tdd-katas/lib/gilded_rose.dart

// WARNING: DO NOT modify the Item class - the goblin in the corner will insta-rage!

class Item {
  String name;
  int sellIn;
  int quality;

  Item(this.name, this.sellIn, this.quality);

  @override
  String toString() => '$name, $sellIn, $quality';
}

class GildedRose {
  List<Item> items;

  GildedRose(this.items);

  void updateQuality() {
    for (final item in items) {
      if (item.name == 'Sulfuras, Hand of Ragnaros') {
        _updateSulfuras(item);
      } else if (item.name == 'Aged Brie') {
        _updateAgedBrie(item);
      } else if (item.name == 'Backstage passes to a TAFKAL80ETC concert') {
        _updateBackstagePasses(item);
      } else {
        _updateNormalItem(item);
      }
    }
  }

  void _updateNormalItem(Item item) {
    // Quality decreases by 1 each day
    if (item.quality > 0) {
      item.quality -= 1;
    }

    item.sellIn -= 1;

    // After sell-by date, quality degrades twice as fast
    if (item.sellIn < 0 && item.quality > 0) {
      item.quality -= 1;
    }
  }

  void _updateAgedBrie(Item item) {
    // Quality increases as it ages
    if (item.quality < 50) {
      item.quality += 1;
    }

    item.sellIn -= 1;

    // After sell-by date, quality increases twice as fast
    if (item.sellIn < 0 && item.quality < 50) {
      item.quality += 1;
    }
  }

  void _updateBackstagePasses(Item item) {
    // Quality increases as concert approaches
    if (item.quality < 50) {
      item.quality += 1;

      // 10 days or less: +2 quality/day
      if (item.sellIn < 11 && item.quality < 50) {
        item.quality += 1;
      }

      // 5 days or less: +3 quality/day
      if (item.sellIn < 6 && item.quality < 50) {
        item.quality += 1;
      }
    }

    item.sellIn -= 1;

    // After concert, quality drops to 0
    if (item.sellIn < 0) {
      item.quality = 0;
    }
  }

  void _updateSulfuras(Item item) {
    // Legendary item never changes
    // Quality always 80, sellIn never decreases
  }
}