import Foundation

struct MastodonClient: PostingService {
    let account: Account
    private let token: String
    private let baseURL: String

    init(account: Account, token: String) throws {
        self.account = account
        self.token = token
        self.baseURL = try URLNormalizer.normalizeBaseURL(
            account.instanceURL, fieldName: "Mastodon instance URL"
        )
    }

    func uploadMedia(imageData: Data, filename: String, altText: String?) async throws -> String {
        let url = try URLNormalizer.endpointURL(base: baseURL, path: "/api/v2/media")
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.timeoutInterval = 30
        request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")

        var form = MultipartFormData()
        form.addFile(name: "file", filename: filename, mimeType: mimeTypeForImage(filename), data: imageData)
        if let altText, !altText.isEmpty {
            form.addField(name: "description", value: altText)
        }

        request.setValue(form.contentType, forHTTPHeaderField: "Content-Type")
        request.httpBody = form.finalized

        let (data, response) = try await NetworkSupport.data(
            for: request,
            context: "Mastodon media upload"
        )
        let statusCode = response.statusCode

        guard (200...202).contains(statusCode) else {
            let body = NetworkSupport.responseBody(data)
            throw PostingError(message: "Mastodon media upload failed (\(statusCode)): \(body)")
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let mediaID = json["id"] as? String
        else {
            throw PostingError(message: "Invalid response from Mastodon media upload")
        }

        return mediaID
    }

    func createPost(text: String, mediaIDs: [String]) async throws -> URL {
        let url = try URLNormalizer.endpointURL(base: baseURL, path: "/api/v1/statuses")
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.timeoutInterval = 30
        request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.setValue(UUID().uuidString, forHTTPHeaderField: "Idempotency-Key")

        var body: [String: Any] = ["status": text, "visibility": "public"]
        if !mediaIDs.isEmpty {
            body["media_ids"] = mediaIDs
        }

        request.httpBody = try JSONSerialization.data(withJSONObject: body)

        let (data, response) = try await NetworkSupport.data(
            for: request,
            context: "Mastodon post"
        )
        let statusCode = response.statusCode

        guard statusCode == 200 else {
            let errorBody = NetworkSupport.responseBody(data)
            throw PostingError(message: "Mastodon post failed (\(statusCode)): \(errorBody)")
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let urlString = json["url"] as? String,
              let postURL = URL(string: urlString)
        else {
            throw PostingError(message: "Invalid response from Mastodon")
        }

        return postURL
    }

    // MARK: - OAuth Registration

    static func registerApp(instanceURL: String) async throws -> (clientID: String, clientSecret: String) {
        let url = try URLNormalizer.endpointURL(
            baseURL: instanceURL,
            path: "/api/v1/apps",
            fieldName: "Mastodon instance URL"
        )
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.timeoutInterval = 30
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")

        let body: [String: String] = [
            "client_name": "qStatus",
            "redirect_uris": "qstatus://mastodon-callback",
            "scopes": "write:statuses write:media",
        ]
        request.httpBody = try JSONSerialization.data(withJSONObject: body)

        let (data, response) = try await NetworkSupport.data(
            for: request,
            context: "Mastodon app registration"
        )
        let statusCode = response.statusCode

        guard statusCode == 200 else {
            throw PostingError(
                message: "Failed to register app on \(instanceURL) (\(statusCode)): \(NetworkSupport.responseBody(data))"
            )
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let clientID = json["client_id"] as? String,
              let clientSecret = json["client_secret"] as? String
        else {
            throw PostingError(message: "Invalid registration response")
        }

        return (clientID, clientSecret)
    }

    static func authorizeURL(instanceURL: String, clientID: String) throws -> URL {
        let base = (try? URLNormalizer.normalizeBaseURL(instanceURL, fieldName: "Mastodon instance URL"))
            ?? instanceURL.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard var components = URLComponents(string: "\(base)/oauth/authorize") else {
            throw PostingError(message: "Invalid Mastodon authorization URL.")
        }
        components.queryItems = [
            URLQueryItem(name: "client_id", value: clientID),
            URLQueryItem(name: "scope", value: "write:statuses write:media"),
            URLQueryItem(name: "redirect_uri", value: "qstatus://mastodon-callback"),
            URLQueryItem(name: "response_type", value: "code"),
        ]
        guard let authURL = components.url else {
            throw PostingError(message: "Failed to build Mastodon authorization URL.")
        }
        return authURL
    }

    static func exchangeCode(
        instanceURL: String, clientID: String, clientSecret: String, code: String
    ) async throws -> String {
        let base = try URLNormalizer.normalizeBaseURL(instanceURL, fieldName: "Mastodon instance URL")
        guard let url = URL(string: "\(base)/oauth/token") else {
            throw PostingError(message: "Invalid Mastodon token endpoint URL.")
        }
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.timeoutInterval = 30
        request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")

        var components = URLComponents()
        components.queryItems = [
            URLQueryItem(name: "grant_type", value: "authorization_code"),
            URLQueryItem(name: "client_id", value: clientID),
            URLQueryItem(name: "client_secret", value: clientSecret),
            URLQueryItem(name: "redirect_uri", value: "qstatus://mastodon-callback"),
            URLQueryItem(name: "code", value: code),
        ]
        let params = components.percentEncodedQuery ?? ""
        request.httpBody = params.data(using: .utf8)

        let (data, response) = try await NetworkSupport.data(
            for: request,
            context: "Mastodon token exchange"
        )
        let statusCode = response.statusCode

        guard statusCode == 200 else {
            throw PostingError(
                message: "Token exchange failed (\(statusCode)): \(NetworkSupport.responseBody(data))"
            )
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let token = json["access_token"] as? String
        else {
            throw PostingError(message: "Invalid token response")
        }

        return token
    }

    static func verifyCredentials(instanceURL: String, token: String) async throws -> String {
        let url = try URLNormalizer.endpointURL(
            baseURL: instanceURL,
            path: "/api/v1/accounts/verify_credentials",
            fieldName: "Mastodon instance URL"
        )
        var request = URLRequest(url: url)
        request.timeoutInterval = 30
        request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")

        let (data, response) = try await NetworkSupport.data(
            for: request,
            context: "Mastodon credential verification"
        )
        let statusCode = response.statusCode

        guard statusCode == 200 else {
            throw PostingError(
                message: "Credential verification failed (\(statusCode)): \(NetworkSupport.responseBody(data))"
            )
        }

        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let username = json["username"] as? String
        else {
            throw PostingError(message: "Invalid credentials response")
        }

        return username
    }
}