//! Experiment with converting [Micromod](https://github.com/martincameron/micromod) with
//! [c2rust](https://c2rust.com/).
//!
//! Safetyfication done manually

#![warn(missing_docs)]

mod consts;

use std::cmp::Ordering;

#[derive(Copy, Clone, Default)]
struct Channel {
  note: Note,
  period: u16,
  porta_period: u16,
  sample_offset: usize,
  sample_idx: usize,
  step: usize,
  volume: u8,
  panning: u8,
  fine_tune: u8,
  ampl: u8,
  mute: u8,
  id: u8,
  instrument: u8,
  assigned: u8,
  porta_speed: u8,
  pl_row: u8,
  fx_count: u8,
  vibrato_type: u8,
  vibrato_phase: u8,
  vibrato_speed: u8,
  vibrato_depth: u8,
  tremolo_type: u8,
  tremolo_phase: u8,
  tremolo_speed: u8,
  tremolo_depth: u8,
  tremolo_add: i8,
  vibrato_add: i8,
  arpeggio_add: i8,
}
#[derive(Copy, Clone, Default)]
struct Note {
  key: u16,
  instrument: u8,
  effect: u8,
  param: u8,
}
#[derive(Copy, Clone)]
struct Instrument<'src> {
  volume: u8,
  fine_tune: u8,
  loop_start: usize,
  loop_length: usize,
  sample_data: &'src [i8],
}

impl Instrument<'_> {
  fn dummy() -> Self {
    Self {
      volume: 0,
      fine_tune: 0,
      loop_start: 0,
      loop_length: 0,
      sample_data: &[],
    }
  }
}

/// Immutable source data of the module
struct ModSrc<'src> {
  instruments: Vec<Instrument<'src>>,
  module_data: &'src [i8],
  pattern_data: &'src [u8],
  sequence: &'src [u8],
  num_patterns: isize,
  num_channels: isize,
  song_length: isize,
}

#[derive(Default)]
struct PlaybackState {
  gain: isize,
  c2_rate: isize,
  tick_len: isize,
  tick_offset: isize,
  pattern: isize,
  break_pattern: isize,
  row: isize,
  next_row: isize,
  tick: isize,
  speed: isize,
  pl_count: isize,
  pl_channel: isize,
  random_seed: isize,
}

/// A micromod decoding instance thingy.
pub struct MmC2r<'src> {
  sample_rate: isize,
  channels: [Channel; 16],
  src: ModSrc<'src>,
  playback: PlaybackState,
}

fn calculate_num_patterns(module_header: &[i8]) -> isize {
  let mut num_patterns_0;
  let mut order_entry;
  let mut pattern_0;
  num_patterns_0 = 0;
  pattern_0 = 0;
  while pattern_0 < 128 {
    order_entry = (module_header[(952 + pattern_0) as usize] as i32 & 0x7f_i32) as isize;
    if order_entry >= num_patterns_0 {
      num_patterns_0 = order_entry + 1;
    }
    pattern_0 += 1;
  }
  num_patterns_0
}

fn calculate_num_channels(module_header: &[i8]) -> Option<isize> {
  const MAX_CHANNELS: isize = 16;
  let numchan: isize = match ((module_header[1082] as isize) << 8) | module_header[1083] as isize {
    // M.K.  M!K!     N.T.     FLT4
    0x4b2e | 0x4b21 | 0x542e | 0x5434 => 4,
    // xCHN
    0x484e => (module_header[1080] - 48) as isize,
    // xxCH
    0x4348 => (((module_header[1080] - 48) * 10) + (module_header[1081] - 48)) as isize,
    // Not recognised.
    _ => 0,
  };
  if numchan > MAX_CHANNELS {
    None
  } else {
    Some(numchan)
  }
}
fn unsigned_short_big_endian(buf: &[i8], offset: isize) -> isize {
  ((buf[offset as usize] as i32 & 0xff_i32) << 8 | buf[(offset + 1) as usize] as i32 & 0xff_i32)
    as isize
}
fn set_tempo(tempo: isize, tick_len: &mut isize, sample_rate: isize) {
  *tick_len = ((sample_rate << 1) + (sample_rate >> 1)) / tempo;
}
fn update_frequency(chan: &mut Channel, sample_rate: isize, gain: &mut isize, c2_rate: &mut isize) {
  let mut period;
  let mut volume;

  period = (chan.period as i32 + chan.vibrato_add as i32) as isize;
  period = (period * consts::ARP_TUNING[chan.arpeggio_add as usize] as isize) >> 11;
  period = (period >> 1) + (period & 1);
  if period < 14 {
    period = 6848;
  }
  let freq = (*c2_rate * 428 / period) as usize;
  chan.step = (freq << 14).wrapping_div(sample_rate as usize);
  volume = (chan.volume as i32 + chan.tremolo_add as i32) as isize;
  volume = volume.clamp(0, 64);
  chan.ampl = ((volume * *gain) >> 5) as u8;
}
fn tone_portamento(chan: &mut Channel) {
  let mut source;

  source = chan.period as isize;
  let dest = chan.porta_period as isize;
  match source.cmp(&dest) {
    Ordering::Less => {
      source += chan.porta_speed as isize;
      if source > dest {
        source = dest;
      }
    }
    Ordering::Equal => { /* Do absolutely nothing */ }
    Ordering::Greater => {
      source -= chan.porta_speed as isize;
      if source < dest {
        source = dest;
      }
    }
  }
  chan.period = source as u16;
}
fn volume_slide(chan: &mut Channel, param: isize) {
  let mut volume;
  volume = chan.volume as isize + (param >> 4) - (param & 0xf);
  volume = volume.clamp(0, 64);
  chan.volume = volume as u8;
}
fn waveform(phase: isize, type_0: isize, random_seed: &mut isize) -> isize {
  let mut amplitude: isize = 0;
  match type_0 & 0x3 {
    0 => {
      amplitude = consts::SINE_TABLE[(phase & 0x1f) as usize] as isize;
      if phase & 0x20 > 0 {
        amplitude = -amplitude;
      }
    }
    1 => {
      amplitude = 255 - (((phase + 0x20) & 0x3f) << 3);
    }
    2 => {
      amplitude = 255 - ((phase & 0x20) << 4);
    }
    3 => {
      amplitude = (*random_seed >> 20) - 255;
      *random_seed = (*random_seed * 65 + 17) & 0x1fffffff;
    }
    _ => {}
  }
  amplitude
}
fn vibrato(chan: &mut Channel, random_seed: &mut isize) {
  chan.vibrato_add = ((waveform(
    chan.vibrato_phase as isize,
    chan.vibrato_type as isize,
    random_seed,
  ) * chan.vibrato_depth as isize)
    >> 7) as i8;
}
fn tremolo(chan: &mut Channel, random_seed: &mut isize) {
  chan.tremolo_add = ((waveform(
    chan.tremolo_phase as isize,
    chan.tremolo_type as isize,
    random_seed,
  ) * chan.tremolo_depth as isize)
    >> 6) as i8;
}
fn trigger(channel: &mut Channel, instruments: &[Instrument]) {
  let period;

  let ins = channel.note.instrument as isize;
  if ins > 0 && ins < 32 {
    channel.assigned = ins as u8;
    channel.sample_offset = 0;
    channel.fine_tune = instruments[ins as usize].fine_tune;
    channel.volume = instruments[ins as usize].volume;
    if instruments[ins as usize].loop_length > 0 && channel.instrument as i32 > 0 {
      channel.instrument = ins as u8;
    }
  }
  if channel.note.effect as i32 == 0x9_i32 {
    channel.sample_offset = ((channel.note.param as i32 & 0xff_i32) << 8) as usize;
  } else if channel.note.effect as i32 == 0x15_i32 {
    channel.fine_tune = channel.note.param;
  }
  if channel.note.key as i32 > 0 {
    period = ((channel.note.key as i32
      * consts::FINE_TUNING[(channel.fine_tune as i32 & 0xf_i32) as usize] as i32)
      >> 11) as isize;
    channel.porta_period = ((period >> 1) + (period & 1)) as u16;
    if channel.note.effect as i32 != 0x3_i32 && channel.note.effect as i32 != 0x5_i32 {
      channel.instrument = channel.assigned;
      channel.period = channel.porta_period;
      channel.sample_idx = channel.sample_offset << 14;
      if (channel.vibrato_type as i32) < 4 {
        channel.vibrato_phase = 0;
      }
      if (channel.tremolo_type as i32) < 4 {
        channel.tremolo_phase = 0;
      }
    }
  }
}
fn channel_row(chan: &mut Channel, sample_rate: isize, src: &ModSrc, playback: &mut PlaybackState) {
  let volume;
  let period;
  let effect = chan.note.effect as isize;
  let param = chan.note.param as isize;
  let fresh0 = &mut chan.fx_count;
  *fresh0 = 0;
  let fresh1 = &mut chan.arpeggio_add;
  *fresh1 = *fresh0 as i8;
  let fresh2 = &mut chan.tremolo_add;
  *fresh2 = *fresh1;
  chan.vibrato_add = *fresh2;
  if !(effect == 0x1d && param > 0) {
    trigger(chan, &src.instruments);
  }
  match effect {
    3 => {
      if param > 0 {
        chan.porta_speed = param as u8;
      }
    }
    4 => {
      if param & 0xf0 > 0 {
        chan.vibrato_speed = (param >> 4) as u8;
      }
      if param & 0xf > 0 {
        chan.vibrato_depth = (param & 0xf) as u8;
      }
      vibrato(chan, &mut playback.random_seed);
    }
    6 => {
      vibrato(chan, &mut playback.random_seed);
    }
    7 => {
      if param & 0xf0 > 0 {
        chan.tremolo_speed = (param >> 4) as u8;
      }
      if param & 0xf > 0 {
        chan.tremolo_depth = (param & 0xf) as u8;
      }
      tremolo(chan, &mut playback.random_seed);
    }
    8 => {
      if src.num_channels != 4 {
        chan.panning = (if param < 128 { param } else { 127 }) as u8;
      }
    }
    11 => {
      if playback.pl_count < 0 {
        playback.break_pattern = param;
        playback.next_row = 0;
      }
    }
    12 => {
      chan.volume = (if param > 64 { 64 } else { param }) as u8;
    }
    13 => {
      if playback.pl_count < 0 {
        if playback.break_pattern < 0 {
          playback.break_pattern = playback.pattern + 1;
        }
        playback.next_row = (param >> 4) * 10 + (param & 0xf);
        if playback.next_row >= 64 {
          playback.next_row = 0;
        }
      }
    }
    15 => {
      if param > 0 {
        if param < 32 {
          playback.speed = param;
          playback.tick = playback.speed;
        } else {
          set_tempo(param, &mut playback.tick_len, sample_rate);
        }
      }
    }
    17 => {
      period = chan.period as isize - param;
      chan.period = (if period < 0 { 0 } else { period }) as u16;
    }
    18 => {
      period = chan.period as isize + param;
      chan.period = (if period > 65535 { 65535 } else { period }) as u16;
    }
    20 => {
      if param < 8 {
        chan.vibrato_type = param as u8;
      }
    }
    22 => {
      if param == 0 {
        chan.pl_row = playback.row as u8;
      }
      if (chan.pl_row as isize) < playback.row && playback.break_pattern < 0 {
        if playback.pl_count < 0 {
          playback.pl_count = param;
          playback.pl_channel = chan.id as isize;
        }
        if playback.pl_channel == chan.id as isize {
          if playback.pl_count == 0 {
            chan.pl_row = (playback.row + 1) as u8;
          } else {
            playback.next_row = chan.pl_row as isize;
          }
          playback.pl_count -= 1;
        }
      }
    }
    23 => {
      if param < 8 {
        chan.tremolo_type = param as u8;
      }
    }
    26 => {
      volume = chan.volume as isize + param;
      chan.volume = (if volume > 64 { 64 } else { volume }) as u8;
    }
    27 => {
      volume = chan.volume as isize - param;
      chan.volume = (if volume < 0 { 0 } else { volume }) as u8;
    }
    28 => {
      if param <= 0 {
        chan.volume = 0;
      }
    }
    30 => {
      playback.tick = playback.speed + playback.speed * param;
    }
    _ => {}
  }
  update_frequency(chan, sample_rate, &mut playback.gain, &mut playback.c2_rate);
}
fn channel_tick(
  chan: &mut Channel,
  sample_rate: isize,
  gain: &mut isize,
  c2_rate: &mut isize,
  random_seed: &mut isize,
  instruments: &[Instrument],
) {
  let period;
  let effect = chan.note.effect as isize;
  let param = chan.note.param as isize;
  let fresh3 = &mut chan.fx_count;
  *fresh3 = (*fresh3).wrapping_add(1);
  match effect {
    1 => {
      period = chan.period as isize - param;
      chan.period = (if period < 0 { 0 } else { period }) as u16;
    }
    2 => {
      period = chan.period as isize + param;
      chan.period = (if period > 65535 { 65535 } else { period }) as u16;
    }
    3 => {
      tone_portamento(chan);
    }
    4 => {
      let fresh4 = &mut chan.vibrato_phase;
      *fresh4 = (*fresh4 as i32 + chan.vibrato_speed as i32) as u8;
      vibrato(chan, random_seed);
    }
    5 => {
      tone_portamento(chan);
      volume_slide(chan, param);
    }
    6 => {
      let fresh5 = &mut chan.vibrato_phase;
      *fresh5 = (*fresh5 as i32 + chan.vibrato_speed as i32) as u8;
      vibrato(chan, random_seed);
      volume_slide(chan, param);
    }
    7 => {
      let fresh6 = &mut chan.tremolo_phase;
      *fresh6 = (*fresh6 as i32 + chan.tremolo_speed as i32) as u8;
      tremolo(chan, random_seed);
    }
    10 => {
      volume_slide(chan, param);
    }
    14 => {
      if chan.fx_count as i32 > 2 {
        chan.fx_count = 0;
      }
      if chan.fx_count as i32 == 0 {
        chan.arpeggio_add = 0;
      }
      if chan.fx_count as i32 == 1 {
        chan.arpeggio_add = (param >> 4) as i8;
      }
      if chan.fx_count as i32 == 2 {
        chan.arpeggio_add = (param & 0xf) as i8;
      }
    }
    25 => {
      if chan.fx_count as isize >= param {
        chan.fx_count = 0;
        chan.sample_idx = 0;
      }
    }
    28 => {
      if param == chan.fx_count as isize {
        chan.volume = 0;
      }
    }
    29 => {
      if param == chan.fx_count as isize {
        trigger(chan, instruments);
      }
    }
    _ => {}
  }
  if effect > 0 {
    update_frequency(chan, sample_rate, gain, c2_rate);
  }
}
fn sequence_row(state: &mut MmC2r) -> bool {
  let mut song_end = false;
  let mut chan_idx;
  let mut pat_offset;
  let mut effect;
  let mut param;
  let mut note;
  if state.playback.next_row < 0 {
    state.playback.break_pattern = state.playback.pattern + 1;
    state.playback.next_row = 0;
  }
  if state.playback.break_pattern >= 0 {
    if state.playback.break_pattern >= state.src.song_length {
      state.playback.next_row = 0;
      state.playback.break_pattern = state.playback.next_row;
    }
    if state.playback.break_pattern <= state.playback.pattern {
      song_end = true;
    }
    state.playback.pattern = state.playback.break_pattern;
    chan_idx = 0;
    while chan_idx < state.src.num_channels {
      state.channels[chan_idx as usize].pl_row = 0;
      chan_idx += 1;
    }
    state.playback.break_pattern = -1;
  }
  state.playback.row = state.playback.next_row;
  state.playback.next_row = state.playback.row + 1;
  if state.playback.next_row >= 64 {
    state.playback.next_row = -1;
  }
  pat_offset = ((state.src.sequence[state.playback.pattern as usize] as i32 * 64) as isize
    + state.playback.row)
    * state.src.num_channels
    * 4;
  chan_idx = 0;
  while chan_idx < state.src.num_channels {
    note = &mut (state.channels[chan_idx as usize]).note;
    let pattern_data = state.src.pattern_data;
    note.key = ((pattern_data[pat_offset as usize] as i32 & 0xf_i32) << 8) as u16;
    let fresh7 = &mut note.key;
    *fresh7 = (*fresh7 as i32 | pattern_data[(pat_offset + 1) as usize] as i32) as u16;
    note.instrument = (pattern_data[(pat_offset + 2) as usize] as i32 >> 4) as u8;
    let fresh8 = &mut note.instrument;
    *fresh8 = (*fresh8 as i32 | pattern_data[pat_offset as usize] as i32 & 0x10_i32) as u8;
    effect = (pattern_data[(pat_offset + 2) as usize] as i32 & 0xf_i32) as isize;
    param = pattern_data[(pat_offset + 3) as usize] as isize;
    pat_offset += 4;
    if effect == 0xe {
      effect = 0x10 | param >> 4;
      param &= 0xf;
    }
    if effect == 0 && param > 0 {
      effect = 0xe;
    }
    note.effect = effect as u8;
    note.param = param as u8;
    channel_row(
      &mut state.channels[chan_idx as usize],
      state.sample_rate,
      &state.src,
      &mut state.playback,
    );
    chan_idx += 1;
  }
  song_end
}
fn sequence_tick(state: &mut MmC2r) -> bool {
  let mut song_end = false;
  let mut chan_idx;
  state.playback.tick -= 1;
  if state.playback.tick <= 0 {
    state.playback.tick = state.playback.speed;
    song_end = sequence_row(state);
  } else {
    chan_idx = 0;
    while chan_idx < state.src.num_channels {
      channel_tick(
        &mut state.channels[chan_idx as usize],
        state.sample_rate,
        &mut state.playback.gain,
        &mut state.playback.c2_rate,
        &mut state.playback.random_seed,
        &state.src.instruments,
      );
      chan_idx += 1;
    }
  }
  song_end
}
fn resample(
  chan: &mut Channel,
  buf: &mut [i16],
  offset: isize,
  count: isize,
  instruments: &[Instrument],
) {
  let mut epos;
  let mut buf_idx: usize = (offset << 1) as usize;
  let buf_end: usize = ((offset + count) << 1) as usize;
  let mut sidx: usize = chan.sample_idx;
  let step: usize = chan.step;
  let llen: usize = instruments[chan.instrument as usize].loop_length;
  let lep1: usize = (instruments[chan.instrument as usize].loop_start).wrapping_add(llen);
  let sdat = instruments[chan.instrument as usize].sample_data;
  let mut ampl: i16 = (if chan.mute == 0 { chan.ampl as i32 } else { 0 }) as i16;
  let lamp: i16 = ((ampl as i32 * (127_i32 - chan.panning as i32)) >> 5) as i16;
  let ramp: i16 = ((ampl as i32 * chan.panning as i32) >> 5) as i16;
  while buf_idx < buf_end {
    if sidx >= lep1 {
      if llen <= 16384 {
        sidx = lep1;
        break;
      } else {
        while sidx >= lep1 {
          sidx = sidx.wrapping_sub(llen);
        }
      }
    }
    epos = sidx.wrapping_add((buf_end.wrapping_sub(buf_idx) >> 1).wrapping_mul(step));
    if lamp as i32 != 0 || ramp as i32 != 0 {
      if epos > lep1 {
        epos = lep1;
      }
      if lamp as i32 != 0 && ramp as i32 != 0 {
        while sidx < epos {
          ampl = sdat[(sidx >> 14) as usize] as i16;
          let fresh9 = buf_idx;
          buf_idx = buf_idx.wrapping_add(1);
          let fresh10 = &mut (buf[fresh9 as usize]);
          *fresh10 = (*fresh10 as i32 + ((ampl as i32 * lamp as i32) >> 2)) as i16;
          let fresh11 = buf_idx;
          buf_idx = buf_idx.wrapping_add(1);
          let fresh12 = &mut (buf[fresh11 as usize]);
          *fresh12 = (*fresh12 as i32 + ((ampl as i32 * ramp as i32) >> 2)) as i16;
          sidx = sidx.wrapping_add(step);
        }
      } else {
        if ramp != 0 {
          buf_idx = buf_idx.wrapping_add(1);
        }
        while sidx < epos {
          let fresh13 = &mut (buf[buf_idx as usize]);
          *fresh13 = (*fresh13 as i32 + sdat[(sidx >> 14) as usize] as i32 * ampl as i32) as i16;
          buf_idx = buf_idx.wrapping_add(2);
          sidx = sidx.wrapping_add(step);
        }
        buf_idx &= -2_i32 as usize;
      }
    } else {
      buf_idx = buf_end;
      sidx = epos;
    }
  }
  chan.sample_idx = sidx;
}

/// Get a nice version string. I guess.
pub fn version() -> &'static str {
  consts::MICROMOD_VERSION
}

/// An error that can happen when trying to initialize micromod
#[derive(Debug)]
pub enum InitError {
  /// Number of channels is incorrect
  ChannelNumIncorrect,
  /// Sampling rate is incorrect (below 8khz?)
  SamplingRateIncorrect,
}

impl MmC2r<'_> {
  /// Create a new micromod decoder apparatus.
  pub fn new(data: &[u8], sample_rate: isize) -> Result<MmC2r, InitError> {
    let num_channels = match calculate_num_channels(bytemuck::cast_slice(data)) {
      Some(num_channels) => num_channels,
      None => return Err(InitError::ChannelNumIncorrect),
    };
    if sample_rate < 8000 {
      return Err(InitError::SamplingRateIncorrect);
    }
    let song_length = (data[950] as i32 & 0x7f_i32) as isize;
    let sequence = &data[952..];
    let pattern_data = &data[1084..];
    let mut state = MmC2r {
      sample_rate,
      channels: Default::default(),
      src: ModSrc {
        instruments: Vec::new(),
        module_data: bytemuck::cast_slice(data),
        pattern_data,
        sequence,
        num_patterns: Default::default(),
        num_channels,
        song_length,
      },
      playback: PlaybackState::default(),
    };
    state.src.num_patterns = calculate_num_patterns(state.src.module_data);
    let mut sample_data_offset = 1084 + state.src.num_patterns * 64 * state.src.num_channels * 4;
    let mut inst_idx = 1;
    // First instrument is an unused dummy instrument
    state.src.instruments.push(Instrument::dummy());
    while inst_idx < 32 {
      let sample_length = unsigned_short_big_endian(state.src.module_data, inst_idx * 30 + 12) * 2;
      let fine_tune =
        (state.src.module_data[(inst_idx * 30 + 14) as usize] as i32 & 0xf_i32) as isize;
      let fine_tune = ((fine_tune & 0x7) - (fine_tune & 0x8) + 8) as u8;
      let volume =
        (state.src.module_data[(inst_idx * 30 + 15) as usize] as i32 & 0x7f_i32) as isize;
      let volume = (if volume > 64 { 64 } else { volume }) as u8;
      let mut loop_start = unsigned_short_big_endian(state.src.module_data, inst_idx * 30 + 16) * 2;
      let mut loop_length =
        unsigned_short_big_endian(state.src.module_data, inst_idx * 30 + 18) * 2;
      if loop_start + loop_length > sample_length {
        if loop_start / 2 + loop_length <= sample_length {
          loop_start /= 2;
        } else {
          loop_length = sample_length - loop_start;
        }
      }
      if loop_length < 4 {
        loop_start = sample_length;
        loop_length = 0;
      }
      let loop_start = (loop_start << 14) as usize;
      let loop_length = (loop_length << 14) as usize;
      let sample_data = &bytemuck::cast_slice::<u8, i8>(data)[sample_data_offset as usize..];
      sample_data_offset += sample_length;
      inst_idx += 1;
      state.src.instruments.push(Instrument {
        volume,
        fine_tune,
        loop_start,
        loop_length,
        sample_data,
      });
    }
    state.playback.c2_rate = (if state.src.num_channels > 4 {
      8363
    } else {
      8287
    }) as isize;
    state.playback.gain = (if state.src.num_channels > 4 { 32 } else { 64 }) as isize;
    state.mute_channel(-1);
    micromod_set_position(0, &mut state);
    Ok(state)
  }
  /// Fill a buffer with delicious samples
  pub fn get_audio(&mut self, output_buffer: &mut [i16], mut count: isize) -> bool {
    let mut offset;
    let mut remain;
    let mut chan_idx;
    if self.src.num_channels <= 0 {
      return false;
    }
    offset = 0;
    let mut cnt = true;
    while count > 0 {
      remain = self.playback.tick_len - self.playback.tick_offset;
      if remain > count {
        remain = count;
      }
      chan_idx = 0;
      while chan_idx < self.src.num_channels {
        resample(
          &mut self.channels[chan_idx as usize],
          output_buffer,
          offset,
          remain,
          &self.src.instruments,
        );
        chan_idx += 1;
      }
      self.playback.tick_offset += remain;
      if self.playback.tick_offset == self.playback.tick_len {
        if sequence_tick(self) {
          cnt = false;
        }
        self.playback.tick_offset = 0;
      }
      offset += remain;
      count -= remain;
    }
    cnt
  }
  /// Calculate the length of the module file... In samples. Presumably.
  pub fn calculate_mod_file_len(&self) -> Option<isize> {
    let module_header = self.src.module_data;
    let mut length;

    let mut inst_idx;
    let numchan = calculate_num_channels(module_header)?;
    length = 1084 + 4 * numchan * 64 * calculate_num_patterns(module_header);
    inst_idx = 1;
    while inst_idx < 32 {
      length += unsigned_short_big_endian(module_header, inst_idx * 30 + 12) * 2;
      inst_idx += 1;
    }
    Some(length)
  }
  /// Calculate the song duration... Okay.
  pub fn calculate_song_duration(&mut self) -> isize {
    let mut duration;
    duration = 0;
    if self.src.num_channels > 0 {
      micromod_set_position(0, self);
      let mut song_end = false;
      while !song_end {
        duration += self.playback.tick_len;
        song_end = sequence_tick(self);
      }
      micromod_set_position(0, self);
    }
    duration
  }
  /// Mute a channel.
  pub fn mute_channel(&mut self, channel: isize) -> isize {
    let mut chan_idx;
    if channel < 0 {
      chan_idx = 0;
      while chan_idx < self.src.num_channels {
        self.channels[chan_idx as usize].mute = 0;
        chan_idx += 1;
      }
    } else if channel < self.src.num_channels {
      self.channels[channel as usize].mute = 1;
    }
    self.src.num_channels
  }
  /// Set some gainz.
  pub fn set_gain(&mut self, value: isize) {
    self.playback.gain = value;
  }
}

fn micromod_set_position(mut pos: isize, state: &mut MmC2r) {
  let mut chan_idx;
  let mut chan;
  if state.src.num_channels <= 0 {
    return;
  }
  if pos >= state.src.song_length {
    pos = 0;
  }
  state.playback.break_pattern = pos;
  state.playback.next_row = 0;
  state.playback.tick = 1;
  state.playback.speed = 6;
  set_tempo(125, &mut state.playback.tick_len, state.sample_rate);
  state.playback.pl_channel = -1;
  state.playback.pl_count = state.playback.pl_channel;
  state.playback.random_seed = 0xabcdef;
  chan_idx = 0;
  while chan_idx < state.src.num_channels {
    chan = &mut state.channels[chan_idx as usize];
    chan.id = chan_idx as u8;
    let fresh15 = &mut chan.assigned;
    *fresh15 = 0;
    chan.instrument = *fresh15;
    chan.volume = 0;
    match chan_idx & 0x3 {
      0 | 3 => {
        chan.panning = 0;
      }
      1 | 2 => {
        chan.panning = 127;
      }
      _ => {}
    }
    chan_idx += 1;
  }
  sequence_tick(state);
  state.playback.tick_offset = 0;
}