package categorization_test

import (
	"math/rand"
	"testing"
	"time"

	"github.com/treytartt/casera-api/internal/models"
	"github.com/treytartt/casera-api/internal/task/categorization"
)

// validColumns is the complete set of KanbanColumn values the chain may return.
var validColumns = map[categorization.KanbanColumn]bool{
	categorization.ColumnOverdue:    true,
	categorization.ColumnDueSoon:    true,
	categorization.ColumnUpcoming:   true,
	categorization.ColumnInProgress: true,
	categorization.ColumnCompleted:  true,
	categorization.ColumnCancelled:  true,
}

// FuzzCategorizeTask feeds random task states into CategorizeTask and asserts
// that the result is always a non-empty, valid KanbanColumn constant.
func FuzzCategorizeTask(f *testing.F) {
	f.Add(false, false, false, false, false, 0, false, 0)
	f.Add(true, false, false, false, false, 0, false, 0)
	f.Add(false, true, false, false, false, 0, false, 0)
	f.Add(false, false, true, false, false, 0, false, 0)
	f.Add(false, false, false, true, false, 0, false, 0)
	f.Add(false, false, false, false, true, -5, false, 0)
	f.Add(false, false, false, false, false, 0, true, -5)
	f.Add(false, false, false, false, false, 0, true, 5)
	f.Add(false, false, false, false, false, 0, true, 60)
	f.Add(true, true, true, true, true, -10, true, -10)
	f.Add(false, false, false, false, true, 100, true, 100)

	f.Fuzz(func(t *testing.T,
		isCancelled, isArchived, inProgress, hasCompletions bool,
		hasDueDate bool, dueDateOffsetDays int,
		hasNextDueDate bool, nextDueDateOffsetDays int,
	) {
		now := time.Date(2025, 12, 15, 0, 0, 0, 0, time.UTC)

		task := &models.Task{
			IsCancelled: isCancelled,
			IsArchived:  isArchived,
			InProgress:  inProgress,
		}

		if hasDueDate {
			d := now.AddDate(0, 0, dueDateOffsetDays)
			task.DueDate = &d
		}
		if hasNextDueDate {
			d := now.AddDate(0, 0, nextDueDateOffsetDays)
			task.NextDueDate = &d
		}
		if hasCompletions {
			task.Completions = []models.TaskCompletion{
				{BaseModel: models.BaseModel{ID: 1}},
			}
		} else {
			task.Completions = []models.TaskCompletion{}
		}

		result := categorization.CategorizeTask(task, 30)

		if result == "" {
			t.Fatalf("CategorizeTask returned empty string for task %+v", task)
		}
		if !validColumns[result] {
			t.Fatalf("CategorizeTask returned invalid column %q for task %+v", result, task)
		}
	})
}

// === Property Tests (1000 random tasks) ===

// TestCategorizeTask_PropertyEveryTaskMapsToExactlyOneColumn uses random tasks
// to validate the property that every task maps to exactly one column.
func TestCategorizeTask_PropertyEveryTaskMapsToExactlyOneColumn(t *testing.T) {
	rng := rand.New(rand.NewSource(42)) // Deterministic seed for reproducibility
	now := time.Date(2025, 6, 15, 0, 0, 0, 0, time.UTC)

	for i := 0; i < 1000; i++ {
		task := randomTask(rng, now)
		column := categorization.CategorizeTask(task, 30)

		if !validColumns[column] {
			t.Fatalf("Task %d mapped to invalid column %q: %+v", i, column, task)
		}
	}
}

// TestCategorizeTask_CancelledAlwaysWins validates that cancelled takes priority
// over all other states regardless of other flags using randomized tasks.
func TestCategorizeTask_CancelledAlwaysWins(t *testing.T) {
	rng := rand.New(rand.NewSource(42))
	now := time.Date(2025, 6, 15, 0, 0, 0, 0, time.UTC)

	for i := 0; i < 500; i++ {
		task := randomTask(rng, now)
		task.IsCancelled = true

		column := categorization.CategorizeTask(task, 30)
		if column != categorization.ColumnCancelled {
			t.Fatalf("Cancelled task %d mapped to %q instead of cancelled_tasks: %+v", i, column, task)
		}
	}
}

// === Timezone / DST Boundary Tests ===

// TestCategorizeTask_UTCMidnightBoundary tests task categorization at exactly
// UTC midnight, which is the boundary between days.
func TestCategorizeTask_UTCMidnightBoundary(t *testing.T) {
	midnight := time.Date(2025, 3, 9, 0, 0, 0, 0, time.UTC)
	dueDate := midnight

	task := &models.Task{
		DueDate: &dueDate,
	}

	// At midnight of the due date, task is NOT overdue (due today)
	column := categorization.CategorizeTaskWithTime(task, 30, midnight)
	if column == categorization.ColumnOverdue {
		t.Errorf("Task due today should not be overdue at midnight, got %q", column)
	}

	// One day later, task IS overdue
	nextDay := midnight.AddDate(0, 0, 1)
	column = categorization.CategorizeTaskWithTime(task, 30, nextDay)
	if column != categorization.ColumnOverdue {
		t.Errorf("Task due yesterday should be overdue, got %q", column)
	}
}

// TestCategorizeTask_DSTSpringForward tests categorization across DST spring-forward.
// In US Eastern time, 2:00 AM jumps to 3:00 AM on the second Sunday of March.
func TestCategorizeTask_DSTSpringForward(t *testing.T) {
	loc, err := time.LoadLocation("America/New_York")
	if err != nil {
		t.Skip("America/New_York timezone not available")
	}

	// March 9, 2025 is DST spring-forward in Eastern Time
	dueDate := time.Date(2025, 3, 9, 0, 0, 0, 0, time.UTC) // Stored as UTC
	task := &models.Task{DueDate: &dueDate}

	// Check at start of March 9 in Eastern time
	nowET := time.Date(2025, 3, 9, 0, 0, 0, 0, loc)
	column := categorization.CategorizeTaskWithTime(task, 30, nowET)
	if column == categorization.ColumnOverdue {
		t.Errorf("Task due March 9 should not be overdue on March 9 (DST spring-forward), got %q", column)
	}

	// Check at March 10 - should be overdue now
	nextDayET := time.Date(2025, 3, 10, 0, 0, 0, 0, loc)
	column = categorization.CategorizeTaskWithTime(task, 30, nextDayET)
	if column != categorization.ColumnOverdue {
		t.Errorf("Task due March 9 should be overdue on March 10, got %q", column)
	}
}

// TestCategorizeTask_DSTFallBack tests categorization across DST fall-back.
// In US Eastern time, 2:00 AM jumps back to 1:00 AM on the first Sunday of November.
func TestCategorizeTask_DSTFallBack(t *testing.T) {
	loc, err := time.LoadLocation("America/New_York")
	if err != nil {
		t.Skip("America/New_York timezone not available")
	}

	// November 2, 2025 is DST fall-back in Eastern Time
	dueDate := time.Date(2025, 11, 2, 0, 0, 0, 0, time.UTC)
	task := &models.Task{DueDate: &dueDate}

	// On the due date itself - not overdue
	nowET := time.Date(2025, 11, 2, 0, 0, 0, 0, loc)
	column := categorization.CategorizeTaskWithTime(task, 30, nowET)
	if column == categorization.ColumnOverdue {
		t.Errorf("Task due Nov 2 should not be overdue on Nov 2 (DST fall-back), got %q", column)
	}

	// Next day - should be overdue
	nextDayET := time.Date(2025, 11, 3, 0, 0, 0, 0, loc)
	column = categorization.CategorizeTaskWithTime(task, 30, nextDayET)
	if column != categorization.ColumnOverdue {
		t.Errorf("Task due Nov 2 should be overdue on Nov 3, got %q", column)
	}
}

// TestIsOverdue_UTCMidnightEdge validates the overdue predicate at exact midnight.
func TestIsOverdue_UTCMidnightEdge(t *testing.T) {
	dueDate := time.Date(2025, 12, 31, 0, 0, 0, 0, time.UTC)
	task := &models.Task{DueDate: &dueDate}

	// On due date: NOT overdue
	atDueDate := time.Date(2025, 12, 31, 0, 0, 0, 0, time.UTC)
	column := categorization.CategorizeTaskWithTime(task, 30, atDueDate)
	if column == categorization.ColumnOverdue {
		t.Error("Task should not be overdue on its due date")
	}

	// One second after midnight next day: overdue
	afterDueDate := time.Date(2026, 1, 1, 0, 0, 1, 0, time.UTC)
	column = categorization.CategorizeTaskWithTime(task, 30, afterDueDate)
	if column != categorization.ColumnOverdue {
		t.Errorf("Task should be overdue after its due date, got %q", column)
	}
}

// === Helper ===

func randomTask(rng *rand.Rand, baseTime time.Time) *models.Task {
	task := &models.Task{
		IsCancelled: rng.Intn(10) == 0, // 10% chance
		IsArchived:  rng.Intn(10) == 0, // 10% chance
		InProgress:  rng.Intn(5) == 0,  // 20% chance
	}

	if rng.Intn(4) > 0 { // 75% have due date
		d := baseTime.AddDate(0, 0, rng.Intn(120)-60)
		task.DueDate = &d
	}

	if rng.Intn(3) == 0 { // 33% recurring
		d := baseTime.AddDate(0, 0, rng.Intn(120)-60)
		task.NextDueDate = &d
	}

	if rng.Intn(3) == 0 { // 33% have completions
		count := rng.Intn(3) + 1
		for i := 0; i < count; i++ {
			task.Completions = append(task.Completions, models.TaskCompletion{
				BaseModel: models.BaseModel{ID: uint(i + 1)},
			})
		}
	}

	return task
}