package bootstrap

import (
	"context"
	"fmt"
	"net"
	"strings"

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

// quietUDP are processes whose UDP sockets every fresh machine has — name resolution, address
// configuration, time — and which serve nobody. ss names a process by its first fifteen characters,
// so both spellings are here.
//
// **Still to be measured** (novox/hq ADR 0100): this list is what a fresh machine is expected to
// hold, and it must be checked against a freshly installed lab machine before it is trusted.
var quietUDP = map[string]bool{
	"systemd-resolved": true, "systemd-resolve": true,
	"systemd-networkd": true, "systemd-network": true,
	"systemd-timesyncd": true, "systemd-timesyn": true,
	"dhcpcd": true,
}

// InUse says what makes this machine a machine in use (novox/hq ADR 0100): every running container
// no host made, and every socket listening on an address other than loopback that is not ssh's — a
// UDP one only when it is held by something other than what every fresh machine runs. ours names
// what the mesh itself runs, which a re-run of genesis finds and does not count.
func InUse(ctx context.Context, run Runner, ours func(name string) bool) ([]string, []reachable.Reach, error) {
	var containers []string
	out, err := run(ctx, "docker", "ps", "--format", "{{.Names}}\t{{.Label \"mesh-host.spec\"}}")
	if err != nil {
		return nil, nil, fmt.Errorf("cannot ask the container runtime what is running here: %w", err)
	}
	for _, line := range strings.Split(out, "\n") {
		name, label, _ := strings.Cut(strings.TrimSpace(line), "\t")
		label = strings.TrimSpace(label)
		if name == "" || (label != "" && label != "<no value>") || ours(name) {
			continue
		}
		containers = append(containers, name)
	}

	listening, err := run(ctx, "ss", "-Hltunp")
	if err != nil {
		return nil, nil, fmt.Errorf("cannot read what listens on this machine: %w", err)
	}
	var listeners []reachable.Reach
	for _, r := range reachable.Sockets(listening) {
		if counts(r) && !ours(r.By) {
			listeners = append(listeners, r)
		}
	}
	return containers, listeners, nil
}

func counts(r reachable.Reach) bool {
	if ip := net.ParseIP(r.Address); ip != nil && ip.IsLoopback() {
		return false
	}
	switch r.Protocol {
	case "tcp":
		return r.By != "sshd" && !(r.By == "" && r.Port == 22)
	case "udp":
		return !quietUDP[r.By]
	}
	return false
}

// RefuseAMachineInUse is the check a converged genesis makes before changing anything: a machine
// in use is refused, naming every container and listener counted, because raising the foundation's
// filter there would close what it serves — a forgotten --adopted must not close a working machine.
// An adopted genesis is told what it found, and goes on.
func RefuseAMachineInUse(ctx context.Context, o Options, run Runner, say func(string)) error {
	known, err := store.Load(o.State)
	if err != nil {
		return err
	}
	if len(known.Resources) > 0 {
		// What genesis raised on an earlier run is the mesh's, and it is what the machine now
		// serves; the question was answered the first time.
		say("  in use            not asked: this machine carries what an earlier genesis raised")
		return nil
	}
	containers, listeners, err := InUse(ctx, run, func(string) bool { return false })
	if err != nil {
		return err
	}
	if len(containers) == 0 && len(listeners) == 0 {
		say("  in use            no: no container runs and nothing listens beyond ssh")
		return nil
	}
	var named []string
	for _, c := range containers {
		named = append(named, "container "+c)
	}
	for _, l := range listeners {
		by := l.By
		if by == "" {
			by = "an unnamed process"
		}
		named = append(named, fmt.Sprintf("%s %s:%d by %s", l.Protocol, l.Address, l.Port, by))
	}
	if o.Adopted {
		say(fmt.Sprintf("  in use            yes, and adopted: %d thing(s) found are kept", len(named)))
		return nil
	}
	return fmt.Errorf("this machine is in use, and a converged genesis would close what it serves:\n  - %s\n"+
		"If it is meant to join the mesh keeping what it runs, pass --adopted: its firewall stays in "+
		"force and every module is taken on it one at a time. Nothing was changed",
		strings.Join(named, "\n  - "))
}