#!/usr/bin/env racket
;;
;; SPDX-License-Identifier: ISC
;;
;; Copyright © 2019 rsiddharth <s@ricketyspace.net>
;;

#lang racket/base

(require racket/date)
(require racket/list)
(require racket/port)
(require racket/format)
(require racket/string)

(require net/http-client)
(require openssl)

(require html-parsing)
(require sxml)
(require sxml/sxpath)


(define HOST "news.ycombinator.com")


(define (fmt n w) (~a n #:width w #:align 'right #:pad-string "0"))

(define (slug)
  (let* ((d (current-date)))
    (string-join `(,(fmt (date-year d) 4)
                   ,(fmt (date-month d) 2)
                   ,(fmt (date-day d) 2)) "")))

(define (fp)
  "Fetch HN Front Page."
  (let ((hc (http-conn-open HOST #:ssl? (ssl-make-client-context 'secure)
                            #:port 443)))
    (define-values (status headers port) (http-conn-sendrecv! hc "/"))
    (port->string port)))

(define (athings)
  "Get top 20 athings from HN front page."
  (let ((x (html->xexp (fp)))
        (s (sxpath "//tr[@class=\"athing\"]")))
    (take (s x) 20)))

(define (athing:id a)
  "Return athing id"
  (let ((id (sxml:attr a 'id)))
    (if (empty? id) (error "athing:id: Unable to get id") id)))

(define (athing:link a)
  "Return athing link (HREF DESC)"
  (let* ((s (sxpath "//a[@class=\"storylink\"]"))
         (l (s a)))
    (list (sxml:text l) (sxml:attr (car l) 'href))))

(define (athings:latest h athings:sxml)
  (cond ((empty? athings:sxml) h)
        (else
         (let* ((athing (car athings:sxml))
                (id (athing:id athing))
                (link (athing:link athing)))
           (athings:latest (hash-set h (string->symbol id) link)
                           (cdr athings:sxml))))))

(define (athings:data-dir)
  (let ((dir (build-path (find-system-path 'orig-dir) "data")))
    (unless (directory-exists? dir) (make-directory dir))
    dir))

(define (athings:file)
  (build-path (athings:data-dir) (slug)))

(define (athings:hash f)
  (cond ((file-exists? f)
         (call-with-input-file f (λ (in) (read-json in))))
        (else (make-immutable-hash))))