import Foundation
import HealthKit

enum Formatters {
    static func percent(for number: Double) -> String {
        let formater = NumberFormatter()
        formater.numberStyle = .percent
        return formater.string(for: number)!
    }

    static func timeFor(minutes: Int) -> String {
        let formater = DateComponentsFormatter()
        formater.unitsStyle = .abbreviated
        formater.allowedUnits = [.hour, .minute]
        return formater.string(from: TimeInterval(minutes * 60))!
    }
}

extension Formatter {
    static let iso8601withFractionalSeconds: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        return formatter
    }()

    static let iso8601: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime]
        return formatter
    }()

    static let decimalFormatterWithTwoFractionDigits: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.maximumFractionDigits = 2
        return formatter
    }()

    static let dateFormatter: DateFormatter = {
        let dateFormatter = DateFormatter()
        dateFormatter.timeStyle = .short
        return dateFormatter
    }()

    static let decimalFormatterWithOneFractionDigit: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.maximumFractionDigits = 1
        return formatter
    }()

    static let integerFormatter: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.maximumFractionDigits = 0
        return formatter
    }()

    static func glucoseFormatter(for units: GlucoseUnits) -> NumberFormatter {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.roundingMode = .halfUp

        switch units {
        case .mmolL:
            formatter.maximumFractionDigits = 1
        case .mgdL:
            formatter.maximumFractionDigits = 0
        }

        return formatter
    }

    static let bolusFormatter: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.minimumIntegerDigits = 0
        formatter.maximumFractionDigits = 2
        formatter.decimalSeparator = "."
        return formatter
    }()
}

extension JSONDecoder.DateDecodingStrategy {
    static let customISO8601 = custom {
        let container = try $0.singleValueContainer()
        let string = try container.decode(String.self)
        if let date = Formatter.iso8601withFractionalSeconds.date(from: string) ?? Formatter.iso8601.date(from: string) {
            return date
        }
        throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
    }
}

extension JSONEncoder.DateEncodingStrategy {
    static let customISO8601 = custom {
        var container = $1.singleValueContainer()
        try container.encode(Formatter.iso8601withFractionalSeconds.string(from: $0))
    }
}