import Foundation
import UIKit

final class StickerStore {
	static let shared = StickerStore()

	private let packsKey = "savedPacks"
	private let suiteName = "group.de.felixfoertsch.StickerCloner"
	private let fileManager = FileManager.default
	private let thumbnailCache = NSCache<NSString, UIImage>()

	private lazy var defaults: UserDefaults = {
		guard let defaults = UserDefaults(suiteName: suiteName) else {
			fatalError("App Group '\(suiteName)' is not configured")
		}
		return defaults
	}()

	private init() {
		migrateIfNeeded()
	}

	// MARK: - Pack persistence

	var savedPacks: [SavedPack] {
		get {
			guard let data = defaults.data(forKey: packsKey) else { return [] }
			return (try? JSONDecoder().decode([SavedPack].self, from: data)) ?? []
		}
		set {
			let data = try? JSONEncoder().encode(newValue)
			defaults.set(data, forKey: packsKey)
		}
	}

	// MARK: - File management

	private var stickersDirectory: URL {
		let container = fileManager.containerURL(forSecurityApplicationGroupIdentifier: suiteName)!
		return container.appendingPathComponent("stickers", isDirectory: true)
	}

	private func packDirectory(name: String) -> URL {
		stickersDirectory.appendingPathComponent(name, isDirectory: true)
	}

	// MARK: - Add / remove packs

	func addPack(response: StickerSetResponse) async throws {
		let pack = SavedPack(name: response.name, title: response.title, stickerCount: response.stickerCount)

		let packDir = packDirectory(name: response.name)
		try fileManager.createDirectory(at: packDir, withIntermediateDirectories: true)

		for sticker in response.stickers {
			let localURL = packDir.appendingPathComponent("\(sticker.id).png")
			if fileManager.fileExists(atPath: localURL.path) { continue }
			try await StickerClonerAPI.downloadSticker(from: sticker.pngUrl, to: localURL)
		}

		var packs = savedPacks
		packs.removeAll { $0.name == pack.name }
		packs.append(pack)
		savedPacks = packs
	}

	func removePack(name: String) {
		var packs = savedPacks
		packs.removeAll { $0.name == name }
		savedPacks = packs
		thumbnailCache.removeObject(forKey: name as NSString)

		let packDir = packDirectory(name: name)
		try? fileManager.removeItem(at: packDir)
	}

	// MARK: - Load sticker file URLs

	func stickerFileURLs() -> [URL] {
		var urls: [URL] = []

		for pack in savedPacks {
			let packDir = packDirectory(name: pack.name)
			guard let files = try? fileManager.contentsOfDirectory(at: packDir, includingPropertiesForKeys: nil) else { continue }

			for file in files.sorted(by: { $0.lastPathComponent < $1.lastPathComponent }) {
				guard file.pathExtension == "png" else { continue }
				urls.append(file)
			}
		}

		return urls
	}

	func stickerFileURLs(forPack name: String) -> [URL] {
		let packDir = packDirectory(name: name)
		guard let files = try? fileManager.contentsOfDirectory(at: packDir, includingPropertiesForKeys: nil) else { return [] }
		return files
			.filter { $0.pathExtension == "png" }
			.sorted { $0.lastPathComponent < $1.lastPathComponent }
	}

	func firstStickerURL(forPack name: String) -> URL? {
		let packDir = packDirectory(name: name)
		guard let files = try? fileManager.contentsOfDirectory(at: packDir, includingPropertiesForKeys: nil) else { return nil }
		return files
			.filter { $0.pathExtension == "png" }
			.sorted { $0.lastPathComponent < $1.lastPathComponent }
			.first
	}

	func thumbnail(forPack name: String) -> UIImage? {
		let key = name as NSString
		if let cached = thumbnailCache.object(forKey: key) { return cached }
		guard let url = firstStickerURL(forPack: name),
			  let data = try? Data(contentsOf: url),
			  let image = UIImage(data: data) else { return nil }
		thumbnailCache.setObject(image, forKey: key)
		return image
	}

	// MARK: - Migration from old sandbox

	private func migrateIfNeeded() {
		let migrated = defaults.bool(forKey: "didMigrateToAppGroup")
		guard !migrated else { return }

		let oldDefaults = UserDefaults.standard
		if let data = oldDefaults.data(forKey: packsKey) {
			defaults.set(data, forKey: packsKey)
			oldDefaults.removeObject(forKey: packsKey)
		}

		let oldCaches = fileManager.urls(for: .cachesDirectory, in: .userDomainMask).first!
		let oldStickersDir = oldCaches.appendingPathComponent("stickers", isDirectory: true)
		if fileManager.fileExists(atPath: oldStickersDir.path) {
			let newStickersDir = stickersDirectory
			try? fileManager.createDirectory(at: newStickersDir.deletingLastPathComponent(), withIntermediateDirectories: true)
			if !fileManager.fileExists(atPath: newStickersDir.path) {
				try? fileManager.moveItem(at: oldStickersDir, to: newStickersDir)
			}
		}

		defaults.set(true, forKey: "didMigrateToAppGroup")
	}
}