;;; Copyright (c) 2017, Sudhir Shenoy.  All rights reserved.

;;; Redistribution and use in source and binary forms, with or without
;;; modification, are permitted provided that the following conditions
;;; are met:

;;;   * Redistributions of source code must retain the above copyright
;;;     notice, this list of conditions and the following disclaimer.

;;;   * Redistributions in binary form must reproduce the above
;;;     copyright notice, this list of conditions and the following
;;;     disclaimer in the documentation and/or other materials
;;;     provided with the distribution.

;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;;; ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

(in-package :cl-dates)

;; hash table containing mappings from time zone abbreviation to GMT offset
(defparameter +tz-info+ (make-hash-table :test #'equalp))

(defun str-to-tz-offset (str)
  (gethash str +tz-info+))

(defun zone-to-offset (zone)
  (typecase zone
    (number zone)
    (string (or (str-to-tz-offset zone) 0))
    (t 0)))

(progn
  ;; Time zone abbreviation to offset mapping table (source: Wikipedia)
  ;; Wherever there are duplicate abbreviations, the more economically significant
  ;; (in terms of trading centres) zone has been retained
  (let ((info '(("ACDT" 10.5 "Australian Central Daylight Savings Time")
		("ACST" 9.5 "Australian Central Standard Time")
		("ACT" -5 "Acre Time")
		("ADT" -3 "Atlantic Daylight Time")
		("AEDT" 11 "Australian Eastern Daylight Savings Time")
		("AEST" 10 "Australian Eastern Standard Time")
		("AFT" 4.5 "Afghanistan Time")
		("AKDT" -8 "Alaska Daylight Time")
		("AKST" -9 "Alaska Standard Time")
		("AMST" -3 "Amazon Summer Time (Brazil)")
		("AMT" -4 "Amazon Time (Brazil)")
		("AMT" 4 "Armenia Time")
		("ART" -3 "Argentina Time")
		("AST" 3 "Arabia Standard Time")
		;; ("AST" -4 "Atlantic Standard Time")
		("AWST" 8 "Australian Western Standard Time")
		("AZOST" 0 "Azores Summer Time")
		("AZOT" -1 "Azores Standard Time")
		("AZT" 4 "Azerbaijan Time")
		("BDT" 8 "Brunei Time")
		("BIOT" 6 "British Indian Ocean Time")
		("BIT" -12 "Baker Island Time")
		("BOT" -4 "Bolivia Time")
		("BRST" -2 "Brasilia Summer Time")
		("BRT" -3 "Brasilia Time")
		;; ("BST" 6 "Bangladesh Standard Time")
		;; ("BST" 11 "Bougainville Standard Time")
		("BST" 1 "British Summer Time")
		("BTT" 6 "Bhutan Time")
		("CAT" 2 "Central Africa Time")
		("CCT" 6.5 "Cocos Islands Time")
		("CDT" -5 "Central Daylight Time (North America)")
		;; ("CDT" -4 "Cuba Daylight Time")
		("CEST" 2 "Central European Summer Time (Cf. HAEC)")
		("CET" 1 "Central European Time")
		("CHADT" 13.75 "Chatham Daylight Time")
		("CHAST" 12.75 "Chatham Standard Time")
		("CHOT" 8 "Choibalsan Standard Time")
		("CHOST" 9 "Choibalsan Summer Time")
		("CHST" 10 "Chamorro Standard Time")
		("CHUT" 10 "Chuuk Time")
		("CIST" -8 "Clipperton Island Standard Time")
		("CIT" 8 "Central Indonesia Time")
		("CKT" -10 "Cook Island Time")
		("CLST" -3 "Chile Summer Time")
		("CLT" -4 "Chile Standard Time")
		("COST" -4 "Colombia Summer Time")
		("COT" -5 "Colombia Time")
		("CST" -6 "Central Standard Time (North America)")
		;; ("CST" 8 "China Standard Time")
		;; ("CST" -5 "Cuba Standard Time")
		("ACST" 9.5 "Central Standard Time (Australia)")
		("ACDT" 10.5 "Central Summer Time (Australia)")
		("CT" 8 "China time")
		("CVT" -1 "Cape Verde Time")
		("CXT" 7 "Christmas Island Time")
		("DAVT" 7 "Davis Time")
		("DDUT" 10 "Dumont d'Urville Time")
		("DFT" 1 "AIX specific equivalent of Central European Time")
		("EASST" -5 "Easter Island Summer Time")
		("EAST" -6 "Easter Island Standard Time")
		("EAT" 3 "East Africa Time")
		("ECT" -4 "Eastern Caribbean Time (does not recognise DST)")
		;; ("ECT" -5 "Ecuador Time")
		("EDT" -4 "Eastern Daylight Time (North America)")
		("AEDT" 11 "Eastern Summer Time (Australia)")
		("EEST" 3 "Eastern European Summer Time")
		("EET" 2 "Eastern European Time")
		("EGST" 0 "Eastern Greenland Summer Time")
		("EGT" -1 "Eastern Greenland Time")
		("EIT" 9 "Eastern Indonesian Time")
		("EST" -5 "Eastern Standard Time (North America)")
		("AEST" 10 "Eastern Standard Time (Australia)")
		("FET" 3 "Further-eastern European Time")
		("FJT" 12 "Fiji Time")
		("FKST" -3 "Falkland Islands Summer Time")
		("FKT" -4 "Falkland Islands Time")
		("FNT" -2 "Fernando de Noronha Time")
		("GALT" -6 "Galapagos Time")
		("GAMT" -9 "Gambier Islands")
		("GET" 4 "Georgia Standard Time")
		("GFT" -3 "French Guiana Time")
		("GILT" 12 "Gilbert Island Time")
		("GIT" -9 "Gambier Island Time")
		("GMT" 0 "Greenwich Mean Time")
		;; ("GST" -2 "South Georgia and the South Sandwich Islands")
		("GST" 4 "Gulf Standard Time")
		("GYT" -4 "Guyana Time")
		("HADT" -9 "Hawaii-Aleutian Daylight Time")
		("HAEC" 2 "Heure Avancée d'Europe Centrale francised name for CEST")
		("HAST" -10 "Hawaii-Aleutian Standard Time")
		("HKT" 8 "Hong Kong Time")
		("HMT" 5 "Heard and McDonald Islands Time")
		("HOVST" 8 "Khovd Summer Time")
		("HOVT" 7 "Khovd Standard Time")
		("ICT" 7 "Indochina Time")
		("IDT" 3 "Israel Daylight Time")
		("IOT" 3 "Indian Ocean Time")
		("IRDT" 4.5 "Iran Daylight Time")
		("IRKT" 8 "Irkutsk Time")
		("IRST" 3.5 "Iran Standard Time")
		("IST" 5.5 "Indian Standard Time")
		;; ("IST" 1 "Irish Standard Time[6]")
		;; ("IST" 2 "Israel Standard Time")
		("JST" 9 "Japan Standard Time")
		("KGT" 6 "Kyrgyzstan time")
		("KOST" 11 "Kosrae Time")
		("KRAT" 7 "Krasnoyarsk Time")
		("KST" 9 "Korea Standard Time")
		("LHST" 10.5 "Lord Howe Standard Time")
		;; ("LHST" 11 "Lord Howe Summer Time")
		("LINT" 14 "Line Islands Time")
		("MAGT" 12 "Magadan Time")
		("MART" -9.5 "Marquesas Islands Time")
		("MAWT" 5 "Mawson Station Time")
		("MDT" -6 "Mountain Daylight Time (North America)")
		("MET" 1 "Middle European Time Same zone as CET")
		("MEST" 2 "Middle European Summer Time Same zone as CEST")
		("MHT" 12 "Marshall Islands")
		("MIST" 11 "Macquarie Island Station Time")
		("MIT" -9.5 "Marquesas Islands Time")
		("MMT" 6.5 "Myanmar Standard Time")
		("MSK" 3 "Moscow Time")
		;; ("MST" 8 "Malaysia Standard Time")
		("MST" -7 "Mountain Standard Time (North America)")
		("MUT" 4 "Mauritius Time")
		("MVT" 5 "Maldives Time")
		("MYT" 8 "Malaysia Time")
		("NCT" 11 "New Caledonia Time")
		("NDT" -2.5 "Newfoundland Daylight Time")
		("NFT" 11 "Norfolk Time")
		("NPT" 5.75 "Nepal Time")
		("NST" -3.5 "Newfoundland Standard Time")
		("NT" -3.5 "Newfoundland Time")
		("NUT" -11 "Niue Time")
		("NZDT" 13 "New Zealand Daylight Time")
		("NZST" 12 "New Zealand Standard Time")
		("OMST" 6 "Omsk Time")
		("ORAT" 5 "Oral Time")
		("PDT" -7 "Pacific Daylight Time (North America)")
		("PET" -5 "Peru Time")
		("PETT" 12 "Kamchatka Time")
		("PGT" 10 "Papua New Guinea Time")
		("PHOT" 13 "Phoenix Island Time")
		("PHT" 8 "Philippine Time")
		("PKT" 5 "Pakistan Standard Time")
		("PMDT" -2 "Saint Pierre and Miquelon Daylight time")
		("PMST" -3 "Saint Pierre and Miquelon Standard Time")
		("PONT" 11 "Pohnpei Standard Time")
		("PST" -8 "Pacific Standard Time (North America)")
		;; ("PST" 8 "Philippine Standard Time")
		("PYST" -3 "Paraguay Summer Time (South America)[7]")
		("PYT" -4 "Paraguay Time (South America)[8]")
		("RET" 4 "Réunion Time")
		("ROTT" -3 "Rothera Research Station Time")
		("SAKT" 11 "Sakhalin Island time")
		("SAMT" 4 "Samara Time")
		("SAST" 2 "South African Standard Time")
		("SBT" 11 "Solomon Islands Time")
		("SCT" 4 "Seychelles Time")
		("SGT" 8 "Singapore Time")
		("SLST" 5.5 "Sri Lanka Standard Time")
		("SRET" 11 "Srednekolymsk Time")
		("SRT" -3 "Suriname Time")
		;; ("SST" -11 "Samoa Standard Time")
		("SST" 8 "Singapore Standard Time")
		("SYOT" 3 "Showa Station Time")
		("TAHT" -10 "Tahiti Time")
		("THA" 7 "Thailand Standard Time")
		("TFT" 5 "Indian/Kerguelen")
		("TJT" 5 "Tajikistan Time")
		("TKT" 13 "Tokelau Time")
		("TLT" 9 "Timor Leste Time")
		("TMT" 5 "Turkmenistan Time")
		("TRT" 3 "Turkey Time")
		("TOT" 13 "Tonga Time")
		("TVT" 12 "Tuvalu Time")
		("ULAST" 9 "Ulaanbaatar Summer Time")
		("ULAT" 8 "Ulaanbaatar Standard Time")
		("USZ1" 2 "Kaliningrad Time")
		("UTC" 0 "Coordinated Universal Time")
		("UYST" -2 "Uruguay Summer Time")
		("UYT" -3 "Uruguay Standard Time")
		("UZT" 5 "Uzbekistan Time")
		("VET" -4 "Venezuelan Standard Time")
		("VLAT" 10 "Vladivostok Time")
		("VOLT" 4 "Volgograd Time")
		("VOST" 6 "Vostok Station Time")
		("VUT" 11 "Vanuatu Time")
		("WAKT" 12 "Wake Island Time")
		("WAST" 2 "West Africa Summer Time")
		("WAT" 1 "West Africa Time")
		("WEST" 1 "Western European Summer Time")
		("WET" 0 "Western European Time")
		("WIT" 7 "Western Indonesian Time")
		("WST" 8 "Western Standard Time")
		("YAKT" 9 "Yakutsk Time")
		("YEKT" 5 "Yekaterinburg Time"))))
    (dolist (tz info)
      (setf (gethash (car tz) +tz-info+) (cadr tz))))

  ;; add Military time zones 
  (loop for ch across "ABCDEFGHI"
	do (let ((offset (1+ (- (char-code ch) (char-code #\A)))))
	     (setf (gethash (string ch) +tz-info+) offset)))
  (setf (gethash "K" +tz-info+) 10
	(gethash "L" +tz-info+) 11
	(gethash "M" +tz-info+) 12
	(gethash "C*" +tz-info+) 3.5
	(gethash "D*" +tz-info+) 4.5
	(gethash "E*" +tz-info+) 5.5
	(gethash "F*" +tz-info+) 6.5)
  (loop for ch across "NOPQRSTUVWXY"
	do (let ((offset (- (1+ (- (char-code ch) (char-code #\N))))))
	     (setf (gethash (string ch) +tz-info+) offset)))
  (setf (gethash "Z" +tz-info+) 0))