/* SPDX-License-Identifier: MIT */
/*
 * konsave.c
 *
 * Copyright (c) 2026 KonAki
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "konsave.h"

#include <stdio.h>
#include <string.h>

/*** checksum ***/

static uint32_t crc32(const uint8_t *p, size_t n)
{
	uint32_t crc = 0xFFFFFFFFu;
	size_t i;
	int bit;

	for (i = 0; i < n; i++) {
		crc ^= p[i];
		for (bit = 0; bit < 8; bit++) crc = (crc >> 1) ^ (0xEDB88320u & (0u - (crc & 1u)));
	}
	return ~crc;
}

/*** writing ***/

static void putAt(uint8_t *p, uint32_t v)
{
	p[0] = (uint8_t)(v & 0xFF);
	p[1] = (uint8_t)((v >> 8) & 0xFF);
	p[2] = (uint8_t)((v >> 16) & 0xFF);
	p[3] = (uint8_t)((v >> 24) & 0xFF);
}

static uint32_t getAt(const uint8_t *p)
{
	return (uint32_t)p[0] | ((uint32_t)p[1] << 8) | ((uint32_t)p[2] << 16) | ((uint32_t)p[3] << 24);
}

static int room(kon_saveWriter_t *w, size_t n)
{
	if (w->error) return 0;
	if (!w->buf || n > w->cap - w->len) {
		w->error = 1;
		return 0;
	}
	return 1;
}

static void closeChunk(kon_saveWriter_t *w)
{
	if (!w->open || w->error) return;
	if (w->len - w->chunk - 8 > 0xFFFFFFFFu) {
		w->error = 1;
		return;
	}
	putAt(w->buf + w->chunk + 4, (uint32_t)(w->len - w->chunk - 8));
	w->open = 0;
}

void kon_saveBegin(kon_saveWriter_t *w, void *buf, size_t cap, uint32_t version)
{
	kon_saveWriter_t zero = {0};

	*w = zero;
	w->buf = buf;
	w->cap = buf ? cap : 0;
	if (!room(w, 8)) return;
	memcpy(w->buf, "KONS", 4);
	putAt(w->buf + 4, version);
	w->len = 8;
}

void kon_saveChunk(kon_saveWriter_t *w, const char *tag)
{
	closeChunk(w);
	if (!tag || strlen(tag) != 4 || !room(w, 8)) {
		w->error = 1;
		return;
	}
	w->chunk = w->len;
	memcpy(w->buf + w->len, tag, 4);
	putAt(w->buf + w->len + 4, 0);
	w->len += 8;
	w->open = 1;
}

void kon_savePutBytes(kon_saveWriter_t *w, const void *data, size_t n)
{
	if (!w->open) {
		w->error = 1;
		return;
	}
	if (!room(w, n)) return;
	if (n) memcpy(w->buf + w->len, data, n);
	w->len += n;
}

void kon_savePutU8(kon_saveWriter_t *w, unsigned v)
{
	uint8_t b = (uint8_t)(v & 0xFF);

	kon_savePutBytes(w, &b, 1);
}

void kon_savePutU16(kon_saveWriter_t *w, unsigned v)
{
	uint8_t b[2];

	b[0] = (uint8_t)(v & 0xFF);
	b[1] = (uint8_t)((v >> 8) & 0xFF);
	kon_savePutBytes(w, b, 2);
}

void kon_savePutU32(kon_saveWriter_t *w, uint32_t v)
{
	uint8_t b[4];

	putAt(b, v);
	kon_savePutBytes(w, b, 4);
}

void kon_savePutI32(kon_saveWriter_t *w, int32_t v)
{
	kon_savePutU32(w, (uint32_t)v);
}

void kon_savePutF32(kon_saveWriter_t *w, float v)
{
	uint32_t bits;

	memcpy(&bits, &v, sizeof bits);
	kon_savePutU32(w, bits);
}

void kon_savePutString(kon_saveWriter_t *w, const char *s)
{
	size_t n = s ? strlen(s) : 0;

	if (n > 65535u) n = 65535u;
	kon_savePutU16(w, (unsigned)n);
	kon_savePutBytes(w, s, n);
}

void kon_savePutSwitches(kon_saveWriter_t *w, const uint8_t *switches, int count)
{
	int i;

	if (count < 0 || !switches) count = 0;
	kon_savePutU32(w, (uint32_t)count);
	for (i = 0; i < count; i++) kon_savePutU8(w, switches[i] ? 1 : 0);
}

void kon_savePutVars(kon_saveWriter_t *w, const int32_t *vars, int count)
{
	int i;

	if (count < 0 || !vars) count = 0;
	kon_savePutU32(w, (uint32_t)count);
	for (i = 0; i < count; i++) kon_savePutI32(w, vars[i]);
}

size_t kon_saveEnd(kon_saveWriter_t *w)
{
	closeChunk(w);
	if (!room(w, 4)) return 0;
	putAt(w->buf + w->len, crc32(w->buf, w->len));
	w->len += 4;
	return w->len;
}

/*** reading ***/

int kon_saveOpen(kon_saveReader_t *r, const void *buf, size_t len)
{
	const uint8_t *p = buf;
	size_t at;

	memset(r, 0, sizeof *r);
	if (!p || len < 12 || memcmp(p, "KONS", 4) != 0) return 0;
	if (crc32(p, len - 4) != getAt(p + len - 4)) return 0;
	at = 8;
	while (at < len - 4) {
		size_t size;

		if (len - 4 - at < 8) return 0;
		size = getAt(p + at + 4);
		if (size > len - 4 - at - 8) return 0;
		at += 8 + size;
	}
	r->buf = p;
	r->len = len;
	r->version = getAt(p + 4);
	return 1;
}

int kon_saveFind(const kon_saveReader_t *r, const char *tag, kon_saveCursor_t *c)
{
	size_t at = 8;

	c->p = c->end = NULL;
	c->error = 0;
	if (!r->buf || !tag || strlen(tag) != 4) {
		c->error = 1;
		return 0;
	}
	while (at + 8 <= r->len - 4) {
		size_t size = getAt(r->buf + at + 4);

		if (memcmp(r->buf + at, tag, 4) == 0) {
			c->p = r->buf + at + 8;
			c->end = c->p + size;
			return 1;
		}
		at += 8 + size;
	}
	c->error = 1;
	return 0;
}

void kon_saveGetBytes(kon_saveCursor_t *c, void *out, size_t n)
{
	if (c->error || !c->p || (size_t)(c->end - c->p) < n) {
		c->error = 1;
		if (out) memset(out, 0, n);
		return;
	}
	if (n) memcpy(out, c->p, n);
	c->p += n;
}

unsigned kon_saveGetU8(kon_saveCursor_t *c)
{
	uint8_t b = 0;

	kon_saveGetBytes(c, &b, 1);
	return b;
}

unsigned kon_saveGetU16(kon_saveCursor_t *c)
{
	uint8_t b[2];

	kon_saveGetBytes(c, b, 2);
	return (unsigned)b[0] | ((unsigned)b[1] << 8);
}

uint32_t kon_saveGetU32(kon_saveCursor_t *c)
{
	uint8_t b[4];

	kon_saveGetBytes(c, b, 4);
	return getAt(b);
}

int32_t kon_saveGetI32(kon_saveCursor_t *c)
{
	uint32_t v = kon_saveGetU32(c);

	return v > 0x7FFFFFFFu ? -(int32_t)(0xFFFFFFFFu - v) - 1 : (int32_t)v;
}

float kon_saveGetF32(kon_saveCursor_t *c)
{
	uint32_t bits = kon_saveGetU32(c);
	float v;

	memcpy(&v, &bits, sizeof v);
	return v;
}

void kon_saveGetString(kon_saveCursor_t *c, char *out, size_t size)
{
	size_t n = kon_saveGetU16(c);

	if (c->error || (size_t)(c->end - c->p) < n) {
		c->error = 1;
		if (out && size) out[0] = '\0';
		return;
	}
	if (out && size) {
		size_t keep = n < size - 1 ? n : size - 1;

		memcpy(out, c->p, keep);
		out[keep] = '\0';
	}
	c->p += n;
}

int kon_saveGetSwitches(kon_saveCursor_t *c, uint8_t *switches, int count)
{
	uint32_t saved = kon_saveGetU32(c);
	uint32_t i;

	for (i = 0; i < saved; i++) {
		unsigned v = kon_saveGetU8(c);

		if (c->error) break;
		if (switches && i < (uint32_t)count) switches[i] = v ? 1 : 0;
	}
	for (i = saved; switches && i < (uint32_t)count; i++) switches[i] = 0;
	return c->error ? 0 : (saved > 0x7FFFFFFFu ? 0x7FFFFFFF : (int)saved);
}

int kon_saveGetVars(kon_saveCursor_t *c, int32_t *vars, int count)
{
	uint32_t saved = kon_saveGetU32(c);
	uint32_t i;

	for (i = 0; i < saved; i++) {
		int32_t v = kon_saveGetI32(c);

		if (c->error) break;
		if (vars && i < (uint32_t)count) vars[i] = v;
	}
	for (i = saved; vars && i < (uint32_t)count; i++) vars[i] = 0;
	return c->error ? 0 : (saved > 0x7FFFFFFFu ? 0x7FFFFFFF : (int)saved);
}

/*** files ***/

int kon_saveWriteFile(const char *path, const void *buf, size_t len)
{
	char temp[1024];
	FILE *f;
	size_t n;

	if (!path || (!buf && len)) return 0;
	n = strlen(path);
	if (n + 5 > sizeof temp) return 0;
	memcpy(temp, path, n);
	memcpy(temp + n, ".tmp", 5);
	f = fopen(temp, "wb");
	if (!f) return 0;
	if ((len && fwrite(buf, 1, len, f) != len) || fflush(f) != 0) {
		fclose(f);
		remove(temp);
		return 0;
	}
	if (fclose(f) != 0) {
		remove(temp);
		return 0;
	}
	if (rename(temp, path) != 0) {
		remove(path);
		if (rename(temp, path) != 0) {
			remove(temp);
			return 0;
		}
	}
	return 1;
}

long kon_saveReadFile(const char *path, void *buf, size_t cap)
{
	FILE *f;
	size_t n;
	int extra;

	if (!path || (!buf && cap)) return -1;
	f = fopen(path, "rb");
	if (!f) return -1;
	n = cap ? fread(buf, 1, cap, f) : 0;
	extra = fgetc(f);
	fclose(f);
	if (extra != EOF || n > 0x7FFFFFFFu) return -1;
	return (long)n;
}