;;; comint-ledger.el --- Command interpreter for the Ledger CLI  -*- lexical-binding: t; -*-

;; Author: Bram Schoenmakers
;; URL: https://apps.bram85.nl/git/bram/comint-ledger
;; Version: 0.1
;; Keywords: processes
;; Package-Requires: ((emacs "28.1"))

;;; This file is NOT part of GNU Emacs

;;; Commentary:
;;
;; Command interpreter (comint) for the Ledger CLI tool.
;; Starting point for this mode is Mickey Petersen's article on writing comint modes.
;;
;; https://www.masteringemacs.org/article/comint-writing-command-interpreter
;;
;;; Code:

(require 'comint)

(defvar ledger-cli-path (executable-find "ledger")
  "Path to the program used by `run-ledger'.")

(defvar ledger-file-path nil
  "Path to the ledger data file.")

(defvar ledger-cli-arguments '()
  "Commandline arguments to pass to `ledger'.")

(defvar ledger-mode-map
  (let ((map (nconc (make-sparse-keymap) comint-mode-map)))
    ;; example definition
    (define-key map "\t" 'completion-at-point)
    map)
  "Basic mode map for `run-ledger'.")

(defvar ledger-prompt-regexp (rx bol "] ")
  "Prompt for `run-ledger'.")

(defvar ledger-buffer-name "*Ledger*"
  "Name of the buffer to use for the `run-ledger' comint instance.")

;;;###autoload
(defun run-ledger ()
  "Run an inferior instance of `ledger' inside Emacs."
  (interactive)
  (let* ((ledger-program ledger-cli-path)
         (ledger-file-arguments (list "-f" ledger-file-path))
         (ledger-arguments (append ledger-file-arguments ledger-cli-arguments))
         (buffer (get-buffer-create ledger-buffer-name))
         (proc-alive (comint-check-proc buffer)))
    ;; if the process is dead then re-create the process and reset the
    ;; mode.
    (unless proc-alive
      (with-current-buffer buffer
        (apply 'make-comint-in-buffer "Ledger" buffer
               ledger-program nil ledger-arguments)
        (comint-ledger-mode)))
    ;; Regardless, provided we have a valid buffer, we pop to it.
    (when buffer
      (pop-to-buffer buffer))))

(defun ledger--initialize ()
  "Helper function to initialize ledger."
  (setq comint-process-echoes t)
  (setq comint-use-prompt-regexp t))

(define-derived-mode comint-ledger-mode comint-mode "comint-ledger"
  "Major mode for `run-ledger'.

\\<ledger-mode-map>"
  ;; this sets up the prompt so it matches things like: [foo@bar]
  (setq comint-prompt-regexp ledger-prompt-regexp)
  ;; this makes it read only; a contentious subject as some prefer the
  ;; buffer to be overwritable.
  (setq comint-prompt-read-only t)
  ;; this makes it so commands like M-{ and M-} work.
  (set (make-local-variable 'paragraph-separate) "\\'")
  (set (make-local-variable 'font-lock-defaults) '(ledger-font-lock-keywords t))
  (set (make-local-variable 'paragraph-start) ledger-prompt-regexp))

(add-hook 'ledger-mode-hook 'ledger--initialize)

(defconst ledger-keywords
  '()
  "List of keywords to highlight in `ledger-font-lock-keywords'.")

(defvar ledger-font-lock-keywords
  (list
   ;; highlight all the reserved commands.
   `(,(concat "\\_<" (regexp-opt ledger-keywords) "\\_>") . font-lock-keyword-face))
  "Additional expressions to highlight in `comint-ledger-mode'.")

(provide 'comint-ledger)

;;; comint-ledger.el ends here