package inventory

import (
	"context"
	"fmt"

	"github.com/novox/mesh-controller/internal/broker"
	"github.com/novox/mesh-controller/internal/catalogue"
)

// What the bus's user list is derived from, read out of the mesh's records.
//
// The deriving itself is pure and lives in the broker package; this is the reading, and it is kept
// apart for the reason that package keeps its own types: a permission must be a function of what a
// module declared, and a query that decided anything would be a second place authority came from.

// BusRecords is every fact the composer needs about who may reach the bus.
//
// **A module's authority comes from the manifest, not from the assignment.** The assignment says
// *where* it runs; what it may say is in what it declared, so the two are read together and the
// manifest is the one that decides.
func (i *Inventory) BusRecords(ctx context.Context) (broker.Records, error) {
	nodes, err := i.Nodes(ctx)
	if err != nil {
		return broker.Records{}, fmt.Errorf("cannot read the mesh's machines: %w", err)
	}
	declared, err := i.Catalogue(ctx)
	if err != nil {
		return broker.Records{}, fmt.Errorf("cannot read the catalogue: %w", err)
	}

	// Every seat any module declares, by name, so a module's claim can be resolved to the protocol
	// that seat promises. **Across the whole catalogue, not one manifest**: a seat is declared by
	// one module and held by another, which is the whole reason a seat exists (ADR 0118).
	seats := map[string]catalogue.SeatDeclaration{}
	for _, m := range declared {
		for _, s := range m.Seats {
			seats[s.Name] = s
		}
	}

	out := broker.Records{Assigned: map[string][]broker.Declared{}, People: map[string][]string{}}
	for _, n := range nodes {
		out.Nodes = append(out.Nodes, n.Name)
		modules, err := i.Assigned(ctx, n.Name)
		if err != nil {
			return broker.Records{}, fmt.Errorf("cannot read what %s runs: %w", n.Name, err)
		}
		for _, module := range modules {
			m, known := declared[module]
			if !known {
				// Assigned and not in the catalogue. Said rather than composed with no authority:
				// a user with an empty permission list is a module that starts, connects, and is
				// refused by the server on its first publish — an authorisation error that says
				// nothing about a missing manifest.
				//
				// **The catalogue refuses to forget an assigned module, so this is the second line
				// and not the first.** It earns its place there anyway: relying on another
				// package's invariant is how a rule ends up enforced by nothing.
				return broker.Records{}, fmt.Errorf(
					"%s is assigned to %s and is not in the catalogue, so what it may say cannot "+
						"be derived", module, n.Name)
			}
			out.Assigned[n.Name] = append(out.Assigned[n.Name], declaredFor(m, seats))
		}
	}

	enrolling, err := i.NodesWithALiveToken(ctx)
	if err != nil {
		return broker.Records{}, err
	}
	out.Enrolling = enrolling

	// People are not recorded yet: the account model is built (design 25 §7's first item) and
	// `operator issue` is not, so there is nobody to derive. Left empty rather than guessed at.
	return out, nil
}

// declaredFor is one module's manifest as the composer needs it: what it says about itself, and the
// protocol of every seat it holds or uses.
func declaredFor(m catalogue.Manifest, seats map[string]catalogue.SeatDeclaration) broker.Declared {
	d := broker.Declared{
		Module:   m.Module,
		Emits:    m.Emits,
		Consumes: m.Consumes,
		// The tools it answers, which is `tools` and not `serves`: the manifest's `serves` is the
		// facts a consumer needs to reach a provision, a different meaning under a similar word.
		Serves: m.Tools,
	}
	for _, c := range m.Claims {
		// A seat the mesh defines for itself carries no protocol, so holding one grants nothing here:
		// those seats say who does a job, not who may say what.
		if s, declaredSomewhere := seats[c.Name]; declaredSomewhere {
			d.Holds = append(d.Holds, asSeat(s))
		}
	}
	for _, name := range m.Uses {
		if s, declaredSomewhere := seats[name]; declaredSomewhere {
			d.Uses = append(d.Uses, asSeat(s))
		}
	}
	return d
}

func asSeat(s catalogue.SeatDeclaration) broker.Seat {
	return broker.Seat{Name: s.Name, Accepts: s.Accepts, Emits: s.Emits, Serves: s.Serves}
}

// NodesWithALiveToken is every machine holding a token that could still be presented — issued, not
// expired, not redeemed.
//
// **One enrolment user per such token** (design 25 §6): the inbox an answer goes to is scoped to the
// token, because an answer carries that machine's credentials sealed to it and a shared inbox is one
// machine able to read another's.
func (i *Inventory) NodesWithALiveToken(ctx context.Context) ([]string, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select distinct n.name
		   from enrolment_token t join node n on n.id = t.node
		  where t.redeemed is null and t.expires > now()
		  order by n.name`)
	if err != nil {
		return nil, fmt.Errorf("cannot read which machines hold a live token: %w", err)
	}
	defer rows.Close()
	var out []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		out = append(out, name)
	}
	return out, rows.Err()
}