import FluentKit
import Foundation
import HummingbirdFluent

/// Reads and creates accounts through the default database.
public struct AccountRepository: Sendable {

    // MARK: Constants

    /// The email of the demo buyer the prototype's stubbed passkey signs in.
    public static let demoEmail = Seed.accounts[0].email

    // MARK: Properties

    private let fluent: Fluent

    // MARK: Initializers

    /// Creates a repository backed by the given `Fluent` service.
    /// - Parameter fluent: the service whose default database the repository operates on.
    public init(
        fluent: Fluent
    ) {
        self.fluent = fluent
    }

    // MARK: Methods

    /// Fetches the account with the given email, without creating one.
    /// - Returns: the account, or `nil` when no account has the email.
    public func existingAccount(
        email: String
    ) async throws -> User? {
        try await UserRecord.query(on: fluent.db())
            .filter(\.$email == email)
            .first()?
            .snapshot
    }

    /// Whether a credential identifier is still free to register.
    public func isUnregistered(
        credentialID: String
    ) async throws -> Bool {
        try await PasskeyRecord.query(on: fluent.db())
            .filter(\.$credentialID == credentialID)
            .first() == nil
    }

    /// Creates an account together with its first passkey: one step both joins and enrolls.
    ///
    /// A passkey is only ever added to an account created in the same step. Adding one to an existing account would hand that account to
    /// whoever asks, since the prototype has no other proof of who is asking.
    /// - Returns: the new account, or `nil` when the email already has one.
    public func join(
        email: String,
        credentialID: String,
        publicKey: [UInt8],
        signCount: UInt32
    ) async throws -> User? {
        try await fluent.db().transaction { database in
            guard try await UserRecord.query(on: database)
                .filter(\.$email == email)
                .first() == nil
            else {
                return nil
            }

            let user = UserRecord(
                email: email,
                displayName: String(email.prefix { $0 != "@" })
            )

            try await user.save(on: database)
            try await PasskeyRecord(
                userID: try user.requireID(),
                credentialID: credentialID,
                publicKey: publicKey,
                signCount: signCount,
                at: .init()
            ).save(on: database)

            return try user.snapshot
        }
    }

    /// Fetches the passkey with the given credential identifier, and the account it signs in.
    public func passkey(
        credentialID: String
    ) async throws -> Passkey? {
        try await PasskeyRecord.query(on: fluent.db())
            .filter(\.$credentialID == credentialID)
            .with(\.$user)
            .first()?
            .snapshot
    }

    /// Fetches the passkeys registered to the account with the given email.
    public func passkeys(
        email: String
    ) async throws -> [Passkey] {
        try await PasskeyRecord.query(on: fluent.db())
            .join(UserRecord.self, on: \PasskeyRecord.$user.$id == \UserRecord.$id)
            .filter(UserRecord.self, \.$email == email)
            .with(\.$user)
            .all()
            .map { try $0.snapshot }
    }

    /// Records a passkey's signature counter after a sign-in.
    public func recordUse(
        ofPasskey credentialID: String,
        signCount: UInt32
    ) async throws {
        try await PasskeyRecord.query(on: fluent.db())
            .filter(\.$credentialID == credentialID)
            .set(\.$signCount, to: Int(signCount))
            .update()
    }

    /// Adds a passkey to an account. Only ever for the account's own session: holding one is the proof of who is asking.
    public func addPasskey(
        to user: User,
        credentialID: String,
        publicKey: [UInt8],
        signCount: UInt32
    ) async throws {
        try await PasskeyRecord(
            userID: user.id,
            credentialID: credentialID,
            publicKey: publicKey,
            signCount: signCount,
            at: .init()
        ).save(on: fluent.db())
    }

    /// Replaces every passkey of an account with a new one: what recovering an account comes down to.
    public func replacePasskeys(
        of user: User,
        credentialID: String,
        publicKey: [UInt8],
        signCount: UInt32
    ) async throws {
        try await fluent.db().transaction { database in
            try await PasskeyRecord.query(on: database)
                .filter(\.$user.$id == user.id)
                .delete()
            try await PasskeyRecord(
                userID: user.id,
                credentialID: credentialID,
                publicKey: publicKey,
                signCount: signCount,
                at: .init()
            ).save(on: database)
        }
    }

    /// Fetches the passkeys registered to an account, the oldest first, with when each was created.
    public func passkeys(
        of user: User
    ) async throws -> [(passkey: Passkey, createdAt: Date)] {
        try await PasskeyRecord.query(on: fluent.db())
            .filter(\.$user.$id == user.id)
            .sort(\.$createdAt)
            .with(\.$user)
            .all()
            .map { (try $0.snapshot, $0.createdAt) }
    }

    /// Changes an account's display name.
    /// - Returns: the account, renamed.
    public func rename(
        _ user: User,
        to displayName: String
    ) async throws -> User {
        try await UserRecord.query(on: fluent.db())
            .filter(\.$id == user.id)
            .set(\.$displayName, to: displayName)
            .update()

        return .init(
            id: user.id,
            email: user.email,
            displayName: displayName
        )
    }

    /// Revokes one of an account's passkeys, taking effect at once.
    public func revokePasskey(
        _ credentialID: String,
        of user: User
    ) async throws {
        try await PasskeyRecord.query(on: fluent.db())
            .filter(\.$credentialID == credentialID)
            .filter(\.$user.$id == user.id)
            .delete()
    }

    /// Fetches the account with the given email, creating it when there is none: one step both signs in and joins.
    ///
    /// A new account is named after the email's local part until its owner picks a display name.
    /// - Parameter email: the account's normalized email address.
    /// - Returns: the account, existing or new.
    public func account(
        email: String
    ) async throws -> User {
        try await signIn(email: email).user
    }

    /// Fetches the account with the given email, creating it when there is none, and says which happened.
    /// - Returns: the account, and whether this step created it.
    public func signIn(
        email: String
    ) async throws -> (user: User, isNew: Bool) {
        if let user = try await existingAccount(email: email) {
            return (user, false)
        }

        let record = UserRecord(
            email: email,
            displayName: String(email.prefix { $0 != "@" })
        )

        try await record.save(on: fluent.db())

        return (try record.snapshot, true)
    }

}