;;; bom.el -- Australian weather forecast from the Bureau -*- lexical-binding: t -*-

;; Copyright (C) 2023  Free Software Foundation, Inc.

;; Author: Yuchen Pei <id@ypei.org>
;; Package-Requires: ((emacs "28.2") (web-server "0.0.2"))

;; This file is part of bom.el.

;; bom.el is free software: you can redistribute it and/or modify it
;; under the terms of the GNU Affero General Public License as
;; published by the Free Software Foundation, either version 3 of the
;; License, or (at your option) any later version.

;; bom.el 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 Affero General
;; Public License for more details.

;; You should have received a copy of the GNU Affero General Public
;; License along with bom.el.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Australian weather forecast from the Bureau. A client that
;; downloads weather forecast and serves them using emacs-web-server.

;;; Code:

(require 'hierarchy)
(require 'web-server)

(defvar bom-state-files
  '((act . "IDN11060")
    (nsw . "IDN11060")
    (nt . "IDD10207")
    (qld . "IDQ11295")
    (sa . "IDS10044")
    (tas . "IDT16710")
    (vic . "IDV10753")
    (wa . "IDW14199"))
  "Alist of states and territories and their corresponding filenames on the BOM FTP server, see <http://www.bom.gov.au/catalogue/data-feeds.shtml>.")

(defun bom-api-vic ()
  "Get Victoria weather from the BOM FTP."
  (with-current-buffer
      (find-file-noselect
       "/ftp:anonymous@ftp.bom.gov.au:/anon/gen/fwo/IDV10753.xml")
    (libxml-parse-xml-region (point-min) (point-max))))

(defun bom-get-areas (resp)
  "Given an API response RESP, get all areas."
  (dom-children (dom-by-tag resp 'forecast)))

(defvar bom-areas nil "List of areas with forecasts.")

(defvar bom-area-hierarchy (hierarchy-new)
  "Hierarchy of areas with forecasts.")

(defvar bom-server nil "The BOM server object.")

(defun bom-area-parent (area)
  "Search `bom-areas' for the parent of AREA.

Used as parentfn for hierarchy."
  (let ((parent-aac (dom-attr area 'parent-aac)))
    (cl-find-if
     (lambda (area)
       (equal (dom-attr area 'aac) parent-aac))
     bom-areas)))

(defun bom-format-area (area level)
  "Format an AREA of LEVEL."
  (format "%s %s%s\n"
          (make-string level ?*)
          (dom-attr area 'description)
          (if (dom-children area)
              (concat "\n" (bom-format-forecasts (dom-children area)))
            "")))

(defun bom-area-lessp (a1 a2)
  "Compare two areas A1 and A2 based on their AAC identifier."
  (string-lessp (dom-attr a1 'aac) (dom-attr a2 'aac)))

(defun bom-format-forecasts (forecasts)
  "Format a list of FORECASTS."
  (mapconcat 'bom-format-forecast forecasts "\n"))

(defun bom-format-forecast (forecast)
  "Format a FORECAST period."
  (let ((date (substring (dom-attr forecast 'start-time-local) 5 10))
        (data (dom-children forecast))
        (min-temp) (max-temp) (precis) (prec-prob))
    (dolist (item data)
      (pcase (dom-attr item 'type)
        ("air_temperature_minimum" (setq min-temp (dom-text item)))
        ("air_temperature_maximum" (setq max-temp (dom-text item)))
        ("probability_of_precipitation" (setq prec-prob (dom-text item)))
        ("precis" (setq precis (dom-text item)))))
    (format "- %s :: %s %s %s"
            date prec-prob precis (bom-format-temp-range min-temp max-temp))))

(defun bom-format-temp-range (min-temp max-temp)
  "Format a temperature range from MIN-TEMP to MAX-TEMP."
  (if (or min-temp max-temp)
      (format "%s - %s"
              (if min-temp (concat min-temp "C") "")
              (if max-temp (concat max-temp "C") ""))))

(defun bom-format-areas-org (areas)
  "Format hierarchy of AREAS with forecasts."
  (concat "#+title: Victoria weather forecast\n\n"
          (string-join
           (hierarchy-map 'bom-format-area bom-area-hierarchy 1)
           "\n")))

(defun bom-format-areas-html (areas)
  "Format hierarchy of AREAS with forecasts to html."
  (with-temp-buffer
    (insert (bom-format-areas-org areas))
    (org-export-as 'html)))

(defun bom-get-vic-forecasts ()
  "Call BOM API and return hierarchy of VIC areas with forecasts."
  (let ((areas (hierarchy-new)))
    (hierarchy-add-trees
     bom-area-hierarchy
     (setq bom-areas (bom-get-areas (bom-api-vic)))
     'bom-area-parent)
    (hierarchy-sort bom-area-hierarchy 'bom-area-lessp)
    areas))

;;;###autoload
(defun bom-start ()
  "Start serving weather forecasts."
  (when bom-server (bom-stop))
  (setq bom-server
        (ws-start
         (lambda (request)
           (with-slots (process headers) request
             (ws-response-header process 200 '("Content-type" . "text/html"))
             (process-send-string
              process
              (bom-format-areas-html
               (bom-get-vic-forecasts)))))
         9000)))

(defun bom-stop ()
  "Stop serving weather forecasts."
  (ws-stop bom-server))

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