//
//  RemindersGroceryStore.swift
//  Nextcloud Cookbook iOS Client
//

import EventKit
import Foundation
import OSLog

/// Maps a reminder's calendarItemIdentifier to its recipe context.
struct ReminderMapping: Codable {
    let reminderIdentifier: String
    let recipeId: String
    let recipeName: String
    let itemName: String
}

/// Persisted mapping file: keyed by recipeId, each holding an array of reminder mappings.
struct ReminderMappingStore: Codable {
    var recipes: [String: RecipeMappingEntry] = [:]
}

struct RecipeMappingEntry: Codable {
    let recipeName: String
    var mappings: [ReminderMapping]
}

@MainActor
class RemindersGroceryStore {
    private let eventStore = EKEventStore()
    private(set) var groceryDict: [String: GroceryRecipe] = [:]
    var onDataChanged: (() -> Void)?

    private let dataStore = DataStore()
    private let mappingPath = "reminder_mappings.data"
    private var mappingStore = ReminderMappingStore()

    /// When true, the next `EKEventStoreChanged` notification is skipped because
    /// it was triggered by our own save. Prevents a race where `load()` reads stale
    /// mapping data from disk before `saveMappings()` finishes writing.
    private var ignoreNextExternalChange = false

    init() {
        NotificationCenter.default.addObserver(
            forName: .EKEventStoreChanged,
            object: eventStore,
            queue: .main
        ) { [weak self] _ in
            Task { @MainActor in
                guard let self else { return }
                if self.ignoreNextExternalChange {
                    self.ignoreNextExternalChange = false
                    return
                }
                await self.load()
                self.onDataChanged?()
            }
        }
    }

    deinit {
        NotificationCenter.default.removeObserver(self, name: .EKEventStoreChanged, object: eventStore)
    }

    // MARK: - Permission

    func checkPermissionStatus() -> EKAuthorizationStatus {
        EKEventStore.authorizationStatus(for: .reminder)
    }

    func requestAccess() async -> Bool {
        do {
            return try await eventStore.requestFullAccessToReminders()
        } catch {
            Logger.view.error("Failed to request Reminders access: \(error.localizedDescription)")
            return false
        }
    }

    // MARK: - Lists

    func availableReminderLists() -> [EKCalendar] {
        eventStore.calendars(for: .reminder)
    }

    private func targetCalendar() -> EKCalendar? {
        let identifier = UserSettings.shared.remindersListIdentifier
        if !identifier.isEmpty,
           let calendar = eventStore.calendar(withIdentifier: identifier) {
            return calendar
        }
        return eventStore.defaultCalendarForNewReminders()
    }

    // MARK: - Fetch Helper

    private nonisolated func fetchReminders(matching predicate: NSPredicate, in store: EKEventStore) async -> [EKReminder] {
        await withCheckedContinuation { continuation in
            store.fetchReminders(matching: predicate) { reminders in
                continuation.resume(returning: reminders ?? [])
            }
        }
    }

    // MARK: - CRUD

    func addItem(_ itemName: String, toRecipe recipeId: String, recipeName: String? = nil) {
        guard let calendar = targetCalendar() else {
            Logger.view.error("No target Reminders calendar available")
            return
        }
        let reminder = EKReminder(eventStore: eventStore)
        reminder.title = itemName
        reminder.calendar = calendar
        do {
            ignoreNextExternalChange = true
            try eventStore.save(reminder, commit: true)
            let name = recipeName ?? "-"
            addMapping(reminderIdentifier: reminder.calendarItemIdentifier, recipeId: recipeId, recipeName: name, itemName: itemName)
            appendToCache(itemName: itemName, recipeId: recipeId, recipeName: name)
        } catch {
            ignoreNextExternalChange = false
            Logger.view.error("Failed to save reminder: \(error.localizedDescription)")
        }
    }

    func addItems(_ items: [String], toRecipe recipeId: String, recipeName: String? = nil) {
        guard let calendar = targetCalendar() else {
            Logger.view.error("No target Reminders calendar available")
            return
        }
        let name = recipeName ?? "-"
        for item in items {
            let reminder = EKReminder(eventStore: eventStore)
            reminder.title = item
            reminder.calendar = calendar
            do {
                try eventStore.save(reminder, commit: false)
                addMapping(reminderIdentifier: reminder.calendarItemIdentifier, recipeId: recipeId, recipeName: name, itemName: item)
                appendToCache(itemName: item, recipeId: recipeId, recipeName: name)
            } catch {
                Logger.view.error("Failed to save reminder: \(error.localizedDescription)")
            }
        }
        do {
            ignoreNextExternalChange = true
            try eventStore.commit()
        } catch {
            ignoreNextExternalChange = false
            Logger.view.error("Failed to commit reminders: \(error.localizedDescription)")
        }
        saveMappings()
    }

    func deleteItem(_ itemName: String, fromRecipe recipeId: String) {
        // Find the reminder identifier from our mapping
        guard let entry = mappingStore.recipes[recipeId],
              let mapping = entry.mappings.first(where: { $0.itemName == itemName }) else { return }
        let identifier = mapping.reminderIdentifier

        // Find and remove the actual reminder
        guard let calendar = targetCalendar() else { return }
        let predicate = eventStore.predicateForReminders(in: [calendar])
        let store = eventStore
        Task {
            let reminders = await fetchReminders(matching: predicate, in: store)
            for reminder in reminders where reminder.calendarItemIdentifier == identifier {
                do {
                    self.ignoreNextExternalChange = true
                    try self.eventStore.remove(reminder, commit: true)
                } catch {
                    self.ignoreNextExternalChange = false
                    Logger.view.error("Failed to remove reminder: \(error.localizedDescription)")
                }
                break
            }
            self.removeMapping(reminderIdentifier: identifier, recipeId: recipeId)
            self.removeFromCache(itemName: itemName, recipeId: recipeId)
        }
    }

    func deleteGroceryRecipe(_ recipeId: String) {
        guard let entry = mappingStore.recipes[recipeId] else { return }
        let identifiers = Set(entry.mappings.map(\.reminderIdentifier))

        guard let calendar = targetCalendar() else { return }
        let predicate = eventStore.predicateForReminders(in: [calendar])
        let store = eventStore
        Task {
            let reminders = await fetchReminders(matching: predicate, in: store)
            for reminder in reminders where identifiers.contains(reminder.calendarItemIdentifier) {
                do {
                    try self.eventStore.remove(reminder, commit: false)
                } catch {
                    Logger.view.error("Failed to remove reminder: \(error.localizedDescription)")
                }
            }
            do {
                self.ignoreNextExternalChange = true
                try self.eventStore.commit()
            } catch {
                self.ignoreNextExternalChange = false
                Logger.view.error("Failed to commit reminder removal: \(error.localizedDescription)")
            }
            self.mappingStore.recipes.removeValue(forKey: recipeId)
            self.saveMappings()
            self.groceryDict.removeValue(forKey: recipeId)
            self.onDataChanged?()
        }
    }

    func deleteAll() {
        let allIdentifiers = Set(mappingStore.recipes.values.flatMap { $0.mappings.map(\.reminderIdentifier) })
        guard !allIdentifiers.isEmpty else { return }

        guard let calendar = targetCalendar() else { return }
        let predicate = eventStore.predicateForReminders(in: [calendar])
        let store = eventStore
        Task {
            let reminders = await fetchReminders(matching: predicate, in: store)
            for reminder in reminders where allIdentifiers.contains(reminder.calendarItemIdentifier) {
                do {
                    try self.eventStore.remove(reminder, commit: false)
                } catch {
                    Logger.view.error("Failed to remove reminder: \(error.localizedDescription)")
                }
            }
            do {
                self.ignoreNextExternalChange = true
                try self.eventStore.commit()
            } catch {
                self.ignoreNextExternalChange = false
                Logger.view.error("Failed to commit reminder removal: \(error.localizedDescription)")
            }
            self.mappingStore.recipes = [:]
            self.saveMappings()
            self.groceryDict = [:]
            self.onDataChanged?()
        }
    }

    func containsItem(at recipeId: String, item: String) -> Bool {
        guard let recipe = groceryDict[recipeId] else { return false }
        return recipe.items.contains(where: { $0.name == item })
    }

    func containsRecipe(_ recipeId: String) -> Bool {
        groceryDict[recipeId] != nil
    }

    // MARK: - Load / Sync

    func load() async {
        // Load the local mapping first
        if let stored: ReminderMappingStore = try? await dataStore.load(fromPath: mappingPath) {
            mappingStore = stored
        }

        guard checkPermissionStatus() == .fullAccess else { return }
        guard let calendar = targetCalendar() else { return }
        let predicate = eventStore.predicateForReminders(in: [calendar])
        let store = eventStore
        let reminders = await fetchReminders(matching: predicate, in: store)

        // Build a set of live reminder identifiers for cleanup
        let liveIdentifiers = Set(reminders.map(\.calendarItemIdentifier))

        // Prune mappings for reminders that no longer exist (deleted externally)
        var pruned = false
        for (recipeId, entry) in mappingStore.recipes {
            let before = entry.mappings.count
            let filtered = entry.mappings.filter { liveIdentifiers.contains($0.reminderIdentifier) }
            if filtered.isEmpty {
                mappingStore.recipes.removeValue(forKey: recipeId)
                pruned = true
            } else if filtered.count != before {
                mappingStore.recipes[recipeId] = RecipeMappingEntry(recipeName: entry.recipeName, mappings: filtered)
                pruned = true
            }
        }
        if pruned {
            saveMappings()
        }

        // Rebuild groceryDict from mappings (source of truth for grouping)
        var dict: [String: GroceryRecipe] = [:]
        for (recipeId, entry) in mappingStore.recipes {
            let items = entry.mappings.map { GroceryRecipeItem($0.itemName) }
            dict[recipeId] = GroceryRecipe(name: entry.recipeName, items: items)
        }
        groceryDict = dict
    }

    // MARK: - Mapping Persistence

    private func addMapping(reminderIdentifier: String, recipeId: String, recipeName: String, itemName: String) {
        let mapping = ReminderMapping(
            reminderIdentifier: reminderIdentifier,
            recipeId: recipeId,
            recipeName: recipeName,
            itemName: itemName
        )
        if mappingStore.recipes[recipeId] != nil {
            mappingStore.recipes[recipeId]?.mappings.append(mapping)
        } else {
            mappingStore.recipes[recipeId] = RecipeMappingEntry(recipeName: recipeName, mappings: [mapping])
        }
        saveMappings()
    }

    private func removeMapping(reminderIdentifier: String, recipeId: String) {
        guard var entry = mappingStore.recipes[recipeId] else { return }
        entry.mappings.removeAll { $0.reminderIdentifier == reminderIdentifier }
        if entry.mappings.isEmpty {
            mappingStore.recipes.removeValue(forKey: recipeId)
        } else {
            mappingStore.recipes[recipeId] = entry
        }
        saveMappings()
    }

    private func saveMappings() {
        Task {
            await dataStore.save(data: mappingStore, toPath: mappingPath)
        }
    }

    // MARK: - Cache Helpers

    private func appendToCache(itemName: String, recipeId: String, recipeName: String) {
        if groceryDict[recipeId] != nil {
            groceryDict[recipeId]?.items.append(GroceryRecipeItem(itemName))
        } else {
            groceryDict[recipeId] = GroceryRecipe(name: recipeName, item: GroceryRecipeItem(itemName))
        }
    }

    private func removeFromCache(itemName: String, recipeId: String) {
        guard let itemIndex = groceryDict[recipeId]?.items.firstIndex(where: { $0.name == itemName }) else { return }
        groceryDict[recipeId]?.items.remove(at: itemIndex)
        if groceryDict[recipeId]?.items.isEmpty == true {
            groceryDict.removeValue(forKey: recipeId)
        }
    }
}