Evaluando Reglas: Recorrido por el Motor

// Continuing the Rule/RuleOutcome vocabulary from the previous lesson.
// PricingDecision is what the engine hands back to the caller.
sealed class PricingDecision {
    data class Offer(val amount: Double, val appliedBoosts: List<String>) : PricingDecision()
    data class Refused(val reason: String) : PricingDecision()
    data class Escalated(val reason: String) : PricingDecision()
}

class RulesEngine(rules: List<Rule>, private val maxBoostAmount: Double = 1_500.0) {
    // Sorted once, at construction time -- not on every valuation request.
    private val orderedRules = rules.sortedBy { it.priority }

    fun decide(context: ValuationContext): PricingDecision {
        val outcomes = orderedRules.mapNotNull { it.evaluate(context) }

        // Step 1: any hard stop -- Guardrail or NoBuy -- wins immediately.
        val hardStop = outcomes.firstOrNull { it is RuleOutcome.Guardrail || it is RuleOutcome.NoBuy }
        if (hardStop != null) {
            val reason = when (hardStop) {
                is RuleOutcome.Guardrail -> hardStop.reason
                is RuleOutcome.NoBuy -> hardStop.reason
                else -> error("unreachable")
            }
            return PricingDecision.Refused(reason)
        }

        // Step 2: NoOffer defers to a human without refusing the vehicle outright.
        val noOffer = outcomes.filterIsInstance<RuleOutcome.NoOffer>().firstOrNull()
        if (noOffer != null) {
            return PricingDecision.Escalated(noOffer.reason)
        }

        // Step 3: boosts stack, but never past the cap.
        val boosts = outcomes.filterIsInstance<RuleOutcome.Boost>()
        val totalBoost = boosts.sumOf { it.amount }.coerceAtMost(maxBoostAmount)
        val finalAmount = context.providerValuation + totalBoost

        return PricingDecision.Offer(finalAmount, boosts.map { it.reason })
    }
}

data class ValuationContext(
    val vin: String,
    val mileage: Int,
    val modelYear: Int,
    val accidentCount: Int,
    val providerValuation: Double,
)

sealed class RuleOutcome {
    data class Guardrail(val reason: String) : RuleOutcome()
    data class Boost(val amount: Double, val reason: String) : RuleOutcome()
    data class NoBuy(val reason: String) : RuleOutcome()
    data class NoOffer(val reason: String) : RuleOutcome()
}

interface Rule {
    val name: String
    val priority: Int
    fun evaluate(context: ValuationContext): RuleOutcome?
}

sealed class PricingDecision {
    data class Offer(val amount: Double, val appliedBoosts: List<String>) : PricingDecision()
    data class Refused(val reason: String) : PricingDecision()
    data class Escalated(val reason: String) : PricingDecision()
}

class RulesEngine(rules: List<Rule>, private val maxBoostAmount: Double = 1_500.0) {
    private val orderedRules = rules.sortedBy { it.priority }

    fun decide(context: ValuationContext): PricingDecision {
        val outcomes = orderedRules.mapNotNull { it.evaluate(context) }

        val hardStop = outcomes.firstOrNull { it is RuleOutcome.Guardrail || it is RuleOutcome.NoBuy }
        if (hardStop != null) {
            val reason = when (hardStop) {
                is RuleOutcome.Guardrail -> hardStop.reason
                is RuleOutcome.NoBuy -> hardStop.reason
                else -> error("unreachable")
            }
            return PricingDecision.Refused(reason)
        }

        val noOffer = outcomes.filterIsInstance<RuleOutcome.NoOffer>().firstOrNull()
        if (noOffer != null) {
            return PricingDecision.Escalated(noOffer.reason)
        }

        val boosts = outcomes.filterIsInstance<RuleOutcome.Boost>()
        val totalBoost = boosts.sumOf { it.amount }.coerceAtMost(maxBoostAmount)
        val finalAmount = context.providerValuation + totalBoost

        return PricingDecision.Offer(finalAmount, boosts.map { it.reason })
    }
}

class MaxAgeGuardrail(override val priority: Int = 0) : Rule {
    override val name = "max-age-guardrail"
    override fun evaluate(context: ValuationContext): RuleOutcome? =
        if (context.modelYear < 2012) RuleOutcome.Guardrail("Model year ${context.modelYear} is too old to buy") else null
}

class TotalLossNoBuy(override val priority: Int = 1) : Rule {
    override val name = "total-loss-no-buy"
    override fun evaluate(context: ValuationContext): RuleOutcome? =
        if (context.accidentCount >= 5) RuleOutcome.NoBuy("Accident count ${context.accidentCount} indicates a total loss") else null
}

class HighAccidentNoOffer(override val priority: Int = 5) : Rule {
    override val name = "high-accident-no-offer"
    override fun evaluate(context: ValuationContext): RuleOutcome? =
        if (context.accidentCount in 2..4) RuleOutcome.NoOffer("Accident count ${context.accidentCount} requires manual review") else null
}

class LowMileageBoost(override val priority: Int = 10) : Rule {
    override val name = "low-mileage-boost"
    override fun evaluate(context: ValuationContext): RuleOutcome? =
        if (context.mileage < 30_000) RuleOutcome.Boost(500.0, "Mileage ${context.mileage} is under 30,000") else null
}

class RecentModelYearBoost(override val priority: Int = 11) : Rule {
    override val name = "recent-model-year-boost"
    override fun evaluate(context: ValuationContext): RuleOutcome? =
        if (context.modelYear >= 2023) RuleOutcome.Boost(1200.0, "Model year ${context.modelYear} is recent") else null
}

fun main() {
    val engine = RulesEngine(
        rules = listOf(
            LowMileageBoost(),
            MaxAgeGuardrail(),
            TotalLossNoBuy(),
            HighAccidentNoOffer(),
            RecentModelYearBoost(),
        ),
        maxBoostAmount = 1_500.0,
    )

    val vehicles = listOf(
        ValuationContext("VIN-100", mileage = 12_000, modelYear = 2024, accidentCount = 0, providerValuation = 28_000.0),
        ValuationContext("VIN-101", mileage = 80_000, modelYear = 2010, accidentCount = 0, providerValuation = 5_000.0),
        ValuationContext("VIN-102", mileage = 45_000, modelYear = 2019, accidentCount = 3, providerValuation = 14_000.0),
        ValuationContext("VIN-103", mileage = 60_000, modelYear = 2018, accidentCount = 6, providerValuation = 9_000.0),
    )

    for (vehicle in vehicles) {
        println("${vehicle.vin} -> ${engine.decide(vehicle)}")
    }
}