// Package store persists webhook telemetry events from the ExploreDNS API
// server into MySQL or SQLite through a shared database/sql layer.
package store

import (
	"context"
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"time"

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

// Traversal status values, mirroring the job statuses in web/api.
const (
	StatusRunning  = "running"
	StatusComplete = "complete"
	StatusError    = "error"
)

// schemaVersion is recorded in the schema_version table on first open so
// future releases can detect and migrate older layouts.
const schemaVersion = 1

// dbTimeLayout is the canonical datetime encoding: fixed-width so sqlite
// TEXT comparisons order chronologically, and a valid MySQL DATETIME(6)
// literal.
const dbTimeLayout = "2006-01-02 15:04:05.000000"

// Store persists traversal telemetry events.
type Store struct {
	db *sql.DB
	d  dialect
}

// OpenSQLite opens (creating if needed) a SQLite-backed store at path,
// creating parent directories first.
func OpenSQLite(path string) (*Store, error) {
	if dir := filepath.Dir(path); dir != "." && dir != "" {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return nil, fmt.Errorf("create sqlite directory: %w", err)
		}
	}
	db, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, fmt.Errorf("open sqlite %s: %w", path, err)
	}
	// A single connection serialises writers so concurrent ingests never
	// see SQLITE_BUSY.
	db.SetMaxOpenConns(1)
	return open(db, sqliteDialect{})
}

// OpenMySQL opens a MySQL-backed store using a go-sql-driver DSN
// (user:pass@tcp(host:port)/dbname).
func OpenMySQL(dsn string) (*Store, error) {
	if _, err := mysql.ParseDSN(dsn); err != nil {
		return nil, fmt.Errorf("parse mysql dsn: %w", err)
	}
	db, err := sql.Open("mysql", dsn)
	if err != nil {
		return nil, fmt.Errorf("open mysql: %w", err)
	}
	return open(db, mysqlDialect{})
}

// RedactMySQLDSN returns dsn with any password replaced, safe for logging.
func RedactMySQLDSN(dsn string) string {
	cfg, err := mysql.ParseDSN(dsn)
	if err != nil {
		return "(unparsable DSN)"
	}
	if cfg.Passwd != "" {
		cfg.Passwd = "xxxxx"
	}
	return cfg.FormatDSN()
}

func open(db *sql.DB, d dialect) (*Store, error) {
	s := &Store{db: db, d: d}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	if err := s.init(ctx); err != nil {
		db.Close()
		return nil, fmt.Errorf("init %s schema: %w", d.name(), err)
	}
	return s, nil
}

// Backend names the database backend ("sqlite" or "mysql").
func (s *Store) Backend() string { return s.d.name() }

// Close releases the underlying database handle.
func (s *Store) Close() error { return s.db.Close() }

// init creates the schema if missing and stamps schema_version.
func (s *Store) init(ctx context.Context) error {
	dt := s.d.datetimeType()
	stmts := []string{
		`CREATE TABLE IF NOT EXISTS schema_version (version INTEGER NOT NULL)`,
		fmt.Sprintf(`CREATE TABLE IF NOT EXISTS traversals (
			id VARCHAR(64) NOT NULL PRIMARY KEY,
			domain VARCHAR(255) NOT NULL DEFAULT '',
			query_type VARCHAR(16) NOT NULL DEFAULT '',
			all_roots BOOLEAN NOT NULL DEFAULT 0,
			client_ip VARCHAR(64) NOT NULL DEFAULT '',
			started_at %s NULL,
			done_at %s NULL,
			duration_ms BIGINT NULL,
			status VARCHAR(16) NOT NULL DEFAULT '',
			error TEXT NULL,
			result_count INT NULL,
			summary TEXT NULL,
			first_seen %s NOT NULL,
			last_seen %s NOT NULL
		)`, dt, dt, dt, dt),
	}
	for _, q := range stmts {
		if _, err := s.db.ExecContext(ctx, q); err != nil {
			return err
		}
	}
	for _, idx := range [][2]string{
		{"idx_traversals_started_at", "started_at"},
		{"idx_traversals_domain", "domain"},
		{"idx_traversals_client_ip", "client_ip"},
		{"idx_traversals_status", "status"},
	} {
		if err := s.d.createIndex(ctx, s.db, idx[0], "traversals", idx[1]); err != nil {
			return err
		}
	}
	// Stamp the version on first creation only. Checked in Go because
	// MySQL and sqlite disagree on FROM-less SELECT ... WHERE syntax.
	var n int
	if err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM schema_version`).Scan(&n); err != nil {
		return err
	}
	if n == 0 {
		_, err := s.db.ExecContext(ctx, `INSERT INTO schema_version (version) VALUES (?)`, schemaVersion)
		return err
	}
	return nil
}

// RecordStart upserts a "start" event. Duplicate deliveries refresh the
// request attributes but never touch status or completion fields, so a
// retried start arriving after the complete event cannot clobber the
// terminal state.
func (s *Store) RecordStart(ctx context.Context, ev StartEvent) error {
	now := fmtTime(time.Now())
	q := s.d.upsert(`INSERT INTO traversals
		(id, domain, query_type, all_roots, client_ip, started_at, status, first_seen, last_seen)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
		[]string{"domain", "query_type", "all_roots", "client_ip", "started_at", "last_seen"})
	_, err := s.db.ExecContext(ctx, q,
		ev.ID, ev.Domain, ev.QueryType, ev.AllRoots, ev.ClientIP,
		dbTime(ev.StartedAt), StatusRunning, now, now)
	return err
}

// RecordComplete upserts a "complete" event. It creates the row when the
// start event has not arrived (out-of-order delivery) and overwrites the
// completion fields on duplicates; all_roots and first_seen are start-only
// and left untouched.
func (s *Store) RecordComplete(ctx context.Context, ev CompleteEvent) error {
	now := fmtTime(time.Now())
	q := s.d.upsert(`INSERT INTO traversals
		(id, domain, query_type, client_ip, started_at, done_at, duration_ms,
		 status, error, result_count, summary, first_seen, last_seen)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
		[]string{"domain", "query_type", "client_ip", "started_at", "done_at",
			"duration_ms", "status", "error", "result_count", "summary", "last_seen"})
	var summary any
	if len(ev.Summary) > 0 {
		summary = string(ev.Summary)
	}
	_, err := s.db.ExecContext(ctx, q,
		ev.ID, ev.Domain, ev.QueryType, ev.ClientIP,
		dbTime(ev.StartedAt), dbTime(ev.DoneAt), ev.DurationMS,
		ev.Status, nullIfEmpty(ev.Error), ev.ResultCount, summary, now, now)
	return err
}

// fmtTime encodes t for storage.
func fmtTime(t time.Time) string { return t.UTC().Format(dbTimeLayout) }

// dbTime encodes t for a nullable datetime column; zero times become NULL
// (MySQL DATETIME cannot hold year 1).
func dbTime(t time.Time) any {
	if t.IsZero() {
		return nil
	}
	return fmtTime(t)
}

func nullIfEmpty(s string) any {
	if s == "" {
		return nil
	}
	return s
}

// parseDBTime decodes a stored datetime. Besides the canonical layout it
// accepts second precision and RFC 3339 in case the MySQL DSN enables
// parseTime (database/sql then hands strings back in RFC 3339).
func parseDBTime(s string) (time.Time, error) {
	for _, layout := range []string{dbTimeLayout, "2006-01-02 15:04:05", time.RFC3339Nano} {
		if t, err := time.ParseInLocation(layout, s, time.UTC); err == nil {
			return t, nil
		}
	}
	return time.Time{}, fmt.Errorf("unrecognised datetime %q", s)
}