// Package graphstore stores the brain knowledge graph (entities +
// directed edges) in PostgreSQL on the shared postgres18 instance,
// alongside the pgvector embeddings in [vectorstore].
//
// Schema (created idempotently by Init):
//
//	brain_entities(slug PK, type, wing, hall, doc_path, title, updated_at)
//	brain_edges(id PK, src_slug FK, dst_slug, edge_type, src_doc, src_line,
//	            weight, updated_at)
//
// Edges fan-out from a source document; calling [PGStore.ReplaceEdgesForDoc]
// replaces every edge previously emitted from that document so re-ingest is
// idempotent without bookkeeping.
//
// All slug strings are stored verbatim — callers are expected to canonicalise
// before persisting. Dst slugs may reference entities that don't yet exist
// (dangling edges); resolution is deferred to query time so ingestion order
// doesn't matter.
package graphstore

import (
	"context"
	"errors"
	"fmt"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"github.com/mathiasbq/hyperguild/ingestion/internal/graph"
)

// PGStore is the postgres-backed brain knowledge-graph store. Construct
// with New + call Init once to create tables and indexes. Use Close to
// release the pool.
type PGStore struct {
	pool *pgxpool.Pool
}

// New opens a pgxpool against dsn and pings to verify connectivity. The
// caller owns the resulting PGStore and must invoke Close.
func New(ctx context.Context, dsn string) (*PGStore, error) {
	pool, err := pgxpool.New(ctx, dsn)
	if err != nil {
		return nil, fmt.Errorf("pgxpool: %w", err)
	}
	if err := pool.Ping(ctx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("ping: %w", err)
	}
	return &PGStore{pool: pool}, nil
}

// Close releases the underlying connection pool.
func (s *PGStore) Close() {
	if s.pool != nil {
		s.pool.Close()
	}
}

// Init creates brain_entities + brain_edges tables and their indexes if
// they don't yet exist. Safe to call on every startup. No-op when the
// schema already matches.
func (s *PGStore) Init(ctx context.Context) error {
	const ddl = `
CREATE TABLE IF NOT EXISTS brain_entities (
    slug       TEXT PRIMARY KEY,
    type       TEXT NOT NULL DEFAULT 'knowledge',
    wing       TEXT NOT NULL DEFAULT '',
    hall       TEXT NOT NULL DEFAULT '',
    doc_path   TEXT NOT NULL,
    title      TEXT NOT NULL DEFAULT '',
    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
CREATE INDEX IF NOT EXISTS brain_entities_wing_idx
    ON brain_entities (wing) WHERE wing <> '';
CREATE INDEX IF NOT EXISTS brain_entities_type_idx
    ON brain_entities (type);

CREATE TABLE IF NOT EXISTS brain_edges (
    id         BIGSERIAL PRIMARY KEY,
    src_slug   TEXT NOT NULL,
    dst_slug   TEXT NOT NULL,
    edge_type  TEXT NOT NULL DEFAULT 'wikilink',
    src_doc    TEXT NOT NULL,
    src_line   INTEGER NOT NULL DEFAULT 0,
    weight     REAL NOT NULL DEFAULT 1.0,
    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
);
CREATE INDEX IF NOT EXISTS brain_edges_src_idx
    ON brain_edges (src_slug, edge_type);
CREATE INDEX IF NOT EXISTS brain_edges_dst_idx
    ON brain_edges (dst_slug, edge_type);
CREATE INDEX IF NOT EXISTS brain_edges_src_doc_idx
    ON brain_edges (src_doc);
`
	_, err := s.pool.Exec(ctx, ddl)
	return err
}

// UpsertEntity inserts or updates one entity by slug.
func (s *PGStore) UpsertEntity(ctx context.Context, e graph.Entity) error {
	if e.Slug == "" {
		return errors.New("entity slug is required")
	}
	if e.Type == "" {
		e.Type = "knowledge"
	}
	_, err := s.pool.Exec(ctx, `
        INSERT INTO brain_entities (slug, type, wing, hall, doc_path, title, updated_at)
        VALUES ($1, $2, $3, $4, $5, $6, now())
        ON CONFLICT (slug) DO UPDATE
        SET type       = EXCLUDED.type,
            wing       = EXCLUDED.wing,
            hall       = EXCLUDED.hall,
            doc_path   = EXCLUDED.doc_path,
            title      = EXCLUDED.title,
            updated_at = now()
    `, e.Slug, e.Type, e.Wing, e.Hall, e.DocPath, e.Title)
	if err != nil {
		return fmt.Errorf("upsert entity %q: %w", e.Slug, err)
	}
	return nil
}

// ReplaceEdgesForDoc deletes every edge previously emitted from docPath
// and inserts the new set in one transaction. Caller should pass the
// complete edge set for the doc — partial updates are not supported.
func (s *PGStore) ReplaceEdgesForDoc(ctx context.Context, docPath string, edges []graph.Edge) error {
	if docPath == "" {
		return errors.New("doc path is required")
	}
	tx, err := s.pool.BeginTx(ctx, pgx.TxOptions{})
	if err != nil {
		return fmt.Errorf("begin: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	if _, err := tx.Exec(ctx, `DELETE FROM brain_edges WHERE src_doc = $1`, docPath); err != nil {
		return fmt.Errorf("delete prior edges for %q: %w", docPath, err)
	}
	for _, e := range edges {
		if e.SrcSlug == "" || e.DstSlug == "" {
			continue
		}
		if _, err := tx.Exec(ctx, `
            INSERT INTO brain_edges (src_slug, dst_slug, edge_type, src_doc, src_line, weight)
            VALUES ($1, $2, $3, $4, $5, 1.0)
        `, e.SrcSlug, e.DstSlug, e.EdgeType, e.SrcDoc, e.SrcLine); err != nil {
			return fmt.Errorf("insert edge %s->%s: %w", e.SrcSlug, e.DstSlug, err)
		}
	}
	if err := tx.Commit(ctx); err != nil {
		return fmt.Errorf("commit: %w", err)
	}
	return nil
}

// DeleteByDoc removes the entity at docPath and every edge it sourced.
// Use when a wiki page is deleted on disk.
func (s *PGStore) DeleteByDoc(ctx context.Context, docPath string) error {
	if docPath == "" {
		return errors.New("doc path is required")
	}
	tx, err := s.pool.BeginTx(ctx, pgx.TxOptions{})
	if err != nil {
		return fmt.Errorf("begin: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	if _, err := tx.Exec(ctx, `DELETE FROM brain_edges WHERE src_doc = $1`, docPath); err != nil {
		return fmt.Errorf("delete edges: %w", err)
	}
	if _, err := tx.Exec(ctx, `DELETE FROM brain_entities WHERE doc_path = $1`, docPath); err != nil {
		return fmt.Errorf("delete entity: %w", err)
	}
	return tx.Commit(ctx)
}

// Neighbor is one row in a Neighbors / Subgraph response.
type Neighbor struct {
	Slug     string
	Type     string
	Wing     string
	Hall     string
	DocPath  string
	Title    string
	EdgeType string
	Distance int // hop count from origin; 1 for direct neighbors
}

// Neighbors returns the direct (1-hop) outgoing neighbours of slug.
// edgeType filters by relationship kind; "" returns all kinds.
// limit defaults to 25 when <= 0.
func (s *PGStore) Neighbors(ctx context.Context, slug, edgeType string, limit int) ([]Neighbor, error) {
	if slug == "" {
		return nil, errors.New("slug is required")
	}
	if limit <= 0 {
		limit = 25
	}
	q := `
SELECT e.dst_slug, COALESCE(t.type,''), COALESCE(t.wing,''), COALESCE(t.hall,''),
       COALESCE(t.doc_path,''), COALESCE(t.title,''), e.edge_type, 1
FROM brain_edges e
LEFT JOIN brain_entities t ON t.slug = e.dst_slug
WHERE e.src_slug = $1
  AND ($2 = '' OR e.edge_type = $2)
ORDER BY e.updated_at DESC
LIMIT $3
`
	rows, err := s.pool.Query(ctx, q, slug, edgeType, limit)
	if err != nil {
		return nil, fmt.Errorf("query neighbors: %w", err)
	}
	defer rows.Close()
	return scanNeighbors(rows)
}

// Subgraph returns every distinct slug reachable from origin within
// depth outgoing hops, annotated with the shortest hop distance. The
// origin itself is omitted. depth defaults to 2 when <= 0; values
// above 6 are clamped to 6 to bound traversal cost.
func (s *PGStore) Subgraph(ctx context.Context, origin string, depth int) ([]Neighbor, error) {
	if origin == "" {
		return nil, errors.New("origin slug is required")
	}
	if depth <= 0 {
		depth = 2
	}
	if depth > 6 {
		depth = 6
	}
	q := `
WITH RECURSIVE walk(slug, edge_type, distance) AS (
    SELECT e.dst_slug, e.edge_type, 1
    FROM brain_edges e
    WHERE e.src_slug = $1
  UNION
    SELECT e.dst_slug, e.edge_type, w.distance + 1
    FROM walk w
    JOIN brain_edges e ON e.src_slug = w.slug
    WHERE w.distance < $2
)
SELECT w.slug, COALESCE(t.type,''), COALESCE(t.wing,''), COALESCE(t.hall,''),
       COALESCE(t.doc_path,''), COALESCE(t.title,''), w.edge_type, MIN(w.distance)
FROM walk w
LEFT JOIN brain_entities t ON t.slug = w.slug
WHERE w.slug <> $1
GROUP BY w.slug, t.type, t.wing, t.hall, t.doc_path, t.title, w.edge_type
ORDER BY MIN(w.distance), w.slug
`
	rows, err := s.pool.Query(ctx, q, origin, depth)
	if err != nil {
		return nil, fmt.Errorf("query subgraph: %w", err)
	}
	defer rows.Close()
	return scanNeighbors(rows)
}

// PathStep is one hop in a Path response.
type PathStep struct {
	FromSlug string
	ToSlug   string
	EdgeType string
}

// Path returns the shortest directed path from src to dst within
// maxDepth hops, as an ordered list of edges. Empty slice means no
// path exists. maxDepth defaults to 4 when <= 0; values above 8 are
// clamped to 8.
func (s *PGStore) Path(ctx context.Context, src, dst string, maxDepth int) ([]PathStep, error) {
	if src == "" || dst == "" {
		return nil, errors.New("src and dst are required")
	}
	if maxDepth <= 0 {
		maxDepth = 4
	}
	if maxDepth > 8 {
		maxDepth = 8
	}
	q := `
WITH RECURSIVE walk(cur, path_slugs, path_edges, distance) AS (
    SELECT e.dst_slug,
           ARRAY[e.src_slug, e.dst_slug]::TEXT[],
           ARRAY[e.edge_type]::TEXT[],
           1
    FROM brain_edges e
    WHERE e.src_slug = $1
  UNION ALL
    SELECT e.dst_slug,
           w.path_slugs || e.dst_slug,
           w.path_edges || e.edge_type,
           w.distance + 1
    FROM walk w
    JOIN brain_edges e ON e.src_slug = w.cur
    WHERE w.distance < $3
      AND NOT (e.dst_slug = ANY(w.path_slugs))
)
SELECT path_slugs, path_edges
FROM walk
WHERE cur = $2
ORDER BY distance ASC
LIMIT 1
`
	row := s.pool.QueryRow(ctx, q, src, dst, maxDepth)
	var (
		slugs []string
		kinds []string
	)
	if err := row.Scan(&slugs, &kinds); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		}
		return nil, fmt.Errorf("scan path: %w", err)
	}
	if len(slugs) < 2 || len(kinds) == 0 {
		return nil, nil
	}
	steps := make([]PathStep, 0, len(kinds))
	for i := 0; i < len(kinds) && i+1 < len(slugs); i++ {
		steps = append(steps, PathStep{
			FromSlug: slugs[i],
			ToSlug:   slugs[i+1],
			EdgeType: kinds[i],
		})
	}
	return steps, nil
}

// CountEdges is a debug helper — returns the total edges currently stored.
// Used by tests and by the volume-gate diagnostic.
func (s *PGStore) CountEdges(ctx context.Context) (int64, error) {
	var n int64
	err := s.pool.QueryRow(ctx, `SELECT count(*) FROM brain_edges`).Scan(&n)
	return n, err
}

func scanNeighbors(rows pgx.Rows) ([]Neighbor, error) {
	var out []Neighbor
	for rows.Next() {
		var n Neighbor
		if err := rows.Scan(
			&n.Slug, &n.Type, &n.Wing, &n.Hall,
			&n.DocPath, &n.Title, &n.EdgeType, &n.Distance,
		); err != nil {
			return nil, fmt.Errorf("scan: %w", err)
		}
		out = append(out, n)
	}
	return out, rows.Err()
}