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

#include "byteorder.h"
#include "lbx.h"

#define LBX_MAGIC 0x0000fead

int lbx_errno = 0;

struct lbx_state {
	FILE *f;
	long offset;

	uint16_t nfiles;
	uint32_t offsets[];
};

struct lbx_state *lbx_fopen(FILE *f)
{
	struct lbx_state *new = NULL;
	uint16_t nfiles, version;
	uint32_t magic;

	if (fread(&nfiles,  sizeof nfiles,  1, f) != 1) goto readerr;
	if (fread(&magic,   sizeof magic,   1, f) != 1) goto readerr;
	if (fread(&version, sizeof version, 1, f) != 1) goto readerr;

	nfiles  = letohs(nfiles);
	magic   = letohl(magic);
	version = letohs(version);

	if (magic != LBX_MAGIC) {
		lbx_errno = LBX_EMAGIC;
		return NULL;
	}
	
	new = malloc(sizeof *new + (nfiles+1)*(sizeof *new->offsets));
	if (!new) {
		lbx_errno = -errno;
		return NULL;
	}
	
	*new = (struct lbx_state){
		.nfiles = nfiles,
		.f = f,
	};
	
	if (fread(new->offsets, sizeof *new->offsets, nfiles+1, f) != nfiles+1)
		goto readerr;

	return new;
readerr:
	if (feof(f)) {
		lbx_errno = LBX_EEOF;
	} else {
		lbx_errno = -errno;
	}

	free(new);
	return NULL;
}

struct lbx_state *lbx_open(const char *path)
{
	struct lbx_state *new = NULL;
	FILE *f;
	
	if ((f = fopen(path, "rb"))) {
		new = lbx_fopen(f);
	} else {
		lbx_errno = -errno;
	}

	return new;
}

size_t lbx_numfiles(struct lbx_state *lbx)
{
	return lbx->nfiles;
}

void lbx_close(struct lbx_state *lbx)
{
	if (!lbx) return;

	fclose(lbx->f);
	free(lbx);
}

const char *lbx_strerror(void)
{
	if (lbx_errno < 0)
		return strerror(-lbx_errno);

	switch (lbx_errno) {
	case LBX_ESUCCESS: return "Success";
	case LBX_EMAGIC:   return "Bad magic number";
	case LBX_EEOF:     return "Unexpected end-of-file";
	}

	return "Unknown error";
}