import XCTest
@testable import KisaniCal

final class StreakLogicTests: XCTestCase {

    private let cal = Calendar.current
    private let fmt: DateFormatter = {
        let f = DateFormatter(); f.dateFormat = "yyyy-MM-dd"; return f
    }()

    private func day(_ offset: Int, from ref: Date) -> String {
        fmt.string(from: cal.date(byAdding: .day, value: offset, to: ref)!)
    }

    // MARK: - Workout weekly-goal streak

    /// A skipped day within the weekly goal must NOT reset the streak.
    /// Scenario from the field: 6-day schedule, goal 5, Thursday skipped,
    /// 5 workouts done that week → streak counts all 5, not 1.
    func testSkippedDayWithinGoalKeepsStreak() {
        let today = cal.startOfDay(for: Date())
        // Build "this week": every day up to today except one gap two days ago.
        var dates = Set<String>()
        guard let week = cal.dateInterval(of: .weekOfYear, for: today) else { return XCTFail() }
        var d = week.start, added = 0
        while d <= today {
            let key = fmt.string(from: d)
            if key != day(-2, from: today) { dates.insert(key); added += 1 }
            d = cal.date(byAdding: .day, value: 1, to: d)!
        }
        guard added >= 2 else { return } // too early in the week to be meaningful

        let streak = WorkoutViewModel.weeklyGoalStreak(
            workoutDates: dates, scheduledDayCount: 6, goal: 5,
            today: today, calendar: cal)
        XCTAssertEqual(streak, added, "days this week minus the gap should all count")
        XCTAssertGreaterThan(streak, 1, "a mid-week skip must not collapse the streak to 1")
    }

    /// Rest days (no workout, none scheduled) never break the chain:
    /// a full previous week meeting the goal chains into this week.
    func testRestDaysDoNotBreakChainAcrossWeeks() {
        let today = cal.startOfDay(for: Date())
        guard let thisWeek = cal.dateInterval(of: .weekOfYear, for: today),
              let prevRef = cal.date(byAdding: .weekOfYear, value: -1, to: today),
              let prevWeek = cal.dateInterval(of: .weekOfYear, for: prevRef)
        else { return XCTFail() }

        var dates = Set<String>()
        // Previous week: 5 workout days (goal met), 2 rest days.
        var d = prevWeek.start
        for i in 0..<7 {
            if i < 5 { dates.insert(fmt.string(from: d)) }
            d = cal.date(byAdding: .day, value: 1, to: d)!
        }
        // This week: workout on the first day only.
        dates.insert(fmt.string(from: thisWeek.start))
        guard thisWeek.start <= today else { return XCTFail() }

        let streak = WorkoutViewModel.weeklyGoalStreak(
            workoutDates: dates, scheduledDayCount: 5, goal: 5,
            today: today, calendar: cal)
        XCTAssertEqual(streak, 6, "5 from the kept previous week + 1 this week")
    }

    /// A previous week below the goal ends the chain — current week still counts.
    func testFailedWeekBreaksChain() {
        let today = cal.startOfDay(for: Date())
        guard let thisWeek = cal.dateInterval(of: .weekOfYear, for: today),
              let prevRef = cal.date(byAdding: .weekOfYear, value: -1, to: today),
              let prevWeek = cal.dateInterval(of: .weekOfYear, for: prevRef)
        else { return XCTFail() }

        var dates = Set<String>()
        dates.insert(fmt.string(from: prevWeek.start))      // only 1 day done last week
        dates.insert(fmt.string(from: thisWeek.start))      // 1 day this week

        let streak = WorkoutViewModel.weeklyGoalStreak(
            workoutDates: dates, scheduledDayCount: 5, goal: 5,
            today: today, calendar: cal)
        XCTAssertEqual(streak, 1, "chain stops at the failed week; this week still counts")
    }

    /// Goal is capped by the schedule: a 3-day program with goal 5 keeps the
    /// chain at 3 workouts/week.
    func testGoalCappedByScheduledDays() {
        let today = cal.startOfDay(for: Date())
        guard let prevRef = cal.date(byAdding: .weekOfYear, value: -1, to: today),
              let prevWeek = cal.dateInterval(of: .weekOfYear, for: prevRef)
        else { return XCTFail() }

        var dates = Set<String>()
        var d = prevWeek.start
        for i in 0..<7 {
            if i < 3 { dates.insert(fmt.string(from: d)) }  // 3 of 3 scheduled
            d = cal.date(byAdding: .day, value: 1, to: d)!
        }

        let streak = WorkoutViewModel.weeklyGoalStreak(
            workoutDates: dates, scheduledDayCount: 3, goal: 5,
            today: today, calendar: cal)
        XCTAssertEqual(streak, 3, "3-day schedule meets its capped goal and chains")
    }

    func testEmptyDataIsZero() {
        let streak = WorkoutViewModel.weeklyGoalStreak(
            workoutDates: [], scheduledDayCount: 6, goal: 5,
            today: Date(), calendar: cal)
        XCTAssertEqual(streak, 0)
    }

    // MARK: - Task completion counting (recurring occurrences)

    private func makeRecurring(title: String, completedOn keys: [String]) -> TaskItem {
        var t = TaskItem(title: title, dueDate: cal.date(byAdding: .day, value: -30, to: Date()))
        t.isRecurring = true
        t.recurrenceLabel = "Daily"
        t.completedOccurrences = keys
        return t
    }

    /// Recurring completions must count toward per-day stats even though the
    /// stored task's isComplete/completedAt stay untouched.
    func testRecurringOccurrencesCountedPerDay() {
        let today = cal.startOfDay(for: Date())
        let todayKey = fmt.string(from: today)
        let recurring = makeRecurring(title: "Morning routine", completedOn: [todayKey])

        var oneOff = TaskItem(title: "Buy milk")
        oneOff.isComplete = true
        oneOff.completedAt = today.addingTimeInterval(3600)

        let n = TaskViewModel.completionCount(in: [recurring, oneOff], on: today, calendar: cal)
        XCTAssertEqual(n, 2, "one recurring occurrence + one one-off completion")
    }

    func testRecurringNotCountedOnOtherDays() {
        let today = cal.startOfDay(for: Date())
        let yesterdayKey = day(-1, from: today)
        let recurring = makeRecurring(title: "Morning routine", completedOn: [yesterdayKey])

        XCTAssertEqual(TaskViewModel.completionCount(in: [recurring], on: today, calendar: cal), 0)
        let yesterday = cal.date(byAdding: .day, value: -1, to: today)!
        XCTAssertEqual(TaskViewModel.completionCount(in: [recurring], on: yesterday, calendar: cal), 1)
    }

    func testIncompleteOneOffNotCounted() {
        let today = cal.startOfDay(for: Date())
        let t = TaskItem(title: "Open task")
        XCTAssertEqual(TaskViewModel.completionCount(in: [t], on: today, calendar: cal), 0)
    }
}