package main

import (
	"context"
	"fmt"

	"github.com/novox/mesh-control/internal/catalogue"
)

// The things the mesh can be asked to do, separated from how it was asked.
//
// **A surface is an adapter with no decisions in it** (novox/hq ADR 0035). The command line and
// the command API call the same functions here, so an assignment refused at one is refused at the
// other for the same reason and in the same words. The moment a surface can accept something
// another would reject, the mesh has two answers to one question and people learn which to trust.
//
// Each returns what happened as text a person can read and a caller can pass on. Neither surface
// composes its own explanation, because two explanations of one refusal drift.

// assign puts a module on a node, and says at once whether the whole set still resolves.
//
// The assignment is kept even when it does not: it is what a person meant, and the refusal is
// about the set rather than about this one. That is a decision, so it lives here rather than in
// whichever surface asked.
func assign(ctx context.Context, open *stores, node, module string) (string, error) {
	if err := open.inventory.Assign(ctx, node, module); err != nil {
		return "", err
	}
	said := fmt.Sprintf("%s is assigned %s", node, module)
	plan, _, err := planFor(ctx, open, node)
	if err != nil {
		// Kept, and still refused. Both halves are the answer.
		return said, err
	}
	// Kept, and cannot be hosted here. Said at once rather than discovered at push: a module whose
	// capability the machine lacks is on the wrong machine, and the assignment records what a person
	// meant while this line says it will not run until it moves. The rest of the node still pushes.
	for _, u := range plan.Unhostable {
		if u.Module != module {
			continue
		}
		for _, c := range u.Missing {
			said += "\n  but " + catalogue.WrongMachine(u.Module, c, node)
		}
	}
	return said + fmt.Sprintf("\n  run `push %s` to send it", node), nil
}

// unassign takes a module off a node. What it leaves behind is the host's business: a directory
// holding anything the mesh did not put there is kept (novox/hq ADR 0030).
func unassign(ctx context.Context, open *stores, node, module string) (string, error) {
	if err := open.inventory.Unassign(ctx, node, module); err != nil {
		return "", err
	}
	return fmt.Sprintf("%s no longer runs %s — run `push %s` to make it so",
		node, module, node), nil
}