Land division and Jubilee

globals [
  land-patches            ;; a subset of all patches, that we consider to be land-plots
  num-of-deals-made       ;; counts the number of land deals done so far in the current period
  num-of-deals-canceled   ;; counts the number of land deals canceled so far in the current Jubilee
  period-past-jubilee     ;; number of period, relative to the previous jubilee
]

turtles-own [
  explored?
  lands      ;; list of lands (=patches) owned by this turtle
]

patches-own [
  owner           ;; citizen (=turtle) that ownes this land.  
  original-owner  ;; citizen (=turtle) that owned this land at the beginning of the current Jubilee cycle.
]

;;;;;;;;;;;;;;;;;;;;;;;;
;;; Setup Procedures ;;;
;;;;;;;;;;;;;;;;;;;;;;;;

to setup
  clear-all
  set-default-shape turtles "person"
  
  create-turtles num-citizens [
    set lands []
    set color (10 * random 10 + 4)  ;; citizens have dark colors.
  ]
  ask patches [
    set owner nobody  
    set original-owner nobody
  ]
  set land-patches n-of num-citizens patches

  random-land-division

  ask turtles with [length lands = 0] [
    let land-with-no-owner one-of patches with [owner = nobody]
    setxy [pxcor] of land-with-no-owner [pycor] of land-with-no-owner
  ]

  ask turtles with [length lands > 0] [
    let my-land one-of lands
    setxy [pxcor] of my-land [pycor] of my-land
  ]

  layout

  set period-past-jubilee 0

  reset-ticks
end 

;;;;;;;;;;;;;;;;;;;;;;
;;; Main Procedure ;;;
;;;;;;;;;;;;;;;;;;;;;;

to go
  if period-past-jubilee = 0 [
    ;; initialize the land records at the start of the next period:
    ask land-patches [
      set original-owner owner
      ask original-owner [ 
        setxy [pxcor] of myself [pycor] of myself 
      ]
    ]
    ask links [die]
    set num-of-deals-made 0
    set num-of-deals-canceled 0
  ]

  set period-past-jubilee period-past-jubilee + 1

  citizens-trade-lands
  if period-past-jubilee >= periods-per-jubilee [
    ;; in the Jubilee year, some lands return to original owners:
    run jubilee-procedure
    set period-past-jubilee 0
  ]
  layout
  tick
end 

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Land division procedures ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to random-land-division
  ask land-patches [
    assign-land self one-of turtles
  ]
end 

to citizens-trade-lands
  ask land-patches [
    if random 100 < probability-of-deal-per-period [
      sell-land self one-of turtles
    ]
  ]
end 

to sell-land [the-land new-owner]
  assign-land the-land new-owner
  set num-of-deals-made num-of-deals-made + 1
end 

to return-land [the-land new-owner]
  assign-land the-land new-owner
  set num-of-deals-canceled num-of-deals-canceled + 1
end 

;; Assign the given land (=patch) to the given owner (=turtle): 

to assign-land [the-land new-owner]
  let current-owner  [owner] of the-land
  
  if current-owner = new-owner [stop]
  
  if current-owner != nobody [
    ask current-owner [
      set lands remove the-land lands
    ]
  ]

  ask the-land [
    set owner new-owner
    if original-owner != nobody [
      ask original-owner [
        if out-link-to current-owner != nobody [
           ask out-link-to current-owner [die]
        ]
        if self != new-owner [       ;; cannot create a link from turtle to itself
          create-link-to new-owner
        ]
      ] 
    ]
    set pcolor [color + 2] of new-owner  ;; lands have lighter colors.
  ]

  ask new-owner [
    if not member? the-land lands [
      set lands lput the-land lands
    ]
  ]
end 

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Jubilee procedures       ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to no-jubilee
end 

to jubilee-for-landless
  let landless-citizens turtles with [empty? lands]
  let change? false
  ask landless-citizens [
    let returned-land  ;; to each landless citizen, return one of the lands he originally owned:
        one-of land-patches with [original-owner = myself]
    if returned-land != nobody [
      return-land returned-land self
      set change? true
    ]
  ]
  
  ;; if anything was changed in this iteration, do it again:
  if change? [jubilee-for-landless]
end 

to jubilee-for-all
  ask turtles [
    let returned-lands 
        land-patches with [original-owner = myself and owner != myself]
    ;; show returned-lands
    ask returned-lands [
        return-land self myself
    ]
  ]
end 


;;;;;;;;;;;;;;
;;; Layout ;;;
;;;;;;;;;;;;;;

to layout
  if not layout? [ stop ]
  ;; the number 10 here is arbitrary; more repetitions slows down the
  ;; model, but too few gives poor layouts
  repeat 10 [
    do-layout
    display  ;; so we get smooth animation
  ]
end 

to do-layout
  layout-spring (turtles) links 0.4 6 1
  ;; layout-circle turtles max-pxcor - 1
end 


; Copyright 2005 Uri Wilensky.
; See Info tab for full copyright and license.