import Foundation
import ManaCore

/// Persistenter Disk-Cache für Cards-Media-Files. Bilder/Audio werden
/// einmal vom Server geladen und danach lokal serviert — der Server
/// setzt `Cache-Control: private, immutable`, das honorieren wir hier.
///
/// LRU-Verdrängung mit Soft-Limit (Default 200 MB).
actor MediaCache {
    private let root: URL
    private let api: CardsAPI
    private let maxBytes: Int

    init(api: CardsAPI, maxBytes: Int = 200 * 1024 * 1024) {
        self.api = api
        self.maxBytes = maxBytes
        let caches = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)[0]
        root = caches.appendingPathComponent("cards-media", isDirectory: true)
        try? FileManager.default.createDirectory(at: root, withIntermediateDirectories: true)
    }

    /// Liefert die lokale URL eines Media-Files. Lädt vom Server, falls
    /// nicht im Cache. Wirft `AuthError`, wenn der Download scheitert.
    func localURL(for mediaId: String) async throws -> URL {
        let target = root.appendingPathComponent(mediaId)
        if FileManager.default.fileExists(atPath: target.path) {
            try? FileManager.default.setAttributes([.modificationDate: Date.now], ofItemAtPath: target.path)
            return target
        }
        let data = try await api.fetchMedia(id: mediaId)
        try data.write(to: target, options: .atomic)
        try? await pruneIfNeeded()
        return target
    }

    /// Direktes Lesen — für UI-Komponenten, die `Data` brauchen (z.B. AVAudioPlayer).
    func data(for mediaId: String) async throws -> Data {
        try await Data(contentsOf: localURL(for: mediaId))
    }

    /// LRU-Eviction: bei Überschreitung des Limits ältesten zuerst löschen.
    private struct CacheEntry {
        let url: URL
        let size: Int
        let date: Date
    }

    private func pruneIfNeeded() async throws {
        let resourceKeys: Set<URLResourceKey> = [.fileSizeKey, .contentModificationDateKey]
        guard let items = try? FileManager.default.contentsOfDirectory(
            at: root,
            includingPropertiesForKeys: Array(resourceKeys)
        ) else { return }

        let withMeta = items.compactMap { url -> CacheEntry? in
            let values = try? url.resourceValues(forKeys: resourceKeys)
            guard let size = values?.fileSize, let date = values?.contentModificationDate else { return nil }
            return CacheEntry(url: url, size: size, date: date)
        }

        let totalBytes = withMeta.reduce(0) { $0 + $1.size }
        guard totalBytes > maxBytes else { return }

        let sortedOldestFirst = withMeta.sorted { $0.date < $1.date }
        var remaining = totalBytes
        for item in sortedOldestFirst {
            if remaining <= maxBytes { break }
            try? FileManager.default.removeItem(at: item.url)
            remaining -= item.size
            let name = item.url.lastPathComponent
            let size = item.size
            Log.sync.info("MediaCache evicted \(name, privacy: .public) (\(size, privacy: .public)B)")
        }
    }

    /// Wipe — für Sign-out o.ä.
    func clear() {
        try? FileManager.default.removeItem(at: root)
        try? FileManager.default.createDirectory(at: root, withIntermediateDirectories: true)
    }
}