package broker

import (
	"fmt"
	"strings"

	"github.com/novox/mesh-controller/internal/envfile"
)

// Whether this mesh's own traffic is on the bus being built.
//
// **One switch, read in one place** (novox/hq ADR 0116 step 5). Every seam the bus change went
// behind ships both implementations, and until the rollout every one of them chooses the bus the
// mesh runs on today. This is what the rollout flips, and it is deliberately a single fact rather
// than a fact per component: a controller whose outbound is on one bus and whose inbound is on the
// other is a mesh that hears nothing, and no test of either half would catch it.

// NATSVar is where the controller finds the bus being built. Unset is the ordinary case and means
// the mesh runs on the bus it has always run on.
const NATSVar = "MESH_BUS_NATS"

// OnNATS is the address of the bus being built, and whether the mesh is on it.
//
// Read from the node's own settings rather than baked in, for the reason the broker's address is
// (novox/hq 04-ISSUES/102): an address recorded once does not follow a node's ports.
func OnNATS() (address string, on bool, err error) {
	address, err = envfile.Placed(NATSVar)
	if err != nil {
		return "", false, err
	}
	address = strings.TrimSpace(address)
	if address == "" {
		return "", false, nil
	}
	return address, true, nil
}

// BusAddress is where the mesh's bus is, with this process's credential, and refuses to be empty:
// there is one bus, and a control plane without it can hold records and answer nothing (novox/hq
// ADR 0131, design 28 task 5.5).
func BusAddress() (string, error) {
	address, _, err := OnNATS()
	if err != nil {
		return "", err
	}
	if address == "" {
		return "", fmt.Errorf("this control plane has no %s, so it cannot reach the mesh's bus", NATSVar)
	}
	return address, nil
}