package telemetry

import (
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/codes"
	"go.uber.org/zap"
)

// tracerName names the instrumentation scope for backend HTTP spans.
const tracerName = "scrabble/backend/server"

// Middleware returns gin middleware that, for every request, opens a server
// span, measures server-side latency, and emits a structured access log
// correlated with the active trace. It uses the globally-registered tracer, so
// spans are exported only when an exporter is configured, while the timing log
// is always emitted. Probe paths (/healthz, /readyz) log at debug level to keep
// the default log clean.
func Middleware(logger *zap.Logger) gin.HandlerFunc {
	if logger == nil {
		logger = zap.NewNop()
	}
	tracer := otel.Tracer(tracerName)

	return func(c *gin.Context) {
		start := time.Now()
		route := c.FullPath()
		if route == "" {
			route = c.Request.URL.Path
		}

		ctx, span := tracer.Start(c.Request.Context(), c.Request.Method+" "+route)
		c.Request = c.Request.WithContext(ctx)

		c.Next()

		status := c.Writer.Status()
		elapsed := time.Since(start)

		span.SetAttributes(
			attribute.String("http.request.method", c.Request.Method),
			attribute.String("http.route", route),
			attribute.Int("http.response.status_code", status),
		)
		if status >= http.StatusInternalServerError {
			span.SetStatus(codes.Error, http.StatusText(status))
		}
		span.End()

		fields := []zap.Field{
			zap.String("method", c.Request.Method),
			zap.String("path", route),
			zap.Int("status", status),
			zap.Duration("latency", elapsed),
		}
		fields = append(fields, TraceFieldsFromContext(ctx)...)

		if isProbePath(c.Request.URL.Path) {
			logger.Debug("http request", fields...)
			return
		}
		logger.Info("http request", fields...)
	}
}

// isProbePath reports whether path is one of the unauthenticated infrastructure
// probes, whose access logs are demoted to debug level.
func isProbePath(path string) bool {
	return path == "/healthz" || path == "/readyz"
}