package models

import (
	"testing"
	"time"
)

// A car collected new sits at 0 km; its first service is still due a full
// interval later, and the reminder must show the distance left to run.
func TestZeroKmStillYieldsNextService(t *testing.T) {
	car := &Car{ServiceIntervalDays: 365, ServiceIntervalKm: 15000, CurrentKm: 0}
	pickup := time.Date(2026, 8, 10, 0, 0, 0, 0, time.UTC)
	rec := ServiceRecord{Date: pickup, Km: 0}
	rec.ComputeDerived(car)

	if rec.NextServiceDate == nil || !rec.NextServiceDate.Equal(pickup.AddDate(0, 0, 365)) {
		t.Fatalf("next service date = %v", rec.NextServiceDate)
	}
	if rec.NextServiceKm == nil {
		t.Fatal("next service km is nil for a 0 km car")
	}
	if *rec.NextServiceKm != 15000 {
		t.Fatalf("next service km = %d, want 15000", *rec.NextServiceKm)
	}

	rem := Reminder{DueKm: *rec.NextServiceKm}
	rem.ComputeReminderDerived(time.Now(), car.CurrentKm)
	if rem.KmLeft == nil || *rem.KmLeft != 15000 {
		t.Fatalf("km left = %v, want 15000", rem.KmLeft)
	}
	if rem.Status != "upcoming" {
		t.Fatalf("status = %q, want upcoming", rem.Status)
	}
}

// A repeating km reminder completed on a car that reads 0 rolls from 0, not
// from the old target — the odometer is where the car is, not a missing value.
func TestZeroKmReminderStatus(t *testing.T) {
	for _, tc := range []struct {
		name      string
		currentKm int
		dueKm     int
		wantLeft  int
		wantState string
	}{
		{"collected new", 0, 15000, 15000, "upcoming"},
		{"nearly due", 14500, 15000, 500, "due_soon"},
		{"overdue", 15500, 15000, -500, "overdue"},
	} {
		t.Run(tc.name, func(t *testing.T) {
			rem := Reminder{DueKm: tc.dueKm}
			rem.ComputeReminderDerived(time.Now(), tc.currentKm)
			if rem.KmLeft == nil || *rem.KmLeft != tc.wantLeft {
				t.Fatalf("km left = %v, want %d", rem.KmLeft, tc.wantLeft)
			}
			if rem.Status != tc.wantState {
				t.Fatalf("status = %q, want %q", rem.Status, tc.wantState)
			}
		})
	}
}