package link

import (
	"context"
	"encoding/json"
)

// **The composition names the withheld subjects** (design 46 approval mark §6, lead answer A-239): the node-engine reads them
// through the seat mesh-grants' verb withheld, never from the grants part's state; when the verb does not answer, it says so.

// GrantsSeat is the seat of the grants part, whose verb withheld names the marked subjects withheld from a node's runtime.
const GrantsSeat = "mesh-grants"

// WithheldUnknown is what a composition says when the grants part does not answer withheld (design 46 approval mark §6).
const WithheldUnknown = "withheld unknown: the grants part does not answer"

// WithheldSubject is one marked subject withheld from this node's runtime, and why.
type WithheldSubject struct {
	Subject string `json:"subject"`
	Why     string `json:"why"`
}

// WithheldOf is what the grants part withholds of module on this node, asked through its verb withheld: the subjects, or,
// when the verb does not answer or answers what is not its answer, WithheldUnknown as unknown.
func (q *Session) WithheldOf(ctx context.Context, module string) (subjects []WithheldSubject, unknown string) {
	raw, err := q.askCalled(ctx, GrantsSeat, "withheld", map[string]string{"node": q.Membership.Node}, VaultWithin,
		"the grants part's withheld")
	if err != nil {
		return nil, WithheldUnknown
	}
	var answer struct {
		Node    string `json:"node"`
		Modules []struct {
			Module   string            `json:"module"`
			Subjects []WithheldSubject `json:"subjects"`
		} `json:"modules"`
	}
	if json.Unmarshal(raw, &answer) != nil || answer.Node != q.Membership.Node {
		return nil, WithheldUnknown
	}
	for _, m := range answer.Modules {
		if m.Module == module {
			subjects = append(subjects, m.Subjects...)
		}
	}
	return subjects, ""
}