package lexicon

import (
	"context"
	"database/sql"
	"encoding/json"
	"log"
	"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
}

// HanziRoutes returns the router mounted at /api/hanzi — a Chinese word to its
// pinyin and English senses, for a writer going the other way through the zh
// pair (`users.direction = 'learning_pair'`).
//
// It does not go through [Handler.providerFor], and that is not an oversight.
// providerFor picks a dictionary by the writer's *pair*, to answer "what does
// this English word mean in her language" — a question whose answer differs per
// pair. This endpoint asks the opposite question of exactly one language: it
// reads hanzi, and hanzi are Chinese whoever is looking them up. Routing it
// through the pair would add a database read per hover to choose between one
// option and itself.
//
// What no longer holds is the reason this used to give — that
// [auth.SupportsLearnerDirection] guarantees the caller is on the zh pair. Since
// Portuguese joined `learnerPairs` a learning_pair account may be Portuguese, so
// the guarantee now comes from the *caller*: the client only ever asks this
// route about a token its Chinese segmenter found, and that segmenter is loaded
// only for the zh pair (see useSegmenter in App.tsx). A stray lookup is still
// answered safely — a word the Chinese dictionary has never heard of is a 200
// with empty lists, exactly like any other miss.
func (h *Handler) HanziRoutes() chi.Router {
	r := chi.NewRouter()
	r.Get("/{word}", h.hanzi)
	return r
}

// hanzi answers a Chinese word lookup. Like the other two, a miss is a 200 with
// empty lists — a hover that lands on a word the dictionary has never heard of
// is an ordinary thing to happen while reading, and the tooltip simply doesn't
// open.
func (h *Handler) hanzi(w http.ResponseWriter, r *http.Request) {
	res, err := h.Set.Hanzi(pathWord(r))
	if err != nil {
		writeLookupErr(w, err)
		return
	}
	writeLookup(w, res)
}

// 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)
}

// writeLookupErr answers a failed lookup. The real error is a dictionary or
// database fault — a file path, a SQLite message — and belongs in the log, not
// in a tooltip. The client treats any non-200 the same way, so nothing is lost
// by saying less.
func writeLookupErr(w http.ResponseWriter, err error) {
	log.Printf("lexicon: lookup failed: %v", err)
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusInternalServerError)
	_ = json.NewEncoder(w).Encode(map[string]string{"error": "lookup failed"})
}

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)
}