/*******************************************************
* compression.c
* This program performs Huffman Compression on
* the text in an input file and outputs the
* compressed data to a specified output file
* Useage: compression <inputfile.txt> <outputfile.txt>
********************************************************/

#include "compress.h"

void main(int argc, char *argv[]) {
	FILE *input,*output;			/*Pointers to input and output files*/
	qtptr qfirst;					/*Pointer to first element in queue*/

	/*Check for proper number of arguments and exit if not*/
	if(argc != 3) {			
		printf("Usage: compress <inputfilename.txt> <outputfilename.txt>\n");
		return;
	}

	/*Attempt to open designated input file in read-only mode*/
	input = fopen(argv[1],"r");
	/*Check to see that file has been successfully open and exit if not*/
	if(!input) {
		printf("Error: Cannot open input file.\n"); 
		printf("File should be in the same folder as compress.exe.\n");
		return;
	}

	/*Attempt to open designated output file in write-only mode*/
	output = fopen(argv[2],"w");
	/*Check to see that file has been successfully open and exit if not*/
	if(!output) {
		printf("Error: Cannot create output file.\n");
		printf("Invalid name for output file.\n");
		return;
	}
	/*Function called to create queue*/
	qfirst = createQueue(input,output);
	/*Reset input to beginning of input file by closing and opening the file again*/
	fclose(input);
	input = fopen(argv[1],"r");
	/*Compress the data of the input file and output the result to the output file*/
	encode(qfirst,input,output);
	
	/*Close both the input and output files*/
	fclose(input);
	fclose(output);
}

/*****************************************************************
* createQueue: This	function obtains a FILE	argument and 
* creates a	priority queue based upon the contents of the file.
* it then returns the pointer to the first element in the queue.
******************************************************************/

qtptr createQueue (FILE *input, FILE *output) {

	char ctemp;						/*Temporary	character*/
	qtptr qfirst;					/*Pointer to first element in priority queue*/
	
	qfirst = q_mknode(fgetc(input));
	while(TRUE)	{
		/*Obtain next character	and	make sure it is	not	the	end	of the file*/
		ctemp =	fgetc(input);
		qfirst = q_addchar(qfirst,ctemp);
		/*Break AFTER EOF character has been stored in queue so that EOF is known for decoding*/
		if(ctemp ==	EOF) {
			break;
		}
	}
	/*Store the priority queue into the file*/
	q_filestore(qfirst,output);
	/*Return pointer to first element in queue*/
	return qfirst;
}

/*encode: This function takes three arguments. The first argument is 
to the beginning of the priority queue, the second is a pointer to the input file,
and the third is a pointer to the output file. This function calls two other
tree functions that first create a tree and then encode the input file using
Huffman compression*/
void encode(qtptr qfirst, FILE *input, FILE *output) {
	qtptr tptr;								/*Pointer to root of tree*/
	
	/*Create the tree*/
	tptr = t_create(qfirst);
	/*Use the tree to encode the characters and store them into a file*/
	t_charencode(tptr,input,output);
}