package opentunnel

import (
	"bufio"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"time"

	"github.com/johnandersen777/socialweb-computer-kcp/internal/assets"
	"github.com/johnandersen777/socialweb-computer-kcp/internal/contract/component"
	"github.com/johnandersen777/socialweb-computer-kcp/internal/contract/ingress"
	"github.com/johnandersen777/socialweb-computer-kcp/internal/kit/childproc"
	"github.com/johnandersen777/socialweb-computer-kcp/internal/kit/clock"
	"github.com/johnandersen777/socialweb-computer-kcp/internal/kit/loopback"
)

const (
	DefaultListenHost = "127.0.0.1"

	DefaultCommandPath = "/usr/local/bin/opentunnel"

	URLTimeout = 30 * time.Second

	MinRestartBackoff = time.Second

	MaxRestartBackoff = 30 * time.Second
)

var (
	urlPattern = regexp.MustCompile(`https://[^\s"'<>]+`)

	routePattern = regexp.MustCompile(`^[a-z0-9]([a-z0-9-]*[a-z0-9])?$`)
)

type Config struct {
	Command []string

	RouteName string

	ProxyProtocol string

	LocalHost string

	StateDir string

	Log *slog.Logger
}

var (
	_ ingress.Provider = (*Provider)(nil)

	_ ingress.Registrar = (*Provider)(nil)

	_ ingress.Registration = (*registration)(nil)
)

func (c Config) Check() error {
	command := c.command()
	path := strings.TrimSpace(command[0])
	switch {
	case path == "":
		return errors.New("ingressproxy opentunnel: spec.opentunnel.command[0] is empty")
	case filepath.IsAbs(path):
		st, err := os.Stat(path)
		if err != nil {
			return fmt.Errorf("ingressproxy opentunnel: command: %w", err)
		}
		if st.IsDir() || st.Mode().Perm()&0o111 == 0 {
			return fmt.Errorf("ingressproxy opentunnel: command %s is not an executable file", path)
		}
	default:
		if _, err := exec.LookPath(path); err != nil {
			return fmt.Errorf("ingressproxy opentunnel: command %q: %w", path, err)
		}
	}
	host := strings.TrimSpace(c.LocalHost)
	if host != "" {
		if strings.ContainsAny(host, ":/[]/ \t") {
			return fmt.Errorf("ingressproxy opentunnel: localHost %q is a host without a port", host)
		}
		if lower := strings.ToLower(host); net.ParseIP(host) == nil && (len(lower) > 63 || !routePattern.MatchString(lower)) {
			return fmt.Errorf("ingressproxy opentunnel: localHost %q is not a host name or IP address", host)
		}
	}
	return nil
}

func (c Config) command() []string {
	if len(c.Command) > 0 {
		return append([]string(nil), c.Command...)
	}
	if path := strings.TrimSpace(os.Getenv("SOCIALWEB_OPENTUNNEL_PATH")); path != "" {
		return []string{path}
	}
	if st, err := os.Stat(DefaultCommandPath); err == nil && !st.IsDir() && st.Mode().Perm()&0o111 != 0 {
		return []string{DefaultCommandPath}
	}
	return []string{"opentunnel"}
}

func (p *Provider) usePinnedCommand(log *slog.Logger) error {
	if len(p.cfg.Command) > 0 || strings.TrimSpace(os.Getenv("SOCIALWEB_OPENTUNNEL_PATH")) != "" {
		return nil
	}
	if st, err := os.Stat(DefaultCommandPath); err == nil && !st.IsDir() && st.Mode().Perm()&0o111 != 0 {
		return nil
	}
	cache := ""
	if dir := strings.TrimSpace(p.cfg.StateDir); dir != "" {
		cache = filepath.Join(dir, "runtime")
	}
	executable, err := assets.Resolve(assets.Options{Cache: cache, Log: log}, "opentunnel")
	if err != nil {
		return fmt.Errorf("ingressproxy opentunnel: resolving the pinned asset: %w", err)
	}
	p.cfg.Command = []string{executable.Path}
	return nil
}

func routeName(configured string, spec ingress.Spec) string {
	if name := strings.TrimSpace(configured); name != "" {
		return name
	}
	label := strings.ToLower(spec.Workspace + "-" + spec.Exposure)
	var b strings.Builder
	lastDash := false
	for _, r := range label {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
			lastDash = false
		default:
			if !lastDash && b.Len() > 0 {
				b.WriteByte('-')
				lastDash = true
			}
		}
	}
	name := strings.Trim(b.String(), "-")
	if len(name) > 63 {
		name = strings.TrimRight(name[:63], "-")
	}
	if name == "" {
		return "pds"
	}
	return name
}

func (c Config) localHost() string {
	host := strings.TrimSpace(c.LocalHost)
	if host == "" {
		return DefaultListenHost
	}
	return host
}

type Provider struct {
	cfg Config

	mu sync.Mutex

	log *slog.Logger

	args []string

	ctx context.Context

	cancel context.CancelFunc

	stopCh chan struct{}

	stopOnce sync.Once

	ready bool

	readiness component.ReadySignal

	registrations map[*registration]struct{}

	wg sync.WaitGroup
}

func New(cfg Config) *Provider {
	return &Provider{cfg: cfg}
}

func (p *Provider) Start(ctx context.Context) error {
	log := p.cfg.Log
	if log == nil {
		log = slog.New(slog.DiscardHandler)
	}
	if err := p.usePinnedCommand(log); err != nil {
		return err
	}
	if err := p.cfg.Check(); err != nil {
		return err
	}
	args := p.cfg.command()
	path := args[0]
	if !filepath.IsAbs(path) {
		resolved, err := exec.LookPath(path)
		if err != nil {
			return fmt.Errorf("ingressproxy opentunnel: command %q: %w", path, err)
		}
		path = resolved
	}
	args[0] = path
	runCtx, cancel := context.WithCancel(ctx)
	p.mu.Lock()
	if p.ctx != nil {
		p.mu.Unlock()
		cancel()
		return errors.New("ingressproxy opentunnel: the provider already started")
	}
	p.log = log
	p.args = args
	p.ctx = runCtx
	p.cancel = cancel
	p.stopCh = make(chan struct{})
	p.stopOnce = sync.Once{}
	p.ready = true
	p.registrations = map[*registration]struct{}{}
	stopCh := p.stopCh
	p.mu.Unlock()

	log.Info("ingressproxy_opentunnel_started", "provider", "opentunnel", "command", strings.Join(args, " "),
		"localHost", p.cfg.localHost(), "route", p.cfg.RouteName, "proxyProtocol", p.cfg.ProxyProtocol)
	p.readiness.Signal()

	select {
	case <-ctx.Done():
	case <-stopCh:
	}
	cancel()
	p.mu.Lock()
	p.ready = false
	p.ctx = nil
	p.cancel = nil
	p.mu.Unlock()
	p.closeAll()
	p.wg.Wait()
	return nil
}

func (p *Provider) Ready() component.Readiness {
	return &p.readiness
}

func (p *Provider) Stop(ctx context.Context) error {
	p.mu.Lock()
	stopCh := p.stopCh
	p.mu.Unlock()
	if stopCh == nil {
		return nil
	}
	p.stopOnce.Do(func() { close(stopCh) })
	p.closeAll()
	return nil
}

func (p *Provider) Endpoints() []component.Endpoint {
	return nil
}

func (p *Provider) Register(ctx context.Context, spec ingress.Spec, target ingress.Target) (ingress.Registration, error) {
	p.mu.Lock()
	ready := p.ready
	root := p.ctx
	args := append([]string(nil), p.args...)
	log := p.log
	p.mu.Unlock()
	if !ready || root == nil || len(args) == 0 {
		return nil, errors.New("ingressproxy opentunnel: the provider is not started")
	}
	if target == nil {
		return nil, errors.New("ingressproxy opentunnel: the handler registry is not configured")
	}
	bridge, err := loopback.Start(root, loopback.Config{
		Host:     p.cfg.localHost(),
		Protocol: spec.Protocol,
	}, target)
	if err != nil {
		return nil, err
	}
	runCtx, cancel := context.WithCancel(root)
	reg := &registration{
		provider: p,
		spec:     spec,
		bridge:   bridge,
		args:     args,
		log:      log.With("workspace", spec.Workspace, "exposure", spec.Exposure),
		cancel:   cancel,
		done:     make(chan struct{}),
	}
	child, err := reg.startChild(runCtx)
	if err != nil {
		cancel()
		_ = bridge.Close()
		return nil, err
	}
	if err := p.rememberURL(spec, child.url); err != nil {
		child.stop()
		cancel()
		_ = bridge.Close()
		return nil, err
	}
	reg.mu.Lock()
	reg.cmd = child.cmd
	reg.url = child.url + spec.Path
	reg.mu.Unlock()
	p.mu.Lock()
	running := p.ctx == root
	if running {
		if p.registrations == nil {
			p.registrations = map[*registration]struct{}{}
		}
		p.registrations[reg] = struct{}{}
		p.wg.Go(func() { reg.supervise(runCtx, child) })
	}
	p.mu.Unlock()
	if !running {
		cancel()
		child.stop()
		_ = bridge.Close()
		return nil, errors.New("ingressproxy opentunnel: the provider stopped")
	}
	return reg, nil
}

func (p *Provider) closeAll() {
	p.mu.Lock()
	registrations := p.registrations
	p.registrations = nil
	p.mu.Unlock()
	for registration := range registrations {
		_ = registration.Close()
	}
}

func (p *Provider) forget(registration *registration) {
	p.mu.Lock()
	if p.registrations != nil {
		delete(p.registrations, registration)
	}
	p.mu.Unlock()
}

func (p *Provider) rememberURL(spec ingress.Spec, raw string) error {
	origin := originOf(raw)
	if origin == "" {
		return fmt.Errorf("ingressproxy opentunnel: printed URL %q has no https origin", raw)
	}
	dir := strings.TrimSpace(p.cfg.StateDir)
	if dir == "" {
		return nil
	}
	sum := sha256.Sum256([]byte(spec.Workspace + "/" + spec.Exposure))
	path := filepath.Join(dir, "opentunnel", hex.EncodeToString(sum[:8])+".url")
	current, err := os.ReadFile(path)
	switch {
	case err == nil:
		if previous := strings.TrimSpace(string(current)); previous != "" && !strings.EqualFold(previous, origin) {
			return fmt.Errorf("%w: opentunnel route %q for %s/%s is %s, was %s",
				ingress.ErrStableHostMismatch, routeName(p.cfg.RouteName, spec), spec.Workspace, spec.Exposure, origin, previous)
		}
		return nil
	case !errors.Is(err, os.ErrNotExist):
		return fmt.Errorf("ingressproxy opentunnel: reading the stable host %s: %w", path, err)
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return fmt.Errorf("ingressproxy opentunnel: the stable host dir: %w", err)
	}
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, []byte(origin+"\n"), 0o600); err != nil {
		return fmt.Errorf("ingressproxy opentunnel: writing the stable host: %w", err)
	}
	if err := os.Rename(tmp, path); err != nil {
		_ = os.Remove(tmp)
		return fmt.Errorf("ingressproxy opentunnel: placing the stable host: %w", err)
	}
	return nil
}

func (p *Provider) rememberRestart(spec ingress.Spec, raw string) error {
	return p.rememberURL(spec, raw)
}

func originOf(raw string) string {
	parsed, err := url.Parse(strings.TrimSpace(raw))
	if err != nil || parsed.Scheme != "https" || parsed.Host == "" {
		return ""
	}
	return parsed.Scheme + "://" + parsed.Host
}

type registration struct {
	provider *Provider

	spec ingress.Spec

	bridge *loopback.Bridge

	args []string

	log *slog.Logger

	cancel context.CancelFunc

	done chan struct{}

	closeOnce sync.Once

	mu sync.Mutex

	cmd *exec.Cmd

	url string
}

func (r *registration) URL() string {
	r.mu.Lock()
	defer r.mu.Unlock()
	return r.url
}

func (r *registration) Provider() string {
	return "opentunnel (https URL)"
}

func (r *registration) Close() error {
	r.closeOnce.Do(func() {
		r.cancel()
		r.mu.Lock()
		cmd := r.cmd
		r.mu.Unlock()
		if cmd != nil && cmd.Process != nil {
			_ = cmd.Process.Kill()
		}
		_ = r.bridge.Close()
		<-r.done
		r.provider.forget(r)
	})
	return nil
}

type child struct {
	cmd *exec.Cmd

	url string

	tail *childproc.Tail

	started time.Time

	output *sync.WaitGroup
}

func (c *child) stop() {
	childproc.Kill(c.cmd)
	c.output.Wait()
}

func (r *registration) startChild(ctx context.Context) (*child, error) {
	args := append([]string(nil), r.args...)
	if _, _, err := net.SplitHostPort(r.bridge.Address()); err != nil {
		return nil, fmt.Errorf("ingressproxy opentunnel: the loopback address %q: %w", r.bridge.Address(), err)
	}
	args = append(args, "route", "add", r.bridge.Address())
	args = append(args, "--name", routeName(r.provider.cfg.RouteName, r.spec))
	switch strings.ToLower(strings.TrimSpace(r.provider.cfg.ProxyProtocol)) {
	case "v1", "v2":
		args = append(args, "--proxy-protocol", strings.ToLower(strings.TrimSpace(r.provider.cfg.ProxyProtocol)))
	}
	cmd := exec.CommandContext(ctx, args[0], args[1:]...)
	cmd.Env = os.Environ()
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("ingressproxy opentunnel: stdout: %w", err)
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, fmt.Errorf("ingressproxy opentunnel: stderr: %w", err)
	}
	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("ingressproxy opentunnel: starting %s: %w", args[0], err)
	}
	tail := &childproc.Tail{}
	found := make(chan string, 1)
	var pumps sync.WaitGroup
	pumps.Go(func() { pump(stdout, tail, found) })
	pumps.Go(func() { pump(stderr, tail, found) })
	output := &sync.WaitGroup{}
	output.Go(func() {
		pumps.Wait()
		close(found)
	})
	stop := func() {
		childproc.Kill(cmd)
		output.Wait()
	}
	timer := time.NewTimer(URLTimeout)
	defer timer.Stop()
	for {
		select {
		case <-ctx.Done():
			stop()
			return nil, ctx.Err()
		case <-timer.C:
			stop()
			return nil, fmt.Errorf("ingressproxy opentunnel: %s printed no URL within %s: %s", args[0], URLTimeout, strings.TrimSpace(tail.String()))
		case raw, ok := <-found:
			if !ok {
				stop()
				return nil, fmt.Errorf("ingressproxy opentunnel: %s ended before printing a URL: %s", args[0], strings.TrimSpace(tail.String()))
			}
			r.log.Info("ingressproxy_opentunnel_route_added", "address", r.bridge.Address(), "url", raw)
			return &child{cmd: cmd, url: raw, tail: tail, started: time.Now(), output: output}, nil
		}
	}
}

func (r *registration) supervise(ctx context.Context, first *child) {
	defer close(r.done)
	current := first
	backoff := MinRestartBackoff
	for {
		if current == nil {
			next, err := r.startChild(ctx)
			if err != nil {
				if ctx.Err() != nil {
					return
				}
				r.log.Warn("ingressproxy_opentunnel_restart_failed", "err", err.Error())
				backoff = childproc.NextBackoff(backoff, MinRestartBackoff, MaxRestartBackoff)
				if !clock.Sleep(ctx, backoff) {
					return
				}
				continue
			}
			if err := r.provider.rememberRestart(r.spec, next.url); err != nil {
				next.stop()
				r.log.Error("ingressproxy_opentunnel_url_changed", "workspace", r.spec.Workspace,
					"exposure", r.spec.Exposure, "err", err.Error())
				return
			}
			current = next
			r.mu.Lock()
			r.cmd = next.cmd
			r.url = next.url + r.spec.Path
			r.mu.Unlock()
		}
		started := current.started
		err := current.cmd.Wait()
		current.output.Wait()
		stderr := strings.TrimSpace(current.tail.String())
		r.mu.Lock()
		if r.cmd == current.cmd {
			r.cmd = nil
		}
		r.mu.Unlock()
		current = nil
		if ctx.Err() != nil {
			return
		}
		if time.Since(started) >= time.Minute {
			backoff = MinRestartBackoff
		}
		r.log.Warn("ingressproxy_opentunnel_exited", "err", fmt.Sprint(err), "output", stderr)
		if !clock.Sleep(ctx, backoff) {
			return
		}
		backoff = childproc.NextBackoff(backoff, MinRestartBackoff, MaxRestartBackoff)
	}
}

func pump(reader io.Reader, tail *childproc.Tail, found chan<- string) {
	scanner := bufio.NewScanner(reader)
	scanner.Buffer(make([]byte, 4096), 64*1024)
	for scanner.Scan() {
		line := scanner.Text()
		tail.Write([]byte(line + "\n"))
		if raw, ok := urlIn(line); ok {
			select {
			case found <- raw:
			default:
			}
		}
	}
}

func urlIn(line string) (string, bool) {
	for _, match := range urlPattern.FindAllString(line, -1) {
		candidate := strings.TrimRight(match, ".,;:)]}")
		parsed, err := url.Parse(candidate)
		if err != nil || parsed.Host == "" {
			continue
		}
		host := strings.ToLower(parsed.Hostname())
		if host != "opentunnel.xyz" && strings.HasSuffix(host, ".opentunnel.xyz") && strings.Count(host, ".") >= 2 {
			return candidate, true
		}
	}
	return "", false
}