package main

import (
	"context"
)

// heldKey carries the nodes this call already holds, so an act that holds a node and then sends
// through sendTo does not wait on itself.
type heldKey struct{}

// holdNodes holds the named nodes for composing and sending their declarations (novox/hq ADR
// 0100), skipping any the context already holds, and returns a context that says it holds them.
// Release gives back only what this call took.
func holdNodes(ctx context.Context, open *stores, names []string) (context.Context, func(), error) {
	already, _ := ctx.Value(heldKey{}).(map[string]bool)
	var take []string
	for _, n := range names {
		if !already[n] {
			take = append(take, n)
		}
	}
	if len(take) == 0 {
		return ctx, func() {}, nil
	}
	release, err := open.inventory.HoldNodes(ctx, take)
	if err != nil {
		return ctx, nil, err
	}
	held := map[string]bool{}
	for n := range already {
		held[n] = true
	}
	for _, n := range take {
		held[n] = true
	}
	return context.WithValue(ctx, heldKey{}, held), release, nil
}