porting hackernews -> org-mode from js to elisp https://gist.github.com/dharmatech/2ef271907cb73298318fdb50a4ee7d54

hn.el

;;; hn.el --- convert hacker news post into org-mode buffer  -*- lexical-binding: t -*-

;; Copyright (C) 2018- Free Software Foundation, Inc.

;; Author: Johan Ponin <[email protected]>
;; Version: 0.0.1
;; Package-Version: 20181103.0001
;; Keywords: hackernews, org-mode

;; 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:

;; Given an Hacker News story ID, generates an org-mode buffer of the comments
;;
;; @TODO: hn id caching (memoize hn/json)
;; @TODO: clean hidden http buffers
;; @TODO: unquote-html in text
;;
;; See documentation on <none>
;;
;; **Please note** The lexical binding in this file is not utilised at the
;; moment.  We will take full advantage of lexical binding in an upcoming 3.0
;; release of Dash.  In the meantime, we've added the pragma to avoid a bug that
;; you can read more about in https://github.com/magnars/dash.el/issues/130.
;;

;;; Code:

(require 'dash)
(require 'json)
(require 's)

(defvar *hn/ids-cache* '())

(defvar *hn/json-endpoint* "https://hacker-news.firebaseio.com/v0/item/%s.json?print=pretty")

;;; FP

(defun memoize (f) "Memoize F." :todo)

(defun alist-map (a k v c)
  "Combinator to map over alist."
  (-map (lambda (p) (funcall c
			     (funcall k (car p))
			     (funcall v (cdr p))))
	a))

(defun walk (r n d c s)
  "Generic walk combinator.
R: Root
N: function applied on a Node
D: function to go Down one level
C: function to combine N(n) with walk over childrens D(n)
S: state variable"
  (funcall c (funcall n r s)
	   (let ((ns (1+ s)))
	     (-map (lambda (_) (walk _ n d c ns)) (funcall d r)))))

(defun walk! (node xform down io state)
  "Generic walk effectful combinator.
NODE: node being walked
XFORM: function applied on NODE (with STATE)
DOWN: function to generate [child] form NODE
IO: effect function applied on XFORM(NODE, STATE)
STATE: state variable"
  (let ((x (funcall xform node state)))
    (funcall io x)
    (let ((state (1+ state))
	  (children (funcall down node)))
      (-each children (lambda (c) (walk! c xform down io state))))))

;;; ALIST

(defalias 'prop 'alist-get)

(defun props (o &rest ps)
  "Helper to project an alist O on a list of keys PS.
ALIST -> ALIST"
  (-zip ps (-map (lambda (p) (prop p o)) ps)))

;;; HTTP

(defun url-retrieve-synchronously:json (u)
  "Fetch JSON from URL U."
  (with-current-buffer (url-retrieve-synchronously u)
    (goto-char url-http-end-of-headers)
    (json-read)))

;;; HN

(defun hn/json (id)
  "Convert HN ID to JSON.
ID: An Hacker news object ID"
  (->> id
       (format *hn/json-endpoint*)
       (url-retrieve-synchronously:json)))

(defun hn/type (o)
  "Accessor for type of O."
  (prop 'type o))

(defun hn/kids (o)
  "Hn object -> kids id list (from json response vector).
O: JSON Object"
  (-map #'identity (cdr (assoc 'kids o))))

;;; FORMAT

(defun hn/render-text (s)
  "Clean S by unquoting HTML."
  (list :todo s))

(defun hn/format-properties (o s)
  "ALIST a b -> ALIST str str -> str.
O: Alist
S: Stateful variable used for formatting"
  (let* ((indent (indent s ? ))
	 (props-list (alist-map o
				(lambda (k) (format "%s:%s:" indent (upcase (format "%S" k))))
				(lambda (v) (format "%S" v))
				(lambda (a b) (format "%s    %s" a b))))
	 (props (mapconcat #'identity props-list "\n")))
    (format "%s:PROPERTIES:\n%s\n%s:END:\n" indent props indent)))

(defun hn/format (o s)
  "Format a JSON Object.
O: JSON Object
S: Stateful information"
  (let ((k (hn/type o))
	(indent (indent s ?*))
	(author (prop 'by o))
	(ps (hn/format-properties o s)))
    (cond ((equal k "comment")
	   (let ((props (hn/format-properties o s))
		 (text (prop 'text o)))
	     (s-lex-format "${indent} ${author}\n${ps}\n\n    ${text}")))
	  ((equal k "story")
	   (let ((title (prop 'title o)))
	     (s-lex-format "#+TITLE ${title}\n#+AUTHOR ${author}\n${indent} ${title} by ${author}\n${ps}\n\n")))
	  (t (format "[unknown] %S \n" o)))))

;;; HELPERS

(defalias 'indent 'make-string)

;;; MAIN

;;; id -> json -> walk

(defun hn/to-org-mode! (id)
  "Main function (effectful).
ID: Hacker News Story ID"
  (let ((output (get-buffer-create (format "hn-%s" id))))
    (walk! (hn/json id)
	   #'hn/format
	   (lambda (r) (-map #'hn/json (hn/kids r)))
	   (lambda (s)
	     (with-current-buffer output
	       (insert s)
	       (insert "\n")))
	   1)
    (with-current-buffer output
      (org-mode)
      (switch-to-buffer-other-window output))))

(defun hn/hn (id)
  "Main command.
ID: Hacker News Story ID"
  (interactive "sid: ")
  (message "> %s" id)
  (hn/to-org-mode id))

;;; TEST

(defvar *hn-ids*
  '("https://news.ycombinator.com/item?id=18363974"
    "https://news.ycombinator.com/item?id=18370208"
    "https://news.ycombinator.com/item?id=18360847"))

(defun hn/test! ()
  "Test."
  (interactive)
  (hn/to-org-mode! "18360847"))

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