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+;;; eshell-prompt.el --- Generating a good prompt for Eshell  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024  Aryadev Chavali
+
+;; Author: Aryadev Chavali <aryadev@aryadevchavali.com>
+;; Keywords:
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation version 2 of the License.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; We provide a function +eshell-prompt which generates a prompt on
+;; demand.
+
+;;; Code:
+
+(defvar +eshell-prompt/user-prompt "𝜆> "
+  "Prompt for user to input.")
+
+(defun +eshell-prompt/--colour-on-last-command ()
+  "Returns an Emacs colour based on ESHELL-LAST-COMMAND-STATUS."
+  (if (zerop eshell-last-command-status)
+      "forestgreen"
+    "darkred"))
+
+(defun +eshell-prompt/--git-remote-status ()
+  "Returns a propertized string for the status of a repository
+in comparison to its remote.  3 differing strings are returned
+dependent on:
+
+- Is it equivalent to the remote?
+- Is it ahead of the remote?
+- Is it behind the remote?
+
+The latter 2 also have a number for exactly how many commits
+behind or ahead the local repository is."
+  (let* ((git-cmd "git status | grep 'Your branch is'")
+         (branch-status (split-string (shell-command-to-string git-cmd)))
+         (status (nth 3 branch-status))
+         (diff (cl-position "by" branch-status :test #'string=)))
+    (if (null diff)
+        (propertize "=" 'font-lock-face '(:foreground "green"))
+      (let ((n (nth (+ 1 diff) branch-status)))
+        (concat
+         (cond
+          ((string= status "ahead")
+           (propertize "→ " 'font-lock-face '(:foreground "dodger blue")))
+          ((string= status "behind")
+           (propertize "← " 'font-lock-face '(:foreground "orange red"))))
+         n)))))
+
+(defun +eshell-prompt/--git-change-status ()
+  "Returns a propertized string for the condition of the worktree in
+a repository.  If there are no changes i.e. the worktree is clean
+then a green tick is returned, but if there are changes then the
+number of files affected are returned in red."
+  (let* ((git-cmd "git status -s")
+         (command-output (split-string git-cmd))
+         (changed-files (- (length command-output) 1)))
+    (if (= changed-files 0)
+        (propertize "✓" 'font-lock-face '(:foreground "green"))
+      (propertize (number-to-string changed-files) 'font-lock-face '(:foreground "red")))))
+
+(defun +eshell-prompt/--git-status ()
+  "Returns a completely formatted string of
+form (BRANCH-NAME<CHANGES>[REMOTE-STATUS])."
+  (let ((git-branch (shell-command-to-string "git brnach")))
+    (if (or (string= git-branch "")
+           (not (string= "*" (substring git-branch 0 1))))
+        ""
+      (format
+       "(%s<%s>[%s])"
+       (nth 2 (split-string git-branch "\n\\|\\*\\| "))
+       (+eshell-prompt/--git-change-status)
+       (+eshell-prompt/--git-remote-status)))))
+
+(defun +eshell-prompt/make-prompt ()
+  (let ((git (+eshell-prompt/--git-status)))
+    (mapconcat
+     (lambda (item)
+       (if (listp item)
+           (propertize (car item)
+                       'read-only t
+                       'font-lock-face (cdr item)
+                       'front-sticky   '(font-lock-face read-only)
+                       'rear-nonsticky '(font-lock-face read-only))
+         item))
+     (list
+      "["
+      `(,(abbreviate-file-name (eshell/pwd)) :foreground "LimeGreen")
+      "]"
+      (if (string= git "")
+          ""
+        (concat "-" git ""))
+      "\n"
+      `(,(format-time-string "[%H:%M:%S]") :foreground "purple")
+      "\n"
+      (list "𝜆> " ':foreground (+eshell-prompt/--colour-on-last-command))))))
+
+
+(provide 'eshell-prompt)
+;;; eshell-prompt.el ends here