/* SPDX-License-Identifier: Apache-2.0 */

/* Copyright 2025 Thorsten Töpper
 *
 * dir_monitor - print specified stat() information from entries of a given
 * directory to stdout. Call it via watch for repeated output to a terminal.
 *
 * vim:ts=4:sw=4:expandtab
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ctype.h>
#include <getopt.h>
#include <stdint.h>
#include <stdbool.h>
#include <errno.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <time.h>
#include <sys/ioctl.h>


#define LOGERR(...) {fprintf(stderr, "[%s:%d] %s: ", __FILE__, __LINE__, __func__); fprintf(stderr, __VA_ARGS__);}

#ifdef DEBUGBUILD
#define DBGTRC(...) LOGERR(__VA_ARGS__)
#else
#define DBGTRC(...)
#endif



/* === DEFINITIONS === */
#define PATH_SEP '/'

enum esort_type { SORT_BY_SIZE, SORT_BY_TIME };
struct list_node {
    struct list_node *next;
    size_t fsize;
    char fname[256];
    time_t ftime; /* can be creation, access or modification */
};

struct list_head {
    struct list_node *first;
};

struct list_node *create_node(char *fname, size_t fsize, time_t ftime);
struct list_head *create_list_sort_reversed(struct list_head *list);
void destroy_list(struct list_head *list);
int fputc_all_cols(char c, FILE *fdout);
int fputc_width_x(char c, size_t x, FILE *fdout);
struct list_head *get_data_from_directory(char *path);
int insert_sorted_by_size(struct list_head *list, struct list_node *node);
int insert_sorted_by_time(struct list_head *list, struct list_node *node);
int parse_arguments(int argc, char **argv);
void print_list(struct list_head *list);
void set_option(const char *option_name, char *option_argument);
void usage(char *executable);



/* === GLOBAL VARIABLES === */
struct option long_options[] = {
    { "reverse-sort", no_argument, 0, 0 },
    { "show-hidden-entries", no_argument, 0, 0 },
    { "sort-by", required_argument, 0, 0 },
    { "long-timestamp", no_argument, 0, 0 },
    { 0, 0, 0, 0 }
};
bool option_sort_reverse_order = false;
enum esort_type option_sort_type = SORT_BY_SIZE;
bool option_show_hidden_entries = false;
bool option_timestamp_long = false;


/* === IMPLEMENTATION === */
inline struct list_node *create_node(char *fname, size_t fsize, time_t ftime) {
    struct list_node *node = NULL;
    
    if (fname == NULL || fname[0] == '\0') {
        LOGERR("ERROR: No valid filename given\n");
        return NULL;
    }

    if ((node = calloc(1, sizeof(struct list_node))) == NULL) {
        LOGERR("ERROR: Failed allocate memory for node: %s\n", strerror(errno));
        return NULL;
    }

    node->next  = NULL;
    node->fsize = fsize;
    node->ftime = ftime;
    strncpy(node->fname, fname, 256);
    return node;
}


inline void destroy_list(struct list_head *list) {
    struct list_node *ptr = NULL;
    if (list == NULL)
        return;
    while (list->first != NULL) {
        ptr = list->first->next;
        if (ptr == NULL) {
            free(list->first);
            break;
        }
        list->first->next = ptr->next;
        free(ptr);
    }
    free(list);
}


inline int fputc_all_cols(char c, FILE *fdout) {
    struct winsize terminal;
    ioctl(STDOUT_FILENO, TIOCGWINSZ, &terminal);
    return fputc_width_x(c, ((terminal.ws_col == 0) ? 72 : terminal.ws_col), fdout);
}


/* Not the most performant way, but during output the time critical tasks are already done. */
inline int fputc_width_x(char c, size_t x, FILE *fdout) {
    size_t i=0;

    if (fdout == NULL) {
        LOGERR("ERROR: No output stream given.\n");
        return EOF;
    }

    if ( ! isprint(c) ) { c = '?'; }

    for (i=0; i<x; i++) {
        if (fputc(c, fdout) == EOF) {
            LOGERR("ERROR: Failed to write char 0x%02X to stream %d\n", c, fdout->_fileno);
            return EOF;
        }
    }

    return 1;
}

/* dirty... */
#define INSERT_BY_NUMERIC_FIELD(list, node, field) \
{ struct list_node *ptr = NULL; \
    if (node->field > list->first->field) { \
        node->next = list->first; list->first = node; return 0; } \
    ptr = list->first; \
    while (ptr != NULL) { \
        if (ptr->next == NULL) { ptr->next = node; return 0; } \
        if (node->field > ptr->next->field) { \
            node->next = ptr->next; ptr->next = node; \
            return 0; } \
        ptr = ptr->next; \
    } \
}


/* TODO: later when, other parameters are actively used move the action to a template */
inline int insert_sorted_by_size(struct list_head *list, struct list_node *node) {
    if (list == NULL) { LOGERR("ERROR: No list given.\n"); return -1; }
    if (node == NULL) { LOGERR("ERROR: No node given.\n"); return -2; }

    if (list->first == NULL) {
        list->first = node;
        return 0;
    }
    INSERT_BY_NUMERIC_FIELD(list, node, fsize);
    return -3;
}

inline int insert_sorted_by_time(struct list_head *list, struct list_node *node) {
    if (list == NULL) { LOGERR("ERROR: No list given.\n"); return -1; }
    if (node == NULL) { LOGERR("ERROR: No node given.\n"); return -2; }

    if (list->first == NULL) {
        list->first = node;
        return 0;
    }
    INSERT_BY_NUMERIC_FIELD(list, node, ftime);
    return -3;
}
#undef INSERT_BY_NUMERIC_FIELD

/* The most simple default output, formatted output is planned */
void print_list(struct list_head *list) {
    struct list_head *lh = list;
    struct list_node *ptr;
    struct tm *tm = NULL;
    char timestamp[128];
    size_t total_size = 0;

    if (list == NULL) return;
    if (option_sort_reverse_order) {
        lh = create_list_sort_reversed(list);
        /* be tolerant */
        if (lh == NULL) {
            lh = list;
        }
    }

    ptr = lh->first;
    while (ptr != NULL) {
        printf(" %8lu %2s ", ((ptr->fsize>=1024) ? (ptr->fsize/1024) : ptr->fsize),
                ((ptr->fsize >= 1024) ? "kB" : ""));

        tm = localtime(&ptr->ftime);
        if (option_timestamp_long) {
            strftime(timestamp, sizeof(timestamp), "%Y%m%d %H:%M:%S %Z", tm);
            printf(" %20s ", timestamp);
        } else {
            strftime(timestamp, sizeof(timestamp), "%H:%M:%S", tm);
            printf(" %8s ", timestamp);
        }
        printf(" %s\n", ptr->fname);
        total_size += ptr->fsize;
        ptr = ptr->next;
    }
    fputc_all_cols('=', stdout);
    printf("\nTotal size: %lu %s\n", ((total_size>1024) ? total_size/1024 : total_size),
            ((total_size >= 1024) ? "kB" : ""));

    if (lh != list) destroy_list(lh);
}



struct list_head *create_list_sort_reversed(struct list_head *list) {
    struct list_head *lh = NULL;
    struct list_node *cpynode = NULL, *ptr = NULL;
    if (list == NULL) {
        LOGERR("ERROR: No list given\n");
        return NULL;
    }
    if ((lh = calloc(1, sizeof(struct list_head))) == NULL) {
        LOGERR("ERROR: Failed to allocate memory for a struct list_head\n");
        return NULL;
    }

    lh->first = NULL;
    ptr = list->first;

    while (ptr != NULL) {
        cpynode = create_node(ptr->fname, ptr->fsize, ptr->ftime);
        if (cpynode == NULL) {
            destroy_list(lh);
            return NULL;
        }
        cpynode->next = lh->first;
        lh->first = cpynode;
        ptr = ptr->next;
    }

    return lh;
}


/* This function contains the only time critical code. The loop over
 * the directory content.
 *
 * Note for future:
 * I myself use the dir_monitor in combination with watch on a directory
 * containing temporary data, it may happen that a run into an error occurs,
 * but it's not tragic. To reduce the chance of the error the first step
 * would be to optimize the loop with putting the data into a list in stack
 * form and moving the nodes into a sorted list afterwards.
 */
struct list_head *get_data_from_directory(char *path) {
    char *fullpath = NULL, *fname_in_path = NULL;
    DIR *dir = NULL;
    size_t l;
    struct dirent *de = NULL;
    struct list_node *tmp = NULL;
    struct list_head *list = NULL;
    struct stat stat_res;

    if (path == NULL) {
        LOGERR("ERROR: No path given.\n");
        return NULL;
    }

    l = strlen(path);
    /* 258 filename and possibly required PATH_SEP and of course string termination */
    if ((fullpath = calloc(l+258, sizeof(char))) == NULL) {
        LOGERR("ERROR: Failed to allocate memory for list head.\n");
        return NULL;
    }
    sprintf(fullpath, "%s%c", path, ((path[l-1] == PATH_SEP) ? '\0' : PATH_SEP));
    fname_in_path = (fullpath[l] == PATH_SEP) ? &(fullpath[l+1]) : &(fullpath[l]) ;

    if ((dir = opendir(path)) == NULL) {
        LOGERR("ERROR: Failed to open directory '%s': %s (errno %d)\n",
                path, strerror(errno), errno);
        return NULL;
    }

    /* TBH: In case those few bytes are not available, the process will be killed anyways */
    if ((list = calloc(1, sizeof(struct list_head))) == NULL) {
        LOGERR("ERROR: Failed to allocate memory for list head.\n");
        closedir(dir);
        return NULL;
    }

    errno = 0;
    /* Currently the code is specific UNIXoid, needs to be adjusted in case someone ports it. */
    while ((de = readdir(dir)) != NULL) {
        if (de->d_name[0] == '.' && option_show_hidden_entries == false)
            continue;

        sprintf(fname_in_path, "%s", de->d_name);
        DBGTRC("DEBUG: fullpath: '%s'\n", fullpath);
        if (lstat(fullpath, &stat_res) != 0) {
            LOGERR("ERROR: lstat call on '%s' failed: %s (errno %d)\n",
                    fullpath, strerror(errno), errno);
            continue;
        }
        if ((tmp = create_node(de->d_name, stat_res.st_size, stat_res.st_mtime)) == NULL) {
            LOGERR("ERROR: Skipping entry %s\n", de->d_name);
            continue;
        }
        /* SORT_BY_SIZE is the default value, always check it first. */
        switch (option_sort_type) {
            case SORT_BY_SIZE:
                insert_sorted_by_size(list, tmp);
                break;
            case SORT_BY_TIME:
                insert_sorted_by_time(list, tmp);
                break;
        };
    }

    free(fullpath);
    closedir(dir);
    return list;
}


void set_option(const char *option_name, char *option_argument) {

    DBGTRC("DEBUG: called with option_name '%s' and option_argument '%s'\n",
            option_name, option_argument);

    if (option_name == NULL)
        return;

    /* options WITHOUT arguments */
    if (strcmp(option_name, "show-hidden-entries") == 0) {
        option_show_hidden_entries = true;
        return;
    }

    if (strcmp(option_name, "long-timestamp") == 0) {
        option_timestamp_long = true;
        return;
    }

    if (strcmp("reverse-sort", option_name) == 0) {
        option_sort_reverse_order = true;
        return;
    }

    /* options WITH arguments */
    if (option_argument == NULL || option_argument[0] == '\0') {
        LOGERR("ERROR: option_name %s with missing option_argument\n",
                option_name);
        return;
    }

    if (strcmp(option_name, "sort-by") == 0) {
        if (strncmp("size", option_argument, 4) == 0) {
            option_sort_type = SORT_BY_SIZE;
        } else if (strncmp("time", option_argument, 4) == 0) {
            option_sort_type = SORT_BY_TIME;
        } else {
            LOGERR("WARNING: '%s' is an invalig argument for %s\n",
                    option_argument, option_name);
        }
        return;
    }

    LOGERR("ERROR: Option '%s' not recognized\n.", option_name);
}

int parse_arguments(int argc, char **argv) {
    int c = 0, index;

    while(1) {
        index = 0;
        c = getopt_long(argc, argv, "tv", long_options, &index);

        if (c == -1) {
            break;
        }

        switch (c) {
            case 0:
                set_option(long_options[index].name, optarg);
                break;
            case 't':
                option_timestamp_long = true;
                break;
            case 'v':
                option_show_hidden_entries = true;
                break;
            case '?':
                break;
            default:
                LOGERR("ERROR: unrecognized option 0x%02X '%c'\n", c, c);
                break;
        }
    }

    return optind;
}


void usage(char *executable) {
    fprintf(stderr, "Call: %s OPTIONS path_to_open\n", executable);
    fprintf(stderr, "\nOPTIONS are\n");
    /* long name, short name, optional argument, explanation */
    fprintf(stderr, " %-25s %2s %10s %s\n", "--long-timestamp", "-t", "",
            "Print timestamp in long form yyyymmdd HH:MM:SS ZONE");
    fprintf(stderr, " %-25s %2s %10s %s\n", "--reverse-sort", "", "",
            "Sort reversed");
    fprintf(stderr, " %-25s %2s %10s %s\n", "--show-hidden-entries", "-v", "",
            "Show hidden entries in the directory");
    fprintf(stderr, " %-25s %2s %10s %s\n", "--sort-by", "", "size|time",
            "Sort either by time or size");
}

int main(int argc, char **argv) {
    struct list_head *list = NULL;
    int path_index = 1;
    /* TODO: Handle options */
    if (argc < 2) {
        usage(argv[0]);
        return EXIT_FAILURE;
    }
    path_index = parse_arguments(argc, argv);
    if (path_index == argc) {
        usage(argv[0]);
        return EXIT_FAILURE;
    }
    list = get_data_from_directory(argv[path_index]);
    print_list(list);
    destroy_list(list);
    return EXIT_SUCCESS;
}