Contract calculation by using visitor pattern

ContractCalculation.kt

interface IReportVisitable {
    fun accept(visitor: IReportVisitor): Int
}

data class FixedPriceContract(
        val costPerYear: Int
) : IReportVisitable {
    override fun accept(visitor: IReportVisitor): Int {
        return visitor.visit(this)
    }
}


data class TimeAndMaterialsContract(
        val costPerHour: Int,
        val totalHours: Int
) : IReportVisitable {
    override fun accept(visitor: IReportVisitor): Int {
        return visitor.visit(this)
    }
}


data class SupportContract(
        val costPerMonth: Int
) : IReportVisitable {
    override fun accept(visitor: IReportVisitor): Int {
        return 0
    }
}

interface IReportVisitor {
    fun visit(contract: FixedPriceContract): Int
    fun visit(contract: TimeAndMaterialsContract): Int
    fun visit(contract: SupportContract): Int
}

class YearCostReportVisitor: IReportVisitor {
    override fun visit(contract: FixedPriceContract): Int {
        return contract.costPerYear
    }

    override fun visit(contract: TimeAndMaterialsContract): Int {
        return contract.totalHours * contract.costPerHour
    }

    override fun visit(contract: SupportContract): Int {
        return contract.costPerMonth * 12
    }
}

val projectAlpha = FixedPriceContract(costPerYear = 10000)
val projectGamma = TimeAndMaterialsContract(totalHours = 150, costPerHour = 10)
val projectBeta = SupportContract(costPerMonth = 500)
val projectKappa = TimeAndMaterialsContract(totalHours = 50, costPerHour = 50)

val visitor = YearCostReportVisitor()

val projects = arrayOf(projectAlpha, projectBeta, projectGamma, projectKappa)
val cost = projects.map { it.accept(visitor) }.sum()
print(cost)