import Foundation

private struct StreamResolutionError: LocalizedError {
    let message: String
    var errorDescription: String? { message }
}

enum StreamURL: Sendable {
    case youtube(URL)
    case miruro(mediaID: String, episode: Int)
    case anilist(mediaID: String, episode: Int)

    static func parse(_ text: String) throws -> StreamURL {
        let text = text.trimmingCharacters(in: .whitespacesAndNewlines)
        let url = try YouTubeResolver.validateURL(text)
        if url.host?.lowercased() == "zokoanime.video" {
            let invalid = StreamResolutionError(message: "Enter https://zokoanime.video/stream/ani/<AniList ID>/<episode>/sub with canonical positive numbers.")
            guard let c = URLComponents(string: text), c.scheme == "https", c.user == nil, c.password == nil,
                  c.port == nil || c.port == 443, c.query == nil, c.fragment == nil,
                  c.percentEncodedPath == c.path,
                  !text.contains(where: { $0.isWhitespace || $0 == "\\" }) else { throw invalid }
            let p = c.path.split(separator: "/", omittingEmptySubsequences: false)
            guard p.count == 6, p[0].isEmpty, p[1] == "stream", p[2] == "ani", p[5] == "sub",
                  let episode = Int(p[4]), String(episode) == p[4],
                  ResolvedSource.validAniListIdentity(mediaID: String(p[3]), episode: episode) else { throw invalid }
            return .anilist(mediaID: String(p[3]), episode: episode)
        }
        if url.host?.lowercased() != "barelystarted.miruro.tv" { return .youtube(url) }
        let invalid = StreamResolutionError(message: "Enter a Miruro episode URL from barelystarted.miruro.tv with an explicit positive episode number.")
        guard !text.unicodeScalars.contains(where: {
            CharacterSet.whitespacesAndNewlines.contains($0) || CharacterSet.controlCharacters.contains($0)
        }), let components = URLComponents(string: text),
              components.scheme?.lowercased() == "https",
              components.host?.lowercased() == "barelystarted.miruro.tv",
              components.user == nil, components.password == nil,
              components.port == nil || components.port == 443,
              components.fragment == nil,
              components.percentEncodedPath == components.path,
              components.url != nil else { throw invalid }
        let path = components.path.split(separator: "/", omittingEmptySubsequences: false)
        guard path.count == 4, path[0].isEmpty, path[1] == "watch",
              !path[3].isEmpty, path[3].utf8.count <= 512,
              path[3].utf8.allSatisfy({ isSegmentByte($0) }),
              let query = components.queryItems, query.count == 1, query[0].name == "ep",
              let number = query[0].value, let episode = Int(number),
              components.percentEncodedQuery == "ep=\(episode)",
              ResolvedSource.validIdentity(mediaID: String(path[2]), episode: episode) else { throw invalid }
        return .miruro(mediaID: String(path[2]), episode: episode)
    }

    private static func isSegmentByte(_ byte: UInt8) -> Bool {
        (65...90).contains(byte) || (97...122).contains(byte) ||
            (48...57).contains(byte) || byte == 45 || byte == 95
    }
}

struct MiruroProxy: Decodable, Sendable {
    let rotate: Bool
    let segments: Bool

    enum CodingKeys: String, CodingKey { case rotate, segments }
    init(rotate: Bool, segments: Bool) {
        self.rotate = rotate
        self.segments = segments
    }
    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        rotate = try values.decodeIfPresent(Bool.self, forKey: .rotate) ?? false
        segments = try values.decodeIfPresent(Bool.self, forKey: .segments) ?? true
    }
}

struct MiruroPlaybackRequirements: Sendable {
    var proxy: MiruroProxy? = nil
    var segmentOrigin: String? = nil
    var playlistQuery: [String: String] = [:]
    var embed = false
    var zoko = false
}

struct MiruroSelection: Sendable {
    let source: ResolvedSource
    let videoProvider: String
    let captionProvider: String?
}

struct MiruroSources: Sendable {
    fileprivate struct Candidate: Sendable {
        let provider: String
        let track: String
        let source: ResolvedSource
        var id: String { "\(provider):\(track)" }
    }
    fileprivate struct Captions: Sendable {
        let provider: String
        let track: String
        let subtitles: [ResolvedSubtitle]
        var id: String { "\(provider):\(track)" }
    }
    fileprivate let videos: [Candidate]
    fileprivate let captions: [Captions]

    let videoProviders: [String]
    let captionProviders: [String]

    fileprivate init(videos: [Candidate], captions: [Captions]) {
        self.videos = videos
        self.captions = captions
        videoProviders = videos.map(\.id)
        captionProviders = captions.map(\.id)
    }

    func select(videoProvider: String? = nil, captionProvider: String? = nil) throws -> MiruroSelection {
        func requested(_ preference: String?, provider: String, track: String) -> Bool {
            preference == "\(provider):\(track)" ||
                (preference == provider && track != "dub")
        }
        let japanese = videos.lazy.filter { $0.track != "dub" }
        guard let video = videos.first(where: { requested(videoProvider, provider: $0.provider, track: $0.track) }) ??
                japanese.first(where: { $0.provider == "sun" }) ?? japanese.first else {
            throw StreamResolutionError(message: "Miruro Japanese source is unavailable. Select an available provider and track explicitly.")
        }
        let compatibleCaptions = captions.lazy.filter { $0.track == video.track || (video.track != "dub" && $0.track != "dub") }
        let caption = captions.first(where: { requested(captionProvider, provider: $0.provider, track: $0.track) }) ??
            captions.first(where: { $0.id == video.id }) ??
            compatibleCaptions.first(where: { $0.provider == video.provider }) ??
            compatibleCaptions.first(where: { $0.provider == "sun" }) ?? compatibleCaptions.first
        let source = video.source.replacingSubtitles(caption?.subtitles ?? [])
        return MiruroSelection(source: source, videoProvider: video.id, captionProvider: caption?.id)
    }
}

enum MiruroResolver {
    static let bodyLimit = 2 * 1024 * 1024

    static func resolve(mediaID: String, episode: Int) async throws -> MiruroSources {
        try Task.checkCancellation()
        guard ResolvedSource.validIdentity(mediaID: mediaID, episode: episode) else {
            throw StreamResolutionError(message: "Invalid Miruro episode identity.")
        }
        var components = URLComponents(string: "https://barelystarted.miruro.tv/api/sources")!
        components.queryItems = [URLQueryItem(name: "id", value: mediaID), URLQueryItem(name: "n", value: String(episode))]
        var request = URLRequest(url: components.url!)
        request.timeoutInterval = 25
        request.setValue("application/json", forHTTPHeaderField: "Accept")
        let configuration = URLSessionConfiguration.ephemeral
        configuration.timeoutIntervalForRequest = 25
        configuration.timeoutIntervalForResource = 25
        configuration.httpShouldSetCookies = false
        configuration.httpCookieStorage = nil
        configuration.urlCache = nil
        let session = URLSession(configuration: configuration, delegate: MiruroRedirectPolicy(), delegateQueue: nil)
        defer { session.invalidateAndCancel() }
        do {
            let (bytes, response) = try await session.bytes(for: request)
            try validateResponse(response)
            var data = Data()
            if response.expectedContentLength > 0 { data.reserveCapacity(Int(response.expectedContentLength)) }
            for try await byte in bytes {
                try Task.checkCancellation()
                guard data.count < bodyLimit else {
                    throw StreamResolutionError(message: "Miruro source response exceeded 2 MiB.")
                }
                data.append(byte)
            }
            try Task.checkCancellation()
            return try decode(data, mediaID: mediaID, episode: episode)
        } catch {
            if Task.isCancelled || error is CancellationError || (error as? URLError)?.code == .cancelled {
                throw CancellationError()
            }
            if let error = error as? StreamResolutionError { throw error }
            throw StreamResolutionError(message: "Miruro request failed or timed out. No retry was attempted.")
        }
    }

    static func validateResponse(_ response: URLResponse) throws {
        guard let response = response as? HTTPURLResponse else {
            throw StreamResolutionError(message: "Miruro returned an invalid HTTP response.")
        }
        guard response.statusCode == 200 else {
            throw StreamResolutionError(message: "Miruro HTTP \(response.statusCode). No retry was attempted.")
        }
        guard response.mimeType?.lowercased() == "application/json" else {
            throw StreamResolutionError(message: "Miruro returned an unexpected content type; protection pages are not supported.")
        }
        guard response.expectedContentLength <= Int64(bodyLimit) else {
            throw StreamResolutionError(message: "Miruro source response exceeded 2 MiB.")
        }
    }

    static func decode(_ data: Data, mediaID: String, episode: Int) throws -> MiruroSources {
        do {
            guard data.count <= bodyLimit,
                  ResolvedSource.validIdentity(mediaID: mediaID, episode: episode) else { throw InvalidProjection() }
            let response = try JSONDecoder().decode(Sources.self, from: data)
            guard response.episodeNumber == episode else { throw InvalidProjection() }
            var videos: [MiruroSources.Candidate] = []
            var captions: [MiruroSources.Captions] = []
            var videoIDs = Set<String>()
            var captionIDs = Set<String>()
            for track in response.tracks.lazy.compactMap(\.value) where ["ssub", "sub", "dub"].contains(track.track) {
                for provider in track.providers.lazy.compactMap(\.value) {
                    let name = provider.provider
                    guard validProviderName(name) else { continue }
                    let id = "\(name):\(track.track)"
                    let config = response.config[name]?.value
                    let servers = provider.servers.compactMap(\.value)
                    // Prefer supplied server headers, but do not require a playable video to use them.
                    let captionServer = servers.first { !($0.headers ?? [:]).isEmpty && ResolvedSource.validHeaders($0.headers ?? [:]) } ??
                        servers.first { ResolvedSource.validHeaders($0.headers ?? [:]) }
                    if !captionIDs.contains(id), captionServer != nil || servers.isEmpty {
                        var headers = captionServer?.headers ?? [:]
                        var proxy = config?.proxy
                        let returned = provider.subtitles.compactMap(\.value)
                        // Iframe captions may be exact copies of a parent's resources.
                        // Reuse only that verified caption transport, never its video rules.
                        if headers.isEmpty, config?.player == "iframe", let parentName = config?.parent,
                           let parent = track.providers.compactMap(\.value).first(where: { $0.provider == parentName }),
                           parent.subtitles.compactMap(\.value) == returned,
                           let parentServer = parent.servers.compactMap(\.value).first(where: {
                               !($0.headers ?? [:]).isEmpty && ResolvedSource.validHeaders($0.headers ?? [:])
                           }) {
                            headers = parentServer.headers ?? [:]
                            proxy = response.config[parentName]?.value?.proxy
                        }
                        let subtitles = returned.lazy
                            .filter { $0.format == "vtt" }.map {
                                ResolvedSubtitle(url: $0.file, format: $0.format, language: $0.language,
                                    label: $0.label, isDefault: $0.default, headers: headers, proxy: proxy)
                            }
                        let values = Array(subtitles)
                        if !values.isEmpty, ResolvedSource.validSubtitles(values) {
                            captions.append(.init(provider: name, track: track.track, subtitles: values))
                            captionIDs.insert(id)
                        }
                    }
                    for server in servers {
                        let headers = server.headers ?? [:]
                        guard ResolvedSource.validHeaders(headers) else { continue }
                        guard !videoIDs.contains(id), let config,
                              var requirements = try? config.requirements() else { continue }
                        var locations: [(String, Bool)] = []
                        if config.player == "native", server.embed == nil {
                            locations = server.streams.compactMap(\.value).compactMap { stream in
                                guard stream.embed == nil,
                                      ["hls", "m3u8", "application/vnd.apple.mpegurl", "application/x-mpegurl"].contains(stream.format) else { return nil }
                                return (stream.url, false)
                            }
                        } else if config.player == "iframe" {
                            if let embed = server.embed { locations.append((embed.url, true)) }
                            locations.append(contentsOf: server.streams.lazy.compactMap(\.value).compactMap { stream in
                                stream.embed.map { ($0.url, true) }
                            })
                        }
                        for (url, embed) in locations {
                            guard var source = try? ResolvedSource.validated(.init(version: 1, url: url,
                                headers: headers, identity: .init(provider: "miruro", media_id: mediaID, episode: episode),
                                title: nil, subtitles: [])) else { continue }
                            requirements.embed = embed
                            source.requirements = requirements
                            videos.append(.init(provider: name, track: track.track, source: source))
                            videoIDs.insert(id)
                            break
                        }
                    }
                }
            }
            // Provider order is advisory and deduplicated; each provider retains all usable tracks.
            var seen = Set<String>()
            let providerOrder = ((response.providerOrder ?? []) + videos.map(\.provider) + captions.map(\.provider))
                .filter { seen.insert($0).inserted }
            func variants(_ name: String) -> [String] {
                var seen = Set<String>()
                return ((response.config[name]?.value?.variantOrder ?? []) + ["ssub", "sub", "dub"])
                    .filter { seen.insert($0).inserted }
            }
            let orderedVideos = providerOrder.flatMap { name in
                variants(name).compactMap { variant in videos.first { $0.provider == name && $0.track == variant } }
            }
            let orderedCaptions = providerOrder.flatMap { name in
                variants(name).compactMap { variant in captions.first { $0.provider == name && $0.track == variant } }
            }
            guard !orderedVideos.isEmpty || !orderedCaptions.isEmpty else { throw InvalidProjection() }
            return MiruroSources(videos: orderedVideos, captions: orderedCaptions)
        } catch {
            if let error = error as? StreamResolutionError { throw error }
            throw StreamResolutionError(message: "Miruro returned invalid or unsupported source metadata.")
        }
    }

    private static func validProviderName(_ name: String) -> Bool {
        !name.isEmpty && name.utf8.count <= 128 && name.utf8.allSatisfy {
            (65...90).contains($0) || (97...122).contains($0) || (48...57).contains($0) || $0 == 45 || $0 == 95
        }
    }

    private struct InvalidProjection: Error {}
    // A malformed entry must not discard valid neighboring providers, servers or streams.
    private struct Entry<Value: Decodable>: Decodable {
        let value: Value?
        init(from decoder: Decoder) throws { value = try? Value(from: decoder) }
    }
    private struct Sources: Decodable {
        let episodeNumber: Int
        let tracks: [Entry<Track>]
        let config: [String: Entry<ProviderConfig>]
        let providerOrder: [String]?
        enum CodingKeys: String, CodingKey { case episodeNumber, tracks, config, providerOrder }
        init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            episodeNumber = try values.decode(Int.self, forKey: .episodeNumber)
            tracks = try values.decode([Entry<Track>].self, forKey: .tracks)
            config = try values.decodeIfPresent([String: Entry<ProviderConfig>].self, forKey: .config) ?? [:]
            providerOrder = try values.decodeIfPresent([String].self, forKey: .providerOrder)
        }
    }
    private struct ProviderConfig: Decodable {
        let player: String
        let proxy: MiruroProxy?
        let hls: HLS?
        let variantOrder: [String]?
        let parent: String?
        enum CodingKeys: String, CodingKey { case player, proxy, hls, variantOrder, parent }
        init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            player = try values.decode(String.self, forKey: .player)
            if let flag = try? values.decode(Bool.self, forKey: .proxy) {
                guard !flag else { throw InvalidProjection() }
                proxy = nil
            } else {
                proxy = try values.decode(MiruroProxy.self, forKey: .proxy)
            }
            hls = try values.decodeIfPresent(HLS.self, forKey: .hls)
            variantOrder = try values.decodeIfPresent([String].self, forKey: .variantOrder)
            parent = try values.decodeIfPresent(String.self, forKey: .parent)
        }

        func requirements() throws -> MiruroPlaybackRequirements {
            guard player == "native" || player == "iframe" else { throw InvalidProjection() }
            var result = MiruroPlaybackRequirements(proxy: proxy)
            if let segments = hls?.segments, segments.enabled == true {
                guard let origin = segments.origin, ResolvedSource.validURL(origin) else { throw InvalidProjection() }
                result.segmentOrigin = origin
            }
            if let query = hls?.query, query.enabled == true {
                guard let params = query.params, params.count <= 64,
                      params.allSatisfy({ !$0.key.isEmpty && ResolvedSource.validText($0.key, limit: 256) &&
                          ResolvedSource.validText($0.value, limit: 16384) }) else { throw InvalidProjection() }
                result.playlistQuery = params
            }
            return result
        }
    }
    private struct HLS: Decodable {
        struct Segments: Decodable { let enabled: Bool?; let origin: String? }
        struct Query: Decodable { let enabled: Bool?; let params: [String: String]? }
        let segments: Segments?
        let query: Query?
    }
    private struct Track: Decodable {
        let track: String
        let providers: [Entry<Provider>]
    }
    private struct Provider: Decodable {
        let provider: String
        let servers: [Entry<Server>]
        let subtitles: [Entry<Subtitle>]
        enum CodingKeys: String, CodingKey { case provider, servers, subtitles }
        init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            provider = try values.decode(String.self, forKey: .provider)
            servers = try values.decodeIfPresent([Entry<Server>].self, forKey: .servers) ?? []
            subtitles = try values.decodeIfPresent([Entry<Subtitle>].self, forKey: .subtitles) ?? []
        }
    }
    private struct Embed: Decodable { let url: String }
    private struct Server: Decodable {
        let headers: [String: String]?
        let streams: [Entry<Stream>]
        let embed: Embed?
        enum CodingKeys: String, CodingKey { case headers, streams, embed }
        init(from decoder: Decoder) throws {
            let values = try decoder.container(keyedBy: CodingKeys.self)
            headers = try values.decodeIfPresent([String: String].self, forKey: .headers)
            streams = try values.decodeIfPresent([Entry<Stream>].self, forKey: .streams) ?? []
            embed = try values.decodeIfPresent(Embed.self, forKey: .embed)
        }
    }
    private struct Stream: Decodable {
        let url: String
        let format: String
        let embed: Embed?
    }
    private struct Subtitle: Decodable, Equatable {
        let file: String
        let format: String
        let language: String
        let label: String
        let `default`: Bool
    }
}

private final class MiruroRedirectPolicy: NSObject, URLSessionTaskDelegate, @unchecked Sendable {
    func urlSession(_ session: URLSession, task: URLSessionTask,
                    willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest,
                    completionHandler: @escaping (URLRequest?) -> Void) {
        completionHandler(nil)
    }
}