#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <inttypes.h>

#define DATABUF_LEN 16
char DATA_BUFFER[DATABUF_LEN]; // data buffer for funny casts

void
die(char *format, ...) {
	va_list args;
	va_start(args, format);
	vfprintf(stderr, format, args);
	va_end(args);

	exit(1);
}

/* this function performs required json escaping from stdin
 * and prints out the correct stuff
 */
void
json_string_stdin(int32_t *doc_size)
{
	int c;
	putchar('"');
	for (c = getchar(); c != 0x00 && c != EOF; c = getchar()) {
		*doc_size -= 1;
		switch (c) {
		case '"':
			fputs("\\\"", stdout);
			break;
		case '\\':
			fputs("\\\\", stdout);
			break;
		case '/':
			fputs("\\/", stdout);
			break;
		case '\b':
			fputs("\\b", stdout);
			break;
		case '\f':
			fputs("\\f", stdout);
			break;
		case '\n':
			fputs("\\n", stdout);
			break;
		case '\r':
			fputs("\\r", stdout);
			break;
		case '\t':
			fputs("\\t", stdout);
			break;
		default:
			if (c <= 0x1F) {
				fprintf(stderr, "warning: invalid control character %x in string, ignoring\n", c);
				continue;
			}
			putchar(c);
		}
	}
	putchar('"');
	*doc_size -= 1;
}

/* this function simply discards stdin while removing size
 * this is for array keys in an array
 */
void
json_trash_string_stdin(int32_t *doc_size)
{
	while (getchar() != 0x00) {
		*doc_size -= 1;
	}
	*doc_size -= 1;
}

// prints bson document as json, returns complete size of the document
int32_t
print_bson(uint8_t is_array)
{
	int32_t size;
	int32_t size_ret;
	int c;
	fread(&size, 4, 1, stdin);
	size_ret = size;
	size -= 4;

	if (is_array) {
		putchar('[');
	} else {
		putchar('{');
	}

	while (1) {
		c = getchar();
		size -= 1;

		if (c == 0x00) {
			if (size == 0) {
				if (is_array) {
					putchar(']');
				} else {
					putchar('}');
				}
				return size_ret;
			}
			die("bson2json: error: 0x00 byte reached prematurely! check your data.\n");
		}

		if (is_array) {
			json_trash_string_stdin(&size);
		} else {
			json_string_stdin(&size);
			putchar(':');
		}

		switch (c) {
		case 0x01: // double
			fread(&DATA_BUFFER, 8, 1, stdin);
			printf("%.19f", *((double*)DATA_BUFFER));
			size -= 8;
			break;
		case 0x02: case 0x0D: case 0x0E: // string, javascript code, symbol
			fread(&DATA_BUFFER, 4, 1, stdin);
			size -= 4;
			json_string_stdin(&size);
			break;
		case 0x03: // document
			size -= print_bson(0);
			break;
		case 0x04: // array
			size -= print_bson(1);
			break;
		case 0x05: // binary
			fread(&DATA_BUFFER, 4, 1, stdin);
			getchar(); // just throw the next char away
			size -= 5 + *((int32_t*)DATA_BUFFER);
			putchar('"');
			while (*((int32_t*)DATA_BUFFER) > 0) {
				c = getchar();
				printf("%02x", c);
				*((int32_t*)DATA_BUFFER) -= 1;
			}
			putchar('"');
			break;
		case 0x06: // undefined (deprecated)
			fputs("null", stdout);
			break;
		case 0x07: // objectid
			fread(&DATA_BUFFER, 4, 1, stdin);
			printf("{\"$ObjectId:timestamp\":%"PRIu32",", *((uint32_t*)DATA_BUFFER));
			memset(DATA_BUFFER, 0, 8);
			fread(&DATA_BUFFER, 5, 1, stdin);
			printf("\"$ObjectId:rand\":%"PRIu64",", *((uint64_t*)DATA_BUFFER));
			memset(DATA_BUFFER, 0, 4);
			fread(&DATA_BUFFER, 3, 1, stdin);
			printf("\"$ObjectId:counter\":%"PRIu32"}", *((uint32_t*)DATA_BUFFER));
			size -= 12;
			break;
		case 0x08: // boolean
			fread(&DATA_BUFFER, 1, 1, stdin);
			if (*DATA_BUFFER == 0x00) {
				fputs("false", stdout);
			} else {
				// technically it should only be true if it == 0x01
				// and invalid otherwise but idc
				fputs("true", stdout);
			}
			size -= 1;
			break;
		case 0x09: case 0x12: // 64 bit ints (utc datetime and int64)
			fread(&DATA_BUFFER, 8, 1, stdin);
			printf("%"PRId64, *((int64_t*)DATA_BUFFER));
			size -= 8;
			break;
		case 0x0A: // null
			fputs("null", stdout);
			break;
		case 0x0B: // regex
			fputs("{\"$regex:pattern\":", stdout);
			json_string_stdin(&size);
			fputs(",\"$regex:options\":", stdout);
			json_string_stdin(&size);
			putchar('}');
			break;
		case 0x0C: // dbpointer
			fread(&DATA_BUFFER, 4, 1, stdin);
			fputs("{\"$DBPointer:string\":", stdout);
			json_string_stdin(&size);
			memset(&DATA_BUFFER, 0, 16);
			fread(&DATA_BUFFER, 12, 1, stdin);
			printf(",\"$DBPointer:pointer\":%"PRIu64"}", *((uint64_t*)DATA_BUFFER));
			size -= 16;
			break;
		case 0x0F: // code with scope
			fread(&DATA_BUFFER, 4, 1, stdin); // entire
			fread(&DATA_BUFFER, 4, 1, stdin); // string
			fputs("{\"$code_w_s:code\":", stdout);
			json_string_stdin(&size);
			fputs(",\"$code_w_s:scope\":", stdout);
			size -= 8 + print_bson(0);
			putchar('}');
			break;
		case 0x10: // 32 bit int
			fread(&DATA_BUFFER, 4, 1, stdin);
			printf("%"PRId32, *((int32_t*)DATA_BUFFER));
			size -= 4;
			break;
		case 0x11: // timestamp (uint64)
			fread(&DATA_BUFFER, 8, 1, stdin);
			printf("%"PRId64, *((uint64_t*)DATA_BUFFER));
			size -= 8;
			break;
		case 0x13: // 128-bit decimal
			fputs("warning: decimal128 number in input. these are a binary string until c23 support is better\n", stderr);
			putchar('"');
			for (uint8_t i = 0; i < 16; i++) {
				printf("%02x", getchar());
			}
			putchar('"');
			size -= 16;
			break;
		case 0xFF: case 0x7F: // min/max type idc about these
			fputs("null", stdout);
			break;
		default:
			die("bson2json: error: unknown byte for item type. this is most likely the result of some other data bug.\n");
		}
		if (size > 1) {
			putchar(',');
		}
	}
}

int
main(void)
{
	print_bson(0);
	printf("\n");

	return 0;
}