// Package kg implements the knowledge graph pillar — notes, cells, facts,
// and graph edges that connect ideas and reference artifacts.
package kg

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"time"

	"git.wntrmute.dev/kyle/exo/core"
	"git.wntrmute.dev/kyle/exo/db"
)

// NodeType distinguishes notes from artifact links in the graph.
type NodeType string

const (
	NodeTypeNote         NodeType = "note"
	NodeTypeArtifactLink NodeType = "artifact_link"
)

// Node is an entity in the knowledge graph.
type Node struct {
	ID         string
	ParentID   string // parent node ID (empty for root nodes)
	Name       string // human-readable name (C2 wiki style)
	Type       NodeType
	Created    time.Time
	Modified   time.Time
	Children   []string // child node IDs (populated by Get)
	Tags       map[string]bool
	Categories map[string]bool
}

// NewNode creates a Node with a new UUID and current timestamps.
func NewNode(name string, nodeType NodeType) *Node {
	now := time.Now().UTC()
	return &Node{
		ID:         core.NewUUID(),
		Name:       name,
		Type:       nodeType,
		Created:    now,
		Modified:   now,
		Tags:       map[string]bool{},
		Categories: map[string]bool{},
	}
}

// Store persists a Node to the database.
func (n *Node) Store(ctx context.Context, tx *sql.Tx) error {
	parentID := sql.NullString{String: n.ParentID, Valid: n.ParentID != ""}

	_, err := tx.ExecContext(ctx,
		`INSERT INTO nodes (id, parent_id, name, type, created, modified) VALUES (?, ?, ?, ?, ?, ?)`,
		n.ID, parentID, n.Name, string(n.Type), db.ToDBTime(n.Created), db.ToDBTime(n.Modified))
	if err != nil {
		return fmt.Errorf("kg: failed to store node: %w", err)
	}

	// Link tags.
	for tag := range n.Tags {
		var tagID string
		row := tx.QueryRowContext(ctx, `SELECT id FROM tags WHERE tag=?`, tag)
		if err := row.Scan(&tagID); err != nil {
			return fmt.Errorf("kg: unknown tag %q: %w", tag, err)
		}
		_, err := tx.ExecContext(ctx,
			`INSERT INTO node_tags (node_id, tag_id) VALUES (?, ?)`, n.ID, tagID)
		if err != nil {
			return fmt.Errorf("kg: failed to link node tag: %w", err)
		}
	}

	// Link categories.
	for cat := range n.Categories {
		var catID string
		row := tx.QueryRowContext(ctx, `SELECT id FROM categories WHERE category=?`, cat)
		if err := row.Scan(&catID); err != nil {
			return fmt.Errorf("kg: unknown category %q: %w", cat, err)
		}
		_, err := tx.ExecContext(ctx,
			`INSERT INTO node_categories (node_id, category_id) VALUES (?, ?)`, n.ID, catID)
		if err != nil {
			return fmt.Errorf("kg: failed to link node category: %w", err)
		}
	}

	return nil
}

// Get retrieves a Node by its ID, including children, tags, and categories.
func (n *Node) Get(ctx context.Context, tx *sql.Tx) error {
	if n.ID == "" {
		return fmt.Errorf("kg: node missing ID: %w", core.ErrNoID)
	}

	var parentID sql.NullString
	var created, modified, nodeType string
	row := tx.QueryRowContext(ctx,
		`SELECT parent_id, name, type, created, modified FROM nodes WHERE id=?`, n.ID)
	if err := row.Scan(&parentID, &n.Name, &nodeType, &created, &modified); err != nil {
		return fmt.Errorf("kg: failed to retrieve node: %w", err)
	}
	n.Type = NodeType(nodeType)
	if parentID.Valid {
		n.ParentID = parentID.String
	}

	var err error
	n.Created, err = db.FromDBTime(created, nil)
	if err != nil {
		return err
	}
	n.Modified, err = db.FromDBTime(modified, nil)
	if err != nil {
		return err
	}

	// Load children.
	n.Children = nil
	childRows, err := tx.QueryContext(ctx,
		`SELECT id FROM nodes WHERE parent_id=?`, n.ID)
	if err != nil {
		return fmt.Errorf("kg: failed to load node children: %w", err)
	}
	defer func() { _ = childRows.Close() }()
	for childRows.Next() {
		var childID string
		if err := childRows.Scan(&childID); err != nil {
			return err
		}
		n.Children = append(n.Children, childID)
	}
	if err := childRows.Err(); err != nil {
		return err
	}

	// Load tags.
	n.Tags = map[string]bool{}
	tagRows, err := tx.QueryContext(ctx,
		`SELECT t.tag FROM node_tags nt JOIN tags t ON nt.tag_id = t.id WHERE nt.node_id=?`, n.ID)
	if err != nil {
		return fmt.Errorf("kg: failed to load node tags: %w", err)
	}
	defer func() { _ = tagRows.Close() }()
	for tagRows.Next() {
		var tag string
		if err := tagRows.Scan(&tag); err != nil {
			return err
		}
		n.Tags[tag] = true
	}
	if err := tagRows.Err(); err != nil {
		return err
	}

	// Load categories.
	n.Categories = map[string]bool{}
	catRows, err := tx.QueryContext(ctx,
		`SELECT c.category FROM node_categories nc JOIN categories c ON nc.category_id = c.id WHERE nc.node_id=?`, n.ID)
	if err != nil {
		return fmt.Errorf("kg: failed to load node categories: %w", err)
	}
	defer func() { _ = catRows.Close() }()
	for catRows.Next() {
		var cat string
		if err := catRows.Scan(&cat); err != nil {
			return err
		}
		n.Categories[cat] = true
	}
	return catRows.Err()
}

// GetNodeByName retrieves a Node by its name.
func GetNodeByName(ctx context.Context, tx *sql.Tx, name string) (*Node, error) {
	var id string
	row := tx.QueryRowContext(ctx, `SELECT id FROM nodes WHERE name=?`, name)
	if err := row.Scan(&id); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, nil
		}
		return nil, fmt.Errorf("kg: failed to look up node by name: %w", err)
	}
	n := &Node{ID: id}
	if err := n.Get(ctx, tx); err != nil {
		return nil, err
	}
	return n, nil
}