import Foundation

enum AppNavigationCommand: Equatable {
    case mailbox(mailbox: Mailbox, search: String?, unreadOnly: Bool?)
    case thread(
        threadRouteID: String,
        mailbox: Mailbox?,
        messageRouteID: String?,
        search: String?,
        unreadOnly: Bool?
    )
    case compose(draft: ComposeDraft)

    static let routeEnvironmentKey = "SOCIALIO_ROUTE"
    static let jsonEnvironmentKey = "SOCIALIO_COMMAND_JSON"

    static func from(environment: [String: String]) -> AppNavigationCommand? {
        if let json = environment[jsonEnvironmentKey] {
            return from(json: json)
        }

        if let route = environment[routeEnvironmentKey] {
            return parse(route)
        }

        return nil
    }

    static func parse(_ rawValue: String) -> AppNavigationCommand? {
        let trimmed = rawValue.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return nil }

        if trimmed.hasPrefix("{") {
            return from(json: trimmed)
        }

        guard let url = URL(string: trimmed) else { return nil }
        return from(url: url)
    }

    static func from(url: URL) -> AppNavigationCommand? {
        guard let components = URLComponents(url: url, resolvingAgainstBaseURL: false) else {
            return nil
        }

        let host = (components.host ?? "").lowercased()
        let pathComponents = url.path
            .split(separator: "/")
            .map(String.init)

        let queryItems = components.queryItems ?? []
        let mailbox = queryItems.value(named: "mailbox").flatMap(Mailbox.init(rawValue:))
        let threadRouteID = queryItems.value(named: "thread")
        let messageRouteID = queryItems.value(named: "message")
        let search = queryItems.value(named: "search")
        let unreadOnly = queryItems.value(named: "unreadOnly").flatMap(Bool.init)

        switch host {
        case "mailbox":
            guard let mailboxID = pathComponents.first, let mailbox = Mailbox(rawValue: mailboxID) else {
                return nil
            }
            return .mailbox(mailbox: mailbox, search: search, unreadOnly: unreadOnly)

        case "thread":
            guard let routeID = pathComponents.first else { return nil }
            return .thread(
                threadRouteID: routeID,
                mailbox: mailbox,
                messageRouteID: messageRouteID,
                search: search,
                unreadOnly: unreadOnly
            )

        case "compose":
            return .compose(
                draft: ComposeDraft(
                    to: queryItems.value(named: "to") ?? "",
                    subject: queryItems.value(named: "subject") ?? "",
                    body: queryItems.value(named: "body") ?? ""
                )
            )

        case "open", "":
            if let threadRouteID {
                return .thread(
                    threadRouteID: threadRouteID,
                    mailbox: mailbox,
                    messageRouteID: messageRouteID,
                    search: search,
                    unreadOnly: unreadOnly
                )
            }

            if let mailbox {
                return .mailbox(mailbox: mailbox, search: search, unreadOnly: unreadOnly)
            }

            if queryItems.value(named: "to") != nil ||
                queryItems.value(named: "subject") != nil ||
                queryItems.value(named: "body") != nil {
                return .compose(
                    draft: ComposeDraft(
                        to: queryItems.value(named: "to") ?? "",
                        subject: queryItems.value(named: "subject") ?? "",
                        body: queryItems.value(named: "body") ?? ""
                    )
                )
            }

            return nil

        default:
            return nil
        }
    }

    static func from(json: String) -> AppNavigationCommand? {
        guard let data = json.data(using: .utf8) else { return nil }
        let decoder = JSONDecoder()

        do {
            let payload = try decoder.decode(AppNavigationPayload.self, from: data)
            return payload.command
        } catch {
            return nil
        }
    }
}

private struct AppNavigationPayload: Decodable {
    enum Kind: String, Decodable {
        case mailbox
        case thread
        case compose
    }

    let kind: Kind?
    let mailbox: Mailbox?
    let threadID: String?
    let messageID: String?
    let search: String?
    let unreadOnly: Bool?
    let to: String?
    let subject: String?
    let body: String?

    var command: AppNavigationCommand? {
        switch kind {
        case .mailbox:
            guard let mailbox else { return nil }
            return .mailbox(mailbox: mailbox, search: search, unreadOnly: unreadOnly)

        case .thread:
            guard let threadID else { return nil }
            return .thread(
                threadRouteID: threadID,
                mailbox: mailbox,
                messageRouteID: messageID,
                search: search,
                unreadOnly: unreadOnly
            )

        case .compose:
            return .compose(
                draft: ComposeDraft(
                    to: to ?? "",
                    subject: subject ?? "",
                    body: body ?? ""
                )
            )

        case nil:
            if let threadID {
                return .thread(
                    threadRouteID: threadID,
                    mailbox: mailbox,
                    messageRouteID: messageID,
                    search: search,
                    unreadOnly: unreadOnly
                )
            }

            if let mailbox {
                return .mailbox(mailbox: mailbox, search: search, unreadOnly: unreadOnly)
            }

            if to != nil || subject != nil || body != nil {
                return .compose(
                    draft: ComposeDraft(
                        to: to ?? "",
                        subject: subject ?? "",
                        body: body ?? ""
                    )
                )
            }

            return nil
        }
    }
}

private extension [URLQueryItem] {
    func value(named name: String) -> String? {
        first(where: { $0.name == name })?.value
    }
}