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Parse Json API BX thailand Swift 4.0

import Foundation

struct Welcome: Codable {
    let greeting: String
    let instructions: [InstructionElement]
}

enum InstructionElement: Codable {
    case instructionClass(InstructionClass)
    case string(String)

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        if let x = try? container.decode(String.self) {
            self = .string(x)
            return
        }
        if let x = try? container.decode(InstructionClass.self) {
            self = .instructionClass(x)
            return
        }
        throw DecodingError.typeMismatch(InstructionElement.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for InstructionElement"))
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        switch self {
        case .instructionClass(let x):
            try container.encode(x)
        case .string(let x):
            try container.encode(x)
        }
    }
}

struct InstructionClass: Codable {
    let the1: The1
    let the21: The21
    let the22: The22
    let the23: The1
    let the20, the27: The13
    let the4: The14
    let the28, the6: The13
    let the24: The22
    let the13: The13
    let the30: The22
    let the2, the3, the26: The13
    let the14: The14
    let the31: The13
    let the5: The14
    let the19, the15: The13
    let the7: The7
    let the17: The13
    let the25: The25
    let the29, the8: The13

    enum CodingKeys: String, CodingKey {
        case the1 = "1"
        case the21 = "21"
        case the22 = "22"
        case the23 = "23"
        case the20 = "20"
        case the27 = "27"
        case the4 = "4"
        case the28 = "28"
        case the6 = "6"
        case the24 = "24"
        case the13 = "13"
        case the30 = "30"
        case the2 = "2"
        case the3 = "3"
        case the26 = "26"
        case the14 = "14"
        case the31 = "31"
        case the5 = "5"
        case the19 = "19"
        case the15 = "15"
        case the7 = "7"
        case the17 = "17"
        case the25 = "25"
        case the29 = "29"
        case the8 = "8"
    }
}

struct The1: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change: Double
    let lastPrice: Int
    let volume24Hours: Double
    let orderbook: The1_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The1_Orderbook: Codable {
    let bids, asks: PurpleAsks
}

struct PurpleAsks: Codable {
    let total: Int
    let volume: Double
    let highbid: Int
}

struct The13: Codable {
    let pairingID: Int
    let primaryCurrency: PrimaryCurrency
    let secondaryCurrency: String
    let change, lastPrice, volume24Hours: Double
    let orderbook: The13_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The13_Orderbook: Codable {
    let bids, asks: FluffyAsks
}

struct FluffyAsks: Codable {
    let total: Int
    let volume, highbid: Double
}

enum PrimaryCurrency: String, Codable {
    case btc = "BTC"
    case thb = "THB"
}

struct The14: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change: Int
    let lastPrice, volume24Hours: Double
    let orderbook: The13_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The21: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change: Double
    let lastPrice: Int
    let volume24Hours: Double
    let orderbook: The21_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The21_Orderbook: Codable {
    let bids: PurpleAsks
    let asks: FluffyAsks
}

struct The22: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change, lastPrice, volume24Hours: Double
    let orderbook: The21_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The25: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change: Double
    let lastPrice: Int
    let volume24Hours: Double
    let orderbook: The13_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}

struct The7: Codable {
    let pairingID: Int
    let primaryCurrency, secondaryCurrency: String
    let change: Int
    let lastPrice: Double
    let volume24Hours: Int
    let orderbook: The13_Orderbook

    enum CodingKeys: String, CodingKey {
        case pairingID = "pairing_id"
        case primaryCurrency = "primary_currency"
        case secondaryCurrency = "secondary_currency"
        case change
        case lastPrice = "last_price"
        case volume24Hours = "volume_24hours"
        case orderbook
    }
}