;;; eshell-starship.el --- Starship-like (https://starship.rs) prompt for eshell -*- lexical-binding: t; -*-
;;; Commentary:
;;; Code:

(require 'vc)
(require 'vc-git)
(require 'eshell)
(require 'cl-lib)

(defun eshell-starship--file-names-present-p (&rest names)
  "Test if any of NAMES (wildcards supported) exist in default directory."
  (catch 'found
    (dolist (name names)
      (when (seq-filter #'(lambda (name)
                            (not (string-prefix-p "." name)))
                        (file-expand-wildcards name))
        (throw 'found t)))))

(cl-defmacro eshell-starship-defmodule (name &body body
                                             &key files
                                             icon color allow-remote)
  "Define a starship module called NAME.
FILES s used to detect weather to call the module.  It is a list of wildcard
expressions.  SYMBOL and COLOR control the output of the module.  BODY should
return the string for the module, or nil if it could not be found."
  (declare (indent defun))
  `(defun ,(intern (format "eshell-starship--module-%s-func"
                           name)) ()
     ,(format "Module function for eshell-starship module %s." name)
     (or (when (and ,(if allow-remote t
                       '(not (file-remote-p default-directory)))
                    (eshell-starship--file-names-present-p ,files))
           (if-let (res (progn ,body))
               (concat " via " (propertize (concat ,icon " " res)
                                           'face (:foreground
                                                  ,color)))))
         "")))

(eshell-starship-defmodule cc
  :files '("*.c" "*.h")
  :icon "C"
  :color "green yellow")

(defun eshell-starship--cc-status ()
  "Return the current CC version if C files exist in `default-directory'.
Returns an empty string if no C .c or .h files exist or if current dir is
remote."
  (or (unless (file-remote-p default-directory)
        (when (eshell-starship--file-names-exist-p "*.h" "*.c")
          (with-temp-buffer
            (when (zerop (process-file "cc" nil t nil "-v"))
              (goto-char (point-min))
              (when (re-search-forward
                     "^\\([-a-zA-Z]+\\) version \\([0-9]+\\.[0-9]+\\.[0-9]+\\)"
                     nil t)
                (concat " via "
                        (propertize (concat "C v"
                                            (match-string 2)
                                            "-"
                                            (match-string 1))
                                    'face
                                    '(:foreground "green yellow")))
                ))))) ""))

(defun eshell-starship--replace-home-with-tilda (path)
  "If PATH beings with $HOME (the environment variable), replace it with ~."
  (let ((home (getenv "HOME")))
    (if (equal home path)
        "~"
      (setq home (file-name-as-directory home))
      (if (string-prefix-p home path)
          (concat "~/" (seq-subseq path (length home)))
        path))))

(defun eshell-starship--limit-path-parts (num path)
  "Cut PATH down to NUM components.
Example:
/this/is/a/path 3-> is/a/path"
  (let ((parts (string-split path "/" t nil)))
    (concat
     (when (and (file-name-absolute-p path)
                (not (equal "~" (car parts)))
                (<=  (length parts) num))
       "/")
     (string-join (last parts num) "/"))))

(defun eshell-starship--get-current-dir ()
  "Get dir for `eshell-starship--prompt-function'."
  (eshell-starship--limit-path-parts
   3 (if-let ((worktree (vc-root-dir))
              (parent (file-name-parent-directory worktree)))
         (file-relative-name default-directory parent)
       (eshell-starship--replace-home-with-tilda
        default-directory))))

(defun eshell-starship--git-parse-status-headers ()
  "Parse the status headers (read from the current buffer).
The headers are as described in the porcelain v2 section of the git-status(3)
man page.

The return value is a list of the form (oid head upstream ahead behind stash)"
  (let ((oid nil)
        (head nil)
        (upstream nil)
        (ahead nil)
        (behind nil)
        (stash nil))
    (while (and (char-after) (= (char-after) ?#))
      (forward-char 2)
      (cond
       ((looking-at "branch\\.oid ")
        (setq oid (buffer-substring-no-properties
                   (match-end 0)
                   (pos-eol))))
       ((looking-at "branch\\.head ")
        (setq head (buffer-substring-no-properties
                    (match-end 0)
                    (pos-eol))))
       ((looking-at "branch\\.upstream ")
        (setq upstream (buffer-substring-no-properties
                        (match-end 0)
                        (pos-eol))))
       ((looking-at "branch\\.ab ")
        (let ((ab-str (buffer-substring-no-properties
                       (match-end 0)
                       (pos-eol))))
          (when (string-match "\\(+[0-9]+\\) \\(-[0-9]+\\)$"
                              ab-str)
            (setq ahead (string-to-number (match-string 1 ab-str))
                  behind (string-to-number (match-string 2 ab-str))))))
       ((looking-at "stash ")
        (setq stash (string-to-number (buffer-substring-no-properties
                                       (match-end 0)
                                       (pos-eol))))))
      (forward-line))
    (list oid head upstream (or ahead 0) (or behind 0) stash)))

(defun eshell-starship--git-interpret-file-status (x y)
  "Return the prompt character for the status X and Y.
A description of X and Y can be found in the git-status(3) man page."
  (cond
   ((or (= x ?D) (= y ?D))
    ?)
   ((or (= x ?R) (= y ?R))
    ?»)
   ((= y ?M)
    ?!)
   ((or (= x ?A) (= x ?M))
    ?+)))

(defun eshell-starship--git-interpret-branch-status (ahead behind)
  "Get the status char for the current branch and its remote.
AHEAD should evaluate to t if the current branch is ahead of its remote, and
BEHIND should evaluate to t if the current branch is behind its remote."
  (cond
   ((and ahead behind) "󰹺")
   (ahead "󰜷")
   (behind "󰜮")))

(defun eshell-starship--git-file-status (stash ahead behind)
  "Get the file status string for the git prompt module.
STASH should be t if there is current stashed data stash.  AHEAD and BEHIND
should be as for `eshell-starship--git-interpret-branch-status'."
  (let ((merge-conflicts nil)
        (status-chars nil))
    (while (not (eobp))
      (cond
       ((= (char-after) ??)
        (push ?? status-chars))
       ((= (char-after) ?u)
        (setq merge-conflicts t))
       ((or (= (char-after) ?1)
            (= (char-after) ?2))
        (push (eshell-starship--git-interpret-file-status
               (char-after (+ 2 (point)))
               (char-after (+ 3 (point))))
              status-chars)))
      (forward-line))
    (concat (eshell-starship--git-interpret-branch-status (not (zerop ahead))
                                                          (not (zerop behind)))
            (when merge-conflicts "=")
            (when stash "$")
            (apply 'string (sort (seq-uniq status-chars) #'<)))))

(defun eshell-starship--git-current-operation ()
  "Return the current git operation.
For example, a revert.  If there is no current operation, return nil."
  (let ((git-dir (expand-file-name ".git" (vc-git-root default-directory))))
    (cond
     ((file-exists-p (expand-file-name "rebase-apply/applying" git-dir))
      "AM")
     ((file-exists-p (expand-file-name "rebase-apply/rebasing" git-dir))
      "REBASE")
     ((file-exists-p (expand-file-name "rebase-apply" git-dir))
      "AM/REBASE")
     ((file-exists-p (expand-file-name "rebase-merge" git-dir))
      "REBASING")
     ((file-exists-p (expand-file-name "CHERRY_PICK_HEAD" git-dir))
      "CHERRY-PICKING")
     ((file-exists-p (expand-file-name "MERGE_HEAD" git-dir))
      "MERGING")
     ((file-exists-p (expand-file-name "BISECT_LOG" git-dir))
      "BISECTING")
     ((file-exists-p (expand-file-name "REVERT_HEAD" git-dir))
      "REVERTING"))))

(defun eshell-starship--git-status ()
  "Return the text for the git module for `eshell-starship--prompt-function'."
  (with-temp-buffer
    (when (zerop (vc-git-command t nil nil "status" "--porcelain=v2"
                                 "--branch" "--show-stash"))
      (goto-char (point-min))
      (cl-destructuring-bind (oid head upstream ahead behind stash)
          (eshell-starship--git-parse-status-headers)
        (let ((file-status (eshell-starship--git-file-status stash ahead
                                                             behind))
              (operation (eshell-starship--git-current-operation)))
          (concat
           (if (string= "(detached)" head)
               (propertize (concat " (" (substring oid 0 7) ")")
                           'face '(:foreground "lawn green"))
             (propertize (concat " 󰊢 " head)
                         'face '(:foreground "medium purple")))
           (unless (string-empty-p file-status)
             (propertize (concat " [" file-status "]")
                         'face '(:foreground "red")))
           (when operation
             (concat " (" (propertize
                           operation 'face
                           '(:inherit bold :foreground "yellow")) ")"))))))))

(defun eshell-starship--vc-status ()
  "Get vc status for `eshell-starship--prompt-function'."
  (if-let (backend (vc-responsible-backend default-directory t))
      (if (eq backend 'Git)
          (eshell-starship--git-status)
        (propertize
         (concat "  " (downcase (symbol-name backend)))
         'face '(:foreground "purple")))))

(defvar-local eshell-starship--last-start-time nil
  "Start time of last eshell command.")

(defun eshell-starship--timer-pre-cmd ()
  "Command run before each eshell program to record the time."
  (setq eshell-starship--last-start-time (current-time)))

(add-hook 'eshell-pre-command-hook #'eshell-starship--timer-pre-cmd)

(defun eshell-starship--prompt-format-span (span)
  "Format SPAN as \"XhXms\"."
  (let* ((hours (/ span 3600))
         (mins (% (/ span 60) 60))
         (secs (% span 60)))
    (concat (unless (= hours 0)
              (format "%dh" hours))
            (unless (= mins 0)
              (format "%dm" mins))
            (format "%ds" secs))))

(defun eshell-starship--last-command-time (end-time)
  "Return the prompt component for the time of the last command.
END-TIME is the time when the command finished executing."
  (if-let ((eshell-starship--last-start-time)
           (len (time-subtract end-time
                               eshell-starship--last-start-time))
           (float-len (float-time len))
           ((< 3 float-len))
           (int-len (round float-len)))
      (concat " time "
              (propertize (eshell-starship--prompt-format-span int-len)
                          'face '(:foreground "gold1")))))

(defun eshell-starship--prompt-function ()
  "Function for `eshell-prompt-function'."
  (let* ((end-time (current-time))
         (dir (eshell-starship--get-current-dir))
         (prompt (concat
                  "\n"
                  (propertize dir 'face '(:foreground "dark turquoise"))
                  (unless (file-writable-p dir)
                    " ")
                  (eshell-starship--vc-status)
                  (eshell-starship--cc-status)
                  (eshell-starship--last-command-time end-time)
                  (propertize "\n" 'read-only t 'rear-nonsticky t)
                  (propertize
                   "❯ " 'face `(:foreground
                                ,(if (= eshell-last-command-status 0)
                                     "lime green"
                                   "red"))
                   'rear-nonsticky t))))
    (setq eshell-starship--last-start-time nil)
    prompt))

(defvar-local ehsell-starship--restore-state nil
  "State of various variables set by `eshell-starship-prompt-mode'.")

;;;###autoload
(define-minor-mode eshell-starship-prompt-mode
  "Minor mode to make eshell prompts look like starship (https://starship.rs)."
  :global nil
  :init-value nil
  :interactive (eshell-mode)
  (if eshell-starship-prompt-mode
      (setq-local eshell-starship--restore-state
                  (buffer-local-set-state eshell-prompt-function
                                          'eshell-starship--prompt-function
                                          eshell-prompt-regexp "^❯ "
                                          eshell-highlight-prompt nil))
    (buffer-local-restore-state eshell-starship--restore-state)))

(provide 'eshell-starship)
;;; eshell-starship.el ends here