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

// typedef uint8_t bool;
#define true 1
#define false 0

typedef struct
{
	uint8_t BootJumpInstruction[3];
	uint8_t OemIdentifier[8];
	uint16_t BytesPerSector;
	uint8_t SectorsPerCluster;
	uint16_t ReservedSectors;
	uint8_t FatCount;
	uint16_t DirEntryCount;
	uint16_t TotalSectors;
	uint8_t MediaDescriptorType;
	uint16_t SectorsPerFat;
	uint16_t SectorsPerTrack;
	uint16_t Heads;
	uint32_t HiddenSectors;
	uint32_t LargeSectorCount;
	
//Extended Boot Record
	uint8_t DriveNumber;
	uint8_t _Reserved;
	uint8_t Signature;
	uint32_t VolumeId;			//Serial Can be whatever
	uint8_t VolumeLabel[11];		//11 Bytes MUST Be padded with spaces!
	uint8_t SystemId[8];		//8 Bytes padded with spaces (use MSWIN4.1 for best compatibility!)
	
} __attribute__((packed)) BootSector;

typedef struct
{
	uint8_t Name[11];
	uint8_t Attributes;
	uint8_t _Reserved;
	uint8_t CreatedTimeTenths;
	uint16_t CreatedTime;
	uint16_t CreatedDate;
	uint16_t AccessedDate;
	uint16_t FirstClusterHigh;
	uint16_t ModifiedTime;
	uint16_t ModifiedDate;
	uint16_t FirstClusterLow;
	uint32_t Size;
	
} __attribute__((packed)) DirectoryEntry;

BootSector g_BootSector;
uint8_t* g_Fat = NULL;
DirectoryEntry* g_RootDirectory = NULL;
uint32_t g_RootDirectoryEnd;

bool readBootSector(FILE* disk)
 {
 	return fread(&g_BootSector, sizeof(g_BootSector), 1, disk) > 0;
 }

bool readSectors(FILE* disk, uint32_t lba, uint32_t count, void* bufferout)
{
	bool ok = true;
	ok = ok && (fseek(disk, lba * g_BootSector.BytesPerSector, SEEK_SET) == 0);
	ok = ok && (fread(bufferout, g_BootSector.BytesPerSector, count, disk) == count);
	return ok;
}

bool readFat(FILE* disk)
{
	g_Fat = (uint8_t*) malloc(g_BootSector.SectorsPerFat * g_BootSector.BytesPerSector);
	return readSectors(disk, g_BootSector.ReservedSectors, g_BootSector.SectorsPerFat, g_Fat);
}

bool readRootDirectory(FILE* disk)
{
	uint32_t lba = g_BootSector.ReservedSectors + g_BootSector.SectorsPerFat * g_BootSector.FatCount;
	uint32_t size = sizeof(DirectoryEntry) * g_BootSector.DirEntryCount;
	uint32_t sector = (size / g_BootSector.BytesPerSector);
	if (size % g_BootSector.BytesPerSector > 0)
		sector++;
		
	g_RootDirectoryEnd = lba + sector;
	g_RootDirectory = (DirectoryEntry*) malloc(sector * g_BootSector.BytesPerSector);
	return readSectors(disk, lba, sector, g_RootDirectory);
}

DirectoryEntry* findFile(const char* name)
{
	for (uint32_t i = 0; i < g_BootSector.DirEntryCount; i++)
	{
		if (memcmp(name, g_RootDirectory[i].Name, 11) == 0)
		return &g_RootDirectory[i];
		
	}

	return NULL;
}

bool readFile(DirectoryEntry* fileEntry, FILE* disk, uint8_t* outputBuffer)
{
	bool ok = true;
	uint16_t currentCluster = fileEntry->FirstClusterLow;

	do {
		uint32_t lba = g_RootDirectoryEnd + (currentCluster - 2) * g_BootSector.SectorsPerCluster;
		ok = ok && readSectors(disk, lba, g_BootSector.SectorsPerCluster, outputBuffer);
		outputBuffer += g_BootSector.SectorsPerCluster * g_BootSector.BytesPerSector;

		uint32_t fatIndex = currentCluster * 3 / 2;
		if (currentCluster % 2 == 0)
			currentCluster = (*(uint16_t*)(g_Fat + fatIndex)) & 0x0FFF;
		else
			currentCluster = (*(uint16_t*)(g_Fat + fatIndex)) >> 4;
			
	} while (ok && currentCluster < 0x0FF8);

	return ok;
}

int main(int argc, char** argv)
{
	if (argc < 3){
		printf("Syntax: %s <disk image> <file name>\n", argv[0]);
		return -1;
	}

	FILE* disk = fopen(argv[1], "rb");
	if (!disk) {
		fprintf(stderr, "Cannot open disk image %s!\n", argv[1]);
		return -1;
	}

	if (!readBootSector(disk)) {
		fprintf(stderr, "Could not read boot sector!\n");
		return -2;
	}

	if (!readFat(disk)) {
		fprintf(stderr, "Could not read FAT!\n");
		free(g_Fat);
		return -3;
	}

	if (!readRootDirectory(disk)) {
		fprintf(stderr, "Could not read root!\n");
		free(g_Fat);
		free(g_RootDirectory);
		return -4;
	}

	DirectoryEntry* fileEntry = findFile(argv[2]);
	if (!fileEntry) {
		fprintf(stderr, "Could not locate file %s!\n", argv[2]);
		free(g_Fat);
		free(g_RootDirectory);
		return -5;
	}

	uint8_t* buffer = (uint8_t*) malloc(fileEntry->Size + g_BootSector.BytesPerSector);
	if (!readFile(fileEntry, disk, buffer)) {
		fprintf(stderr, "Could not read file %s!\n", argv[2]);
		free(g_Fat);
		free(g_RootDirectory);
		free(buffer);
		return -5;
	}

	for (size_t i = 0; i < fileEntry->Size; i++)
	{
		if (isprint(buffer[i])) fputc(buffer[i], stdout);
		//else printf("<%02x>", buffer[i]);
	}
	printf("\n");
	
	free(g_Fat);
	free(g_RootDirectory);
	return 0;
}