;;; erts-mode.el --- major mode to edit erts files  -*- lexical-binding: t; -*-

;; Copyright (C) 2021-2025 Free Software Foundation, Inc.

;; Keywords: tools

;; This file is part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;;; Code:

(eval-when-compile (require 'cl-lib))
(require 'ert)

(defgroup erts-mode nil
  "Major mode for editing Emacs test files."
  :group 'lisp)

(defface erts-mode-specification-name
  '((((class color)
      (background dark))
     :foreground "green")
    (((class color)
      (background light))
     :foreground "cornflower blue")
    (t
     :bold t))
  "Face used for displaying specification names."
  :group 'erts-mode)

(defface erts-mode-specification-value
  '((((class color)
      (background dark))
     :foreground "DeepSkyBlue1")
    (((class color)
      (background light))
     :foreground "blue")
    (t
     :bold t))
  "Face used for displaying specification values."
  :group 'erts-mode)

(defface erts-mode-start-test
  '((t :inherit font-lock-keyword-face))
  "Face used for displaying specification test start markers."
  :group 'erts-mode)

(defface erts-mode-end-test
  '((t :inherit font-lock-comment-face))
  "Face used for displaying specification test start markers."
  :group 'erts-mode)

(defvar-keymap erts-mode-map
  :parent prog-mode-map
  "C-c C-r" #'erts-tag-region
  "C-c C-c" #'erts-run-test)

(defvar erts-mode-font-lock-keywords
  ;; Specifications.
  `((erts-mode--match-not-in-test
     ("^\\([^ \t\n:]+:\\)[ \t]*\\(.*\\(\n[ \t].*\\)*\\)\n?"
      (progn (goto-char (match-beginning 0)) (match-end 0)) nil
      (1 'erts-mode-specification-name)
      (2 'erts-mode-specification-value)))
    ("^=-=$" 0 'erts-mode-start-test)
    ("^=-=-=$" 0 'erts-mode-end-test)))

(defun erts-mode--match-not-in-test (_limit)
  (when (erts-mode--in-test-p (point))
    (erts-mode--end-of-test))
  (let ((start (point)))
    (goto-char
     (if (re-search-forward "^=-=$" nil t)
         (match-beginning 0)
       (point-max)))
    (if (< (point) start)
        nil
      ;; Here we disregard LIMIT so that we may extend the area again.
      (set-match-data (list start (point)))
      (point))))

(defun erts-mode--end-of-test ()
  (search-forward "^=-=-=\n" nil t))

(defun erts-mode--in-test-p (point)
  "Say whether POINT is in a test."
  (save-excursion
    (goto-char point)
    (beginning-of-line)
    (if (looking-at "=-=\\(-=\\)?$")
        t
      (let ((test-start (save-excursion
                          (re-search-backward "^=-=\n" nil t))))
        ;; Before the first test.
        (and test-start
             (let ((test-end (re-search-backward "^=-=-=\n" nil t)))
               (or (null test-end)
                   ;; Between tests.
                   (> test-start test-end))))))))

;;;###autoload
(define-derived-mode erts-mode prog-mode "erts"
  "Major mode for editing erts (Emacs testing) files.
This mode mainly provides some font locking.

\\{erts-mode-map}"
  (setq-local font-lock-defaults '(erts-mode-font-lock-keywords t)))

(defun erts-tag-region (start end name)
  "Tag the region between START and END as a test.
Interactively, this is the region.

NAME should be a string appropriate for output by ert if the test fails.
If NAME is nil or the empty string, a name will be auto-generated."
  (interactive "r\nsTest name: " erts-mode)
  ;; Automatically make a name.
  (when (zerop (length name))
    (save-excursion
      (goto-char (point-min))
      (let ((names nil))
        (while (re-search-forward "^Name:[ \t]*\\(.*\\)" nil t)
          (let ((name (match-string 1)))
            (unless (erts-mode--in-test-p (point))
              (push name names))))
        (setq name
              (cl-loop with base = (file-name-sans-extension (buffer-name))
                       for i from 1
                       for name = (format "%s%d" base i)
                       unless (member name names)
                       return name)))))
  (save-excursion
    (goto-char end)
    (unless (bolp)
      (insert "\n"))
    (insert "=-=-=\n")
    (goto-char start)
    (insert "Name: " name "\n\n")
    (insert "=-=\n")))

(defun erts-mode--preceding-spec (name)
  (save-excursion
    ;; Find the name, but skip if it's in a test.
    (while (and (re-search-backward (format "^%s:" name)  nil t)
                (erts-mode--in-test-p (point))))
    (and (not (erts-mode--in-test-p (point)))
         (re-search-forward "^=-=$" nil t)
         (progn
           (goto-char (match-beginning 0))
           (cdr (assq (intern (downcase name))
                      (ert--erts-specifications (point))))))))

(defun erts-run-test (test-function &optional verbose)
  "Run the current test.
If the current erts file doesn't define a test function, the user
will be prompted for one.

If VERBOSE (interactively, the prefix), display a diff of the
expected results and the actual results in a separate buffer."
  (interactive
   (list (or (erts-mode--preceding-spec "Code")
             (read-string "Transformation function: "))
         current-prefix-arg)
   erts-mode)
  (save-excursion
    (erts-mode--goto-start-of-test)
    (condition-case arg
        (ert-test--erts-test
         (list (cons 'dummy t)
               (cons 'code (car (read-from-string test-function)))
               (cons 'point-char (save-match-data
                                   (erts-mode--preceding-spec "Point-Char"))))
         (buffer-file-name))
      (:success (message "Test successful"))
      (ert-test-failed
       (if (not verbose)
           (message "Test failure; result: \n%s"
                    (substring-no-properties (cadr (cadr arg))))
         (message "Test failure")
         (let (expected got)
           (unwind-protect
               (progn
                 (with-current-buffer
                     (setq expected (generate-new-buffer "erts expected"))
                   (insert (nth 1 (cadr arg))))
                 (with-current-buffer
                     (setq got (generate-new-buffer "erts results"))
                   (insert (nth 2 (cadr arg))))
                 (diff-buffers expected got))
             (kill-buffer expected)
             (kill-buffer got))))))))

(defun erts-mode--goto-start-of-test ()
  (if (not (erts-mode--in-test-p (point)))
      (re-search-forward "^=-=\n" nil t)
    (re-search-backward "^=-=\n" nil t)
    (let ((potential-start (match-end 0)))
      ;; See if we're in a two-clause ("before" and "after") test or not.
      (if-let ((start (and (save-excursion (re-search-backward "^=-=\n" nil t))
                           (match-end 0))))
          (let ((end (save-excursion (re-search-backward "^=-=-=\n" nil t))))
            (if (or (not end)
                    (> start end))
                ;; We are, so go to the real start.
                (goto-char start)
              (goto-char potential-start)))
        (goto-char potential-start)))))

(provide 'erts-mode)

;;; erts-mode.el ends here
