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/**
 * @file datatop_fileops.c
 * @brief Declares functions for reading and writing to files.
 *
 * Declares functions called when reading from files which data is collected.
 * Also contains methods to handle files which will be written to.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include "datatop_interface.h"
#include "datatop_linked_list.h"
#include "datatop_opt.h"
#include "datatop_fileops.h"

/**
 * @brief Reads the lines from files which we are collecting data from.
 *
 * @param file File which is read from
 * @param buffer Pointer to buffer where data will be read. The buffer is allocated
 *               in dt_read_file() and passed back to the caller. Caller should
 *               free this when done.
 * @param len Maximum amount of data which should be read from the file.
 * @return Number of bytes of data placed in *buffer.
 */
int dt_read_file(const char *file, char **buffer, int len)
{
	int read;
	FILE *fp;

	*buffer = (char *)malloc(len);
	if (!(*buffer)) {
		fprintf(stderr, "%s(): malloc(%d) failed\n", __func__, len);
		return 0;
	}

	fp = fopen(file, "r");
	if (!fp) {
		fprintf(stderr, "%s(): Failed to open %s: ", __func__, file);
		fprintf(stderr, "Error: %s\n", strerror(errno));
		free(*buffer);
		*buffer = 0;
		return 0;
	}
	read = fread(*buffer, sizeof(char), len, fp);
	fclose(fp);

	return read;
}

/**
 * @brief Deallocates memory no longer being used.
 *
 * @param buffer Buffer to be deallocated.
 */
void dt_free(char **buffer)
{
	free(*buffer);
	*buffer = 0;
}

/**
 * @brief Checks for access to a file for writing.
 *
 * @param fw File to check access of.
 * @return INVALID - File already exists or write access denied.
 * @return VALID - File does not exist and can be written to.
 */
int dtop_check_writefile_access(char *fw)
{
	if (!access(fw, F_OK)) {
		printf("File specified already exists\n");
		return INVALID;
	}

	if (!access(fw, W_OK)) {
		printf("Permission to write to specified file denied\n");
		return INVALID;
	}

	return VALID;
}

/**
 * @brief Opens file and handles possible errors.
 *
 * @param fw File path to be opened.
 * @param to_file Pointer to the *file that is opened.
 * @return VALID - File opened successfully.
 * @return INVALID - File could not be opened.
 */
int dtop_open_writing_file(char *fw, FILE **to_file)
{
	*to_file = fopen(fw, "w");
	if (*to_file) {
		return VALID;
	} else {
		fprintf(stderr, "Value of errno: %d\n", errno);
		fprintf(stderr, "Error opening file: %s\n", strerror(errno));
		fprintf(stderr, "Please try writing to a non-existent file\n");
		printf("See datatop -h for help\n");
		return INVALID;
	}
}

/**
 * @brief Closes a file if not a standard stream.
 *
 * @param fw File to be closed.
 */
void dtop_close_file(FILE *fw)
{
	if (fw != stdout && fw != stderr && fw != stdin)
		fclose(fw);
}

/**
 * @brief Helper function to find number of lines in dual_line file.
 *
 * @return Number of lines in a dual_line file.
 */
int dtop_get_file_line_amount(char *name)
{
	signed char rc = 0;
	int line_count = 0;
	FILE *file = fopen(name, "r");
	while (rc != EOF) {
		if (rc == '\n')
			line_count++;
		rc = fgetc(file);
	}

	fclose(file);
	return line_count;
}