(require 'org)
(require 'org-agenda)
(require 'dash)
(require 'cl-lib)

(defun org-agenda-ng--filter-tree (tree &key filter-fns)
  (let* ((types '(headline))
         (info nil)
         (first-match nil)
         (fun (lambda (element)
                (when (--all? (cl-typecase it
                                (function (funcall it element))
                                (cons (apply (car it) element (cdr it))))
                              filter-fns)
                  element))))
    (org-element-map tree types fun info first-match)))


(defun org-agenda-ng--test ()
  (let ((tree (cddr (org-element-parse-buffer 'headline)))
        (filter-fns '((org-agenda-ng--todo-p "TODO")
                      (org-agenda-ng--scheduled-p < "2017-08-04"))))
    (org-agenda-ng--filter-tree tree :filter-fns filter-fns)))



(defun org-agenda-ng--todo-p (element &optional keyword)
  "Return non-nil if ELEMENT is a TODO item.
With KEYWORD, return non-nil if it has the same TODO keyword."
  (when-let ((element-keyword (org-element-property :todo-keyword element)))
    (pcase keyword
      ('nil t)
      ((pred stringp)
       (string= element-keyword keyword))
      (otherwise (error "Invalid keyword argument: %s" otherwise)))))

(defun org-agenda-ng--scheduled-p (entry &optional comparator target-date)
  "Return non-nil if ENTRY is scheduled.
With COMPARATOR and DATE, return non-nil if entry's scheduled
date compares with TARGET-DATE according to COMPARATOR."

  (when-let ((scheduled-date (org-element-property :scheduled entry)))
    ;; Append time to target-date because `date-to-day' requires it
    (setq target-date (concat target-date " 00:00"))
    (setq target-day-number (date-to-day target-date))
    (pcase comparator
      ('nil t)
      ((and (pred functionp) (guard target-day-number))
       (pcase (org-element-property :type scheduled-date)
         ((or 'active 'inactive)
          (funcall comparator
                   (org-time-string-to-absolute
                    (org-element-timestamp-interpreter scheduled-date 'ignore))
                   target-day-number))))
      (otherwise (error "COMPARATOR (%s) must be a function, and DATE (%s) must be a string" comparator target-date)))))

(defun org-agenda-ng--add-scheduled-faces (entry)
  "Add faces to ENTRY for its scheduled status."
  (if-let ((today-day-number (org-today))
           (scheduled-date (org-element-property :scheduled entry))
           (scheduled-day-number (org-time-string-to-absolute
                                  (org-element-timestamp-interpreter scheduled-date 'ignore)))
           (todo-keyword (org-element-property :todo-keyword))
           (done-p (member todo-keyword org-done-keywords))
           (today-p (= today-day-number scheduled-day-number))
           (face (cond
                  (donep 'org-agenda-done)
                  (today-p 'org-scheduled-today)
                  (t 'org-scheduled))))
      (org-add-props entry nil
        'face face)
    entry))

(defun org-agenda-ng--add-text-properties (element)
  "Return ELEMENT as a string with its text-properties set according to its property list.
Its property list should be the second item in the list, as returned by `org-element-parse-buffer'."
  (let* ((string (org-element-property :title element))
         (properties (second element))
         (properties (seq-subseq properties 0 24))  ;; FIXME
         (properties (cl-loop for (key val) on properties by #'cddr
                              for key = (intern (cl-subseq (symbol-name key) 1))
                              unless (equal key 'raw-value)

                              append (list key val))))
    (setq string (org-add-props string properties))
    (setq string (org-agenda-ng--add-scheduled-faces string))
    string))

(find-file-noselect "~/org/main.org")
(let ((buffer (find-buffer-visiting "~/org/main.org")))
  (with-current-buffer buffer
    (length (org-agenda-ng--test))))

(defun argh ()
  (interactive)
  (with-current-buffer (find-buffer-visiting "~/org/main.org")
    (let* ((entries (cl-subseq (org-agenda-ng--test) 0 2))
           (result-string (org-agenda-finalize-entries (mapcar #'org-agenda-ng--add-text-properties
                                                               entries)
                                                       'agenda))
           (target-buffer (get-buffer-create "test-agenda-ng")))
      (with-current-buffer target-buffer
        (read-only-mode -1)
        (erase-buffer)
        (insert result-string)
        (read-only-mode 1)
        (pop-to-buffer (current-buffer))))))

;; (with-current-buffer (find-file "~/src/org-agenda-ng/org-agenda-ng.el")
;;   (eval-buffer))

;; (decode-time (days-to-time 730119))
;; (date-to-day "2017-08-04")

;; (date-to-day "2017-08-03")