;;; company-clang.el --- company-mode completion backend for Clang  -*- lexical-binding: t -*-

;; Copyright (C) 2009, 2011, 2013-2016  Free Software Foundation, Inc.

;; Author: Nikolaj Schumacher

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


;;; Commentary:
;;

;;; Code:

(require 'company)
(require 'company-template)
(require 'cl-lib)

(defgroup company-clang nil
  "Completion backend for Clang."
  :group 'company)

(defcustom company-clang-executable
  (executable-find "clang")
  "Location of clang executable."
  :type 'file)

(defcustom company-clang-begin-after-member-access t
  "When non-nil, automatic completion will start whenever the current
symbol is preceded by \".\", \"->\" or \"::\", ignoring
`company-minimum-prefix-length'.

If `company-begin-commands' is a list, it should include `c-electric-lt-gt'
and `c-electric-colon', for automatic completion right after \">\" and
\":\".")

(defcustom company-clang-arguments nil
  "Additional arguments to pass to clang when completing.
Prefix files (-include ...) can be selected with `company-clang-set-prefix'
or automatically through a custom `company-clang-prefix-guesser'."
  :type '(repeat (string :tag "Argument")))

(defcustom company-clang-prefix-guesser 'company-clang-guess-prefix
  "A function to determine the prefix file for the current buffer."
  :type '(function :tag "Guesser function" nil))

(defvar company-clang-modes '(c-mode c++-mode objc-mode)
  "Major modes which clang may complete.")

(defcustom company-clang-insert-arguments t
  "When non-nil, insert function arguments as a template after completion."
  :type 'boolean
  :package-version '(company . "0.8.0"))

;; prefix ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defvar company-clang--prefix nil)

(defsubst company-clang--guess-pch-file (file)
  (let ((dir (directory-file-name (file-name-directory file))))
    (when (equal (file-name-nondirectory dir) "Classes")
      (setq dir (file-name-directory dir)))
    (car (directory-files dir t "\\([^.]h\\|[^h]\\).pch\\'" t))))

(defsubst company-clang--file-substring (file beg end)
  (with-temp-buffer
    (insert-file-contents-literally file nil beg end)
    (buffer-string)))

(defun company-clang-guess-prefix ()
  "Try to guess the prefix file for the current buffer."
  ;; Prefixes seem to be called .pch.  Pre-compiled headers do, too.
  ;; So we look at the magic number to rule them out.
  (let* ((file (company-clang--guess-pch-file buffer-file-name))
         (magic-number (and file (company-clang--file-substring file 0 4))))
    (unless (member magic-number '("CPCH" "gpch"))
      file)))

(defun company-clang-set-prefix (&optional prefix)
  "Use PREFIX as a prefix (-include ...) file for clang completion."
  (interactive (let ((def (funcall company-clang-prefix-guesser)))
     (unless (stringp def)
       (setq def default-directory))
     (list (read-file-name "Prefix file: "
                           (when def (file-name-directory def))
                           def t (when def (file-name-nondirectory def))))))
  ;; TODO: pre-compile?
  (setq company-clang--prefix (and (stringp prefix)
                                   (file-regular-p prefix)
                                   prefix)))

;; Clean-up on exit.
(add-hook 'kill-emacs-hook 'company-clang-set-prefix)

;; parsing ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; TODO: Handle Pattern (syntactic hints would be neat).
;; Do we ever see OVERLOAD (or OVERRIDE)?
(defconst company-clang--completion-pattern
  "^COMPLETION: \\_<\\(%s[a-zA-Z0-9_:]*\\)\\(?: : \\(.*\\)$\\)?$")

(defconst company-clang--error-buffer-name "*clang-error*")

(defun company-clang--lang-option ()
     (if (eq major-mode 'objc-mode)
         (if (string= "m" (file-name-extension buffer-file-name))
             "objective-c" "objective-c++")
       (substring (symbol-name major-mode) 0 -5)))

(defun company-clang--parse-output (prefix _objc)
  (goto-char (point-min))
  (let ((pattern (format company-clang--completion-pattern
                         (regexp-quote prefix)))
        (case-fold-search nil)
        lines match)
    (while (re-search-forward pattern nil t)
      (setq match (match-string-no-properties 1))
      (unless (equal match "Pattern")
        (save-match-data
          (when (string-match ":" match)
            (setq match (substring match 0 (match-beginning 0)))))
        (let ((meta (match-string-no-properties 2)))
          (when (and meta (not (string= match meta)))
            (put-text-property 0 1 'meta
                               (company-clang--strip-formatting meta)
                               match)))
        (push match lines)))
    lines))

(defun company-clang--meta (candidate)
  (get-text-property 0 'meta candidate))

(defun company-clang--annotation (candidate)
  (let ((ann (company-clang--annotation-1 candidate)))
    (if (not (and ann (string-prefix-p "(*)" ann)))
        ann
      (with-temp-buffer
        (insert ann)
        (search-backward ")")
        (let ((pt (1+ (point))))
          (re-search-forward ".\\_>" nil t)
          (delete-region pt (point)))
        (buffer-string)))))

(defun company-clang--annotation-1 (candidate)
  (let ((meta (company-clang--meta candidate)))
    (cond
     ((null meta) nil)
     ((string-match "[^:]:[^:]" meta)
      (substring meta (1+ (match-beginning 0))))
     ((string-match "\\((.*)[ a-z]*\\'\\)" meta)
      (let ((paren (match-beginning 1)))
        (if (not (eq (aref meta (1- paren)) ?>))
            (match-string 1 meta)
          (with-temp-buffer
            (insert meta)
            (goto-char paren)
            (substring meta (1- (search-backward "<"))))))))))

(defun company-clang--strip-formatting (text)
  (replace-regexp-in-string
   "#]" " "
   (replace-regexp-in-string "[<{[]#\\|#[>}]" "" text t)
   t))

(defun company-clang--handle-error (res args)
  (goto-char (point-min))
  (let* ((buf (get-buffer-create company-clang--error-buffer-name))
         (cmd (concat company-clang-executable " " (mapconcat 'identity args " ")))
         (pattern (format company-clang--completion-pattern ""))
         (err (if (re-search-forward pattern nil t)
                  (buffer-substring-no-properties (point-min)
                                                  (1- (match-beginning 0)))
                ;; Warn the user more aggressively if no match was found.
                (message "clang failed with error %d:\n%s" res cmd)
                (buffer-string))))

    (with-current-buffer buf
      (let ((inhibit-read-only t))
        (erase-buffer)
        (insert (current-time-string)
                (format "\nclang failed with error %d:\n" res)
                cmd "\n\n")
        (insert err)
        (setq buffer-read-only t)
        (goto-char (point-min))))))

(defun company-clang--start-process (prefix callback &rest args)
  (let ((objc (derived-mode-p 'objc-mode))
        (buf (get-buffer-create "*clang-output*"))
        ;; Looks unnecessary in Emacs 25.1 and later.
        (process-adaptive-read-buffering nil))
    (if (get-buffer-process buf)
        (funcall callback nil)
      (with-current-buffer buf
        (erase-buffer)
        (setq buffer-undo-list t))
      (let ((process (apply #'start-process "company-clang" buf
                            company-clang-executable args)))
        (set-process-sentinel
         process
         (lambda (proc status)
           (unless (string-match-p "hangup" status)
             (funcall
              callback
              (let ((res (process-exit-status proc)))
                (with-current-buffer buf
                  (unless (eq 0 res)
                    (company-clang--handle-error res args))
                  ;; Still try to get any useful input.
                  (company-clang--parse-output prefix objc)))))))
        (unless (company-clang--auto-save-p)
          (send-region process (point-min) (point-max))
          (send-string process "\n")
          (process-send-eof process))))))

(defsubst company-clang--build-location (pos)
  (save-excursion
    (goto-char pos)
    (format "%s:%d:%d"
            (if (company-clang--auto-save-p) buffer-file-name "-")
            (line-number-at-pos)
            (1+ (length
                 (encode-coding-region
                  (line-beginning-position)
                  (point)
                  'utf-8
                  t))))))

(defsubst company-clang--build-complete-args (pos)
  (append '("-fsyntax-only" "-Xclang" "-code-completion-macros")
          (unless (company-clang--auto-save-p)
            (list "-x" (company-clang--lang-option)))
          company-clang-arguments
          (when (stringp company-clang--prefix)
            (list "-include" (expand-file-name company-clang--prefix)))
          (list "-Xclang" (format "-code-completion-at=%s"
                                  (company-clang--build-location pos)))
          (list (if (company-clang--auto-save-p) buffer-file-name "-"))))

(defun company-clang--candidates (prefix callback)
  (and (company-clang--auto-save-p)
       (buffer-modified-p)
       (basic-save-buffer))
  (when (null company-clang--prefix)
    (company-clang-set-prefix (or (funcall company-clang-prefix-guesser)
                                  'none)))
  (apply 'company-clang--start-process
         prefix
         callback
         (company-clang--build-complete-args (- (point) (length prefix)))))

(defun company-clang--prefix ()
  (if company-clang-begin-after-member-access
      (company-grab-symbol-cons "\\.\\|->\\|::" 2)
    (company-grab-symbol)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defconst company-clang-required-version 1.1)

(defvar company-clang--version nil)

(defun company-clang--auto-save-p ()
  (< company-clang--version 2.9))

(defsubst company-clang-version ()
  "Return the version of `company-clang-executable'."
  (with-temp-buffer
    (call-process company-clang-executable nil t nil "--version")
    (goto-char (point-min))
    (if (re-search-forward "clang\\(?: version \\|-\\)\\([0-9.]+\\)" nil t)
        (let ((ver (string-to-number (match-string-no-properties 1))))
          (if (> ver 100)
              (/ ver 100)
            ver))
      0)))

(defun company-clang (command &optional arg &rest ignored)
  "`company-mode' completion backend for Clang.
Clang is a parser for C and ObjC.  Clang version 1.1 or newer is required.

Additional command line arguments can be specified in
`company-clang-arguments'.  Prefix files (-include ...) can be selected
with `company-clang-set-prefix' or automatically through a custom
`company-clang-prefix-guesser'.

With Clang versions before 2.9, we have to save the buffer before
performing completion.  With Clang 2.9 and later, buffer contents are
passed via standard input."
  (interactive (list 'interactive))
  (cl-case command
    (interactive (company-begin-backend 'company-clang))
    (init (when (memq major-mode company-clang-modes)
            (unless company-clang-executable
              (error "Company found no clang executable"))
            (setq company-clang--version (company-clang-version))
            (when (< company-clang--version company-clang-required-version)
              (error "Company requires clang version 1.1"))))
    (prefix (and (memq major-mode company-clang-modes)
                 buffer-file-name
                 company-clang-executable
                 (not (company-in-string-or-comment))
                 (or (company-clang--prefix) 'stop)))
    (candidates (cons :async
                      (lambda (cb) (company-clang--candidates arg cb))))
    (meta       (company-clang--meta arg))
    (annotation (company-clang--annotation arg))
    (post-completion (let ((anno (company-clang--annotation arg)))
                       (when (and company-clang-insert-arguments anno)
                         (insert anno)
                         (if (string-match "\\`:[^:]" anno)
                             (company-template-objc-templatify anno)
                           (company-template-c-like-templatify
                            (concat arg anno))))))))

(provide 'company-clang)
;;; company-clang.el ends here