import Foundation

final class APIClient {
    static let shared = APIClient()

    let baseURL = URL(string: "https://banyaro.app")!
    var token: String?

    private let session: URLSession = .shared
    private let decoder: JSONDecoder = {
        let d = JSONDecoder()
        d.keyDecodingStrategy = .convertFromSnakeCase
        return d
    }()
    private let encoder: JSONEncoder = {
        let e = JSONEncoder()
        return e
    }()

    func get<T: Decodable>(_ path: String) async throws -> T {
        try await perform(method: "GET", path: path, body: nil)
    }

    func post<T: Decodable, B: Encodable>(_ path: String, body: B) async throws -> T {
        let data = try encoder.encode(body)
        return try await perform(method: "POST", path: path, body: data)
    }

    func post<T: Decodable>(_ path: String) async throws -> T {
        try await perform(method: "POST", path: path, body: nil)
    }

    private func perform<T: Decodable>(method: String, path: String, body: Data?) async throws -> T {
        let url = baseURL.appending(path: path)
        var req = URLRequest(url: url)
        req.httpMethod = method
        req.setValue("application/json", forHTTPHeaderField: "Accept")
        if let token {
            req.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        }
        if let body {
            req.setValue("application/json", forHTTPHeaderField: "Content-Type")
            req.httpBody = body
        }

        let (data, response) = try await session.data(for: req)
        guard let http = response as? HTTPURLResponse else {
            throw APIError.invalidResponse
        }
        guard (200..<300).contains(http.statusCode) else {
            let detail = Self.parseErrorDetail(from: data)
            throw APIError.server(status: http.statusCode, message: detail)
        }
        return try decoder.decode(T.self, from: data)
    }

    /// FastAPI returns errors as {"detail": "message"} or {"detail": [{...}]}.
    private static func parseErrorDetail(from data: Data) -> String? {
        if let obj = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
            if let s = obj["detail"] as? String { return s }
            if let arr = obj["detail"] as? [[String: Any]],
               let first = arr.first,
               let msg = first["msg"] as? String { return msg }
        }
        return nil
    }
}