// Copyright (C) 2025 Thies Lennart Alff
//
// 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
// USA

#include "i2c.h"
#include "common.h"
#include "macros.h"
#include <samd21.h>
#include <stddef.h>

#define DELIMITER 0

static uint8_t rx_buffer[64];
static uint8_t rx_index = 0;

static uint8_t tx_buffer[64];
static uint8_t tx_index = 0;

static i2c_data_received_cb_fun data_received_cb_fun = NULL;

static inline uint8_t is_rx_buffer_full() {
  return !(rx_index < LEN(rx_buffer));
}

static inline void i2c_ack() {
  I2C_SERCOM->I2CS.CTRLB.bit.ACKACT = 0;
  I2C_SERCOM->I2CS.CTRLB.bit.CMD = 0x03;
}

static inline void i2c_nack() {
  I2C_SERCOM->I2CS.CTRLB.bit.ACKACT = 1;
  I2C_SERCOM->I2CS.CTRLB.bit.CMD = 0x02;
}

static inline void i2c_handle_received_data(uint8_t data) {
  if (is_rx_buffer_full()) {
    rx_index = 0;
    i2c_nack();
    return;
  }

  rx_buffer[rx_index++] = data;
  if (is_rx_buffer_full() && (data != DELIMITER)) {
    DEBUG_PRINT(
        "Receive buffer full (%hu bytes) but no delimiter. Discarding.\n",
        rx_index);
    rx_index = 0;
    i2c_nack();
    return;
  }

  if (data == DELIMITER) {
    DEBUG_PRINT("Delimiter received!\n");
    for (int i = 0; i < rx_index; ++i) {
      DEBUG_PRINT("%hu ", rx_buffer[i]);
    }
    DEBUG_PRINT("\n");
    // we seem to have received a complete message.
    if (data_received_cb_fun != NULL) {
      if (data_received_cb_fun(rx_buffer, rx_index)) {
        DEBUG_PRINT("ACK valid msg\n");
        i2c_ack();
        return;
      } else {
          DEBUG_PRINT("NACK invalid crc\n");
        i2c_nack();
        return;
      }
    }
    i2c_nack(); 
    rx_index = 0;
    return;
  }
  i2c_ack();
}
void i2c_set_data_received_cb(i2c_data_received_cb_fun cb) {
  data_received_cb_fun = cb;
}

void I2C_SERCOM_HANDLER() {
  if (I2C_SERCOM->I2CS.INTFLAG.bit.AMATCH) {
    DEBUG_PRINT("i2c address match interrupt.\n");
    if (I2C_SERCOM->I2CS.STATUS.bit.SR) {
      DEBUG_PRINT("i2c repeated start!\n");
    } else {
      DEBUG_PRINT("i2c normal start\n");
    }
    if (I2C_SERCOM->I2CS.STATUS.bit.DIR) {
      DEBUG_PRINT("i2c master read\n");
      tx_index = 0;
    } else {
      DEBUG_PRINT("i2c master write\n");
      rx_index = 0;
    }
    i2c_ack();
  }
  if (I2C_SERCOM->I2CS.INTFLAG.bit.DRDY) {
    if (I2C_SERCOM->I2CS.STATUS.bit.DIR) {
      // slave write
      if (0) {
        I2C_SERCOM->I2CS.CTRLB.bit.ACKACT = 1;
        I2C_SERCOM->I2CS.CTRLB.bit.CMD = 0x02;
      } else {
        I2C_SERCOM->I2CS.DATA.bit.DATA = 0x11;
        // continue sending data to master
        I2C_SERCOM->I2CS.CTRLB.bit.ACKACT = 0;
        I2C_SERCOM->I2CS.CTRLB.bit.CMD = 0x03;
      }
    } else {
      i2c_handle_received_data(I2C_SERCOM->I2CS.DATA.reg);
    }
  }
  if (I2C_SERCOM->I2CS.INTFLAG.bit.PREC) {
    DEBUG_PRINT("i2c stop condition received\n");
    rx_index = 0;
    I2C_SERCOM->I2CS.INTFLAG.reg = SERCOM_I2CS_INTFLAG_PREC;
    // we are done. cleanup?
  }
}

void i2c_init() {
  while (I2C_SERCOM->I2CS.SYNCBUSY.bit.ENABLE)
    ;
  I2C_SERCOM->I2CS.CTRLA.bit.ENABLE = 0;

  while (I2C_SERCOM->I2CS.SYNCBUSY.bit.SWRST)
    ;
  I2C_SERCOM->I2CS.CTRLA.bit.SWRST = 1;
  while (I2C_SERCOM->I2CS.SYNCBUSY.bit.SWRST)
    ;

  PORT->Group[0].WRCONFIG.reg =
      PORT_WRCONFIG_WRPINCFG // declare pincfg shall be edited
      | PORT_WRCONFIG_WRPMUX // declare mux config shall be edited
      | PORT_WRCONFIG_PMUXEN // enable multiplexing
      | PORT_WRCONFIG_PMUX(MUX_PA08C_SERCOM0_PAD0 // choose mux C option
                           ) |
      PORT_WRCONFIG_PINMASK((uint16_t)(I2C_SDA_PIN | I2C_SCL_PIN));

  // enable peripheral clock
  PM->APBCMASK.reg |= PM_APBCMASK_SERCOM0;
  GCLK->CLKCTRL.reg = GCLK_CLKCTRL_ID(SERCOM0_GCLK_ID_CORE) |
                      GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN(0);
  while (GCLK->STATUS.bit.SYNCBUSY)
    ;

  I2C_SERCOM->I2CS.CTRLA.reg =
      SERCOM_I2CS_CTRLA_SPEED(0)         // 100kHz/400kHz
      | SERCOM_I2CS_CTRLA_SDAHOLD(0x2)   // hold SDA line after SCL falling edge
      | SERCOM_I2CS_CTRLA_RUNSTDBY       // keep running in standby
      | SERCOM_I2CS_CTRLA_MODE_I2C_SLAVE // run as slave
      ;

  I2C_SERCOM->I2CS.ADDR.reg = I2C_ADDRESS << 1;
  I2C_SERCOM->I2CS.INTENSET.reg = SERCOM_I2CS_INTENSET_PREC     // stop received
                                  | SERCOM_I2CS_INTENSET_AMATCH // addr matched
                                  | SERCOM_I2CS_INTENSET_DRDY   // data ready
      ;

  I2C_SERCOM->I2CS.CTRLA.reg |= SERCOM_I2CS_CTRLA_ENABLE;
  while (I2C_SERCOM->I2CS.SYNCBUSY.bit.ENABLE)
    ;
  NVIC_SetPriority(SERCOM0_IRQn, 3);
  NVIC_EnableIRQ(SERCOM0_IRQn);
}