;;; multi-eshell.el --- multi-eshell                 -*- lexical-binding: t; -*-

;; Copyright (C) 2023  Thanos Apollo

;; Author: Thanos Apollo <public@thanosapollo.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, either version 3 of the License, or
;; (at your option) any later version.

;; 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:

;;

;;; Code:

(defun if-void (arg default)
  (if (boundp arg)
      (eval arg)
    default
    ))

(defgroup multi-eshell nil
  "Simple support for having multiple shells open."
  :group 'languages)

(defcustom multi-eshell-shell-function '(eshell)
  "Command called to create shell"
  :group 'multi-eshell)

(defcustom multi-eshell-name "*eshell*" "The name of the buffer opened by the shell command."
  :type 'string
  :group 'multi-eshell)

(defun multi-eshell-function ()
  "This function opens the appropriate shell."
  (eval multi-eshell-shell-function))

(defvar multi-eshell-ring (make-ring 100)
  "This stores a bunch of buffers, which are shells created by multi-eshell." )
(setq multi-eshell-index 0 )
(defvar multi-eshell-last-buffer nil)

(defun multi-eshell-is-current-buffer-current-multi-eshell (&optional ignored)
  "Checks if current buffer is the current multi-eshell."
  (eq (current-buffer) (ring-ref multi-eshell-ring multi-eshell-index)))

(defun multi-eshell-switch-to-current-shell (&optional ignored)
  "Switch to shell buffer."
  (if (buffer-live-p (ring-ref multi-eshell-ring multi-eshell-index))
      (switch-to-buffer (ring-ref multi-eshell-ring multi-eshell-index))))

(defun multi-eshell-current-shell (&optional ignored)
  "Returns the current multi-eshell."
  (ring-ref multi-eshell-ring multi-eshell-index))

(defun multi-eshell-switch-to-next-live-shell (&optional ignored)
  "Switches to the next live shell. Creates one if none exists."
  (interactive "p")
  (let ((still-looking t)
	(empty nil))
    (while (and still-looking (not empty))
      (if (ring-empty-p multi-eshell-ring)
	  (progn
	    (setq empty t)
	    (multi-eshell 1))
	(progn
	  (if (buffer-live-p (ring-ref multi-eshell-ring multi-eshell-index))
	      (progn
		(setq multi-eshell-index (+ multi-eshell-index 1))
		(switch-to-buffer (ring-ref multi-eshell-ring multi-eshell-index))
		(setq still-looking nil))
	    (ring-remove multi-eshell-ring multi-eshell-index)))))))

;;;###autoload
(defun multi-eshell-go-back (&optional ignored)
  "Switch to buffer multi-eshell-last-buffer."
  (interactive "p")
  (if (buffer-live-p multi-eshell-last-buffer)
      (switch-to-buffer multi-eshell-last-buffer)
    (message "Last buffer visited before multi-eshell is gone. Nothing to go back to..")))


;;;###autoload
(defun multi-eshell-switch (&optional ignored)
  "If current buffer is not an multi-eshell, switch to current multi-eshell buffer. Otherwise, switch to next multi-eshell buffer."
  (interactive "p")
  (progn
    (setq multi-eshell-last-buffer (current-buffer))
    (let ((still-looking t)
	  (empty nil))
      (if (ring-empty-p multi-eshell-ring)
	  (multi-eshell 1)
	(if (and (buffer-live-p (multi-eshell-current-shell) )
		 (not (eq (multi-eshell-current-shell) (current-buffer))))
	    (switch-to-buffer (multi-eshell-current-shell))
	  (multi-eshell-switch-to-next-live-shell))))))

;;;###autoload
(defun multi-eshell (&optional numshells)
  "Creates a shell buffer. If one already exists, this creates a new buffer, with the name '*shell*<n>', where n is chosen by the function generate-new-buffer-name."
  (interactive "p")
  (progn
    (setq multi-eshell-last-buffer (current-buffer))
    (dotimes (i (if-void 'numshells 1) nil)
      (let ( (tempname (generate-new-buffer-name "*tempshell*"))
	     (new-buff-name (generate-new-buffer-name multi-eshell-name))
	     (localdir default-directory))
	(if (eq (get-buffer multi-eshell-name) nil)
	    (progn
	      (multi-eshell-function)
	      (ring-insert multi-eshell-ring (current-buffer))
	      (setq multi-eshell-index (+ multi-eshell-index 1)))
	  (progn
	    (interactive)
	    (multi-eshell-function)
	    (rename-buffer tempname)
	    (multi-eshell-function)
	    (rename-buffer new-buff-name )
	    (switch-to-buffer tempname)
	    (rename-buffer multi-eshell-name)
	    (switch-to-buffer new-buff-name)
	    (ring-insert multi-eshell-ring (current-buffer) )
	    (setq multi-eshell-index (+ multi-eshell-index 1))))))))

(defun shell-with-name (name)
  "Creates a shell with name given by the first argument, and switches to it. If a buffer with name already exists, we simply switch to it."
  (let ((buffer-of-name (get-buffer name))
	(tempname (generate-new-buffer-name "*tempshell*") ) )
    (cond ((bufferp buffer-of-name) ;If the buffer exists, switch to it (assume it is a shell)
	   (switch-to-buffer name))
	  ((bufferp (get-buffer multi-eshell-name))
	   (progn
	     (multi-eshell-function)
	     (rename-buffer tempname)
	     (multi-eshell-function)
	     (rename-buffer name)
	     (switch-to-buffer tempname)
	     (rename-buffer multi-eshell-name)
	     (switch-to-buffer name)))
	  (t
	   (progn
	     (multi-eshell-function)
	     (rename-buffer name))))))

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