algae<fish<shark

breed [ sharks shark ]
breed [ fish a-fish ]

turtles-own [energy]

to setup
  clear-all
  setup-patches
  setup-fish
  setup-sharks
  reset-ticks
end 

to go
  if ticks >= 1000 [ stop ]
  move-fish
  move-sharks
  eat-grass
  reproduce
  check-death
  regrow-grass
  tick
end 

to setup-patches
  ask patches [ set pcolor green ]
end 

to move-fish
  ask fish [
    right random 360
    forward 1
    set energy energy - 1
  ]
end 

to move-sharks
  ask sharks [
    right random 360
    forward 1
    set energy energy - 1
    eat-fish
  ]
end 

to setup-fish
  create-fish number-of-fish [ setxy random-xcor random-ycor ]
  ask fish [ setxy random-xcor random-ycor ]
  ask fish [ set shape "fish" set size 1.5 set color orange ]
end 

to setup-sharks
  create-sharks number-of-sharks [ setxy random-xcor random-ycor ]
  ask sharks [ setxy random-xcor random-ycor ]
  ask sharks [ set shape "fish 2" set size 3 set color gray]
   ask sharks [
    eat-fish
  ]
end 

to reproduce
  ask turtles [
    if energy > birth-energy + 10 [
      set energy energy - birth-energy
      hatch 1 [ set energy birth-energy ]
    ]
  ]
end 

to check-death
  ask turtles [
    if energy <= 0 [ die ]
  ]
end 

to eat-grass
  ask fish [
    if pcolor = green [
      set pcolor blue
      set energy (energy + energy-from-grass)
    ]
    ifelse show-energy?
      [ set label energy ]
      [ set label " " ]
  ]
end 

to regrow-grass
  ask patches [
    if random 100 < 3 [ set pcolor green]
  ]
end 

to eat-fish
  let prey one-of fish-here
  if prey != nobody  [
    ask prey [ die ]
    set energy (energy + energy-from-grass)
  ]
  ifelse show-energy?
    [ set label energy ]
    [ set label " " ]
end