package ucca

import (
	"context"
	"os"
	"sort"
	"strings"
	"sync"
)

// routerBaseCollections is the broad authority base the Authority Router fans out over. It mirrors
// the Advisor's historical multi-collection set; the KB-2026.1 slice is added separately when the
// query is in scope. Override via RAG_ROUTER_COLLECTIONS (comma-separated) per environment.
func (c *LegalRAGClient) routerBaseCollections() []string {
	if v := strings.TrimSpace(os.Getenv("RAG_ROUTER_COLLECTIONS")); v != "" {
		var out []string
		for _, p := range strings.Split(v, ",") {
			if s := strings.TrimSpace(p); s != "" {
				out = append(out, s)
			}
		}
		if len(out) > 0 {
			return out
		}
	}
	return []string{
		"bp_compliance_gesetze",
		"bp_compliance_ce",
		"bp_compliance_datenschutz",
		"bp_dsfa_corpus",
		"bp_compliance_recht",
		"bp_legal_templates",
	}
}

const routerPerCollectionTopK = 3

// Retrieve is the Authority Router entry point: callers (the Advisor) pass ONLY a query and stay
// collection-agnostic. The router fans out over the broad authority base and ADDS the KB-2026.1
// slice when the query is in scope (inKBScope), then merges all hits, deduplicates, and returns the
// top-K by authority score. This moves the former Advisor-side collection fan-out into the retrieval
// layer (the "Retriever" tier of the quality pyramid), so the proven KB-2026.1 slice gain reaches
// the product path without the Advisor knowing about individual collections.
//
// The merged set is ordered by the per-collection authority score that rerankByAuthority already
// produced inside searchInternal — i.e. binding-vs-guidance ordering is preserved across the merge.
// Per-collection failures (e.g. a collection absent on an environment) degrade gracefully.
func (c *LegalRAGClient) Retrieve(ctx context.Context, query string, topK int) ([]LegalSearchResult, error) {
	if topK <= 0 {
		topK = 8
	}

	collections := c.routerBaseCollections()
	if c.kbScopeRoutingEnabled && c.kbSliceCollection != "" && inKBScope(query) {
		collections = append(collections, c.kbSliceCollection)
	}

	// Warm the full-text indexes sequentially first so the concurrent fan-out below only READS the
	// shared textIndexEnsured map (the writes happen here, serialized) — closes the cold-start map
	// race deterministically. Best-effort: a missing collection just stays un-indexed (hybrid then
	// falls back to dense, or the per-collection search degrades to nothing).
	if c.hybridEnabled {
		for _, coll := range collections {
			_ = c.ensureTextIndex(ctx, coll)
		}
	}

	out := make([][]LegalSearchResult, len(collections))
	var wg sync.WaitGroup
	for i, coll := range collections {
		wg.Add(1)
		go func(i int, coll string) {
			defer wg.Done()
			if res, err := c.searchInternal(ctx, coll, query, nil, routerPerCollectionTopK); err == nil {
				out[i] = res
			}
		}(i, coll)
	}
	wg.Wait()

	merged := make([]LegalSearchResult, 0, len(collections)*routerPerCollectionTopK)
	for _, r := range out {
		merged = append(merged, r...)
	}
	merged = dedupResults(merged)
	sort.SliceStable(merged, func(a, b int) bool { return merged[a].Score > merged[b].Score })
	if len(merged) > topK {
		merged = merged[:topK]
	}
	return merged, nil
}

// dedupResults removes duplicate passages that can appear when collections overlap, keeping the
// highest-scoring occurrence. Identity = regulation_code + article_label + a text prefix.
func dedupResults(in []LegalSearchResult) []LegalSearchResult {
	pos := make(map[string]int, len(in))
	out := make([]LegalSearchResult, 0, len(in))
	for _, r := range in {
		text := r.Text
		if len(text) > 80 {
			text = text[:80]
		}
		key := r.RegulationCode + "|" + r.ArticleLabel + "|" + text
		if idx, ok := pos[key]; ok {
			if r.Score > out[idx].Score {
				out[idx] = r
			}
			continue
		}
		pos[key] = len(out)
		out = append(out, r)
	}
	return out
}