#include "arena_allocator.h"
#include <assert.h>
#include <stddef.h>
#include <stdlib.h>

#define DEFAUL_REGION_SIZE 1048576 /* 8 * 1024 * 1024 = 8MB */

Region *new_region(size_t capacity) {
  if (capacity < DEFAUL_REGION_SIZE) {
    capacity = DEFAUL_REGION_SIZE;
  }
  Region *region = malloc(capacity + sizeof(Region));
  assert(region != NULL);
  *region = (Region){.next = NULL, .capacity = capacity, .cursor = 0};
  return region;
}

Arena arena_init(Arena *parent, size_t capacity) {
  Region *region = new_region(capacity);

  if (parent != NULL) {
    // Allocate new arena in parent to reduce likelyhood of loss
    Arena *current_arena = arena_alloc(parent, sizeof(Arena));
    *current_arena =
        (Arena){.begin = region, .end = region, .child = NULL, .sibling = NULL};

    // if parent has no children this arena is now it's child
    if (parent->child == NULL) {
      parent->child = current_arena;
      return *current_arena;
    }

    // Push the arena onto the first childs sibling list
    current_arena->sibling = parent->child;
    parent->child = current_arena;
    return *current_arena;
  }

  // This is the root of the arena tree
  Arena arena = {
      .begin = region, .end = region, .child = NULL, .sibling = NULL};
  return arena;
}

void arena_deinit(Arena *arena) {
  if (arena == NULL) {
    return;
  }
  // Recursively deinit children
  while (arena->child != NULL) {
    Arena *current_child = arena->child;
    arena->child = current_child->sibling;
    arena_deinit(current_child);
  }

  // actually free the data
  assert(arena->begin != NULL && arena->end != NULL);
  Region *region = arena->begin;
  while (region != NULL) {
    Region *next_region = region->next;
    free(region);
    region = next_region;
  }

  *arena = (Arena){.begin = NULL, .end = NULL};
}

void *arena_alloc(Arena *arena, size_t size) {
  // TODO: only align when needed
  size = (size + 7) & ~7; // align size increase to multiple of 8
  Region *region = arena->end;
  assert(region != NULL);

  if (region->cursor + size > region->capacity) {
    region->next = new_region(size);
    arena->end = region->next;
    region = region->next;
  }

  void *result = &region->data[region->cursor];
  region->cursor += size;
  return result;
}

// void *arena_clear(Arena *arena) {
//   arena->size = 0;
//   return arena->data;
// }