draft/mlp/booster.go

package mlp

import (
	"math/rand"

	"git.fromouter.space/mcg/draft"
)

/*

(This data was taken from the MLP:CCG wikia at mlpccg.fandom.com and confirmed
 by people at the MLP:CCG Discord)

Distribution rates for packs is usually 8 commons, 3 uncommons and 1 rare.

No Fixed or Promo cards can be found in packs.

UR distribution depends on set:
	- PR has 1/13 chance of UR replacing a common
	- CN->AD has 1/11 chance of UR replacing a common
	- EO->FF has 1/3 chance of SR/UR replacing a common

SR are twice as common as UR, so that's one more thing to keep in mind.

Lastly, RR can replace another common in the ratio of ~1/2 every 6 boxes, depending
on set. Specifically, this is the RR ratio for each set:
	- EO->HM: 1/108
	- MT->FF: 1/216

*/

// BoxSchema returns the pack schema from a booster box for a specific set
func (set *Set) BoxSchema() draft.PackSchema {
	// Return blank schemas for invalid sets
	if set.ID == SetRockNRave || set.ID == SetCelestialSolstice {
		return draft.PackSchema{}
	}

	var rr []draft.AlternateProvider
	var srur []draft.AlternateProvider

	// Check for RR chances
	switch set.ID {
	case SetEquestrialOdysseys,
		SetHighMagic:
		rr = []draft.AlternateProvider{
			{
				Probability: 1.0 / 108.0,
				Provider:    set.ProviderByRarity(RarityRoyalRare),
			},
		}
	case SetMarksInTime,
		SetDefendersOfEquestria,
		SetSeaquestriaBeyond,
		SetFriendsForever:
		rr = []draft.AlternateProvider{
			{
				Probability: 1.0 / 216.0,
				Provider:    set.ProviderByRarity(RarityRoyalRare),
			},
		}
	}

	// Check for SR/UR chances
	switch set.ID {
	case SetPremiere:
		srur = []draft.AlternateProvider{
			{
				Probability: 1.0 / 13.0,
				Provider:    set.ProviderByRarity(RarityUltraRare),
			},
		}
	case SetCanterlotNights,
		SetCrystalGames,
		SetAbsoluteDiscord:
		srur = []draft.AlternateProvider{
			{
				Probability: 1.0 / 11.0,
				Provider:    set.ProviderByRarity(RarityUltraRare),
			},
		}
	default:
		srur = []draft.AlternateProvider{
			{
				Probability: (1.0 / 9.0) * 2.0,
				Provider:    set.ProviderByRarity(RaritySuperRare),
			}, {
				Probability: 1.0 / 9.0,
				Provider:    set.ProviderByRarity(RarityUltraRare),
			},
		}
	}

	return draft.PackSchema{
		Slots: []draft.PackSlot{
			// Fixed common slots
			{Amount: 6, Provider: set.ProviderByRarity(RarityCommon)},
			// Common slot that can be replaced by RR
			{Amount: 1, Provider: set.ProviderByRarity(RarityCommon), Alternate: rr},
			// Common slot that can be replaced by SR/UR
			{Amount: 1, Provider: set.ProviderByRarity(RarityCommon), Alternate: srur},
			// Fixed rare and uncommon slots
			{Amount: 1, Provider: set.ProviderByRarity(RarityRare)},
			{Amount: 3, Provider: set.ProviderByRarity(RarityUncommon)},
		},
	}
}

// ProviderByRarity returns a provider for a given rarity level from a given set
func (set *Set) ProviderByRarity(rarity Rarity) draft.CardProvider {
	var collection []draft.Card
	// RR flow is super easy, just pick one from our hardcoded list
	if rarity == RarityRoyalRare {
		rr, ok := royalRares[set.ID]
		// If asking for RR from a set that doesn't have one, exit early
		if !ok {
			return nil
		}
		collection = rr
	} else {
		for _, card := range set.Cards {
			if card.Rarity == rarity {
				collection = append(collection, draft.Card{ID: card.ID})
			}
		}
	}
	return func(n int) []draft.Card {
		out := make([]draft.Card, n)
		for n := range out {
			// Pick a RR at random
			idx := rand.Intn(len(collection))
			out[n] = collection[idx]
		}
		return out
	}
}