package db

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"sort"
	"strings"

	_ "modernc.org/sqlite"
)

//go:embed migrations/*.sql
var migrationsFS embed.FS

type DB struct {
	conn *sql.DB
}

func Open(path string) (*DB, error) {
	conn, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}
	if _, err := conn.Exec(`PRAGMA foreign_keys = ON`); err != nil {
		_ = conn.Close()
		return nil, fmt.Errorf("enable foreign keys: %w", err)
	}
	return &DB{conn: conn}, nil
}

func (d *DB) Close() error {
	return d.conn.Close()
}

func (d *DB) Conn() *sql.DB {
	return d.conn
}

func (d *DB) Migrate() error {
	if err := d.createMigrationsTable(); err != nil {
		return fmt.Errorf("create migrations table: %w", err)
	}

	entries, err := fs.ReadDir(migrationsFS, "migrations")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}
	sort.Slice(entries, func(i, j int) bool {
		return entries[i].Name() < entries[j].Name()
	})

	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}
		name := entry.Name()

		applied, err := d.isMigrationApplied(name)
		if err != nil {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		if applied {
			continue
		}

		content, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}

		if err := d.runMigration(name, string(content)); err != nil {
			return fmt.Errorf("apply migration %s: %w", name, err)
		}

		if name == "0002_nfs_structured.sql" {
			if err := d.PopulateLegacyFSIDs(); err != nil {
				return fmt.Errorf("populate legacy fsids: %w", err)
			}
		}
	}
	return nil
}

func (d *DB) createMigrationsTable() error {
	_, err := d.conn.Exec(`
		CREATE TABLE IF NOT EXISTS schema_migrations (
			name TEXT PRIMARY KEY,
			applied_at TEXT NOT NULL DEFAULT (datetime('now'))
		)
	`)
	return err
}

func (d *DB) isMigrationApplied(name string) (bool, error) {
	var count int
	err := d.conn.QueryRow(
		"SELECT COUNT(*) FROM schema_migrations WHERE name = ?",
		name,
	).Scan(&count)
	if err != nil {
		return false, err
	}
	return count > 0, nil
}

func (d *DB) runMigration(name, content string) error {
	if _, err := d.conn.Exec(content); err != nil {
		if isIgnorableMigrationError(err) {
			// Schema is already in target state (e.g. columns already added
			// by a previous partial run). Continue to record the migration.
		} else {
			return fmt.Errorf("execute: %w", err)
		}
	}

	if _, err := d.conn.Exec(
		"INSERT INTO schema_migrations (name) VALUES (?)",
		name,
	); err != nil {
		return fmt.Errorf("record migration: %w", err)
	}
	return nil
}

func isIgnorableMigrationError(err error) bool {
	if err == nil {
		return false
	}
	msg := strings.ToLower(err.Error())
	return strings.Contains(msg, "duplicate column name") ||
		strings.Contains(msg, "already exists")
}