globals [
  board-areas
  dev-areas
  area-width
  board-counters  ; patches that carry the activity counters
  capacities      ; from user input
  activities      ; calculated from user input
  efforts         ; calculated from user input
  wip-limit       ; calculated from user input
  idle-time       ; total of developers * idle ticks
  max-wip         ; maximum of wip per activity
  cum-wip         ; cumulative wip per activity
]

breed [ demands demand] 
breed [ developers developer ]

demands-own [
  status        ; number of activity, start with 0, done if = activities
  sp            ; number of story points
]

developers-own [
  busy-until    ; tick when task is finished, 0 = not busy
  skill         ; number of activity the developer is able to do
]

to setup
  ;; (for this model to work with NetLogo's new plotting features,
  ;; __clear-all-and-reset-ticks should be replaced with clear-all at
  ;; the beginning of your setup procedure and reset-ticks at the end
  ;; of the procedure.)
  __clear-all-and-reset-ticks
  
  ; check activity range
  if sp-min > sp-max [ user-message "sp-min > sp-max" stop ]
  set capacities read-from-string capacity-input
  set wip-limit ifelse-value (wip-limit-input = "") [[]] [read-from-string wip-limit-input]
  set activities length capacities
  set efforts read-from-string effort-distribution

  set area-width floor (world-width / (activities + 2))
  ask patches with [ (pxcor - min-pxcor) mod area-width = 0 or pycor = 0]
  [ set pcolor blue ]
  
  ; reset max-wip
  set max-wip n-values activities [ 0 ]

  ; define areas for developers
  set dev-areas n-values (activities + 2) [
    patches with [ pycor < 0 and pxcor > min-pxcor + ? * area-width and pxcor < min-pxcor + (? + 1) * area-width ]
  ]
  foreach but-first but-last dev-areas [ ask ? [ set pcolor white ]]
  
  ; define areas for each activity
  set board-areas n-values (activities + 2) [
    patches with [ pycor > 0 and pxcor > min-pxcor + ? * area-width and pxcor < min-pxcor + (? + 1) * area-width ]
  ]
  ask first board-areas [ set pcolor red ]
  foreach but-first but-last board-areas [ ask ? [ set pcolor yellow ]]
  ask last board-areas [ set pcolor green ]
  
  ; determine labelled patches
  set board-counters n-values (activities + 2) [
    one-of patches with [ pycor = 0 and pxcor = min-pxcor + floor((? + 0.5) * area-width) ]
  ]
  foreach board-counters [ ask ? [set plabel "?" set plabel-color black ]]
  
  ; define demands and set them to the first activity area
  set-default-shape demands "star"
  create-demands demand-pool [
    move-to one-of first board-areas
    set heading 0
    set status 0
    set sp sp-min + random (sp-max - sp-min + 1)
  ] 
  set-default-shape developers "person"
  foreach n-values activities [ ? + 1 ] [
    create-developers item (? - 1) capacities [
      move-to one-of item ? dev-areas
      set busy-until 0
      set skill ?
    ]
  ]
  set cum-wip n-values activities [0]
  reset-ticks
  update-counters
end

to go
  ; release finished tasks
  ask developers with [ busy-until = ticks and busy-until > 0]
  [
    let act one-of link-neighbors 
    ask my-links [ die ]
    set busy-until 0
    
    ; check for errors
    ifelse random-float 1 < error-rate [
      ask act [
        set status status - 1
        move-to one-of item status board-areas
        set shape "face sad"
      ]  
    ]
    [ ; count successful demands
      set cum-wip replace-item ([status] of act - 1) cum-wip ((item ([status] of act - 1) cum-wip) + 1)
    ]
  ]
  ; pull a task by a free developer
  ask developers with [ busy-until = 0 ]
  [
    ; the developer is skilled only in one tasks
    let dev-skill skill
    ; select task for the developer's skill
    let act one-of demands with [ status = dev-skill - 1 and not any? my-links ]
    ;selecty any task
    ;let act one-of demands with [ status < activities and not any? my-links ]
    
    if act != nobody and ifelse-value (wip-limit = []) [true] [(item (dev-skill - 1) wip-limit) > (count demands with [ status = dev-skill] )]  
    [ 
      ask act [ 
        if infinite-pool and dev-skill = 1 [ hatch 1 ]
        set status status + 1 
        move-to one-of item status board-areas
      ]
      create-link-with act
      ; set busy time
      set busy-until ticks + ceiling (([ sp ] of act) * (item ([ status ] of act - 1) efforts))
    ]
  ]
  ; pull finished demands
  ask demands with [ status = activities and not any? my-links ]
  [
    set status activities + 1
    move-to one-of last board-areas 
    set shape "face happy"
  ]
  ; calculate idle time
  set idle-time idle-time + count (developers with [ busy-until = 0 ])
  
  update-counters
  do-plotting
  tick
  if not any? demands with [ status = 0 ] and not any? developers with [ busy-until > 0 ]
  [ stop ]  
end

to-report demands-done
  report count demands with [ status = activities + 1 ]
end

to update-counters
  ; calculate actual wip
  let actual-wip n-values (activities + 2) [ count demands with [status = ? ] ]

  ; update max-wip
  set max-wip (map [max list ?1 ?2] but-first but-last actual-wip max-wip)

  foreach board-counters [ ask ? [
    set plabel item floor ( (pxcor - min-pxcor) / area-width ) actual-wip
  ]]

end

to do-plotting ;; plotting procedure
  set-current-plot-pen "activity1"
  if activities > 0 [plotxy ticks item 0 cum-wip]
  set-current-plot-pen "activity2"
  if activities > 1 [plotxy ticks item 1 cum-wip]
  set-current-plot-pen "activity3"
  if activities > 2 [plotxy ticks item 2 cum-wip]
  set-current-plot-pen "activity4"
  if activities > 3 [plotxy ticks item 3 cum-wip]
  set-current-plot-pen "demands-done"
  plotxy ticks demands-done
end
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@#$#@#$#@
## WHAT IS IT?

This agent based model simulates an n-step Kanban process, i.e. a pull system with n activities and limited work in progress (WIP). 

## HOW IT WORKS

The input of the model are demands taken out of a demand pool. 
The developers are onyl skilled in one activity. If the developer is skilled in activity a he pulls finished demands of activity a-1 and starts working on it.
The developer does not pull a new demand if the WIP limit would be exceeded.  
The time to process an activity is equal to the story point value of the demand times a given effort factor.  

While a developer is working on a demand a link between the developer_s agent and the demand is shown to make the visible part more interesting.

The delivery of an activity might not be accepted as input for the following activity (due to errors, missunderstanding, delays, etc.). In this case the activity is pushed back to the previous step and needs to be re-pulled by a develper of the previous step.  
The rejected demands are indicated by a sad smiley.  
The finished demands are indicated by a happy simley. 

## HOW TO USE IT

To run the simulation the following input has to be provided:

  * demand-pool: number of demands to be processed
  * infinite-pool: if yes, the demand-pool will not diminish. I.e. when a developer pulls a demand, a new deman in the pool is created
  * capacity-input: a list with the number of developers of each step able to process the n-th step
  * wip-limit-input: a list with the WIP limits for each step/activity. Leave empty for no limits.
  * error-rate: the rate of wich demands are rejected by the following step.
  * sp-min, sp-max: Range of story points assigned to a demand		

After setup of these parameters, press "setup" to initalize the model's world.  
Press "go" to perform the whole simulation. Press "go one" to perform only one step.

## THINGS TO NOTICE

The following data is monitored:

  * idle-time: total time (= ticks * developer) the developers were idle. The idle time results in additional costs of the model compared to a plain waterfall with zero buffer time.
  * max-wip: The maximum number of demands that have been located in one activity at one time. max-wip cannot be bigger than wip-limit.
  * cum-wip: Cumulated wip per activity 
  * ticks: total time neede to process all demands.

## THINGS TO TRY

Watch out the total time (=ticks) needed to complete the demands and the developer's idle time while changing the WIP limits. Leave the WIP limit field empty to run a simulaiton with unlimited WIP.  

Try setups with bottlenecks - e.g. [10 1 5] developers. Run it with infiite demand pool and unlimited WIP to see a growing heap of waste after the first activity.

## EXTENDING THE MODEL

In the programming section (in the "go" procedure), there is a line of code uncommented to run the simultion with developers skilled in all activities. Then model yould be made more flexible by defining skillset per developer.

## NETLOGO FEATURES

The simulation uses many features of the NetLogo language: Agents, Agentsets, Patches, Links, Lists, Ticks, ...  
Sometimes local variables are used to access variables of outer loops. 

## RELATED MODELS

The simulation uses ideas out of many examples of the module library. However, I am not aware of any NetLogo simulation of software development processes.

## CREDITS AND REFERENCES

So far, it's my first try in NetLogo.  
Mirko Blueming, mirko@blueming.de  
Duesseldorf, 08.01.2012.
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