ai-code-battle/cmd/acb-evolver/internal/meta/builder.go

// Package meta builds meta-game descriptions for the evolution prompt.
//
// The meta builder aggregates data about the current competitive landscape:
//   - Leaderboard: top-rated bots and their ratings
//   - Dominant strategies: what tactics are currently winning
//   - Island population stats: fitness and diversity per island
package meta

import (
	"context"
	"sort"
	"strings"

	evolverdb "github.com/aicodebattle/acb/cmd/acb-evolver/internal/db"
)

// BotInfo represents a bot's competitive summary.
type BotInfo struct {
	Name    string
	Rating  float64
	Island  string
	Evolved bool
}

// IslandStats captures population metrics for a single island.
type IslandStats struct {
	Count      int
	AvgFitness float64
	TopFitness float64
	Diversity  float64 // behavioral diversity (0-1)
}

// Description holds the complete meta-game snapshot.
type Description struct {
	// TotalBots is the number of active bots on the ladder.
	TotalBots int
	// TopBots lists the highest-rated bots.
	TopBots []BotInfo
	// DominantStrategy describes the current meta.
	DominantStrategy string
	// IslandStats holds population metrics per island.
	IslandStats map[string]IslandStats
}

// Builder creates meta descriptions from database state.
type Builder struct {
	store *evolverdb.Store
}

// NewBuilder creates a meta builder backed by the program store.
func NewBuilder(store *evolverdb.Store) *Builder {
	return &Builder{store: store}
}

// Build constructs a meta description from current database state.
func (b *Builder) Build(ctx context.Context, topBotLimit int) (*Description, error) {
	desc := &Description{
		IslandStats: make(map[string]IslandStats),
	}

	// Gather island population stats
	for _, island := range evolverdb.AllIslands {
		programs, err := b.store.ListByIsland(ctx, island)
		if err != nil {
			return nil, err
		}

		stats := IslandStats{
			Count: len(programs),
		}

		if len(programs) > 0 {
			// Calculate average and top fitness
			var sum float64
			for _, p := range programs {
				sum += p.Fitness
			}
			stats.AvgFitness = sum / float64(len(programs))
			stats.TopFitness = programs[0].Fitness // Already sorted by fitness DESC

			// Calculate behavioral diversity using behavior vectors
			stats.Diversity = calculateDiversity(programs)
		}

		desc.IslandStats[island] = stats
	}

	// Get promoted programs to represent the live ladder
	promoted, err := b.store.ListPromoted(ctx)
	if err != nil {
		return nil, err
	}

	desc.TotalBots = len(promoted)

	// Convert to BotInfo and sort by fitness (as proxy for rating)
	topBots := make([]BotInfo, 0, len(promoted))
	for _, p := range promoted {
		topBots = append(topBots, BotInfo{
			Name:    p.BotName,
			Rating:  1500 + p.Fitness*100, // Approximate rating from fitness
			Island:  p.Island,
			Evolved: true,
		})
	}

	// Sort by rating descending
	sort.Slice(topBots, func(i, j int) bool {
		return topBots[i].Rating > topBots[j].Rating
	})

	// Limit to top N bots
	if len(topBots) > topBotLimit {
		topBots = topBots[:topBotLimit]
	}
	desc.TopBots = topBots

	// Infer dominant strategy from top performers
	desc.DominantStrategy = b.inferDominantStrategy(desc)

	return desc, nil
}

// calculateDiversity computes behavioral diversity from behavior vectors.
// Returns a value between 0 (all identical) and 1 (maximally diverse).
func calculateDiversity(programs []*evolverdb.Program) float64 {
	if len(programs) < 2 {
		return 0
	}

	// Calculate average pairwise distance
	var totalDist float64
	var pairs int

	for i := 0; i < len(programs); i++ {
		for j := i + 1; j < len(programs); j++ {
			dist := behaviorDistance(programs[i].BehaviorVector, programs[j].BehaviorVector)
			totalDist += dist
			pairs++
		}
	}

	if pairs == 0 {
		return 0
	}

	avgDist := totalDist / float64(pairs)
	// Normalize: max distance in 2D unit square is sqrt(2) ≈ 1.414
	return avgDist / 1.414
}

// behaviorDistance computes Euclidean distance between behavior vectors.
func behaviorDistance(a, b []float64) float64 {
	if len(a) < 2 || len(b) < 2 {
		return 0
	}
	dx := a[0] - b[0]
	dy := a[1] - b[1]
	return dx*dx + dy*dy // Squared distance is sufficient for diversity
}

// inferDominantStrategy analyzes the top bots and describes the meta.
func (b *Builder) inferDominantStrategy(desc *Description) string {
	if len(desc.TopBots) == 0 {
		return "unknown (no promoted bots)"
	}

	// Count strategies by island
	islandCounts := make(map[string]int)
	for _, bot := range desc.TopBots {
		islandCounts[bot.Island]++
	}

	// Find dominant island(s)
	var dominantIslands []string
	maxCount := 0
	for island, count := range islandCounts {
		if count > maxCount {
			maxCount = count
			dominantIslands = []string{island}
		} else if count == maxCount {
			dominantIslands = append(dominantIslands, island)
		}
	}

	// Map islands to strategy descriptions
	strategyMap := map[string]string{
		evolverdb.IslandAlpha: "aggressive core-rushing",
		evolverdb.IslandBeta:  "energy-focused economy",
		evolverdb.IslandGamma: "defensive adaptation",
		evolverdb.IslandDelta: "experimental mixed",
	}

	var strategies []string
	for _, island := range dominantIslands {
		if s, ok := strategyMap[island]; ok {
			strategies = append(strategies, s)
		}
	}

	if len(strategies) == 0 {
		return "diverse meta with no clear dominant strategy"
	}

	return strings.Join(strategies, " / ")
}

// BuildSimple creates a meta description without database access.
// This is useful for testing or when database is not available.
func BuildSimple(totalBots int, topBots []BotInfo, islandStats map[string]IslandStats) *Description {
	desc := &Description{
		TotalBots:   totalBots,
		TopBots:     topBots,
		IslandStats: islandStats,
	}

	// Infer dominant strategy
	if len(topBots) > 0 {
		islandCounts := make(map[string]int)
		for _, bot := range topBots {
			islandCounts[bot.Island]++
		}

		// Find most common island
		maxCount := 0
		dominantIsland := ""
		for island, count := range islandCounts {
			if count > maxCount {
				maxCount = count
				dominantIsland = island
			}
		}

		strategyMap := map[string]string{
			evolverdb.IslandAlpha: "aggressive core-rushing",
			evolverdb.IslandBeta:  "energy-focused economy",
			evolverdb.IslandGamma: "defensive adaptation",
			evolverdb.IslandDelta: "experimental mixed",
		}

		if s, ok := strategyMap[dominantIsland]; ok {
			desc.DominantStrategy = s
		} else {
			desc.DominantStrategy = "diverse meta"
		}
	}

	return desc
}