#include "kernel.h"
#include "timer.h"

#include "asm_x86.h"
#include "asm_pit.h"

static volatile uint64_t task_system_clock_start=0;

// CMOS RTC
 
// read real time clock register
static unsigned char get_rtc_reg(int reg) {
      x86_outb(0x70, reg);	//cmos at addr 0x70
      return x86_inb(0x71);	//cmos data at addr 0x71
}

// check if cmos rtc update in progress
static int get_rtc_update_flag() {
      x86_outb(0x70, 0x0A);
      return (x86_inb(0x71) & 0x80);
}

// get real time clock rom cmos (seconds since jan)
static uint64_t get_rtc_time()
{
      int CURRENT_YEAR = 2018;        // Change this each year!
 
      int century_register = 0x00;    // Set by ACPI table parsing code if possible
    
      unsigned char second;
      unsigned char minute;
      unsigned char hour;
      unsigned char day;
      unsigned char month;
      unsigned int year;

      unsigned char century;
      unsigned char last_second;
      unsigned char last_minute;
      unsigned char last_hour;
      unsigned char last_day;
      unsigned char last_month;
      unsigned char last_year;
      unsigned char last_century;
      unsigned char registerB;
 
      // Note: This uses the "read registers until you get the same values twice in a row" technique
      //       to avoid getting dodgy/inconsistent values due to RTC updates
 
      while (get_rtc_update_flag());                // Make sure an update isn't in progress
      second = get_rtc_reg(0x00);
      minute = get_rtc_reg(0x02);
      hour = get_rtc_reg(0x04);
      day = get_rtc_reg(0x07);
      month = get_rtc_reg(0x08);
      year = get_rtc_reg(0x09);

      if(century_register != 0) {
            century = get_rtc_reg(century_register);
      }
 
      do {
            last_second = second;
            last_minute = minute;
            last_hour = hour;
            last_day = day;
            last_month = month;
            last_year = year;
            last_century = century;
 
            while (get_rtc_update_flag());           // Make sure an update isn't in progress
            second = get_rtc_reg(0x00);
            minute = get_rtc_reg(0x02);
            hour = get_rtc_reg(0x04);
            day = get_rtc_reg(0x07);
            month = get_rtc_reg(0x08);
            year = get_rtc_reg(0x09);
            if(century_register != 0) {
                  century = get_rtc_reg(century_register);
            }
      } while( (last_second != second) || (last_minute != minute) || (last_hour != hour) ||
               (last_day != day) || (last_month != month) || (last_year != year) ||
               (last_century != century) );
 
      registerB = get_rtc_reg(0x0B);
 
      // Convert BCD to binary values if necessary
      if (!(registerB & 0x04)) {
            second = (second & 0x0F) + ((second / 16) * 10);
            minute = (minute & 0x0F) + ((minute / 16) * 10);
            hour = ( (hour & 0x0F) + (((hour & 0x70) / 16) * 10) ) | (hour & 0x80);
            day = (day & 0x0F) + ((day / 16) * 10);
            month = (month & 0x0F) + ((month / 16) * 10);
            year = (year & 0x0F) + ((year / 16) * 10);
            if(century_register != 0) {
                  century = (century & 0x0F) + ((century / 16) * 10);
            }
      }
 
      // Convert 12 hour clock to 24 hour clock if necessary
      if (!(registerB & 0x02) && (hour & 0x80)) {
            hour = ((hour & 0x7F) + 12) % 24;
      }
 
      // Calculate the full (4-digit) year
      if(century_register != 0) {
            year += century * 100;
      } else {
            year += (CURRENT_YEAR / 100) * 100;
            if(year < CURRENT_YEAR) year += 100;
      }
    
     // thank you doug16k @ #osdev
     // https://github.com/doug65536/dgos/blob/eab7080e69360493381669e7ce0ff27587d3127a/kernel/lib/time.cc
          int days[] = {
        31,
        (year-1900) % 4 ? 28 :
        (year-1900) % 100 ? 29 :
        (year-1900) % 400 ? 28 :
        29,
        31,
        30,
        31,
        30,
        31,
        31,
        30,
        31,
        30,
        31
    };

    int yday = 0;
    for (int m = 1; m < month; ++m)
        yday += days[m-1];
    yday += day - 1;

      uint64_t epoch_seconds= ((uint64_t)(second)) +
            minute * 60 +
            hour * 3600 +
            (yday) * 86400 +
            (year-1900 - 70) * 365 * 86400 +
            ((year-1900 - 69) / 4) * 86400 -
            ((year-1900 - 1) / 100) * 86400 +
            ((year-1900 + 299) / 400) * 86400;

      return epoch_seconds;
}


// PIT
uint64_t timer_init()
{
    uint64_t epoch_time=get_rtc_time();
    task_system_clock_start=epoch_time*25; // since pit ticks 25times a second
    asm_pit_rate_40ms();
    fixme("pit rate once did not work anymore 1/25 seconds?? but now ok?" );
    return epoch_time;
}

uint64_t timer_get_ms()
{
    return (asm_pit_get_ticks()+task_system_clock_start)*40;
}

uint64_t timer_get_uptime_ms()
{
    return asm_pit_get_ticks()*40;
}