import Foundation

/// Persists the inbox PR list to disk so the landing screen can render
/// instantly from the last load, then refresh in the background.
struct InboxCache {
    private let fileURL: URL

    init() {
        let dir = FileManager.default.urls(for: .cachesDirectory,
                                           in: .userDomainMask)[0]
        fileURL = dir.appendingPathComponent("inbox.json")
    }

    func load() -> [PRRow] {
        guard let data = try? Data(contentsOf: fileURL) else { return [] }
        return (try? Self.decoder.decode([PRRow].self, from: data)) ?? []
    }

    func save(_ rows: [PRRow]) {
        guard let data = try? JSONEncoder().encode(rows) else { return }
        try? data.write(to: fileURL)
    }

    /// Same ISO8601-with-offset date strategy the API decoder uses, so the
    /// cached `Date?` fields decode correctly.
    private static let decoder: JSONDecoder = {
        let d = JSONDecoder()
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        d.dateDecodingStrategy = .custom { decoder in
            let container = try decoder.singleValueContainer()
            let str = try container.decode(String.self)
            if let date = formatter.date(from: str) { return date }
            let plain = ISO8601DateFormatter()
            plain.formatOptions = [.withInternetDateTime]
            if let date = plain.date(from: str) { return date }
            throw DecodingError.dataCorruptedError(
                in: container,
                debugDescription: "Cannot decode date string \(str)")
        }
        return d
    }()
}