/*
 *  Copyright (C) 2010-2019 Fabio Cavallo (aka FHorse)
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

// additional modifications by tildearrow for furnace

#include <string.h>
#include "apu.h"

void apu_tick(struct NESAPU* a, int len) {
  if (len<=a->timestamp) return;

  int rem=len-a->timestamp;
  if (rem>1) {
    // output now just in case
    int sample=(pulse_output(a)+tnd_output(a))<<6;
    if (sample!=a->lastSample) {  
      blip_add_delta(a->bb,a->timestamp,sample-a->lastSample);
      a->lastSample=sample;
    }
  }

  while (rem>0) {
    // predict advance
    int advance=rem;
    if (a->r4017.jitter.delay) {
      advance=1;
    }
    if (advance>a->apu.cycles) {
      advance=a->apu.cycles;
    }
    if (advance>a->S1.frequency) {
      advance=a->S1.frequency;
    }
    if (advance>a->S2.frequency) {
      advance=a->S2.frequency;
    }
    if (advance>a->TR.frequency) {
      advance=a->TR.frequency;
    }
    if (advance>a->NS.frequency) {
      advance=a->NS.frequency;
    }
    if (advance>a->DMC.frequency) {
      advance=a->DMC.frequency;
    }
    if (advance<1) advance=1;

    /* sottraggo il numero di cicli eseguiti */
    a->apu.cycles-=advance;
    /*
    * questo flag sara' a TRUE solo nel ciclo
    * in cui viene eseguito il length counter.
    */
    a->apu.length_clocked = FALSE;
    /*
    * se e' settato il delay del $4017, essendo
    * questo il ciclo successivo, valorizzo il
    * registro.
    */
#if defined (VECCHIA_GESTIONE_JITTER)
    if (r4017.jitter.delay) {
      r4017.jitter.delay = FALSE;
      r4017_jitter();
    }
#else
    if (a->r4017.jitter.delay) {
      a->r4017.jitter.delay = FALSE;
      r4017_jitter(0)
    }
    r4017_reset_frame()
#endif

    /* quando apu.cycles e' a 0 devo eseguire uno step */
    if (!a->apu.cycles) {
      switch (a->apu.step) {
        case 0:
          /*
          * nel mode 1 devo eseguire il
          * length counter e lo sweep.
          */
          if (a->apu.mode == APU_48HZ) {
            length_clock()
            sweep_clock()
          }
          envelope_clock()
          /* triangle's linear counter */
          linear_clock()
          /* passo al prossimo step */
          apu_change_step(++a->apu.step);
          break;
        case 1:
          /* nel mode 0 devo eseguire il length counter */
          if (a->apu.mode == APU_60HZ) {
            length_clock()
            sweep_clock()
          }
          envelope_clock()
          /* triangle's linear counter */
          linear_clock()
          /* passo al prossimo step */
          apu_change_step(++a->apu.step);
          break;
        case 2:
          /*
          * nel mode 1 devo eseguire il
          * length counter e lo sweep.
          */
          if (a->apu.mode == APU_48HZ) {
            length_clock()
            sweep_clock()
          }
          envelope_clock()
          /* triangle's linear counter */
          linear_clock()
          /* passo al prossimo step */
          apu_change_step(++a->apu.step);
          break;
        case 3:
          /*
          * gli step 3, 4 e 5 settano il bit 6 del $4015
          * ma solo nel 4 genero un IRQ.
          */
          if (a->apu.mode == APU_60HZ) {
            /*
            * se e' a 0 il bit 6 del $4017 (interrupt
            * inhibit flag) allora devo generare un IRQ.
            */
            if (!(a->r4017.value & 0x40)) {
              /* setto il bit 6 del $4015 */
              a->r4015.value |= 0x40;
            }
          } else {
            /* nel mode 1 devo eseguire l'envelope */
            envelope_clock()
            /* triangle's linear counter */
            linear_clock()
          }
          /* passo al prossimo step */
          apu_change_step(++a->apu.step);
          break;
        case 4:
          /*
          * gli step 3, 4 e 5 settano il bit 6 del $4015
          * ma solo nel 4 genero un IRQ.
          */
          if (a->apu.mode == APU_60HZ) {
            length_clock()
            sweep_clock()
            envelope_clock()
            /* triangle's linear counter */
            linear_clock()
            /*
            * se e' a 0 il bit 6 del $4017 (interrupt
            * inhibit flag) allora devo generare un IRQ.
            */
            if (!(a->r4017.value & 0x40)) {
              /* setto il bit 6 del $4015 */
              a->r4015.value |= 0x40;
            }
          }
          /* passo al prossimo step */
          apu_change_step(++a->apu.step);
          break;
        case 5:
          /*
          * gli step 3, 4 e 5 settano il bit 6 del $4015
          * ma solo nel 4 genero un IRQ.
          */
          if (a->apu.mode == APU_60HZ) {
            /*
            * se e' a 0 il bit 6 del $4017 (interrupt
            * inhibit flag) allora devo generare un IRQ.
            */
            if (!(a->r4017.value & 0x40)) {
              /* setto il bit 6 del $4015 */
              a->r4015.value |= 0x40;
            }
            a->apu.step++;
          } else {
            /* nel mode 1 devo ricominciare il ciclo */
            a->apu.step = 0;
          }
          /* passo al prossimo step */
          apu_change_step(a->apu.step);
          break;
        case 6:
          /* da qui ci passo solo nel mode 0 */
          envelope_clock()
          /* triangle's linear counter */
          linear_clock()
          /* questo e' il passaggio finale del mode 0 */
          a->apu.step = 1;
          /* passo al prossimo step */
          apu_change_step(a->apu.step);
          break;
      }
    }

    /*
    * eseguo un ticket per ogni canale
    * valorizzandone l'output.
    */
    // SQUARE 1 TICK
    if (!(a->S1.frequency-=advance)) {
      square_output(a->S1, 0)
      a->S1.frequency = (a->S1.timer + 1) << 1;
      a->S1.sequencer = (a->S1.sequencer + 1) & 0x07;
    }

    // SQUARE 2 TICK
    if (!(a->S2.frequency-=advance)) {
      square_output(a->S2, 0)
      a->S2.frequency = (a->S2.timer + 1) << 1;
      a->S2.sequencer = (a->S2.sequencer + 1) & 0x07;
    }

    // TRIANGLE TICK
    if (!(a->TR.frequency-=advance)) {
      a->TR.frequency = a->TR.timer + 1;
      if (a->TR.length.value && a->TR.linear.value) {
        a->TR.sequencer = (a->TR.sequencer + 1) & 0x1F;
        triangle_output()
      }
    }

    // NOISE TICK
    if (!(a->NS.frequency-=advance)) {
      if (a->NS.mode) {
        a->NS.shift = (a->NS.shift >> 1) | (((a->NS.shift ^ (a->NS.shift >> 6)) & 0x0001) << 14);
      } else {
        a->NS.shift = (a->NS.shift >> 1) | (((a->NS.shift ^ (a->NS.shift >> 1)) & 0x0001) << 14);
      }
      a->NS.shift &= 0x7FFF;
      noise_output()
      a->NS.frequency = noise_timer[a->apu.type][a->NS.timer];
    }

    // DMC TICK
    if (!(a->DMC.frequency-=advance)) {
      if (!a->DMC.silence) {
        if (!(a->DMC.shift & 0x01)) {
          if (a->DMC.counter > 1) {
            a->DMC.counter -= 2;
          }
        } else {
          if (a->DMC.counter < 126) {
            a->DMC.counter += 2;
          }
        }
      }
      a->DMC.shift >>= 1;
      dmc_output();
      if (!(--a->DMC.counter_out)) {
        a->DMC.counter_out = 8;
        if (!a->DMC.empty) {
          a->DMC.shift = a->DMC.buffer;
          a->DMC.empty = TRUE;
          a->DMC.silence = FALSE;
        } else {
          a->DMC.silence = TRUE;
        }
      }
      a->DMC.frequency = dmc_rate[a->apu.type][a->DMC.rate_index];
    }
    if (a->DMC.empty && a->DMC.remain) {
      BYTE tick = 4;
      switch (a->DMC.tick_type) {
        case DMC_CPU_WRITE:
          tick = 3;
          break;
        case DMC_R4014:
          tick = 2;
          break;
        case DMC_NNL_DMA:
          tick = 1;
          break;
      }
      {
        a->DMC.buffer = a->readDMC(a->readDMCUser,a->DMC.address);
      }
      /* e naturalmente incremento anche quelli eseguiti dall'opcode */
      a->apu.cpu_cycles += tick;
      /* salvo a che ciclo dell'istruzione avviene il dma */
      a->DMC.dma_cycle = a->apu.cpu_opcode_cycle;
      /* il DMC non e' vuoto */
      a->DMC.empty = FALSE;
      if (++a->DMC.address > 0xFFFF) {
        a->DMC.address = 0x8000;
      }
      if (!(--a->DMC.remain)) {
        if (a->DMC.loop) {
          a->DMC.remain = a->DMC.length;
          a->DMC.address = a->DMC.address_start;
        } else if (a->DMC.irq_enabled) {
          a->r4015.value |= 0x80;
        }
      }
    }

    a->r4011.cycles+=advance;
    if (advance&1) {
      a->apu.odd_cycle=!a->apu.odd_cycle;
    }

    // output sample
    a->timestamp+=advance-1;
    int sample=(pulse_output(a)+tnd_output(a))<<6;
    if (sample!=a->lastSample) {  
      blip_add_delta(a->bb,a->timestamp,sample-a->lastSample);
      a->lastSample=sample;
    }
    
    rem-=advance;
    a->timestamp++;
  }
  a->timestamp=len;
}

void apu_turn_on(struct NESAPU* a, BYTE apu_type) {
  memset(&a->apu, 0x00, sizeof(a->apu));
  memset(&a->r4015, 0x00, sizeof(a->r4015));
  memset(&a->r4017, 0x00, sizeof(a->r4017));
  /* azzero tutte le variabili interne dei canali */
  memset(&a->S1, 0x00, sizeof(a->S1));
  memset(&a->S2, 0x00, sizeof(a->S2));
  memset(&a->TR, 0x00, sizeof(a->TR));
  memset(&a->NS, 0x00, sizeof(a->NS));
  memset(&a->DMC, 0x00, sizeof(a->DMC));
  /* al reset e' sempre settato a 60Hz */
  a->apu.mode = APU_60HZ;
  /* per favore non fatemi questo... e' terribile */
  a->apu.type = apu_type;
  apu_change_step(a->apu.step);
  /* valori iniziali dei vari canali */
  a->S1.frequency = 1;
  a->S1.sweep.delay = 1;
  a->S1.sweep.divider = 1;
  a->S2.frequency = 1;
  a->S2.sweep.delay = 1;
  a->S2.sweep.divider = 1;
  a->TR.frequency = 1;
  /* questo era 0 ma produce click nell'audio */
  a->TR.sequencer = 7;
  a->NS.frequency = 1;
  a->NS.shift = 1;
  a->DMC.frequency = 1;
  a->DMC.empty = TRUE;
  a->DMC.silence = TRUE;
  a->DMC.counter_out = 8;
  // sembra che l'address del DMC al power on dia valorizzato a 0xC000
  // e la lunghezza del sample sia settato a 1 byte.
  // http://forums.nesdev.com/viewtopic.php?f=3&t=18278
  a->DMC.length = 1;
  a->DMC.address_start = 0xC000;
  a->apu.odd_cycle = 0;
  // come non viene inizializzato? Vorrei qualche spiegazione...
  a->r4011.frames = 0;
  a->lastSample = 0;

  a->S1.timer=2048;
  a->S2.timer=2048;
  a->TR.timer=2048;
  a->NS.timer=0x0FE4;
}