import Foundation

/// Errors from relay API calls.
public enum RelayError: Error, Sendable {
    case httpError(statusCode: Int)
    case invalidResponse
    case networkError(underlying: String)
}

extension RelayError: LocalizedError {
    public var errorDescription: String? {
        switch self {
        case .httpError(let code): return "Relay returned HTTP \(code)."
        case .invalidResponse:    return "Relay response could not be parsed."
        case .networkError(let m): return "Network error: \(m)"
        }
    }
}

/// Interacts with an Org Social relay server.
///
/// The relay exposes a `GET /feeds/` endpoint that returns the list of all
/// registered feed URLs in the network.
public struct RelayClient: Sendable {

    private let session: URLSession

    public init(session: URLSession = .shared) {
        self.session = session
    }

    /// Fetches the list of all feed URLs known to the relay.
    ///
    /// - Parameter relayURL: Base URL of the relay (e.g. `https://relay.org-social.org`).
    /// - Returns: Array of feed URLs.
    /// - Throws: `RelayError` on failure.
    public func fetchFeeds(from relayURL: URL) async throws -> [URL] {
        let endpoint = relayURL
            .absoluteString
            .trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard let url = URL(string: endpoint + "/feeds/") else {
            throw RelayError.invalidResponse
        }

        let data: Data
        let response: URLResponse
        do {
            (data, response) = try await session.data(from: url)
        } catch {
            throw RelayError.networkError(underlying: error.localizedDescription)
        }

        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }

        // Expected: {"data": ["https://...", "https://...", ...]}
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let rawFeeds = json["data"] as? [String] else {
            throw RelayError.invalidResponse
        }

        return rawFeeds.compactMap { URL(string: $0) }
    }

    /// Fetches vote counts for each option of a poll post.
    ///
    /// - Parameters:
    ///   - postURL: Canonical URL of the poll post (`feed#timestamp`).
    ///   - relayURL: Base URL of the relay.
    public func fetchPollVotes(for postURL: String, from relayURL: URL) async throws -> [OrgSocialPollVote] {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        var allowed = CharacterSet.urlQueryAllowed
        allowed.remove(charactersIn: "+")
        let encoded = postURL.addingPercentEncoding(withAllowedCharacters: allowed) ?? postURL
        guard let url = URL(string: "\(base)/polls/votes/?post=\(encoded)") else {
            throw RelayError.invalidResponse
        }
        let (data, response) = try await fetchData(from: url)
        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let items = json["data"] as? [[String: Any]] else {
            throw RelayError.invalidResponse
        }
        return items.compactMap { item in
            guard let option = item["option"] as? String else { return nil }
            let votes = (item["votes"] as? [String]) ?? []
            return OrgSocialPollVote(option: option, voterURLs: votes)
        }
    }

    /// Fetches the list of groups known to the relay.
    ///
    /// - Returns: Array of `(name, slug)` pairs.
    public func fetchGroupList(from relayURL: URL) async throws -> [(name: String, slug: String)] {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard let url = URL(string: "\(base)/groups/") else { throw RelayError.invalidResponse }
        let (data, response) = try await fetchData(from: url)
        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let links = json["_links"] as? [String: Any],
              let groupLinks = links["groups"] as? [[String: Any]] else {
            throw RelayError.invalidResponse
        }
        return groupLinks.compactMap { g in
            guard let name = g["name"] as? String,
                  let href = g["href"] as? String,
                  let slug = href.split(separator: "/").last.map(String.init) else { return nil }
            return (name: name, slug: slug)
        }
    }

    /// Fetches post URLs in a group (raw, unresolved).
    ///
    /// - Parameters:
    ///   - slug: Group slug (e.g. `"emacs"`, `"org-social"`).
    ///   - relayURL: Base URL of the relay.
    public func fetchGroupPostURLs(slug: String, from relayURL: URL) async throws -> [String] {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard let url = URL(string: "\(base)/groups/\(slug)/") else { throw RelayError.invalidResponse }
        let (data, response) = try await fetchData(from: url)
        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let items = json["data"] as? [[String: Any]] else {
            throw RelayError.invalidResponse
        }
        return items.compactMap { $0["post"] as? String }
    }

    /// Searches for post URLs matching `query` (text or tag search).
    ///
    /// - Parameters:
    ///   - query: Search term or tag name.
    ///   - isTag: If `true`, uses `?tag=` parameter; otherwise `?q=`.
    ///   - relayURL: Base URL of the relay.
    /// - Returns: Array of matching post URLs.
    public func searchPostURLs(query: String, isTag: Bool, from relayURL: URL) async throws -> [String] {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        let param = isTag ? "tag" : "q"
        let encoded = query.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) ?? query
        guard let url = URL(string: "\(base)/search/?\(param)=\(encoded)") else {
            throw RelayError.invalidResponse
        }
        let (data, response) = try await fetchData(from: url)
        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any] else {
            return []
        }
        // The relay returns `data` as a flat array of post URL strings.
        if let urls = json["data"] as? [String] {
            return urls
        }
        // Accept the older object form in case the relay changes its schema.
        if let items = json["data"] as? [[String: Any]] {
            return items.compactMap { $0["post"] as? String }
        }
        return []
    }

    /// Registers a feed URL with the relay so it gets indexed.
    ///
    /// - Parameters:
    ///   - feedURL: The public feed URL to register.
    ///   - relayURL: Base URL of the relay.
    /// - Throws: `RelayError` on failure (ignores 4xx as feed may already be registered).
    public func registerFeed(_ feedURL: URL, with relayURL: URL) async throws {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard let url = URL(string: "\(base)/feeds/") else { throw RelayError.invalidResponse }
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.httpBody = try? JSONSerialization.data(withJSONObject: ["feed": feedURL.absoluteString])
        let (_, response) = try await session.data(for: request)
        if let http = response as? HTTPURLResponse, http.statusCode >= 500 {
            throw RelayError.httpError(statusCode: http.statusCode)
        }
    }

    /// Fetches notifications (mentions, reactions, replies, boosts) for `feedURL`.
    ///
    /// - Parameters:
    ///   - feedURL: The public feed URL of the user (e.g. `https://andros.dev/social.org`).
    ///   - relayURL: Base URL of the relay.
    /// - Returns: Array of notifications, most recent first.
    /// - Throws: `RelayError` on failure.
    public func fetchNotifications(for feedURL: URL, from relayURL: URL) async throws -> [OrgSocialNotification] {
        let base = relayURL.absoluteString.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        let encodedFeed = feedURL.absoluteString.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) ?? feedURL.absoluteString
        guard let url = URL(string: "\(base)/notifications/?feed=\(encodedFeed)") else {
            throw RelayError.invalidResponse
        }

        let data: Data
        let response: URLResponse
        do {
            (data, response) = try await session.data(from: url)
        } catch {
            throw RelayError.networkError(underlying: error.localizedDescription)
        }

        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw RelayError.httpError(statusCode: http.statusCode)
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let items = json["data"] as? [[String: Any]] else {
            throw RelayError.invalidResponse
        }

        return items.compactMap { item in
            guard let post = item["post"] as? String,
                  let typeStr = item["type"] as? String else { return nil }
            let kind = OrgSocialNotification.Kind(rawValue: typeStr) ?? .unknown
            let emoji = item["emoji"] as? String
            let parent = item["parent"] as? String
            return OrgSocialNotification(kind: kind, post: post, emoji: emoji, parent: parent)
        }
    }

    // MARK: - Private helpers

    private func fetchData(from url: URL) async throws -> (Data, URLResponse) {
        var request = URLRequest(url: url)
        request.timeoutInterval = 10
        do { return try await session.data(for: request) }
        catch { throw RelayError.networkError(underlying: error.localizedDescription) }
    }
}