// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.

import Foundation
import GRDB

public struct Identity: Codable, Identifiable, FetchableRecord, PersistableRecord, TableRecord, ColumnExpressible {
    public static var databaseTableName: String { "identity" }
    
    public typealias Columns = CodingKeys
    public enum CodingKeys: String, CodingKey, ColumnExpression {
        case variant
        case data
    }
    
    public enum Variant: String, Codable, CaseIterable, DatabaseValueConvertible {
        case ed25519SecretKey
        case ed25519PublicKey
        case x25519PrivateKey
        case x25519PublicKey
    }
    
    public var id: Variant { variant }
    
    public let variant: Variant
    public let data: Data
    
    // MARK: - Initialization
    
    public init(
        variant: Variant,
        data: Data
    ) {
        self.variant = variant
        self.data = data
    }
}

// MARK: - GRDB Interactions

public extension Identity {
    static func generate(
        from seed: Data,
        using dependencies: Dependencies
    ) throws -> (ed25519KeyPair: KeyPair, x25519KeyPair: KeyPair) {
        guard (seed.count == 16) else { throw CryptoError.invalidSeed }

        let padding = Data(repeating: 0, count: 16)
        
        guard
            let ed25519KeyPair: KeyPair = dependencies[singleton: .crypto].generate(
                .ed25519KeyPair(seed: Array(seed + padding))
            ),
            let x25519PublicKey: [UInt8] = dependencies[singleton: .crypto].generate(
                .x25519(ed25519Pubkey: ed25519KeyPair.publicKey)
            ),
            let x25519SecretKey: [UInt8] = dependencies[singleton: .crypto].generate(
                .x25519(ed25519Seckey: ed25519KeyPair.secretKey)
            )
        else { throw CryptoError.keyGenerationFailed }
        
        return (
            ed25519KeyPair: KeyPair(
                publicKey: ed25519KeyPair.publicKey,
                secretKey: ed25519KeyPair.secretKey
            ),
            x25519KeyPair: KeyPair(
                publicKey: x25519PublicKey,
                secretKey: x25519SecretKey
            )
        )
    }

    static func store(_ db: Database, ed25519KeyPair: KeyPair, x25519KeyPair: KeyPair) throws {
        try Identity(variant: .ed25519SecretKey, data: Data(ed25519KeyPair.secretKey)).upsert(db)
        try Identity(variant: .ed25519PublicKey, data: Data(ed25519KeyPair.publicKey)).upsert(db)
        try Identity(variant: .x25519PrivateKey, data: Data(x25519KeyPair.secretKey)).upsert(db)
        try Identity(variant: .x25519PublicKey, data: Data(x25519KeyPair.publicKey)).upsert(db)
    }
    
    static func userExists(
        _ db: Database? = nil,
        using dependencies: Dependencies
    ) -> Bool {
        guard let db: Database = db else {
            return (dependencies[singleton: .storage].read { db in Identity.userExists(db, using: dependencies) } ?? false)
        }
        
        return (fetchUserEd25519KeyPair(db) != nil)
    }
    
    static func fetchUserKeyPair(_ db: Database) -> KeyPair? {
        guard
            let publicKey: Data = try? Identity.fetchOne(db, id: .x25519PublicKey)?.data,
            let secretKey: Data = try? Identity.fetchOne(db, id: .x25519PrivateKey)?.data
        else { return nil }
        
        return KeyPair(
            publicKey: publicKey.bytes,
            secretKey: secretKey.bytes
        )
    }
    
    static func fetchUserEd25519KeyPair(_ db: Database) -> KeyPair? {
        guard
            let publicKey: Data = try? Identity.fetchOne(db, id: .ed25519PublicKey)?.data,
            let secretKey: Data = try? Identity.fetchOne(db, id: .ed25519SecretKey)?.data
        else { return nil }
        
        return KeyPair(
            publicKey: publicKey.bytes,
            secretKey: secretKey.bytes
        )
    }
    
    static func mnemonic(using dependencies: Dependencies) throws -> String {
        guard
            let ed25519KeyPair: KeyPair = dependencies[singleton: .storage]
                .read({ db in Identity.fetchUserEd25519KeyPair(db) }),
            let seedData: Data = dependencies[singleton: .crypto].generate(
                .ed25519Seed(ed25519SecretKey: ed25519KeyPair.secretKey)
            ),
            seedData.count >= 16    // Just to be safe
        else {
            let dbIsValid: Bool = dependencies[singleton: .storage].isValid
            let dbHasRead: Bool = dependencies[singleton: .storage].hasSuccessfullyRead
            let dbHasWritten: Bool = dependencies[singleton: .storage].hasSuccessfullyWritten
            let dbIsSuspended: Bool = dependencies[singleton: .storage].isSuspended
            let (hasStoredXKeyPair, hasStoredEdKeyPair) = dependencies[singleton: .storage].read { db -> (Bool, Bool) in
                (
                    (Identity.fetchUserKeyPair(db) != nil),
                    (Identity.fetchUserEd25519KeyPair(db) != nil)
                )
            }.defaulting(to: (false, false))

            // stringlint:ignore_start
            let dbStates: [String] = [
                "dbIsValid: \(dbIsValid)",
                "dbHasRead: \(dbHasRead)",
                "dbHasWritten: \(dbHasWritten)",
                "dbIsSuspended: \(dbIsSuspended)",
                "userXKeyPair: \(hasStoredXKeyPair)",
                "userEdKeyPair: \(hasStoredEdKeyPair)"
            ]
            // stringlint:ignore_stop

            SNLog("Failed to retrieve keys for mnemonic generation (\(dbStates.joined(separator: ", ")))")
            throw StorageError.objectNotFound
        }

        // Our account is generated with a 16-byte seed where the second 16-bytes are just padding so
        // only use the first 16 bytes to generate the mnemonic
        return Mnemonic.encode(hexEncodedString: Data(seedData[0..<16]).toHexString())
    }
}