package bootstrap

import (
	"context"
	"fmt"
	"os"
	"strings"
	"time"

	"github.com/novox/mesh-host/internal/declaration"
	"github.com/novox/mesh-host/internal/image"
	"github.com/novox/mesh-host/internal/profile"
)

// DefaultRegistry is where an image reference that names no host comes from.
const DefaultRegistry = "registry-1.docker.io:443"

// Preflight refuses early and plainly, and returns the bundle template it read.
//
// Everything here is a thing that will otherwise be discovered half way through: a machine with
// no runtime found after a bundle has been written, a template that does not parse found after an
// image has been loaded, a registry that cannot be reached found inside a `docker pull` that
// reports a network error and not a missing image. The order is cheapest first, so a mistake in
// what the installer was pointed at costs nothing to find.
func Preflight(ctx context.Context, o Options, d Deps, say func(string)) ([]byte, error) {
	// 1. Does this installer carry what it claims to?
	//
	// Asked before the machine is touched, for the same reason `mesh-host bundle` exists: a host
	// that carries no substrate must say so when somebody asks, not on a first node
	// (internal/bundle). An installer built without an image would otherwise get a machine as far
	// as a running store and a running broker and stop.
	if image.IsEmpty() {
		return nil, image.ErrEmpty
	}
	saved, err := image.Saved()
	if err != nil {
		return nil, err
	}
	carriedID, err := image.ID(saved)
	if err != nil {
		return nil, err
	}
	say(fmt.Sprintf("  control plane     %s carried (%s)",
		firstOr(image.Tags(saved), "untagged"), carriedID))

	// 2. Is the template there, and is it a substrate?
	template, err := os.ReadFile(o.Template)
	if err != nil {
		return nil, fmt.Errorf(
			"the bundle template could not be read: %w\n"+
				"It is what this machine will be asked to be, so there is nothing to do without "+
				"it. Point --bundle at one; mesh-host's examples/substrate-first-node.lock is "+
				"the shape", err)
	}
	// Parsed here as well as at the rewrite, because a template that is not a declaration should
	// cost a second rather than an image load and a written file.
	parsed, err := declaration.ParseFileTrusted(template)
	if err != nil {
		return nil, fmt.Errorf("the bundle template is not a declaration: %w", err)
	}
	if _, err := controlPlaneIn(parsed); err != nil {
		return nil, err
	}
	say(fmt.Sprintf("  bundle template   %s (%d resources)", o.Template, len(parsed.Resources)))

	// 3. Does a container runtime ANSWER?
	//
	// Not "is it installed" — novox/hq 04-ISSUES/007 is exactly that mistake, and the detector
	// this uses is the one written for it: it asks the daemon for its server version, which fails
	// when the daemon is down however complete the installation is.
	//
	// **Yes, the bundle installs the runtime itself**, and that is not a contradiction. The
	// installer needs one BEFORE the apply, because the control plane's image is loaded into it
	// first; the bundle still declares the package and the service because the host must own them
	// and reassert them at every reconcile. So this is not a duplicate check — it is the one thing
	// the bootstrap cannot bootstrap.
	//
	// Polled rather than asked once. A socket-activated daemon queued behind
	// `network-online.target` is not absent, it is a few seconds away, and `docker load` against
	// one blocks silently rather than failing (04-ISSUES/024). Waiting is the honest reading.
	if err := waitForRuntime(ctx, d.Run, o.Timeout, o.Wait, say); err != nil {
		return nil, err
	}

	// 4. Can this machine reach what the bundle's images come from?
	//
	// Asked of the hosts the bundle actually names rather than of the internet in general. The
	// mesh's own image is carried and needs nothing served — it is skipped here for exactly that
	// reason. Everything else is somebody else's image at somebody else's registry, and a machine
	// that cannot reach it fails inside a pull, which reports a network error where a person
	// reads a missing image.
	for _, host := range registriesIn(parsed) {
		dialing, cancel := context.WithTimeout(ctx, o.Timeout)
		err := d.Dial(dialing, host)
		cancel()
		if err != nil {
			return nil, fmt.Errorf(
				"this machine cannot reach %s, and the bundle's images are served from there: "+
					"%w\nThe apply would fail inside a pull, which says the wrong thing. Fix the "+
					"machine's network, or point the bundle at a registry it can reach",
				host, err)
		}
		say("  reachable         " + host)
	}
	return template, nil
}

// waitForRuntime asks the runtime, repeatedly, until it answers or the wait runs out.
func waitForRuntime(ctx context.Context, run Runner, probe, wait time.Duration, say func(string)) error {
	detector := containerRuntimeDetector(run)

	deadline := time.Now().Add(wait)
	var last string
	for {
		probing, cancel := context.WithTimeout(ctx, probe)
		verdict := detector.Detect(probing)
		cancel()
		if verdict.Present {
			say("  container runtime " + verdict.Detail)
			return nil
		}
		last = verdict.Detail

		if time.Now().After(deadline) {
			break
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-time.After(runtimeAskEvery):
		}
	}
	return fmt.Errorf(
		"this machine has no container runtime that answers, after waiting %s: %s\n"+
			"An installed package is not a capability (novox/hq 04-ISSUES/007) — the daemon was "+
			"asked and did not reply. Start it, then run this again; every step is idempotent",
		wait, last)
}

// runtimeAskEvery is how often the runtime is asked again while waiting for it.
var runtimeAskEvery = 2 * time.Second

// containerRuntimeDetector is the host's OWN detector for a working runtime, not a second
// implementation of the same question. Two answers to "is there a container runtime here" is how
// the installer and the host come to disagree about a machine.
func containerRuntimeDetector(run Runner) profile.Detector {
	for _, detector := range profile.Default(profile.Runner(run)) {
		if detector.Name() == profile.CapContainerRuntime {
			return detector
		}
	}
	// Unreachable unless the host's own detector set loses its container runtime, which would be
	// a change nobody would make on purpose — said rather than nil-dereferenced.
	panic("the host detects no container runtime capability, and the installer needs that answer")
}

// registriesIn is every host the bundle's images would be fetched from, without duplicates and in
// the order they appear.
func registriesIn(d *declaration.Declaration) []string {
	var hosts []string
	seen := map[string]bool{}
	for _, r := range d.Resources {
		container, ok := r.(*declaration.Container)
		if !ok {
			continue
		}
		host, served := registryOf(container.Image)
		if !served || seen[host] {
			continue
		}
		seen[host] = true
		hosts = append(hosts, host)
	}
	return hosts
}

// registryOf says where an image would be fetched from, and whether anything has to serve it.
//
// The second return is false for an image named by the digest of its own configuration: nothing
// serves those and nothing can (see `internal/declaration`'s checkImage). That is the whole reason
// the mesh's own control plane can be raised on a machine with no registry anywhere.
//
// The rule for the rest is the container runtime's own: the part before the first slash is a
// registry host if it looks like one — it has a dot, or a port, or it is `localhost` — and
// otherwise it is part of a repository name on the default registry.
func registryOf(reference string) (string, bool) {
	if reference == "" || strings.HasPrefix(reference, "sha256:") {
		return "", false
	}
	name := reference
	if at := strings.Index(name, "@"); at >= 0 {
		name = name[:at]
	}

	first, _, hasPath := strings.Cut(name, "/")
	if !hasPath || !(strings.Contains(first, ".") || strings.Contains(first, ":") || first == "localhost") {
		return DefaultRegistry, true
	}
	if !strings.Contains(first, ":") {
		// A registry with no port is reached over HTTPS, which is where a pull would go.
		return first + ":443", true
	}
	return first, true
}

func firstOr(values []string, fallback string) string {
	if len(values) == 0 || strings.TrimSpace(values[0]) == "" {
		return fallback
	}
	return values[0]
}