package metrics

import (
	"strconv"
	"time"

	"github.com/labstack/echo/v5"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

var (
	httpRequests = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "http_requests_total",
		Help: "HTTP requests by method, route and status code.",
	}, []string{"method", "route", "code"})

	httpDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name: "http_request_duration_seconds",
		Help: "HTTP request latency by method and route. Song downloads include the transfer.",
		// Up to 30 s, since songs can take long to send to slow clients.
		Buckets: []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10, 30},
	}, []string{"method", "route"})
)

// unmatchedRoute labels requests that matched no route, so raw URLs never become labels.
const unmatchedRoute = "unmatched"

// Middleware records the count and latency of requests per route. The route label is the
// registered pattern, like /api/v1/songs/:uuid, never the URL with its IDs and query.
// Register it outside Recover, so requests that panic are counted as 500.
func Middleware() echo.MiddlewareFunc {
	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c *echo.Context) error {
			start := time.Now()
			err := next(c)

			route := c.Path()
			if route == "" {
				route = unmatchedRoute
			}
			_, status := echo.ResolveResponseStatus(c.Response(), err)
			method := c.Request().Method
			httpRequests.WithLabelValues(method, route, strconv.Itoa(status)).Inc()
			httpDuration.WithLabelValues(method, route).Observe(time.Since(start).Seconds())
			return err
		}
	}
}