package schedule

import (
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

func TestParseRejectsBadExpr(t *testing.T) {
	_, err := Parse("")
	assert.Error(t, err)

	_, err = Parse("0 0 31 2 *") // valid syntactically but never fires; cronutil accepts it
	// cronutil only validates syntax; an impossible date is still parsed.
	// We assert by separately rejecting clearly invalid syntax:
	_, err = Parse("not-a-cron")
	assert.Error(t, err)

	_, err = Parse("0 18 * *") // four fields
	assert.Error(t, err)

	_, err = Parse("0 0 * * * *") // six fields
	assert.Error(t, err)
}

func TestNextNoSkip(t *testing.T) {
	// Fires every day at 18:00 UTC.
	sched, err := Parse("0 18 * * *")
	require.NoError(t, err)

	after := time.Date(2026, 4, 27, 12, 0, 0, 0, time.UTC)
	got, skipped := sched.Next(after, false)

	assert.False(t, skipped)
	assert.Equal(t, time.Date(2026, 4, 27, 18, 0, 0, 0, time.UTC), got)
	assert.Equal(t, time.UTC, got.Location())
}

func TestNextWithSkipAdvancesOneStep(t *testing.T) {
	sched, err := Parse("0 18 * * *")
	require.NoError(t, err)

	after := time.Date(2026, 4, 27, 12, 0, 0, 0, time.UTC)
	got, skipped := sched.Next(after, true)

	assert.True(t, skipped)
	// First slot would be 2026-04-27 18:00 UTC; the skip rule advances
	// to 2026-04-28 18:00 UTC.
	assert.Equal(t, time.Date(2026, 4, 28, 18, 0, 0, 0, time.UTC), got)
}

func TestNextNormalisesNonUTCInput(t *testing.T) {
	sched, err := Parse("*/15 * * * *")
	require.NoError(t, err)

	moscow := time.FixedZone("MSK", 3*60*60)
	// 2026-04-27 15:30 MSK = 2026-04-27 12:30 UTC; next 15-minute slot
	// in UTC is 12:45.
	after := time.Date(2026, 4, 27, 15, 30, 0, 0, moscow)

	got, skipped := sched.Next(after, false)
	assert.False(t, skipped)
	assert.Equal(t, time.Date(2026, 4, 27, 12, 45, 0, 0, time.UTC), got)
	assert.Equal(t, time.UTC, got.Location())
}