;;; bundle--linux.el --- A bundle of useful Linux information

;;; Commentary:
;; This file contains a variety of Emacs Lisp functions that provide
;; helpful descriptions for Linux directories, commands, and options.

;;; Code:

(defvar linux-filesystem-alist
  '(( "/" . "Root directory, the base of the filesystem hierarchy")
    ("/bin" . "Essential command binaries, needed for booting")
    ("/boot" . "Bootloader files, kernel, and other files needed during booting")
    ("/dev" . "Device files representing hardware components")
    ("/etc" . "System-wide configuration files")
    ("/home" . "User home directories")
    ("/lib" . "Shared libraries and kernel modules")
    ("/media" . "Mount points for removable media like CDs and USBs")
    ("/mnt" . "Temporary mount points for filesystems")
    ("/opt" . "Optional application software packages")
    ("/proc" . "Virtual filesystem providing info about processes and system")
    ("/root" . "Home directory for the root user")
    ("/sbin" . "Essential system binaries, usually for the root user")
    ("/srv" . "Data directories for services like HTTP, FTP, etc.")
    ("/sys" . "Virtual filesystem for kernel objects")
    ("/tmp" . "Temporary files, cleared on reboot")
    ("/usr" . "User binaries, documentation, libraries, etc.")
    ("/var" . "Variable files like logs, databases, etc."))
  "Alist mapping Linux directories to their descriptions.")

(defun describe-linux-directory (dirname)
  "Describe the purpose of a Linux directory.
Takes DIRNAME as an argument and prints its description."
  (interactive "sEnter Linux directory name (e.g., /bin): ")
  (let ((description (assoc-default dirname linux-filesystem-alist)))
    (if description
        (message "%s: %s" dirname description)
      (message "Unknown directory: %s" dirname))))

(defvar bash-regex-alist
  '(("empty line" . "^$")
    ("backslash" . "\\\\")
    ("line starts with a dot" . "^\\.")
    ("line ends with a dot" . "\\.$")
    ("line starts with a dollar sign" . "^\\$")
    ("line starts with a caret" . "^\\^")
    ("left square bracket" . "\\[")
    ("right square bracket" . "\\]")
    ("entire line" . "^.*$")
    ("any alphanumeric character" . "[a-zA-Z0-9]")
    ("IP Address" . "\\b(?:[0-9]{1,3}\\.){3}[0-9]{1,3}\\b")
    ("email" . "[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}")
    ("hex color code" . "#[a-fA-F0-9]{6}")
    ("date in yyyy-mm-dd" . "\\b\\d{4}-\\d{2}-\\d{2}\\b")
    ("time in hh:mm:ss" . "\\b\\d{2}:\\d{2}:\\d{2}\\b")
    ("words without vowels" . "\\b[^aeiou\s]+\\b"))
  "Alist mapping Bash regular expressions to their descriptions.")

(defun describe-bash-regex (regex)
  "Describe the purpose of a Bash regular expression.
Takes REGEX as an argument and prints its description."
  (interactive "sEnter Bash regex (e.g., empty line): ")
  (let ((description (assoc-default regex bash-regex-alist)))
    (if description
        (message "%s: %s" regex description)
      (message "Unknown regular expression: %s" regex))))

(defvar linux-process-commands-alist
  '(("ps" . "Shows a snapshot of the current processes")
    ("top" . "Displays dynamic real-time view of system stats and processes")
    ("htop" . "An interactive process viewer, similar to top but more feature-rich")
    ("pgrep" . "Looks up processes based on name and other attributes")
    ("pstree" . "Displays the process tree in a tree-like diagram")
    ("ps -e" . "Lists all the processes running on the system")
    ("ps aux" . "Displays detailed information about all processes")
    ("kill" . "Terminates processes by sending signals")
    ("killall" . "Kills all processes that match the given name")
    ("pkill" . "Send signals to processes based on name and other attributes"))
  "Alist mapping Linux process-checking commands to their descriptions.")

(defun describe-linux-process-command (command)
  "Describe the purpose of a Linux process-checking command.
Takes COMMAND as an argument and prints its description."
  (interactive "sEnter Linux process command (e.g., ps): ")
  (let ((description (assoc-default command linux-process-commands-alist)))
    (if description
        (message "%s: %s" command description)
      (message "Unknown command: %s" command))))

(defvar linux-logfiles-alist
  '(("/var/log/syslog" . "System messages, including the messages that are logged during system startup")
    ("/var/log/auth.log" . "Security/authorization information, including user logins and authentication")
    ("/var/log/kern.log" . "Kernel logs")
    ("/var/log/cron.log" . "Logs for cron jobs")
    ("/var/log/messages" . "General system activity logs")
    ("/var/log/boot.log" . "System boot log")
    ("/var/log/daemon.log" . "Background daemon log messages")
    ("/var/log/dpkg.log" . "Logs for package installations and removals")
    ("/var/log/mail.log" . "Mail server logs")
    ("/var/log/user.log" . "User-level messages"))
  "Alist mapping Linux log files to their descriptions.")

(defun describe-linux-logfile (logfile)
  "Describe the purpose of a Linux log file.
Takes LOGFILE as an argument and prints its description."
  (interactive "sEnter Linux log file path (e.g., /var/log/syslog): ")
  (let ((description (assoc-default logfile linux-logfiles-alist)))
    (if description
        (message "%s: %s" logfile description)
      (message "Unknown log file: %s" logfile))))

(defvar linux-basic-commands-alist
  '(("list directory contents" . "ls")
    ("change directory" . "cd")
    ("move or rename files" . "mv")
    ("copy files" . "cp")
    ("remove files or directories" . "rm")
    ("print working directory" . "pwd")
    ("display variable value" . "echo")
    ("create an empty file" . "touch")
    ("change file permissions" . "chmod")
    ("change file ownership" . "chown"))
  "Alist mapping basic Linux command descriptions to their commands.")

(defun describe-basic-linux-command (command)
  "Describe the purpose of a basic Linux command.
Takes COMMAND as an argument and prints its description."
  (interactive "sEnter basic Linux command (e.g., ls): ")
  (let ((description (assoc-default command linux-basic-commands-alist)))
    (if description
        (message "%s: %s" command description)
      (message "Unknown command: %s" command))))

(defvar chown-options-alist
  '(("-R" . "Operate on files and directories recursively")
    ("--from" . "Change the owner and/or group of each file only if its current owner and/or group match specified values")
    ("--no-dereference" . "Affect symbolic links instead of the files they point to")
    ("--preserve-root" . "Fail when attempting to operate recursively on '/'")
    ("--reference" . "Use owner and group of a reference file")
    ("-c" . "Report when a change is made")
    ("-f" . "Suppress most error messages")
    ("-v" . "Output a diagnostic for every file processed"))
  "Alist mapping chown command options to their descriptions.")

(defun describe-chown-option (option)
  "Describe the purpose of a chown option.
Takes OPTION as an argument and prints its description."
  (interactive "sEnter chown option (e.g., -R): ")
  (let ((description (assoc-default option chown-options-alist)))
    (if description
        (message "%s: %s" option description)
      (message "Unknown chown option: %s" option))))

(defvar chmod-options-alist
  '(("-R" . "Operate on files and directories recursively")
    ("--preserve-root" . "Avoid operating recursively on '/'")
    ("-c" . "Report when a change is made")
    ("-f" . "Suppress most error messages")
    ("-v" . "Output a diagnostic for every file processed")
    ("--reference" . "Use mode of a reference file")
    ("-w" . "Remove write permission")
    ("-x" . "Remove execute permission")
    ("-u" . "Set user ID on execution")
    ("-g" . "Set group ID on execution"))
  "Alist mapping chmod command options to their descriptions.")

(defun describe-chmod-option (option)
  "Describe the purpose of a chmod option.
Takes OPTION as an argument and prints its description."
  (interactive "sEnter chmod option (e.g., -R): ")
  (let ((description (assoc-default option chmod-options-alist)))
    (if description
        (message "%s: %s" option description)
      (message "Unknown chmod option: %s" option))))

(defvar ssh-use-cases-alist
  '(("remote login" . "ssh user@host")
    ("run command" . "ssh user@host 'command'")
    ("file transfer" . "scp file.txt user@host:/path/")
    ("secure ftp" . "sftp user@host")
    ("port forwarding" . "ssh -L local_port:remote_host:remote_port user@host")
    ("dynamic port forwarding" . "ssh -D port user@host")
    ("remote port forwarding" . "ssh -R remote_port:local_host:local_port user@host")
    ("tunneling" . "ssh -L local_port:remote_host:remote_port user@host -f -N")
    ("agent forwarding" . "ssh -A user@host")
    ("ssh multiplexing" . "ssh -M -S /tmp/ssh_socket user@host; ssh -S /tmp/ssh_socket user@host"))
  "Alist mapping SSH use cases to their corresponding commands.")

(defun describe-ssh-use-case (use-case)
  "Describe the SSH command for a given use case."
  (interactive "sEnter the SSH use case: ")
  (let ((command (assoc-default use-case ssh-use-cases-alist)))
    (if command
        (message "Command for %s: %s" use-case command)
      (message "Use case not found"))))

(defvar mk/remote-*host-aliases*
  '(("website" . "marcus@www.marcuskammer.dev")
    ("survey" . "cl@survey.metalisp.dev")
    ("pihole" . "ubuntu@pi-hole.fritz.box"))
  "Alist mapping friendly host names to actual SSH-compatible host strings.")

(defun mk/remote--get-real-host (alias)
  "Lookup the real host name based on a given ALIAS."
  (or (cdr (assoc alias mk/remote-*host-aliases*)) alias))

(defun mk/remote--systemctl-service (alias service command)
  "Execute a systemctl COMMAND on a systemd SERVICE on a remote host identified by ALIAS.

ALIAS is a string that specifies the remote host; it can be an
alias defined in `mk/remote-*host-aliases*'.

SERVICE is the name of the systemd service to operate on.

COMMAND is the systemctl command to execute on the service (e.g.,
'start', 'stop', 'status')."
  (let* ((host (mk/remote--get-real-host alias))
         (buffer (generate-new-buffer (format "*%s-%s-%s*" alias service command)))
         (process-name (format "systemctl-%s-%s" command service)))
    (make-process :name process-name
		          :buffer buffer
		          :command `("ssh" ,host "sudo" "systemctl" ,command ,service)
		          :sentinel (lambda (process signal)
			                  (when (memq (process-status process) '(exit signal))
				                (message "Process: %s %s" process signal))))))

(defmacro mk/remote-define-systemctl-functions (&rest actions)
  "Dynamically create functions to interact with systemd services on a remote host.

Each function will be named `mk/remote-ACTION-service', where
ACTION is one of the symbols in ACTIONS. The functions will take
an ALIAS and SERVICE as arguments and call
`mk/remote--systemctl-service' accordingly."
  `(progn
     ,@(mapcar
        (lambda (action)
          `(defun ,(intern (format "mk/remote-%s-service" action)) (alias service)
             (interactive "sEnter the host alias or name: \nsEnter the service name: ")
             (mk/remote--systemctl-service alias service ,(symbol-name action))))
        actions)))

(mk/remote-define-systemctl-functions start stop status)

(defun mk/remote--log (alias service filename)
  (let* ((filepath (concat "/var/log/" service (unless (string-empty-p filename) (concat "/" filename))))
	     (host (mk/remote--get-real-host alias))
	     (buffer (generate-new-buffer (format "*%s-%s-%s*" alias service filename)))
	     (process-name (format "log-%s-%s" service filename)))
    (make-process :name process-name
		          :buffer buffer
		          :command `("ssh" ,host "sudo" "tail -f" ,filepath)
		          :sentinel (lambda (process signal)
			                  (when (memq (process-status process) '(exit signal))
				                (message "Process: %s %s" process signal))))))

(defmacro mk/define-remote-log-function (alias service &optional filename)
  "Define a function to asynchronously tail a remote log file."
  (let ((fname (if filename filename "")))
    `(defun ,(intern (format "mk/remote-log-%s-%s-%s" alias service filename)) ()
       ,(format "Tail the remote log file: %s" filename)
       (interactive)
       (mk/remote--log ,alias ,service ,fname))))

(mk/define-remote-log-function "website" "nginx" "access.csv")
(mk/define-remote-log-function "website" "nginx" "error.log")
(mk/define-remote-log-function "website" "syslog")
(mk/define-remote-log-function "survey" "nginx" "access.csv")
(mk/define-remote-log-function "survey" "syslog")
(mk/define-remote-log-function "pihole" "pihole" "pihole.log")