import Foundation
import WebKit

/// Between the page and the phone's player.
///
/// The page's half is web/src/native.ts. It replaces the playback surface of the page's media
/// element with one that posts here, so player.ts (the player bar, the row buttons, the keys)
/// carries on unchanged while this side plays. tests/native-bridge.ts holds the page's half to
/// the messages; ios/README.md lists them.
@MainActor
final class Bridge: NSObject, WKScriptMessageHandler {
    static let name = "ipx"

    private weak var webView: WKWebView?
    private let playback: Playback

    init(webView: WKWebView, playback: Playback) {
        self.webView = webView
        self.playback = playback
        super.init()
        playback.onTime = { [weak self] cur, dur in
            // Built up rather than `dur as Any`: a nil cast to Any is an Any holding nil, which
            // JSONSerialization refuses, and every tick before the length was known would drop.
            var m: [String: Any] = ["t": "time", "cur": cur]
            if let dur { m["dur"] = dur }
            self?.send(m)
        }
        playback.onMeta = { [weak self] dur in self?.send(["t": "meta", "dur": dur]) }
        playback.onState = { [weak self] playing in self?.send(["t": "state", "playing": playing]) }
        playback.onEnded = { [weak self] in self?.send(["t": "ended"]) }
        playback.onError = { [weak self] msg in self?.send(["t": "error", "message": msg]) }
        Offline.shared.onChange = { [weak self] in self?.sendKept() }
        Offline.shared.onFail = { [weak self] path, msg in
            self?.send(["t": "keepFailed", "url": path, "message": msg])
        }
    }

    /// What the phone holds, and is fetching, by the paths the page keeps them under (#425).
    private func sendKept() {
        send(["t": "kept", "urls": Offline.shared.store.paths,
              "keeping": Offline.shared.downloading.sorted()])
    }

    // MARK: - page to host

    func userContentController(_ controller: WKUserContentController,
                               didReceive message: WKScriptMessage) {
        guard let m = message.body as? [String: Any], let t = m["t"] as? String else { return }
        switch t {
        case "ready":
            if let r = m["rate"] as? Double { playback.setRate(Float(r)) }
            if let v = m["volume"] as? Double { playback.setVolume(Float(v)) }
            sendKept()
        case "load":
            guard let path = m["url"] as? String, let url = Server.resolveForPlayer(path),
                  let enc = m["enc"] as? Int,
                  let feedId = m["feedId"] as? String, let guid = m["guid"] as? String else { return }
            playback.load(.init(
                url: url, enc: enc, feedId: feedId, guid: guid,
                title: m["title"] as? String ?? "",
                feedTitle: m["feedTitle"] as? String ?? "",
                artwork: m["artwork"] as? String,
                duration: m["duration"] as? Int))
        case "play": playback.play()
        case "pause": playback.pause()
        case "stop": playback.stop()
        case "seek": if let to = m["to"] as? Double { playback.seek(to: to) }
        case "rate": if let v = m["v"] as? Double { playback.setRate(Float(v)) }
        case "volume": if let v = m["v"] as? Double { playback.setVolume(Float(v)) }
        // The page sends the path it would have written to, not a time: ours is the clock that
        // is not stale.
        case "position": playback.savePosition()
        case "keep": if let url = m["url"] as? String { Offline.shared.keep(url) }
        case "unkeep": if let url = m["url"] as? String { Offline.shared.remove(url) }
        case "clearKept": Offline.shared.removeAll()
        default: break
        }
    }

    // MARK: - host to page

    private func send(_ payload: [String: Any]) {
        guard let webView, let data = try? JSONSerialization.data(withJSONObject: payload),
              let json = String(data: data, encoding: .utf8) else { return }
        // A frozen or reloading page misses a tick; the next one puts it right.
        webView.evaluateJavaScript("window.ipxNative && window.ipxNative.on(\(json))", completionHandler: nil)
    }
}