// Package errkind reduces an error to a short kind that is safe to log, store and show.
//
// An error's own text can hold a provider's response body (a gateway that echoes the
// prompt), a file path (ffmpeg names the spool file), or a word from a private
// transcript. None of that may reach a log line, a database column or a page about a
// private recording (ADR-033: "typed, never a provider's string"; ADR-035). Of returns
// only a fixed vocabulary, so it can never carry any.
package errkind

import (
	"context"
	"errors"
	"fmt"
	"net"
)

// HTTPStatuser is implemented by errors that are a non-2xx answer from a service.
type HTTPStatuser interface{ HTTPStatus() int }

// Of is the kind of err: "timeout", "canceled", "http_<code>", "network", or "error".
// It is empty for nil.
func Of(err error) string {
	if err == nil {
		return ""
	}
	var hs HTTPStatuser
	var ne net.Error
	switch {
	case errors.Is(err, context.DeadlineExceeded):
		return "timeout"
	case errors.Is(err, context.Canceled):
		return "canceled"
	case errors.As(err, &hs):
		return fmt.Sprintf("http_%d", hs.HTTPStatus())
	case errors.As(err, &ne):
		if ne.Timeout() {
			return "timeout"
		}
		return "network"
	}
	return "error"
}