「リファクタリング 第2版」Swiftでコーディング その21

# 39-41頁 第1章 型による計算処理の再編成「ポリモーフィズムによる条件記述の置き換え(p.279)」

## Swift版 createStatementData.swift

```swift
import Foundation

struct PerormanceMapPlay {
    let performance: Performance
    let play: Play
    var amount: Int = 0
    var volumeCredits: Int = 0
}

struct StatementData {
    let customer: String
    let performances: [PerormanceMapPlay]
    var totalAmount: Int = 0
    var totalVolumeCredits: Int = 0
}

enum ResultError : Error {
    case failure(String)
}

public class PerformanceCalculator {
    let aPerformance: Performance
    let play: Play

    init(aPerformance: Performance, play: Play) {
        self.aPerformance = aPerformance
        self.play = play
    }

    func amount() throws -> Int {
        throw ResultError.failure("サブクラスの責務")
    }
    
    func volumeCredits() -> Int {
        return max(self.aPerformance.audience - 30, 0)
    }
}

class TragedyCalculator : PerformanceCalculator {
    override func amount() -> Int {
        var result = 40000
        if self.aPerformance.audience > 30 {
            result += 1000 * (self.aPerformance.audience - 30)
        }
        return result
    }
}

class ComedyCalculator : PerformanceCalculator {
    override func amount() throws -> Int {
        var result = 30000
        if self.aPerformance.audience > 20 {
            result += 10000 + 500 * (self.aPerformance.audience - 20)
        }
        result += 300 * self.aPerformance.audience
        return result
    }

    override func volumeCredits() -> Int {
        return super.volumeCredits() + Int(self.aPerformance.audience / 5)
    }
}

func createPerformanceCalculator(aPerformance: Performance, play: Play) throws -> PerformanceCalculator {
    switch play.type {
    case "tragedy":
        return TragedyCalculator(aPerformance: aPerformance, play: play)
    case "comedy":
        return ComedyCalculator(aPerformance: aPerformance, play: play)
    default:
        throw ResultError.failure("未知の演劇の種類:\(play.type)")
    }
}

func playFor(aPerformance:Performance) -> Play {
    return plays[aPerformance.playID]!
}

func usd(aNumber:Int) -> String {
    let format = NumberFormatter()
    format.numberStyle = .currency
    format.locale = Locale(identifier: "en_US")
    return format.string(from: NSNumber(value: aNumber / 100))!
}

func totalVolumeCredits(data:StatementData) -> Int {
    return data.performances.reduce(0) { (num: Int, perf: PerormanceMapPlay) -> Int in
        num + perf.volumeCredits
    }
}

func totalAmount(data:StatementData) -> Int {
    return data.performances.reduce(0) { (num: Int, perf: PerormanceMapPlay) -> Int in
        num + perf.amount
    }
}

func enrichPerfoemance(aPerformance:[Performance], plays:Dictionary<String, Play>) -> [PerormanceMapPlay] {
    var result: [PerormanceMapPlay] = []
    for perf in aPerformance {
        do {
            let calculator = try createPerformanceCalculator(aPerformance: perf, play: playFor(aPerformance: perf))
            var perormanceMapPlay = PerormanceMapPlay(performance: perf, play: calculator.play)
            perormanceMapPlay.amount = try calculator.amount()
            perormanceMapPlay.volumeCredits = calculator.volumeCredits()
            result.append(perormanceMapPlay)
        }
        catch {
            print(error.localizedDescription)
        }
    }
    return result
}

func createStatementData(invoice:Invoice, plays:Dictionary<String, Play>) -> StatementData {
    var result = StatementData(customer: invoice.customer, performances: enrichPerfoemance(aPerformance: invoice.performances, plays: plays))
    result.totalAmount = totalAmount(data: result)
    result.totalVolumeCredits = totalVolumeCredits(data: result)
    return result
}
```