// Copyright 2017-2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with the License. A copy of the License is located at
//
//     http://aws.amazon.com/apache2.0/
//
// or in the "license" file accompanying this file. This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

package xray

import (
	"context"
	"crypto/rand"
	"fmt"
	"net/http"
	"os"
	"runtime"
	"strings"
	"sync/atomic"
	"time"

	"github.com/aws/aws-xray-sdk-go/header"
	"github.com/aws/aws-xray-sdk-go/internal/logger"
	"github.com/aws/aws-xray-sdk-go/internal/plugins"
	"github.com/aws/aws-xray-sdk-go/strategy/sampling"
)

// NewTraceID generates a string format of random trace ID.
func NewTraceID() string {
	var r [12]byte
	_, err := rand.Read(r[:])
	if err != nil {
		panic(err)
	}
	return fmt.Sprintf("1-%08x-%02x", time.Now().Unix(), r)
}

// NewSegmentID generates a string format of segment ID.
func NewSegmentID() string {
	var r [8]byte
	_, err := rand.Read(r[:])
	if err != nil {
		panic(err)
	}
	return fmt.Sprintf("%02x", r)
}

func noOpTraceID() string {
	return "1-00000000-000000000000000000000000"
}

func noOpSegmentID() string {
	return "0000000000000000"
}

// BeginFacadeSegment creates a Segment for a given name and context.
// NOTE: This is an internal API only to be used in Lambda context within the SDK. Consider using BeginSegment instead.
func BeginFacadeSegment(ctx context.Context, name string, h *header.Header) (context.Context, *Segment) {
	seg := basicSegment(name, h)

	if h == nil {
		// generates segment and trace id based on sampling decision and AWS_XRAY_NOOP_ID env variable
		idGeneration(seg)
	}

	cfg := GetRecorder(ctx)
	seg.assignConfiguration(cfg)

	return context.WithValue(ctx, ContextKey, seg), seg
}

// BeginSegment creates a Segment for a given name and context.
func BeginSegment(ctx context.Context, name string) (context.Context, *Segment) {
	return BeginSegmentWithSampling(ctx, name, nil, nil)
}

func BeginSegmentWithSampling(ctx context.Context, name string, r *http.Request, traceHeader *header.Header) (context.Context, *Segment) {
	// If SDK is disabled then return with an empty segment
	if SdkDisabled() {
		seg := &Segment{}
		return context.WithValue(ctx, ContextKey, seg), seg
	}

	if dName := os.Getenv("AWS_XRAY_TRACING_NAME"); dName != "" {
		name = dName
	}

	seg := basicSegment(name, nil)

	cfg := GetRecorder(ctx)
	seg.assignConfiguration(cfg)

	seg.Lock()
	defer seg.Unlock()

	seg.addPlugin(plugins.InstancePluginMetadata)
	seg.addSDKAndServiceInformation()
	if seg.ParentSegment.GetConfiguration().ServiceVersion != "" {
		seg.GetService().Version = seg.ParentSegment.GetConfiguration().ServiceVersion
	}

	if r == nil || traceHeader == nil {
		// No header or request information provided so we can only evaluate sampling based on the serviceName
		sd := seg.ParentSegment.GetConfiguration().SamplingStrategy.ShouldTrace(&sampling.Request{ServiceName: name})
		seg.Sampled = sd.Sample
		logger.Debugf("SamplingStrategy decided: %t", seg.Sampled)
		seg.AddRuleName(sd)
	} else {
		// Sampling strategy for http calls
		seg.Sampled = traceHeader.SamplingDecision == header.Sampled

		switch traceHeader.SamplingDecision {
		case header.Sampled:
			logger.Debug("Incoming header decided: Sampled=true")
		case header.NotSampled:
			logger.Debug("Incoming header decided: Sampled=false")
		}

		if traceHeader.SamplingDecision != header.Sampled && traceHeader.SamplingDecision != header.NotSampled {
			samplingRequest := &sampling.Request{
				Host:        r.Host,
				URL:         r.URL.Path,
				Method:      r.Method,
				ServiceName: seg.Name,
				ServiceType: plugins.InstancePluginMetadata.Origin,
			}
			sd := seg.ParentSegment.GetConfiguration().SamplingStrategy.ShouldTrace(samplingRequest)
			seg.Sampled = sd.Sample
			logger.Debugf("SamplingStrategy decided: %t", seg.Sampled)
			seg.AddRuleName(sd)
		}
	}

	// check whether segment is dummy or not based on sampling decision
	if !seg.ParentSegment.Sampled {
		seg.Dummy = true
	}

	// Dummy segments don't get sent and don't need a goroutine to cancel them.
	if !seg.Dummy {
		// Create a new context for to cancel segment.
		// Start new goroutine to listen for segment close/cancel events.
		// Cancel simply calls `segment.Close()`.
		//
		// This way, even if the client consumes the `ctx.Done()` event, the
		// X-Ray SDK has a way of canceling (closing) the segment in the
		// `segment.Close()` method using this new cancellation context.
		ctx1, cancelCtx := context.WithCancel(ctx)
		seg.cancelCtx = cancelCtx
		go func() {
			<-ctx1.Done()
			seg.handleContextDone()
		}()
	}

	// generates segment and trace id based on sampling decision and AWS_XRAY_NOOP_ID env variable
	idGeneration(seg)

	return context.WithValue(ctx, ContextKey, seg), seg
}

func idGeneration(seg *Segment) {
	noOpID := os.Getenv("AWS_XRAY_NOOP_ID")
	if noOpID != "" && strings.ToLower(noOpID) == "false" {
		seg.TraceID = NewTraceID()
		seg.ID = NewSegmentID()
	} else {
		if !seg.Sampled {
			seg.TraceID = noOpTraceID()
			seg.ID = noOpSegmentID()
		} else {
			seg.TraceID = NewTraceID()
			seg.ID = NewSegmentID()
		}
	}
}

func basicSegment(name string, h *header.Header) *Segment {
	if len(name) > 200 {
		name = name[:200]
	}
	seg := &Segment{parent: nil}
	logger.Debugf("Beginning segment named %s", name)
	seg.ParentSegment = seg

	seg.Lock()
	defer seg.Unlock()

	seg.Name = name
	seg.StartTime = float64(time.Now().UnixNano()) / float64(time.Second)
	seg.InProgress = true
	seg.Dummy = false

	if h == nil {
		seg.Sampled = true
	} else {
		seg.Facade = true
		seg.ID = h.ParentID
		seg.TraceID = h.TraceID
		seg.Sampled = h.SamplingDecision == header.Sampled
	}

	return seg
}

// assignConfiguration assigns value to seg.Configuration
func (seg *Segment) assignConfiguration(cfg *Config) {
	seg.Lock()
	if cfg == nil {
		seg.GetConfiguration().ContextMissingStrategy = globalCfg.contextMissingStrategy
		seg.GetConfiguration().ExceptionFormattingStrategy = globalCfg.exceptionFormattingStrategy
		seg.GetConfiguration().SamplingStrategy = globalCfg.samplingStrategy
		seg.GetConfiguration().StreamingStrategy = globalCfg.streamingStrategy
		seg.GetConfiguration().Emitter = globalCfg.emitter
		seg.GetConfiguration().ServiceVersion = globalCfg.serviceVersion
	} else {
		if cfg.ContextMissingStrategy != nil {
			seg.GetConfiguration().ContextMissingStrategy = cfg.ContextMissingStrategy
		} else {
			seg.GetConfiguration().ContextMissingStrategy = globalCfg.contextMissingStrategy
		}

		if cfg.ExceptionFormattingStrategy != nil {
			seg.GetConfiguration().ExceptionFormattingStrategy = cfg.ExceptionFormattingStrategy
		} else {
			seg.GetConfiguration().ExceptionFormattingStrategy = globalCfg.exceptionFormattingStrategy
		}

		if cfg.SamplingStrategy != nil {
			seg.GetConfiguration().SamplingStrategy = cfg.SamplingStrategy
		} else {
			seg.GetConfiguration().SamplingStrategy = globalCfg.samplingStrategy
		}

		if cfg.StreamingStrategy != nil {
			seg.GetConfiguration().StreamingStrategy = cfg.StreamingStrategy
		} else {
			seg.GetConfiguration().StreamingStrategy = globalCfg.streamingStrategy
		}

		if cfg.Emitter != nil {
			seg.GetConfiguration().Emitter = cfg.Emitter
		} else {
			seg.GetConfiguration().Emitter = globalCfg.emitter
		}

		if cfg.ServiceVersion != "" {
			seg.GetConfiguration().ServiceVersion = cfg.ServiceVersion
		} else {
			seg.GetConfiguration().ServiceVersion = globalCfg.serviceVersion
		}
	}
	seg.Unlock()
}

func BeginSubsegmentWithoutSampling(ctx context.Context, name string) (context.Context, *Segment) {
	newCtx, subseg := BeginSubsegment(ctx, name)
	subseg.Dummy = true
	subseg.Sampled = false
	return newCtx, subseg
}

// BeginSubsegment creates a subsegment for a given name and context.
func BeginSubsegment(ctx context.Context, name string) (context.Context, *Segment) {
	// If SDK is disabled then return with an empty segment
	if SdkDisabled() {
		seg := &Segment{}
		return context.WithValue(ctx, ContextKey, seg), seg
	}

	if len(name) > 200 {
		name = name[:200]
	}

	var parent *Segment
	// first time to create facade segment
	if getTraceHeaderFromContext(ctx) != nil && GetSegment(ctx) == nil {
		_, parent = newFacadeSegment(ctx)
	} else {
		parent = GetSegment(ctx)
		if parent == nil {
			cfg := GetRecorder(ctx)
			failedMessage := fmt.Sprintf("failed to begin subsegment named '%v': segment cannot be found.", name)
			if cfg != nil && cfg.ContextMissingStrategy != nil {
				cfg.ContextMissingStrategy.ContextMissing(failedMessage)
			} else {
				globalCfg.ContextMissingStrategy().ContextMissing(failedMessage)
			}
			return ctx, nil
		}
	}

	seg := &Segment{parent: parent}
	logger.Debugf("Beginning subsegment named %s", name)

	seg.Lock()
	defer seg.Unlock()

	seg.ParentSegment = parent.ParentSegment

	// generates subsegment id based on sampling decision and AWS_XRAY_NOOP_ID env variable
	noOpID := os.Getenv("AWS_XRAY_NOOP_ID")
	if noOpID != "" && strings.ToLower(noOpID) == "false" {
		seg.ID = NewSegmentID()
	} else {
		if !seg.ParentSegment.Sampled {
			seg.ID = noOpSegmentID()
		} else {
			seg.ID = NewSegmentID()
		}
	}

	// check whether segment is dummy or not based on sampling decision
	if !seg.ParentSegment.Sampled {
		seg.Dummy = true
	}

	atomic.AddUint32(&seg.ParentSegment.totalSubSegments, 1)

	parent.Lock()
	parent.rawSubsegments = append(parent.rawSubsegments, seg)
	parent.openSegments++
	parent.Unlock()

	seg.Name = name
	seg.StartTime = float64(time.Now().UnixNano()) / float64(time.Second)
	seg.InProgress = true
	seg.Sampled = seg.ParentSegment.Sampled
	seg.TraceID = seg.ParentSegment.TraceID
	seg.ParentID = seg.ParentSegment.ID

	return context.WithValue(ctx, ContextKey, seg), seg
}

// NewSegmentFromHeader creates a segment for downstream call and add information to the segment that gets from HTTP header.
func NewSegmentFromHeader(ctx context.Context, name string, r *http.Request, h *header.Header) (context.Context, *Segment) {
	con, seg := BeginSegmentWithSampling(ctx, name, r, h)

	if h.TraceID != "" {
		seg.TraceID = h.TraceID
	}
	if h.ParentID != "" {
		seg.ParentID = h.ParentID
	}

	seg.IncomingHeader = h
	seg.RequestWasTraced = true

	return con, seg
}

// Check if SDK is disabled
func SdkDisabled() bool {
	disableKey := os.Getenv("AWS_XRAY_SDK_DISABLED")
	return strings.ToLower(disableKey) == "true"
}

// Close a segment.
func (seg *Segment) Close(err error) {
	// If SDK is disabled then return
	if SdkDisabled() {
		return
	}

	if seg == nil {
		logger.Debugf("No input subsegment to end. No-op")
		return
	}

	seg.Lock()
	if seg.parent != nil {
		logger.Debugf("Closing subsegment named %s", seg.Name)
	} else {
		logger.Debugf("Closing segment named %s", seg.Name)
	}
	seg.EndTime = float64(time.Now().UnixNano()) / float64(time.Second)
	seg.InProgress = false

	if err != nil {
		seg.addError(err)
	}

	cancelSegCtx := seg.cancelCtx

	seg.Unlock()

	// If a goroutine was started to close the extra context (made for
	// cancelling the segment), stop the goroutine before we close the segment
	// and lose access to it.
	if cancelSegCtx != nil {
		cancelSegCtx()
	}

	// If segment is dummy we return
	if seg.Dummy {
		return
	}

	seg.send()
}

// CloseAndStream closes a subsegment and sends it.
func (seg *Segment) CloseAndStream(err error) {
	// If SDK is disabled then return
	if SdkDisabled() {
		return
	}
	
	if seg.parent != nil {
		logger.Debugf("Ending subsegment named: %s", seg.Name)
		seg.Lock()
		seg.EndTime = float64(time.Now().UnixNano()) / float64(time.Second)
		seg.InProgress = false
		seg.Emitted = true
		seg.Unlock()
		if seg.parent.RemoveSubsegment(seg) {
			logger.Debugf("Removing subsegment named: %s", seg.Name)
		}
	}
	
	seg.Lock()
	defer seg.Unlock()

	if err != nil {
		seg.addError(err)
	}

	// If segment is dummy we return
	if seg.Dummy {
		return
	}

	seg.beforeEmitSubsegment(seg.parent)
	seg.emit()
}

// RemoveSubsegment removes a subsegment child from a segment or subsegment.
func (seg *Segment) RemoveSubsegment(remove *Segment) bool {
	seg.Lock()

	for i, v := range seg.rawSubsegments {
		if v == remove {
			seg.rawSubsegments[i] = seg.rawSubsegments[len(seg.rawSubsegments)-1]
			seg.rawSubsegments[len(seg.rawSubsegments)-1] = nil
			seg.rawSubsegments = seg.rawSubsegments[:len(seg.rawSubsegments)-1]
			seg.openSegments--

			if seg.ParentSegment != seg {
				seg.Unlock()

				atomic.AddUint32(&seg.ParentSegment.totalSubSegments, ^uint32(0))
			} else {
				seg.Unlock()
			}

			return true
		}
	}
	seg.Unlock()
	return false
}

func (seg *Segment) isOrphan() bool {
	return seg.parent == nil || seg.Type == "subsegment"
}

func (seg *Segment) emit() {
	seg.ParentSegment.GetConfiguration().Emitter.Emit(seg)
}

func (seg *Segment) handleContextDone() {
	seg.Lock()
	seg.ContextDone = true
	if !seg.InProgress && !seg.Emitted {
		seg.Unlock()
		seg.send()
	} else {
		seg.Unlock()
	}
}

// send tries to emit the current (Sub)Segment. If the (Sub)Segment is ready to send,
// it emits out. If it is ready but has non-nil parent, it traverses to parent and checks whether parent is
// ready to send and sends entire subtree from the parent. The locking and traversal of the tree
// is from child to parent. This method is thread safe.
func (seg *Segment) send() {
	s := seg
	s.Lock()
	for {
		if s.flush() {
			s.Unlock()
			break
		}

		tmp := s.parent
		s.Unlock()

		s = tmp
		s.Lock()
		s.openSegments--
	}
}

// flush emits (Sub)Segment, if it is ready to send.
// The caller of flush should have write lock on seg instance.
func (seg *Segment) flush() bool {
	if (seg.openSegments == 0 && seg.EndTime > 0) || seg.ContextDone {
		if seg.isOrphan() {
			seg.Emitted = true
			seg.emit()
		} else if seg.parent != nil && seg.parent.Facade {
			seg.Emitted = true
			seg.beforeEmitSubsegment(seg.parent)
			logger.Debugf("emit lambda subsegment named: %v", seg.Name)
			seg.emit()
		} else {
			return false
		}
	}
	return true
}

func (seg *Segment) safeInProgress() bool {
	seg.RLock()
	b := seg.InProgress
	seg.RUnlock()
	return b
}

// getName returns name of the segment. This method is thread safe.
func (seg *Segment) getName() string {
	seg.RLock()
	n := seg.Name
	seg.RUnlock()
	return n
}

func (seg *Segment) root() *Segment {
	if seg.parent == nil {
		return seg
	}
	return seg.parent.root()
}

func (seg *Segment) addPlugin(metadata *plugins.PluginMetadata) {
	// Only called within a seg locked code block
	if metadata == nil {
		return
	}

	if metadata.EC2Metadata != nil {
		seg.GetAWS()[plugins.EC2ServiceName] = metadata.EC2Metadata
	}

	if metadata.ECSMetadata != nil {
		seg.GetAWS()[plugins.ECSServiceName] = metadata.ECSMetadata
	}

	if metadata.BeanstalkMetadata != nil {
		seg.GetAWS()[plugins.EBServiceName] = metadata.BeanstalkMetadata
	}

	if metadata.Origin != "" {
		seg.Origin = metadata.Origin
	}
}

func (seg *Segment) addSDKAndServiceInformation() {
	seg.GetAWS()["xray"] = SDK{Version: SDKVersion, Type: SDKType}

	seg.GetService().Runtime = runtime.Compiler
	seg.GetService().RuntimeVersion = runtime.Version()
}

func (seg *Segment) beforeEmitSubsegment(s *Segment) {
	// Only called within a subsegment locked code block
	seg.TraceID = s.root().TraceID
	seg.ParentID = s.ID
	seg.Type = "subsegment"
	seg.RequestWasTraced = s.RequestWasTraced
}

// AddAnnotation allows adding an annotation to the segment.
func (seg *Segment) AddAnnotation(key string, value interface{}) error {
	// If SDK is disabled then return
	if SdkDisabled() {
		return nil
	}

	seg.Lock()
	defer seg.Unlock()

	// If segment is dummy we return
	if seg.Dummy {
		return nil
	}

	switch value.(type) {
	case bool, int, uint, float32, float64, string:
	default:
		return fmt.Errorf("failed to add annotation key: %q value: %q to subsegment %q. value must be of type string, number or boolean", key, value, seg.Name)
	}

	if seg.Annotations == nil {
		seg.Annotations = map[string]interface{}{}
	}
	seg.Annotations[key] = value
	return nil
}

// AddMetadata allows adding metadata to the segment.
func (seg *Segment) AddMetadata(key string, value interface{}) error {
	// If SDK is disabled then return
	if SdkDisabled() {
		return nil
	}

	seg.Lock()
	defer seg.Unlock()

	// If segment is dummy we return
	if seg.Dummy {
		return nil
	}

	if seg.Metadata == nil {
		seg.Metadata = map[string]map[string]interface{}{}
	}
	if seg.Metadata["default"] == nil {
		seg.Metadata["default"] = map[string]interface{}{}
	}
	seg.Metadata["default"][key] = value
	return nil
}

// AddMetadataToNamespace allows adding a namespace into metadata for the segment.
func (seg *Segment) AddMetadataToNamespace(namespace string, key string, value interface{}) error {
	// If SDK is disabled then return
	if SdkDisabled() {
		return nil
	}

	seg.Lock()
	defer seg.Unlock()

	// If segment is dummy we return
	if seg.Dummy {
		return nil
	}

	if seg.Metadata == nil {
		seg.Metadata = map[string]map[string]interface{}{}
	}
	if seg.Metadata[namespace] == nil {
		seg.Metadata[namespace] = map[string]interface{}{}
	}
	seg.Metadata[namespace][key] = value
	return nil
}

// AddError allows adding an error to the segment.
func (seg *Segment) AddError(err error) error {
	// If SDK is disabled then return
	if SdkDisabled() {
		return nil
	}

	seg.Lock()
	defer seg.Unlock()

	seg.addError(err)

	return nil
}

func (seg *Segment) addError(err error) {
	seg.Fault = true
	seg.GetCause().WorkingDirectory, _ = os.Getwd()
	seg.GetCause().Exceptions = append(seg.GetCause().Exceptions, seg.ParentSegment.GetConfiguration().ExceptionFormattingStrategy.ExceptionFromError(err))
}