;;; vlfi.el --- View Large Files Improved
;;; -*- lexical-bind: t -*-

;; Copyright (C) 2006, 2012, 2013  Free Software Foundation, Inc.

;; Version: 0.3
;; Keywords: large files, utilities
;; Authors: 2006 Mathias Dahl <mathias.dahl@gmail.com>
;;          2012 Sam Steingold <sds@gnu.org>
;;          2013 Andrey Kotlarski <m00naticus@gmail.com>

;; This file 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 2, or (at your option)
;; any later version.

;; This file 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; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; This package provides the M-x vlfi command, which visits part of a
;; large file in a read-only buffer without visiting the entire file.
;; The buffer uses VLFI mode, which defines the commands M-<next>
;; (vlfi-next-batch) and M-<prior> (vlfi-prev-batch) to visit other
;; parts of the file.  The option `vlfi-batch-size' specifies the size
;; of each batch, in bytes.

;; This package is an improved fork of the vlf.el package.

;;; Code:

(defgroup vlfi nil
  "View Large Files in Emacs."
  :prefix "vlfi-"
  :group 'files)

(defcustom vlfi-batch-size 1024
  "Defines how large each batch of file data is (in bytes)."
  :type 'integer
  :group 'vlfi)

;; Keep track of file position.
(defvar vlfi-start-pos)
(defvar vlfi-end-pos)
(defvar vlfi-file-size)

(defvar vlfi-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map [M-next] 'vlfi-next-batch)
    (define-key map [M-prior] 'vlfi-prev-batch)
    (define-key map (kbd "M-+") 'vlfi-change-batch-size)
    (define-key map (kbd "M--")
      (lambda () "Decrease vlfi batch size by factor of 2."
        (interactive)
        (vlfi-change-batch-size t)))
    (define-key map "\C-c\C-s" 'vlfi-re-search-forward)
    map)
  "Keymap for `vlfi-mode'.")

(define-derived-mode vlfi-mode special-mode "VLFI"
  "Mode to browse large files in."
  (setq buffer-read-only t)
  (set-buffer-modified-p nil)
  (make-local-variable 'vlfi-batch-size)
  (make-local-variable 'vlfi-start-pos)
  (make-local-variable 'vlfi-file-size))

(defun vlfi-change-batch-size (decrease)
  "Change the buffer-local value of `vlfi-batch-size'.
Normally, the value is doubled;
with the prefix argument DECREASE it is halved."
  (interactive "P")
  (or (assq 'vlfi-batch-size (buffer-local-variables))
      (error "%s is not local in this buffer" 'vlfi-batch-size))
  (setq vlfi-batch-size
        (if decrease
            (/ vlfi-batch-size 2)
          (* vlfi-batch-size 2)))
  (vlfi-update-buffer-name))

(defun vlfi-format-buffer-name ()
  "Return format for vlfi buffer name."
  (let ((vlfi-file-size-float (float vlfi-file-size)))
    (format "%s(%s)[%.2f-%.2f%%%%](%d)"
            (file-name-nondirectory buffer-file-name)
            (file-size-human-readable vlfi-file-size)
            (* 100 (/ vlfi-start-pos vlfi-file-size-float))
            (* 100 (/ vlfi-end-pos vlfi-file-size-float))
            vlfi-batch-size)))

(defun vlfi-update-buffer-name ()
  "Update the current buffer name."
  (rename-buffer (vlfi-format-buffer-name) t))

(defun vlfi-next-batch (append)
  "Display the next batch of file data.
When prefix argument is supplied and positive
 jump over APPEND number of batches.
When prefix argument is negative
 append next APPEND number of batches to the existing buffer."
  (interactive "p")
  (let ((end (+ vlfi-end-pos (* vlfi-batch-size
                                (abs append)))))
    (when (< vlfi-file-size end)		; re-check file size
      (setq vlfi-file-size (nth 7 (file-attributes buffer-file-name)))
      (cond ((= vlfi-end-pos vlfi-file-size)
             (error "Already at EOF"))
            ((< vlfi-file-size end)
             (setq end vlfi-file-size))))
    (let ((inhibit-read-only t)
          (do-append (< append 0)))
      (if do-append
          (goto-char (point-max))
        (setq vlfi-start-pos (- end vlfi-batch-size))
        (erase-buffer))
      (insert-file-contents buffer-file-name nil
                            (if do-append
                                vlfi-end-pos
                              vlfi-start-pos)
                            end))
    (setq vlfi-end-pos end))
  (set-buffer-modified-p nil)
  (vlfi-update-buffer-name))

(defun vlfi-prev-batch (prepend)
  "Display the previous batch of file data.
When prefix argument is supplied and positive
 jump over PREPEND number of batches.
When prefix argument is negative
 append previous PREPEND number of batches to the existing buffer."
  (interactive "p")
  (if (zerop vlfi-start-pos)
      (error "Already at BOF"))
  (let ((inhibit-read-only t)
        (start (max 0 (- vlfi-start-pos (* vlfi-batch-size
                                           (abs prepend)))))
        (do-prepend (< prepend 0)))
    (if do-prepend
        (goto-char (point-min))
      (setq vlfi-end-pos (+ start vlfi-batch-size))
      (erase-buffer))
    (insert-file-contents buffer-file-name nil start
                          (if do-prepend
                              vlfi-start-pos
                            vlfi-end-pos))
    (setq vlfi-start-pos start))
  (set-buffer-modified-p nil)
  (vlfi-update-buffer-name))

;;;###autoload
(defun vlfi (from-end file)
  "View a Large File in Emacs.
With FROM-END prefix, view from the back.
FILE is the file to open.
Batches of the file data from FILE will be displayed in a
 read-only buffer.
You can customize the number of bytes to
 display by customizing `vlfi-batch-size'."
  (interactive "P\nfFile to open: ")
  (with-current-buffer (generate-new-buffer "*vlfi*")
    (buffer-disable-undo)
    (setq buffer-file-name file
          vlfi-file-size (nth 7 (file-attributes file)))
    (if from-end
        (setq vlfi-start-pos (max 0
                                  (- vlfi-file-size vlfi-batch-size))
              vlfi-end-pos vlfi-file-size)
      (setq vlfi-start-pos 0
            vlfi-end-pos (min vlfi-batch-size vlfi-file-size)))
    (vlfi-update-buffer-name)
    (insert-file-contents buffer-file-name nil
                          vlfi-start-pos vlfi-end-pos)
    (vlfi-mode)
    (switch-to-buffer (current-buffer))))

;;;###autoload
(defun dired-vlfi (from-end)
  "In Dired, visit the file on this line in VLFI mode.
With FROM-END prefix, view from the back."
  (interactive "P")
  (vlfi from-end (dired-get-file-for-visit)))

;;;###autoload
(eval-after-load "dired"
  '(define-key dired-mode-map "V" 'dired-vlfi))

;;;###autoload
(defun vlfi-if-file-too-large (size op-type &optional filename)
  "If file SIZE larger than `large-file-warning-threshold', \
allow user to view file with `vlfi', open it normally or abort.
OP-TYPE specifies the file operation being performed over FILENAME."
  (and large-file-warning-threshold size
       (> size large-file-warning-threshold)
       (let ((char nil))
         (while (not (memq (setq char
                                 (read-event
                                  (propertize
                                   (format "File %s is large (%s): \
%s normally (o), %s with vlfi (v) or abort (a)"
                                           (file-name-nondirectory filename)
                                           (file-size-human-readable size)
                                           op-type op-type)
                                   'face 'minibuffer-prompt)))
                           '(?o ?O ?v ?V ?a ?A))))
         (cond ((memq char '(?o ?O)))
               ((memq char '(?v ?V))
                (vlfi nil filename)
                (error ""))
               ((memq char '(?a ?A))
                (error "Aborted"))))))

;;; hijack `abort-if-file-too-large'
;;;###autoload
(fset 'abort-if-file-too-large 'vlfi-if-file-too-large)

;;; search
(defun vlfi-re-search-forward (regexp &optional count)
  "Search for REGEXP COUNT number of times."
  (interactive "sSearch: \np")
  (let ((start vlfi-start-pos)
        (end vlfi-end-pos)
        (pos (point))
        (to-find count)
        (search-reporter (make-progress-reporter
                          (concat "Searching for " regexp)
                          vlfi-start-pos vlfi-file-size)))
    (unwind-protect
        (catch 'end-of-file
          (while (not (zerop to-find))
            (cond ((re-search-forward regexp nil t)
                   (setq to-find (1- to-find)))
                  ((= vlfi-end-pos vlfi-file-size)
                   (throw 'end-of-file nil))
                  (t (vlfi-next-batch 1)
                     (progress-reporter-update search-reporter
                                               vlfi-end-pos)))))
      (progress-reporter-done search-reporter)
      (or (zerop to-find)
          (if (< to-find count)
              (message "Moved to the %d match which is last"
                       (- count to-find))
            (let ((inhibit-read-only t))
              (erase-buffer)
              (insert-file-contents buffer-file-name nil start end))
            (goto-char pos)
            (setq vlfi-start-pos start
                  vlfi-end-pos end)
            (set-buffer-modified-p nil)
            (vlfi-update-buffer-name)
            (message "Not found"))))))

(provide 'vlfi)

;;; vlfi.el ends here