/**
 * @file main.c
 * @brief Automated Debian System Maintenance Utility
 * 
 * Automates package list updates, conditional upgrades, orphaned dependency 
 * purging, package archive cleaning, and temporary user cache removal.
 *
 * Requirements: Debian-based distribution (Debian, Ubuntu, Linux Mint) with apt, sed, 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 <sys/wait.h>
#include <sys/stat.h>
#include <sys/types.h>

#define VERSION "1.1.0"
#define MAX_CMD_LEN 512
#define MAX_MSG_LEN 128
#define MAX_LINE_LEN 1024
#define PATH_MAX_LEN 512

/* 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).
 * 
 * Creates parent directories if they do not exist.
 * 
 * @param path_buf Buffer to write the path string to.
 * @param max_len Maximum capacity of path_buf.
 * @return true if path resolved and directories exist/created, false otherwise.
 */
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;
    }

    /* Ensure ~/.local/state/ud directories exist */
    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 Opens the log file using $PAGER or less.
 */
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) {
        pager = "less";
    }

    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");
    }
}

/**
 * @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 Counts files matching a shell glob pattern via popen/ls.
 * 
 * @param glob_pattern Shell glob string (e.g., ~/.cache/thumbnails/).
 * @return Number of matching files, or 0 if none found/error.
 */
static int count_glob_files(const char *glob_pattern) {
    char cmd[MAX_CMD_LEN];
    snprintf(cmd, sizeof(cmd), "ls -1d %s 2>/dev/null | wc -l", glob_pattern);

    FILE *fp = popen(cmd, "r");
    if (!fp) return 0;

    int count = 0;
    if (fscanf(fp, "%d", &count) != 1) {
        count = 0;
    }
    pclose(fp);
    return count;
}

/**
 * @brief Queries autoremove simulation to count candidate orphaned packages.
 * 
 * @return Count of auto-installed packages eligible for autoremove.
 */
static int count_orphaned_packages(void) {
    int count = 0;
    FILE *sim_fp = popen("apt-get autoremove -s 2>/dev/null | grep -E '^Remv ' | wc -l", "r");
    if (sim_fp) {
        if (fscanf(sim_fp, "%d", &count) != 1) {
            count = 0;
        }
        pclose(sim_fp);
    }
    return count;
}

/**
 * @brief Counts cached package archives (.deb) in /var/cache/apt/archives.
 * 
 * @return Count of downloaded package files.
 */
static int count_cached_debs(void) {
    FILE *fp = popen("ls -1 /var/cache/apt/archives/*.deb 2>/dev/null | wc -l", "r");
    if (!fp) return 0;

    int count = 0;
    if (fscanf(fp, "%d", &count) != 1) {
        count = 0;
    }
    pclose(fp);
    return count;
}

/**
 * @brief Prints an underlined section header to standard output.
 * 
 * @param message Header text to display.
 */
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 Formats and executes a shell command with indented stdout.
 * 
 * Routes standard error to /dev/null and pipes standard output to sed for terminal display.
 * Writes a high-level completion status summary to the persistent log file.
 * 
 * @param message Display title for the task.
 * @param command Command string to execute via subshell.
 * @param log_msg_override Optional detailed message for log file (or NULL to use message).
 * @return true if command returned status 0, false otherwise.
 */
static bool run_task(const char *message, const char *command, const char *log_msg_override) {
    print_message(message);

    const char *log_text = log_msg_override ? log_msg_override : message;

    char full_cmd[MAX_CMD_LEN];
    int bytes_written = snprintf(full_cmd, sizeof(full_cmd), 
                                 "%s 2>/dev/null | sed 's/^/  /'", command);

    if (bytes_written < 0 || (size_t)bytes_written >= sizeof(full_cmd)) {
        fprintf(stderr, "Error: Command string truncated or invalid.\n");
        if (log_file) {
            fprintf(log_file, "  [FAIL] %s (Command string truncated)\n", log_text);
            fflush(log_file);
        }
        return false;
    }

    int status = system(full_cmd);

    if (status == -1) {
        perror("Error invoking shell process");
        if (log_file) {
            fprintf(log_file, "  [FAIL] %s (Subshell invocation error)\n", log_text);
            fflush(log_file);
        }
        return false;
    }

    if (WIFEXITED(status)) {
        int exit_code = WEXITSTATUS(status);
        if (exit_code != 0) {
            fprintf(stderr, "  [!] Command returned non-zero 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;
        }
    } else {
        fprintf(stderr, "  [!] Command terminated abnormally.\n");
        if (log_file) {
            fprintf(log_file, "  [FAIL] %s (Abnormal termination)\n", log_text);
            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.
 * 
 * Spawns a read pipeline to apt list --upgradable and tallies target lines.
 * 
 * @return Count of upgradable packages, or -1 on execution error.
 */
static int count_upgradable_packages(void) {
    FILE *fp = popen("apt list --upgradable 2>/dev/null", "r");
    if (!fp) {
        perror("Error opening pipe to apt");
        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 for current session */
    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 with parallel fetch queue */
    run_task("UPDATING LOCAL CACHE `apt update`",
             "sudo apt " APT_OPT " update", NULL);

    /* Step 2: Query for upgrades */
    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];
        int bytes = snprintf(msg, sizeof(msg),
                             "%d UPDATE%s AVAILABLE | UPGRADING `apt full-upgrade`",
                             upgrade_count, (upgrade_count > 1) ? "S" : "");

        if (bytes > 0 && (size_t)bytes < sizeof(msg)) {
            char cmd[MAX_CMD_LEN];
            snprintf(cmd, sizeof(cmd), "sudo apt full-upgrade -y");
            run_task(msg, cmd, NULL);
        }
    }

    /* Step 3: Remove lingering packages and clear package archive caches */
    int orphan_count = count_orphaned_packages();
    char orphan_log[MAX_MSG_LEN];
    snprintf(orphan_log, sizeof(orphan_log), 
             "PURGING ORPHANED DEPENDENCIES & CONFIGS (`apt autoremove`) - %d package%s removed",
             orphan_count, (orphan_count == 1) ? "" : "s");
    run_task("PURGING ORPHANED DEPENDENCIES & CONFIGS `apt autoremove --purge`",
             "sudo apt autoremove --purge -y", orphan_log);

    int deb_count = count_cached_debs();
    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("WIPING ALL DOWNLOADED PACKAGE FILES `apt clean`",
             "sudo apt clean", deb_log);

    /* Step 4: Clean local user caches safely (suppressing error if glob matches 0 files) */
    int thumb_count = count_glob_files("~/.cache/thumbnails/*/*");
    if (thumb_count == 0) thumb_count = count_glob_files("~/.cache/thumbnails/*");
    char thumb_log[MAX_MSG_LEN];
    snprintf(thumb_log, sizeof(thumb_log),
             "CLEARING LOCAL THUMBNAIL CACHE - %d item%s deleted",
             thumb_count, (thumb_count == 1) ? "" : "s");
    run_task("CLEARING LOCAL THUMBNAIL CACHE `rm -rf ~/.cache/thumbnails/*`",
             "rm -rf ~/.cache/thumbnails/* 2>/dev/null || true", thumb_log);

    int shot_count = count_glob_files("~/Pictures/Screenshots/*");
    char shot_log[MAX_MSG_LEN];
    snprintf(shot_log, sizeof(shot_log),
             "CLEARING SCREENSHOTS FOLDER - %d file%s deleted",
             shot_count, (shot_count == 1) ? "" : "s");
    run_task("CLEARING SCREENSHOTS FOLDER `rm -rf ~/Pictures/Screenshots/*`",
             "rm -rf ~/Pictures/Screenshots/* 2>/dev/null || true", shot_log);

    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;
}