import Foundation

/// A `Sendable` snapshot of a conversation between a buyer and a shop, as one of them sees it.
public struct Conversation: Sendable, Equatable {

    // MARK: Properties

    /// The conversation's identifier.
    public let id: UUID
    /// The account buying.
    public let buyer: User
    /// The shop selling.
    public let shop: Shop
    /// The listing the conversation is about, or `nil` when it is about the shop at large.
    public let listing: Listing?
    /// Which side of the conversation the viewer is on.
    public let side: Side
    /// What was said, offered, and stamped, oldest first.
    public let entries: [Entry]
    /// The number of entries from the other side the viewer has not seen yet.
    public let unreadCount: Int
    /// The number of the sale agreed in the conversation, or `nil` when none was.
    public let saleNumber: Int?

    // MARK: Initializers

    public init(
        id: UUID,
        buyer: User,
        shop: Shop,
        listing: Listing?,
        side: Side,
        entries: [Entry],
        unreadCount: Int,
        saleNumber: Int?
    ) {
        self.id = id
        self.buyer = buyer
        self.shop = shop
        self.listing = listing
        self.side = side
        self.entries = entries
        self.unreadCount = unreadCount
        self.saleNumber = saleNumber
    }

}

// MARK: - Structs

public extension Conversation {
    /// One thing in a conversation: something said, an offer made, or an event stamped.
    struct Entry: Sendable, Equatable {

        // MARK: Properties

        /// What the entry is.
        public let kind: Kind
        /// Who wrote the message, made the offer, or caused the event.
        public let sender: User
        /// The message, the offer's note, or the event in a sentence.
        public let body: String
        /// The offer made, for an offer entry.
        public let offer: Offer?
        /// The number of the sale an event opened, or `nil`.
        public let saleNumber: Int?
        /// When the entry was made.
        public let createdAt: Date

        // MARK: Initializers

        public init(
            kind: Kind,
            sender: User,
            body: String,
            offer: Offer? = nil,
            saleNumber: Int? = nil,
            createdAt: Date
        ) {
            self.kind = kind
            self.sender = sender
            self.body = body
            self.offer = offer
            self.saleNumber = saleNumber
            self.createdAt = createdAt
        }

        // MARK: Enumerations

        /// What a conversation entry is.
        public enum Kind: String, Sendable {
            /// Something a party wrote.
            case text
            /// An offer, with its optional note.
            case offer
            /// Something that happened: an offer answered, a sale agreed, a step of the handshake taken.
            case event
        }

    }
}

// MARK: - Enumerations

public extension Conversation {
    /// A side of a conversation.
    enum Side: String, Sendable {
        case buying
        case selling
    }
}

// MARK: - Extensions

public extension Conversation {

    // MARK: Computed

    /// The latest entry, or `nil` in a conversation nothing was said in yet.
    var latest: Entry? {
        entries.last
    }

    /// The offer still waiting for an answer, or `nil` when there is none.
    var openOffer: Offer? {
        entries
            .compactMap(\.offer)
            .last { $0.status == .open }
    }

}