package prom

import (
	"net/url"
	"strings"
)

// ParseGeneratorURL splits an Alertmanager generatorURL into the Prometheus it
// points at and the expression of the rule that fired. Prometheus builds it as
// <external-url>/graph?g0.expr=<expr>&g0.tab=1 (/query on Prometheus 3), and the
// external URL may carry a path prefix, which is kept in base.
//
// ok is false for anything else: a non-HTTP scheme, credentials in the URL, a
// page that is not the graph page, or no expression. The caller then has
// nothing to query and falls back to showing the link.
func ParseGeneratorURL(raw string) (base *url.URL, expr string, ok bool) {
	u, err := url.Parse(strings.TrimSpace(raw))
	if err != nil || u.Host == "" || u.User != nil {
		return nil, "", false
	}
	if u.Scheme != "http" && u.Scheme != "https" {
		return nil, "", false
	}
	prefix := ""
	switch {
	case strings.HasSuffix(u.Path, "/graph"):
		prefix = strings.TrimSuffix(u.Path, "/graph")
	case strings.HasSuffix(u.Path, "/query"):
		prefix = strings.TrimSuffix(u.Path, "/query")
	default:
		return nil, "", false
	}
	expr = strings.TrimSpace(u.Query().Get("g0.expr"))
	if expr == "" {
		return nil, "", false
	}
	return &url.URL{Scheme: u.Scheme, Host: u.Host, Path: prefix}, expr, true
}