package broker

import (
	"fmt"
	"sort"
)

// Every user the composed file should contain, derived from what the mesh knows.
//
// **The list is derived, never kept.** A stored user list would be a second account of who may
// reach the bus, able to disagree with the records it came from — and the disagreement would be
// invisible, because both would look internally consistent. So this is a pure function of the
// mesh's records, run again every time the file is written.
//
// Records are mirrored into this package's own types rather than imported from the catalogue, for
// the reason DeclaredSeat is: composing authority is a different job from parsing a manifest, and
// this package stays free of the other's types so a change to a manifest field cannot quietly widen
// a permission.

// Declared is one module on one node, as composing its authority needs it.
type Declared struct {
	Module   string
	Emits    []string
	Consumes []string
	Serves   []string
	// Holds are the seats this module claims, with the protocol each seat declares. A seat the
	// mesh defines for itself declares no protocol, so holding one grants nothing on the bus —
	// which is right: those seats are about who does a job, not about who may say what.
	Holds []Seat
	// Uses are the seats this module sends to.
	Uses []Seat
}

// Records is what composing a user list needs to know about the mesh, and nothing more.
type Records struct {
	// Nodes is every machine the mesh knows. Each gets a host user.
	Nodes []string
	// Assigned is the modules on each node, as they declare themselves.
	Assigned map[string][]Declared
	// Enrolling is every node with a live token — one enrolment user each, because the inbox an
	// answer goes to is scoped to the token and a shared one is one machine reading another's
	// sealed credentials (design 25 §6).
	Enrolling []string
	// People is each person's name against the tools they may invoke, `*` for an administrator.
	People map[string][]string
}

// Users is every user the composed file should contain, in the order it will be written.
//
// The controller is always first and always present: a mesh whose own controller is not in the file
// is a mesh that cannot be told anything, and there is no state of the records in which that is
// correct.
func Users(r Records) ([]Principal, error) {
	out := []Principal{{Kind: KindController}}

	for _, node := range sortedCopy(r.Nodes) {
		out = append(out, Principal{Kind: KindNode, Node: node})
		for _, d := range r.Assigned[node] {
			out = append(out, Principal{
				Kind: KindModule, Node: node, Module: d.Module,
				Emits: d.Emits, Consumes: d.Consumes, Serves: d.Serves,
				Holds: d.Holds, Uses: d.Uses,
			})
		}
	}
	for _, node := range sortedCopy(r.Enrolling) {
		out = append(out, Principal{Kind: KindEnrolment, Node: node})
	}
	for _, person := range sortedNames(r.People) {
		out = append(out, Principal{Kind: KindPerson, Module: person, Invokes: r.People[person]})
	}

	// Refused here rather than discovered by the server. Two users with one name is a file the
	// server reads as one of them, and which one depends on the order — so a module assigned to a
	// node twice, or a person named after nothing, is a composition that must not be written.
	seen := map[string]string{}
	for _, p := range out {
		name := p.Username()
		if name == "" || name == "." {
			return nil, fmt.Errorf("a %s user has no name, so nothing could authenticate as it", p.Kind)
		}
		if first, already := seen[name]; already {
			return nil, fmt.Errorf(
				"two users would be called %q (a %s and a %s): the server would read the file as "+
					"one of them, and which one depends on the order", name, first, p.Kind)
		}
		seen[name] = string(p.Kind)
	}
	return out, nil
}

// WithPasswords fills each user's hash from what the mesh minted, and says which users have none.
//
// **Separated from Users because they fail differently.** A user missing from the records is a bug
// in deriving them; a user with no password is a step that has not happened yet — a module assigned
// but never given a credential, a node enrolled before this existed. The second is ordinary and its
// remedy is to mint one, so it is named rather than returned as an error, and the caller decides
// whether a partial composition is worth writing.
func WithPasswords(principals []Principal, hashes map[string]string) (filled []Principal, missing []string) {
	for _, p := range principals {
		hash, ok := hashes[p.Username()]
		if !ok || hash == "" {
			missing = append(missing, p.Username())
			continue
		}
		p.PasswordHash = hash
		filled = append(filled, p)
	}
	return filled, missing
}

func sortedCopy(in []string) []string {
	out := append([]string(nil), in...)
	sort.Strings(out)
	return out
}

func sortedNames(in map[string][]string) []string {
	out := make([]string, 0, len(in))
	for k := range in {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}