package lexicon

import (
	"context"
	"database/sql"
	"encoding/json"
	"net/http"
	"net/url"

	"github.com/go-chi/chi/v5"

	"gitea.parodia.dev/drwily/petal/internal/auth"
)

// Handler serves the word-lookup endpoints. It holds the shared provider Set
// and the database, because which provider answers depends on who is asking.
type Handler struct {
	Set *Set
	db  *sql.DB
}

// NewHandler constructs a Handler over a provider Set. db is used for one
// thing: reading the caller's pair language.
func NewHandler(db *sql.DB, set *Set) *Handler { return &Handler{Set: set, db: db} }

// Routes returns the router mounted at /api/word. The word is a path segment so
// "/api/word/happy" reads naturally; it's URL-decoded to tolerate the rare
// punctuated token.
func (h *Handler) Routes() chi.Router {
	r := chi.NewRouter()
	r.Get("/{word}", h.lookup)
	return r
}

// GlossRoutes returns the router mounted at /api/gloss — the lightweight
// translation-only lookup behind the inline hover/select gloss. It shares the
// Handler's Set, so the embedded datasets and dict.db are still opened once.
func (h *Handler) GlossRoutes() chi.Router {
	r := chi.NewRouter()
	r.Get("/{word}", h.gloss)
	return r
}

// providerFor returns the provider for the caller's language pair.
//
// The pair language is read here rather than threaded down because a word
// lookup has no other query to piggyback on — unlike the document handlers,
// which take pair_lang from the row-scoped query that already proves
// ownership. It is one indexed primary-key read against a local SQLite file,
// which costs less than encoding the response it feeds.
//
// A read that fails, or a caller with no user row, resolves to the empty
// language, and [Set.For] maps that to today's embedded behaviour. Falling back
// to a working dictionary beats failing the lookup.
func (h *Handler) providerFor(ctx context.Context) Provider {
	var lang string
	if h.db != nil {
		_ = h.db.QueryRowContext(ctx,
			`SELECT COALESCE(pair_lang, '') FROM users WHERE id = ?`,
			auth.UserID(ctx),
		).Scan(&lang)
	}
	return h.Set.For(lang)
}

// pathWord reads the {word} segment, URL-decoded.
func pathWord(r *http.Request) string {
	word := chi.URLParam(r, "word")
	if decoded, err := url.PathUnescape(word); err == nil {
		word = decoded
	}
	return word
}

// lookup returns the definition + synonyms for one word. A word found in no
// dataset still returns 200 with empty lists, so the popover can show a
// friendly "nothing found" rather than an error state.
func (h *Handler) lookup(w http.ResponseWriter, r *http.Request) {
	res, err := h.providerFor(r.Context()).Lookup(pathWord(r))
	if err != nil {
		writeLookupErr(w, err)
		return
	}
	writeLookup(w, res)
}

// gloss returns just the translation for one word. Like lookup, a miss is a 200
// with an empty gloss so the hover tooltip can quietly skip rather than error.
func (h *Handler) gloss(w http.ResponseWriter, r *http.Request) {
	res, err := h.providerFor(r.Context()).Gloss(pathWord(r))
	if err != nil {
		writeLookupErr(w, err)
		return
	}
	writeLookup(w, res)
}

func writeLookupErr(w http.ResponseWriter, err error) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusInternalServerError)
	_ = json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
}

func writeLookup(w http.ResponseWriter, v any) {
	w.Header().Set("Content-Type", "application/json")
	// A lookup is stable for the life of the deployment, so let the browser
	// keep it — repeated right-clicks on the same word are then instant. It is
	// `private` rather than `public` because the gloss is now in *her*
	// language: a shared cache keyed on the URL alone would hand one writer
	// another writer's language.
	w.Header().Set("Cache-Control", "private, max-age=86400")
	_ = json.NewEncoder(w).Encode(v)
}