mesh-controller/cmd/mesh-controller/seats.go

package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"os"
	"sort"
	"strings"
	"text/tabwriter"

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

// What this mesh can have one of, and who fills each (novox/hq ADR 0110).
//
// **Derived every time, never stored.** A seat is held by a module assignment, so the answer is
// computed from assignments by the same resolution that decides what every machine runs. A table
// of holders kept beside the assignments would be a second copy of one fact, and the first thing
// to be wrong about it.

// seatHolder is one assignment holding a seat.
type seatHolder struct {
	Node   string `json:"node"`
	Module string `json:"module"`
}

// seatRow is one seat and who holds it. Unheld is an answer — "this mesh has no X" — not a fault.
type seatRow struct {
	Seat     string       `json:"seat"`
	Scope    string       `json:"scope"`
	Delivers string       `json:"delivers,omitempty"`
	Decision string       `json:"decision"`
	Holders  []seatHolder `json:"holders"`
}

// seatsHeld is every seat the mesh defines with its holders, and every claim held that names no
// seat in the set.
//
// **The second list is not empty by construction.** Manifests are held to the set when they are
// registered, and a mesh can hold one registered before the set closed. Leaving its claim out of the
// overview would make the one thing the overview is for — what does this mesh have — quietly
// incomplete.
func seatsHeld(seats []catalogue.Seat, held []catalogue.Held) ([]seatRow, []catalogue.Held) {
	rows := make([]seatRow, 0, len(seats))
	for _, s := range seats {
		row := seatRow{Seat: s.Name, Scope: s.Scope, Delivers: s.Delivers, Decision: s.Decision,
			Holders: []seatHolder{}}
		seen := map[seatHolder]bool{}
		for _, h := range held {
			// Resolve the held claim to a seat rather than comparing names, so a record naming a
			// seat's former name groups under it after a rename (novox/hq ADR 0122).
			hs, ok := catalogue.SeatNamed(h.Claim)
			if !ok || hs.Name != s.Name || h.Scope != s.Scope {
				continue
			}
			holder := seatHolder{Node: h.Node, Module: h.Module}
			if !seen[holder] {
				seen[holder] = true
				row.Holders = append(row.Holders, holder)
			}
		}
		sort.Slice(row.Holders, func(i, j int) bool {
			if row.Holders[i].Node != row.Holders[j].Node {
				return row.Holders[i].Node < row.Holders[j].Node
			}
			return row.Holders[i].Module < row.Holders[j].Module
		})
		rows = append(rows, row)
	}
	var outside []catalogue.Held
	for _, h := range held {
		// Outside the set only if it resolves to no seat at all — a former name still resolves.
		if _, ok := catalogue.SeatNamed(h.Claim); !ok {
			outside = append(outside, h)
		}
	}
	sort.Slice(outside, func(i, j int) bool {
		if outside[i].Claim != outside[j].Claim {
			return outside[i].Claim < outside[j].Claim
		}
		return outside[i].Node < outside[j].Node
	})
	return rows, outside
}

// seatCommand changes the set — the whole point of it being data (novox/hq ADR 0122).
func seatCommand(ctx context.Context, args []string) error {
	if len(args) == 3 && args[0] == "rename" {
		from, to := args[1], args[2]
		open, err := openStores(ctx)
		if err != nil {
			return err
		}
		defer open.Close()
		if err := open.inventory.RenameSeat(ctx, from, to); err != nil {
			return err
		}
		fmt.Printf("%s is now %s — its former name still resolves, so nothing is rebuilt, "+
			"re-registered or frozen (novox/hq ADR 0122)\n", from, to)
		return nil
	}
	return fmt.Errorf("seat rename <from> <to>")
}

func seatsCommand(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("seats", flag.ContinueOnError)
	asJSON := set.Bool("json", false, "the same, as JSON")
	if err := set.Parse(args); err != nil {
		return err
	}

	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory
	shelf, err := inv.Catalogue(ctx)
	if err != nil {
		return err
	}
	// Every node, none excluded: the same view of what each machine holds that planning uses.
	world, err := theRestOfTheMesh(ctx, inv, shelf, "")
	if err != nil {
		return err
	}
	rows, outside := seatsHeld(catalogue.Seats(), world.Held)

	if *asJSON {
		out := struct {
			Seats   []seatRow        `json:"seats"`
			Outside []catalogue.Held `json:"outside,omitempty"`
		}{rows, outside}
		body, err := json.MarshalIndent(out, "", "  ")
		if err != nil {
			return err
		}
		fmt.Println(string(body))
		return nil
	}

	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
	fmt.Fprintln(w, "SEAT\tSCOPE\tDELIVERS\tHELD BY")
	for _, r := range rows {
		delivers := r.Delivers
		if delivers == "" {
			delivers = "—"
		}
		holders := "unheld"
		if len(r.Holders) > 0 {
			parts := make([]string, 0, len(r.Holders))
			for _, h := range r.Holders {
				parts = append(parts, h.Module+" on "+h.Node)
			}
			holders = strings.Join(parts, ", ")
		}
		fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", r.Seat, r.Scope, delivers, holders)
	}
	if err := w.Flush(); err != nil {
		return err
	}
	if len(outside) > 0 {
		fmt.Println("\nheld, and not a seat this mesh defines (registered before the set closed — novox/hq ADR 0110):")
		for _, h := range outside {
			fmt.Printf("  %s  %s on %s\n", h.Claim, h.Module, h.Node)
		}
	}
	return nil
}