package stdio

import (
	"encoding/json"
	"fmt"
	"time"
)

// **Who answers a verb, asked by the bus's discovery** (D-root and D3 of the seat mesh-self-check; issue 1955): the
// runtime asks the services protocol on the account it runs as (ADR 0197) and answers each machine and module that
// says it serves the verb. The bundle never asks the bus itself.

// Answerer is one module on one machine that answers a verb.
type Answerer struct {
	Machine string `json:"machine"`
	Module  string `json:"module"`
}

const discoverTimeout = 10 * time.Second

// Discover is every module that answers verb (`<seat>.<verb>` or `<module>.<tool>`), on node when one is named: runtime
// verb `mesh/discover {verb, node?}`, answered as a list. None answering is an empty list and no error; an error is a
// question that could not be asked.
func Discover(verb, node string) ([]Answerer, error) {
	if verb == "" {
		return nil, fmt.Errorf("discover names the verb it asks about")
	}
	c, err := live()
	if err != nil {
		return nil, err
	}
	params := map[string]any{"verb": verb}
	if node != "" {
		params["node"] = node
	}
	raw, err := c.ask("mesh/discover", params, discoverTimeout)
	if err != nil {
		return nil, err
	}
	out := []Answerer{}
	if len(raw) == 0 || string(raw) == "null" {
		return out, nil
	}
	if err := json.Unmarshal(raw, &out); err != nil {
		return nil, fmt.Errorf("the runtime's answer to discover is not readable: %w", err)
	}
	return out, nil
}