import Foundation

/// Uploads via the Org Social vhost multipart endpoint.
///
/// The vfile token URL is sent as the `vfile` form field so the host knows
/// which file to replace. Only `POST /upload` is used; GET on a vfile URL
/// always returns 404 and must not be used for downloading.
public struct VFileUploader: FeedUploader {

    private let tokenURL: URL
    private let session: URLSession

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

    public func upload(content: String) async throws {
        guard let scheme = tokenURL.scheme, let host = tokenURL.host else {
            throw UploadError.invalidConfiguration("Cannot derive host from vfile token URL.")
        }
        let base = tokenURL.port.map { "\(scheme)://\(host):\($0)" } ?? "\(scheme)://\(host)"
        guard let uploadURL = URL(string: "\(base)/upload") else {
            throw UploadError.invalidConfiguration("Could not build upload URL.")
        }

        let boundary = "----OrgSocialBoundary\(UInt32.random(in: 0..<UInt32.max))"
        var body = Data()

        func append(_ s: String) { body.append(Data(s.utf8)) }
        let crlf = "\r\n"

        append("--\(boundary)\(crlf)")
        append("Content-Disposition: form-data; name=\"vfile\"\(crlf)\(crlf)")
        append(tokenURL.absoluteString)
        append(crlf)

        append("--\(boundary)\(crlf)")
        append("Content-Disposition: form-data; name=\"file\"; filename=\"social.org\"\(crlf)")
        append("Content-Type: text/plain; charset=utf-8\(crlf)\(crlf)")
        body.append(Data(content.utf8))
        append(crlf)
        append("--\(boundary)--\(crlf)")

        var request = URLRequest(url: uploadURL)
        request.httpMethod = "POST"
        request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
        request.httpBody = body

        let (_, response) = try await perform(request)
        if let http = response as? HTTPURLResponse, !(200..<300).contains(http.statusCode) {
            throw UploadError.uploadFailed(statusCode: http.statusCode)
        }
    }

    private func perform(_ request: URLRequest) async throws -> (Data, URLResponse) {
        do { return try await session.data(for: request) }
        catch { throw UploadError.networkError(underlying: error.localizedDescription) }
    }
}