// APIClient.swift
// Jarvis — REST networking layer

import Foundation

enum APIError: Error, LocalizedError {
    case invalidURL
    case serverError(code: String, message: String, status: Int)
    case decodingError(Error)
    case networkError(Error)
    case notConnected

    var errorDescription: String? {
        switch self {
        case .invalidURL:           return "Invalid server URL"
        case .notConnected:         return "Not connected to a Jarvis server"
        case .serverError(_, let msg, _): return msg
        case .decodingError(let e): return "Decode error: \(e.localizedDescription)"
        case .networkError(let e):  return e.localizedDescription
        }
    }

    /// A benign URLSession cancellation (-999), e.g. a request superseded or
    /// dropped on a network-path change. Should not be shown or wipe state.
    var isCancelled: Bool {
        if case .networkError(let e) = self { return (e as? URLError)?.code == .cancelled }
        return false
    }
}

private struct APIErrorResponse: Decodable {
    struct Inner: Decodable { let code, message: String; let status: Int }
    let error: Inner
}

actor APIClient {
    static let shared = APIClient()

    private var baseURL: URL?
    private let session: URLSession
    private let decoder: JSONDecoder

    private init() {
        let config = URLSessionConfiguration.default
        config.timeoutIntervalForRequest = 10
        self.session = URLSession(configuration: config)

        self.decoder = JSONDecoder()
        self.decoder.dateDecodingStrategy = .iso8601
        self.decoder.keyDecodingStrategy = .convertFromSnakeCase
    }

    func configure(host: String) throws {
        guard let url = URL(string: "http://\(host)/api/v1") else {
            throw APIError.invalidURL
        }
        self.baseURL = url
    }

    // MARK: - Health

    func checkHealth() async throws -> ServerHealth {
        try await get("/health")
    }

    // MARK: - Stories

    func fetchStories(
        cursor: String? = nil,
        topic: String? = nil,
        tags: Set<String> = [],
        minSignal: Int? = nil,
        limit: Int = 20
    ) async throws -> PaginatedStories {
        var params: [String: String] = ["limit": "\(limit)"]
        if let cursor   { params["after"] = cursor }
        if let topic    { params["topic"] = topic }
        if !tags.isEmpty { params["tags"] = tags.sorted().joined(separator: ",") }
        if let minSignal { params["min_signal"] = "\(minSignal)" }
        return try await get("/stories", params: params)
    }

    func fetchStory(id: String) async throws -> StoryDetail {
        try await get("/stories/\(id)")
    }

    // MARK: - Articles

    func fetchArticle(id: String) async throws -> Article {
        try await get("/articles/\(id)")
    }

    // MARK: - Feeds

    func fetchFeeds() async throws -> [Feed] {
        struct FeedsResponse: Decodable { let data: [Feed] }
        let response: FeedsResponse = try await get("/feeds")
        return response.data
    }

    func addFeed(url: String, name: String, pollInterval: Int = 900) async throws -> Feed {
        let body = ["url": url, "name": name, "pollIntervalSeconds": pollInterval] as [String: Any]
        return try await post("/feeds", body: body)
    }

    func deleteFeed(id: String) async throws {
        try await delete("/feeds/\(id)")
    }

    // MARK: - Private helpers

    private func get<T: Decodable>(_ path: String, params: [String: String] = [:]) async throws -> T {
        guard let base = baseURL else { throw APIError.notConnected }
        var components = URLComponents(url: base.appendingPathComponent(path), resolvingAgainstBaseURL: false)!
        if !params.isEmpty {
            components.queryItems = params.map { URLQueryItem(name: $0.key, value: $0.value) }
        }
        guard let url = components.url else { throw APIError.invalidURL }
        var request = URLRequest(url: url)
        request.httpMethod = "GET"
        return try await execute(request)
    }

    private func post<T: Decodable>(_ path: String, body: [String: Any]) async throws -> T {
        guard let base = baseURL else { throw APIError.notConnected }
        let url = base.appendingPathComponent(path)
        var request = URLRequest(url: url)
        request.httpMethod = "POST"
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.httpBody = try JSONSerialization.data(withJSONObject: body)
        return try await execute(request)
    }

    private func delete(_ path: String) async throws {
        guard let base = baseURL else { throw APIError.notConnected }
        let url = base.appendingPathComponent(path)
        var request = URLRequest(url: url)
        request.httpMethod = "DELETE"
        let (_, response) = try await session.data(for: request)
        guard let http = response as? HTTPURLResponse, http.statusCode == 204 else {
            throw APIError.serverError(code: "delete_failed", message: "Delete failed", status: 500)
        }
    }

    private func execute<T: Decodable>(_ request: URLRequest) async throws -> T {
        do {
            let (data, response) = try await session.data(for: request)
            guard let http = response as? HTTPURLResponse else {
                throw APIError.networkError(URLError(.badServerResponse))
            }
            if !(200...299).contains(http.statusCode) {
                if let err = try? decoder.decode(APIErrorResponse.self, from: data) {
                    throw APIError.serverError(code: err.error.code, message: err.error.message, status: err.error.status)
                }
                throw APIError.serverError(code: "unknown", message: "HTTP \(http.statusCode)", status: http.statusCode)
            }
            do {
                return try decoder.decode(T.self, from: data)
            } catch {
                throw APIError.decodingError(error)
            }
        } catch let error as APIError {
            throw error
        } catch {
            throw APIError.networkError(error)
        }
    }
}