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

#define HD_SECTOR_SIZE 512
#define PARTITION_TABLE_START 0x1BE
#define PARTITION_TABLE_SIZE 64

typedef struct {
	uint8_t bootSign;
	uint8_t startHead;
	uint8_t startSector:6;
	uint16_t startCylinder:10;
	uint8_t fsID;
	uint8_t endHead;
	uint8_t endSector:6;
	uint16_t endCylinder:10;
	uint32_t startLBA;
	uint32_t sectorCount;
}__attribute__((packed)) T_PartitionTable;

int main(int argc, char* argv[]) {
	if(argc == 4) {
		char *diskPath = argv[1];
		int partNum = atoi(argv[2]);
		char* field = argv[3];
		
		T_PartitionTable pt[4];
		
		if(partNum < 0 || partNum > 3) {
			fprintf(stderr, "Invalid partiton number\n");
			return -1;
		}

		int fd = open(diskPath, O_RDONLY, 0664);
		if(fd == -1) {
			close(fd);
			fprintf(stderr, "Error when openning the file <%s>\n", diskPath);
			return -2;
		}

		lseek(fd, PARTITION_TABLE_START, SEEK_SET);

		int bytesRead = read(fd, pt, PARTITION_TABLE_SIZE);
		if(bytesRead == -1) {
			close(fd);
			fprintf(stderr, "Error when reading the file <%s>\n", diskPath);
			return -3;
		}
		close(fd);

		if(!strcmp(field, "boot_sign"))
			printf("%u", pt[partNum].bootSign);
		else if(!strcmp(field, "start_head"))
			printf("%u", pt[partNum].startHead);
		else if(!strcmp(field, "start_sector"))
			printf("%u", pt[partNum].startSector);
		else if(!strcmp(field, "start_cylinder"))
			printf("%u", pt[partNum].startCylinder);
		else if(!strcmp(field, "fs_ID"))
			printf("%u", pt[partNum].fsID);
		else if(!strcmp(field, "end_head"))
			printf("%u", pt[partNum].endHead);
		else if(!strcmp(field, "end_sector"))
			printf("%u", pt[partNum].endSector);
		else if(!strcmp(field, "end_cylinder"))
			printf("%u", pt[partNum].endCylinder);
		else if(!strcmp(field, "start_LBA"))
			printf("%u", pt[partNum].startLBA);
		else if(!strcmp(field, "sector_count"))
			printf("%u", pt[partNum].sectorCount);
		else {
			perror("Invalid field name\n");
			return -4;
		}
	} else {
		fprintf(stderr, "[help] : readpt <disk> <partition> <field>\n");
		fprintf(stderr, "Valid field names : boot_sign,start_head,start_sector,start_cylinder,fs_ID,end_head,end_sector,end_cylinder,start_LBA,sectorCount\n");
		return -5;
	}
	return 0;
}