//
//  GopenPGPInterface.swift
//  passKit
//
//  Created by Danny Moesch on 08.09.19.
//  Copyright © 2019 Bob Sun. All rights reserved.
//

import Crypto

struct GopenPGPInterface: PGPInterface {
    private static let errorMapping: [String: Error] = [
        "gopenpgp: error in unlocking key: openpgp: invalid data: private key checksum failure": AppError.WrongPassphrase,
        "openpgp: incorrect key": AppError.KeyExpiredOrIncompatible,
    ]

    private var publicKeys: [String: CryptoKey] = [:]
    private var privateKeys: [String: CryptoKey] = [:]

    init(publicArmoredKey: String, privateArmoredKey: String) throws {
        let pubKeys = extractKeysFromArmored(str: publicArmoredKey)
        let prvKeys = extractKeysFromArmored(str: privateArmoredKey)

        for key in pubKeys {
            var error: NSError?
            guard let k = CryptoNewKeyFromArmored(key, &error) else {
                guard error == nil else {
                    throw error!
                }
                throw AppError.KeyImport
            }
            publicKeys[k.getFingerprint().lowercased()] = k
        }

        for key in prvKeys {
            var error: NSError?
            guard let k = CryptoNewKeyFromArmored(key, &error) else {
                guard error == nil else {
                    throw error!
                }
                throw AppError.KeyImport
            }
            privateKeys[k.getFingerprint().lowercased()] = k
        }
    }

    func extractKeysFromArmored(str: String) -> [String] {
        var keys: [String] = []
        var key: String = ""
        for line in str.splitByNewline() {
            if line.trimmed.uppercased().hasPrefix("-----BEGIN PGP") {
                key = ""
                key += line
            } else if line.trimmed.uppercased().hasPrefix("-----END PGP") {
                key += line
                keys.append(key)
            } else {
                key += line
            }
            key += "\n"
        }
        return keys
    }

    func containsPublicKey(with keyID: String) -> Bool {
        publicKeys.keys.contains(where: { key in key.hasSuffix(keyID.lowercased()) })
    }

    func containsPrivateKey(with keyID: String) -> Bool {
        privateKeys.keys.contains(where: { key in key.hasSuffix(keyID.lowercased()) })
    }

    func decrypt(encryptedData: Data, keyID: String, passphrase: String) throws -> Data? {
        guard let e = privateKeys.first(where: { key, _ in key.hasSuffix(keyID.lowercased()) }),
            let privateKey = privateKeys[e.key] else {
            throw AppError.Decryption
        }

        do {
            let unlockedKey = try privateKey.unlock(passphrase.data(using: .utf8))
            var error: NSError?

            guard let keyRing = CryptoNewKeyRing(unlockedKey, &error) else {
                guard error == nil else {
                    throw error!
                }
                throw AppError.Decryption
            }

            let message = createPgpMessage(from: encryptedData)
            return try keyRing.decrypt(message, verifyKey: nil, verifyTime: 0).data
        } catch {
            throw Self.errorMapping[error.localizedDescription, default: error]
        }
    }

    func encrypt(plainData: Data, keyID: String) throws -> Data {
        guard let e = publicKeys.first(where: { key, _ in key.hasSuffix(keyID.lowercased()) }),
            let publicKey = publicKeys[e.key] else {
            throw AppError.Encryption
        }

        var error: NSError?

        guard let keyRing = CryptoNewKeyRing(publicKey, &error) else {
            guard error == nil else {
                throw error!
            }
            throw AppError.Encryption
        }

        let encryptedData = try keyRing.encrypt(CryptoNewPlainMessage(plainData.mutable as Data), privateKey: nil)
        if Defaults.encryptInArmored {
            var error: NSError?
            let armor = encryptedData.getArmored(&error)
            guard error == nil else {
                throw error!
            }
            return armor.data(using: .ascii)!
        }
        return encryptedData.getBinary()!
    }

    var keyID: [String] {
        publicKeys.keys.map { $0.uppercased() }
    }

    var shortKeyID: [String] {
        publicKeys.keys.map { $0.suffix(8).uppercased() }
    }

    private func createPgpMessage(from encryptedData: Data) -> CryptoPGPMessage? {
        // Important note:
        // Even if Defaults.encryptInArmored is true now, it could be different during the encryption.
        var error: NSError?
        let message = CryptoNewPGPMessageFromArmored(String(data: encryptedData, encoding: .ascii), &error)
        if error == nil {
            return message
        }
        return CryptoNewPGPMessage(encryptedData.mutable as Data)
    }
}