// Copyright 2011 Google Inc. All rights reserved.
// Use of this source code is governed by the Apache 2.0
// license that can be found in the LICENSE file.

package internal

import (
	"bytes"
	netcontext "context"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"os"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/golang/protobuf/proto"

	remotepb "google.golang.org/appengine/v2/internal/remote_api"
)

const (
	apiPath             = "/rpc_http"
	defaultTicketSuffix = "/default.20150612t184001.0"
)

var (
	// Incoming headers.
	ticketHeader       = http.CanonicalHeaderKey("X-AppEngine-API-Ticket")
	dapperHeader       = http.CanonicalHeaderKey("X-Google-DapperTraceInfo")
	traceHeader        = http.CanonicalHeaderKey("X-Cloud-Trace-Context")
	curNamespaceHeader = http.CanonicalHeaderKey("X-AppEngine-Current-Namespace")
	userIPHeader       = http.CanonicalHeaderKey("X-AppEngine-User-IP")
	remoteAddrHeader   = http.CanonicalHeaderKey("X-AppEngine-Remote-Addr")
	devRequestIdHeader = http.CanonicalHeaderKey("X-Appengine-Dev-Request-Id")

	// Outgoing headers.
	apiEndpointHeader      = http.CanonicalHeaderKey("X-Google-RPC-Service-Endpoint")
	apiEndpointHeaderValue = []string{"app-engine-apis"}
	apiMethodHeader        = http.CanonicalHeaderKey("X-Google-RPC-Service-Method")
	apiMethodHeaderValue   = []string{"/VMRemoteAPI.CallRemoteAPI"}
	apiDeadlineHeader      = http.CanonicalHeaderKey("X-Google-RPC-Service-Deadline")
	apiContentType         = http.CanonicalHeaderKey("Content-Type")
	apiContentTypeValue    = []string{"application/octet-stream"}
	logFlushHeader         = http.CanonicalHeaderKey("X-AppEngine-Log-Flush-Count")

	apiHTTPClient = &http.Client{
		Transport: &http.Transport{
			Proxy:               http.ProxyFromEnvironment,
			Dial:                limitDial,
			MaxIdleConns:        1000,
			MaxIdleConnsPerHost: 10000,
			IdleConnTimeout:     90 * time.Second,
		},
	}

	defaultTicketOnce     sync.Once
	defaultTicket         string
	backgroundContextOnce sync.Once
	backgroundContext     netcontext.Context

	logStream io.Writer        = os.Stderr // For test hooks.
	timeNow   func() time.Time = time.Now  // For test hooks.
)

func apiURL() *url.URL {
	host, port := "appengine.googleapis.internal", "10001"
	if h := os.Getenv("API_HOST"); h != "" {
		host = h
	}
	if p := os.Getenv("API_PORT"); p != "" {
		port = p
	}
	return &url.URL{
		Scheme: "http",
		Host:   host + ":" + port,
		Path:   apiPath,
	}
}

func handleHTTP(w http.ResponseWriter, r *http.Request) {
	c := &context{
		req:       r,
		outHeader: w.Header(),
		apiURL:    apiURL(),
	}
	r = r.WithContext(withContext(r.Context(), c))
	c.req = r

	// Patch up RemoteAddr so it looks reasonable.
	if addr := r.Header.Get(userIPHeader); addr != "" {
		r.RemoteAddr = addr
	} else if addr = r.Header.Get(remoteAddrHeader); addr != "" {
		r.RemoteAddr = addr
	} else {
		// Should not normally reach here, but pick a sensible default anyway.
		r.RemoteAddr = "127.0.0.1"
	}
	// The address in the headers will most likely be of these forms:
	//	123.123.123.123
	//	2001:db8::1
	// net/http.Request.RemoteAddr is specified to be in "IP:port" form.
	if _, _, err := net.SplitHostPort(r.RemoteAddr); err != nil {
		// Assume the remote address is only a host; add a default port.
		r.RemoteAddr = net.JoinHostPort(r.RemoteAddr, "80")
	}

	executeRequestSafely(c, r)
	c.outHeader = nil // make sure header changes aren't respected any more

	// Avoid nil Write call if c.Write is never called.
	if c.outCode != 0 {
		w.WriteHeader(c.outCode)
	}
	if c.outBody != nil {
		w.Write(c.outBody)
	}
}

func executeRequestSafely(c *context, r *http.Request) {
	defer func() {
		if x := recover(); x != nil {
			logf(c, 4, "%s", renderPanic(x)) // 4 == critical
			c.outCode = 500
		}
	}()

	http.DefaultServeMux.ServeHTTP(c, r)
}

func renderPanic(x interface{}) string {
	buf := make([]byte, 16<<10) // 16 KB should be plenty
	buf = buf[:runtime.Stack(buf, false)]

	// Remove the first few stack frames:
	//   this func
	//   the recover closure in the caller
	// That will root the stack trace at the site of the panic.
	const (
		skipStart  = "internal.renderPanic"
		skipFrames = 2
	)
	start := bytes.Index(buf, []byte(skipStart))
	p := start
	for i := 0; i < skipFrames*2 && p+1 < len(buf); i++ {
		p = bytes.IndexByte(buf[p+1:], '\n') + p + 1
		if p < 0 {
			break
		}
	}
	if p >= 0 {
		// buf[start:p+1] is the block to remove.
		// Copy buf[p+1:] over buf[start:] and shrink buf.
		copy(buf[start:], buf[p+1:])
		buf = buf[:len(buf)-(p+1-start)]
	}

	// Add panic heading.
	head := fmt.Sprintf("panic: %v\n\n", x)
	if len(head) > len(buf) {
		// Extremely unlikely to happen.
		return head
	}
	copy(buf[len(head):], buf)
	copy(buf, head)

	return string(buf)
}

// context represents the context of an in-flight HTTP request.
// It implements the appengine.Context and http.ResponseWriter interfaces.
type context struct {
	req *http.Request

	outCode   int
	outHeader http.Header
	outBody   []byte

	apiURL *url.URL
}

var contextKey = "holds a *context"

// jointContext joins two contexts in a superficial way.
// It takes values and timeouts from a base context, and only values from another context.
type jointContext struct {
	base       netcontext.Context
	valuesOnly netcontext.Context
}

func (c jointContext) Deadline() (time.Time, bool) {
	return c.base.Deadline()
}

func (c jointContext) Done() <-chan struct{} {
	return c.base.Done()
}

func (c jointContext) Err() error {
	return c.base.Err()
}

func (c jointContext) Value(key interface{}) interface{} {
	if val := c.base.Value(key); val != nil {
		return val
	}
	return c.valuesOnly.Value(key)
}

// fromContext returns the App Engine context or nil if ctx is not
// derived from an App Engine context.
func fromContext(ctx netcontext.Context) *context {
	c, _ := ctx.Value(&contextKey).(*context)
	return c
}

func withContext(parent netcontext.Context, c *context) netcontext.Context {
	ctx := netcontext.WithValue(parent, &contextKey, c)
	if ns := c.req.Header.Get(curNamespaceHeader); ns != "" {
		ctx = withNamespace(ctx, ns)
	}
	return ctx
}

func toContext(c *context) netcontext.Context {
	return withContext(netcontext.Background(), c)
}

func IncomingHeaders(ctx netcontext.Context) http.Header {
	if c := fromContext(ctx); c != nil {
		return c.req.Header
	}
	return nil
}

func ReqContext(req *http.Request) netcontext.Context {
	return req.Context()
}

func WithContext(parent netcontext.Context, req *http.Request) netcontext.Context {
	return jointContext{
		base:       parent,
		valuesOnly: req.Context(),
	}
}

// DefaultTicket returns a ticket used for background context or dev_appserver.
func DefaultTicket() string {
	defaultTicketOnce.Do(func() {
		if IsDevAppServer() {
			defaultTicket = "testapp" + defaultTicketSuffix
			return
		}
		appID := partitionlessAppID()
		escAppID := strings.Replace(strings.Replace(appID, ":", "_", -1), ".", "_", -1)
		majVersion := VersionID(nil)
		if i := strings.Index(majVersion, "."); i > 0 {
			majVersion = majVersion[:i]
		}
		defaultTicket = fmt.Sprintf("%s/%s.%s.%s", escAppID, ModuleName(nil), majVersion, InstanceID())
	})
	return defaultTicket
}

func BackgroundContext() netcontext.Context {
	backgroundContextOnce.Do(func() {
		// Compute background security ticket.
		ticket := DefaultTicket()

		c := &context{
			req: &http.Request{
				Header: http.Header{
					ticketHeader: []string{ticket},
				},
			},
			apiURL: apiURL(),
		}
		backgroundContext = toContext(c)
	})

	return backgroundContext
}

// RegisterTestRequest registers the HTTP request req for testing, such that
// any API calls are sent to the provided URL. It returns a closure to delete
// the registration.
// It should only be used by aetest package.
func RegisterTestRequest(req *http.Request, apiURL *url.URL, decorate func(netcontext.Context) netcontext.Context) (*http.Request, func()) {
	c := &context{
		req:    req,
		apiURL: apiURL,
	}
	ctx := withContext(decorate(req.Context()), c)
	req = req.WithContext(ctx)
	c.req = req
	return req, func() {}
}

var errTimeout = &CallError{
	Detail:  "Deadline exceeded",
	Code:    int32(remotepb.RpcError_CANCELLED),
	Timeout: true,
}

func (c *context) Header() http.Header { return c.outHeader }

// Copied from $GOROOT/src/pkg/net/http/transfer.go. Some response status
// codes do not permit a response body (nor response entity headers such as
// Content-Length, Content-Type, etc).
func bodyAllowedForStatus(status int) bool {
	switch {
	case status >= 100 && status <= 199:
		return false
	case status == 204:
		return false
	case status == 304:
		return false
	}
	return true
}

func (c *context) Write(b []byte) (int, error) {
	if c.outCode == 0 {
		c.WriteHeader(http.StatusOK)
	}
	if len(b) > 0 && !bodyAllowedForStatus(c.outCode) {
		return 0, http.ErrBodyNotAllowed
	}
	c.outBody = append(c.outBody, b...)
	return len(b), nil
}

func (c *context) WriteHeader(code int) {
	if c.outCode != 0 {
		logf(c, 3, "WriteHeader called multiple times on request.") // error level
		return
	}
	c.outCode = code
}

func (c *context) post(body []byte, timeout time.Duration) (b []byte, err error) {
	hreq := &http.Request{
		Method: "POST",
		URL:    c.apiURL,
		Header: http.Header{
			apiEndpointHeader: apiEndpointHeaderValue,
			apiMethodHeader:   apiMethodHeaderValue,
			apiContentType:    apiContentTypeValue,
			apiDeadlineHeader: []string{strconv.FormatFloat(timeout.Seconds(), 'f', -1, 64)},
		},
		Body:          ioutil.NopCloser(bytes.NewReader(body)),
		ContentLength: int64(len(body)),
		Host:          c.apiURL.Host,
	}
	if info := c.req.Header.Get(dapperHeader); info != "" {
		hreq.Header.Set(dapperHeader, info)
	}
	if info := c.req.Header.Get(traceHeader); info != "" {
		hreq.Header.Set(traceHeader, info)
	}

	tr := apiHTTPClient.Transport.(*http.Transport)

	var timedOut int32 // atomic; set to 1 if timed out
	t := time.AfterFunc(timeout, func() {
		atomic.StoreInt32(&timedOut, 1)
		tr.CancelRequest(hreq)
	})
	defer t.Stop()
	defer func() {
		// Check if timeout was exceeded.
		if atomic.LoadInt32(&timedOut) != 0 {
			err = errTimeout
		}
	}()

	hresp, err := apiHTTPClient.Do(hreq)
	if err != nil {
		return nil, &CallError{
			Detail: fmt.Sprintf("service bridge HTTP failed: %v", err),
			Code:   int32(remotepb.RpcError_UNKNOWN),
		}
	}
	defer hresp.Body.Close()
	hrespBody, err := ioutil.ReadAll(hresp.Body)
	if hresp.StatusCode != 200 {
		return nil, &CallError{
			Detail: fmt.Sprintf("service bridge returned HTTP %d (%q)", hresp.StatusCode, hrespBody),
			Code:   int32(remotepb.RpcError_UNKNOWN),
		}
	}
	if err != nil {
		return nil, &CallError{
			Detail: fmt.Sprintf("service bridge response bad: %v", err),
			Code:   int32(remotepb.RpcError_UNKNOWN),
		}
	}
	return hrespBody, nil
}

func Call(ctx netcontext.Context, service, method string, in, out proto.Message) error {
	if ns := NamespaceFromContext(ctx); ns != "" {
		if fn, ok := NamespaceMods[service]; ok {
			fn(in, ns)
		}
	}

	if f, ctx, ok := callOverrideFromContext(ctx); ok {
		return f(ctx, service, method, in, out)
	}

	// Handle already-done contexts quickly.
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	c := fromContext(ctx)
	if c == nil {
		// Give a good error message rather than a panic lower down.
		return errNotAppEngineContext
	}

	// Apply transaction modifications if we're in a transaction.
	if t := transactionFromContext(ctx); t != nil {
		if t.finished {
			return errors.New("transaction context has expired")
		}
		applyTransaction(in, &t.transaction)
	}

	// Default RPC timeout is 60s.
	timeout := 60 * time.Second
	if deadline, ok := ctx.Deadline(); ok {
		timeout = deadline.Sub(time.Now())
	}

	data, err := proto.Marshal(in)
	if err != nil {
		return err
	}

	ticket := c.req.Header.Get(ticketHeader)
	// Use a test ticket under test environment.
	if ticket == "" {
		if appid := ctx.Value(&appIDOverrideKey); appid != nil {
			ticket = appid.(string) + defaultTicketSuffix
		}
	}
	// Fall back to use background ticket when the request ticket is not available in Flex or dev_appserver.
	if ticket == "" {
		ticket = DefaultTicket()
	}
	if dri := c.req.Header.Get(devRequestIdHeader); IsDevAppServer() && dri != "" {
		ticket = dri
	}
	req := &remotepb.Request{
		ServiceName: &service,
		Method:      &method,
		Request:     data,
		RequestId:   &ticket,
	}
	hreqBody, err := proto.Marshal(req)
	if err != nil {
		return err
	}

	hrespBody, err := c.post(hreqBody, timeout)
	if err != nil {
		return err
	}

	res := &remotepb.Response{}
	if err := proto.Unmarshal(hrespBody, res); err != nil {
		return err
	}
	if res.RpcError != nil {
		ce := &CallError{
			Detail: res.RpcError.GetDetail(),
			Code:   *res.RpcError.Code,
		}
		switch remotepb.RpcError_ErrorCode(ce.Code) {
		case remotepb.RpcError_CANCELLED, remotepb.RpcError_DEADLINE_EXCEEDED:
			ce.Timeout = true
		}
		return ce
	}
	if res.ApplicationError != nil {
		return &APIError{
			Service: *req.ServiceName,
			Detail:  res.ApplicationError.GetDetail(),
			Code:    *res.ApplicationError.Code,
		}
	}
	if res.Exception != nil || res.JavaException != nil {
		// This shouldn't happen, but let's be defensive.
		return &CallError{
			Detail: "service bridge returned exception",
			Code:   int32(remotepb.RpcError_UNKNOWN),
		}
	}
	return proto.Unmarshal(res.Response, out)
}

func (c *context) Request() *http.Request {
	return c.req
}

func ContextForTesting(req *http.Request) netcontext.Context {
	return toContext(&context{req: req})
}