import Foundation
import SwiftData

@Model
final class Habit {
    var uuid: UUID = UUID()
    var name: String
    var symbolName: String
    var colorHex: String
    var createdAt: Date
    /// Time of day for the daily reminder; nil means no reminder.
    var reminderTime: Date?

    @Relationship(deleteRule: .cascade, inverse: \HabitEntry.habit)
    var entries: [HabitEntry] = []

    init(
        name: String,
        symbolName: String = "star.fill",
        colorHex: String = "#34C759",
        createdAt: Date = .now,
        reminderTime: Date? = nil
    ) {
        self.name = name
        self.symbolName = symbolName
        self.colorHex = colorHex
        self.createdAt = createdAt
        self.reminderTime = reminderTime
    }
}

extension Habit {
    /// Whether this habit was checked off on the given day.
    func isCompleted(on day: Date, calendar: Calendar = .current) -> Bool {
        entries.contains { calendar.isDate($0.date, inSameDayAs: day) }
    }

    var isCompletedToday: Bool {
        isCompleted(on: .now)
    }

    /// Number of consecutive days (counting back from today) the habit was done.
    var currentStreak: Int {
        let calendar = Calendar.current
        let doneDays = Set(entries.map { calendar.startOfDay(for: $0.date) })
        var day = calendar.startOfDay(for: .now)

        // A streak stays alive if today isn't done yet but yesterday was.
        if !doneDays.contains(day) {
            day = calendar.date(byAdding: .day, value: -1, to: day)!
        }

        var streak = 0
        while doneDays.contains(day) {
            streak += 1
            day = calendar.date(byAdding: .day, value: -1, to: day)!
        }
        return streak
    }

    /// Longest run of consecutive completed days, ever.
    var longestStreak: Int {
        let calendar = Calendar.current
        let days = Set(entries.map { calendar.startOfDay(for: $0.date) }).sorted()
        guard !days.isEmpty else { return 0 }

        var longest = 1
        var run = 1
        for i in 1..<days.count {
            let expectedPrev = calendar.date(byAdding: .day, value: -1, to: days[i])!
            if calendar.isDate(expectedPrev, inSameDayAs: days[i - 1]) {
                run += 1
            } else {
                run = 1
            }
            longest = max(longest, run)
        }
        return longest
    }

    var totalCompletions: Int {
        entries.count
    }
}