// Package server serves RouteWatch's web pages and JSON API:
//   - the home page, the status figures and the health check
//   - the AS, prefix and prefix length pages, and the JSON answers behind them
//   - the IP lookups
//   - the AS name search
//
// Every route it shows comes from the routing table in memory. AS names,
// WHOIS details and the times a prefix and an AS were first seen come from
// the database.
package server

import (
	"context"
	"errors"
	"fmt"
	"net"
	"net/http"
	"net/netip"
	"strconv"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/blocklist"
	"git.eeqj.de/sneak/routewatch/internal/config"
	"git.eeqj.de/sneak/routewatch/internal/database"
	"git.eeqj.de/sneak/routewatch/internal/logger"
	"git.eeqj.de/sneak/routewatch/internal/routetable"
	"git.eeqj.de/sneak/routewatch/internal/streamer"
	"github.com/go-chi/chi/v5"
)

// ASNFetcherStats contains WHOIS fetcher statistics.
type ASNFetcherStats struct {
	SuccessesLastHour int
	ErrorsLastHour    int
	CurrentInterval   time.Duration
	ConsecutiveFails  int
}

// ASNFetcher is an interface for queuing ASN WHOIS lookups.
type ASNFetcher interface {
	QueueImmediate(asn int)
	GetStats() ASNFetcherStats
}

// Blocklists tells which public blocklists list an address, from copies it
// keeps in memory, as *blocklist.Blocklists does.
type Blocklists interface {
	Lookup(addr netip.Addr) []blocklist.Listing
	ShortestInterval() time.Duration
}

// dnsResolver looks up the addresses of host names and the names of addresses
// in DNS, as *net.Resolver does.
type dnsResolver interface {
	LookupHost(ctx context.Context, host string) ([]string, error)
	LookupAddr(ctx context.Context, addr string) ([]string, error)
}

// Server provides HTTP endpoints for status monitoring
type Server struct {
	router     *chi.Mux
	db         database.Store
	table      *routetable.Table
	streamer   *streamer.Streamer
	logger     *logger.Logger
	port       int
	srv        *http.Server
	asnFetcher ASNFetcher
	blocklists Blocklists

	// trustedProxies are the reverse proxies whose X-Forwarded-For header
	// RealIPMiddleware believes
	trustedProxies []netip.Prefix

	// resolver makes the IP lookup's DNS lookups: net.DefaultResolver, or a
	// fake in tests
	resolver dnsResolver
}

// New creates a new HTTP server that reads routes from table, the routing
// table that the prefix handler keeps current.
func New(
	db database.Store,
	table *routetable.Table,
	streamer *streamer.Streamer,
	logger *logger.Logger,
	cfg *config.Config,
) *Server {
	s := &Server{
		db:             db,
		table:          table,
		streamer:       streamer,
		logger:         logger,
		port:           cfg.Port,
		trustedProxies: cfg.TrustedProxies,
		resolver:       net.DefaultResolver,
	}

	s.setupRoutes()

	return s
}

// Start listens on the configured port and serves HTTP in the background.
// It returns an error if it cannot listen, for example because the port is
// already in use. ctx bounds only opening the port, not serving.
func (s *Server) Start(ctx context.Context) error {
	const (
		network           = "tcp"
		readHeaderTimeout = 40 * time.Second
		readTimeout       = 60 * time.Second
		writeTimeout      = 60 * time.Second
		idleTimeout       = 120 * time.Second
	)

	s.srv = &http.Server{
		Addr:              ":" + strconv.Itoa(s.port),
		Handler:           s.router,
		ReadHeaderTimeout: readHeaderTimeout,
		ReadTimeout:       readTimeout,
		WriteTimeout:      writeTimeout,
		IdleTimeout:       idleTimeout,
	}

	s.logger.Info("Starting HTTP server", "port", s.port, "addr", s.srv.Addr)

	var listenConfig net.ListenConfig

	listener, err := listenConfig.Listen(ctx, network, s.srv.Addr)
	if err != nil {
		return fmt.Errorf("starting HTTP server: %w", err)
	}

	s.logger.Info("HTTP server listening", "addr", listener.Addr().String())

	go func() {
		err := s.srv.Serve(listener)
		if err != nil && !errors.Is(err, http.ErrServerClosed) {
			s.logger.Error("HTTP server error", "error", err)
		}
	}()

	return nil
}

// Stop stops the HTTP server. It waits, until ctx ends, for the requests in
// progress to finish, and then closes the connections of those still running
// and returns ctx's error.
func (s *Server) Stop(ctx context.Context) error {
	if s.srv == nil {
		return nil
	}

	s.logger.Info("Stopping HTTP server")

	err := s.srv.Shutdown(ctx)
	if err != nil {
		return errors.Join(err, s.srv.Close())
	}

	return nil
}

// SetASNFetcher sets the ASN WHOIS fetcher for on-demand lookups. Call it
// before Start: the handlers read the fetcher without a lock.
func (s *Server) SetASNFetcher(fetcher ASNFetcher) {
	s.asnFetcher = fetcher
}

// SetBlocklists sets the blocklists the IP lookups report. Call it before
// Start: the handlers read the blocklists without a lock.
func (s *Server) SetBlocklists(blocklists Blocklists) {
	s.blocklists = blocklists
}