import Foundation
import Observation
import SwiftData

@MainActor
@Observable
final class DashboardViewModel {
    private(set) var dailyGoalProgress: [GoalProgress] = []
    private(set) var remainingTasks: [TaskItem] = []
    private(set) var completedTaskCount: Int = 0
    private(set) var totalTaskCount: Int = 0

    private var context: ModelContext?

    var overallProgress: Double {
        if !dailyGoalProgress.isEmpty {
            let sum = dailyGoalProgress.reduce(0.0) { $0 + $1.ratio }
            return sum / Double(dailyGoalProgress.count)
        }
        guard totalTaskCount > 0 else { return 0 }
        return Double(completedTaskCount) / Double(totalTaskCount)
    }

    var topGoalProgress: [GoalProgress] {
        Array(dailyGoalProgress.sorted { $0.ratio < $1.ratio }.prefix(3))
    }

    func setup(context: ModelContext) {
        self.context = context
        refresh()
    }

    func refresh() {
        guard let context else { return }

        let goalDescriptor = FetchDescriptor<Goal>()
        let goals = (try? context.fetch(goalDescriptor)) ?? []
        let dailyGoals = goals.filter { $0.frequency == .daily }
        dailyGoalProgress = dailyGoals.map { goal in
            let current = todayValue(for: goal)
            return GoalProgress(goal: goal, current: current, target: goal.conditions)
        }

        let taskDescriptor = FetchDescriptor<TaskItem>(sortBy: [SortDescriptor(\.name)])
        let tasks = (try? context.fetch(taskDescriptor)) ?? []
        totalTaskCount = tasks.count
        remainingTasks = tasks.filter { !isCompletedToday($0) }
        completedTaskCount = totalTaskCount - remainingTasks.count
    }

    func addCount(to task: TaskItem) {
        guard let context else { return }
        let log = TaskLog(date: .now, duration: 0, count: 1)
        log.task = task
        context.insert(log)
        try? context.save()
        refresh()
    }

    private func isCompletedToday(_ task: TaskItem) -> Bool {
        let todayLogs = task.logs.filter { Calendar.current.isDateInToday($0.date) }
        switch task.type {
        case .count:
            return todayLogs.reduce(0) { $0 + $1.count } > 0
        case .time:
            return !todayLogs.isEmpty
        }
    }

    private func todayValue(for goal: Goal) -> Double {
        let logs: [TaskLog]
        if let task = goal.task {
            logs = task.logs
        } else if let category = goal.category {
            logs = category.tasks.flatMap { $0.logs }
        } else {
            logs = []
        }
        let todayLogs = logs.filter { Calendar.current.isDateInToday($0.date) }
        return goal.targetType == "count"
            ? Double(todayLogs.reduce(0) { $0 + $1.count })
            : todayLogs.reduce(0.0) { $0 + $1.duration }
    }
}