#include <stdio.h>
#include <stdlib.h>

#include "upkg.h"
#include "pack.h"

struct upkg_table {
	size_t offset;
	size_t count;
};

struct upkg_private {
	FILE *f;

	struct upkg_table names, exports, imports;
	unsigned char guid[16];
};

static struct upkg *init_upkg(unsigned char hdr[static UPKG_HDR_SIZE])
{
	struct upkg *pkg;

	pkg = malloc(sizeof *pkg);
	if (!pkg) {
		return NULL;
	}

	pkg->priv = malloc(sizeof *pkg->priv);
	if (!pkg->priv) {
		free(pkg);
		return NULL;
	}

	pkg->version = unpack_16_le(hdr+4);
	pkg->license = unpack_16_le(hdr+6);
	pkg->flags   = unpack_32_le(hdr+8);

	pkg->priv->names = (struct upkg_table) {
		.count  = unpack_32_le(hdr+12),
		.offset = unpack_32_le(hdr+16),
	};
	pkg->priv->exports = (struct upkg_table) {
		.count  = unpack_32_le(hdr+20),
		.offset = unpack_32_le(hdr+24),
	};
	pkg->priv->imports = (struct upkg_table) {
		.count  = unpack_32_le(hdr+28),
		.offset = unpack_32_le(hdr+32),
	};

	return pkg;
}

struct upkg *upkg_fopen(const char *path)
{
	unsigned char hdr_buf[UPKG_HDR_SIZE];
	struct upkg *pkg;
	FILE *f;
	
	f = fopen(path, "rb");
	if (!f) {
		return NULL;
	}

	if (fread(hdr_buf, sizeof hdr_buf, 1, f) != 1) {
		goto err;
	}

	if (unpack_32_le(hdr_buf) != UPKG_HDR_MAGIC) {
		goto err;
	}

	pkg = init_upkg(hdr_buf);
	if (!pkg) {
		goto err;
	}

	pkg->priv->f = f;
	return pkg;
err:
	fclose(f);
	return NULL;
}