// Command mesh-bootstrap brings a mesh into existence on a bare machine.
//
// Tier 0, beside `mesh-host` and not inside it. Bootstrapping is done by hand and it changes a
// machine, which is what tier 0 is (novox/hq 03-DESIGN/01-to-be/05-the-node-host.md) — but
// `mesh-host` states of itself that it connects to nothing and listens on nothing and that what it
// applies comes from a file, and that is the whole reason an always-running root daemon can be
// audited by reading one page. An installer that loads images and interrogates a control plane
// cannot be folded into it without making that sentence false. Same tier, same repository,
// different program.
//
// What it does not do is enrol this machine, register modules or assign them. It stops at a
// running substrate with a control plane that answers, which is a mesh of one node.
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"net"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/novox/mesh-host/internal/apply"
	"github.com/novox/mesh-host/internal/bootstrap"
	"github.com/novox/mesh-host/internal/store"
)

// version is stamped at build time. Unset in a development build, and said so rather than
// defaulted to something that looks like a release.
var version = "development build"

const (
	defaultTemplate = "substrate.lock"
	defaultOut      = "/var/lib/mesh-host/substrate.lock"
)

const usage = `mesh-bootstrap — make a bare machine into a mesh

  bootstrap   preflight, load, bundle, apply, verify   (the default)
  version

  --bundle    the substrate template to build this machine's bundle from
              (default ` + defaultTemplate + `)
  --out       where the produced bundle is written, for a person to read
              (default ` + defaultOut + `)
  --state     where this node records what it has applied
              (default ` + store.DefaultPath + `)
  --system    which operating system this is; by default it is asked
  --timeout   how long any single probe may take (default 30s)
  --wait      how long a thing that is merely starting is given (default 3m)
  --dry-run   everything that does not change the machine
  --json      machine-readable output

It carries the control plane's image and applies a substrate. Every step is idempotent:
run it again after fixing whatever it named, and the steps that already succeeded say so.
`

func main() {
	// Ctrl-C must stop the installer, not be swallowed by whatever it is waiting for — and it
	// waits on pulls, on a runtime starting, and on a control plane opening its stores.
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	command, opts, jsonOut, err := parseArgs(os.Args[1:])
	if err == nil {
		err = run(ctx, command, opts, jsonOut)
	}
	if err != nil {
		fmt.Fprintf(os.Stderr, "mesh-bootstrap: %v\n", err)
		os.Exit(1)
	}
}

// parseArgs takes an optional subcommand first, then its flags.
//
// Parsed in a loop for the reason `mesh-host` records: the standard library stops at the FIRST
// non-flag argument, so a flag sitting after one is silently dropped and the command exits zero
// having ignored what it was asked. That fault has been paid for twice in this repository and is
// not being paid for a third time.
func parseArgs(args []string) (string, bootstrap.Options, bool, error) {
	opts := bootstrap.Options{
		Template: defaultTemplate,
		Out:      defaultOut,
		State:    store.DefaultPath,
		// Longer than the host's 10s: these probes reach a container runtime that may be busy
		// pulling, and a probe that times out on a working machine is a false refusal.
		Timeout: 30 * time.Second,
		// A socket-activated runtime queued behind the network, and a control plane running its
		// first `initdb`-shaped wait, are both minutes rather than seconds.
		Wait: 3 * time.Minute,
	}
	var jsonOut bool

	command := "bootstrap"
	if len(args) > 0 && len(args[0]) > 0 && args[0][0] != '-' {
		command = args[0]
		args = args[1:]
	}

	set := newFlagSet(&opts, &jsonOut)
	var positionals []string
	rest := args
	for {
		if err := set.Parse(rest); err != nil {
			return "", opts, false, err
		}
		rest = set.Args()
		if len(rest) == 0 {
			break
		}
		positionals = append(positionals, rest[0])
		rest = rest[1:]
	}

	// Refused rather than ignored: a mistyped argument that changes nothing and reports success is
	// worse than an error, and this program's whole job is to change a machine.
	if len(positionals) > 0 {
		return "", opts, false, fmt.Errorf(
			"unexpected argument %q — try `mesh-bootstrap help`", positionals[0])
	}
	return command, opts, jsonOut, nil
}

func newFlagSet(opts *bootstrap.Options, jsonOut *bool) *flag.FlagSet {
	set := flag.NewFlagSet("mesh-bootstrap", flag.ContinueOnError)
	set.SetOutput(os.Stderr)
	set.Usage = func() { fmt.Fprint(os.Stderr, usage) }
	set.StringVar(&opts.Template, "bundle", opts.Template, "the substrate template to build from")
	set.StringVar(&opts.Out, "out", opts.Out, "where the produced bundle is written")
	set.StringVar(&opts.State, "state", opts.State, "where this node records what it has applied")
	set.StringVar(&opts.System, "system", opts.System, "which operating system this is")
	set.DurationVar(&opts.Timeout, "timeout", opts.Timeout, "how long any single probe may take")
	set.DurationVar(&opts.Wait, "wait", opts.Wait, "how long something merely starting is given")
	set.BoolVar(&opts.DryRun, "dry-run", false, "everything that does not change the machine")
	set.BoolVar(jsonOut, "json", false, "machine-readable output")
	return set
}

func run(ctx context.Context, command string, opts bootstrap.Options, jsonOut bool) error {
	switch command {
	case "bootstrap":
		say := func(line string) {
			if !jsonOut {
				fmt.Println(line)
			}
		}
		result, err := bootstrap.Run(ctx, opts, bootstrap.Deps{
			Run:  apply.ExecRunner,
			Dial: dial,
		}, say)

		// Printed whichever way it went. What the installer got through before it stopped is on
		// the machine either way, and a report that only exists on success describes a machine
		// nobody has (novox/hq ADR 0018).
		if jsonOut {
			encoder := json.NewEncoder(os.Stdout)
			encoder.SetIndent("", "  ")
			if encodeErr := encoder.Encode(result); encodeErr != nil && err == nil {
				return encodeErr
			}
		}
		return err

	case "version":
		fmt.Println(version)
		return nil

	case "help", "-h", "--help":
		fmt.Fprint(os.Stderr, usage)
		return nil

	default:
		return fmt.Errorf("unknown command %q — try `mesh-bootstrap help`", command)
	}
}

// dial answers whether a TCP address responds.
//
// A connection rather than a ping or a name lookup: what has to work is a pull, and a pull opens a
// connection to exactly this address. A machine whose DNS resolves and whose route is missing
// passes a lookup and fails the thing that matters.
func dial(ctx context.Context, address string) error {
	var dialer net.Dialer
	conn, err := dialer.DialContext(ctx, "tcp", address)
	if err != nil {
		return err
	}
	return conn.Close()
}