from datetime import datetime

from django.db import models
from django.utils import timezone

# maximum time in years of a material part until being replaced
MAX_TIME_MATERIAL = 5


# Create your models here.
class MaterialPart(models.Model):
    name = models.CharField(max_length=30)
    buy_date = models.DateField('purchase date')
    # owner = models.ForeignKey(Leiter)  to be added later when there are user

    def __repr__(self):
        return self.name

    def should_be_replaced(self):
        buy_time = timezone.make_aware(datetime.combine(self.buy_date,
                                                        datetime.min.time()))
        return yearsago(MAX_TIME_MATERIAL) >= buy_time

    should_be_replaced.admin_order_field = 'buy_date'
    should_be_replaced.boolean = True
    should_be_replaced.short_description = 'Should be replaced?'


def yearsago(years, from_date=None):
    if from_date is None:
        from_date = timezone.now()
    try:
        return from_date.replace(year=from_date.year - years)
    except ValueError:
        # 29.02 -> use 28.02
        assert from_date.month == 2 and from_date.day == 29
        return from_date.replace(month=2, day=28, year=from_date.year - years)