;;; fcomp.el --- fcomp front-end                     -*- lexical-binding: t; -*-

;; Copyright (C) 2019  Anastasis Grammenos

;; Author: Anastasis Grammenos <anastasis.gramm2@gmail.com>
;; Keywords: lisp
;; Version: 0.0.1

;; 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:

;; Emacs front-end for fcomp. Get it from https://ubuntos.dynu.net/git/fcomp

;;; Install:

;; git clone https://ubuntos.dynu.net/git/fcomp && cd fcomp
;; make && make install # install copies the binary under /usr/local/bin

;; In the emacs init file:
;; (add-to-list 'load-path "/your/custom/path")
;; (require 'fcomp)
;; (setq fcomp-path "/your/custom/path/fcomp")
;; (global-set-key (kbd "C-<tab>") 'fcomp-autocomplete)

;; or with use-package
;; (use-package fcomp
;;   :load-path "/your/custom/path"
;;   :bind (("C-<tab>" . fcomp-autocomplete))
;;   :config
;;   (setq fcomp-path "/your/custom/path/fcomp"))


;;; Code:

(require 'ido)
(require 'subr-x)

(defvar fcomp-path "/usr/local/bin/fcomp")
(defvar fcomp-min-word-length 3)
(defvar fcomp-extra-valid-chars "")
(defvar fcomp-extra-invalid-chars "")

(defun empty-string-p (string)
  "Return true if the string is empty or nil. Expects string."
  (or (null string)
      (zerop (length (string-trim string)))))

(defun fcomp--start (query)
  "Initiaize fcomp variables"
  (setq fcomp--query query)
  (setq fcomp--output ""))

(defun fcomp--filter (proc str)
  "Fill the output buffer"
  (let* ((fcomp-pre
          (if (empty-string-p (process-get proc 'input-word))
              nil
            (format "%s" (process-get proc 'input-word)))))
    (setq fcomp--output (concat fcomp--output str))))

(defun fcomp--handle-output ()
  "Handle output buffer"
  (let ((initial-input fcomp--query)
        (out-string fcomp--output)
        (result nil))
    (if (empty-string-p fcomp--output)
        nil
      (setq result (ido-completing-read
                    "Complete:"
                    (remove "" (split-string fcomp--output "\n"))
                    nil nil
                    initial-input)))
    (if (empty-string-p result)
        (message "%s" "No completion candidates")
      (insert (string-remove-prefix
               (if (empty-string-p initial-input)
                   (format "%s" "")
                 (format "%s" initial-input))
               result)))
    (setq fcomp--query "")
    (setq fcomp--output "")))

(defun fcomp-autocomplete ()
  "Autocompete using fcomp.c

When `thing-at-point' is a word, autocomplete it based on buffer contents.

When invoked with no `thing-at-point' show a list of all possible candidates.

Requires fcomp. Get it at URL `https://ubuntos.dynu.net/git/fcomp'"
  ;; Thanks Dan for the syntax-table trick
  ;; https://emacs.stackexchange.com/questions/9583/how-to-treat-underscore-as-part-of-the-word
  (interactive)
  (let ((table (copy-syntax-table (syntax-table))))
    (modify-syntax-entry ?- "w" table)
    (with-syntax-table table
      (fcomp--autocomplete (thing-at-point 'word 'no-properties)))))

(defun fcomp--autocomplete (word)
  "Start fcomp process and orchistrate it's output."
  (let ((term (if (empty-string-p word)
                  (format "%s" "-a")
                (format "%s" word)))
        (input (buffer-substring-no-properties (point-min) (point-max))))
    (fcomp--start word)
    (set-process-filter
     (start-process
      "fcomp"
      nil
      (format "%s"fcomp-path)
      "-w" (format "%s" fcomp-min-word-length)
      "-F" (format "%s" input)
      "-v" (format "%s" fcomp-extra-valid-chars)
      "-i" (format "%s" fcomp-extra-invalid-chars)
      term)
     #'fcomp--filter)
    (process-put (get-process "fcomp") 'input-word word)
    (accept-process-output (get-process "fcomp"))
    (fcomp--handle-output)))

(provide 'fcomp)
;;; fcomp.el ends here