galaxy-game/internal/model/game/battle.go

package game

import (
	"fmt"
	"maps"
	"math"
	"math/rand/v2"
	"slices"

	"github.com/google/uuid"
)

type Battle struct {
	Planet       uint
	BattleReport BattleReport

	shipAmmo map[int]uint
	attacker map[int]map[int]float64 // a group able to attack and destroy an opponent with some probability
}

type BattleReport struct {
	BattleAction []BattleAction
}

type BattleAction struct {
	Attacker  int
	Defenter  int
	Destroyed bool
}

func CollectPlanetGroups(g *Game, cacheShipGroupRaceID map[int]int, cacheShipClass map[int]*ShipType) map[uint][]int {
	planetGroup := make(map[uint][]int)
	for groupIndex := range g.ShipGroups {
		if g.ShipGroups[groupIndex].State() == StateInOrbit {
			planetNumber := g.ShipGroups[groupIndex].Destination
			planetGroup[planetNumber] = append(planetGroup[planetNumber], groupIndex)

			if _, ok := cacheShipGroupRaceID[groupIndex]; !ok {
				cacheShipGroupRaceID[groupIndex] = RaceIndex(g, g.ShipGroups[groupIndex].OwnerID)
			}
			ri := cacheShipGroupRaceID[groupIndex]

			if _, ok := cacheShipClass[groupIndex]; !ok {
				sti, ok := ShipClassIndex(g, ri, g.ShipGroups[groupIndex].TypeID)
				if !ok {
					panic(fmt.Sprintf("CollectPlanetGroups: ship class not found for race=%q group=%v", g.Race[ri].Name, g.ShipGroups[groupIndex].Index))
				}
				cacheShipClass[groupIndex] = &g.Race[ri].ShipTypes[sti]
			}
		}
	}
	for pl := range planetGroup {
		if len(planetGroup[pl]) < 2 {
			delete(planetGroup, pl)
		}
	}
	return planetGroup
}

func CacheRelations(g *Game, cacheShipGroupRaceID map[int]int) map[int]map[int]Relation {
	cache := make(map[int]map[int]Relation)
	ri := make(map[int]bool)
	for _, raceIdx := range cacheShipGroupRaceID {
		ri[raceIdx] = true
	}
	for r1 := range ri {
		for r2 := range ri {
			if r1 == r2 {
				continue
			}
			rel, err := g.relationInternal(r1, r2)
			if err != nil {
				panic(err)
			}
			if _, ok := cache[r1]; !ok {
				cache[r1] = make(map[int]Relation)
			}
			cache[r1][r2] = rel.Relation
		}
	}
	return cache
}

func FilterBattleOpponents(
	g *Game,
	attIdx, defIdx int,
	cacheShipGroupRaceID map[int]int,
	cacheRelation map[int]map[int]Relation,
	cacheShipClass map[int]*ShipType,
	cacheProbability map[int]map[int]float64,
) bool {
	// Same Race's groups can't attack themselves
	if attIdx == defIdx || g.ShipGroups[attIdx].OwnerID == g.ShipGroups[defIdx].OwnerID {
		return true
	}

	// If any opponent has War relation to another, both will stay in battle
	if cacheRelation[cacheShipGroupRaceID[attIdx]][cacheShipGroupRaceID[defIdx]] == RelationPeace &&
		cacheRelation[cacheShipGroupRaceID[defIdx]][cacheShipGroupRaceID[attIdx]] == RelationPeace {
		return true
	}

	p := DestructionProbability(
		cacheShipClass[attIdx].Weapons,
		g.ShipGroups[attIdx].TechLevel(TechWeapons),
		cacheShipClass[defIdx].Shields,
		g.ShipGroups[defIdx].TechLevel(TechShields),
		g.ShipGroups[defIdx].FullMass(cacheShipClass[defIdx]),
	)
	// Exclude opponent's group which cannot be probably destroyed
	if p <= 0 {
		return true
	}

	if _, ok := cacheProbability[attIdx]; !ok {
		cacheProbability[attIdx] = make(map[int]float64)
	}
	cacheProbability[attIdx][defIdx] = p

	return false

}

func ProduceBattles(g *Game) []*Battle {
	cacheShipGroupRaceID := make(map[int]int)
	cacheShipClass := make(map[int]*ShipType)
	cacheProbability := make(map[int]map[int]float64)

	defer func() {
		clear(cacheShipGroupRaceID)
		clear(cacheShipClass)
		clear(cacheProbability)
	}()

	planetGroup := CollectPlanetGroups(g, cacheShipGroupRaceID, cacheShipClass)
	if len(planetGroup) == 0 {
		return nil
	}

	cacheRelation := CacheRelations(g, cacheShipGroupRaceID)
	defer func() {
		clear(cacheRelation)
	}()

	result := make([]*Battle, 0)

	for pl, groups := range planetGroup {
		b := &Battle{
			Planet:   pl,
			attacker: make(map[int]map[int]float64),
			shipAmmo: make(map[int]uint),
		}

		for i := range groups {
			attIdx := groups[i]

			// Ships with no Ammo will never attack somebody
			if cacheShipClass[attIdx].Armament == 0 {
				continue
			}

			// TODO: remove slices.Clone?
			opponents := slices.DeleteFunc(slices.Clone(groups), func(defIdx int) bool {
				return FilterBattleOpponents(g, attIdx, defIdx, cacheShipGroupRaceID, cacheRelation, cacheShipClass, cacheProbability)
			})
			if len(opponents) > 0 {
				b.shipAmmo[attIdx] = cacheShipClass[attIdx].Armament
				for _, defIdx := range opponents {
					b.attacker[attIdx][defIdx] = cacheProbability[attIdx][defIdx]
				}
			}
		}

		if len(b.attacker) > 0 {
			SingleBattle(g, b)
			result = append(result, b)
		}

		clear(b.attacker)
		clear(b.shipAmmo)
	}

	return result
}

func SingleBattle(g *Game, b *Battle) {
	for len(b.attacker) > 0 {
		attackers := slices.Collect(maps.Keys(b.attacker))
		attIdx := attackers[rand.IntN(len(attackers))]

		for range b.shipAmmo[attIdx] {
			defenders := slices.Collect(maps.Keys(b.attacker[attIdx]))
			defIdx := defenders[rand.IntN(len(defenders))]
			destroyed := false

			probability := b.attacker[attIdx][defIdx]
			switch {
			case probability >= 1:
				destroyed = true
			case probability > 0:
				destroyed = rand.Float64() >= probability
			default:
				panic("probabilities cache returned unexpected value")
			}

			b.BattleReport.BattleAction = append(b.BattleReport.BattleAction, BattleAction{
				Attacker:  attIdx,
				Defenter:  defIdx,
				Destroyed: destroyed,
			})

			if destroyed {
				g.ShipGroups[defIdx].Number--
			}
			if g.ShipGroups[defIdx].Number == 0 {
				delete(b.attacker, defIdx) // Eliminated group cant attack anyone
				for attIdx := range b.attacker {
					delete(b.attacker[attIdx], defIdx) // Attackers can't attack eliminated group anymore
					if len(b.attacker[attIdx]) == 0 {
						delete(b.attacker, attIdx) // Remove attacker if he lost all opponents
					}
				}
			}
			if len(b.attacker) == 0 {
				break
			}
		}
	}
}

func RaceIndex(g *Game, ID uuid.UUID) int {
	i := slices.IndexFunc(g.Race, func(r Race) bool { return r.ID == ID })
	if i < 0 {
		panic(fmt.Sprintf("RaceIndex: race not found by ID=%v", ID))
	}
	return i
}

func DestructionProbability(attWeapons, attWeaponsTech, defShields, defShiledsTech, defFullMass float64) float64 {
	effAttack := attWeapons * attWeaponsTech
	effDefence := EffectiveDefence(defShields, defShiledsTech, defFullMass)
	return (math.Log10(effAttack/effDefence)/math.Log10(4) + 1) / 2
}

func EffectiveDefence(defShields, defShiledsTech, defFullMass float64) float64 {
	return defShields * defShiledsTech / math.Pow(defFullMass, 1./3.) * math.Pow(30., 1./3.)
}