//
//  MealPlanManager.swift
//  Nextcloud Cookbook iOS Client
//

import Foundation
import OSLog

@MainActor
class MealPlanManager: ObservableObject {
    @Published var entriesByDate: [String: [MealPlanEntry]] = [:]

    private var assignmentsByRecipe: [String: MealPlanAssignment] = [:]
    private var recipeNames: [String: String] = [:]
    private let dataStore = DataStore()
    var syncManager: MealPlanSyncManager?

    private static let persistencePath = "meal_plan.data"

    // MARK: - Persistence

    struct PersistenceData: Codable {
        var assignmentsByRecipe: [String: MealPlanAssignment]
        var recipeNames: [String: String]
    }

    func load() async {
        do {
            guard let data: PersistenceData = try await dataStore.load(fromPath: Self.persistencePath) else { return }
            assignmentsByRecipe = data.assignmentsByRecipe
            recipeNames = data.recipeNames
            pruneOldEntries()
            rebuildEntries()
        } catch {
            Logger.data.error("Unable to load meal plan data")
        }
    }

    func save() {
        pruneOldEntries()
        let data = PersistenceData(assignmentsByRecipe: assignmentsByRecipe, recipeNames: recipeNames)
        Task {
            await dataStore.save(data: data, toPath: Self.persistencePath)
        }
    }

    func configureSyncManager(appState: AppState) {
        syncManager = MealPlanSyncManager(appState: appState, mealPlanManager: self)
    }

    // MARK: - CRUD

    func assignRecipe(recipeId: String, recipeName: String, toDates dates: [Date]) {
        recipeNames[recipeId] = recipeName
        var assignment = assignmentsByRecipe[recipeId] ?? MealPlanAssignment()

        for date in dates {
            let dayStr = MealPlanDate.dayString(from: date)
            assignment.dates[dayStr] = MealPlanDateEntry(status: .assigned)
        }
        assignment.lastModified = MealPlanDate.now()
        assignmentsByRecipe[recipeId] = assignment

        rebuildEntries()
        save()
        syncManager?.scheduleSync(forRecipeId: recipeId)
    }

    func removeRecipe(recipeId: String, fromDate dateString: String) {
        guard var assignment = assignmentsByRecipe[recipeId] else { return }

        assignment.dates[dateString] = MealPlanDateEntry(status: .removed)
        assignment.lastModified = MealPlanDate.now()
        assignmentsByRecipe[recipeId] = assignment

        rebuildEntries()
        save()
        syncManager?.scheduleSync(forRecipeId: recipeId)
    }

    func removeAllAssignments(forRecipeId recipeId: String) {
        guard var assignment = assignmentsByRecipe[recipeId] else { return }

        let now = MealPlanDate.now()
        for key in assignment.dates.keys {
            assignment.dates[key] = MealPlanDateEntry(status: .removed, modifiedAt: now)
        }
        assignment.lastModified = now
        assignmentsByRecipe[recipeId] = assignment

        rebuildEntries()
        save()
        syncManager?.scheduleSync(forRecipeId: recipeId)
    }

    // MARK: - Queries

    func entries(for date: Date) -> [MealPlanEntry] {
        let dayStr = MealPlanDate.dayString(from: date)
        return entriesByDate[dayStr] ?? []
    }

    func isRecipeAssigned(_ recipeId: String, on date: Date) -> Bool {
        let dayStr = MealPlanDate.dayString(from: date)
        guard let assignment = assignmentsByRecipe[recipeId],
              let entry = assignment.dates[dayStr] else { return false }
        return entry.status == .assigned
    }

    func assignedDates(forRecipeId recipeId: String) -> [String] {
        guard let assignment = assignmentsByRecipe[recipeId] else { return [] }
        return assignment.dates.compactMap { key, entry in
            entry.status == .assigned ? key : nil
        }
    }

    func assignment(forRecipeId recipeId: String) -> MealPlanAssignment? {
        assignmentsByRecipe[recipeId]
    }

    // MARK: - Reconciliation (Pull)

    func reconcileFromServer(serverAssignment: MealPlanAssignment?, recipeId: String, recipeName: String) {
        guard let serverAssignment, !serverAssignment.dates.isEmpty else { return }

        recipeNames[recipeId] = recipeName
        var local = assignmentsByRecipe[recipeId] ?? MealPlanAssignment()

        for (dayStr, serverEntry) in serverAssignment.dates {
            if let localEntry = local.dates[dayStr] {
                let localDate = MealPlanDate.date(from: localEntry.modifiedAt) ?? .distantPast
                let serverDate = MealPlanDate.date(from: serverEntry.modifiedAt) ?? .distantPast
                if serverDate > localDate {
                    local.dates[dayStr] = serverEntry
                }
            } else {
                local.dates[dayStr] = serverEntry
            }
        }

        local.lastModified = MealPlanDate.now()
        assignmentsByRecipe[recipeId] = local

        rebuildEntries()
        save()
    }

    // MARK: - Internal

    private func pruneOldEntries() {
        let cutoff = Calendar.current.date(byAdding: .day, value: -30, to: Calendar.current.startOfDay(for: Date()))!
        var emptyRecipeIds: [String] = []

        for (recipeId, var assignment) in assignmentsByRecipe {
            assignment.dates = assignment.dates.filter { dayStr, _ in
                guard let date = MealPlanDate.dateFromDay(dayStr) else { return true }
                return date >= cutoff
            }
            if assignment.dates.isEmpty {
                emptyRecipeIds.append(recipeId)
            } else {
                assignmentsByRecipe[recipeId] = assignment
            }
        }

        for recipeId in emptyRecipeIds {
            assignmentsByRecipe.removeValue(forKey: recipeId)
            recipeNames.removeValue(forKey: recipeId)
        }
    }

    private func rebuildEntries() {
        var newEntries: [String: [MealPlanEntry]] = [:]

        for (recipeId, assignment) in assignmentsByRecipe {
            let name = recipeNames[recipeId] ?? "Recipe \(recipeId)"
            for (dayStr, entry) in assignment.dates where entry.status == .assigned {
                guard let date = MealPlanDate.dateFromDay(dayStr) else { continue }
                let mealEntry = MealPlanEntry(
                    recipeId: recipeId,
                    recipeName: name,
                    date: date,
                    dateString: dayStr,
                    mealType: entry.mealType
                )
                newEntries[dayStr, default: []].append(mealEntry)
            }
        }

        // Sort entries within each day by recipe name
        for key in newEntries.keys {
            newEntries[key]?.sort(by: { $0.recipeName < $1.recipeName })
        }

        entriesByDate = newEntries
    }
}