// Package appdb stores application-owned state outside PowerDNS.
package appdb

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

	_ "github.com/go-sql-driver/mysql"
)

// ErrNotFound indicates that a requested database record does not exist.
var ErrNotFound = errors.New("not found")

// DynamicRecord describes an RRset with dynamic DNS updates enabled.
type DynamicRecord struct {
	ZoneID    string
	Name      string
	Type      string
	TTL       uint32
	TokenHash string
	Enabled   bool
}

// MySQLStore persists application state in MySQL.
type MySQLStore struct {
	db *sql.DB
}

// NewMySQLStore opens a MySQL-backed application store.
func NewMySQLStore(dsn string) (*MySQLStore, error) {
	db, err := sql.Open("mysql", strings.TrimSpace(dsn))
	if err != nil {
		return nil, fmt.Errorf("open mysql database: %w", err)
	}
	return &MySQLStore{db: db}, nil
}

// Close releases the underlying database connection pool.
func (s *MySQLStore) Close() error {
	return s.db.Close()
}

// Ping verifies that MySQL is reachable.
func (s *MySQLStore) Ping(ctx context.Context) error {
	if err := s.db.PingContext(ctx); err != nil {
		return fmt.Errorf("ping mysql database: %w", err)
	}
	return nil
}

// EnsureSchema creates required application tables when they do not exist.
func (s *MySQLStore) EnsureSchema(ctx context.Context) error {
	const query = `
CREATE TABLE IF NOT EXISTS dynamic_records (
	id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
	zone_id VARCHAR(255) NOT NULL,
	name VARCHAR(255) NOT NULL,
	type VARCHAR(10) NOT NULL,
	ttl INT UNSIGNED NOT NULL,
	token_hash CHAR(64) NOT NULL,
	enabled BOOLEAN NOT NULL DEFAULT TRUE,
	created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
	updated_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
	PRIMARY KEY (id),
	UNIQUE KEY uniq_dynamic_record (zone_id, name, type),
	KEY idx_dynamic_name_token (name, token_hash)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci`
	if _, err := s.db.ExecContext(ctx, query); err != nil {
		return fmt.Errorf("ensure dynamic_records schema: %w", err)
	}
	return nil
}

// ListDynamicRecords returns enabled dynamic DNS records for a zone.
func (s *MySQLStore) ListDynamicRecords(ctx context.Context, zoneID string) ([]DynamicRecord, error) {
	const query = `
SELECT zone_id, name, type, ttl, token_hash, enabled
FROM dynamic_records
WHERE zone_id = ? AND enabled = TRUE`
	rows, err := s.db.QueryContext(ctx, query, zoneID)
	if err != nil {
		return nil, fmt.Errorf("list dynamic records: %w", err)
	}
	defer rows.Close()

	records := make([]DynamicRecord, 0)
	for rows.Next() {
		record, err := scanDynamicRecord(rows)
		if err != nil {
			return nil, err
		}
		records = append(records, record)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("iterate dynamic records: %w", err)
	}
	return records, nil
}

// FindDynamicRecordByNameAndTokenHash returns the enabled record matching name and token hash.
func (s *MySQLStore) FindDynamicRecordByNameAndTokenHash(ctx context.Context, name, tokenHash string) (DynamicRecord, error) {
	const query = `
SELECT zone_id, name, type, ttl, token_hash, enabled
FROM dynamic_records
WHERE name = ? AND token_hash = ? AND enabled = TRUE`
	row := s.db.QueryRowContext(ctx, query, name, tokenHash)
	record, err := scanDynamicRecord(row)
	if err != nil {
		return DynamicRecord{}, err
	}
	return record, nil
}

// GetDynamicRecord returns an enabled dynamic DNS record by identity.
func (s *MySQLStore) GetDynamicRecord(ctx context.Context, zoneID, name, recordType string) (DynamicRecord, error) {
	const query = `
SELECT zone_id, name, type, ttl, token_hash, enabled
FROM dynamic_records
WHERE zone_id = ? AND name = ? AND type = ? AND enabled = TRUE`
	row := s.db.QueryRowContext(ctx, query, zoneID, name, recordType)
	record, err := scanDynamicRecord(row)
	if err != nil {
		return DynamicRecord{}, err
	}
	return record, nil
}

// UpsertDynamicRecord enables dynamic DNS for a record and stores its token hash.
func (s *MySQLStore) UpsertDynamicRecord(ctx context.Context, record DynamicRecord) error {
	const query = `
INSERT INTO dynamic_records (zone_id, name, type, ttl, token_hash, enabled)
VALUES (?, ?, ?, ?, ?, TRUE)
ON DUPLICATE KEY UPDATE
	ttl = VALUES(ttl),
	token_hash = VALUES(token_hash),
	enabled = TRUE`
	if _, err := s.db.ExecContext(ctx, query, record.ZoneID, record.Name, record.Type, record.TTL, record.TokenHash); err != nil {
		return fmt.Errorf("upsert dynamic record: %w", err)
	}
	return nil
}

// DisableDynamicRecord disables dynamic DNS for a record.
func (s *MySQLStore) DisableDynamicRecord(ctx context.Context, zoneID, name, recordType string) error {
	const query = `
UPDATE dynamic_records
SET enabled = FALSE
WHERE zone_id = ? AND name = ? AND type = ?`
	if _, err := s.db.ExecContext(ctx, query, zoneID, name, recordType); err != nil {
		return fmt.Errorf("disable dynamic record: %w", err)
	}
	return nil
}

type dynamicScanner interface {
	Scan(...any) error
}

func scanDynamicRecord(scanner dynamicScanner) (DynamicRecord, error) {
	var record DynamicRecord
	var ttl uint64
	if err := scanner.Scan(&record.ZoneID, &record.Name, &record.Type, &ttl, &record.TokenHash, &record.Enabled); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return DynamicRecord{}, ErrNotFound
		}
		return DynamicRecord{}, fmt.Errorf("scan dynamic record: %w", err)
	}
	record.TTL = uint32(ttl)
	return record, nil
}