// holds list of already existing entities ('a list)
// Allows to check if new entities already exist in list.
// if entity already exists - add it's id into idsList
// if entity doesn't exists - add to existing, add to list of notExistedEntities, add it's id into idsList

type EntityHolder(initialEntities: 'a seq, idGetter: 'a -> string, entityComparator: 'a -> 'a -> bool) =

    let mutable existingEntities : 'a list = initialEntities |> Seq.toList

    member this.Add (entities: 'a seq) : 'a list * string list =
        let notExistedEntities, ids =
                                  entities
                                  |> Seq.fold
                                           (
                                            fun (entitiesToSave: 'a list, idsList: string list) currentEntity ->
                                                match List.tryFind (entityComparator currentEntity) existingEntities  with
                                                | Some alreadyExitingEntity ->
                                                    let id = idGetter alreadyExitingEntity
                                                    (entitiesToSave, (id :: idsList))
                                                | None ->
                                                    existingEntities <- currentEntity :: existingEntities
                                                    let id = idGetter currentEntity
                                                    (currentEntity :: entitiesToSave, id :: idsList)
                                           )
                                           ([], [])
        notExistedEntities, ids

type EntityHolderMap(initialEntities: 'a seq, idGetter: 'a -> string, hashGetter: 'a -> string) =

    let mutable existingEntities : Map<string, 'a> = initialEntities |> Seq.map (fun entity -> (hashGetter entity), entity)  |> Map.ofSeq

    member this.Add (entities: 'a seq) : 'a list * string list =
        let notExistedEntities, ids =
                                  entities
                                  |> Seq.fold
                                           (
                                            fun (entitiesToSave: 'a list, idsList: string list) currentEntity ->
                                                let currentHash = hashGetter currentEntity
                                                match existingEntities.TryFind currentHash  with
                                                | Some alreadyExitingEntity ->
                                                    let id = idGetter alreadyExitingEntity
                                                    (entitiesToSave, (id :: idsList))
                                                | None ->
                                                    existingEntities <- existingEntities.Add (currentHash, currentEntity)
                                                    let id = idGetter currentEntity
                                                    (currentEntity :: entitiesToSave, id :: idsList)
                                           )
                                           ([], [])
        notExistedEntities, ids

let AddEntities
    (idGetter: 'a -> string)
    (entityComparator: 'a -> 'a -> bool)
    (initialEntities: 'a list)
    (addingEntities: 'a list) : 'a list * 'a list * string list =

    addingEntities
    |> Seq.fold
             (
              fun (existingEntities: 'a list, entitiesToSave: 'a list , idsList: string list) currentEntity ->
                  match List.tryFind (entityComparator currentEntity) existingEntities  with
                  | Some alreadyExitingEntity ->
                      let id = idGetter alreadyExitingEntity
                      (existingEntities, entitiesToSave, (id :: idsList))
                  | None ->
                      let id = idGetter currentEntity
                      (currentEntity :: existingEntities, currentEntity :: entitiesToSave, id :: idsList)
             )
             (initialEntities, [], [])

let AddEntitiesMap
    (idGetter: 'a -> string)
    (hashGetter: 'a -> string)
    (initialEntities: Map<string, 'a>)
    (addingEntities: 'a list) : Map<string, 'a> * 'a list * string list =

    addingEntities
    |> Seq.fold
             (
              fun (existingEntities: Map<string, 'a>, entitiesToSave: 'a list , idsList: string list) currentEntity ->
                  let currentHash = hashGetter currentEntity
                  match existingEntities.TryFind currentHash  with
                  | Some alreadyExitingEntity ->
                      let id = idGetter alreadyExitingEntity
                      (existingEntities, entitiesToSave, (id :: idsList))
                  | None ->
                      let id = idGetter currentEntity
                      (existingEntities.Add (currentHash, currentEntity), currentEntity :: entitiesToSave, id :: idsList)
             )
             (initialEntities, [], [])

// Example
let AddInts = AddEntities (fun i -> i.ToString()) (fun (i: int) (j: int) -> i = j)
val existingInts : int list = [1; 2; 3]

let existingInts, adding, ids = AddInts existingInts [5; 10]

// Output
val ids : string list = ["10"; "5"]
val existingInts : int list = [10; 5; 1; 2; 3]
val adding : int list = [10; 5]

// Example
let AddIntsMap = AddEntitiesMap (fun i -> i.ToString()) (fun (i: int) -> i.ToString())
let existingIntsMap = Map.ofList [("1", 1); ("2", 2); ("3", 3)]

let existingIntsMap, adding, ids = AddIntsMap existingIntsMap [8; 13]

// Output
val ids : string list = ["13"; "8"]
val existingIntsMap : Map<string,int> = map [("1", 1); ("13", 13); ("2", 2); ("3", 3); ("8", 8)]
val adding : int list = [13; 8]