Iterator Pattern Example

IteratorPatternExample.kt

class IteratorPatternExample {
    companion object {
        @JvmStatic
        fun main(args: Array<String>) {
            val holder = VerifyTickets.getTicketHolder()

            /*Printing several tickets*/
            println("Printing next tickets...")
            holder.ticketIterator.nextTicket()
            holder.ticketIterator.nextTicket()
            holder.ticketIterator.nextTicket()

            /*Find a specific ticket*/
            println()
            println("Finding tickets...")
            holder.ticketIterator.findTicket(10)
            holder.ticketIterator.findTicket(55)

            /*Update a specific ticket*/
            println()
            println("Update ticket...")
            println("Ticket update successfully :${holder.ticketIterator.updateTicket(1, "Updated Name")}")
            println("Ticket update successfully :${holder.ticketIterator.updateTicket(55, "Exception")}")

            /*Find a specific ticket*/
            println()
            println("Find ticket...")
            holder.ticketIterator.findTicket(1)

            /*Reset the iterator position*/
            println()
            println("Reset iterator position...")
            holder.ticketIterator.resetPositionTo(0)

            /*Print all tickets*/
            VerifyTickets.printAll(holder)
        }
    }
}

/**
 * A model class that represent a ticket for a bus/train/any other vehicles.
 *
 * @param id Unique ticket ID.
 * @param name Ticket owner name.
 */
data class TicketModel(val id: Int, var name: String = "")

/**
 * An interface that define all APIs to store or remove [TicketModel] or list of [TicketModel],
 * and provide access to [TicketIterator] to iterate though the list of [TicketModel].
 */
interface TicketHolder {
    /*Add a ticket to the ticket holder*/
    fun addTicket(ticketModel: TicketModel)

    /*Add list of tickets to the ticket holder*/
    fun addTickets(ticketModel: MutableList<TicketModel>)

    /*Remove a ticket from the ticket holder*/
    fun removeTicket(ticketModel: TicketModel)

    /*Remove list of tickets from the ticket holder*/
    fun removeTickets(ticketModel: MutableList<TicketModel>)

    /*Clear all stored tickets*/
    fun clearAll(): Boolean

    /*Return an initialized instance of TicketIterator*/
    val ticketIterator: TicketIterator
}

/**
 * Implementation of [TicketHolder], where all APIs logic are defined.
 * Initialize [TicketIterator] by providing the [ticketList] as the prerequisites.
 */
class TicketHolderImpl : TicketHolder {
    /*Initialize empty holder*/
    private var ticketList: MutableList<TicketModel> = ArrayList()

    /*Initialize TicketIterator with empty holder*/
    private var iterator: TicketIterator = TicketIteratorImpl(ticketList)

    override fun addTicket(ticketModel: TicketModel) {
        ticketList.add(ticketModel)
    }

    override fun addTickets(ticketModel: MutableList<TicketModel>) {
        ticketList.addAll(ticketModel)
    }

    override fun removeTicket(ticketModel: TicketModel) {
        ticketList.remove(ticketModel)
    }

    override fun removeTickets(ticketModel: MutableList<TicketModel>) {
        ticketList.removeAll(ticketModel)
    }

    override fun clearAll(): Boolean {
        this.ticketList.clear()
        return true
    }

    override val ticketIterator: TicketIterator
        get() = iterator

}

/**
 * An interface that expose some APIs to the client to access, find, update, traverse
 * thorough the elements of Ticket Holder system.
 */
interface TicketIterator {
    /*Return the next ticket*/
    fun nextTicket(): TicketModel

    /*Find a specific ticket*/
    fun findTicket(id: Int): TicketModel?

    /*Update a specific ticket*/
    fun updateTicket(id: Int, name: String): Boolean

    /*Check if holder has more tickets or not*/
    val hasNextTicket: Boolean

    /*Reset the position to 0*/
    fun resetPositionTo(newPosition: Int)
}


/**
 * Implementation of [TicketIterator] where of APIs logic are defined.
 *
 * @param ticketList List of [TicketModel] to iterate, return ticket, find a ticket or update a ticket.
 */
class TicketIteratorImpl(private var ticketList: List<TicketModel>) : TicketIterator {
    private var position: Int = 0
    override fun nextTicket(): TicketModel {
        val ticket = ticketList[position]
        println("Ticket Info at position : $position - $ticket")
        position++
        return ticket
    }

    override fun findTicket(id: Int): TicketModel? =
        ticketList.find { it.id == id; }?.apply {
            println("Ticket found: $this")
        } ?: kotlin.run { println("No ticket found with id :${id}"); null }

    override fun updateTicket(id: Int, name: String): Boolean {
        return ticketList.find { it.id == id }?.let {
            it.name = name
            return true
        } ?: kotlin.run { println("No ticket found with id :${id}"); return@run false }
    }

    override val hasNextTicket: Boolean
        get() = position >= ticketList.size

    override fun resetPositionTo(newPosition: Int) {
        this.position = newPosition
        println("Position reset to $newPosition")
    }

}

/**
 * Clients access point to the [VerifyTickets] system.
 */
object VerifyTickets {
    private val ticketHolder: TicketHolder = TicketHolderImpl()

    fun getTicketHolder(freshStart: Boolean = true): TicketHolder {
        if (freshStart) ticketHolder.clearAll(); ticketHolder.addTickets(provideValidBusTickets())
        return ticketHolder
    }

    fun printAll(holder: TicketHolder) {
        println()
        println("Starting to print....")
        while (!holder.ticketIterator.hasNextTicket) {
            holder.ticketIterator.nextTicket()
        }
        println("Ending of print....")
        println()
    }

    /*Return a list of valid Tickets*/
    private fun provideValidBusTickets(): MutableList<TicketModel> = mutableListOf(
        TicketModel(0).apply { name = "Something $id" },
        TicketModel(1).apply { name = "Something $id" },
        TicketModel(2).apply { name = "Something $id" },
        TicketModel(3).apply { name = "Something $id" },
        TicketModel(4).apply { name = "Something $id" },
        TicketModel(5).apply { name = "Something $id" },
        TicketModel(6).apply { name = "Something $id" },
        TicketModel(7).apply { name = "Something $id" },
        TicketModel(8).apply { name = "Something $id" },
        TicketModel(9).apply { name = "Something $id" },
        TicketModel(10).apply { name = "Something $id" },
        TicketModel(11).apply { name = "Something $id" }
    )
}