/* Calcite, src/kernel/scheduler.c
 * Copyright 2025-2026 Benji Dial
 *
 * 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 3 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, see <https://www.gnu.org/licenses/>.
 */

#include "scheduler.h"
#include "process.h"
#include "utility.h"
#include "debug.h"
#include "heap.h"

struct continuation_queue ready_continuations;

void init_scheduler() {
  create_queue(&ready_continuations, 128);
}

//defined in scheduler.asm
[[noreturn]] void resume_continuation(const struct continuation_info *info);

[[noreturn]] void resume_next_continuation() {

  running_thread = 0;

  struct continuation_info ci;
  while (!take_from_queue(&ready_continuations, &ci)) {
    __asm__ ("sti");
    __asm__ ("hlt");
    __asm__ ("cli");
  }

  assert(running_thread == 0)
  assert(ci.running_thread != 0)
  resume_continuation(&ci);

}

void create_queue(struct continuation_queue *queue, int buffer_size) {
  queue->cis = heap_alloc(buffer_size * sizeof(struct continuation_info));
  queue->next_read_index = 0;
  queue->buffer_size = buffer_size;
  queue->count = 0;
}

void destroy_queue(struct continuation_queue *queue) {
  assert(queue->count == 0)
  heap_dealloc(queue->cis, queue->buffer_size * sizeof(struct continuation_info));
}

void add_to_queue(struct continuation_queue *queue, struct continuation_info *ci) {

  if (queue->count == queue->buffer_size) {

    struct continuation_info *new_buffer =
      heap_alloc(2 * queue->buffer_size * sizeof(struct continuation_info));

    memcpy(
      new_buffer, &queue->cis[queue->next_read_index],
      (queue->buffer_size - queue->next_read_index) * sizeof(struct continuation_info));
    memcpy(
      &new_buffer[queue->buffer_size - queue->next_read_index],
      queue->cis, queue->next_read_index * sizeof(struct continuation_info));

    heap_dealloc(queue->cis, queue->buffer_size * sizeof(struct continuation_info));
    queue->cis = new_buffer;
    queue->buffer_size *= 2;
    queue->next_read_index = 0;

  }

  memcpy(
    &queue->cis[(queue->next_read_index + queue->count) % queue->buffer_size],
    ci, sizeof(struct continuation_info));
  ++queue->count;

}

int take_from_queue(struct continuation_queue *queue, struct continuation_info *ci) {

  if (queue->count == 0)
    return 0;

  memcpy(ci, &queue->cis[queue->next_read_index], sizeof(struct continuation_info));
  queue->next_read_index = (queue->next_read_index + 1) % queue->buffer_size;
  --queue->count;
  return 1;

}