import Foundation
import Testing

@testable import Todos

@Suite("TaskGroupListView view model tests")
struct TaskGroupListViewModelTests {

    // MARK: Properties

    private let calendar: Calendar = .current

    // MARK: Computed tests

    @Test("groups returns cases in predetermined order")
    func groups() {
        // GIVEN
        let viewModel = TaskGroupListView.ViewModel()

        // WHEN
        let groups = viewModel.groups

        // THEN
        #expect(groups.count == 4)
        #expect(groups[0] == .today)
        #expect(groups[1] == .upcoming)
        #expect(groups[2] == .overdue)
        #expect(groups[3] == .completed)
    }

    // MARK: Functions tests

    @Test(
        "count returns zero when empty data",
        arguments: TodoGroup.allCases
    )
    func countWhenEmptyData(for group: TodoGroup) throws {
        // GIVEN
        let viewModel = TaskGroupListView.ViewModel()

        // WHEN
        let count = viewModel.count(emptyTasks, for: group)

        // THEN
        #expect(count == 0)
    }

    @Test(
        "count returns correct count when filled data",
        arguments: TodoGroup.allCases
    )
    func countWhenFilledData(for group: TodoGroup) throws {
        // GIVEN
        let viewModel = TaskGroupListView.ViewModel()

        // WHEN
        let count = viewModel.count(sampleTasks, for: group)

        // THEN
        #expect(count == 2)
    }

}

// MARK: - Helpers

private extension TaskGroupListViewModelTests {

    // MARK: Computed
    
    var emptyTasks: [Todo] { [] }

    var sampleTasks: [Todo] {
        let today: Date = .now
        let tomorrow = calendar.date(byAdding: .day, value: 1, to: today) ?? today
        let yesterday = calendar.date(byAdding: .day, value: -1, to: today) ?? today
        let nextWeek = calendar.date(byAdding: .day, value: 7, to: today) ?? today
        let lastWeek = calendar.date(byAdding: .day, value: -7, to: today) ?? today

        return [
            Todo(title: "Today task #1", due: today),
            Todo(title: "Today task #2", due: today),
            Todo(title: "Tomorrow task #1", due: tomorrow),
            Todo(title: "Next week task #1", due: nextWeek),
            Todo(title: "Yesterday task #1", due: yesterday),
            Todo(title: "Last week task #1", due: lastWeek),
            Todo(title: "Completed task #1", due: tomorrow, completed: today),
            Todo(title: "Completed task #2", due: yesterday, completed: today),
        ]
    }

}