-- ============================================================================
-- Knowledge vector search: rank exactly within the caller's visible chunks
-- ============================================================================
--
-- Problem (20260410000004_pgvector_knowledge.sql)
--   * idx_knowledge_chunks_embedding was an IVFFlat index (lists = 100) built
--     in the same migration that added the embedding column, so it was
--     trained on zero vectors and its centroids are meaningless. Nothing ever
--     ran the REINDEX that the comment asked for.
--   * match_knowledge_chunks ended with
--       ORDER BY kc.embedding <=> query_embedding LIMIT match_count
--     which lets the planner walk that ANN index across ALL tenants with the
--     default ivfflat.probes = 1, and only then apply the user/team filter,
--     the similarity threshold and RLS. A user whose chunks are a small share
--     of the table usually got 0-1 rows although exact matches existed, so
--     search-knowledge returned `results: []` and answers were generated
--     without the user's documents.
--
-- Fix
--   1) Drop the broken IVFFlat index. It is not replaced by another ANN index
--      (HNSW etc.): match_knowledge_chunks below never orders the whole table
--      by distance, so an ANN index could not serve it and would only add
--      write cost to embed-chunks. Per-caller candidate sets (own documents +
--      teams the caller belongs to) are small and are reached through
--      idx_knowledge_chunks_document.
--   2) match_knowledge_chunks first materializes the ids of the documents the
--      caller can see, computes the exact cosine distance for their chunks
--      only, and ranks inside that set. The MATERIALIZED CTEs are an
--      optimization fence: the planner cannot turn the ORDER BY back into a
--      global approximate index scan, so recall is exact regardless of what
--      indexes exist on knowledge_chunks.
--   3) match_count is clamped to [0, 50] (NULL -> default 5). LIMIT NULL used
--      to mean "no limit". The search-knowledge edge function already caps
--      requests at 20, so it is unaffected.
--
-- Signature, return columns, SECURITY INVOKER (RLS still applies) and the
-- existing EXECUTE grants are unchanged (CREATE OR REPLACE keeps the ACL).
-- ============================================================================

DROP INDEX IF EXISTS public.idx_knowledge_chunks_embedding;

CREATE OR REPLACE FUNCTION public.match_knowledge_chunks(
  query_embedding vector(1536),
  match_count integer DEFAULT 5,
  similarity_threshold double precision DEFAULT 0.5
)
RETURNS TABLE (
  id uuid,
  document_id uuid,
  chunk_index integer,
  content text,
  similarity double precision
)
LANGUAGE plpgsql
STABLE
AS $$
DECLARE
  -- Upper bound on rows one call may return. Keep >= search-knowledge's
  -- MAX_MATCH_COUNT (20).
  max_match_count CONSTANT integer := 50;
  effective_count integer := LEAST(GREATEST(COALESCE(match_count, 5), 0), max_match_count);
BEGIN
  IF effective_count = 0 OR query_embedding IS NULL THEN
    RETURN;
  END IF;

  RETURN QUERY
  WITH visible_documents AS MATERIALIZED (
    SELECT kd.id AS visible_document_id
    FROM public.knowledge_documents kd
    WHERE
      kd.user_id = auth.uid()
      OR (
        kd.team_id IS NOT NULL
        AND kd.team_id IN (
          SELECT tm.team_id FROM public.team_members tm WHERE tm.user_id = auth.uid()
        )
      )
  ),
  candidates AS MATERIALIZED (
    SELECT
      kc.id AS chunk_id,
      kc.document_id AS chunk_document_id,
      kc.chunk_index AS chunk_position,
      kc.content AS chunk_content,
      (kc.embedding <=> query_embedding)::double precision AS distance
    FROM visible_documents vd
    INNER JOIN public.knowledge_chunks kc ON kc.document_id = vd.visible_document_id
    WHERE kc.embedding IS NOT NULL
  )
  SELECT
    c.chunk_id,
    c.chunk_document_id,
    c.chunk_position,
    c.chunk_content,
    (1 - c.distance)::double precision AS similarity
  FROM candidates c
  WHERE (1 - c.distance) > similarity_threshold
  ORDER BY c.distance, c.chunk_id
  LIMIT effective_count;
END;
$$;