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

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

(defun eshell-starship--git-process-lines (&rest flags)
  "Run `vc-git-program' and return an array of its output lines.
FLAGS are passed to `vc-git-program' as its arguments."
  (with-temp-buffer
    (apply 'vc-git-command t 0 nil flags)
    (if (zerop (buffer-size))
        '()
      (string-lines (buffer-substring-no-properties 1 (buffer-size))))))

(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--prompt-cut-path (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--prompt-get-dir ()
  "Get dir for `eshell-starship--prompt-function'."
  (eshell-starship--prompt-cut-path 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--prompt-current-branch-status (status-line)
  "Get the status char for the current branch and its remote.
STATUS-LINE is the first line of output from \"git status --porcelain=v1 -b\"."
  (when (string-match
         "\\[\\(?:ahead \\([0-9]+\\)\\)?,? ?\\(?:behind \\([0-9]+\\)\\)?\\]$"
         status-line)
    (let ((ahead (match-string 1 status-line))
          (behind (match-string 2 status-line)))
      (cond
       ((and ahead behind) ?󰹺)
       (ahead ?󰜷)
       (behind ?󰜮)))))

(defun eshell-starship--prompt-git-has-stash ()
  "Return t if the current git directory has a stash, nil otherwise."
  (= (process-file vc-git-program nil nil nil
                   "rev-parse" "--verify" "refs/stash") 0))

(defun eshell-starship--prompt-git-state-chars ()
  "Get chars, like + and ✘ for `eshell-starship--prompt-function'."
  (let* ((lines (eshell-starship--git-process-lines "status" "--porcelain=v1" "-b"))
         (branch-status (eshell-starship--prompt-current-branch-status
                         (car lines)))
         (status-arr))
    (dolist (line (cdr lines))
      (cl-loop with fields = (string-split line " " t " *")
               with status-str = (car-safe fields)
               for status-char across status-str
               do
               (cond ((or (= status-char ?M) (= status-char ?T))
                      (push ?! status-arr))
                     ((= status-char ??)
                      (push ?? status-arr))
                     ((or (= status-char ?A) (= status-char ?C))
                      (push ?+ status-arr))
                     ((= status-char ?D)
                      (push ? status-arr))
                     ((= status-char ?R)
                      (push ?» status-arr))
                     ((= status-char ?U)
                      (push ?= status-arr)))))
    (when (eshell-starship--prompt-git-has-stash)
      (push ?$ status-arr))
    (sort status-arr #'<)
    (when branch-status
      (push branch-status status-arr))
    (apply 'string (seq-uniq status-arr))))

(defun eshell-starship--prompt-git-get-operation ()
  "Return the current git operation.  For example, a revert."
  (let ((git-dir (expand-file-name ".git" (vc-git-root default-directory))))
    (cond
     ((file-exists-p (expand-file-name "REVERT_HEAD" git-dir))
      "REVERTING")
     ((file-exists-p (expand-file-name "rebase-merge" git-dir))
      "REBASING")
     ((file-exists-p (expand-file-name "MERGE_HEAD" git-dir))
      "MERGING"))))

(defun eshell-starship--prompt-git-status ()
  "Get git status for `eshell-starship--prompt-function'."
  (let ((branch (car (vc-git-branches)))
        (state (eshell-starship--prompt-git-state-chars))
        (operation (eshell-starship--prompt-git-get-operation)))
    (concat
     (propertize (concat " 󰊢 " branch) 'face '(:foreground "medium purple"))
     (unless (string-empty-p state)
       (propertize (concat " [" state "]") 'face '(:foreground "red")))
     (when operation
       (concat " (" (propertize operation 'face
                                '(:inherit 'bold :foreground "yellow")) ")")))))

(defun eshell-starship--prompt-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--prompt-git-status)
        (propertize
         (concat "  " (downcase (symbol-name backend)))
         'face '(:foreground "purple")))))

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

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

(add-hook 'eshell-pre-command-hook #'eshell-starship--prompt-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--prompt-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--prompt-last-start-time)
           (len (time-subtract end-time
                               eshell-starship--prompt-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--prompt-get-dir))
         (prompt (concat
                  "\n"
                  (propertize dir 'face '(:foreground "dark turquoise"))
                  (unless (file-writable-p dir)
                    " ")
                  (eshell-starship--prompt-vc-status)
                  (eshell-starship--prompt-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--prompt-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