;;; haskell-move-nested.el --- Change the column of text nested below a line -*- lexical-binding: t -*-

;; Copyright (C) 2010  Chris Done

;; Author: Chris Done <chrisdone@gmail.com>

;; This file is not part of GNU Emacs.

;; 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
;; <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This module is intended for Haskell mode users, but is
;; independent of Haskell mode.

;; Example usage:

;; (define-key haskell-mode-map (kbd "C-,") 'haskell-move-nested-left)
;; (define-key haskell-mode-map (kbd "C-.") 'haskell-move-nested-right)

;;; Code:

;;;###autoload
(defun haskell-move-nested (cols)
  "Shift the nested off-side-rule block adjacent to point by COLS columns to the right.

In Transient Mark mode, if the mark is active, operate on the contents
of the region instead.
"
  (save-excursion
    (if (and transient-mark-mode mark-active)
        (progn
          (indent-rigidly (region-beginning) (region-end) cols)
          (setq deactivate-mark nil))
      (let ((region (haskell-move-nested-region)))
        (when region
          (indent-rigidly (car region) (cdr region) cols))))))

;;;###autoload
(defun haskell-move-nested-right (cols)
  "Increase indentation of the following off-side-rule block adjacent to point.

Use a numeric prefix argument to indicate amount of indentation to apply.

In Transient Mark mode, if the mark is active, operate on the contents
of the region instead."
  (interactive "p")
  (haskell-move-nested cols))

;;;###autoload
(defun haskell-move-nested-left (cols)
  "Decrease indentation of the following off-side-rule block adjacent to point.

Use a numeric prefix argument to indicate amount of indentation to apply.

In Transient Mark mode, if the mark is active, operate on the contents
of the region instead."
  (interactive "p")
  (haskell-move-nested (- cols)))

(defun haskell-move-nested-region ()
  "Infer region off-side-rule block adjacent to point.
Used by `haskell-move-nested'.
"
  (save-excursion
    (let ((starting-level (current-column)))
      (forward-line)
      (let ((current-level (haskell-move-nested-indent-level)))
        (let ((start-point (line-beginning-position))
              (start-end-point (line-end-position))
              (end-point nil)
              (last-line 0))
          (forward-line)
          (while (and (not (= (line-beginning-position) last-line))
                      (or (> (haskell-move-nested-indent-level) starting-level)
                          (and (> current-level starting-level)
                               (>= (haskell-move-nested-indent-level) current-level))))
            (setq last-line (line-beginning-position))
            (setq end-point (line-end-position))
            (forward-line))
          (cons start-point (or end-point
                                start-end-point)))))))

(defun haskell-move-nested-indent-level ()
  (max
   0
   (1- (length
        (buffer-substring-no-properties
         (line-beginning-position)
         (or (save-excursion (goto-char (line-beginning-position))
                             (search-forward-regexp "[^ ]" (line-end-position) t 1))
             (line-beginning-position)))))))

(defun haskell-kill-nested ()
  "Kill the nested region after point."
  (interactive)
  (let ((start (point))
        (reg (save-excursion
               (search-backward-regexp "^[ ]+" (line-beginning-position) t 1)
               (search-forward-regexp "[^ ]" (line-end-position) t 1)
               (haskell-move-nested-region))))
    (kill-region start (cdr reg))))

(defun haskell-delete-nested ()
  "Kill the nested region after point."
  (interactive)
  (let ((start (point))
        (reg (save-excursion
               (search-backward-regexp "^[ ]+" (line-beginning-position) t 1)
               (search-forward-regexp "[^ ]" (line-end-position) t 1)
               (haskell-move-nested-region))))
    (delete-region start (cdr reg))))

(provide 'haskell-move-nested)

;;; haskell-move-nested.el ends here
