import Foundation

/// Uploads the social.org file to a GitHub repository via the Contents API.
///
/// Uses `GET /repos/{owner}/{repo}/contents/{path}` to fetch the current SHA,
/// then `PUT` to create or update the file.
/// Required token scope: `repo` (or `public_repo` for public repositories).
public struct GitHubUploader: FeedUploader {

    public let token: String
    public let owner: String
    public let repo: String
    public let path: String
    public let branch: String
    private let session: URLSession

    private static let apiBase = "https://api.github.com"

    public init(
        token: String,
        owner: String,
        repo: String,
        path: String = "social.org",
        branch: String = "main",
        session: URLSession = .shared
    ) {
        self.token = token
        self.owner = owner
        self.repo = repo
        self.path = path
        self.branch = branch
        self.session = session
    }

    public func upload(content: String) async throws {
        let sha = try? await fetchCurrentSHA()
        let encoded = Data(content.utf8).base64EncodedString()

        var body: [String: Any] = [
            "message": "Update social.org via iOS",
            "content": encoded,
            "branch": branch
        ]
        if let sha { body["sha"] = sha }

        let url = try contentsURL()
        var request = URLRequest(url: url)
        request.httpMethod = "PUT"
        request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        request.setValue("application/vnd.github+json", forHTTPHeaderField: "Accept")
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.httpBody = try? JSONSerialization.data(withJSONObject: 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 fetchCurrentSHA() async throws -> String {
        let url = try contentsURL()
        var request = URLRequest(url: url)
        request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        request.setValue("application/vnd.github+json", forHTTPHeaderField: "Accept")
        let (data, response) = try await perform(request)
        if let http = response as? HTTPURLResponse, http.statusCode == 404 { throw UploadError.fileNotFound }
        guard let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
              let sha = json["sha"] as? String else { throw UploadError.fileNotFound }
        return sha
    }

    private func contentsURL() throws -> URL {
        let urlString = "\(Self.apiBase)/repos/\(owner)/\(repo)/contents/\(path)"
        guard let url = URL(string: urlString) else {
            throw UploadError.invalidConfiguration("Invalid GitHub API URL: \(urlString)")
        }
        return url
    }

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

    /// Derives the public raw URL for the file (usable as `publicFeedURL`).
    public var derivedPublicURL: String {
        "https://raw.githubusercontent.com/\(owner)/\(repo)/\(branch)/\(path)"
    }
}