/**
 * @file main.c
 * @brief Automated Debian System Maintenance Utility (Optimized)
 * 
 * Automates package list updates, conditional upgrades, orphaned dependency 
 * purging, package archive cleaning, and temporary user cache removal.
 *
 * Requirements: Debian-based distribution with apt and sudo.
 */

#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <time.h>
#include <getopt.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/types.h>

#define VERSION "1.2.0"
#define MAX_CMD_LEN 512
#define MAX_MSG_LEN 128
#define MAX_LINE_LEN 1024
#define PATH_MAX_LEN 512
#define TAIL_LINE_COUNT 100

/* Optimization flags for parallel package downloads */
#define APT_OPT "-o Acquire::Queue-Mode=\"access\" -o Acquire::http::Pipeline-Depth=\"10\""

static FILE *log_file = NULL;

/**
 * @brief Resolves the default XDG log file path (~/.local/state/ud/ud.log).
 */
static bool get_log_path(char *path_buf, size_t max_len) {
    const char *home = getenv("HOME");
    if (!home) return false;

    char dir_path[PATH_MAX_LEN];
    if (snprintf(dir_path, sizeof(dir_path), "%s/.local/state/ud", home) >= (int)sizeof(dir_path)) {
        return false;
    }

    char sub_path[PATH_MAX_LEN];
    snprintf(sub_path, sizeof(sub_path), "%s/.local", home);
    mkdir(sub_path, 0755);
    snprintf(sub_path, sizeof(sub_path), "%s/.local/state", home);
    mkdir(sub_path, 0755);
    mkdir(dir_path, 0755);

    if (snprintf(path_buf, max_len, "%s/ud.log", dir_path) >= (int)max_len) {
        return false;
    }

    return true;
}

/**
 * @brief Views the log file using $PAGER, or streams the last 100 lines 
 *        directly to stdout if $PAGER is unset.
 */
static void view_log(void) {
    char log_path[PATH_MAX_LEN];
    if (!get_log_path(log_path, sizeof(log_path))) {
        fprintf(stderr, "Error resolving log file path.\n");
        exit(EXIT_FAILURE);
    }

    if (access(log_path, F_OK) != 0) {
        printf("No log file found at %s\n", log_path);
        exit(EXIT_SUCCESS);
    }

    const char *pager = getenv("PAGER");
    if (pager && strlen(pager) > 0) {
        char view_cmd[PATH_MAX_LEN * 2];
        snprintf(view_cmd, sizeof(view_cmd), "%s %s", pager, log_path);
        
        int status = system(view_cmd);
        if (status == -1) {
            perror("Error launching log pager");
        }
    } else {
        FILE *f = fopen(log_path, "r");
        if (!f) {
            perror("Error reading log file");
            exit(EXIT_FAILURE);
        }

        /* Ring buffer to hold the last TAIL_LINE_COUNT lines */
        char lines[TAIL_LINE_COUNT][MAX_LINE_LEN];
        int count = 0;
        char buffer[MAX_LINE_LEN];

        while (fgets(buffer, sizeof(buffer), f) != NULL) {
            strncpy(lines[count % TAIL_LINE_COUNT], buffer, MAX_LINE_LEN - 1);
            lines[count % TAIL_LINE_COUNT][MAX_LINE_LEN - 1] = '\0';
            count++;
        }
        fclose(f);

        int start = 0;
        int print_count = count;

        if (count > TAIL_LINE_COUNT) {
            start = count % TAIL_LINE_COUNT;
            print_count = TAIL_LINE_COUNT;
        }

        for (int i = 0; i < print_count; i++) {
            fputs(lines[(start + i) % TAIL_LINE_COUNT], stdout);
        }
    }
}

/**
 * @brief Truncates the persistent log file.
 */
static void clear_log(void) {
    char log_path[PATH_MAX_LEN];
    if (!get_log_path(log_path, sizeof(log_path))) {
        fprintf(stderr, "Error resolving log file path.\n");
        exit(EXIT_FAILURE);
    }

    FILE *f = fopen(log_path, "w");
    if (f) {
        fclose(f);
        printf("Log cleared: %s\n", log_path);
    } else {
        perror("Error clearing log file");
    }
}

/**
 * @brief Prints the utility version string.
 */
static void print_version(void) {
    printf("ud version %s\n", VERSION);
}

/**
 * @brief Natively counts non-hidden files in a directory.
 */
static int count_directory_files(const char *dir_path) {
    DIR *dir = opendir(dir_path);
    if (!dir) return 0;

    int count = 0;
    struct dirent *entry;
    while ((entry = readdir(dir)) != NULL) {
        if (entry->d_name[0] != '.') {
            count++;
        }
    }
    closedir(dir);
    return count;
}

/**
 * @brief Recursively counts files in nested directories.
 */
static int count_recursive_files(const char *dir_path) {
    DIR *dir = opendir(dir_path);
    if (!dir) return 0;

    int count = 0;
    struct dirent *entry;
    char full_path[PATH_MAX_LEN];

    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0) {
            continue;
        }

        snprintf(full_path, sizeof(full_path), "%s/%s", dir_path, entry->d_name);
        struct stat st;
        if (stat(full_path, &st) == 0) {
            if (S_ISDIR(st.st_mode)) {
                count += count_recursive_files(full_path);
            } else if (S_ISREG(st.st_mode)) {
                count++;
            }
        }
    }
    closedir(dir);
    return count;
}

/**
 * @brief Helper to count files matching extension in a directory.
 */
static int count_extension_files(const char *dir_path, const char *ext) {
    DIR *dir = opendir(dir_path);
    if (!dir) return 0;

    int count = 0;
    struct dirent *entry;
    size_t ext_len = strlen(ext);

    while ((entry = readdir(dir)) != NULL) {
        size_t len = strlen(entry->d_name);
        if (len > ext_len && strcmp(entry->d_name + len - ext_len, ext) == 0) {
            count++;
        }
    }
    closedir(dir);
    return count;
}

/**
 * @brief Safely removes contents of a directory using POSIX system APIs.
 */
static void remove_directory_contents(const char *dir_path) {
    DIR *dir = opendir(dir_path);
    if (!dir) return;

    struct dirent *entry;
    char full_path[PATH_MAX_LEN];

    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0) {
            continue;
        }

        snprintf(full_path, sizeof(full_path), "%s/%s", dir_path, entry->d_name);
        struct stat st;
        if (stat(full_path, &st) == 0) {
            if (S_ISDIR(st.st_mode)) {
                remove_directory_contents(full_path);
                rmdir(full_path);
            } else {
                unlink(full_path);
            }
        }
    }
    closedir(dir);
}

/**
 * @brief Prints an underlined section header to standard output.
 */
static void print_message(const char *message) {
    if (!message) return;

    printf("\n%s\n", message);
    size_t len = strlen(message);
    for (size_t i = 0; i < len; i++) {
        putchar('-');
    }
    putchar('\n');
}

/**
 * @brief Executes command directly, streams stdout with native indentation, 
 *        and optionally matches output patterns on the fly.
 */
static bool run_task_stream(const char *message, const char *command, const char *log_msg_override, 
                             const char *match_pattern, int *match_counter) {
    print_message(message);

    const char *log_text = log_msg_override ? log_msg_override : message;

    char full_cmd[MAX_CMD_LEN];
    snprintf(full_cmd, sizeof(full_cmd), "%s 2>/dev/null", command);

    FILE *fp = popen(full_cmd, "r");
    if (!fp) {
        perror("Error invoking subprocess");
        if (log_file) {
            fprintf(log_file, "  [FAIL] %s (Subprocess execution error)\n", log_text);
            fflush(log_file);
        }
        return false;
    }

    char line[MAX_LINE_LEN];
    if (match_counter) *match_counter = 0;

    while (fgets(line, sizeof(line), fp) != NULL) {
        printf("  %s", line);

        if (match_pattern && match_counter) {
            if (strstr(line, match_pattern) != NULL) {
                (*match_counter)++;
            }
        }
    }

    int status = pclose(fp);

    if (status == -1 || (WIFEXITED(status) && WEXITSTATUS(status) != 0)) {
        int exit_code = WEXITSTATUS(status);
        fprintf(stderr, "  [!] Command failed or returned exit code: %d\n", exit_code);
        if (log_file) {
            fprintf(log_file, "  [FAIL] %s (Exit code %d)\n", log_text, exit_code);
            fflush(log_file);
        }
        return false;
    }

    if (log_file) {
        fprintf(log_file, "  [OK]   %s\n", log_text);
        fflush(log_file);
    }

    return true;
}

/**
 * @brief Queries APT for pending upgradable packages.
 */
static int count_upgradable_packages(void) {
    FILE *fp = popen("apt list --upgradable 2>/dev/null", "r");
    if (!fp) return -1;

    int count = 0;
    char buffer[MAX_LINE_LEN];

    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        if (strstr(buffer, "upgradable from:") != NULL) {
            count++;
        }
    }

    int status = pclose(fp);
    if (status == -1 || (WIFEXITED(status) && WEXITSTATUS(status) != 0)) {
        return 0;
    }

    return count;
}

static void print_usage(const char *prog_name) {
    printf("Usage: %s [OPTIONS]\n\n", prog_name);
    printf("Options:\n");
    printf("  -v, --view-log   Open the maintenance log (~/.local/state/ud/ud.log) using $PAGER\n");
    printf("  -c, --clear-log  Clear the maintenance log file\n");
    printf("  -V, --version    Display version information and exit\n");
    printf("  -h, --help       Display this help message and exit\n");
}

int main(int argc, char *argv[]) {
    static struct option long_options[] = {
        {"view-log",  no_argument, 0, 'v'},
        {"clear-log", no_argument, 0, 'c'},
        {"version",   no_argument, 0, 'V'},
        {"help",      no_argument, 0, 'h'},
        {0, 0, 0, 0}
    };

    int opt;
    while ((opt = getopt_long(argc, argv, "vcVh", long_options, NULL)) != -1) {
        switch (opt) {
            case 'v':
                view_log();
                return EXIT_SUCCESS;
            case 'c':
                clear_log();
                return EXIT_SUCCESS;
            case 'V':
                print_version();
                return EXIT_SUCCESS;
            case 'h':
                print_usage(argv[0]);
                return EXIT_SUCCESS;
            default:
                print_usage(argv[0]);
                return EXIT_FAILURE;
        }
    }

    /* Initialize persistent logger */
    char log_path[PATH_MAX_LEN];
    if (get_log_path(log_path, sizeof(log_path))) {
        log_file = fopen(log_path, "a");
        if (log_file) {
            time_t now = time(NULL);
            char date_str[64];
            strftime(date_str, sizeof(date_str), "%Y-%m-%d %H:%M:%S", localtime(&now));
            fprintf(log_file, "[%s] MAINTENANCE SESSION STARTED\n", date_str);
            fflush(log_file);
        }
    }

    /* Step 1: Update local package index */
    run_task_stream("UPDATING LOCAL CACHE `apt update`",
                     "sudo apt " APT_OPT " update", NULL, NULL, NULL);

    /* Step 2: Query and perform upgrades conditionally */
    int upgrade_count = count_upgradable_packages();

    if (upgrade_count < 0) {
        fprintf(stderr, "Failed to query pending updates.\n");
        if (log_file) {
            fprintf(log_file, "  [FAIL] Querying pending package updates\n");
            fflush(log_file);
        }
    } else if (upgrade_count == 0) {
        print_message("NO UPDATES AVAILABLE | UPGRADE SKIPPED");
        if (log_file) {
            fprintf(log_file, "  [INFO] 0 packages upgradable (Upgrade skipped)\n");
            fflush(log_file);
        }
    } else {
        char msg[MAX_MSG_LEN];
        snprintf(msg, sizeof(msg),
                 "%d UPDATE%s AVAILABLE | UPGRADING `apt full-upgrade`",
                 upgrade_count, (upgrade_count > 1) ? "S" : "");

        run_task_stream(msg, "sudo apt full-upgrade -y", NULL, NULL, NULL);
    }

    /* Step 3: Single-pass autoremove and stream-based removal counting */
    int orphan_count = 0;
    run_task_stream("PURGING ORPHANED DEPENDENCIES & CONFIGS `apt autoremove --purge`",
                     "sudo apt autoremove --purge -y", NULL, "Removing ", &orphan_count);

    if (log_file) {
        fprintf(log_file, "  [INFO] %d orphaned packages purged\n", orphan_count);
        fflush(log_file);
    }

    /* Count cached debs natively using POSIX dirent */
    int deb_count = count_extension_files("/var/cache/apt/archives", ".deb");
    char deb_log[MAX_MSG_LEN];
    snprintf(deb_log, sizeof(deb_log),
             "WIPING ALL DOWNLOADED PACKAGE FILES (`apt clean`) - %d .deb archive%s purged",
             deb_count, (deb_count == 1) ? "" : "s");
    run_task_stream("WIPING ALL DOWNLOADED PACKAGE FILES `apt clean`",
                     "sudo apt clean", deb_log, NULL, NULL);

    /* Step 4: Clean local user caches natively using dirent */
    const char *home = getenv("HOME");
    if (home) {
        char thumb_path[PATH_MAX_LEN];
        snprintf(thumb_path, sizeof(thumb_path), "%s/.cache/thumbnails", home);
        int thumb_count = count_recursive_files(thumb_path);
        
        print_message("CLEARING LOCAL THUMBNAIL CACHE `rm -rf ~/.cache/thumbnails/*`");
        remove_directory_contents(thumb_path);
        printf("  Cleared %d thumbnail items.\n", thumb_count);
        if (log_file) {
            fprintf(log_file, "  [OK]   CLEARING LOCAL THUMBNAIL CACHE - %d items deleted\n", thumb_count);
            fflush(log_file);
        }

        char shot_path[PATH_MAX_LEN];
        snprintf(shot_path, sizeof(shot_path), "%s/Pictures/Screenshots", home);
        int shot_count = count_directory_files(shot_path);

        print_message("CLEARING SCREENSHOTS FOLDER `rm -rf ~/Pictures/Screenshots/*`");
        remove_directory_contents(shot_path);
        printf("  Cleared %d screenshot files.\n", shot_count);
        if (log_file) {
            fprintf(log_file, "  [OK]   CLEARING SCREENSHOTS FOLDER - %d files deleted\n", shot_count);
            fflush(log_file);
        }
    }

    putchar('\n');

    if (log_file) {
        time_t end_time = time(NULL);
        char end_str[64];
        strftime(end_str, sizeof(end_str), "%Y-%m-%d %H:%M:%S", localtime(&end_time));
        fprintf(log_file, "[%s] MAINTENANCE SESSION COMPLETED\n\n", end_str);
        fclose(log_file);
    }

    return EXIT_SUCCESS;
}