// This program emulates a two-pass assembler for a SIC Machine. It
// requires the presence of an 'assemble.txt' file in C:\CPROGS directory
// containing a program written for said machine. It then 'assembles' the
// code present in the file and outputs the object code into 'objcode.txt',
// also created in the same directory.

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

#define APOS 0x27

// GLOBAL VARIABLES

char OPTAB[18][7] = {"STL","JSUB","LDA","COMP","JEQ","J","STA","LDL","RSUB","LDX","TD","RD","STCH","JLT","STX","LDCH","WD","TIX"};
char OPVAL[18][3] = {"14","48","00","28","30","3C","0C","08","4C","04","E0","D8","54","38","10","50","DC","2C"};

char SYMTAB[20][10];
int SYMVAL[20], numberOfSymbols = 0;

int OPTABVal, SYMTABVal;

char outputString[30];

char gotLine[50][50], OPCODE[20], OPERAND[20], LABEL[20];

int nLines = 0, programLength, startAddress = 0, currentAddress = 0, progress = 0;

FILE *fpIN, *fpOUT;

char startAddressAsString[7] = {'0','0','0','0','\0'};

int processFile() {
	char c;
	int location = 0, endNow = 0;
	if((fpIN = fopen("c:/cprogs/assemble.txt", "r+")) == NULL) {
		printf("Error! File not found!\n" );
		return(1);
	}

	printf("File Opened! Reading contents...\n\n"); getch();

	c = getc(fpIN);
	while(endNow != 1) {
		if(c != '\n') {
			gotLine[nLines][location] = c;
			location++;
		}
		else {
			gotLine[nLines][location] = '\0';
			location = 0;
			while(gotLine[nLines][location] != '\0') {
				printf("%c", gotLine[nLines][location]);
				location++;
			}
			printf("\n");
			location = 0;
			nLines++;
		}
		if((c = getc(fpIN)) == EOF) {
			endNow = 1;
		}
	}
	printf("File has ended! Contents have been stored in local array. Closing file...");
	getch();
	fclose(fpIN);
	return(0);
}

void getCodesFromLine(int line) {
	int location = 0, nWords = 1, inLoc = 0;
	while(gotLine[line][location] != '\0') {
		if(gotLine[line][location] == ' ') {
			nWords++;
		}
		location++;
	}
	location = 0;
	if(nWords > 2) {
		while(gotLine[line][location] != ' ') {
			LABEL[inLoc] = gotLine[line][location];
			location++;
			inLoc++;
		}
		LABEL[inLoc] = '\0';
		inLoc = 0;
		location++;
		while(gotLine[line][location] != ' ') {
			OPCODE[inLoc] = gotLine[line][location];
			location++;
			inLoc++;
		}
		OPCODE[inLoc] = '\0';
		inLoc = 0;
		location++;
		while(gotLine[line][location] != '\0') {
			OPERAND[inLoc] = gotLine[line][location];
			location++;
			inLoc++;
		}
		OPERAND[inLoc] = '\0';
	}
	else if(nWords > 1) {
		while(gotLine[line][location] != ' '){
			OPCODE[inLoc] = gotLine[line][location];
			inLoc++;
			location++;
		}
		OPCODE[inLoc] = '\0';
		inLoc = 0;
		location++;
		while(gotLine[line][location] != '\0') {
			OPERAND[inLoc] = gotLine[line][location];
			inLoc++;
			location++;
		}
		OPERAND[inLoc] = '\0';
		
		LABEL[0] = 'N';
		LABEL[1] = 'U';
		LABEL[2] = 'L';
		LABEL[3] = 'L';
		LABEL[4] = '\0';
	}
	else {
		while(gotLine[line][location] != ' ' && gotLine[line][location] != '\0') {
			OPCODE[inLoc] = gotLine[line][location];
			inLoc++;
			location++;
		}
		OPCODE[inLoc] = '\0';
	
		OPERAND[0] = 'N';
		OPERAND[1] = 'U';
		OPERAND[2] = 'L';
		OPERAND[3] = 'L';
		OPERAND[4] = '\0';
		
		LABEL[0] = 'N';
		LABEL[1] = 'U';
		LABEL[2] = 'L';
		LABEL[3] = 'L';
		LABEL[4] = '\0';
	}
}

int opInt() {
        int b = 0, i = 0;
        while(OPERAND[i] != '\0') {
		b = b + OPERAND[i] - 48;
                b*=10;
                i++;
        }
        b/=10;
        return(b);
}

int isDuplicateLabel() {
	int i = 0;
	while(i < 18) {
		if(strcmp(LABEL, SYMTAB[i]) == 0)
			return(1);
		i++;
	}
	return(0);
}

int isOPERANDinSYMTAB() {
	int i = 0;
	while(i < numberOfSymbols) {
		if(strcmp(OPERAND, SYMTAB[i]) == 0) {
			SYMTABVal = SYMVAL[i];
			return(1);
		}
		i++;
	}
	return(0);
}

int isOPCODEValid() {
	int i = 0;
	while(i < 18) {
		if(strcmp(OPCODE, OPTAB[i]) == 0) {
			OPTABVal = i;
			return(1);
		}
		i++;
	}
	return(0);
}

void insertIntoSYMTAB(int location) {
	int i = numberOfSymbols;
	numberOfSymbols++;
	strcpy(SYMTAB[i], LABEL);
	SYMVAL[i] = location;
}

void initOutputFile() {
	char output[50] = {'H','\0'}, start[8], length[8], endline[2] = {'\n', '\0'};
	int nameLength, startLength, lengthLength;
	
	printf("\n\nInserting header record... Name: %s", LABEL);
	
	fpOUT = fopen("c:/cprogs/objcode.txt", "w+");
	
	itoa(startAddress, start, 10);
	itoa(programLength, length, 10);
	
	printf("\nStarting address: %s\nProgram Length: %s\n", start, length);
	
	nameLength = strlen(LABEL) + 1;
	startLength = strlen(start) + 1;
	lengthLength = strlen(length) + 1;
		
	strcat(output, LABEL);
	while(nameLength <= 7) {
		output[nameLength] = ' ';
		nameLength++;
	}
	while(startLength < 7) {
		output[nameLength] = '0';
		startLength++;
		nameLength++;
	}
	output[nameLength] = '\0';
	strcat(output, start);
	nameLength += startLength;
	while(lengthLength < 7) {
		output[nameLength] = '0';
		lengthLength++;
		nameLength++;
	}
	output[nameLength] = '\0';
	strcat(output, length);
	nameLength += lengthLength;
	
	output[nameLength] = '\0';
	strcat(output, endline);
	fputs(output, fpOUT);
}

void writeToFile(int lengthOfString) {
	char output[50] = {'T','\0'}, start[8], length[3], endline[2] = {'\n', '\0'};
	itoa(lengthOfString, length, 10);
	currentAddress += progress;
	progress = lengthOfString;
	itoa(currentAddress, start, 10);
	strcat(output, start);
	strcat(output, length);
	strcat(output, outputString);
	strcat(output, endline);
	fputs(output, fpOUT);
}

void writeEndRecordAndClose() {
	char output[50] = {'E','0','0','\0'};
	strcat(output, startAddressAsString);
	fputs(output, fpOUT);
	fclose(fpOUT);
}

int main() {
	int fileReadError = 0, LOCCTR, currentLine = 0, digit1, digit2, digit3, digit4, inLoc, constLength, i, j, lengthOfOutputString;

	char operationCode[10], operandAddress[5] = {'0','0','0','0','\0'}, tempOPERAND[20], tempString[10];

	clrscr();

	fileReadError = processFile();

	if(fileReadError == 1) {
		printf("\nPlease ensure that 'assemble.txt' is present in root of C drive.\nPress any key to exit...");
		getch();
		return(1);
	}

	// BEGIN Pass 1

	getCodesFromLine(currentLine);
	
	if(strcmp(OPCODE, "START") == 0) {
		startAddress = opInt();
		LOCCTR = startAddress;
		currentAddress = startAddress;
		itoa(startAddress, startAddressAsString, 10);
		currentLine++;
		getCodesFromLine(currentLine);
	}
	else
		LOCCTR = 0;

	printf("\n\nSYMTAB is as follows: ");
	while(strcmp(OPCODE, "END") != 0) {	// While OPCODE is not 'END'
		if(gotLine[currentLine][0] != '.') {	// If current line is not a comment line
			if(strcmp(LABEL, "NULL") != 0) {	// If there is a label
				if(isDuplicateLabel() == 1) {	// If there is a duplicate label in SYMTAB
					printf("\n\nError! Duplicate Label Encountered!\nThe assembly program is invalid. Press any key to exit...");
					getch();
					return(1);
				}
				else {	// If there is no duplicate
					insertIntoSYMTAB(LOCCTR);
					printf("\n%s - %d", LABEL, LOCCTR);
				}
			}
			if(isOPCODEValid() == 1)
				LOCCTR += 3;
			else if(strcmp(OPCODE, "WORD") == 0)
				LOCCTR += 3;
			else if(strcmp(OPCODE, "RESW") == 0)
				LOCCTR += (3 * opInt());
			else if(strcmp(OPCODE, "RESB") == 0)
				LOCCTR += 1000;
			else if(strcmp(OPCODE, "BYTE") == 0) {
				if(OPERAND[0] == 'X') {
					LOCCTR++;
				}
				else {
					LOCCTR += 3; // INCOMPLETE. This simplification is insufficient. Refer algorithm for detail.
				}
			}
			else {
				printf("\n\nError! Invalid Operation Code Encountered!\nThe assembly program is invalid. Press any key to exit...");
				getch();
				return(1);
			}
		}
		currentLine++;
		getCodesFromLine(currentLine);
	}
	programLength = LOCCTR - startAddress;
	getch();

	// END Pass 1

	currentLine = 0;
	outputString[0] = '\0';	// Purge outputString

	// BEGIN Pass 2

	getCodesFromLine(currentLine);

	if(strcmp(OPCODE, "START") == 0) {
		currentLine++;	
	}
	
	initOutputFile();	// write Header record to object program & initialize first Text Record
	
	getCodesFromLine(currentLine);
	
	while(strcmp(OPCODE, "END") != 0) {	//while OPCODE is not 'END'
		if(gotLine[currentLine][0] != '.') {	// If current line is not a comment line
			if(isOPCODEValid() == 1) {	// If OPCODE exists
				if(strcmp(OPERAND, "NULL") != 0) {	// If OPERAND is available
					if(isOPERANDinSYMTAB() == 1) {	// If OPERAND is in SYMTAB
						itoa(SYMTABVal, operandAddress, 10);	// strore SYMBOL value as Operand address
					}
					else {
						printf("\nError! Undefined Symbol Encountered on Line %d!\nContinuing execution by placing '0000'.", (currentLine + 1));
					}
				}
				else {	// Operand Address default value is '0000'
					operandAddress[0] = '0';
					operandAddress[1] = '0';
					operandAddress[2] = '0';
					operandAddress[3] = '0';
					operandAddress[4] = '\0';
				}
				strcpy(operationCode, OPVAL[OPTABVal]);	// set Operation Code
				strcat(outputString, OPVAL[OPTABVal]);
				strcat(outputString, operandAddress);
			}
			else if(strcmp(OPCODE, "BYTE") == 0 || strcmp(OPCODE, "WORD") == 0) {	// convert constant to object code
				if(strcmp(OPCODE, "WORD") == 0) {
					i = 0;
					constLength = strlen(OPERAND);
					while(constLength < 6) {
						tempOPERAND[i] = '0';
						constLength++;
						i++;
					}
					tempOPERAND[i] = '\0';
					strcat(tempOPERAND, OPERAND);
					strcat(outputString, tempOPERAND);
				}
				else {
					i = 2;
					j = 0;
					if(OPERAND[0] == 'X') {
						while(APOS != OPERAND[i]) {
							tempString[j] = OPERAND[i];
							j++;
							i++;
						}
						tempString[j] = '\0';
					}
					else {
						tempString[0] = '4';
						tempString[1] = '5';
						tempString[2] = '4';
						tempString[3] = 'F';
						tempString[4] = '4';
						tempString[5] = '6';
						tempString[6] = '\0';
					}
					strcat(outputString, tempString);
				}
			}
			if(strcmp(outputString, "000000") != 0) {
				printf("\nObject Code Array: %s", outputString);
				getch();
			}
			lengthOfOutputString = (strlen(outputString) / 2);
			if(lengthOfOutputString >= 12) {	// if object code will not fit into the current text record then
				writeToFile(lengthOfOutputString);	//write Text record to object program
				outputString[0] = '\0';	//initialize new Text record
				printf("\nObject Code Array has reached maximum size. Purging to file..."); getch();
			}
		}
		currentLine++;
		getCodesFromLine(currentLine);
	}
	printf("\nFinished assembling code...\nPurging remainging object code to file and writing End Record..."); getch();
	lengthOfOutputString = strlen(outputString);	// write last Text record to object program
	writeToFile(lengthOfOutputString);
	
	writeEndRecordAndClose();	// write End record to object program
	
	// END Pass 2
		
	printf("\nEnd Record has been written. Press any key to exit..."); getch();
	
	return(0);
}

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