// Package deploy implements the once-add recipe for adding a LAN-reachable
// Once site as a single-label <name>.local host.
//
// Once's binary is statically linked (pure-Go resolver), so its post-deploy
// HTTP verify resolves /etc/hosts + real DNS only — never mDNS. The TUI install
// also forces TLS on and can't get a cert for a private .local host. So we add
// an /etc/hosts entry (verify resolves to loopback) and deploy from the CLI with
// --disable-tls; once-mdns-sync then publishes <name>.local to the LAN.
package deploy

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
	"os/exec"
	"regexp"
	"sort"
	"strings"
	"time"
)

const (
	hostsPath     = "/etc/hosts"
	verifyTimeout = 60 * time.Second
)

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

// ValidateName enforces a single DNS label: lowercase letters, digits and
// hyphens, not starting or ending with a hyphen, 63 characters or fewer.
func ValidateName(name string) error {
	switch {
	case name == "":
		return fmt.Errorf("name is required")
	case strings.Contains(name, "."):
		return fmt.Errorf("name must be a single label (no dots), e.g. 'book'")
	case len(name) > 63:
		return fmt.Errorf("name must be 63 characters or fewer")
	case !nameRe.MatchString(name):
		return fmt.Errorf("use lowercase letters, digits and hyphens (not leading/trailing)")
	}
	return nil
}

// Host returns the .local hostname for a name.
func Host(name string) string { return name + ".local" }

var hostLabelRe = regexp.MustCompile(`"host"\s*:\s*"([^"]+)"`)

// InUseHosts returns the set of *.local hosts currently served by running Once
// apps. It mirrors once-mdns-sync: read each app container's `once` label (Once
// stores ApplicationSettings as JSON there) and pull its "host" field, keeping
// only the *.local names — so image names and env values can't false-match.
func InUseHosts() (map[string]bool, error) { return dockerHosts(false) }

// PresentHosts returns *.local hosts on this box's Once containers including
// stopped ones — the right check for "does this app still exist?" before
// attempting removal.
func PresentHosts() (map[string]bool, error) { return dockerHosts(true) }

func dockerHosts(includeStopped bool) (map[string]bool, error) {
	psArgs := []string{"ps", "-q"}
	if includeStopped {
		psArgs = []string{"ps", "-a", "-q"}
	}
	out, err := exec.Command("docker", psArgs...).Output()
	if err != nil {
		return nil, fmt.Errorf("docker ps: %w", err)
	}
	ids := strings.Fields(string(out))
	hosts := map[string]bool{}
	if len(ids) == 0 {
		return hosts, nil
	}
	args := append([]string{"inspect", "--format", `{{ index .Config.Labels "once" }}`}, ids...)
	out, err = exec.Command("docker", args...).Output()
	if err != nil {
		return nil, fmt.Errorf("docker inspect: %w", err)
	}
	return parseHosts(string(out)), nil
}

// parseHosts extracts the *.local "host" values from concatenated `once` label
// JSON blobs.
func parseHosts(blob string) map[string]bool {
	hosts := map[string]bool{}
	for _, m := range hostLabelRe.FindAllStringSubmatch(blob, -1) {
		h := strings.ToLower(m[1])
		if strings.HasSuffix(h, ".local") {
			hosts[h] = true
		}
	}
	return hosts
}

// DeployedHosts returns the *.local hosts currently served by running Once
// apps, sorted — the candidates for removal.
func DeployedHosts() ([]string, error) {
	m, err := InUseHosts()
	if err != nil {
		return nil, err
	}
	hosts := make([]string, 0, len(m))
	for h := range m {
		hosts = append(hosts, h)
	}
	sort.Strings(hosts)
	return hosts, nil
}

// EnsureHostsEntry adds `127.0.0.1 <host>` to /etc/hosts if no line already
// resolves host. It reports whether it added a line. Requires root.
func EnsureHostsEntry(host string) (bool, error) {
	data, err := os.ReadFile(hostsPath)
	if err != nil {
		return false, err
	}
	present := regexp.MustCompile(`(?m)^[0-9.]+[ \t]+` + regexp.QuoteMeta(host) + `([ \t]|$)`)
	if present.Match(data) {
		return false, nil
	}
	f, err := os.OpenFile(hostsPath, os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return false, err
	}
	defer f.Close()
	var b strings.Builder
	if len(data) > 0 && data[len(data)-1] != '\n' {
		b.WriteByte('\n') // don't fuse onto a file that lacks a trailing newline
	}
	b.WriteString("127.0.0.1 " + host + "\n")
	if _, err := f.WriteString(b.String()); err != nil {
		return false, err
	}
	return true, nil
}

// RemoveHostsEntry deletes any line in /etc/hosts that resolves host. Returns
// whether it removed one. Requires root.
func RemoveHostsEntry(host string) (bool, error) {
	data, err := os.ReadFile(hostsPath)
	if err != nil {
		return false, err
	}
	kept, removed := filterHostLines(string(data), host)
	if !removed {
		return false, nil
	}
	// O_TRUNC keeps the existing file mode; root owns /etc/hosts.
	return true, os.WriteFile(hostsPath, []byte(kept), 0o644)
}

// filterHostLines drops every line resolving host, returning the rewritten file
// content and whether anything was removed. A line matches only when host is the
// first name right after the leading IP — so 'book.local' never matches
// 'mybook.local' or 'book.local2'.
func filterHostLines(data, host string) (string, bool) {
	re := regexp.MustCompile(`^[0-9.]+[ \t]+` + regexp.QuoteMeta(host) + `([ \t]|$)`)
	lines := strings.Split(data, "\n")
	kept := make([]string, 0, len(lines))
	removed := false
	for _, ln := range lines {
		if re.MatchString(ln) {
			removed = true
			continue
		}
		kept = append(kept, ln)
	}
	return strings.Join(kept, "\n"), removed
}

// Verify polls http://<host>/up until it returns 2xx or the timeout elapses.
// The box resolves single-label .local via nss, so this is a real end-to-end
// reachability check.
func Verify(ctx context.Context, host string, timeout time.Duration) error {
	url := "http://" + host + "/up"
	client := &http.Client{Timeout: 5 * time.Second}
	deadline := time.Now().Add(timeout)
	var lastErr error
	for time.Now().Before(deadline) {
		req, _ := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
		resp, err := client.Do(req)
		if err != nil {
			if ctx.Err() != nil {
				return ctx.Err()
			}
			lastErr = err
		} else {
			resp.Body.Close()
			if resp.StatusCode >= 200 && resp.StatusCode < 300 {
				return nil
			}
			lastErr = fmt.Errorf("GET %s returned %d", url, resp.StatusCode)
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-time.After(2 * time.Second):
		}
	}
	if lastErr == nil {
		lastErr = fmt.Errorf("timed out")
	}
	return fmt.Errorf("%s not reachable within %s: %w", url, timeout, lastErr)
}

// Event is one step of progress from Run. Exactly one of the terminal flags is
// set on the final event: Err for failure, Done for success.
type Event struct {
	Line string // progress or streamed command output
	Err  error  // non-nil: terminal failure
	Done bool   // true: terminal success (Line holds the reachable URL note)
}

// Run executes the full recipe for name+image, emitting progress on the
// returned channel. The channel is closed after a terminal Event. Used by both
// the TUI and the non-interactive CLI path.
func Run(ctx context.Context, name, image string) <-chan Event {
	ch := make(chan Event)
	go func() {
		defer close(ch)
		emit := func(s string) { ch <- Event{Line: s} }
		fail := func(err error) { ch <- Event{Err: err} }
		host := Host(name)

		emit("Checking " + host + " isn't already in use…")
		inUse, err := InUseHosts()
		if err != nil {
			fail(err)
			return
		}
		if inUse[host] {
			fail(fmt.Errorf("%s is already served by a running app — pick another name", host))
			return
		}

		added, err := EnsureHostsEntry(host)
		if err != nil {
			fail(fmt.Errorf("updating /etc/hosts: %w", err))
			return
		}
		if added {
			emit("Added '127.0.0.1 " + host + "' to /etc/hosts")
		} else {
			emit("/etc/hosts already resolves " + host)
		}

		emit("Deploying " + image + " as " + host + " (TLS off)…")
		if err := streamCmd(ctx, "once", []string{"deploy", image, "--host", host, "--disable-tls"}, emit); err != nil {
			fail(fmt.Errorf("once deploy failed: %w", err))
			return
		}

		emit("Waiting for " + host + " to come up…")
		if err := Verify(ctx, host, verifyTimeout); err != nil {
			fail(err)
			return
		}
		ch <- Event{Done: true, Line: "http://" + host}
	}()
	return ch
}

// RunRemove tears down the app on host: `once remove <host> [--remove-data]`
// (skipped if no container for host exists — the orphan case, where the Once
// UI already removed the app but left its /etc/hosts line behind), then clears
// that /etc/hosts line (once-mdns-sync drops the LAN publisher on its own).
// Emits progress like Run; channel closes after a terminal Event.
func RunRemove(ctx context.Context, host string, removeData bool) <-chan Event {
	ch := make(chan Event)
	go func() {
		defer close(ch)
		emit := func(s string) { ch <- Event{Line: s} }
		fail := func(err error) { ch <- Event{Err: err} }

		present, err := PresentHosts()
		if err != nil {
			fail(err)
			return
		}
		appRemoved := false
		if present[host] {
			args := []string{"remove", host}
			note := ""
			if removeData {
				args = append(args, "--remove-data")
				note = " (incl. data volume)"
			}
			emit("Removing app " + host + note + "…")
			if err := streamCmd(ctx, "once", args, emit); err != nil {
				fail(fmt.Errorf("once remove failed: %w", err))
				return
			}
			appRemoved = true
		} else {
			emit("No container for " + host + " — cleaning up /etc/hosts only")
		}

		hostsRemoved, err := RemoveHostsEntry(host)
		if err != nil {
			fail(fmt.Errorf("updating /etc/hosts: %w", err))
			return
		}
		if hostsRemoved {
			emit("Removed '" + host + "' from /etc/hosts")
		} else {
			emit("No /etc/hosts entry for " + host)
		}

		ch <- Event{Done: true, Line: removeDoneMsg(host, appRemoved, hostsRemoved)}
	}()
	return ch
}

// removeDoneMsg picks the success-line wording for the four outcomes of remove.
func removeDoneMsg(host string, appRemoved, hostsRemoved bool) string {
	switch {
	case appRemoved && hostsRemoved:
		return "Removed " + host
	case appRemoved:
		return "Removed " + host + " (no /etc/hosts entry to clean)"
	case hostsRemoved:
		return "Cleaned orphan /etc/hosts entry for " + host
	default:
		return "Nothing to remove for " + host
	}
}

// streamCmd runs name+args, streaming combined stdout/stderr line by line
// through emit, and returns the command's exit error.
func streamCmd(ctx context.Context, name string, args []string, emit func(string)) error {
	cmd := exec.CommandContext(ctx, name, args...)
	pr, pw := io.Pipe()
	cmd.Stdout = pw
	cmd.Stderr = pw // same writer: os/exec uses a single pipe, so lines stay ordered
	if err := cmd.Start(); err != nil {
		pw.Close()
		return fmt.Errorf("starting %s: %w", name, err)
	}
	scanDone := make(chan struct{})
	go func() {
		sc := bufio.NewScanner(pr)
		sc.Buffer(make([]byte, 0, 64*1024), 1<<20)
		for sc.Scan() {
			emit(sc.Text())
		}
		close(scanDone)
	}()
	werr := cmd.Wait()
	pw.Close()
	<-scanDone
	return werr
}