core/server/memory/compactor.go

package memory

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"strings"

	"chat-switchboard/models"
	"chat-switchboard/providers"
	"chat-switchboard/roles"
	"chat-switchboard/store"
)

// compactionThreshold is the minimum number of active memories before
// compaction is considered worthwhile for a user.
const compactionThreshold = 30

// compactionPrompt instructs the utility model to merge related memories.
const compactionPrompt = `You are a memory compaction assistant. Given a set of user memories (key-value facts), merge related or redundant entries into fewer, more precise facts.

Rules:
- Combine facts about the same topic into a single entry
- Remove duplicates, keeping the most specific/recent version
- Preserve all unique information — do not drop facts
- Keep keys short (2-5 words, lowercase)
- Keep values concise (1-2 sentences max)
- Set confidence based on how well-supported the merged fact is

Respond ONLY with a JSON array of merged facts:
[{"key": "...", "value": "...", "confidence": 0.0-1.0}]

If no merging is possible, return the original facts unchanged.`

// Compactor merges related memories to reduce count and improve quality.
type Compactor struct {
	stores       store.Stores
	roleResolver *roles.Resolver
}

// NewCompactor creates a memory compaction service.
func NewCompactor(stores store.Stores, rr *roles.Resolver) *Compactor {
	return &Compactor{stores: stores, roleResolver: rr}
}

// CompactResult holds the outcome of a compaction run.
type CompactResult struct {
	Before   int `json:"before"`
	After    int `json:"after"`
	Merged   int `json:"merged"`
	Archived int `json:"archived"`
}

// Compact loads active memories for a user, sends them to the utility model
// for merging, then upserts merged entries and archives originals.
func (c *Compactor) Compact(ctx context.Context, userID string, teamID *string) (*CompactResult, error) {
	if c.stores.Memories == nil {
		return nil, fmt.Errorf("memory store not available")
	}

	// Load all active user-scope memories
	memories, err := c.stores.Memories.List(ctx, models.MemoryFilter{
		Scope:   models.MemoryScopeUser,
		OwnerID: userID,
		Status:  models.MemoryStatusActive,
		Limit:   500,
	})
	if err != nil {
		return nil, fmt.Errorf("list memories: %w", err)
	}

	if len(memories) < compactionThreshold {
		return &CompactResult{Before: len(memories), After: len(memories)}, nil
	}

	// Build memory text for the model
	var sb strings.Builder
	for i, m := range memories {
		sb.WriteString(fmt.Sprintf("%d. [%s] %s (confidence: %.2f)\n", i+1, m.Key, m.Value, m.Confidence))
	}

	apiMessages := []providers.Message{
		{Role: "system", Content: compactionPrompt},
		{Role: "user", Content: fmt.Sprintf("Compact these %d memories:\n\n%s", len(memories), sb.String())},
	}

	result, err := c.roleResolver.Complete(ctx, "utility", userID, teamID, apiMessages)
	if err != nil {
		return nil, fmt.Errorf("compaction completion: %w", err)
	}

	// Parse merged facts
	merged, err := parseExtractionResponse(result.Content)
	if err != nil {
		return nil, fmt.Errorf("parse compaction response: %w", err)
	}

	if len(merged) == 0 || len(merged) >= len(memories) {
		// Model returned nothing useful or didn't reduce — skip
		log.Printf("🧠 memory compaction: user %s — model returned %d facts (was %d), skipping",
			userID, len(merged), len(memories))
		return &CompactResult{Before: len(memories), After: len(memories)}, nil
	}

	// Archive all original memories
	archived := 0
	for _, m := range memories {
		if err := c.stores.Memories.Archive(ctx, m.ID); err == nil {
			archived++
		}
	}

	// Upsert merged memories
	for _, fact := range merged {
		mem := &models.Memory{
			Scope:      models.MemoryScopeUser,
			OwnerID:    userID,
			Key:        fact.Key,
			Value:      fact.Value,
			Confidence: fact.Confidence,
			Status:     models.MemoryStatusActive,
		}
		if err := c.stores.Memories.Upsert(ctx, mem); err != nil {
			log.Printf("⚠ memory compaction upsert failed: key=%s: %v", fact.Key, err)
		}
	}

	log.Printf("🧠 memory compaction: user %s — %d → %d memories (archived %d)",
		userID, len(memories), len(merged), archived)

	return &CompactResult{
		Before:   len(memories),
		After:    len(merged),
		Merged:   len(merged),
		Archived: archived,
	}, nil
}

// parseCompactionResponse parses the model's JSON array response.
// Reuses the same extractedFact struct from extractor.go.
func parseCompactionResponse(content string) ([]extractedFact, error) {
	content = strings.TrimSpace(content)
	// Strip markdown code fences if present
	if strings.HasPrefix(content, "```") {
		lines := strings.Split(content, "\n")
		if len(lines) > 2 {
			content = strings.Join(lines[1:len(lines)-1], "\n")
		}
	}

	var facts []extractedFact
	if err := json.Unmarshal([]byte(content), &facts); err != nil {
		return nil, err
	}
	return facts, nil
}