import Foundation
import CoreData
import Combine

class ImportService {
    static let shared = ImportService()

    private init() {}

    struct ImportResult {
        let accountsCreated: Int
        let sourcesCreated: Int
        let snapshotsCreated: Int
        let errors: [String]
    }

    struct ImportProgress {
        let completed: Int
        let total: Int
        let message: String

        var fraction: Double {
            guard total > 0 else { return 0 }
            return min(max(Double(completed) / Double(total), 0), 1)
        }
    }

    enum ImportFormat {
        case csv
        case json
    }

    struct ImportedAccount {
        let name: String
        let currency: String?
        let inputMode: InputMode
        let notificationFrequency: NotificationFrequency
        let customFrequencyMonths: Int
        let categories: [ImportedCategory]
    }

    struct ImportedCategory {
        let name: String
        let colorHex: String?
        let icon: String?
        let sources: [ImportedSource]
    }

    struct ImportedSource {
        let name: String
        let snapshots: [ImportedSnapshot]
    }

    struct ImportedSnapshot {
        let date: Date
        let value: Decimal
        let contribution: Decimal?
        let notes: String?
    }

    func importData(
        content: String,
        format: ImportFormat,
        allowMultipleAccounts: Bool,
        defaultAccountName: String? = nil
    ) -> ImportResult {
        switch format {
        case .csv:
            let parsed = parseCSV(
                content,
                allowMultipleAccounts: allowMultipleAccounts,
                defaultAccountName: defaultAccountName
            )
            return applyImport(parsed, context: CoreDataStack.shared.viewContext)
        case .json:
            let parsed = parseJSON(content, allowMultipleAccounts: allowMultipleAccounts)
            return applyImport(parsed, context: CoreDataStack.shared.viewContext)
        }
    }

    func importDataAsync(
        content: String,
        format: ImportFormat,
        allowMultipleAccounts: Bool,
        defaultAccountName: String? = nil,
        progress: @escaping (ImportProgress) -> Void
    ) async -> ImportResult {
        await withCheckedContinuation { continuation in
            CoreDataStack.shared.performBackgroundTask { context in
                let parsed: [ImportedAccount]
                switch format {
                case .csv:
                    parsed = self.parseCSV(
                        content,
                        allowMultipleAccounts: allowMultipleAccounts,
                        defaultAccountName: defaultAccountName
                    )
                case .json:
                    parsed = self.parseJSON(content, allowMultipleAccounts: allowMultipleAccounts)
                }

                let totalSnapshots = parsed.reduce(0) { total, account in
                    total + account.categories.reduce(0) { subtotal, category in
                        subtotal + category.sources.reduce(0) { sourceTotal, source in
                            sourceTotal + source.snapshots.count
                        }
                    }
                }

                DispatchQueue.main.async {
                    progress(ImportProgress(completed: 0, total: totalSnapshots, message: "Importing data"))
                }

                let result = self.applyImport(parsed, context: context) { completed in
                    DispatchQueue.main.async {
                        progress(ImportProgress(
                            completed: completed,
                            total: totalSnapshots,
                            message: "Imported \(completed) of \(totalSnapshots) snapshots"
                        ))
                    }
                }

                continuation.resume(returning: result)
            }
        }
    }

    static func sampleCSV() -> String {
        return """
Account,Category,Source,Date,Value,Contribution,Notes
Personal,Stocks,Index Fund,2024-01-01,15000,12000,Long-term
Personal,Crypto,BTC,2024-01-01,3200,,Cold storage
Personal,Real Estate,Rental Property,2024-01-01,82000,80000,Estimated value
"""
    }

    static func sampleJSON() -> String {
        return """
{
  "version": 2,
  "currency": "EUR",
  "accounts": [{
    "name": "Personal",
    "inputMode": "simple",
    "notificationFrequency": "monthly",
    "categories": [{
      "name": "Stocks",
      "color": "#3B82F6",
      "icon": "chart.line.uptrend.xyaxis",
      "sources": [{
        "name": "Index Fund",
        "snapshots": [{
          "date": "2024-01-01T00:00:00Z",
          "value": 15000,
          "contribution": 12000
        }]
      }]
    }]
  }]
}
"""
    }

    // MARK: - Parsing

    private func parseCSV(
        _ content: String,
        allowMultipleAccounts: Bool,
        defaultAccountName: String?
    ) -> [ImportedAccount] {
        let rows = parseCSVRows(content)
        guard rows.count > 1 else { return [] }

        let headers = rows[0].map { $0.lowercased().trimmingCharacters(in: .whitespaces) }
        let indexOfAccount = headers.firstIndex(of: "account")
        let indexOfCategory = headers.firstIndex(of: "category")
        let indexOfSource = headers.firstIndex(of: "source")
        let indexOfDate = headers.firstIndex(of: "date")
        let indexOfValue = headers.firstIndex(where: { $0.hasPrefix("value") })
        let indexOfContribution = headers.firstIndex(where: { $0.hasPrefix("contribution") })
        let indexOfNotes = headers.firstIndex(of: "notes")

        var grouped: [String: [String: [String: [ImportedSnapshot]]]] = [:]

        for row in rows.dropFirst() {
            let providedAccount = indexOfAccount.flatMap { row.safeValue(at: $0) }
            let fallbackAccount = defaultAccountName ?? "Personal"
            let normalizedAccount = (providedAccount ?? "")
                .trimmingCharacters(in: .whitespacesAndNewlines)
            let rawAccountName = normalizedAccount.isEmpty ? fallbackAccount : normalizedAccount
            let accountName = allowMultipleAccounts ? rawAccountName : "Personal"

            guard let categoryName = indexOfCategory.flatMap({ row.safeValue(at: $0) }), !categoryName.isEmpty,
                  let sourceName = indexOfSource.flatMap({ row.safeValue(at: $0) }), !sourceName.isEmpty,
                  let dateString = indexOfDate.flatMap({ row.safeValue(at: $0) }),
                  let valueString = indexOfValue.flatMap({ row.safeValue(at: $0) }) else {
                continue
            }

            guard let date = parseDate(dateString),
                  let value = parseDecimal(valueString) else { continue }

            let contribution = indexOfContribution
                .flatMap { row.safeValue(at: $0) }
                .flatMap(parseDecimal)
            let notes = indexOfNotes
                .flatMap { row.safeValue(at: $0) }
                .flatMap { $0.isEmpty ? nil : $0 }

            let snapshot = ImportedSnapshot(
                date: date,
                value: value,
                contribution: contribution,
                notes: notes
            )

            grouped[accountName, default: [:]][categoryName, default: [:]][sourceName, default: []].append(snapshot)
        }

        return grouped.map { accountName, categories in
            let importedCategories = categories.map { categoryName, sources in
                let importedSources = sources.map { sourceName, snapshots in
                    ImportedSource(name: sourceName, snapshots: snapshots)
                }
                return ImportedCategory(name: categoryName, colorHex: nil, icon: nil, sources: importedSources)
            }

            return ImportedAccount(
                name: accountName,
                currency: nil,
                inputMode: .simple,
                notificationFrequency: .monthly,
                customFrequencyMonths: 1,
                categories: importedCategories
            )
        }
    }

    private func parseJSON(_ content: String, allowMultipleAccounts: Bool) -> [ImportedAccount] {
        guard let data = content.data(using: .utf8),
              let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any] else {
            return []
        }

        if let accountsArray = json["accounts"] as? [[String: Any]] {
            return accountsArray.compactMap { accountDict in
                let rawName = accountDict["name"] as? String ?? "Personal"
                let name = allowMultipleAccounts ? rawName : "Personal"

                let currency = accountDict["currency"] as? String
                let inputMode = InputMode(rawValue: accountDict["inputMode"] as? String ?? "") ?? .simple
                let notificationFrequency = NotificationFrequency(
                    rawValue: accountDict["notificationFrequency"] as? String ?? ""
                ) ?? .monthly
                let customFrequencyMonths = accountDict["customFrequencyMonths"] as? Int ?? 1

                let categoriesArray = accountDict["categories"] as? [[String: Any]] ?? []
                let categories = categoriesArray.map { categoryDict in
                    let categoryName = categoryDict["name"] as? String ?? "Uncategorized"
                    let colorHex = categoryDict["color"] as? String
                    let icon = categoryDict["icon"] as? String
                    let sourcesArray = categoryDict["sources"] as? [[String: Any]] ?? []
                    let sources = sourcesArray.map { sourceDict in
                        let sourceName = sourceDict["name"] as? String ?? "Source"
                        let snapshotsArray = sourceDict["snapshots"] as? [[String: Any]] ?? []
                        let snapshots = snapshotsArray.compactMap { snapshotDict -> ImportedSnapshot? in
                            guard let dateString = snapshotDict["date"] as? String,
                                  let date = ISO8601DateFormatter().date(from: dateString),
                                  let value = snapshotDict["value"] as? Double else {
                                return nil
                            }

                            let contribution = (snapshotDict["contribution"] as? Double).map { Decimal($0) }
                            let notes = snapshotDict["notes"] as? String
                            return ImportedSnapshot(
                                date: date,
                                value: Decimal(value),
                                contribution: contribution,
                                notes: notes
                            )
                        }

                        return ImportedSource(name: sourceName, snapshots: snapshots)
                    }

                    return ImportedCategory(
                        name: categoryName,
                        colorHex: colorHex,
                        icon: icon,
                        sources: sources
                    )
                }

                return ImportedAccount(
                    name: name,
                    currency: currency,
                    inputMode: inputMode,
                    notificationFrequency: notificationFrequency,
                    customFrequencyMonths: customFrequencyMonths,
                    categories: categories
                )
            }
        }

        // Legacy JSON: categories only
        if let categoriesArray = json["categories"] as? [[String: Any]] {
            let categories = categoriesArray.map { categoryDict in
                let categoryName = categoryDict["name"] as? String ?? "Uncategorized"
                let colorHex = categoryDict["color"] as? String
                let icon = categoryDict["icon"] as? String
                let sourcesArray = categoryDict["sources"] as? [[String: Any]] ?? []
                let sources = sourcesArray.map { sourceDict in
                    let sourceName = sourceDict["name"] as? String ?? "Source"
                    let snapshotsArray = sourceDict["snapshots"] as? [[String: Any]] ?? []
                    let snapshots = snapshotsArray.compactMap { snapshotDict -> ImportedSnapshot? in
                        guard let dateString = snapshotDict["date"] as? String,
                              let date = ISO8601DateFormatter().date(from: dateString),
                              let value = snapshotDict["value"] as? Double else {
                            return nil
                        }

                        let contribution = (snapshotDict["contribution"] as? Double).map { Decimal($0) }
                        let notes = snapshotDict["notes"] as? String
                        return ImportedSnapshot(
                            date: date,
                            value: Decimal(value),
                            contribution: contribution,
                            notes: notes
                        )
                    }

                    return ImportedSource(name: sourceName, snapshots: snapshots)
                }

                return ImportedCategory(
                    name: categoryName,
                    colorHex: colorHex,
                    icon: icon,
                    sources: sources
                )
            }

            return [
                ImportedAccount(
                    name: "Personal",
                    currency: json["currency"] as? String,
                    inputMode: .simple,
                    notificationFrequency: .monthly,
                    customFrequencyMonths: 1,
                    categories: categories
                )
            ]
        }

        return []
    }

    // MARK: - Apply Import

    private func applyImport(
        _ accounts: [ImportedAccount],
        context: NSManagedObjectContext,
        snapshotProgress: ((Int) -> Void)? = nil
    ) -> ImportResult {
        let accountRepository = AccountRepository(context: context)
        let categoryRepository = CategoryRepository(context: context)
        let sourceRepository = InvestmentSourceRepository(context: context)
        let snapshotRepository = SnapshotRepository(context: context)

        var accountsCreated = 0
        var sourcesCreated = 0
        var snapshotsCreated = 0
        var errors: [String] = []

        var categoryLookup = buildCategoryLookup(from: categoryRepository.categories)
        let otherCategory = resolveExistingCategory(named: "Other", lookup: categoryLookup) ??
            categoryRepository.createCategory(
                name: "Other",
                colorHex: "#64748B",
                icon: "ellipsis.circle.fill"
            )
        categoryLookup[normalizedCategoryName(otherCategory.name)] = otherCategory

        var completionDatesByMonth: [String: Date] = [:]

        for importedAccount in accounts {
            let existingAccount = accountRepository.accounts.first(where: { $0.name == importedAccount.name })
            let account = existingAccount ?? accountRepository.createAccount(
                name: importedAccount.name,
                currency: importedAccount.currency,
                inputMode: importedAccount.inputMode,
                notificationFrequency: importedAccount.notificationFrequency,
                customFrequencyMonths: importedAccount.customFrequencyMonths
            )

            if existingAccount == nil {
                accountsCreated += 1
            }

            for importedCategory in importedAccount.categories {
                let existingCategory = resolveExistingCategory(
                    named: importedCategory.name,
                    lookup: categoryLookup
                )
                let shouldUseOther = existingCategory == nil &&
                    importedCategory.colorHex == nil &&
                    importedCategory.icon == nil
                let resolvedName = canonicalCategoryName(for: importedCategory.name) ?? importedCategory.name
                let category = existingCategory ?? (shouldUseOther
                    ? otherCategory
                    : categoryRepository.createCategory(
                        name: resolvedName,
                        colorHex: importedCategory.colorHex ?? "#3B82F6",
                        icon: importedCategory.icon ?? "chart.pie.fill"
                    ))
                categoryLookup[normalizedCategoryName(category.name)] = category

                for importedSource in importedCategory.sources {
                    let existingSource = sourceRepository.sources.first(where: {
                        $0.name == importedSource.name && $0.account?.id == account.id
                    })
                    let source = existingSource ?? sourceRepository.createSource(
                        name: importedSource.name,
                        category: category,
                        notificationFrequency: importedAccount.notificationFrequency,
                        customFrequencyMonths: importedAccount.customFrequencyMonths
                    )
                    source.account = account
                    if existingSource == nil {
                        sourcesCreated += 1
                    }

                    for snapshot in importedSource.snapshots {
                        snapshotRepository.createSnapshot(
                            for: source,
                            date: snapshot.date,
                            value: snapshot.value,
                            contribution: snapshot.contribution,
                            notes: snapshot.notes
                        )
                        snapshotsCreated += 1
                        snapshotProgress?(snapshotsCreated)

                        let monthKey = MonthlyCheckInStore.monthKey(for: snapshot.date)
                        if let existingDate = completionDatesByMonth[monthKey] {
                            if snapshot.date > existingDate {
                                completionDatesByMonth[monthKey] = snapshot.date
                            }
                        } else {
                            completionDatesByMonth[monthKey] = snapshot.date
                        }
                    }
                }
            }
        }

        if context.hasChanges {
            do {
                try context.save()
            } catch {
                errors.append("Failed to save imported data.")
            }
        }

        if !completionDatesByMonth.isEmpty {
            for (monthKey, completionDate) in completionDatesByMonth {
                let formatter = DateFormatter()
                formatter.dateFormat = "yyyy-MM"
                if let monthDate = formatter.date(from: monthKey) {
                    MonthlyCheckInStore.setCompletionDate(completionDate, for: monthDate)
                }
            }
        }

        return ImportResult(
            accountsCreated: accountsCreated,
            sourcesCreated: sourcesCreated,
            snapshotsCreated: snapshotsCreated,
            errors: errors
        )
    }

    private func resolveExistingCategory(
        named rawName: String,
        lookup: [String: Category]
    ) -> Category? {
        if let canonical = canonicalCategoryName(for: rawName) {
            let canonicalKey = normalizedCategoryName(canonical)
            if let match = lookup[canonicalKey] {
                return match
            }
        }
        return lookup[normalizedCategoryName(rawName)]
    }

    private func buildCategoryLookup(from categories: [Category]) -> [String: Category] {
        var lookup: [String: Category] = [:]
        for category in categories {
            lookup[normalizedCategoryName(category.name)] = category
        }
        return lookup
    }

    private func canonicalCategoryName(for rawName: String) -> String? {
        let normalized = normalizedCategoryName(rawName)
        for mapping in categoryAliasMappings {
            if mapping.aliases.contains(where: { normalizedCategoryName($0) == normalized }) {
                return mapping.canonical
            }
        }
        return nil
    }

    private func normalizedCategoryName(_ value: String) -> String {
        let trimmed = value.trimmingCharacters(in: .whitespacesAndNewlines)
        let normalized = trimmed.folding(
            options: [.diacriticInsensitive, .caseInsensitive],
            locale: .current
        )
        return normalized.replacingOccurrences(
            of: "\\s+",
            with: " ",
            options: .regularExpression
        )
    }

    private var categoryAliasMappings: [(canonical: String, aliases: [String])] {
        [
            (
                canonical: "Stocks",
                aliases: ["Stocks", "category_stocks", String(localized: "category_stocks"), "Acciones"]
            ),
            (
                canonical: "Bonds",
                aliases: ["Bonds", "category_bonds", String(localized: "category_bonds"), "Bonos"]
            ),
            (
                canonical: "Real Estate",
                aliases: ["Real Estate", "category_real_estate", String(localized: "category_real_estate"), "Inmobiliario"]
            ),
            (
                canonical: "Crypto",
                aliases: ["Crypto", "category_crypto", String(localized: "category_crypto"), "Cripto"]
            ),
            (
                canonical: "Cash",
                aliases: ["Cash", "category_cash", String(localized: "category_cash"), "Efectivo"]
            ),
            (
                canonical: "ETFs",
                aliases: ["ETFs", "category_etfs", String(localized: "category_etfs"), "ETF"]
            ),
            (
                canonical: "Retirement",
                aliases: ["Retirement", "category_retirement", String(localized: "category_retirement"), "Jubilación"]
            ),
            (
                canonical: "Other",
                aliases: [
                    "Other",
                    "category_other",
                    String(localized: "category_other"),
                    "Uncategorized",
                    "uncategorized",
                    String(localized: "uncategorized"),
                    "Otros",
                    "Sin categoría"
                ]
            )
        ]
    }

    // MARK: - CSV Helpers

    private func parseCSVRows(_ content: String) -> [[String]] {
        var rows: [[String]] = []
        var currentRow: [String] = []
        var currentField = ""
        var insideQuotes = false

        for char in content {
            if char == "\"" {
                insideQuotes.toggle()
                continue
            }

            if char == "," && !insideQuotes {
                currentRow.append(currentField)
                currentField = ""
                continue
            }

            if char == "\n" && !insideQuotes {
                currentRow.append(currentField)
                rows.append(currentRow.map { $0.trimmingCharacters(in: .whitespaces) })
                currentRow = []
                currentField = ""
                continue
            }

            currentField.append(char)
        }

        if !currentField.isEmpty || !currentRow.isEmpty {
            currentRow.append(currentField)
            rows.append(currentRow.map { $0.trimmingCharacters(in: .whitespaces) })
        }

        return rows
    }

    private func parseDate(_ value: String) -> Date? {
        let trimmed = value.trimmingCharacters(in: .whitespacesAndNewlines)
        if trimmed.isEmpty { return nil }

        if let iso = ISO8601DateFormatter().date(from: trimmed) {
            return iso
        }

        let formats = [
            "yyyy-MM-dd",
            "yyyy/MM/dd",
            "dd/MM/yyyy",
            "MM/dd/yyyy",
            "dd-MM-yyyy",
            "MM-dd-yyyy",
            "yyyy-MM-dd HH:mm",
            "yyyy-MM-dd HH:mm:ss",
            "yyyy/MM/dd HH:mm",
            "yyyy/MM/dd HH:mm:ss",
            "dd/MM/yyyy HH:mm",
            "dd/MM/yyyy HH:mm:ss",
            "MM/dd/yyyy HH:mm",
            "MM/dd/yyyy HH:mm:ss",
            "dd-MM-yyyy HH:mm",
            "dd-MM-yyyy HH:mm:ss",
            "MM-dd-yyyy HH:mm",
            "MM-dd-yyyy HH:mm:ss",
            "dd/MM/yyyy h:mm a",
            "dd/MM/yyyy h:mm:ss a",
            "MM/dd/yyyy h:mm a",
            "MM/dd/yyyy h:mm:ss a",
            "dd-MM-yyyy h:mm a",
            "dd-MM-yyyy h:mm:ss a",
            "MM-dd-yyyy h:mm a",
            "MM-dd-yyyy h:mm:ss a"
        ]

        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = .current

        for format in formats {
            formatter.dateFormat = format
            if let date = formatter.date(from: trimmed) {
                return date
            }
        }

        return nil
    }

    private func parseDecimal(_ value: String) -> Decimal? {
        let cleaned = value
            .replacingOccurrences(of: ",", with: ".")
            .trimmingCharacters(in: .whitespaces)
        guard !cleaned.isEmpty else { return nil }
        return Decimal(string: cleaned)
    }
}

private extension Array where Element == String {
    func safeValue(at index: Int) -> String? {
        guard index >= 0, index < count else { return nil }
        return self[index]
    }
}