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

const size_t BUFFER_SIZE = 1024;

bool sar_in_line(const char* line, FILE* target, const char* search_text, const char* replacement_text)
{
	// Move in the original line char by char trying to find search_text from that char
	for ( ; *line; ++line)
	{
		const char *s = search_text, *l = line;
		for ( ; *s && tolower(*s) == tolower(*l); ++s, ++l )
			;

		// If all chars of search_text were found in current position of line
		// write replacement_text to the target file and ignore those search_text characteres
		if ( *s == '\0' )
		{
			if ( fputs(replacement_text, target) == EOF )
				return false;
			line = l - 1; // should be line = l, but ++line in for will move it one more char
		}
		else
		{
			// No search_text is found from current position of line, write this char to target
			// file and try with next char of lines
			if ( fputc(*line, target) == EOF )
				return false;
		}
	}
	return true;
}

bool sar_in_open_file(FILE* source, FILE* target, const char* search_text, const char* replacement_text)
{
	// Read one line a time in source file, and write it with replacements to target file
	char buffer[BUFFER_SIZE];
	while ( fgets(buffer, BUFFER_SIZE, source) )
		if ( ! sar_in_line(buffer, target, search_text, replacement_text) )
			return false;

	return true;
}

bool sar_in_file(const char* filename, const char* search_text, const char* replacement_text)
{
	FILE* source = fopen(filename, "r");
	if ( ! source )
	{
		fprintf(stderr, "sar: could not open %s\n", filename);
		return false;
	}

	// Concatenate ".tmp" to source filename
	char target_filename[ strlen(filename) + strlen(".tmp") + 1 ];
	strcpy(target_filename, filename);
	strcat(target_filename, ".tmp");

	FILE* target = fopen(target_filename, "w");
	if ( ! target )
	{
		fprintf(stderr, "sar: could not create %s\n", target_filename);
		fclose(source);
		return false;
	}

	bool result = sar_in_open_file(source, target, search_text, replacement_text);

	fclose(target);
	fclose(source);

	// Replace original file for temporary file on success, remove temporary on error
	if ( result )
	{
		remove(filename);
		rename(target_filename, filename);
	}
	else
	{
		fprintf(stderr, "sar: error writing to %s\n", target_filename);
		remove(target_filename);
	}

	return result;
}

int main(int argc, char* argv[])
{
	// Assumes: "sar -i -W search-text -r replacement-text file1.txt file2.txt ..."
	// position: 0   1  2  3           4  5                6         7         8...
	for ( int i = 6; i < argc; ++i )
		sar_in_file( argv[i], argv[3], argv[5] );

	return 0;
}