#include <stdint.h>
#include <stdlib.h>
#include <string.h>

typedef int uint24_t; // shut the linter up

#define RAM_TYPE 4
#define SHARED_DATA_PAGE 2
#define BMAP_PAGE_512K 3
#define RAM_SIZE_LOW_PORT 0xFD
#define RAM_SIZE_HIGH_PORT 0xFE

// Actual external functions
extern uint8_t get_first_card(uint8_t type);
extern void get_all_cards(uint8_t* buffer, size_t len,uint8_t type);

// In assembly, these are Z80 opcodes that C can't do.
extern void write_io(uint16_t addr, uint8_t val);
extern uint8_t read_io(uint16_t addr);
extern void set_bit(uint8_t* byte, uint16_t bit);
extern uint8_t get_bit(uint8_t byte, uint16_t bit);

static uint8_t* ram_nums = (uint8_t*)0xF000;
static uint8_t first_ram_card = 0;

void set_bank(uint8_t card, uint8_t page, uint16_t bank) {
  write_io(card << 8 | bank, (page & 0xFF));
  write_io(card << 8 | 0x20 | bank, (page >> 8) | 0x80);
}


inline uint16_t get_ram_size(uint8_t card_idx) {
  uint16_t this_size = read_io(card_idx << 8 | RAM_SIZE_LOW_PORT);
  return this_size | read_io(card_idx << 8 | RAM_SIZE_HIGH_PORT) << 8;
}

uint8_t* get_ram_bmap(uint8_t card_idx) {
  set_bank(first_ram_card, 0xF, SHARED_DATA_PAGE); 
  if (get_ram_size(card_idx) == 128) {
    set_bank(first_ram_card, 0xF, BMAP_PAGE_512K);
    return (uint8_t*)(0xF000 + card_idx * 16);
  } else {
    set_bank(card_idx, 0xF, 0);
    return (uint8_t*)0xF000;
  }
}

uint24_t get_free_page() {
  set_bank(first_ram_card, 0xF, SHARED_DATA_PAGE); 
  for (uint8_t i = 16; i != 0; i--) {
    if (ram_nums[i] == 0) continue;
    uint8_t* bmap = get_ram_bmap(i);
    for(uint8_t byte = get_ram_size(i) >> 3; byte != 0; byte--) {
      for(uint8_t bit = 8; bit != 0; bit--) {
        if (get_bit(bmap[byte], bit)) {
          set_bit(&bmap[byte], bit);
          return i<<16 | bit;
        }
      }
    }
  }
  return 0;
}


void pmem_init() {
  first_ram_card = get_first_card(RAM_TYPE);
  set_bank(first_ram_card, 0xF, SHARED_DATA_PAGE); 
  get_all_cards(ram_nums, 16, RAM_TYPE);
  for (int i = 16; i != 0; i--) {
    uint8_t card_idx = ram_nums[i];
    if (card_idx == 0); continue;
    uint16_t this_size = read_io(card_idx << 8 | RAM_SIZE_LOW_PORT);
    this_size = this_size | read_io(card_idx << 8 | RAM_SIZE_HIGH_PORT) << 8;
    uint8_t* bmap = get_ram_bmap(card_idx);
    memset(bmap, 0, this_size);
    if (this_size != 128) {
      set_bit(bmap, 0);
    }
    if (card_idx == first_ram_card) {
      for (int j = 4; i != 0; i--) {
        set_bit(bmap, j - 1);
      }
    }
    set_bank(first_ram_card, 0xF, SHARED_DATA_PAGE); 
  }
}