Initial compose-mode implementation.

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+;;; sx-compose.el --- Major-mode for coposing questions and answers. -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2014  Artur Malabarba
+
+;; Author: Artur Malabarba <bruce.connor.am@gmail.com>
+
+;; 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:
+
+
+;;; Code:
+(require 'markdown-mode)
+
+(require 'sx)
+
+(defgroup sx-compose-mode nil
+  "Customization group for sx-compose-mode."
+  :prefix "sx-compose-mode-"
+  :tag "SX compose Mode"
+  :group 'sx)
+
+
+;;; Faces and Variables
+(defvar sx-compose-before-send-hook nil 
+  "Hook run before POSTing to the API.
+Functions are called without arguments and should return non-nil.
+
+Returning nil indicates something went wrong and the sending will
+be aborted. In this case, the function is responsible for
+notifying the user.
+
+Current buffer is the compose-mode buffer whose content is about
+to be POSTed.")
+
+(defvar sx-compose-after-send-functions nil 
+  "Hook run after POSTing to the API.
+Functions on this hook should take one argument, the data
+returned by `sx-compose--send-function' (usually the object
+created by the API). They are only called if the transaction
+succeeds.")
+
+(defvar sx-compose--send-function nil
+  "Function used by `sx-compose-send' to send the data.
+Is invoked between `sx-compose-before-send-hook' and
+`sx-compose-after-send-functions'.")
+
+
+;;; Major-mode
+(define-derived-mode sx-compose-mode markdown-mode "Compose"
+  "Major mode for coposing questions and answers.
+Most of the functionality comes from `markdown-mode'. This mode
+just implements some extra features related to posting to the
+API.
+
+This mode won't function if `sx-compose--send-function' isn't
+set. To make sure you set it correctly, you can create the buffer
+with the `sx-compose--create' function.
+
+\\<sx-compose-mode>
+\\{sx-compose-mode}")
+
+(define-key sx-compose-mode-map "\C-c\C-c" #'sx-compose-send)
+
+
+;;; Functions to help preparing buffers
+(defun sx-compose--create (site parent &optional before-hooks after-functions)
+  "Create a `sx-compose-mode' buffer.
+SITE is the site where it will be posted. 
+
+If composing questions (not yet supported), PARENT is nil. 
+If composing answers, it is the `question_id'.
+If editing answers or questions, it should be the alist data
+related to that object.
+
+Each element of BEFORE-HOOKS and AFTER-FUNCTIONS are respectively
+added locally to `sx-compose-before-send-hook' and
+`sx-compose-after-send-functions'."
+  (or (integerp parent) (listp parent)
+      (error "Invalid PARENT"))
+  (with-current-buffer (sx-compose--get-buffer-create site parent)
+    (sx-compose-mode)
+    (setq sx-compose--send-function
+          (if (consp parent)
+              (sx-assoc-let parent
+                (lambda () (sx-method-call (if .title 'questions 'answers)
+                        :site site
+                        :keywords (sx-compose--generate-keywords .title)
+                        :id (or .answer_id .question_id)
+                        :submethod 'edit)))
+            (lambda () (sx-method-call 'questions
+                    :site site
+                    :keywords (sx-compose--generate-keywords (null parent))
+                    :id parent
+                    :submethod (if parent 'answers/add 'add)))))
+    ;; Reverse so they're left in the same order.
+    (dolist (it (reverse before-hooks))
+      (add-hook 'sx-compose-before-send-hook it nil t))
+    (dolist (it (reverse after-functions))
+      (add-hook 'sx-compose-after-send-functions it nil t))
+    ;; Return the buffer
+    (current-buffer)))
+
+(defun sx-compose--generate-keywords (is-question)
+  "Reading current buffer, generate a keywords alist.
+Keywords meant to be used in `sx-method-call'.
+
+`body_markdown' is read as the `buffer-string'. If IS-QUESTION is
+non-nil, other keywords are read from the header "
+  (if (null is-question)
+      `((body_markdown . ,(buffer-string)))
+    ;; Question code will go here.
+    ))
+
+(defun sx-compose--get-buffer-create (site data)
+  "Get or create a buffer for use with `sx-compose-mode'.
+SITE is the site for which composing is aimed (just used to
+uniquely identify the buffers).
+
+If DATA is nil, get a fresh compose buffer.
+If DATA is an integer, try to find an existing buffer
+corresponding to that integer, otherwise create one.
+If DATA is an alist (question or answer data), like above but use
+the id property."
+  (cond
+   ((null data)
+    (generate-new-buffer
+     (format "*sx draft question %s*" site)))
+   ((integerp data)
+    (get-buffer-create
+     (format "*sx draft answer %s %s"
+       site data)))
+   (t
+    (get-buffer-create
+     (format "*sx draft edit %s %s"
+       site (sx-assoc-let data (or .answer_id .question_id)))))))
+
+
+;;; Functions
+(defun sx-compose-send ()
+  "Finish composing current buffer and send it.
+Calls `sx-compose-before-send-hook', POSTs the the current buffer
+contents to the API, then calls `sx-compose-after-send-functions'."
+  (interactive)
+  (unless (run-hook-with-args-until-failure
+           sx-compose-before-send-hook)
+    (let ((result (funcall sx-compose--send-function)))
+      (run-hook-with-args sx-compose-after-send-functions
+                          result))))
+
+(provide 'sx-compose)
+;;; sx-compose.el ends here