;;; solar.el --- calendar functions for solar events.

;; Copyright (C) 1992, 1993 Free Software Foundation, Inc.

;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
;; Keywords: calendar
;; Human-Keywords: sunrise, sunset, equinox, solstice, calendar, diary,
;;	holidays

;; This file is part of XEmacs.

;; XEmacs 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 2, or (at your option)
;; any later version.

;; XEmacs 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 XEmacs; see the file COPYING.  If not, write to the Free
;; Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

;;; Commentary:

;; This collection of functions implements the features of calendar.el,
;; diary.el, and holiday.el that deal with times of day, sunrise/sunset, and
;; eqinoxes/solstices.

;; Based on the ``Almanac for Computers 1984,'' prepared by the Nautical
;; Almanac Office, United States Naval Observatory, Washington, 1984 and
;; on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
;; Willmann-Bell, Inc., 1985.
;;
;; WARNINGS:
;;    1. SUNRISE/SUNSET calculations will be accurate only to +/- 2 minutes.
;;       Locations should be between +/- 65 degrees of latitude.
;;       Dates should be in the latter half of the 20th century.
;;
;;    2. Equinox/solstice times will be accurate only to +/- 15 minutes.

;; The author would be delighted to have an astronomically more sophisticated
;; person rewrite the code for the solar calculations in this file!

;; Comments, corrections, and improvements should be sent to
;;  Edward M. Reingold               Department of Computer Science
;;  (217) 333-6733                   University of Illinois at Urbana-Champaign
;;  reingold@cs.uiuc.edu             1304 West Springfield Avenue
;;                                   Urbana, Illinois 61801

;;; Code:

(setq *WARN-ON-FLOATING-POINT-CONTAGION* NIL)
;(if (fboundp 'atan)
;    (require 'lisp-float-type)
;  (error "Solar/lunar calculations impossible since floating point is unavailable."))

;(defconst pi (purecopy (* 4 (atan 1))) "The value of Pi (3.1415926...)")
(defconstant e (exp 1)) 

;; Careful when editing this file ... typos here will be hard to spot.
;; (defconst pi       3.14159265358979323846264338327
;;  "The value of Pi (3.14159265358979323846264338327...)")

(defun quotient (m n)
  ;; TYPE (real non-zero-real) -> integer
  ;; Whole part of m/n.
  (floor m n))

;; XEmacs change (purecopy)
;(defconst degrees-to-radians (purecopy (/ pi 180.0))
;  "Degrees to radian conversion constant")
;(defconst radians-to-degrees (purecopy (/ 180.0 pi))
;  "Radian to degree conversion constant")

;; these expand to a single multiply by a float when byte compiled

(defmacro degrees-to-radians (x)
  "Convert ARG from degrees to radians."
  (list '* (/ pi 180.0) x))
(defmacro radians-to-degrees (x)
  "Convert ARG from radians to degrees."
  (list '* (/ 180.0 pi) x))




;(require 'cal-dst)

;;;###autoload
(defvar calendar-time-display-form
  '(12-hours ":" minutes am-pm
    (if time-zone " (") time-zone (if time-zone ")"))
  "*The pseudo-pattern that governs the way a time of day is formatted.

A pseudo-pattern is a list of expressions that can involve the keywords
`12-hours', `24-hours', and `minutes',  all numbers in string form,
and `am-pm' and `time-zone',  both alphabetic strings.

For example, the form

  '(24-hours \":\" minutes
    (if time-zone \" (\") time-zone (if time-zone \")\"))

would give military-style times like `21:07 (UTC)'.")

;;;###autoload
(defvar calendar-latitude nil
  "*Latitude of `calendar-location-name' in degrees.

The value can be either a decimal fraction (one place of accuracy is
sufficient), + north, - south, such as 40.7 for New York City, or the value
can be a vector [degrees minutes north/south] such as [40 50 north] for New
York City.

This variable should be set in site-local.el.")

;;;###autoload
(defvar calendar-longitude nil
  "*Longitude of `calendar-location-name' in degrees.

The value can be either a decimal fraction (one place of accuracy is
sufficient), + east, - west, such as -73.9 for New York City, or the value
can be a vector [degrees minutes east/west] such as [73 55 west] for New
York City.

This variable should be set in site-local.el.")

(declaim (inline calendar-latitude))
(defun calendar-latitude ()
  "Convert calendar-latitude to a signed decimal fraction, if needed."
  (if (numberp calendar-latitude)
      calendar-latitude
    (let ((lat (+ (aref calendar-latitude 0)
                  (/ (aref calendar-latitude 1) 60.0))))
      (if (equal (aref calendar-latitude 2) 'north)
          lat
        (- lat)))))
(declaim (inline calendar-longitude))
(defun calendar-longitude ()
  "Convert calendar-longitude to a signed decimal fraction, if needed."
  (if (numberp calendar-longitude)
      calendar-longitude
    (let ((long (+ (aref calendar-longitude 0)
                  (/ (aref calendar-longitude 1) 60.0))))
      (if (equal (aref calendar-longitude 2) 'east)
          long
        (- long)))))

;;;###autoload
(defvar calendar-location-name
  '(let ((float-output-format "%.1f"))
     (format nil "~A~A, ~A~A"
             (if (numberp calendar-latitude)
                 (abs calendar-latitude)
               (+ (aref calendar-latitude 0)
                  (/ (aref calendar-latitude 1) 60.0)))
             (if (numberp calendar-latitude)
                 (if (> calendar-latitude 0) "N" "S")
               (if (equal (aref calendar-latitude 2) 'north) "N" "S"))
             (if (numberp calendar-longitude)
                 (abs calendar-longitude)
               (+ (aref calendar-longitude 0)
                  (/ (aref calendar-longitude 1) 60.0)))
             (if (numberp calendar-longitude)
                 (if (> calendar-longitude 0) "E" "W")
               (if (equal (aref calendar-latitude 2) 'east) "E" "W"))))
  "*Expression evaluating to name of `calendar-longitude', calendar-latitude'.
For example, \"New York City\".  Default value is just the latitude, longitude
pair.

This variable should be set in site-local.el.")

(defvar solar-n-hemi-seasons
  '("Vernal Equinox" "Summer Solstice" "Autumnal Equinox" "Winter Solstice")
  "List of season changes for the northern hemisphere.")

(defvar solar-s-hemi-seasons
  '("Autumnal Equinox" "Winter Solstice" "Vernal Equinox" "Summer Solstice")
  "List of season changes for the southern hemisphere.")

(defun solar-setup ()
  "Prompt user for latitude, longitude, and time zone."
  (beep)
  (if (not calendar-longitude)
      (setq calendar-longitude
            (solar-get-number
             "Enter longitude (decimal fraction; + east, - west): ")))
  (if (not calendar-latitude)
      (setq calendar-latitude
            (solar-get-number
             "Enter latitude (decimal fraction; + north, - south): ")))
  (if (not calendar-time-zone)
      (setq calendar-time-zone
            (solar-get-number
             "Enter difference from Coordinated Universal Time (in minutes): "))))

(defun solar-get-number (prompt)
  "Return a number from the minibuffer, prompting with PROMPT.
Returns nil if nothing was entered."
  (let ((x (read-string prompt "")))
    (if (not (string-equal x ""))
        (string-to-int x))))

(declaim (inline solar-sin-degrees))
(defun solar-sin-degrees (x)
  (sin (degrees-to-radians x)))

(declaim (inline solar-cosine-degrees))
(defun solar-cosine-degrees (x)
  (cos (degrees-to-radians x)))

(defun solar-tangent-degrees (x)
  (tan (degrees-to-radians x)))

(defun solar-xy-to-quadrant (x y)
  "Determines the quadrant of the point X, Y."
  (if (> x 0)
      (if (> y 0) 1 4)
      (if (> y 0) 2 3)))

(defun solar-degrees-to-quadrant (angle)
  "Determines the quadrant of ANGLE."
  (1+ (floor (mod angle 360) 90)))

(defun solar-arctan (x quad)
  "Arctangent of X in quadrant QUAD."
  (let ((deg (radians-to-degrees (atan x))))
    (cond ((equal quad 2)   (+ deg 180))
	  ((equal quad 3)   (+ deg 180))
	  ((equal quad 4)   (+ deg 360))
	  (t                deg))))

(defun solar-arccos (x)
  (let ((y (sqrt (- 1 (* x x)))))
    (solar-arctan (/ y x) (solar-xy-to-quadrant x y))))

(defun solar-arcsin (y)
  (let ((x (sqrt (- 1 (* y y)))))
    (solar-arctan (/ y x) (solar-xy-to-quadrant x y))))

(defconstant solar-earth-inclination 23.441884 
  "Inclination of earth's equator to its solar orbit in degrees.")

(defconstant solar-cos-inclination (solar-cosine-degrees solar-earth-inclination) 
  "Cosine of earth's inclination.")

(defconstant solar-sin-inclination (solar-sin-degrees solar-earth-inclination)
  "Sine of earth's inclination.")

(defconstant solar-earth-orbit-eccentricity 0.016718d0
  "Eccentricity of orbit of the earth around the sun.")

(declaim (inline solar-degrees-to-hours))
(defun solar-degrees-to-hours (deg)
  (/ deg 15.d0))

(declaim (inline solar-hours-to-days))
(defun solar-hours-to-days (hour)
  (/ hour 24d0))

(defun solar-longitude-of-sun (day)
  "Longitude of the sun at DAY in the year."
  (let ((mean-anomaly (coerce (- (* 0.9856d0 day) 3.289d0) 'double-float)))
    (mod  (coerce ( + mean-anomaly 
	    (* 1.916d0 (solar-sin-degrees mean-anomaly))
	    (* 0.020d0 (solar-sin-degrees (* 2d0 mean-anomaly)))
	    282.634d0) 'double-float)
	 360.0d0)))

(defun solar-moment (date latitude longitude rise-or-set)
  ;; TYPE (fixed-date angle angle real) -> moment
  ;; Local time (fraction of day) of sunrise/sunset at
  ;; latitude, longitude (in nonpolar regions) for fixed
  ;; date.  rise-or-set is -0.25 for sunrise and +0.25 for
  ;; sunset.
  (let* ((approx  ; Approximate time of event.
          (+ (day-number (gregorian-from-fixed date))
             0.5 rise-or-set (/ longitude -360.0d0)))
         (anomaly ; Anomaly of sun.
          (- (* 0.9856d0 approx) 3.289d0))
         (sun     ; Longitude of sun.
          (degrees (+ anomaly (* 1.916d0
                                 (sin-degrees anomaly))
                      282.634d0
                      (* 0.020d0
                         (sin-degrees (* 2 anomaly))))))
         (right-ascension ; Right ascension of sun.
          (arctan-degrees
           (* (cosine-degrees 23.441884d0)
              (tangent-degrees sun))
           (1+ (quotient sun 90)))) ; Quadrant.
         (declination ; Declination of sun.
          (arcsin-degrees (* (sin-degrees 23.441884d0)
                             (sin-degrees sun))))
         (local (* (signum rise-or-set)
                   (arccos-degrees
                    (/ (- (cosine-degrees 90.833333d0)
                          (* (sin-degrees declination)
                             (sin-degrees latitude)))
                       (cosine-degrees declination)
                       (cosine-degrees latitude))))))
    (mod (- (/ (+ local right-ascension) 360)
            0.27592d0 (* 0.00273792d0 approx))
         1)))



(defun solar-right-ascension (longitude)
  "Right ascension of the sun, given its LONGITUDE."
  (solar-degrees-to-hours
   (solar-arctan
    (* solar-cos-inclination (solar-tangent-degrees longitude))
    (solar-degrees-to-quadrant longitude))))

(defun solar-declination (longitude)
  "Declination of the sun, given its LONGITUDE."
  (solar-arcsin
   (* solar-sin-inclination
      (solar-sin-degrees longitude))))

(defun solar-sunrise (date)
  "Calculates the *standard* time of sunrise for Gregorian DATE.
Calculation is for location given by `calendar-latitude' and
`calendar-longitude'.

Returns a decimal fraction of hours.  Returns nil if the sun does not rise at
that location on that day."
  (let* ((day-of-year (calendar-day-number date))
	 (approx-sunrise
          (+ day-of-year
             (solar-hours-to-days
              (-  6 (solar-degrees-to-hours (calendar-longitude))))))
	 (solar-longitude-of-sun-at-sunrise
          (solar-longitude-of-sun approx-sunrise))
	 (solar-right-ascension-at-sunrise
          (solar-right-ascension solar-longitude-of-sun-at-sunrise))
	 (solar-declination-at-sunrise
          (solar-declination solar-longitude-of-sun-at-sunrise))
	 (cos-local-sunrise
          (/ (- (solar-cosine-degrees (+ 90 (/ 50d0 60d0)))
                (* (solar-sin-degrees solar-declination-at-sunrise)
                   (solar-sin-degrees (calendar-latitude))))
             (* (solar-cosine-degrees solar-declination-at-sunrise)
                (solar-cosine-degrees (calendar-latitude))))))
    (if (<= (abs cos-local-sunrise) 1);; otherwise, no sunrise that day
      (let* ((local-sunrise (solar-degrees-to-hours
                             (- 360 (solar-arccos cos-local-sunrise))))
             (local-mean-sunrise
	      (mod (- (+ local-sunrise solar-right-ascension-at-sunrise)
		      (+ (* 0.065710d0 approx-sunrise)
			 6.622d0))
		   24)))
	(+ (- local-mean-sunrise (solar-degrees-to-hours (calendar-longitude)))
	   (/ calendar-time-zone 60d0))))))

(defun solar-sunset (date)
  "Calculates the *standard* time of sunset for Gregorian DATE.
Calculation is for location given by `calendar-latitude' and
`calendar-longitude'.

Returns a decimal fractions of hours.  Returns nil if the sun does not set at
that location on that day."
  (let* ((day-of-year (calendar-day-number date))
	 (approx-sunset
          (+ day-of-year
             (solar-hours-to-days
              (- 18 (solar-degrees-to-hours (calendar-longitude))))))
	 (solar-longitude-of-sun-at-sunset
          (solar-longitude-of-sun approx-sunset))
	 (solar-right-ascension-at-sunset
          (solar-right-ascension solar-longitude-of-sun-at-sunset))
	 (solar-declination-at-sunset
          (solar-declination solar-longitude-of-sun-at-sunset))
	 (cos-local-sunset
          (/ (- (solar-cosine-degrees (+ 90 (/ 50d0 60d0)))
                (* (solar-sin-degrees solar-declination-at-sunset)
                   (solar-sin-degrees (calendar-latitude))))
             (* (solar-cosine-degrees solar-declination-at-sunset)
                (solar-cosine-degrees (calendar-latitude))))))
    (if (<= (abs cos-local-sunset) 1);; otherwise, no sunset that day
      (let* ((local-sunset (solar-degrees-to-hours
                            (solar-arccos cos-local-sunset)))
             (local-mean-sunset
	      (mod (- (+ local-sunset solar-right-ascension-at-sunset)
		      (+ (* 0.065710d0 approx-sunset) 6.622d0))
		   24)))
	(+ (- local-mean-sunset (solar-degrees-to-hours (calendar-longitude)))
	   (/ calendar-time-zone 60d0))))))

(defun solar-adj-time-for-dst (date time &optional style)
  "Adjust decimal fraction standard TIME on DATE to account for dst.
Returns a list (date adj-time zone) where `date' and `time' are the values
adjusted for `zone'; here `date' is a list (month day year), `time' is a
decimal fraction time, and `zone' is a string.

Optional parameter STYLE forces the result time to be standard time when its
value is 'standard and daylight savings time (if available) when its value is
'daylight.

Conversion to daylight savings time is done according to
`calendar-daylight-savings-starts', `calendar-daylight-savings-ends',
`calendar-daylight-savings-starts-time',
`calendar-daylight-savings-ends-time', and
`calendar-daylight-savings-offset'."

  (let*  ((year (extract-calendar-year date))
	 (rounded-abs-date (+ (calendar-absolute-from-gregorian date)
			      (/ (round (* 60d0 time)) 60d0 24d0)))
         (dst-starts (and calendar-daylight-savings-starts
                          (+ (calendar-absolute-from-gregorian
                              (eval calendar-daylight-savings-starts))
			     (/ calendar-daylight-savings-starts-time
				60d0 24d0))))
         (dst-ends (and calendar-daylight-savings-ends
                        (+ (calendar-absolute-from-gregorian
                            (eval calendar-daylight-savings-ends))
			   (/ (- calendar-daylight-savings-ends-time
				 calendar-daylight-time-offset)
			      60d0 24d0))))
	 (dst (and (not (eq style 'standard))
                   (or (eq style 'daylight)
                       (and dst-starts dst-ends
                            (or (and (< dst-starts dst-ends);; northern hemi.
                                     (<= dst-starts rounded-abs-date)
                                     (< rounded-abs-date dst-ends))
                                (and (< dst-ends dst-starts);; southern hemi.
                                     (or (< rounded-abs-date dst-ends)
                                         (<= dst-starts rounded-abs-date)))))
                       (and dst-starts (not dst-ends)
                            (<= dst-starts rounded-abs-date))
                       (and dst-ends (not dst-starts)
                            (< rounded-abs-date dst-ends)))))
	 (time-zone (if dst
			calendar-daylight-time-zone-name
			calendar-standard-time-zone-name))
	 (time (+ rounded-abs-date
                  (if dst (/ calendar-daylight-time-offset 24d0 60d0) 0d0))))
    (declare (type double-float rounded-abs-date)
	     (type double-float dst-starts)
	     (type double-float dst-ends))
    (list (calendar-gregorian-from-absolute (truncate time))
          (* 24d0 (- time (truncate time)))
          time-zone)))



(defun solar-time-string (time time-zone)
  (declare (special time-zone ))
  
  "Printable form for decimal fraction TIME on DATE.
Format used is given by `calendar-time-display-form'."
  (let* ((time (round (* 60 time)))
	 (24-hours (quotient time 60))
	 (minutes (format nil "~02d" (% time 60)))
	 (12-hours (format nil "~d" (1+ (% (+ 24-hours 11) 12))))
	 (am-pm (if (>= 24-hours 12) "pm" "am"))
	 (24-hours (format nil "~02d" 24-hours )))
    (declare (special 12-hours minutes am-pm time-zone ))
    (format nil "~A"  (eval `(concatenate 'string ,@calendar-time-display-form)))))

(defun mincha-time-string (time time-zone)
  (declare (special time-zone ))
  
  "Printable form for decimal fraction TIME on DATE.
Format used is given by `calendar-time-display-form'."
  (let* ((t1 (round (* 60 time)))
	 (time (floor (* 5 (floor (- t1 15) 5))))
	 (24-hours (quotient time 60))
	 (minutes (format nil "~02d" (% time 60)))
	 (12-hours (format nil "~d" (1+ (% (+ 24-hours 11) 12))))
	 (am-pm (if (>= 24-hours 12) " P.M." " A.M."))
	 (24-hours (format nil "~02d" 24-hours )))

    (declare (special 12-hours minutes am-pm time-zone ))
    (setq time-zone nil)
    (format nil "~A"  (eval `(concatenate 'string ,@calendar-time-display-form)))))


(defun solar-sunrise-sunset (date)
  "String giving local times of sunrise and sunset on Gregorian DATE."
  (let* ((rise (solar-sunrise date))
         (adj-rise (if rise (solar-adj-time-for-dst date rise)))
         (set (solar-sunset date))
         (adj-set (if set (solar-adj-time-for-dst date set))))
    (format nil "~A, ~A at ~A"
	    (if (and rise (calendar-date-equal date (car adj-rise)))
		(concatenate 'string "Sunrise " (apply 'solar-time-string (cdr adj-rise)))
	      "No sunrise")
	    (if (and set (calendar-date-equal date (car adj-set)))
		(concatenate 'string "sunset " (apply 'solar-time-string (cdr adj-set)))
	      "no sunset")
	    (eval calendar-location-name))))

(defun solar-apparent-longitude-of-sun (date)
  "Apparent longitude of the sun on Gregorian DATE."
  (let* ((time (quotient (- (calendar-absolute-from-gregorian date) 
		     (calendar-absolute-from-gregorian '(1 0.5 1900)))
		  36525))
	 (l (+ 279.69668d0
	       (* 36000.76892d0 time)
	       (* 0.0003025d0 time time)))
	 (m (+ 358.47583d0
	       (* 35999.04975d0 time)
	       (* -0.000150d0 time time)
	       (* -0.0000033d0 time time time)))
	 (c (+ (* (+ 1.919460d0
		     (* -0.004789d0 time)
		     (* -0.000014d0 time time))
		  (solar-sin-degrees m))
	       (* (+ 0.020094d0
		     (* -0.000100d0 time))
		  (solar-sin-degrees (* 2 m)))
	       (* 0.000293d0
		  (solar-sin-degrees (* 3 m)))))
	 (L (+ l c))
	 (omega (+ 259.18d0
		   (* -1934.142d0 time)))
	 (app (+ L
		 -0.00569d0
		 (* -0.00479d0 
		    (solar-sin-degrees omega)))))
    app))

(defun solar-ephemeris-correction (year)
  "Difference in minutes between Ephemeris time and UTC in YEAR.
Value is only an approximation."
  (let ((T (/ (- year 1900) 100.0)))
    (+ 0.41d0 (* 1.2053d0 T) (* 0.4992d0 T T))))

(defun solar-equinoxes/solstices (k year)
  "Date of equinox/solstice K for YEAR.  K=0, spring equinox; K=1, summer
solstice; K=2, fall equinox; K=3, winter solstice.  Accurate to within
several minutes."
  (let ((date (list (+ 3 (* k 3)) 21 year))
        app
	(correction 1000))
    (while (> correction 0.00001d0)
      (setq app (mod (solar-apparent-longitude-of-sun date) 360))
      (setq correction (* 58 (solar-sin-degrees (- (* k 90) app))))
      (setq date (list (extract-calendar-month date)
		       (+ (extract-calendar-day date) correction)
		       year)))
    (list (extract-calendar-month date)
          (+ (extract-calendar-day date) (/ calendar-time-zone 60.0d0 24.0d0)
             (- (/ (solar-ephemeris-correction year) 60.0d0 24.0d0)))
          year)))

;;;###autoload
(defun sunrise-sunset (&optional arg)
  "Local time of sunrise and sunset for today.  Accurate to +/- 2 minutes.
If called with an optional prefix argument, prompt for date.

If called with an optional double prefix argument, prompt for longitude,
latitude, time zone, and date, and always use standard time.

This function is suitable for execution in a .emacs file."
 (or arg (setq arg 1))
 (if (and (< arg 16)
          (not (and calendar-latitude calendar-longitude calendar-time-zone)))
     (solar-setup))
 (let* ((calendar-longitude
         (if (< arg 16) calendar-longitude
           (solar-get-number
            "Enter longitude (decimal fraction; + east, - west): ")))
        (calendar-latitude
         (if (< arg 16) calendar-latitude
           (solar-get-number
            "Enter latitude (decimal fraction; + north, - south): ")))
        (calendar-time-zone
         (if (< arg 16) calendar-time-zone
           (solar-get-number
            "Enter difference from Coordinated Universal Time (in minutes): ")))
        (calendar-location-name
         (if (< arg 16) calendar-location-name
           (let ((float-output-format "~.1f"))
             (format nil "~A~A, ~A~A"
                     (if (numberp calendar-latitude)
                         (abs calendar-latitude)
                       (+ (aref calendar-latitude 0)
                          (/ (aref calendar-latitude 1) 60.0)))
                     (if (numberp calendar-latitude)
                         (if (> calendar-latitude 0) "N" "S")
                       (if (equal (aref calendar-latitude 2) 'north) "N" "S"))
                     (if (numberp calendar-longitude)
                         (abs calendar-longitude)
                       (+ (aref calendar-longitude 0)
                          (/ (aref calendar-longitude 1) 60.0)))
                     (if (numberp calendar-longitude)
                         (if (> calendar-longitude 0) "E" "W")
                       (if (equal (aref calendar-latitude 2) 'east)
                           "E" "W"))))))
        (calendar-standard-time-zone-name
         (if (< arg 16) calendar-standard-time-zone-name
           (cond ((= calendar-time-zone 0) "UTC")
                 ((< calendar-time-zone 0)
                     (format nil "UTC~dmin" calendar-time-zone))
                 (t  (format nil "UTC+~dmin" calendar-time-zone)))))
        (calendar-daylight-savings-starts
         (if (< arg 16) calendar-daylight-savings-starts))
        (calendar-daylight-savings-ends
         (if (< arg 16) calendar-daylight-savings-ends))
        (date (if (< arg 4) (calendar-current-date) (calendar-read-date)))
        (date-string (calendar-date-string date t))
        (time-string (solar-sunrise-sunset date))
        (format t "~A: ~A" date-string time-string)
        (one-window (one-window-p t)))
   (if (<= (length msg) (frame-width))
       (message msg)
     (with-output-to-temp-buffer "*temp*"
       (print(concatenate 'string date-string "\n" time-string)))
     (message (substitute-command-keys
               (if one-window
                   (if pop-up-windows
                       "Type \\[delete-other-windows] to remove temp window."
                     "Type \\[switch-to-buffer] RET to remove temp window.")
                 "Type \\[switch-to-buffer-other-window] RET to restore old contents of temp window."))))))
 
(defun calendar-sunrise-sunset ()
  "Local time of sunrise and sunset for date under cursor.
Accurate to +/- 2 minutes."
  (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
      (solar-setup))
  (let ((date (calendar-cursor-to-date t)))
    (message "%s: %s"
             (calendar-date-string date t t)
             (solar-sunrise-sunset date))))

(defun diary-sunrise-sunset ()
  "Local time of sunrise and sunset as a diary entry.
Accurate to +/- 2 minutes."
  (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
      (solar-setup))
  (solar-sunrise-sunset date))

(defun diary-sabbath-candles ()
  "Local time of candle lighting diary entry--applies if date is a Friday.
No diary entry if there is no sunset on that date."
  (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
      (solar-setup))
  (if (= (% (calendar-absolute-from-gregorian date) 7) 5);;  Friday
      (let* ((sunset (solar-sunset date))
	     (light (if sunset
                        (solar-adj-time-for-dst
                         date
                         (- sunset (/ 18.0d0 60.0d0))))))
        (if (and light (calendar-date-equal date (car light)))
            (format nil "~A Candle lighting"
                    (apply 'solar-time-string (cdr light)))))))

;;;###autoload
(defun solar-equinoxes-solstices ()
  "Date and time of equinoxes and solstices, if visible in the calendar window.
Requires floating point."
  (let ((m displayed-month)
        (y displayed-year))
    (increment-calendar-month m y (cond ((= 1 (% m 3)) -1)
					((= 2 (% m 3))  1)
					(t              0)))
    (let* ((calendar-standard-time-zone-name
            (if calendar-time-zone calendar-standard-time-zone-name "UTC"))
           (calendar-daylight-savings-starts
            (if calendar-time-zone calendar-daylight-savings-starts))
           (calendar-daylight-savings-ends
            (if calendar-time-zone calendar-daylight-savings-ends))
           (calendar-time-zone (if calendar-time-zone calendar-time-zone 0))
           (k (1- (/ m 3)))
	   (date (solar-equinoxes/solstices k y))
	   (s-hemi (and calendar-latitude (< (calendar-latitude) 0)))
	   (day (extract-calendar-day date))
           (adj (solar-adj-time-for-dst
                 (list (extract-calendar-month date)
		       (truncate day)
		       (extract-calendar-year date))
                 (* 24 (- day (truncate day))))))
      (list (list (car adj)
		  (format nil "~A ~A"
			  (nth k (if s-hemi solar-s-hemi-seasons
                                   solar-n-hemi-seasons))
			  (apply 'solar-time-string (cdr adj))))))))

;(provide 'solar)

;;; solar.el ends here