import XCTest
@testable import KisaniCal

/// Verifies recurring-task occurrence expansion maps to the correct real calendar
/// days (the calendar's event-date mapping for tasks). Uses Calendar.current — the
/// same calendar the production code uses — so assertions hold in any timezone.
@MainActor
final class RecurrenceTests: XCTestCase {

    private let cal = Calendar.current

    private func day(_ y: Int, _ m: Int, _ d: Int, h: Int = 0, min: Int = 0) -> Date {
        cal.date(from: DateComponents(year: y, month: m, day: d, hour: h, minute: min))!
    }

    private func vm(with tasks: [TaskItem]) -> TaskViewModel {
        let v = TaskViewModel()
        v.tasks = tasks
        return v
    }

    private func task(_ label: String, start: Date, hasTime: Bool = false, end: Date? = nil) -> TaskItem {
        var t = TaskItem(title: "T-\(label)", dueDate: start)
        t.isRecurring = true
        t.recurrenceLabel = label
        t.hasTime = hasTime
        t.recurrenceEnd = end
        return t
    }

    private func hasOccurrence(_ v: TaskViewModel, _ id: UUID, on date: Date) -> Bool {
        v.occurrences(on: date).contains { $0.id == id }
    }

    func testDailyExpandsEveryDayFromStart() {
        let t = task("Daily", start: day(2026, 6, 1))
        let v = vm(with: [t])
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 5, 31)), "no occurrence before start")
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 1)))
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 24)))
    }

    func testWeeklyHitsEverySevenDaysOnly() {
        let t = task("Weekly", start: day(2026, 6, 1)) // Monday
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 8)))
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 22)))
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 9)), "off-cadence day must not match")
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 24)))
    }

    func testEveryWeekdaySkipsWeekend() {
        let t = task("Every Weekday", start: day(2026, 6, 1))
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 24)), "Wed is a weekday")
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 27)), "Sat excluded")
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 28)), "Sun excluded")
    }

    func testMonthlyMatchesDayOfMonth() {
        let t = task("Monthly", start: day(2026, 1, 15))
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 15)))
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 16)))
    }

    func testYearlyMatchesMonthAndDay() {
        let t = task("Yearly", start: day(2025, 6, 24))
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 24)))
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 23)))
    }

    func testRecurrenceEndStopsExpansion() {
        let t = task("Daily", start: day(2026, 6, 1), end: day(2026, 6, 10))
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 10)), "inclusive of end day")
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 11)), "past repeat-until")
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 24)))
    }

    func testOccurrenceCopyPreservesTimeOnTargetLocalDay() {
        let t = task("Daily", start: day(2026, 6, 1, h: 9, min: 30), hasTime: true)
        let v = vm(with: [t])
        let occ = v.occurrences(on: day(2026, 6, 24)).first { $0.id == t.id }
        XCTAssertNotNil(occ)
        XCTAssertTrue(cal.isDate(occ!.dueDate!, inSameDayAs: day(2026, 6, 24)), "mapped to June 24")
        XCTAssertEqual(cal.component(.hour, from: occ!.dueDate!), 9)
        XCTAssertEqual(cal.component(.minute, from: occ!.dueDate!), 30)
    }

    func testNonRecurringTaskAppearsOnlyOnItsDay() {
        var t = TaskItem(title: "Dinner with Jay", dueDate: day(2026, 6, 24))
        t.isRecurring = false
        let v = vm(with: [t])
        XCTAssertTrue(hasOccurrence(v, t.id, on: day(2026, 6, 24)))
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 23)))
        XCTAssertFalse(hasOccurrence(v, t.id, on: day(2026, 6, 25)))
    }
}