/**
 * @file myexpand.c
 * @brief This module enables a user to expand tabs in different ways by choosing
 *        a custom tabstop value.
 * @date 2018-03-10
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include <signal.h>
#include <string.h>

#define BUF_SIZE 1024

/**
 * @details Variable which stores the program name.
 */
static char *pname;

/**
 * @details Variable which stores the desired tabsize. Default is 8.
 */
static int tabstop = 8;

/**
 * @details Variable which gets set when a SIGINT or SIGTERM is received.
 */
volatile sig_atomic_t quit = 0;

/**
 * @details Signal handler.
 * @param signal The number of the received signal.
 * @return This function has no return value.
 */
static void handle_signal(int signal)
{
        quit = 1;
}

/**
 * @details Prints the synopsis.
 * @param void This function takes no parameters.
 * @return Exit code of the program. Always non-zero.
 */
static void usage(void)
{
        fprintf(stderr, "Usage: myexpand [-t tabstop] [file...]\n");
        exit(EXIT_FAILURE);
}

/**
 * @details Safely parses the supplied -t parameter and converts the string
 *          into a long int.
 * @param optarg The argument after -t.
 * @return On success returns the correctly parsed integer for a tabstop.
 *         On error the exit code is non-zero.
 */
static long int strToInt(char *optarg)
{
        long int result = 0;
        char *ptr = NULL;

        result = strtol(optarg, &ptr, 10);
        if (errno == EINVAL) {
                fprintf(stderr, "%s: Conversion error ocurred: %d\n", pname, errno);
                exit(EXIT_FAILURE);
        }
        if (errno == ERANGE) {
                fprintf(stderr, "%s: The value provided was out of range!\n", pname);
                exit(EXIT_FAILURE);
        }
        if (result == 0 || *ptr != '\0') {
                fprintf(stderr, "%s: Conversion error ocurred!\n", pname);
                exit(EXIT_FAILURE);
        }

        return result;
}

/**
 * @details Goes over the supplied text, converts tabs accordingly and prints
 *          the outcome to stdout.
 * @param source A string containing the message to be converted.
 * @return This function has no return value.
 */
static void convert(char *source)
{
        int x = 0;
        for (int i = 0; i < (int)strlen(source); i++) {
                if (source[i] == '\n')
                        x = -1;

                if (source[i] == '\t') {
                        int p = labs(x - tabstop);
                        for (int s = 0; s < p; s++) {
                                fprintf(stdout, " ");
                        }
                        x += p;
                } else {
                        fprintf(stdout, "%c", source[i]);
                }
                x++;
                if (x >= (tabstop))
                        x = 0;
        }
}

/**
 * @details Reads filenames from an array of strings and calls the convert
 *          function for each of them.
 * @param size The size of the array holding the filenames.
 * @param filenames The array containing the filenames.
 * @return Non-zero on failure.
 */
static void readFiles(int size, char *filenames[])
{
        for (int i = 0; i < size; i++) {
                char *source = NULL;
                FILE *fp = fopen(filenames[i], "rb");
                if (fp == NULL) {
                        perror(pname);
                        exit(EXIT_FAILURE);
                }
                if (fseek(fp, 0L, SEEK_END) == 0) {
                        long bufsize = ftell(fp);
                        if (bufsize == -1)
                                perror(pname);

                        source = malloc(sizeof(char) * (bufsize + 1));
                        if (fseek(fp, 0L, SEEK_SET) != 0)
                                perror(pname);

                        size_t newLen = fread(source, sizeof(char), bufsize, fp);
                        if (ferror(fp) != 0) {
                                perror(pname);
                        } else {
                                source[newLen++] = '\0';
                        }
                }
                fclose(fp);
                convert(source);
                free(source);
        }
}

/**
 * The main entry point of the program.
 * @details Reads the supplied command-line arguments and calls the required
 *          functions.
 * @param argc The number of command-line parameters in argv.
 * @param argv The array of command-line arguments, argc elements long.
 * @return 0 on success, non-zero on failure.
 */
int main(int argc, char *argv[])
{
        struct sigaction sa;
        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = handle_signal;
        sigaction(SIGINT, &sa, NULL);

        while (quit != 1) {
                pname = argv[0];

                int opt_ind = 0;
                int tflag = 0;

                while ((opt_ind = getopt(argc, argv, "t:")) != -1) {
                        switch (opt_ind) {
                        case 't':
                                if (tflag != 0) {
                                        usage();
                                } else {
                                        tabstop = strToInt(optarg);
                                        tflag = 1;
                                }
                                break;

                        case '?':
                                usage();

                        default:
                                assert(0);
                        }
                }

                if ((argc - optind) != 0) {
                        char *filenames[argc-optind];
                        for (int i = optind, c = 0; i < argc; i++, c++) {
                                filenames[c] = argv[i];
                        }

                        readFiles(argc-optind, filenames);

                        exit(EXIT_SUCCESS);

                } else {
                        char buffer[BUF_SIZE];
                        size_t contentSize = 1;
                        char *content = malloc(sizeof(char) * BUF_SIZE);
                        if (content == NULL) {
                                perror(pname);
                                exit(EXIT_FAILURE);
                        }
                        content[0] = '\0';
                        while (fgets(buffer, BUF_SIZE, stdin)) {
                                char *old = content;
                                contentSize += strlen(buffer);
                                content = realloc(content, contentSize);
                                if (content == NULL) {
                                        perror(pname);
                                        free(old);
                                        exit(EXIT_FAILURE);
                                }
                                strcat(content, buffer);
                        }
                        if (ferror(stdin)) {
                                free(content);
                                perror(pname);
                                exit(EXIT_FAILURE);
                        }

                        convert(content);

                        free(content);

                        exit(EXIT_SUCCESS);
                }
        }

        exit(EXIT_FAILURE);
}