package servers

import (
	"database/sql"
	"fmt"
	"github.com/blang/semver"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/common/log"
	"sync"
)

// Server describes a connection to a Postgresql database, and describes the
// metric maps and overrides in-place for it.
// Also it contains metrics map and query overrides.
type Server struct {
	db     *sql.DB
	labels prometheus.Labels
	master bool

	// Last version used to calculate metric map. If mismatch on scrape,
	// then maps are recalculated.
	lastMapVersion semver.Version
	// Currently active metric map
	metricMap map[string]MetricMapNamespace
	// Currently active query overrides
	queryOverrides map[string]string
	mappingMtx     sync.RWMutex
	// Currently cached metrics
	metricCache map[string]cachedMetrics
	cacheMtx    sync.Mutex
}

// NewServer establishes a new connection using DSN.
func NewServer(dsn string, opts ...ServerOpt) (*Server, error) {
	fingerprint, err := parseFingerprint(dsn)
	if err != nil {
		return nil, err
	}

	db, err := sql.Open("postgres", dsn)
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(1)
	db.SetMaxIdleConns(1)

	log.Infof("Established new database connection to %q.", fingerprint)

	s := &Server{
		db:     db,
		master: false,
		labels: prometheus.Labels{
			serverLabelName: fingerprint,
		},
		metricCache: make(map[string]cachedMetrics),
	}

	for _, opt := range opts {
		opt(s)
	}

	return s, nil
}

// Close disconnects from Postgres.
func (s *Server) Close() error {
	return s.db.Close()
}

// Ping checks connection availability and possibly invalidates the connection if it fails.
func (s *Server) Ping() error {
	if err := s.db.Ping(); err != nil {
		if cerr := s.Close(); cerr != nil {
			log.Errorf("Error while closing non-pinging DB connection to %q: %v", s, cerr)
		}
		return err
	}
	return nil
}

// String returns server's fingerprint.
func (s *Server) String() string {
	return s.labels[serverLabelName]
}

// Scrape loads metrics.
func (s *Server) Scrape(ch chan<- prometheus.Metric, disableSettingsMetrics bool) error {
	s.mappingMtx.RLock()
	defer s.mappingMtx.RUnlock()

	var err error

	if !disableSettingsMetrics && s.master {
		if err = querySettings(ch, s); err != nil {
			err = fmt.Errorf("error retrieving settings: %s", err)
		}
	}

	errMap := queryNamespaceMappings(ch, s)
	if len(errMap) > 0 {
		err = fmt.Errorf("queryNamespaceMappings returned %d errors", len(errMap))
	}

	return err
}

// AddQueries adds queries to the builtinMetricMaps and queryOverrides maps.
// Added queries do not respect version requirements, because it is assumed
// that the user knows what they are doing with their version of postgres.
func (s *Server) AddQueries() {

}