google-weather.el

   1 ;;; google-weather.el --- Fetch Google Weather forecasts.
   2
   3 ;; Copyright (C) 2010 Julien Danjou
   4
   5 ;; Author: Julien Danjou <julien@danjou.info>
   6 ;; Keywords: comm
   7
   8 ;; This file is NOT part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24 ;; This module allows you to fetch Google Weather forecast from the
  25 ;; Internet.
  26 ;;
  27 ;;; Code:
  28
  29 (require 'url)
  30 (require 'url-cache)
  31 (require 'xml)
  32 (require 'time-date)
  33
  34 (eval-when-compile
  35   (require 'cl))
  36
  37 (defgroup google-weather nil
  38   "Google Weather."
  39   :group 'comm)
  40
  41 (defconst google-weather-url
  42   "http://www.google.com/ig/api"
  43   "URL used to access the Google Weather API.")
  44
  45 (defconst google-weather-image-url
  46   "http://www.google.com"
  47   "URL prefix for images.")
  48
  49 (defcustom google-weather-unit-system-temperature-assoc
  50   '(("SI" . "℃")
  51     ("US" . "℉"))
  52   "Find temperature symbol from unit system."
  53   :group 'google-weather)
  54
  55 (defun google-weather-cache-expired (url expire-time)
  56   "Check if URL is cached for more than EXPIRE-TIME."
  57   (cond (url-standalone-mode
  58          (not (file-exists-p (url-cache-create-filename url))))
  59         (t (let ((cache-time (url-is-cached url)))
  60              (if cache-time
  61                  (time-less-p
  62                   (time-add
  63                    (url-is-cached url)
  64                    (seconds-to-time expire-time))
  65                   (current-time))
  66                t)))))
  67
  68 (defun google-weather-cache-fetch (url)
  69   "Fetch URL from the cache."
  70   (with-current-buffer (generate-new-buffer " *temp*")
  71     (url-cache-extract (url-cache-create-filename url))
  72     (current-buffer)))
  73
  74 (defun google-weather-retrieve-data (url &optional expire-time)
  75   "Retrieve URL and return its data as string.
  76 If EXPIRE-TIME is set, the data will be fetched from the cache if
  77 their are not older than EXPIRE-TIME seconds. Otherwise, they
  78 will be fetched and then cached. Therefore, setting EXPIRE-TIME
  79 to 0 force a cache renewal."
  80   (let* ((expired (if expire-time
  81                       (google-weather-cache-expired url expire-time)
  82                     t))
  83          (buffer (if expired
  84                      (url-retrieve-synchronously url)
  85                    (google-weather-cache-fetch url)))
  86          data)
  87     (with-current-buffer buffer
  88       (goto-char (point-min))
  89       (search-forward "\n\n")
  90       (decode-coding-region
  91        (point) (point-max)
  92        (detect-coding-region (point) (point-max) t))
  93       (set-buffer-multibyte t)
  94       (setq data (xml-parse-region (point) (point-max)))
  95       (when (and expired expire-time)
  96         (url-store-in-cache (current-buffer)))
  97       (kill-buffer (current-buffer))
  98       data)))
  99
 100 (defun google-weather-build-url (location &optional language)
 101   "Build URL to retrieve weather for LOCATION in LANGUAGE."
 102   (concat google-weather-url "?weather=" (url-hexify-string location)
 103           (when language
 104             (concat "&hl=" language))))
 105
 106 (defun google-weather-get-data (location &optional language expire-time)
 107   "Get weather data for LOCATION in LANGUAGE.
 108 See `google-weather-retrieve-data' for the use of EXPIRE-TIME."
 109   (google-weather-retrieve-data
 110    (google-weather-build-url location language) expire-time))
 111
 112 (defun google-weather-data->weather (data)
 113   "Return all weather information from DATA."
 114   (cddr (assoc 'weather (cdr (assoc 'xml_api_reply data)))))
 115
 116 (defun google-weather-data->forecast-information (data)
 117   "Return the forecast information of DATA."
 118   (cddr (assoc 'forecast_information (google-weather-data->weather data))))
 119
 120 (defun google-weather-assoc (key data)
 121   "Do some sort of magic 'assoc to find fields in DATA."
 122   (cdr (assoc 'data (cadr (assoc key data)))))
 123
 124 (defun google-weather-data->city (data)
 125   "Return the city where the DATA come from."
 126   (google-weather-assoc
 127    'city
 128    (google-weather-data->forecast-information data)))
 129
 130 (defun google-weather-data->postal-code (data)
 131   "Return the postal code where the data come from."
 132   (google-weather-assoc
 133    'postal_code
 134    (google-weather-data->forecast-information data)))
 135
 136 (defun google-weather-data->unit-system (data)
 137   "Return the unit system used for data."
 138   (google-weather-assoc
 139    'unit_system
 140    (google-weather-data->forecast-information data)))
 141
 142 (defun google-weather-data->forecast-date (data)
 143   "Return the unit system used for data."
 144   (google-weather-assoc
 145    'forecast_date
 146    (google-weather-data->forecast-information data)))
 147
 148 (defun google-weather-data->forecast (data)
 149   "Get forecast list from DATA."
 150   ;; Compute date of the forecast in the same format as `current-time'
 151   (let ((date (apply 'encode-time
 152                      (parse-time-string
 153                       (concat (google-weather-data->forecast-date data) " 00:00:00")))))
 154     (mapcar
 155      (lambda (forecast)
 156        (let* ((forecast-date (decode-time date))
 157               (forecast-encoded-date (list (nth 4 forecast-date)
 158                                            (nth 3 forecast-date)
 159                                            (nth 5 forecast-date))))
 160          ;; Add one day to `date'
 161          (setq date (time-add date (days-to-time 1)))
 162          `(,forecast-encoded-date
 163            (low ,(google-weather-assoc 'low forecast))
 164            (high ,(google-weather-assoc 'high forecast))
 165            (icon ,(concat google-weather-image-url
 166                           (google-weather-assoc 'icon forecast)))
 167            (condition ,(google-weather-assoc 'condition forecast)))))
 168      (loop for entry in (google-weather-data->weather data)
 169            when (eq (car entry) 'forecast_conditions)
 170            collect entry))))
 171
 172 (defun google-weather-data->forecast-for-date (data date)
 173   "Return forecast for DATE from DATA.
 174 DATE should be in the same format used by calendar i.e. (MONTH DAY YEAR)."
 175   (cdr (assoc date
 176               (google-weather-data->forecast data))))
 177
 178 (defun google-weather-data->temperature-symbol (data)
 179   "Return the temperature to be used according to `google-weather-unit-system-temperature-assoc' in DATA."
 180   (cdr (assoc (google-weather-data->unit-system data) google-weather-unit-system-temperature-assoc)))
 181
 182 (provide 'google-weather)