import Foundation
import SwiftData

@MainActor
@Observable
final class TrackingEngine {
    private(set) var activeSessions: [UUID: Date] = [:]
    private(set) var elapsedTimes: [UUID: TimeInterval] = [:]

    private var tickTask: Task<Void, Never>?

    init() {
        tickTask = Task {
            while !Task.isCancelled {
                try? await Task.sleep(for: .seconds(1))
                self.tick()
            }
        }
    }

    private func tick() {
        let now = Date.now
        for (id, start) in activeSessions {
            elapsedTimes[id] = now.timeIntervalSince(start)
        }
    }

    func isRunning(_ task: TaskItem) -> Bool {
        activeSessions[task.id] != nil
    }

    func elapsed(for task: TaskItem) -> TimeInterval {
        elapsedTimes[task.id] ?? 0
    }

    func startTimer(for task: TaskItem, context: ModelContext) {
        guard !isRunning(task) else { return }
        let now = Date.now
        let record = TrackingRecord(task: task, recordType: .timerSession, startTime: now)
        context.insert(record)
        task.trackingRecords.append(record)
        activeSessions[task.id] = now
        elapsedTimes[task.id] = 0
    }

    func stopTimer(for task: TaskItem, context: ModelContext) {
        guard let startTime = activeSessions[task.id] else { return }
        let now = Date.now
        if let record = task.trackingRecords.first(where: { $0.isRunning }) {
            record.endTime = now
            record.duration = now.timeIntervalSince(startTime)
        }
        activeSessions.removeValue(forKey: task.id)
        elapsedTimes.removeValue(forKey: task.id)
    }

    func incrementCounter(for task: TaskItem, context: ModelContext) {
        let record = TrackingRecord(task: task, recordType: .countLog, timestamp: .now)
        context.insert(record)
        task.trackingRecords.append(record)
    }
}