CommandLineToolkit

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import Foundation
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class NumberValidator {
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    private static let unsupportedCharacterSet = CharacterSet(charactersIn: "-+0123456789eE.").inverted
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    private static let exponentialSeparator = CharacterSet(charactersIn: "eE")
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    static let numberFormatter: NumberFormatter = {
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        let formatter = NumberFormatter()
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        formatter.numberStyle = .decimal
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        formatter.locale = Locale(identifier: "en_US")
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        return formatter
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    }()
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    enum `Error`: Swift.Error {
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        case invalidNumber(String)
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        case invalidIntPart(String)
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        case invalidFractionalPart(String)
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        case invalidExponentialPart(String)
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    }
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    static func validateStringRepresentationOfNumber(_ string: String) throws -> NSNumber {
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        guard string.rangeOfCharacter(from: unsupportedCharacterSet) == nil else {
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            throw Error.invalidNumber(string)
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        }
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        let parts = string.components(separatedBy: ".")
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        if parts.count == 1 {
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            let intAndExponentialParts = parts[0].components(separatedBy: exponentialSeparator)
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            try validateIntPartOfNumber(intAndExponentialParts[0])
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            if intAndExponentialParts.count == 2 {
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                try validateExponentialPartOfNumber(intAndExponentialParts[1])
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            } else if intAndExponentialParts.count > 2 {
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                throw Error.invalidNumber(string)
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            }
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        } else if parts.count == 2 {
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            try validateIntPartOfNumber(parts[0])
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            let fractionalAndExponentialParts = parts[1].components(separatedBy: exponentialSeparator)
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            try validateFractionalPartOfNumber(fractionalAndExponentialParts[0])
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            if fractionalAndExponentialParts.count == 2 {
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                try validateExponentialPartOfNumber(fractionalAndExponentialParts[1])
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            } else if fractionalAndExponentialParts.count > 2 {
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                throw Error.invalidNumber(string)
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            }
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        } else {
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            throw Error.invalidNumber(string)
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        }
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        if let number = numberFormatter.number(from: string) {
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            return number
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        } else {
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            throw Error.invalidNumber(string)
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        }
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    }
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    static func validateIntPartOfNumber(_ string: String) throws {
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        var intPart = string
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        if intPart.starts(with: "-") { intPart.removeFirst() }
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        guard intPart.rangeOfCharacter(from: CharacterSet(charactersIn: "+eE")) == nil else { throw Error.invalidIntPart(string) }
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        guard !intPart.isEmpty else { throw Error.invalidIntPart(string) }
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        if intPart.contains("+") { throw Error.invalidIntPart(string) }
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        if intPart.starts(with: "0") && intPart.count > 1 { throw Error.invalidIntPart(string) }
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    }
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    static func validateFractionalPartOfNumber(_ fractionalPart: String) throws {
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        guard !fractionalPart.isEmpty else { throw Error.invalidFractionalPart(fractionalPart) }
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    }
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    static func validateExponentialPartOfNumber(_ exponentialPart: String) throws {
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        guard !exponentialPart.isEmpty else { throw Error.invalidExponentialPart(exponentialPart) }
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    }
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}
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