"""Writes a test LTC file (biphase mark, 30 fps, 48 kHz) for ltc_listen.swift's decoder test."""
import struct
import sys
import wave


def frame_bits(h, m, s, f):
    bits = [0] * 80
    def put(v, at, n):
        for i in range(n):
            bits[at + i] = (v >> i) & 1
    put(f % 10, 0, 4); put(f // 10, 8, 2); put(s % 10, 16, 4); put(s // 10, 24, 3)
    put(m % 10, 32, 4); put(m // 10, 40, 3); put(h % 10, 48, 4); put(h // 10, 56, 2)
    bits[64:80] = [0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1]
    return bits


def write(path, start=(1, 2, 3, 4), seconds=2, rate=48000, fps=30, amp=0.5):
    h, m, s, f = start
    per_bit = rate / (fps * 80.0)
    level, t, samples = 1, 0.0, []
    for _ in range(seconds * fps):
        for b in frame_bits(h, m, s, f):
            level = -level                                    # a transition at every bit start
            half = per_bit / 2
            for k in range(2):
                if k == 1 and b:
                    level = -level                            # and one in the middle of a 1
                t += half
                while len(samples) < int(round(t)):
                    samples.append(level * amp)
        f += 1
        if f == fps:
            f, s = 0, s + 1
    w = wave.open(path, "wb")
    w.setnchannels(1); w.setsampwidth(2); w.setframerate(rate)
    w.writeframes(b"".join(struct.pack("<h", int(x * 32767)) for x in samples))
    w.close()


if __name__ == "__main__":
    write(sys.argv[1])