package opentracing

import (
	"context"
	"errors"

	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/log"
	"go.unistack.org/micro/v3/metadata"
	"go.unistack.org/micro/v3/tracer"
)

var _ tracer.Tracer = &opentracingTracer{}

type opentracingTracer struct {
	opts   tracer.Options
	tracer opentracing.Tracer
}

func (ot *opentracingTracer) Name() string {
	return ot.opts.Name
}

func (ot *opentracingTracer) Init(opts ...tracer.Option) error {
	for _, o := range opts {
		o(&ot.opts)
	}

	if tr, ok := ot.opts.Context.Value(tracerKey{}).(opentracing.Tracer); ok {
		ot.tracer = tr
	} else {
		return errors.New("Tracer option missing")
	}

	return nil
}

func (ot *opentracingTracer) Start(ctx context.Context, name string, opts ...tracer.SpanOption) (context.Context, tracer.Span) {
	ctx, span, _ := startSpanFromIncomingContext(ctx, ot.tracer, name)
	return ctx, &opentracingSpan{span: span}
}

type opentracingSpan struct {
	span   opentracing.Span
	labels []interface{}
}

func (os *opentracingSpan) Tracer() tracer.Tracer {
	return &opentracingTracer{tracer: os.span.Tracer()}
}

func (os *opentracingSpan) Finish(opts ...tracer.SpanOption) {
	if len(os.labels) > 0 {
		os.span.LogKV(os.labels...)
	}
	os.span.Finish()
}

func (os *opentracingSpan) AddEvent(name string, opts ...tracer.EventOption) {
	os.span.LogFields(log.Event(name))
}

func (os *opentracingSpan) Context() context.Context {
	return tracer.NewSpanContext(context.Background(), os)
}

func (os *opentracingSpan) SetName(name string) {
	os.span = os.span.SetOperationName(name)
}

func (os *opentracingSpan) SetLabels(labels ...interface{}) {
	os.labels = labels
}

func (os *opentracingSpan) AddLabels(labels ...interface{}) {
	os.labels = append(os.labels, labels...)
}

func NewTracer(opts ...tracer.Option) *opentracingTracer {
	options := tracer.NewOptions(opts...)
	return &opentracingTracer{opts: options}
}

func spanFromContext(ctx context.Context) opentracing.Span {
	return opentracing.SpanFromContext(ctx)
}

// startSpanFromOutgoingContext returns a new span with the given operation name and options. If a span
// is found in the context, it will be used as the parent of the resulting span.
func startSpanFromOutgoingContext(ctx context.Context, tracer opentracing.Tracer, name string, opts ...opentracing.StartSpanOption) (context.Context, opentracing.Span, error) {
	var parentCtx opentracing.SpanContext

	md, ok := metadata.FromIncomingContext(ctx)
	// Find parent span.
	if parentSpan := opentracing.SpanFromContext(ctx); parentSpan != nil {
		// First try to get span within current service boundary.
		parentCtx = parentSpan.Context()
	} else if spanCtx, err := tracer.Extract(opentracing.TextMap, opentracing.TextMapCarrier(md)); err == nil && ok {
		// If there doesn't exist, try to get it from metadata(which is cross boundary)
		parentCtx = spanCtx
	}

	if parentCtx != nil {
		opts = append(opts, opentracing.ChildOf(parentCtx))
	}

	nmd := metadata.Copy(md)

	sp := tracer.StartSpan(name, opts...)
	if err := sp.Tracer().Inject(sp.Context(), opentracing.TextMap, opentracing.TextMapCarrier(nmd)); err != nil {
		return nil, nil, err
	}

	ctx = metadata.NewOutgoingContext(opentracing.ContextWithSpan(ctx, sp), nmd)

	return ctx, sp, nil
}

// startSpanFromIncomingContext returns a new span with the given operation name and options. If a span
// is found in the context, it will be used as the parent of the resulting span.
func startSpanFromIncomingContext(ctx context.Context, tracer opentracing.Tracer, name string, opts ...opentracing.StartSpanOption) (context.Context, opentracing.Span, error) {
	var parentCtx opentracing.SpanContext

	// Find parent span.
	md, ok := metadata.FromIncomingContext(ctx)
	if parentSpan := opentracing.SpanFromContext(ctx); parentSpan != nil {
		// First try to get span within current service boundary.
		parentCtx = parentSpan.Context()
	} else if spanCtx, err := tracer.Extract(opentracing.TextMap, opentracing.TextMapCarrier(md)); err == nil && ok {
		// If there doesn't exist, try to get it from metadata(which is cross boundary)
		parentCtx = spanCtx
	}

	if parentCtx != nil {
		opts = append(opts, opentracing.ChildOf(parentCtx))
	}

	var nmd metadata.Metadata
	if ok {
		nmd = metadata.New(len(md))
	} else {
		nmd = metadata.New(0)
	}

	sp := tracer.StartSpan(name, opts...)
	if err := sp.Tracer().Inject(sp.Context(), opentracing.TextMap, opentracing.TextMapCarrier(nmd)); err != nil {
		return nil, nil, err
	}

	for k, v := range md {
		nmd.Set(k, v)
	}

	ctx = metadata.NewIncomingContext(opentracing.ContextWithSpan(ctx, sp), nmd)

	return ctx, sp, nil
}