package automc

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/itzg/mc-router/server"
	"github.com/jackc/pgx/v5"
	"github.com/sirupsen/logrus"
)

const (
	notifyChannel = "automc_routes_changed"
	reconnectMin  = 1 * time.Second
	reconnectMax  = 30 * time.Second
)

type route struct {
	name    string
	domain  string
	address string
}

type syncer struct {
	dsn         string
	waker       *wakerConfig
	current     map[string]route
}

func newSyncer(dsn string, w *wakerConfig) *syncer {
	return &syncer{dsn: dsn, waker: w, current: map[string]route{}}
}

func (s *syncer) run(ctx context.Context) {
	backoff := reconnectMin
	for {
		if ctx.Err() != nil {
			return
		}
		err := s.connectAndLoop(ctx)
		if err != nil && !errors.Is(err, context.Canceled) {
			logrus.WithError(err).Warnf("automc pgsync disconnected; reconnecting in %s", backoff)
		}
		select {
		case <-ctx.Done():
			return
		case <-time.After(backoff):
		}
		backoff *= 2
		if backoff > reconnectMax {
			backoff = reconnectMax
		}
	}
}

func (s *syncer) connectAndLoop(ctx context.Context) error {
	conn, err := pgx.Connect(ctx, s.dsn)
	if err != nil {
		return fmt.Errorf("pgx connect: %w", err)
	}
	defer conn.Close(context.Background())

	if _, err := conn.Exec(ctx, "LISTEN "+notifyChannel); err != nil {
		return fmt.Errorf("LISTEN: %w", err)
	}
	logrus.Infof("automc pgsync connected; LISTEN %s", notifyChannel)

	if err := s.refresh(ctx, conn); err != nil {
		return fmt.Errorf("initial refresh: %w", err)
	}

	for {
		if _, err := conn.WaitForNotification(ctx); err != nil {
			return fmt.Errorf("wait notification: %w", err)
		}
		if err := s.refresh(ctx, conn); err != nil {
			return fmt.Errorf("refresh: %w", err)
		}
	}
}

func (s *syncer) refresh(ctx context.Context, conn *pgx.Conn) error {
	rows, err := conn.Query(ctx, `SELECT name, domain, address FROM servers WHERE domain != '' AND address != ''`)
	if err != nil {
		return err
	}
	defer rows.Close()

	desired := map[string]route{}
	for rows.Next() {
		var r route
		if err := rows.Scan(&r.name, &r.domain, &r.address); err != nil {
			return err
		}
		desired[r.domain] = r
	}
	if err := rows.Err(); err != nil {
		return err
	}

	add, del := diff(s.current, desired)
	s.apply(add, del)
	s.current = desired
	return nil
}

func (s *syncer) apply(add []route, del []string) {
	for _, host := range del {
		if server.Routes.DeleteMapping(host) {
			logrus.Infof("automc route -: %s", host)
		}
	}
	for _, r := range add {
		server.Routes.CreateMapping(r.domain, r.address, "", s.waker.wakerFor(r.name), nil, "", "")
		logrus.Infof("automc route +: %s → %s (%s)", r.domain, r.address, r.name)
	}
}

func diff(prev, next map[string]route) (add []route, del []string) {
	for host, r := range next {
		if p, ok := prev[host]; !ok || p.address != r.address || p.name != r.name {
			add = append(add, r)
		}
	}
	for host := range prev {
		if _, ok := next[host]; !ok {
			del = append(del, host)
		}
	}
	return add, del
}