COVIDResponseLevels.swift

enum COVID {}

extension COVID {
    struct Conditions {
        let caseCount: Int
        let hospitalizationCount: Int
        let caseIncrease: Float
    }

    public struct Response {
        let level: Level
        let criteria: Criteria

        init(_ level: Level) {
            self.level = level
            criteria = .init(level)
        }
    }
}

extension COVID.Conditions {
    func meetCriteria(for response: COVID.Response) -> Bool {
        let criteria = response.criteria
        let satisfactions = [
            criteria.caseRange.contains(caseCount),
            criteria.hospitalizationRange.contains(hospitalizationCount),
            criteria.caseIncreaseRequirement(caseIncrease)
        ]

        let satisfiedCount = satisfactions.filter { $0 }.count
        return satisfiedCount >= 2
    }
}

extension COVID.Response {
    enum Level: Int, CaseIterable {
        case allClear = 1
        case maskPrecautions = 2
        case caution = 3
        case extremeCaution = 4
    }

    struct Criteria {
        let caseRange: CountRange
        let hospitalizationRange: CountRange
        var caseIncreaseRequirement: (Float) -> Bool = { $0 > 0.5 }
    }
}

protocol CountRange {
    func contains(_ count: Int) -> Bool
}

extension Range: CountRange where Bound == Int {}
extension PartialRangeUpTo: CountRange where Bound == Int {}
extension PartialRangeFrom: CountRange where Bound == Int {}

extension COVID.Response.Level {
    init(_ conditions: COVID.Conditions) {
        let responses = Self.allCases.map(COVID.Response.init)
        self = responses.first(where: conditions.meetCriteria)!.level
    }
}

extension COVID.Response.Criteria {
    init(_ level: COVID.Response.Level) {
        switch level {
        case .allClear:
            caseRange = ..<100
            hospitalizationRange = ..<50
            caseIncreaseRequirement = { $0 < 0.5 }
        case .maskPrecautions:
            caseRange = ..<225
            hospitalizationRange = ..<100
        case .caution:
            caseRange = 225..<500
            hospitalizationRange = 100..<500
        case .extremeCaution:
            caseRange = 500...
            hospitalizationRange = 500...
        }
    }
}