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

#include "wv_mem.h"
#include "wv_err.h"

/* Detect alignment pre-C11 */
union wv_max_align { long l; double d; void *p; };

#define WV_ALIGNOF(type) offsetof(struct { char c; type member; }, member)
#define WV_ALIGNMENT  WV_ALIGNOF(union wv_max_align)
#define WV_ALIGN_MASK (WV_ALIGNMENT - 1)

#define WV_ARENA_MIN_SIZE  (256 * 1024)
#define WV_ARENA_RESERVED  WV_ALIGNMENT  /* Reserve 0 as the sentinel "null" ref */

struct wv_arena *wv_arena_create(size_t n)
{
	struct wv_arena *arena;

	if (n < WV_ARENA_MIN_SIZE)
		n = WV_ARENA_MIN_SIZE;

	arena = malloc(sizeof(struct wv_arena));
	if (arena == NULL)
		err(1, "malloc arena struct");

	arena->buf = malloc(n);
	if (arena->buf == NULL)
		err(1, "malloc arena buffer");

	arena->size = n;
	arena->offset = WV_ARENA_RESERVED;

	return arena;
}

wv_ref wv_alloc(struct wv_arena *arena, size_t n)
{
	wv_ref ref;
	unsigned char *new_buf;
	size_t aligned_n, new_size;

	if (n == 0)
		errx(1, "wv_alloc: zero-size allocation");

	if (n > SIZE_MAX - WV_ALIGN_MASK)
		errx(1, "wv_alloc: allocation size overflow");

	aligned_n = (n + WV_ALIGN_MASK) & ~WV_ALIGN_MASK;

	if (aligned_n > SIZE_MAX - arena->offset)
		errx(1, "wv_alloc: arena offset overflow");

	if (arena->offset + aligned_n > arena->size) {
		new_size = arena->size;
		while (new_size < arena->offset + aligned_n) {
			if (new_size > SIZE_MAX / 2)
				errx(1, "wv_alloc: arena growth overflow");
			new_size *= 2;
		}

		new_buf = realloc(arena->buf, new_size);
		if (new_buf == NULL)
			err(1, "realloc arena failed at %zu bytes", new_size);

		arena->buf  = new_buf;
		arena->size = new_size;
	}

	ref = (wv_ref)arena->offset;
	arena->offset += aligned_n;
	return ref;
}

void wv_arena_reset(struct wv_arena *arena)
{
	if (arena == NULL)
		return;

	memset(arena->buf, 0, arena->offset);
	arena->offset = WV_ARENA_RESERVED;
}

void wv_arena_destroy(struct wv_arena *arena)
{
	if (arena == NULL)
		return;

	free(arena->buf);
	free(arena);
}