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
}

// MustBeOneBus refuses a configuration that names both buses for the mesh's own traffic.
//
// **Both clients ship and that is the point; both being live is not.** The rollout moves every node
// at once (ADR 0116 step 5): a mesh half on each is one where a declaration goes out on one bus and
// the report comes back on the other, and nothing anywhere says so — every component would log
// success. Refused at start, where it can be said in one sentence.
func MustBeOneBus(amqp, nats string) error {
	if strings.TrimSpace(amqp) != "" && strings.TrimSpace(nats) != "" {
		return fmt.Errorf(
			"this control plane is told about both buses (%s and %s) and can only be on one. A mesh "+
				"half on each is one where a declaration goes out on one and the report comes back "+
				"on the other, and every component reports success while it happens. The rollout "+
				"moves every node at once: unset %s to stay, or unset %s to move",
			AMQPVarName, NATSVar, NATSVar, AMQPVarName)
	}
	return nil
}

// AMQPVarName is the variable naming the bus the mesh runs on today. Named here rather than
// imported from the link package, for the one direction of dependency.
const AMQPVarName = "MESH_BROKER_AMQP"