import AppKit
import Combine
import Foundation

@MainActor
final class GrammarCheckerViewModel: ObservableObject {
    static let maxWords = 1_000

    @Published var text: String = ""
    @Published private(set) var issues: [GrammarIssue] = []
    @Published private(set) var correctedText: String = ""
    @Published private(set) var hasResults = false
    @Published private(set) var isChecking = false
    @Published private(set) var errorMessage: String?

    private let grammarCheckService: any GrammarCheckServicing
    private let historyStorage: HistoryStoring
    private let textExtractionService: any TextExtracting

    init(
        grammarCheckService: any GrammarCheckServicing = GrammarCheckService(),
        historyStorage: HistoryStoring = HistoryStorageService.shared,
        textExtractionService: any TextExtracting = TextExtractionService()
    ) {
        self.grammarCheckService = grammarCheckService
        self.historyStorage = historyStorage
        self.textExtractionService = textExtractionService
    }

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

    var issueCountLabel: String {
        let count = issues.count
        return "\(count) Issue\(count == 1 ? "" : "s")"
    }

    var canCheck: Bool {
        !text.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty && !isChecking
    }

    func pasteText() {
        guard let clipboard = NSPasteboard.general.string(forType: .string) else { return }
        text = String.importedApplyingWordLimit(clipboard, maxWords: Self.maxWords, setError: { errorMessage = $0 })
        resetResults()
    }

    func uploadFile() {
        Task {
            do {
                guard let extracted = try await textExtractionService.pickAndExtractText() else { return }
                text = String.importedApplyingWordLimit(extracted, maxWords: Self.maxWords, setError: { errorMessage = $0 })
                resetResults()
            } catch {
                errorMessage = error.localizedDescription
            }
        }
    }

    func notifyWordLimitReached() {
        errorMessage = String.wordLimitExceededMessage(maxWords: Self.maxWords)
    }

    func handleTextChange() {
        let (limited, exceeded) = text.applyingWordLimit(maxWords: Self.maxWords)
        if exceeded {
            text = limited
            errorMessage = String.wordLimitExceededMessage(maxWords: Self.maxWords)
        } else if errorMessage == String.wordLimitExceededMessage(maxWords: Self.maxWords) {
            errorMessage = nil
        }
        if hasResults {
            resetResults()
        }
    }

    func clearText() {
        text = ""
        resetResults()
    }

    func resetResults() {
        issues = []
        correctedText = ""
        hasResults = false
        errorMessage = nil
    }

    func checkGrammar() {
        let content = text.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !content.isEmpty else {
            resetResults()
            return
        }

        isChecking = true
        errorMessage = nil

        Task {
            do {
                let result = try await grammarCheckService.checkGrammar(in: content)
                issues = result.issues
                correctedText = result.correctedText
                hasResults = true
                saveToHistory(text: content, issues: result.issues, correctedText: result.correctedText)
            } catch {
                errorMessage = error.localizedDescription
            }

            isChecking = false
        }
    }

    func copyCorrectedText() {
        guard !correctedText.isEmpty else { return }
        NSPasteboard.general.clearContents()
        NSPasteboard.general.setString(correctedText, forType: .string)
    }

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

        text = data.text
        issues = data.issues.map {
            GrammarIssue(original: $0.original, suggestion: $0.suggestion, explanation: $0.explanation)
        }
        correctedText = data.correctedText
        hasResults = true
        errorMessage = nil
    }

    private func saveToHistory(text: String, issues: [GrammarIssue], correctedText: String) {
        let payload = HistoryPayload.grammarChecker(
            GrammarCheckerHistoryData(
                text: text,
                issues: issues.map(\.stored),
                correctedText: correctedText
            )
        )

        let entry = HistoryEntry(
            tool: .grammarChecker,
            title: HistoryHelpers.title(from: text, fallback: "Grammar Check"),
            preview: HistoryHelpers.preview(from: correctedText.isEmpty ? text : correctedText),
            payload: payload
        )

        historyStorage.save(entry)
    }
}