#include "drive.h"
#include "elf.h"
#include "util.h"
#include "idt.h"
#include "log.h"
#include "panic.h"
#include "task.h"
#include "paging.h"

enum {
  IDT_PRESENT = 0x80,

  IDT_INT     = 0x0e,
  IDT_TRAP    = 0x0f
};

struct idt_entry {
  uint16_t addr_low;
  uint16_t cs;
  uint8_t zero;
  uint8_t flags;
  uint16_t addr_high;
} __attribute__ ((packed));

struct idt_entry idt[256];

struct {
  uint16_t limit;
  uint32_t start;
} __attribute__ ((packed)) idtr = {
  .limit = 256 * sizeof(struct idt_entry) - 1,
  .start = (uint32_t)idt
};

//file handles as (drive_number << 8) + file_id_t

static uint32_t sc_open_file(uint32_t drive_number, char *path) {
  return (drive_number << 8) + drives[drive_number].get_file(drives + drive_number, path);
}

static void sc_close_file(uint32_t handle) {
  drives[handle >> 8].free_file(drives + (handle >> 8), handle & 0xff);
}

static uint32_t sc_file_get_size(uint32_t handle) {
  return drives[handle >> 8].get_file_length(drives + (handle >> 8), handle & 0xff);
}

static uint32_t sc_file_read(uint32_t handle, uint32_t file_offset, uint32_t count, void *buffer) {
  uint32_t len = sc_file_get_size(handle);
  if (file_offset + count > len)
    count = len - file_offset;
  fmcpy(buffer, drives + (handle >> 8), handle & 0xff, file_offset, count);
  return count;
}

static bool sc_start_task(uint32_t drive_number, char *path) {
  switch_to_kernel_cr3();
  bool result = try_elf_run(drives + drive_number, path);
  switch_to_task_cr3();
  return result;
}

static void sc_log_string(char *sz) {
  logsz(sz);
}

static char sc_get_key() {
  panic("TODO: get key system call");
}

static void *sc_allocate_ram(uint32_t pages) {
  return pd_user_allocate_anywhere_writable(active_task->page_directory, pages);
}

void const *syscall_table[] = {
  &sc_open_file,
  &sc_close_file,
  &sc_file_read,
  &sc_file_get_size,
  &sc_start_task,
  &sc_log_string,
  &sc_get_key,
  &sc_allocate_ram
};

extern void syscall_isr;
extern void quit_isr;
extern void yield_isr;

static void register_int(uint8_t n, void *isr, uint8_t dpl) {
  idt[n].addr_low = (uint32_t)isr & 0xffff;
  idt[n].addr_high = (uint32_t)isr >> 16;
  idt[n].cs = 0x10;
  idt[n].flags = IDT_PRESENT | (dpl << 5) | IDT_INT;
}

void init_idt() {
  for (uint16_t i = 0; i < 256; ++i) {
    idt[i].flags = 0;
    idt[i].zero = 0;
  }

  register_int(0x30, &syscall_isr, 3);
  register_int(0x38, &quit_isr, 3);
  register_int(0x39, &yield_isr, 3);

  outb(0x0021, 0xff);
  outb(0x00a1, 0xff);

  asm volatile (
    "lidt %0"
  : : "m" (idtr) : "al");
}