Social network (temporal solution)

gistfile1.fs

module SocialNetworkKata

    let mutable timelines = Map.empty
    let mutable followers = Map.empty

    let post userName message =
        let userTimeline = if (Map.containsKey userName timelines ) 
                           then Map.find userName timelines 
                           else []
    
        let newTimeline = message :: userTimeline
        let newMap = Map.add(userName) newTimeline timelines
        timelines <- newMap

    let wall userName =
        let filteredMap = Map.filter (fun key _ -> ( if Map.containsKey userName followers  
                                                   then List.exists (fun elem -> elem = key) (Map.find userName followers)
                                                   else false ) || key = userName) timelines
        Map.fold (fun state key value -> value@state) [] filteredMap

    let follow follower followed =
        let userFollows = if (Map.containsKey follower followers ) 
                          then Map.find follower followers 
                          else []
    
        let newFollows = followed :: userFollows
        let newMap = Map.add(follower) newFollows followers
        followers <- newMap

    let initializeSocialNetwork () =
        timelines <- Map.empty
        followers <- Map.empty
        

    module Tests =
        open NUnit.Framework
        open Swensen.Unquote

        [<Test>]
        let ``Alice can post message to a personal timeline`` () =
            initializeSocialNetwork ()
            post "Alice" "Message 1 from Alice"
            post "Alice" "Message 2 from Alice"

            let aliceTimeline = wall "Alice"
    
            test <@ ["Message 2 from Alice"; "Message 1 from Alice"] = aliceTimeline @>

        [<Test>]
        let ``Bob can post message to a personal timeline`` () =
            initializeSocialNetwork ()
            post "Bob" "Message 1 from Bob"
            post "Bob" "Message 2 from Bob"

            let aliceTimeline = wall "Bob"

            test <@ ["Message 2 from Bob"; "Message 1 from Bob"] = aliceTimeline @>
    
        [<Test>]
        let ``Charlie can subscribe to Alice timeline`` () =
            initializeSocialNetwork ()
            post "Alice" "Message 1 from Alice"
            post "Bob" "Message 1 from Bob"

            follow "Charlie" "Alice"
            let charlieWall = wall "Charlie"

            test <@ ["Message 1 from Alice"] = charlieWall @>