package httputil

import (
	"fmt"
	"strings"

	"github.com/gin-gonic/gin"
	"github.com/samber/lo"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/propagation"
	semconv "go.opentelemetry.io/otel/semconv/v1.12.0"
	oteltrace "go.opentelemetry.io/otel/trace"
)

const (
	tracerKey  = "otel-go-contrib-tracer"
	tracerName = "go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin"
)

// Copy from https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/instrumentation/github.com/gin-gonic/gin/otelgin/gintrace.go
// Modified to pass trace context downstream.
func NewGinServerTracer(service string) gin.HandlerFunc {
	cfg := config{}
	if cfg.TracerProvider == nil {
		cfg.TracerProvider = otel.GetTracerProvider()
	}
	tracer := cfg.TracerProvider.Tracer(
		tracerName,
	)
	if cfg.Propagators == nil {
		cfg.Propagators = otel.GetTextMapPropagator()
	}
	return func(c *gin.Context) {
		if ok := lo.ContainsBy(ignoredPaths, func(item string) bool {
			return strings.Contains(c.Request.URL.Path, item)
		}); ok {
			// Serve the request to the next middleware
			// if a filter rejects the request.
			c.Next()
			return
		}

		c.Set(tracerKey, tracer)
		ctx := cfg.Propagators.Extract(c.Request.Context(), propagation.HeaderCarrier(c.Request.Header))
		opts := []oteltrace.SpanStartOption{
			oteltrace.WithAttributes(semconv.NetAttributesFromHTTPRequest("tcp", c.Request)...),
			oteltrace.WithAttributes(semconv.EndUserAttributesFromHTTPRequest(c.Request)...),
			oteltrace.WithAttributes(semconv.HTTPServerAttributesFromHTTPRequest(service, c.FullPath(), c.Request)...),
			oteltrace.WithSpanKind(oteltrace.SpanKindServer),
		}
		spanName := c.FullPath()
		if spanName == "" {
			spanName = fmt.Sprintf("HTTP %s route not found", c.Request.Method)
		}
		ctx, span := tracer.Start(ctx, spanName, opts...)
		defer span.End()

		// pass the span through the request context
		c.Request = c.Request.WithContext(ctx)

		// serve the request to the next middleware
		c.Next()

		status := c.Writer.Status()
		attrs := semconv.HTTPAttributesFromHTTPStatusCode(status)
		spanStatus, spanMessage := semconv.SpanStatusFromHTTPStatusCodeAndSpanKind(status, oteltrace.SpanKindServer)
		span.SetAttributes(attrs...)
		span.SetStatus(spanStatus, spanMessage)
		if len(c.Errors) > 0 {
			span.SetAttributes(attribute.String("gin.errors", c.Errors.String()))
		}
	}
}

type config struct {
	TracerProvider oteltrace.TracerProvider
	Propagators    propagation.TextMapPropagator
}