// Package graphsync glues the disk-resident brain markdown documents to
// the relational graph in [graphstore]. It is a tiny seam so that the
// MCP handlers can call one function after every successful write or
// ingest without having to know either the parser or the postgres
// schema.
//
// Every operation is best-effort from the caller's perspective: if the
// graph store is unconfigured or the doc parses to nothing usable, the
// helpers return nil. Real database errors are surfaced so the caller
// can log them.
package graphsync

import (
	"context"
	"fmt"
	"os"
	"path/filepath"

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

// Store is the subset of graphstore.PGStore that graphsync requires.
// Tests can substitute a fake by satisfying this interface.
type Store interface {
	UpsertEntity(ctx context.Context, e graph.Entity) error
	ReplaceEdgesForDoc(ctx context.Context, docPath string, edges []graph.Edge) error
	DeleteByDoc(ctx context.Context, docPath string) error
}

// Compile-time assertion that *graphstore.PGStore satisfies Store.
var _ Store = (*graphstore.PGStore)(nil)

// IndexDoc reads docPath under brainDir and pushes one Entity + its
// outgoing wikilink Edges into store. relPath must be the
// forward-slash path relative to brainDir (the same shape returned by
// api.WriteNote).
//
// nil store is a valid no-op so callers can wire the helper
// unconditionally and let configuration decide whether the graph is
// populated.
func IndexDoc(ctx context.Context, store Store, brainDir, relPath string) error {
	if store == nil {
		return nil
	}
	if relPath == "" {
		return nil
	}
	abs := filepath.Join(brainDir, filepath.FromSlash(relPath))
	content, err := os.ReadFile(abs)
	if err != nil {
		return fmt.Errorf("read %q: %w", relPath, err)
	}
	ent, edges, ok := graph.Extract(relPath, content)
	if !ok {
		return nil
	}
	if err := store.UpsertEntity(ctx, ent); err != nil {
		return fmt.Errorf("upsert entity: %w", err)
	}
	if err := store.ReplaceEdgesForDoc(ctx, relPath, edges); err != nil {
		return fmt.Errorf("replace edges: %w", err)
	}
	return nil
}

// BackfillFromBrainDir walks every markdown file under brainDir/wiki/
// and brainDir/knowledge/, parses each, and upserts the resulting
// Entity + Edges. Existing rows are overwritten; orphan rows for
// already-deleted files are NOT cleaned up — call this only on a
// fresh store, or follow with a separate prune pass.
//
// Intended for one-shot startup runs against a populated brain dir.
// Cost scales linearly with corpus size; ~30 wiki pages plus the
// knowledge corpus is a few hundred ms.
func BackfillFromBrainDir(ctx context.Context, store Store, brainDir string) (indexed int, _ error) {
	if store == nil {
		return 0, nil
	}
	roots := []string{"wiki", "knowledge"}
	for _, root := range roots {
		base := filepath.Join(brainDir, root)
		if _, err := os.Stat(base); os.IsNotExist(err) {
			continue
		}
		err := filepath.WalkDir(base, func(path string, d os.DirEntry, walkErr error) error {
			if walkErr != nil {
				return walkErr
			}
			if d.IsDir() {
				return nil
			}
			if filepath.Ext(path) != ".md" {
				return nil
			}
			rel, relErr := filepath.Rel(brainDir, path)
			if relErr != nil {
				return fmt.Errorf("rel %q: %w", path, relErr)
			}
			rel = filepath.ToSlash(rel)
			if err := IndexDoc(ctx, store, brainDir, rel); err != nil {
				return fmt.Errorf("index %q: %w", rel, err)
			}
			indexed++
			return nil
		})
		if err != nil {
			return indexed, fmt.Errorf("walk %s: %w", root, err)
		}
	}
	return indexed, nil
}