// This program animates the transit of Mercury across the sun

use planets.frink
use sun.frink

timezone = "US/Mountain"
lat = 40 degrees North
long = 105 degrees West

df = ### yyyy-MM-dd-HH:mm ###
datef = ### yyyy-MM-dd ###
tf = ### HH:mm ###

// This graphics object is the animated version
g = new graphics
g.font["Monospaced", .008 degree]
g.antialiasedText[false]
anim = new Animation[.3 s]
win = g.show[800,800]

//for planet = [Planet.Mercury, Planet.Venus]
planet = Planet.Mercury
startdate = #2019-11-11 08:00 AM#
startdate = sunrise[startdate, lat, long]
enddate = sunset[startdate, lat, long]

println["Sunrise is " + (startdate->timezone)]
println["Sunset  is " + (enddate->timezone)]

frame = 0
staticsteps = 5
g2 = new graphics
g2.font["Monospaced", .008 degree]
g2.backgroundColor[.8, .8, 1]
// Draw the sun
g2.color[1,1,0]  // Yellow
sunRadius =   sunRadiusAngle[startdate]
g2.fillEllipseCenter[0, 0, 2 sunRadius, 2 sunRadius]

for d = startdate to enddate step 5 min
{
   [azsun, altsun] = refractedSunAzimuthAltitude[d, lat, long]
   [azp, altp]     = planet.refractedAzimuthAltitude[d, lat, long]

   separation = angularSeparation[azsun, altsun, azp, altp]

   sunRadius =   sunRadiusAngle[d]
   mercuryRadius = planet.radiusAngle[d]
   //println[mercuryRadius -> [0, "deg", "arcmin", "arcsec"]]

   flag = ""
   if separation < sunRadius + mercuryRadius // Touching sun?
   {
      flag = "*"
      
      if separation < sunRadius - mercuryRadius  // Fully inside sun?
         flag = "**"

      g = new graphics
      [skyr,skyg,skyb] = skyDarkness[d, lat, long, [[.1,.1,.1], [.1,.1,.2], [.1,.1,.3], [.1,.1,.4], [.8,.8,1]]]
      g.backgroundColor[skyr, skyg, skyb]
      
      // Draw the sun
      g.color[1,1,0]  // Yellow
      g.fillEllipseCenter[(azsun-azsun) cos[-altsun], -(altsun-altsun), 2 sunRadius, 2 sunRadius]

      // Draw Mercury
      // How much more black could it be?  The answer is none.  None more black.
      g.color[0,0,0]
      g.fillEllipseCenter[(azp-azsun) cos[-altp], -(altp-altsun), 2 mercuryRadius, 2 mercuryRadius]
//      g.add[planet.drawPolygonRelativeToZenith[d, lat, long, azp, -altp, mercuryRadius, true]]
      g.text[d->[tf, timezone], (azp-azsun) cos[-altp], -(altp-altsun), "center", "top"]
      win.replaceGraphics[g]
      anim.add[g]
      
      if frame mod staticsteps == 0  OR  flag == "*"   // Step every 5 steps or when just touching
      {
         g2.color[0,0,0]
         g2.fillEllipseCenter[(azp-azsun) cos[-altp], -(altp-altsun), 2 mercuryRadius, 2 mercuryRadius]
         g2.text[d->[tf, timezone], (azp-azsun) cos[-altp], -(altp-altsun), "center", "top"]
      }
   }
   
   println[(d->timezone) + "\t" + format[separation,"deg", 5] + "\t$flag" ]

   frame = frame + 1
}

g2.show[]
filename = "mercurytransit" + (startdate -> datef) + "_$timezone"
filename =~ %s/\//_/g  // Turn slashes into underscores in filemane.
print["Rendering animation..."]
anim.write["$filename.gif", 700, 700]
println["done."]

g2.write["$filename.png", 1024, 1024]
g2.write["$filename.svg", 1024, 1024]
g2.write["$filename.html", 1024, 1024]
browse["file:$filename.gif"]