/* 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 <stdint.h>
#include <errno.h>
#include <sys/types.h>
#include <dirent.h>
#include <sys/stat.h>
#include <time.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 '/'

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);
void destroy_list(struct list_head *list);
int insert_sorted_by_size(struct list_head *list, struct list_node *node);
void print_list(struct list_head *list);



/* === GLOBAL VARIABLES === */
bool option_show_hidden_entries = false;
bool option_timestamp_short = true;


/* === 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);
}


/* 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) {
    struct list_node *ptr = NULL;

    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;
    }

    if (node->fsize > list->first->fsize) {
        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->fsize > ptr->next->fsize) {
            node->next = ptr->next;
            ptr->next = node;
            return 0;
        }
        ptr = ptr->next;
    }

    return -3;
}


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

    if (list == NULL) return;

    ptr = list->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_short) {
            strftime(timestamp, sizeof(timestamp), "%H:%M:%S", tm);
            printf(" %8s ", timestamp);
        } else {
            strftime(timestamp, sizeof(timestamp), "%Y%m%d %H:%M:%S %Z", tm);
            printf(" %20s ", timestamp);
        }

        printf(" %s\n", ptr->fname);
        ptr = ptr->next;
    }
}


/* TODO: When sorting via different parameters is possible, the call needs adjustments */
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);
    /* +2 due to possibly required / and of course string termination */
    if ((fullpath = calloc(l+256+2, 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;
    /* Show hidden entries code is UNIXoid specific, needs to be adjusted for portability */
    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;
        }
        /* currently ignoring return values */
        tmp = create_node(de->d_name, stat_res.st_size, stat_res.st_mtime);
        insert_sorted_by_size(list, tmp);
    }

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


int main(int argc, char **argv) {
    struct list_head *list = NULL;
    list = get_data_from_directory(argv[1]);
    print_list(list);
    destroy_list(list);
    return EXIT_SUCCESS;
}