import AppKit
import Combine
import Foundation

@MainActor
final class LanguageTranslatorViewModel: ObservableObject {
    static let maxWords = 10_000

    @Published var sourceText: String = ""
    @Published var translatedText: String = ""
    @Published var sourceLanguage: TranslationLanguage = .defaultSource
    @Published var targetLanguage: TranslationLanguage = .defaultTarget
    @Published private(set) var isTranslating = false
    @Published private(set) var errorMessage: String?

    private let translationService: any TranslationServicing
    private let historyStorage: HistoryStoring
    private let textExtractionService: any TextExtracting

    init(
        translationService: any TranslationServicing = TranslationService(),
        historyStorage: HistoryStoring = HistoryStorageService.shared,
        textExtractionService: any TextExtracting = TextExtractionService()
    ) {
        self.translationService = translationService
        self.historyStorage = historyStorage
        self.textExtractionService = textExtractionService
    }

    var wordCountLimitLabel: String {
        "\(sourceText.wordCount)/\(Self.maxWords)"
    }

    var canTranslate: Bool {
        !sourceText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && !isTranslating
    }

    var sourceLanguageOptions: [TranslationLanguage] {
        TranslationLanguage.all
    }

    var targetLanguageOptions: [TranslationLanguage] {
        TranslationLanguage.all.filter { $0 != sourceLanguage }
    }

    func pasteText() {
        guard let clipboard = NSPasteboard.general.string(forType: .string) else { return }
        sourceText = clipboard.truncated(toMaxWords: Self.maxWords)
        translatedText = ""
        errorMessage = nil
    }

    func uploadFile() {
        Task {
            do {
                guard let extracted = try await textExtractionService.pickAndExtractText() else { return }
                sourceText = extracted.truncated(toMaxWords: Self.maxWords)
                translatedText = ""
                errorMessage = nil
            } catch {
                errorMessage = error.localizedDescription
            }
        }
    }

    func clearText() {
        sourceText = ""
        translatedText = ""
        errorMessage = nil
    }

    func swapLanguages() {
        let previousSource = sourceLanguage
        sourceLanguage = targetLanguage
        targetLanguage = previousSource

        let previousSourceText = sourceText
        sourceText = translatedText
        translatedText = previousSourceText
    }

    func translate() {
        let trimmed = sourceText.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }

        isTranslating = true
        translatedText = ""
        errorMessage = nil

        Task {
            do {
                translatedText = try await translationService.translate(
                    trimmed,
                    from: sourceLanguage,
                    to: targetLanguage
                )
                saveToHistory(sourceText: trimmed, translatedText: translatedText)
            } catch {
                errorMessage = error.localizedDescription
            }

            isTranslating = false
        }
    }

    func restore(from entry: HistoryEntry) {
        guard case .languageTranslator(let data) = entry.payload else { return }

        sourceText = data.sourceText
        translatedText = data.translatedText
        sourceLanguage = TranslationLanguage.all.first { $0.id == data.sourceLanguageID } ?? .defaultSource
        targetLanguage = TranslationLanguage.all.first { $0.id == data.targetLanguageID } ?? .defaultTarget
        errorMessage = nil
    }

    private func saveToHistory(sourceText: String, translatedText: String) {
        let payload = HistoryPayload.languageTranslator(
            TranslationHistoryData(
                sourceText: sourceText,
                translatedText: translatedText,
                sourceLanguageID: sourceLanguage.id,
                targetLanguageID: targetLanguage.id
            )
        )

        let entry = HistoryEntry(
            tool: .languageTranslator,
            title: HistoryHelpers.title(from: sourceText, fallback: "Translation"),
            preview: HistoryHelpers.preview(from: translatedText),
            payload: payload
        )

        historyStorage.save(entry)
    }

    func syncTargetLanguageIfNeeded() {
        guard targetLanguage == sourceLanguage else { return }
        targetLanguage = TranslationLanguage.all.first { $0 != sourceLanguage } ?? .defaultTarget
    }
}