package rest

import (
	"errors"
	"fmt"
	"net/http"
	"time"

	"git.i2edu.net/i2/go-zero/core/codec"
	"git.i2edu.net/i2/go-zero/core/load"
	"git.i2edu.net/i2/go-zero/core/stat"
	"git.i2edu.net/i2/go-zero/rest/handler"
	"git.i2edu.net/i2/go-zero/rest/httpx"
	"git.i2edu.net/i2/go-zero/rest/internal"
	"git.i2edu.net/i2/go-zero/rest/router"
	"github.com/justinas/alice"
)

// use 1000m to represent 100%
const topCpuUsage = 1000

// ErrSignatureConfig is an error that indicates bad config for signature.
var ErrSignatureConfig = errors.New("bad config for Signature")

type engine struct {
	conf                 RestConf
	routes               []featuredRoutes
	unauthorizedCallback handler.UnauthorizedCallback
	unsignedCallback     handler.UnsignedCallback
	middlewares          []Middleware
	shedder              load.Shedder
	priorityShedder      load.Shedder
}

func newEngine(c RestConf) *engine {
	srv := &engine{
		conf: c,
	}
	if c.CpuThreshold > 0 {
		srv.shedder = load.NewAdaptiveShedder(load.WithCpuThreshold(c.CpuThreshold))
		srv.priorityShedder = load.NewAdaptiveShedder(load.WithCpuThreshold(
			(c.CpuThreshold + topCpuUsage) >> 1))
	}

	return srv
}

func (s *engine) AddRoutes(r featuredRoutes) {
	s.routes = append(s.routes, r)
}

func (s *engine) SetUnauthorizedCallback(callback handler.UnauthorizedCallback) {
	s.unauthorizedCallback = callback
}

func (s *engine) SetUnsignedCallback(callback handler.UnsignedCallback) {
	s.unsignedCallback = callback
}

func (s *engine) Start() error {
	return s.StartWithRouter(router.NewRouter())
}

func (s *engine) StartWithRouter(router httpx.Router) error {
	if err := s.bindRoutes(router); err != nil {
		return err
	}

	if len(s.conf.CertFile) == 0 && len(s.conf.KeyFile) == 0 {
		return internal.StartHttp(s.conf.Host, s.conf.Port, router)
	}

	return internal.StartHttps(s.conf.Host, s.conf.Port, s.conf.CertFile, s.conf.KeyFile, router)
}

func (s *engine) appendAuthHandler(fr featuredRoutes, chain alice.Chain,
	verifier func(alice.Chain) alice.Chain) alice.Chain {
	if fr.jwt.enabled {
		if len(fr.jwt.prevSecret) == 0 {
			chain = chain.Append(handler.Authorize(fr.jwt.secret,
				handler.WithUnauthorizedCallback(s.unauthorizedCallback)))
		} else {
			chain = chain.Append(handler.Authorize(fr.jwt.secret,
				handler.WithPrevSecret(fr.jwt.prevSecret),
				handler.WithUnauthorizedCallback(s.unauthorizedCallback)))
		}
	}

	return verifier(chain)
}

func (s *engine) bindFeaturedRoutes(router httpx.Router, fr featuredRoutes, metrics *stat.Metrics) error {
	verifier, err := s.signatureVerifier(fr.signature)
	if err != nil {
		return err
	}

	for _, route := range fr.routes {
		if err := s.bindRoute(fr, router, metrics, route, verifier); err != nil {
			return err
		}
	}

	return nil
}

func (s *engine) bindRoute(fr featuredRoutes, router httpx.Router, metrics *stat.Metrics,
	route Route, verifier func(chain alice.Chain) alice.Chain) error {
	chain := alice.New(
		handler.TracingHandler,
		s.getLogHandler(),
		handler.PrometheusHandler(route.Path),
		handler.MaxConns(s.conf.MaxConns),
		handler.BreakerHandler(route.Method, route.Path, metrics),
		handler.SheddingHandler(s.getShedder(fr.priority), metrics),
		handler.TimeoutHandler(time.Duration(s.conf.Timeout)*time.Millisecond),
		handler.RecoverHandler,
		handler.MetricHandler(metrics),
		handler.MaxBytesHandler(s.conf.MaxBytes),
		handler.GunzipHandler,
	)
	chain = s.appendAuthHandler(fr, chain, verifier)

	for _, middleware := range s.middlewares {
		chain = chain.Append(convertMiddleware(middleware))
	}
	handle := chain.ThenFunc(route.Handler)

	return router.Handle(route.Method, route.Path, handle)
}

func (s *engine) bindRoutes(router httpx.Router) error {
	metrics := s.createMetrics()

	for _, fr := range s.routes {
		if err := s.bindFeaturedRoutes(router, fr, metrics); err != nil {
			return err
		}
	}

	return nil
}

func (s *engine) createMetrics() *stat.Metrics {
	var metrics *stat.Metrics

	if len(s.conf.Name) > 0 {
		metrics = stat.NewMetrics(s.conf.Name)
	} else {
		metrics = stat.NewMetrics(fmt.Sprintf("%s:%d", s.conf.Host, s.conf.Port))
	}

	return metrics
}

func (s *engine) getLogHandler() func(http.Handler) http.Handler {
	if s.conf.Verbose {
		return handler.DetailedLogHandler
	}

	return handler.LogHandler
}

func (s *engine) getShedder(priority bool) load.Shedder {
	if priority && s.priorityShedder != nil {
		return s.priorityShedder
	}

	return s.shedder
}

func (s *engine) signatureVerifier(signature signatureSetting) (func(chain alice.Chain) alice.Chain, error) {
	if !signature.enabled {
		return func(chain alice.Chain) alice.Chain {
			return chain
		}, nil
	}

	if len(signature.PrivateKeys) == 0 {
		if signature.Strict {
			return nil, ErrSignatureConfig
		}

		return func(chain alice.Chain) alice.Chain {
			return chain
		}, nil
	}

	decrypters := make(map[string]codec.RsaDecrypter)
	for _, key := range signature.PrivateKeys {
		fingerprint := key.Fingerprint
		file := key.KeyFile
		decrypter, err := codec.NewRsaDecrypter(file)
		if err != nil {
			return nil, err
		}

		decrypters[fingerprint] = decrypter
	}

	return func(chain alice.Chain) alice.Chain {
		if s.unsignedCallback != nil {
			return chain.Append(handler.ContentSecurityHandler(
				decrypters, signature.Expiry, signature.Strict, s.unsignedCallback))
		}

		return chain.Append(handler.ContentSecurityHandler(
			decrypters, signature.Expiry, signature.Strict))
	}, nil
}

func (s *engine) use(middleware Middleware) {
	s.middlewares = append(s.middlewares, middleware)
}

func convertMiddleware(ware Middleware) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return ware(next.ServeHTTP)
	}
}