package web

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"mime/multipart"
	"net/http"
	"os"
	"path/filepath"
	"strings"

	"github.com/a-h/templ"
	"github.com/arnef/ebooks/internal/library"
	"github.com/arnef/ebooks/internal/users"
	"github.com/arnef/ebooks/views"
)

const maxUploadBytes = 512 << 20 // 512 MiB

type Handler struct {
	lib   *library.Service
	store *users.Store
}

func NewHandler(lib *library.Service, store *users.Store) *Handler {
	return &Handler{lib: lib, store: store}
}

func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
	// Public
	mux.HandleFunc("GET /login", h.loginPage)
	mux.HandleFunc("POST /login", h.loginSubmit)
	mux.HandleFunc("POST /logout", h.logout)
	mux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.Dir("static"))))

	// Authenticated (any role)
	mux.HandleFunc("GET /", h.requireAuth(h.listBooks))
	mux.HandleFunc("GET /book/{id}", h.requireAuth(h.bookDetails))
	mux.HandleFunc("GET /download/{id}", h.requireAuth(h.downloadBook))
	mux.HandleFunc("GET /cover/{id}", h.requireAuth(h.bookCover))

	// Uploader and above
	mux.HandleFunc("GET /upload", h.requireRole(users.RoleUploader, h.uploadPage))
	mux.HandleFunc("POST /upload", h.requireRole(users.RoleUploader, h.uploadSubmit))
}

func (h *Handler) listBooks(w http.ResponseWriter, r *http.Request) {
	books, err := h.lib.ListBooks()
	if err != nil {
		http.Error(w, "failed to load books", http.StatusInternalServerError)
		return
	}
	sess := sessionFrom(r)
	canUpload := sess != nil && sess.Role.AtLeast(users.RoleUploader)
	render(w, r.Context(), views.IndexPage(books, canUpload))
}

func (h *Handler) bookDetails(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if id == "" {
		http.NotFound(w, r)
		return
	}

	book, err := h.lib.FindBook(id)
	if err != nil {
		http.Error(w, "failed to load book", http.StatusInternalServerError)
		return
	}
	if book == nil {
		http.NotFound(w, r)
		return
	}

	render(w, r.Context(), views.BookPage(*book))
}

func (h *Handler) downloadBook(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if id == "" {
		http.NotFound(w, r)
		return
	}

	book, err := h.lib.FindBook(id)
	if err != nil {
		http.Error(w, "failed to load book", http.StatusInternalServerError)
		return
	}
	if book == nil {
		http.NotFound(w, r)
		return
	}

	cleanBase := filepath.Clean(h.lib.BooksDir())
	cleanPath := filepath.Clean(book.Path)
	if !strings.HasPrefix(cleanPath, cleanBase+string(filepath.Separator)) && cleanPath != cleanBase {
		http.Error(w, "invalid file path", http.StatusBadRequest)
		return
	}

	w.Header().Set("Content-Disposition", "attachment; filename=\""+book.Filename+"\"")
	http.ServeFile(w, r, cleanPath)
}

func (h *Handler) bookCover(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if id == "" {
		http.NotFound(w, r)
		return
	}

	data, contentType, err := h.lib.CoverBytes(id)
	if err != nil {
		http.Error(w, "failed to load cover", http.StatusInternalServerError)
		return
	}
	if len(data) == 0 {
		http.NotFound(w, r)
		return
	}
	if contentType == "" {
		contentType = "application/octet-stream"
	}

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Cache-Control", "public, max-age=3600")
	_, _ = w.Write(data)
}

func render(w http.ResponseWriter, ctx context.Context, c templ.Component) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := c.Render(ctx, w); err != nil && !errors.Is(err, context.Canceled) {
		http.Error(w, "render failed", http.StatusInternalServerError)
	}
}

// --- Auth handlers ---

func (h *Handler) loginPage(w http.ResponseWriter, r *http.Request) {
	render(w, r.Context(), views.LoginPage(""))
}

func (h *Handler) loginSubmit(w http.ResponseWriter, r *http.Request) {
	username := r.FormValue("username")
	password := r.FormValue("password")

	user, err := h.store.Authenticate(username, password)
	if err != nil {
		http.Error(w, "interner Fehler", http.StatusInternalServerError)
		return
	}
	if user == nil {
		render(w, r.Context(), views.LoginPage("Benutzername oder Passwort falsch."))
		return
	}

	sess, err := h.store.CreateSession(user)
	if err != nil {
		http.Error(w, "Session konnte nicht erstellt werden", http.StatusInternalServerError)
		return
	}

	http.SetCookie(w, &http.Cookie{
		Name:     "session",
		Value:    sess.Token,
		Path:     "/",
		Expires:  sess.ExpiresAt,
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
	})
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (h *Handler) logout(w http.ResponseWriter, r *http.Request) {
	cookie, err := r.Cookie("session")
	if err == nil {
		_ = h.store.DeleteSession(cookie.Value)
	}
	http.SetCookie(w, &http.Cookie{
		Name:    "session",
		Value:   "",
		Path:    "/",
		MaxAge:  -1,
		HttpOnly: true,
	})
	http.Redirect(w, r, "/login", http.StatusSeeOther)
}

// --- Upload handlers ---

func (h *Handler) uploadPage(w http.ResponseWriter, r *http.Request) {
	render(w, r.Context(), views.UploadPage(""))
}

func (h *Handler) uploadSubmit(w http.ResponseWriter, r *http.Request) {
	r.Body = http.MaxBytesReader(w, r.Body, maxUploadBytes)
	if err := r.ParseMultipartForm(32 << 20); err != nil {
		render(w, r.Context(), views.UploadPage("Datei zu groß oder ungültige Anfrage."))
		return
	}

	var headers []*multipart.FileHeader
	if r.MultipartForm != nil {
		headers = r.MultipartForm.File["book"]
	}
	if len(headers) == 0 {
		render(w, r.Context(), views.UploadPage("Keine Datei ausgewählt."))
		return
	}

	var errs []string
	saved := 0
	for _, header := range headers {
		if msg := h.saveUpload(header); msg != "" {
			errs = append(errs, fmt.Sprintf("%s: %s", header.Filename, msg))
		} else {
			saved++
		}
	}

	if len(errs) > 0 {
		msg := strings.Join(errs, " ")
		if saved > 0 {
			msg = fmt.Sprintf("%d von %d Dateien hochgeladen. %s", saved, len(headers), msg)
		}
		render(w, r.Context(), views.UploadPage(msg))
		return
	}

	http.Redirect(w, r, "/", http.StatusSeeOther)
}

// saveUpload validates and persists a single uploaded file. It returns a
// user-facing German error message, or "" on success.
func (h *Handler) saveUpload(header *multipart.FileHeader) string {
	ext := strings.ToLower(filepath.Ext(header.Filename))
	if ext != ".epub" {
		return "Nur EPUB-Dateien erlaubt."
	}

	file, err := header.Open()
	if err != nil {
		log.Printf("upload: open %q failed: %v", header.Filename, err)
		return "Datei konnte nicht gelesen werden."
	}
	defer file.Close()

	// Sanitize filename: keep only base name, no path components.
	safeFilename := filepath.Base(header.Filename)
	destPath := filepath.Join(h.lib.BooksDir(), safeFilename)

	// Check it still resolves inside BooksDir.
	cleanBase := filepath.Clean(h.lib.BooksDir())
	cleanDest := filepath.Clean(destPath)
	if !strings.HasPrefix(cleanDest, cleanBase+string(filepath.Separator)) {
		return "Ungültiger Dateiname."
	}

	out, err := os.OpenFile(destPath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
	if err != nil {
		if os.IsExist(err) {
			return fmt.Sprintf("Datei '%s' existiert bereits.", safeFilename)
		}
		log.Printf("upload: create %q failed: %v", destPath, err)
		return "Datei konnte nicht gespeichert werden."
	}
	defer out.Close()

	if _, err := io.Copy(out, file); err != nil {
		log.Printf("upload: write %q failed: %v", destPath, err)
		_ = os.Remove(destPath)
		return "Upload fehlgeschlagen."
	}

	return ""
}