import Foundation

/// Persistent record of interactions (boost, reaction, poll vote) the user
/// performed through this app. Used as an optimistic overlay so the UI can
/// render the "already boosted / already reacted / already voted" state
/// instantly, without waiting for the relay to re-crawl the feed (which takes
/// up to a minute) or having to refetch the user's own feed on every row
/// appear (which hit the CDN cache and could miss just-written entries).
///
/// Lifecycle:
/// - Mutators are called on success from the interaction view models after
///   the upload completes.
/// - Readers hit only `UserDefaults`, so they are synchronous and safe to
///   call from the main thread during `task {}` setup.
/// - Entries persist across app launches until the user explicitly undoes
///   the action (`removeBoost` / `removeReaction` / `removeVote`).
@MainActor
final class OwnInteractionCache {

    static let shared = OwnInteractionCache()

    private let defaults = UserDefaults.standard
    private let boostsKey = "own.interactions.boosts.v1"
    private let reactionsKey = "own.interactions.reactions.v1"
    private let votesKey = "own.interactions.votes.v1"

    // MARK: - Boosts

    /// Records that the user has boosted `postURL`. `timestamp` is the RFC 3339
    /// ID of the boost post in the user's own feed, kept so an unboost can
    /// locate and delete that post without re-scanning.
    func recordBoost(postURL: String, timestamp: String) {
        var map = defaults.dictionary(forKey: boostsKey) as? [String: String] ?? [:]
        map[postURL] = timestamp
        defaults.set(map, forKey: boostsKey)
    }

    func removeBoost(postURL: String) {
        var map = defaults.dictionary(forKey: boostsKey) as? [String: String] ?? [:]
        map.removeValue(forKey: postURL)
        defaults.set(map, forKey: boostsKey)
    }

    /// Returns the boost-post timestamp if the user has boosted `postURL`, else nil.
    func boostTimestamp(for postURL: String) -> String? {
        let map = defaults.dictionary(forKey: boostsKey) as? [String: String] ?? [:]
        return map[postURL]
    }

    // MARK: - Reactions

    /// Entries are encoded as `"<emoji>|<timestamp>"` so we can round-trip both
    /// the emoji the user picked and the RFC 3339 ID of the reaction post.
    func recordReaction(postURL: String, emoji: String, timestamp: String) {
        var map = defaults.dictionary(forKey: reactionsKey) as? [String: String] ?? [:]
        map[postURL] = "\(emoji)|\(timestamp)"
        defaults.set(map, forKey: reactionsKey)
    }

    func removeReaction(postURL: String) {
        var map = defaults.dictionary(forKey: reactionsKey) as? [String: String] ?? [:]
        map.removeValue(forKey: postURL)
        defaults.set(map, forKey: reactionsKey)
    }

    func reaction(for postURL: String) -> (emoji: String, timestamp: String)? {
        let map = defaults.dictionary(forKey: reactionsKey) as? [String: String] ?? [:]
        guard let raw = map[postURL] else { return nil }
        let parts = raw.split(separator: "|", maxSplits: 1, omittingEmptySubsequences: false)
        guard parts.count == 2 else { return nil }
        return (String(parts[0]), String(parts[1]))
    }

    // MARK: - Poll votes

    func recordVote(pollURL: String, option: String, timestamp: String) {
        var map = defaults.dictionary(forKey: votesKey) as? [String: String] ?? [:]
        map[pollURL] = "\(option)|\(timestamp)"
        defaults.set(map, forKey: votesKey)
    }

    func removeVote(pollURL: String) {
        var map = defaults.dictionary(forKey: votesKey) as? [String: String] ?? [:]
        map.removeValue(forKey: pollURL)
        defaults.set(map, forKey: votesKey)
    }

    func vote(for pollURL: String) -> (option: String, timestamp: String)? {
        let map = defaults.dictionary(forKey: votesKey) as? [String: String] ?? [:]
        guard let raw = map[pollURL] else { return nil }
        let parts = raw.split(separator: "|", maxSplits: 1, omittingEmptySubsequences: false)
        guard parts.count == 2 else { return nil }
        return (String(parts[0]), String(parts[1]))
    }
}