package edge

import (
	"net/http"

	"github.com/carlosframework/platform/internal/registry"
	"github.com/carlosframework/platform/internal/seeds"
)

// ImportVerifyHeader carries an uncommitted import's verify token
// (seeded-instances spec §5.4). The CLI's verify sends it (instances_import.go).
const ImportVerifyHeader = "Carlos-Import-Verify"

// importGateAdmit is the import gate (spec §5.4, codex 15). host is the
// request's host and rt the route it resolved to after the door's scope
// check. ServeHTTP calls it before the meter, the password gate, the cache
// and the activator, so a refused request is not served, cached, billed or
// woken.
//
// The verify header is removed from every request that gets this far, so
// the token never reaches an app, gated or not. It is never logged or
// written into an answer.
//
// While host's own row, or the row the request resolved to, carries a gate,
// exactly one request passes: a GET (the CLI's verify, spec §5) whose token
// hashes to the gate, compared in constant time (seeds.TokenMatches), and
// resolved to host's own row. An alias resolves to its primary's row, so an
// alias of a gated host is that host. A path route does not: a prefix under
// a gated host that selects another row is refused, token or not, because
// the verify is the import's own request and a prefix's target is another
// route; and an ungated host's prefix that selects a gated row is refused
// for the same reason. ImportGateClosed (a rollback) matches no token.
//
// Everything else gets 503 with Retry-After: 5 and Cache-Control: no-store.
func (e *Edge) importGateAdmit(w http.ResponseWriter, r *http.Request, host string, rt registry.Route) bool {
	token := r.Header.Get(ImportVerifyHeader)
	r.Header.Del(ImportVerifyHeader)
	front := rt
	if up, ok := lookupIn(e.current(), host); ok {
		front = up.route
	}
	if rt.ImportGate == "" && front.ImportGate == "" {
		return true
	}
	if front.Host == rt.Host && r.Method == http.MethodGet && seeds.TokenMatches(rt.ImportGate, token) {
		return true
	}
	w.Header().Set("Retry-After", "5")
	w.Header().Set("Cache-Control", "no-store")
	http.Error(w, "this instance is being imported. Try again in a few seconds.", http.StatusServiceUnavailable)
	return false
}