Airports?

  patches-own ;; this way turtles can recognize which patches are airports and which aren't
 [airport? ;; patches are either airports (airport? = true) or not (airport? = false)
 num-of-flights ;; so airports keep track of how many turtles have departed from them
 airport-id] ;; this helps us with the plotting.  the airport-id will be on the x-axis and the number of flights that have departed from each airport (corresponding to it's airport-id) will be on the y-axis)

globals [airport-count] ;; to help us keep track of the total number of airports and to keep the airport-id procedure increasing by 1 for each new airport created

to setup
  clear-all
  set airport-count 0 ;; because there are no airports yet!
 ask patches [set airport? false] ;; to make all the black patches not airports
    repeat initial-airports ;; use the slider to set # of initial airports
    [ask patch  random-pxcor random-pycor 
    [ set pcolor green 
      set num-of-flights 0  ;; because no flights have departed yet
      set airport-id airport-count ;; so the first airport created has an airport-id of 0
      set airport-count airport-count + 1] ] ;; we need to increase the airport-count so that next time an airport is created it will have a higher id number
    ask patches with [pcolor = green] [set airport? true] ;; to make the green patches be recognizable to turtles as airports
    crt initial-airports [set color red setxy random-xcor random-ycor ] ;; still working on how to get the airplanes to appear at same location as the airports
    set-default-shape turtles "airplane" ;; for fun and authenticity
    reset-ticks
end 

to go
  ask turtles [fly] ;; asks turtles to fly to an airport
  new-airport ;; creates new airports after a set # of ticks
  tick
end 

to new-airport
  if remainder ticks 25 = 0 ;; this is asking if the total number of ticks divided by twenty five leaves no remainder. this way this procedure will happen only every 25 ticks
  [ask patch  random-pxcor random-pycor 
    [ set pcolor green  set num-of-flights  0  
      set airport-id airport-count 
      set airport-count airport-count + 1]  ;; makes a new airport with a new airport-id
    crt 1 [set color red setxy random-xcor random-ycor] ;; and a new airplane
    ask patches with [pcolor = green] 
    [set airport? true] ]
end 

to fly
 pd ;; so it leaves a nice path we can see
land
end 

to land  ;; turtle procedure
  ifelse airport? 
  [depart] ;; if the patch the turtle is on right now is an airport, it's time to depart and find a new airport
  [ let airports patches with [airport? = true]  ;; this let command tells the turtles that all patches that answer true to airport? are in fact airports
   face one-of airports ;; this tells the turtle to choose just one of the patches it now knows it an airport to face (changes turtle's heading so it heads toward the airport)
   while [airport? = false] [ fd 1 ] ]  ;; as long as the turtle is on a patch that is not an airport it will keep moving forward in it's given heading. 
end 

to depart
 set heading random 170 ;; just to add some randomness
  ask patch-here [set num-of-flights num-of-flights + 1]
 fd 1
land ;; so the turtle will continue to look for another airport
end