// Package web serves palette's HTML routes: paste pages, cans, unlock, and
// the admin page. Templates and static assets are embedded in this package.
package web

import (
	"crypto/hmac"
	cryptorand "crypto/rand"
	"crypto/sha256"
	"embed"
	"encoding/hex"
	"fmt"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"os"
	"strings"
	"time"

	langpkg "palette/internal/lang"
	"palette/internal/store"
)

//go:embed templates/*.html
var tmplFS embed.FS

//go:embed static
var staticFS embed.FS

type UI struct {
	tmpl *template.Template
}

func New() (*UI, error) {
	funcs := template.FuncMap{
		"humanSize": humanSize,
	}
	t, err := template.New("").Funcs(funcs).ParseFS(tmplFS, "templates/*.html")
	if err != nil {
		return nil, err
	}
	return &UI{tmpl: t}, nil
}

func humanSize(n int) string {
	if n < 1024 {
		return fmt.Sprintf("%d B", n)
	}
	if n < 1024*1024 {
		return fmt.Sprintf("%.1f KB", float64(n)/1024)
	}
	return fmt.Sprintf("%.1f MB", float64(n)/(1024*1024))
}

func (u *UI) StaticHandler() http.Handler {
	sub, _ := fs.Sub(staticFS, "static")
	return http.StripPrefix("/static/", http.FileServer(http.FS(sub)))
}

func (h *Handlers) renderPage(w http.ResponseWriter, name string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := h.UI.tmpl.ExecuteTemplate(w, name, data); err != nil {
		http.Error(w, "template error: "+err.Error(), 500)
	}
}

// #34: per-paste unlock tokens. unlockSecret is generated once at startup
// (also derivable from PALETTE_UNLOCK_SECRET for multi-instance deploys) and
// used to HMAC paste ids, so a client can only hold a valid pw_<id> cookie by
// actually submitting the correct password for that paste.
var unlockSecret = resolveUnlockSecret()

func resolveUnlockSecret() []byte {
	if v := os.Getenv("PALETTE_UNLOCK_SECRET"); v != "" {
		return []byte(v)
	}
	b := make([]byte, 32)
	if _, err := cryptorand.Read(b); err != nil {
		log.Fatal("cannot generate unlock secret: ", err)
	}
	return b
}

func unlockToken(id string) string {
	mac := hmac.New(sha256.New, unlockSecret)
	mac.Write([]byte("unlock:" + id))
	return hex.EncodeToString(mac.Sum(nil))
}

func agoString(ts int64) string {
	s := time.Now().Unix() - ts
	switch {
	case s < 60:
		return fmt.Sprintf("%ds ago", s)
	case s < 3600:
		return fmt.Sprintf("%dm ago", s/60)
	case s < 86400:
		return fmt.Sprintf("%dh ago", s/3600)
	default:
		return fmt.Sprintf("%dd ago", s/86400)
	}
}

func expiryString(expiresAt int64) string {
	s := expiresAt - time.Now().Unix()
	switch {
	case s < 3600:
		return fmt.Sprintf("%dm", s/60)
	case s < 86400:
		return fmt.Sprintf("%dh", s/3600)
	default:
		return fmt.Sprintf("%dd", s/86400)
	}
}

// Handlers is the set of store callbacks the web pages need. The web package
// renders HTML; all queries go through the store.
type Handlers struct {
	UI            *UI
	Store         *store.Store
	ViewerID      func(r *http.Request) string
	BurnWindowMin func() int
	RateLimitOK   func(id string, r *http.Request) bool // per-paste unlock limiter
}

func (h *Handlers) rateLimitUnlock(id string, r *http.Request) bool {
	if h.RateLimitOK != nil {
		return h.RateLimitOK(id, r)
	}
	return true
}

func (h *Handlers) writeRateLimited(w http.ResponseWriter, retryAfterSecs int) {
	w.Header().Set("Retry-After", fmt.Sprintf("%d", retryAfterSecs))
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(429)
	w.Write([]byte(`{"error":"rate limit exceeded"}`))
}

func (h *Handlers) renderPaste(w http.ResponseWriter, row *store.PasteRow, justCreated bool, deletionToken string, readsRemaining *int) {
	lines := strings.Count(row.Content, "\n") + 1
	gutter := ""
	for i := 1; i <= lines; i++ {
		gutter += fmt.Sprintf("%d\n", i)
	}
	expIn := ""
	if row.ExpiresAt.Valid {
		expIn = expiryString(row.ExpiresAt.Int64)
	}
	lang := row.Language.String
	if lang == "" {
		lang = "text"
	}
	summary := fmt.Sprintf("%s · %s · %d views · %s", lang, humanSize(len(row.Content)), row.ViewCount, agoString(row.CreatedAt))
	data := map[string]any{
		"Page":          "paste",
		"ID":            row.ID,
		"Title":         row.Title.String,
		"Language":      row.Language.String,
		"StatsSummary":  summary,
		"SizeHuman":     humanSize(len(row.Content)),
		"HasPassword":   row.PasswordHash.Valid,
		"BurnAfterRead": row.BurnAfterRead,
		"CustomSlug":    row.CustomSlug.String,
		"ContentHTML":   template.HTML(langpkg.HighlightCode(row.Content, row.Language.String)), // safe: HighlightCode escapes all non-span text
		"ContentAttr":   row.Content,
		"Gutter":        strings.TrimSuffix(gutter, "\n"),
		"LineCount":     lines,
		"SizeBytes":     len(row.Content),
		"CreatedAgo":    agoString(row.CreatedAt),
		"CreatedAtUnix": row.CreatedAt,
		"ViewCount":     row.ViewCount,
		"Visibility":    row.Visibility,
		"ExpiresAt":     row.ExpiresAt.Valid,
		"ExpiresIn":     expIn,
		"DeletionToken": deletionToken,
		"ReadsLimit":    row.ReadsLimit.Valid,
		"ReadsLeftN":    readsRemaining, // *int: reads remaining after this view
		"ReadsTotal":    int(row.ReadsLimit.Int64),
		"JustCreated":   justCreated,
		"Host":          "this host",
	}
	h.renderPage(w, "paste.html", data)
}

// HandlePasteView renders the paste view; supports both ID and custom slug.
func (h *Handlers) HandlePasteView(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	row, err := h.Store.GetPaste(id)
	if err != nil {
		http.Error(w, "db error", 500)
		return
	}
	if row == nil {
		http.NotFound(w, r)
		return
	}
	if row.ExpiresAt.Valid && row.ExpiresAt.Int64 < time.Now().Unix() {
		http.Error(w, "paste expired", 404)
		return
	}
	if row.PasswordHash.Valid {
		// if a password was submitted via unlock form, verify and set cookie for this paste
		if r.Method == http.MethodPost {
			if !h.rateLimitUnlock(row.ID, r) {
				h.writeRateLimited(w, 60)
				return
			}
			r.ParseForm()
			pw := r.FormValue("password")
			if pw != "" && store.CheckPassword(row.PasswordHash.String, pw) {
				// #34: the unlock cookie must be bound to this specific paste and
				// unforgable. A static value ("1") let anyone bypass the password
				// by setting pw_<id>=1 for any paste id. The token is an HMAC of
				// the paste id under the server's random secret.
				http.SetCookie(w, &http.Cookie{
					Name: "pw_" + row.ID, Value: unlockToken(row.ID), Path: "/",
					MaxAge: 3600, HttpOnly: true, SameSite: http.SameSiteLaxMode,
				})
				// re-render without lock, or redirect if ?next= was given (#26)
				if next := r.FormValue("next"); next != "" {
					// only allow same-origin relative paths
					if len(next) > 0 && next[0] == '/' && !strings.HasPrefix(next, "//") {
						http.Redirect(w, r, next, http.StatusSeeOther)
						return
					}
				}
				h.renderPaste(w, row, false, "", nil)
				return
			}
			h.renderPage(w, "unlock.html", map[string]any{"Page": "unlock", "ID": row.ID, "Wrong": true, "CreatedAgo": agoString(row.CreatedAt), "CreatedAtUnix": row.CreatedAt})
			return
		}
		// check cookie — must carry the valid per-paste unlock token (#34)
		c, err := r.Cookie("pw_" + row.ID)
		if err != nil || c.Value != unlockToken(row.ID) {
			h.renderPage(w, "unlock.html", map[string]any{"Page": "unlock", "ID": row.ID, "Wrong": false, "CreatedAgo": agoString(row.CreatedAt), "CreatedAtUnix": row.CreatedAt})
			return
		}
	}

	justCreated := r.URL.Query().Get("created") == "1"
	token := r.URL.Query().Get("token")
	if justCreated && token != "" {
		// one-time display of the deletion token via the created banner
		http.SetCookie(w, &http.Cookie{Name: "tok_" + row.ID, Value: token, Path: "/", MaxAge: 60, HttpOnly: true, SameSite: http.SameSiteLaxMode})
	}
	// Count the view for every real page render. Raw views increment in
	// handleRaw; the HTML path was missing its increment, so view_count only
	// ever moved via /raw and the API-stored count stayed at 0 (#33).
	// The just-created banner render does not count as a view.
	if !justCreated {
		h.Store.IncrementViews(row.ID)
	}
	// #49: burn-after-N-reads budget (per-viewer dedupe window).
	// Just-created first render does not count as a read for the creator.
	if !justCreated {
		rem, admitted := h.Store.RegisterRead(row, h.ViewerID(r), h.BurnWindowMin())
		if !admitted { // #58: lost the burn claim; do not render content
			http.NotFound(w, r)
			return
		}
		h.renderPaste(w, row, false, "", rem)
		return
	}
	// only pass the token to the template right after creation
	h.renderPaste(w, row, true, token, nil)
}

// HandleNewPage serves /new.
func (h *Handlers) HandleNewPage(w http.ResponseWriter, r *http.Request) {
	h.renderPage(w, "new.html", map[string]any{"Page": "new"})
}

// HandleHistoryPage serves /history.
func (h *Handlers) HandleHistoryPage(w http.ResponseWriter, r *http.Request) {
	h.renderPage(w, "history.html", map[string]any{"Page": "history"})
}

// HandleSettingsPage serves /settings.
func (h *Handlers) HandleSettingsPage(w http.ResponseWriter, r *http.Request) {
	h.renderPage(w, "settings.html", map[string]any{"Page": "settings"})
}

// HandleMinePage serves /mine.
func (h *Handlers) HandleMinePage(w http.ResponseWriter, r *http.Request) {
	h.renderPage(w, "mine.html", map[string]any{"Page": "mine"})
}

// HandleAdminPage serves /admin.
func (h *Handlers) HandleAdminPage(w http.ResponseWriter, r *http.Request) {
	h.renderPage(w, "admin.html", map[string]any{"Page": "admin"})
}

// Handlers builds a web.Handlers bound to this UI.
func (u *UI) Handlers() *Handlers { return &Handlers{UI: u} }

// #59: security headers for rendered HTML pages. Applied wherever the
// response is text/html (page templates and the inline can page); JSON API
// responses and /raw content pass through untouched. script-src allows
// 'unsafe-inline' because the page templates carry inline scripts; CSP
// default-src 'self' still blocks external content and object/frame embeds,
// and frame-ancestors 'none' closes the clickjacking gap flagged in the #34
// pentest. Runs after the handler so the Content-Type is already set.
func SecurityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(w, r)
		h := w.Header()
		if strings.HasPrefix(h.Get("Content-Type"), "text/html") {
			h.Set("Content-Security-Policy",
				"default-src 'self'; script-src 'self' 'unsafe-inline'; frame-ancestors 'none'")
			h.Set("Referrer-Policy", "no-referrer")
			h.Set("X-Content-Type-Options", "nosniff")
		}
	})
}