// Package panel serves the embedded Felis control panel next to the external API.
package panel

import (
	"bytes"
	"crypto/sha256"
	"embed"
	"encoding/base64"
	"encoding/json"
	"errors"
	"io"
	"io/fs"
	"net/http"
	"path"
	"regexp"
	"strings"
)

//go:embed static
var static embed.FS

type runtimeConfig struct {
	Distributed   bool   `json:"distributed,omitempty"`
	APIBase       string `json:"apiBase"`
	RootDomain    string `json:"rootDomain"`
	PanelHostname string `json:"panelHostname,omitempty"`
	AdminHostname string `json:"adminHostname,omitempty"`
	// GamePort is the public Minecraft port, absent when it is the default 25565.
	GamePort    int       `json:"gamePort,omitempty"`
	GameVersion string    `json:"gameVersion,omitempty"`
	Build       buildInfo `json:"build"`
}

// buildInfo is the resolved build stamp the panel renders in its version badge.
// It is derived once, server-side, from the binary's `main.version` — the stamp
// deploy/bootstrap.sh links in per install channel — so the panel needs no brittle
// string parsing — it just renders `Release`, appending `+Commit` when `Dev`.
type buildInfo struct {
	// Version is the raw resolved stamp (e.g. "v1.0.0-earlyAccess+g1a2b3c4").
	Version string `json:"version"`
	// Release is the "big version" — the newest tag with any commit suffix
	// stripped (e.g. "v1.0.0-earlyAccess"). It is what the release channel shows.
	Release string `json:"release"`
	// Commit is the short commit the dev channel was built from (e.g. "1a2b3c4"),
	// empty for a clean release build.
	Commit string `json:"commit,omitempty"`
	// Dev is true for a non-release build — the dev channel (main past the tag), an
	// untagged/bare-SHA build, a dirty tree, or an un-stamped local `go build`.
	Dev bool `json:"dev"`
}

// devSuffix matches the trailing "+g<sha>" that deploy/bootstrap.sh's dev channel
// appends to the newest tag — the shape a dev build actually carries. The "+" is
// deliberate and load-bearing: it is semver BUILD METADATA, ignored for ordering,
// so a dev build ahead of v1.2.3 still compares as newer than v1.2.3. The
// git-describe form below puts that distance in the PRERELEASE field instead,
// which sorts BELOW the bare tag.
var devSuffix = regexp.MustCompile(`\+g([0-9a-f]+)$`)

// describeSuffix matches the trailing "-<commits>-g<sha>" that `git describe`
// appends to the newest tag once HEAD is past it. bootstrap.sh no longer produces
// this form, but a hand-rolled `go build -ldflags "-X main.version=$(git describe)"`
// still does, and parsing it costs one case. Match is anchored at end so a tag whose
// prerelease part itself contains hyphens (v1.0.0-earlyAccess) keeps that part in
// Release.
var describeSuffix = regexp.MustCompile(`-([0-9]+)-g([0-9a-f]+)$`)

// releaseTag matches a clean released semantic-version tag (vMAJOR.MINOR.PATCH
// with an optional -prerelease), i.e. the name the release channel builds. It is
// permissive on the prerelease so tags like v1.0.0-earlyAccess qualify.
var releaseTag = regexp.MustCompile(`^v[0-9]+\.[0-9]+\.[0-9]+(-[0-9A-Za-z.]+)?$`)

// parseBuildVersion splits a build stamp into the fields the panel version badge
// renders. Cases: a dev stamp "<tag>+gSHA" (or the git-describe "<tag>-N-gSHA") →
// Release=<tag>, Commit=SHA, Dev=true; a clean release tag "vX.Y.Z[-pre]" →
// Release=tag, Dev=false; anything else ("dev", "unknown", a bare short SHA, a
// dirty tree) → best-effort Release with Dev=true.
func parseBuildVersion(raw string) buildInfo {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		raw = "dev"
	}
	bi := buildInfo{Version: raw}
	core := strings.TrimSuffix(raw, "-dirty")
	dirty := core != raw

	switch {
	case devSuffix.MatchString(core):
		m := devSuffix.FindStringSubmatch(core)
		bi.Release = core[:len(core)-len(m[0])]
		bi.Commit = m[1]
		bi.Dev = true
	case describeSuffix.MatchString(core):
		m := describeSuffix.FindStringSubmatch(core)
		bi.Release = core[:len(core)-len(m[0])]
		bi.Commit = m[2]
		bi.Dev = true
	case releaseTag.MatchString(core) && !dirty:
		bi.Release = core
		bi.Dev = false
	default:
		bi.Release = core
		bi.Dev = true
	}
	return bi
}

// Handler wraps the external API handler with the panel SPA. version is the
// binary's resolved build stamp (cmd/felis resolvedVersion()); it is surfaced to
// the SPA via /config.json for the version badge. panelHost and adminHost are the
// configured console.<root_domain> and op.console.<root_domain> hostnames (either
// may be empty when that face is not deployed); they let the SPA detect which home
// it is being served from by comparing location.host, so one bundle can render the
// right surface (player console vs SysAdmin console) without a rebuild. gamePort
// is the public Minecraft port ([velocity] game_port), which the SPA appends to
// the server addresses players copy; 0 or 25565 leaves them bare.
func Handler(api http.Handler, rootDomain, panelHost, adminHost string, gamePort int, gameVersion, version string, distributed ...bool) http.Handler {
	files, err := fs.Sub(static, "static")
	if err != nil {
		panic(err)
	}
	return &handler{
		api:           api,
		distributed:   len(distributed) > 0 && distributed[0],
		rootDomain:    rootDomain,
		panelHostname: panelHost,
		adminHostname: adminHost,
		gamePort:      publicGamePort(gamePort),
		gameVersion:   gameVersion,
		build:         parseBuildVersion(version),
		files:         files,
		fileServer:    http.FileServer(http.FS(files)),
		csp:           contentSecurityPolicy(files),
	}
}

// defaultGamePort is the port a Minecraft client dials when the address has none.
const defaultGamePort = 25565

// publicGamePort is the port the SPA should print, or 0 when a bare hostname
// already reaches the proxy.
func publicGamePort(p int) int {
	if p == defaultGamePort {
		return 0
	}
	return p
}

type handler struct {
	distributed   bool
	api           http.Handler
	rootDomain    string
	panelHostname string
	adminHostname string
	gamePort      int
	gameVersion   string
	build         buildInfo
	files         fs.FS
	fileServer    http.Handler
	csp           string
}

// inlineScript matches a <script> with no attributes: the pre-paint theme switch
// in index.html, the one script the page runs inline.
var inlineScript = regexp.MustCompile(`(?s)<script>(.*?)</script>`)

// contentSecurityPolicy is the policy the console's pages are served under. The
// bundle is same-origin, so scripts run only from 'self' plus, by hash, the inline
// scripts index.html carries as built (hashed here, at start, so a rebuilt page
// cannot drift from its policy). Styles allow inline: the UI library sets style
// attributes and injects style tags. Images take data: and blob: for rendered
// QR codes and downloads; every request the page makes goes to its own origin.
func contentSecurityPolicy(files fs.FS) string {
	scripts := "'self'"
	if index, err := fs.ReadFile(files, "index.html"); err == nil {
		for _, m := range inlineScript.FindAllSubmatch(index, -1) {
			sum := sha256.Sum256(m[1])
			scripts += " 'sha256-" + base64.StdEncoding.EncodeToString(sum[:]) + "'"
		}
	}
	return strings.Join([]string{
		"default-src 'self'",
		"script-src " + scripts,
		"style-src 'self' 'unsafe-inline'",
		"img-src 'self' data: blob:",
		"font-src 'self' data:",
		"connect-src 'self'",
		"object-src 'none'",
		"base-uri 'none'",
		"form-action 'self'",
		"frame-ancestors 'none'",
	}, "; ")
}

// setPageHeaders marks every response the console serves: no framing (the
// passkey and approval buttons must not sit under someone else's page), no
// sniffing, no referrer carrying a setup token off the site, and HSTS when the
// request came through a TLS edge. The API sets its own, stricter set on /api/.
func (h *handler) setPageHeaders(w http.ResponseWriter, r *http.Request) {
	hdr := w.Header()
	hdr.Set("Content-Security-Policy", h.csp)
	hdr.Set("X-Content-Type-Options", "nosniff")
	hdr.Set("X-Frame-Options", "DENY")
	hdr.Set("Referrer-Policy", "no-referrer")
	hdr.Set("Permissions-Policy", "camera=(), microphone=(), geolocation=(), payment=()")
	// The tunnel reaches this listener over TLS too, so what the browser saw is
	// the edge's X-Forwarded-Proto. A browser straight on the self-signed listener
	// sends none, and HSTS over a certificate error is ignored (RFC 6797 §8.1).
	if strings.EqualFold(r.Header.Get("X-Forwarded-Proto"), "https") {
		hdr.Set("Strict-Transport-Security", "max-age=31536000")
	}
}

func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path == "/healthz" || r.URL.Path == "/readyz" || strings.HasPrefix(r.URL.Path, "/api/") {
		h.api.ServeHTTP(w, r)
		return
	}
	h.setPageHeaders(w, r)
	// WeChat/QQ in-app browsers cannot run WebAuthn, so steer their document
	// navigations to a "open in your system browser" interstitial before the SPA
	// (which is built around passkey enrollment) ever loads. See webview.go.
	if guardInAppWebView(w, r) {
		return
	}
	switch {
	case r.URL.Path == "/config.json":
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		_ = json.NewEncoder(w).Encode(runtimeConfig{
			APIBase:       "/api/v1",
			Distributed:   h.distributed,
			RootDomain:    h.rootDomain,
			PanelHostname: h.panelHostname,
			AdminHostname: h.adminHostname,
			GamePort:      h.gamePort,
			GameVersion:   h.gameVersion,
			Build:         h.build,
		})
	case h.hasStaticFile(r.URL.Path):
		// Vite names every file under assets/ by its content hash, so a cached
		// copy can never go stale; everything else revalidates.
		if strings.HasPrefix(r.URL.Path, "/assets/") {
			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		} else {
			w.Header().Set("Cache-Control", "no-cache")
		}
		h.fileServer.ServeHTTP(w, r)
	default:
		w.Header().Set("Cache-Control", "no-cache")
		h.serveIndex(w, r)
	}
}

func (h *handler) hasStaticFile(urlPath string) bool {
	name := strings.TrimPrefix(path.Clean("/"+urlPath), "/")
	if name == "" {
		name = "index.html"
	}
	info, err := fs.Stat(h.files, name)
	return err == nil && !info.IsDir()
}

func (h *handler) serveIndex(w http.ResponseWriter, r *http.Request) {
	f, err := h.files.Open("index.html")
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			http.Error(w, "panel assets missing", http.StatusServiceUnavailable)
			return
		}
		http.Error(w, "open panel index", http.StatusInternalServerError)
		return
	}
	defer f.Close()
	info, err := f.Stat()
	if err != nil {
		http.Error(w, "stat panel index", http.StatusInternalServerError)
		return
	}
	body, err := io.ReadAll(f)
	if err != nil {
		http.Error(w, "read panel index", http.StatusInternalServerError)
		return
	}
	http.ServeContent(w, r, "index.html", info.ModTime(), bytes.NewReader(body))
}