draft/pack.go

package draft

import (
	"math/rand"
	"strings"
)

// Pack is a collection of cards from a booster pack
type Pack []Card

// Card is a single card
type Card struct {
	ID string
}

// CardProvider is a function that returns as many cards of a certain types as needed
type CardProvider func(int) []Card

// PackSchema is all that's needed to generate a certain type of pack
type PackSchema struct {
	Slots []PackSlot
}

// PackSlot is part of how packs are made, one or more providers provide
// cards for X cards of the whole pack
type PackSlot struct {
	Amount    int
	Provider  CardProvider
	Alternate []AlternateProvider
}

// AlternateProvider are Card providers that can replace one or more slots
// with special cards (foils, ultra rares)
type AlternateProvider struct {
	Probability float32
	Provider    CardProvider
}

// MakePack makes a booster pack from a given set
// It's a shortcut to `MakePackWithSchema(set.PackSchema())`
func MakePack(set Set) Pack {
	schema := set.PackSchema()
	return MakePackWithSchema(schema)
}

// MakePackWithSchema makes a booster pack from a given schema
func MakePackWithSchema(schema PackSchema) Pack {
	pack := make(Pack, 0)
	for _, slot := range schema.Slots {
		// Default provider
		provider := slot.Provider

		// Check for random alternates
		if slot.Alternate != nil {
			var currentProb float32
			var chosenProb = rand.Float32()
			for _, alt := range slot.Alternate {
				currentProb += alt.Probability
				if currentProb > chosenProb {
					provider = alt.Provider
					break
				}
			}
		}

		// Extract cards from provider and add them to the pack
		cards := provider(slot.Amount)
		pack = append(pack, cards...)
	}
	return pack
}

// String encodes a pack to a list of space-separated IDs
func (p Pack) String() (str string) {
	for _, card := range p {
		str += " " + card.ID
	}
	str = strings.TrimSpace(str)
	return
}