor = index = 0
    codes = []
    for sample in samples:
        step = STEPS[index]
        difference = sample - predictor
        code = 8 if difference < 0 else 0
        difference = abs(difference)
        delta = step >> 3
        for bit, part in ((4,step),(2,step >> 1),(1,step >> 2)):
            if difference >= part:
                code |= bit
                difference -= part
                delta += part
        predictor = max(-32768,min(32767,predictor + (-delta if code & 8 else delta)))
        index = max(0,min(88,index + ADJUST[code & 7]))
        codes.append(code)
    if len(codes) & 1:
        codes.append(0)
    return bytes(a | b << 4 for a,b in zip(codes[::2], codes[1::2]))

def read(path, rate=8000):
    with wave.open(str(path),'rb') as wav:
        if (wav.getnchannels(),wav.getsampwidth(),wav.getframerate()) != (1,2,rate):
            raise ValueError(f'Expected mono 16-bit PCM at {rate} Hz')
        data = wav.readframes(wav.getnframes())
    return struct.unpack('<' + 'h' * (len(data)//2),data)

def shared_prefix(on, off):
    """Return three spans whose concatenations exactly restore both streams.

    A split is byte-based, not a word/codec boundary. Playback must preserve
    adaptive codec state and bit position at the seam. Leave a nonempty tail
    for both phrases, including identical or very short fixture recordings.
    """
    limit = min(len(on), len(off)) - 1
    split = 0
    while split < limit and on[split] == off[split]:
        split += 1
    return on[:split], on[split:], off[split:]

def emit_array(lines, name, data):
    lines.append(f'static const uint8_t {name}Data[] = {{')
    for i in range(0,len(data),20):
        lines.append('  '+','.join(f'0x{b:02x}' for b in data[i:i+20])+',')
    lines.append('};')

def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--on',type=Path,required=True)
    parser.add_argument('--off',type=Path,required=True)
    parser.add_argument('--output',type=Path,required=True)
    parser.add_argument('--rate',type=int,choices=(8000,16000),default=8000)
    parser.add_argument('--voice', help='Speech voice used to synthesize the source WAVs')
    args = parser.parse_args()
    if args.voice is not None and (not args.voice.strip() or '\n' in args.voice or '\r' in args.voice):
        parser.error('--voice must be a nonempty single-line label')
    lines = [f'// Generated by scripts/generate_gps_voice.py. {args.rate/1000:g} kHz IMA ADPCM.',
        '// Phrases: "GPS on", "GPS off". No runtime speech engine.',
        '#pragma once','#include <helpers/ui/GpsVoice.h>',
        'namespace mesh { namespace audio {']
    if args.voice is not None:
        lines.insert(2, f'// Voice: {args.voice}')
    phrases = [read(path,args.rate) for path in (args.on,args.off)]
    if any(not samples or len(samples) > args.rate * 4 for samples in phrases):
        raise ValueError('GPS phrases must be nonempty clips under four seconds')
    encoded = [encode(samples) for samples in phrases]
    prefix, on, off = shared_prefix(*encoded)
    if len(prefix) < 64:
        prefix, on, off = b'', *encoded
    if prefix:
        lines.append('// Three stored spans; preserve decoder state across the shared prefix.')
        emit_array(lines, 'gps', prefix)
    for name,samples,data in zip(('On','Off'),phrases,(on,off)):
        emit_array(lines, 'gps'+name, data)
        fields = f'  gps{name}Data, sizeof(gps{name}Data), {len(samples)}, {args.rate}'
        if prefix:
            fields += ', gpsData, sizeof(gpsData)'
        lines.extend([f'static constexpr VoiceClip gps{name}Clip = {{',
                      fields, '};'])
        print(f'GPS {name.lower()}: {len(samples)/args.rate:.3f}s, {len(data)} tail bytes')
    print(f'GPS shared prefix: {len(prefix)} bytes; audio saved: {len(prefix)} bytes')
    lines.append('}} // namespace mesh::audio')
    args.output.write_text('\n'.join(lines)+'\n',encoding='utf-8')

if __name__ == '__main__':
    main()