package web

import (
	"context"
	"embed"
	"html/template"
	"io/fs"
	"log"
	"math"
	"mime"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"bookmarkmanager/backend/internal/session"
	"bookmarkmanager/backend/internal/store"
	"bookmarkmanager/backend/internal/token"
	"bookmarkmanager/backend/internal/userscript"
)

//go:embed templates
var templateFS embed.FS

//go:embed static
var staticFS embed.FS

// RecentCount is how many series the "Continue reading" strip shows.
const RecentCount = 5

// Handler serves the browser UI: full pages at / and htmx fragments at /ui/.
// It is a separate handler from api.Handler because the two speak different
// representations (HTML versus JSON) to different clients under different auth.
type Handler struct {
	store *store.Store
	// readerID is the owner Reader's id, the only Reader that can exist
	// while registration is closed (issue #23). Every session row points at
	// it, so it is also the Reader the UI acts as.
	readerID int64
	// tokenKey derives Readers' userscript credentials (internal/token): the
	// install endpoints render the scripts with the credential inside, which
	// is the one place the UI needs the secret.
	tokenKey []byte
	// mangaUserscriptPath / novelUserscriptPath are the bindmounted script
	// files the install endpoints render — the same files the /u/ download
	// paths serve.
	mangaUserscriptPath string
	novelUserscriptPath string
	tmpl                *template.Template
	discord             DiscordConfig
	states              *oauthStates
	limiter             *session.LoginLimiter
	// httpClient is the plain stdlib client that talks to Discord. It is not
	// an injected interface: tests point APIBase at a stub server instead.
	httpClient *http.Client
}

// listView is what every list-rendering template receives.
type listView struct {
	// Lib is the library this view renders: store.KindManga or store.KindNovel.
	// Manga is the default and carries no query parameter, so every pre-novel
	// URL keeps meaning exactly what it did.
	Lib    string
	Tab    string // "all", "fav", or "new"
	Recent []store.Bookmark
	Items  []store.Bookmark
	// NewCount is the badge on the Updated tab: how many series being read
	// have a chapter out that has not been read. It is counted over the whole
	// reading set, not the active tab, so the badge does not change meaning as
	// the user moves between tabs.
	NewCount int
	// OOB marks a render of the chrome partials as an out-of-band swap rather
	// than the inline copy app.html lays out.
	OOB bool
	// Rotated marks the setup panel as having just rotated the credential:
	// it swaps the reinstall warning in over the button row.
	Rotated bool
}

// PageURL and ListURL are the two link shapes every tab needs. Building them
// here rather than concatenating in the template is what keeps the library
// parameter from being dropped on one link out of ten.
func (v listView) PageURL(tab string) string {
	if v.Lib == store.KindNovel {
		return "/?lib=novel&tab=" + tab
	}
	return "/?tab=" + tab
}

func (v listView) ListURL(tab string) string {
	if v.Lib == store.KindNovel {
		return "/ui/list?lib=novel&tab=" + tab
	}
	return "/ui/list?tab=" + tab
}

// loginView is what the login template receives.
type loginView struct {
	Error string
}

// New parses every template up front so a broken one kills the process at
// startup rather than the first request that touches it.
func New(s *store.Store, readerID int64, discord DiscordConfig, tokenKey []byte, mangaPath, novelPath string) (*Handler, error) {
	tmpl, err := template.ParseFS(templateFS, "templates/*.html")
	if err != nil {
		return nil, err
	}
	return &Handler{
		store:               s,
		readerID:            readerID,
		tokenKey:            tokenKey,
		mangaUserscriptPath: mangaPath,
		novelUserscriptPath: novelPath,
		tmpl:                tmpl,
		discord:             discord,
		states:              newOAuthStates(),
		limiter:             session.NewLoginLimiter(),
		httpClient:          &http.Client{Timeout: discordTimeout},
	}, nil
}

func (h *Handler) Register(mux *http.ServeMux) {
	mux.HandleFunc("GET /{$}", h.index)
	mux.HandleFunc("GET /auth/discord", h.discordStart)
	mux.HandleFunc("GET /auth/discord/callback", h.discordCallback)
	mux.HandleFunc("POST /logout", h.logout)
	mux.Handle("GET /static/", staticHandler())

	mux.HandleFunc("GET /ui/list", h.requireSession(h.uiList))
	mux.HandleFunc("POST /ui/bookmarks/{key}/favorite", h.requireSession(h.uiFavorite))
	mux.HandleFunc("POST /ui/bookmarks/{key}/status", h.requireSession(h.uiStatus))
	mux.HandleFunc("POST /ui/bookmarks/{key}/chapter", h.requireSession(h.uiChapter))
	mux.HandleFunc("DELETE /ui/bookmarks/{key}", h.requireSession(h.uiDelete))

	// Install endpoints render the script directly under the session: the
	// credential travels inside the served bytes, never in the address bar or
	// the page markup. Updates after install use the credential-bearing /u/
	// path the script embeds, which needs no session.
	mux.HandleFunc("GET /install/manga-bookmark.user.js", h.requireSession(h.installUserscript("manga-bookmark.user.js")))
	mux.HandleFunc("GET /install/novel-bookmark.user.js", h.requireSession(h.installUserscript("novel-bookmark.user.js")))
	mux.HandleFunc("POST /rotate-token", h.requireSession(h.rotateToken))
}

// staticHandler serves the embedded assets. An hour, not longer: assets are
// not fingerprinted, and embed.FS reports a zero ModTime, so http.FileServer
// emits no Last-Modified or ETag and a client has no way to revalidate a
// cached copy after a deploy short of waiting out max-age.
func staticHandler() http.Handler {
	sub, err := fs.Sub(staticFS, "static")
	if err != nil {
		panic("embed static: " + err.Error())
	}
	// Go's built-in table has no .woff2 and the scratch image has no
	// /etc/mime.types, so without this the fonts go out as
	// application/octet-stream.
	if err := mime.AddExtensionType(".woff2", "font/woff2"); err != nil {
		panic("woff2 mime: " + err.Error())
	}
	files := http.FileServer(http.FS(sub))
	return http.StripPrefix("/static/", http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			w.Header().Set("Cache-Control", "public, max-age=3600")
			files.ServeHTTP(w, r)
		}))
}

type ctxKey int

// readerCtxKey is where requireSession stashes the authenticated Reader id.
const readerCtxKey ctxKey = iota

// sessionReader reports whether the request carries a live session, and for
// whom. The cookie holds only the session id; the row behind it is looked up
// on every request, so deleting a session takes effect immediately. Expiry is
// enforced here, in the store, which also removes rows that have lapsed.
func (h *Handler) sessionReader(r *http.Request) (int64, bool) {
	c, err := r.Cookie(session.CookieName)
	if err != nil {
		return 0, false
	}
	sess, ok, err := h.store.GetSession(c.Value, time.Now())
	if err != nil {
		log.Printf("session lookup: %v", err)
		return 0, false
	}
	return sess.ReaderID, ok
}

// requireSession guards the fragment endpoints. It answers 401 rather than
// redirecting, because htmx swaps whatever body it receives into the page and a
// redirected login page would be spliced into the card list.
func (h *Handler) requireSession(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		readerID, ok := h.sessionReader(r)
		if !ok {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next(w, r.WithContext(context.WithValue(r.Context(), readerCtxKey, readerID)))
	}
}

// readerOf returns the authenticated Reader id requireSession stashed.
func readerOf(r *http.Request) int64 { return r.Context().Value(readerCtxKey).(int64) }

func (h *Handler) render(w http.ResponseWriter, status int, name string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := h.tmpl.ExecuteTemplate(w, name, data); err != nil {
		// The status line is already sent, so this can only be logged.
		log.Printf("render %s: %v", name, err)
	}
}

// index renders the list, or the login page when there is no session. The login
// page is served at / with status 200 rather than as a redirect to a separate
// URL: one page, no redirect loop to reason about.
func (h *Handler) index(w http.ResponseWriter, r *http.Request) {
	readerID, ok := h.sessionReader(r)
	if !ok {
		h.render(w, http.StatusOK, "login", loginView{})
		return
	}
	view, err := h.buildListView(readerID, libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
	if err != nil {
		log.Printf("index: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	h.render(w, http.StatusOK, "app", view)
}

// filterBookmarks returns the subset keep reports true for, preserving order.
// It always returns a non-nil slice so an empty tab renders its empty state.
func filterBookmarks(all []store.Bookmark, keep func(store.Bookmark) bool) []store.Bookmark {
	out := []store.Bookmark{}
	for _, b := range all {
		if keep(b) {
			out = append(out, b)
		}
	}
	return out
}

// kindOf reads a bookmark's library. A row cached or written before the kind
// column existed has none; every one of those is manga, which is what the
// column default says too.
func kindOf(b store.Bookmark) string {
	if b.Kind == "" {
		return store.KindManga
	}
	return b.Kind
}

// libOf normalises the query parameter. Anything that is not the novel library
// is the manga one, so a typo lands on the default page rather than an empty
// list.
func libOf(q string) string {
	if q == store.KindNovel {
		return store.KindNovel
	}
	return store.KindManga
}

// buildListView loads one reader's list once and derives both the tab-filtered
// items and the recent strip from it.
//
// Archived and finished series appear in their own tab and nowhere else — not
// in All, not in Updated, not in Favourites, and not in the recent strip. An
// archived favourite therefore shows only under Archived: Favourites means
// "favourites I am currently reading".
func (h *Handler) buildListView(readerID int64, lib, tab string) (listView, error) {
	all, err := h.store.List(readerID) // already ordered updated_at DESC
	if err != nil {
		return listView{}, err
	}
	// Narrow to one library first: reading, withNew and recent all derive from
	// this slice, so doing it later would let the other library's rows into the
	// strip and the Updated badge.
	all = filterBookmarks(all, func(b store.Bookmark) bool { return kindOf(b) == lib })

	// Novels do not offer an Updated tab, so a hand-typed one lands on All.
	if lib == store.KindNovel && tab == "new" {
		tab = "all"
	}
	reading := filterBookmarks(all, func(b store.Bookmark) bool { return b.Status == store.StatusReading })

	withNew := filterBookmarks(reading, func(b store.Bookmark) bool { return b.HasNewChapter() })

	var items []store.Bookmark
	switch tab {
	case "fav":
		items = filterBookmarks(reading, func(b store.Bookmark) bool { return b.Favorite })
	case "new":
		items = withNew
	case "archived":
		items = filterBookmarks(all, func(b store.Bookmark) bool { return b.Status == store.StatusArchived })
	case "finished":
		items = filterBookmarks(all, func(b store.Bookmark) bool { return b.Status == store.StatusFinished })
	default:
		tab = "all"
		items = reading
	}
	// The strip is scoped to series with a chapter waiting, which is the one
	// question the list below it does not already answer: the list is ordered by
	// reading recency, so the head of it *is* the strip whenever the strip is
	// just "the most recent rows". Only on All — on Updated it would render the
	// same set twice, and on the other tabs it would contradict the bucket.
	//
	// It therefore disappears entirely on a library with nothing new. That is
	// the intended reading: an empty strip has nothing to say, and the ~240px it
	// costs on a phone belongs to the list.
	var recent []store.Bookmark
	if tab == "all" {
		recent = withNew
		if len(recent) > RecentCount {
			recent = recent[:RecentCount]
		}
	}
	return listView{Lib: lib, Tab: tab, Recent: recent, Items: items, NewCount: len(withNew)}, nil
}

func (h *Handler) uiList(w http.ResponseWriter, r *http.Request) {
	view, err := h.buildListView(readerOf(r), libOf(r.URL.Query().Get("lib")), r.URL.Query().Get("tab"))
	if err != nil {
		log.Printf("ui list: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	h.render(w, http.StatusOK, "list", view)
	// The chrome is outside this response's swap target, so without this a tab
	// switch would leave the strip and badge from whichever tab the page was
	// loaded on — the same URL would render differently depending on how the
	// reader got there.
	h.writeChromeOOB(w, view)
}

// currentTab is the tab the reader is looking at, read from htmx's own header,
// so out-of-band chrome is rebuilt for that view rather than for a default.
func currentTab(r *http.Request) string {
	u, err := url.Parse(r.Header.Get("HX-Current-URL"))
	if err != nil {
		return ""
	}
	return u.Query().Get("tab")
}

// currentLib is the library the reader is looking at, read from htmx's own
// header for the same reason currentTab is: out-of-band chrome must be rebuilt
// for that view rather than for the default one.
func currentLib(r *http.Request) string {
	u, err := url.Parse(r.Header.Get("HX-Current-URL"))
	if err != nil {
		return store.KindManga
	}
	return libOf(u.Query().Get("lib"))
}

// writeChromeOOB appends the regions that live outside #list — the recent
// strip, the Updated badge and the action key — as out-of-band swaps, so a
// mutation cannot leave them describing the library as it was before the tap.
// The key is in here because it is tab-shaped too: archived and finished swap
// Archive for Restore.
func (h *Handler) writeChromeOOB(w http.ResponseWriter, view listView) {
	view.OOB = true
	names := []string{"recent", "keyrow"}
	if view.Lib == store.KindManga {
		names = append(names, "newcount")
	}
	for _, name := range names {
		if err := h.tmpl.ExecuteTemplate(w, name, view); err != nil {
			// The card is already written; stale chrome beats a torn response.
			log.Printf("render %s oob: %v", name, err)
			return
		}
	}
}

// refreshChrome rebuilds the chrome for the reader's current tab after a
// mutation and appends it to the response.
func (h *Handler) refreshChrome(w http.ResponseWriter, r *http.Request) {
	view, err := h.buildListView(readerOf(r), currentLib(r), currentTab(r))
	if err != nil {
		log.Printf("ui chrome: %v", err)
		return
	}
	h.writeChromeOOB(w, view)
}

// renderLogin renders the login page with an error message, for refused or
// failed sign-ins. Every message is author-written text — nothing Discord
// supplied is ever interpolated into a page.
func (h *Handler) renderLogin(w http.ResponseWriter, status int, msg string) {
	h.render(w, status, "login", loginView{Error: msg})
}

// logout revokes the session row and clears the cookie in one step: the next
// request finds no row and is rejected.
func (h *Handler) logout(w http.ResponseWriter, r *http.Request) {
	if c, err := r.Cookie(session.CookieName); err == nil {
		if err := h.store.DeleteSession(c.Value); err != nil {
			log.Printf("delete session: %v", err)
		}
	}
	session.ClearCookie(w, r)
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

// loadForMutation fetches the row a mutation targets, writing the error
// response itself when there is nothing to mutate.
func (h *Handler) loadForMutation(w http.ResponseWriter, r *http.Request) (store.Bookmark, bool) {
	key := r.PathValue("key")
	if key == "" {
		http.Error(w, "missing key", http.StatusBadRequest)
		return store.Bookmark{}, false
	}
	b, ok, err := h.store.Get(readerOf(r), key)
	if err != nil {
		log.Printf("ui get %q: %v", key, err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return store.Bookmark{}, false
	}
	if !ok {
		http.Error(w, "not found", http.StatusNotFound)
		return store.Bookmark{}, false
	}
	return b, true
}

// saveAndRenderCard upserts and renders the row as stored, then refreshes the
// chrome. Upsert decides whether updated_at moves, so the argument's timestamp
// is only a candidate and the response must come from the return value.
//
// ponytail: the swapped card stays put even when its new status no longer
// matches the active tab. That much is deliberate — the card showing its new
// state is the feedback for the tap. The strip and the badge are not: they
// describe the whole library, so they are rebuilt out of band on every
// mutation, at the cost of one extra list read per toggle.
func (h *Handler) saveAndRenderCard(w http.ResponseWriter, r *http.Request, b store.Bookmark) {
	stored, err := h.store.Upsert(readerOf(r), b)
	if err != nil {
		log.Printf("ui upsert %q: %v", b.Key, err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	h.render(w, http.StatusOK, "card", stored)
	h.refreshChrome(w, r)
}

// uiFavorite flips the favourite flag. last_chapter_num is untouched, so
// Upsert keeps the stored updated_at and the list does not reorder.
func (h *Handler) uiFavorite(w http.ResponseWriter, r *http.Request) {
	b, ok := h.loadForMutation(w, r)
	if !ok {
		return
	}
	b.Favorite = !b.Favorite
	b.UpdatedAt = time.Now().UnixMilli()
	h.saveAndRenderCard(w, r, b)
}

// uiStatus moves a bookmark between lifecycle buckets. This is the only place
// a series can be marked finished — the JSON API refuses that value, so the
// userscript cannot set it even by accident.
//
// last_chapter_num is untouched, so Upsert keeps the stored updated_at and the
// list does not reorder.
func (h *Handler) uiStatus(w http.ResponseWriter, r *http.Request) {
	b, ok := h.loadForMutation(w, r)
	if !ok {
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Error(w, "invalid form", http.StatusBadRequest)
		return
	}
	switch s := r.PostFormValue("status"); s {
	case store.StatusReading, store.StatusArchived, store.StatusFinished:
		b.Status = s
	default:
		http.Error(w, "invalid status", http.StatusBadRequest)
		return
	}
	b.UpdatedAt = time.Now().UnixMilli()
	h.saveAndRenderCard(w, r, b)
}

// uiChapter forces the read chapter to a value the user typed.
//
// Writing the number also clears last_chapter_url: that URL points at the
// chapter actually read, and once the number is forced elsewhere it would send
// the reader backwards. ContinueURL then falls back to the series page, which
// is always right.
//
// A submit that does not change the number touches nothing. The form is
// pre-filled, so a bare tap of Save is an easy accidental submit; it must not
// destroy last_chapter_url, nor rewrite the last_chapter display string ("45.0"
// to "45") behind a frozen updated_at.
func (h *Handler) uiChapter(w http.ResponseWriter, r *http.Request) {
	b, ok := h.loadForMutation(w, r)
	if !ok {
		return
	}
	if err := r.ParseForm(); err != nil {
		http.Error(w, "invalid form", http.StatusBadRequest)
		return
	}
	raw := strings.TrimSpace(r.PostFormValue("chapter"))
	num, err := strconv.ParseFloat(raw, 64)
	if err != nil || num < 0 || math.IsNaN(num) || math.IsInf(num, 0) {
		http.Error(w, "chapter must be a non-negative number", http.StatusBadRequest)
		return
	}

	if num != b.LastChapterNum {
		b.LastChapterURL = ""
		b.LastChapter = raw
		b.LastChapterNum = num
	}
	b.UpdatedAt = time.Now().UnixMilli()
	h.saveAndRenderCard(w, r, b)
}

// uiDelete removes the row and answers with an empty body, which htmx swaps in
// place of the card — removing it from the page.
func (h *Handler) uiDelete(w http.ResponseWriter, r *http.Request) {
	key := r.PathValue("key")
	if key == "" {
		http.Error(w, "missing key", http.StatusBadRequest)
		return
	}
	if err := h.store.Delete(readerOf(r), key); err != nil {
		log.Printf("ui delete %q: %v", key, err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	// The empty body is what removes the card; the chrome still has to be told
	// the library got smaller.
	h.refreshChrome(w, r)
}

// installUserscript renders the bindmounted script with the acting Reader's
// derived credential substituted in. The credential is derived, not stored,
// so installs work after any restart; the Reader never types or copies it —
// clicking Install is the whole setup.
//
// ?download=1 forces a save instead. Mobile Violentmonkey (Chromium) does not
// intercept navigation to a .user.js URL, so the Install link only renders the
// source as text there; the Reader needs the file on disk to add it by hand.
func (h *Handler) installUserscript(name string) http.HandlerFunc {
	path := h.mangaUserscriptPath
	if name == "novel-bookmark.user.js" {
		path = h.novelUserscriptPath
	}
	return func(w http.ResponseWriter, r *http.Request) {
		discordID, epoch, err := h.store.ReaderTokenInfo(readerOf(r))
		if err != nil {
			log.Printf("install %s: %v", name, err)
			http.Error(w, "internal error", http.StatusInternalServerError)
			return
		}
		if r.URL.Query().Has("download") {
			w.Header().Set("Content-Disposition", `attachment; filename="`+name+`"`)
		}
		userscript.Render(w, r, path, token.Token(h.tokenKey, discordID, epoch))
	}
}

// rotateToken issues the acting Reader a new credential: the epoch bumps and
// the stored hash is rewritten, so the old credential stops authenticating
// the moment the statement commits. Every device must reinstall, or its
// script keeps failing silently — the setup panel states that warning next
// to the button, and the response repeats it as confirmation.
func (h *Handler) rotateToken(w http.ResponseWriter, r *http.Request) {
	readerID := readerOf(r)
	discordID, epoch, err := h.store.ReaderTokenInfo(readerID)
	if err != nil {
		log.Printf("rotate token: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	// The hash is computed for epoch+1 and guarded by it in the store, so a
	// concurrent rotation cannot leave the stored hash describing another
	// epoch.
	if err := h.store.RotateToken(readerID, epoch, token.Hash(token.Token(h.tokenKey, discordID, epoch+1))); err != nil {
		log.Printf("rotate token: %v", err)
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	view := listView{Lib: store.KindManga, Rotated: true}
	h.render(w, http.StatusOK, "setup", view)
}