;; text, like this, that start with semi-colons are comments and do not effect anything
;;
;; First we have lists of general and individual properties/slots

globals [max-target colour-list]

breed [nodes node]

;; nodes have:
;; ** an integer, the multiples of which are being sought by this node (root-target)
;; ** the next in the set of multiples the node is seeking (next-target)
;; ** a list of files they have (file-store)
;; ** a list messages to process (messages)
nodes-own [root-target next-target numb-targets-found file-store messages]

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Next we have the procedure to initialise the simulation
;; this is executed when one presses the "setup" button

to setup 
  clear-all ;; this clears everything at the start - a clean slate
  
  ;; the biggest root target is the square root of half the maximum
  set max-target floor sqrt max-file / 2

  ;; initialise nodes 
  create-nodes population [
    set shape "circle"
    set color grey
    set size 2
    setxy random-xcor random-ycor
    ;; root target is an integer from 2... max-target
    set root-target 2 + random (max-target - 1)
    set next-target root-target
    set numb-targets-found 0
    set file-store []
    set messages []
  ]
  
  ;; make the network
  ask nodes [
    create-links-with min-n-of number-links-each other turtles [distance myself]
  ]
  
  ;;  Distribute the files one at a time to a random node
  foreach n-values max-file [?] [
    ask one-of nodes [set file-store fput ? file-store]
  ]
  
  repeat 100 [ layout-spring turtles links 0.2 5 1]  ;; spreads nodes out
  
  ask nodes [update-node]  ;; update nodes' appearence
  
  reset-ticks            ;; this initialises the simulation time system and graphs
end

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Next we have the procedure to progress the simulation one time step
;; this is executed when one presses the "step" button or repeatedly
;; if one presses the "go" button

to go
  
 ask nodes [
      
    ;; if the next-target has already been found set it to the next one needed
    if member? next-target file-store 
      [set next-target next-target + root-target
       set numb-targets-found numb-targets-found + 1]
    
    ;; send out a new flood-fill query requesting the next target
    if with-probability prob-newquery 
      [send-query-on (list next-target self 0)]
    
    ;; process queries recieved and stored in messages list
    foreach messages [
      ;; if have it send file to requesting node other wise pass on query (unless max num of hops reached)
      ifelse have-file? file-of ? 
        [send-file file-of ? requestor-of ?]
        [if hops-of ? < num-hops [ send-query-on ?]]
    ]
    
    set messages []
    
  ]
  
  ;; update appearence of nodes
  ask nodes [update-node]
  
  tick                                   ;; this progresses the tick counter by one
end

to update-node
  ;; remove duplicate copies of files in file-list
  set file-store remove-duplicates file-store
  ;;  set the label to the sorted file-list
  set label sort file-store
  update-colour
end

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Finally we have definitions of the various action words/commands we use in the above
;; this makes the code easier to read and so that chunks of code can be reused at will

to-report with-probability [prob]
  ;; returns value "TRUE" with probability determined by input
  report random-float 1 < prob
end

to-report random-file
  report 1 + random max-file
end

;; put the file in their file-store
to send-file [file requester]
  ask requester [set file-store fput file file-store]
end

to send-query-on [query]
  ;; put query in all neighbours' message queue (but increment hop count)
  ask link-neighbors [
    set messages fput (list file-of query requestor-of query (1 + hops-of query)) messages
  ]
end

to-report have-file? [file]
  report member? file file-store
end

;; next three just make code easier to read, extracting parts of a query, 
;; which is a list of: the requested file, the node asking for it, the number of hops

to-report file-of [query]
  report first query
end

to-report requestor-of [query]
  report item 1 query
end

to-report hops-of [query]
  report item 2 query
end

;; set colour of node according to number of targets found
to update-colour
  let col-num numb-targets-found
  if col-num > 12 [set col-num 12]
  set color item col-num [grey violet blue sky cyan turquoise lime green yellow brown orange red magenta]
end
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@#$#@#$#@
## WHAT IS IT?

This is an example model, used as part of the "2-day Introduction to Agent-Based Modelling".  

It is a simulation of a Peer-2-Peer file sharing network. Computers are joined in a distributed fashion without central servers. Files in their store can be downloaded by others in the network. Nodes can send out queries for files they want – these go out to all its network neighbours 

If a node gets a query for one of its files, it sends it back to the originator of the query. Otherwise nodes pass on queries it gets to its neighbours (unless the query has exceeded the maximum number of hops allowed)

## FILE COLLECTING BEHAVIOUR BY NODES

* Files are represented by integers: 0, 1, 2, …, up to the value of “max-file - 1”
* These are each distributed to random to start with
* Nodes are each given a base-target (a small integer above 1), it then seeks for numbers that are multiples of this, sending out queries in turn for each these
* As files become copied around it becomes increasingly easy to find them

## HOW TO USE IT

Buttons...
"setup" to initialise the simulation, namely the network of nodes with no files
"step" to do a simulation step where nodes may send out queries for files they want or send back files
"go" to repeatedly do simulation steps 

Sliders...
* population – number of nodes
* number-links-each – number of links of each node in the network (both initial number and a target number as the simulation progresses)
* num-hops – maximum number of times a query can be passed on before it “dies”
* max-file – the integer the number representing files go up to
* prob-newquery – the probability each time that each node initiates a new query for the next file in its set that it wants

## THINGS TO NOTICE/TRY

Can you work out the conditions under which files are effectively shared to all that need it?

## EXTENDING THE MODEL

1. Could you add that some nodes are cooperators (share their files) and some not (pass on queries but never send files)?
1. What happens if you add some of the rules from the last example about changing network structure by nodes?

## NETLOGO FEATURES

Note the use of the NetLogo lsit features.  There are a lot of netlogo primitives that can be used to create and manipulate lists.

To collect the files, each node has a list called “file-store”, as it gets files it adds it to this (at its front using first put – fput). To check if it has a file is uses this
member? Each node also has a list of queries it has received called “messages”. When it receives queries from others it adds them to the messages list (using fput as above). Then (once a time click) goes through the list of messages (using foreach) and either sends the file (if it has it) or passes on the query (unless it has reached its maximum allowed hops).

## CREDITS AND REFERENCES

The simulation is a simplified version of that discussed in:

Edmonds, B. & Chattoe, E. (2005) When Simple Measures Fail: Characterising Social Networks Using Simulation. Social Network Analysis: Advances and Empirical Applications Forum, Oxford, July 16-17 2005. http://cfpm.org/cpmrep158.html

Model by Bruce Edmonds, Feb 2013
http://cfpm.org/simulationcourse
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