/*
 * Copyright (C) 2020-2021  Tomasz Kramkowski <tk@the-tk.com>
 * SPDX-License-Identifier: MIT
 */
#include <ctype.h>
#include <inttypes.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>

#include "common.h"
#include "pack.h"
#include "trace.h"

static void write_val(unsigned char *buf, size_t size, enum pack_endian e, uintmax_t val)
{
	for (size_t i = 0; i < size; i++)
		buf[i] = (val >> (e == PACK_ENDIAN_LITTLE ? i : size - i - 1) * 8) & 0xff;
}

enum pack_status pack(void *buf_, size_t size, const char *fmt, ...)
{
	enum pack_endian endianness = PACK_ENDIAN_BIG;
	unsigned char *buf = buf_;
	size_t offset = 0;
	va_list ap;

	tr_call("pack(%p, %" PRIuSIZE ", %s, ...)", (void *)buf, size, fmt);

	va_start(ap, fmt);

	for (int i = 0; fmt[i] != '\0'; i++) {
		bool sign;
		size_t s;
		union { uintmax_t unsigned_; intmax_t signed_; } v;
		tr_debug("i: %d, fmt[i]: %c", i, fmt[i]);
		sign = islower(fmt[i]);
		switch (fmt[i]) {
		case '>': endianness = PACK_ENDIAN_BIG; continue;
		case '<': endianness = PACK_ENDIAN_LITTLE; continue;
		#define T(type, sign, c_type, va_type) \
			case (char)PACK_TYPE_##type: \
				v.sign##_ = va_arg(ap, sign va_type); \
				break;
		ITYPE_MACROS
		#undef T
		case 'x': v.unsigned_ = 0; sign = false; break;
		default: return PACK_FMTINVAL;
		}
		tr_debug("i: %d, fmt[i]: %c, sign: %ssigned", i, fmt[i], sign ? "" : "un");

		s = getsize(fmt[i]);
		tr_debug("s: %" PRIuSIZE, s);
		if (s == (size_t)-1) return PACK_FMTINVAL;

		if (size - offset < s) return PACK_TOOSMALL;

		if (sign) {
			intmax_t n = v.signed_;
			tr_debug("val.s: %" PRIdMAX, v.signed_);
			if (v.signed_ >= 0) {
				v.unsigned_ = n;
			} else {
				uintmax_t offt = BITMASK(s * 8);
				n += 1;
				v.unsigned_ = offt + n;
			}
		}
		tr_debug("val.u: %" PRIuMAX, v.unsigned_);
		write_val(&buf[offset], s, endianness, v.unsigned_);
		offset += s;
	}

	va_end(ap);

	return PACK_OK;
}