#ifndef ARENA_H
#define ARENA_H

#include <stddef.h> // size_t

struct arena_ctx {
    void *buffer;
    size_t size;
    size_t offset;
};


#define ARENA_CTX_INIT(buffer, sz) (struct arena_ctx){(buffer), (sz), 0}
void *arena_allocate(struct arena_ctx *ctx, size_t sz);
void arena_reset(struct arena_ctx *ctx);

#ifdef ARENA_IMPLEMENTATION
#define ARENA_ALLIGNMENT 2

// #include <assert.h>
void *arena_allocate(struct arena_ctx *ctx, size_t sz)
{
    if(sz % ARENA_ALLIGNMENT != 0)
        sz += ARENA_ALLIGNMENT - (sz % ARENA_ALLIGNMENT);

    if(ctx->offset + sz > ctx->size) return NULL;

    void *off = (void *)((intptr_t)ctx->buffer + ctx->offset);
    ctx->offset += sz;

    // assert(((intptr_t)off & 0x1) == 0);
    return off;
}

void arena_reset(struct arena_ctx *ctx) { ctx->offset = 0; }

#endif
#endif