// Package spell owns the personal spelling dictionary — the words a writer has
// told Petal to stop flagging.
//
// It lived in the browser's localStorage until Phase 18, which was wrong twice
// over: two people sharing a device shared one list (built from one person's
// private writing), and one person writing on a laptop and a tablet had two
// lists that never met. It is a small amount of state, but it is *her* state,
// so it belongs to her account rather than to a browser profile.
//
// Everything here is scoped by `lang` as well as by user. That is the language
// of the *dictionary* the word was accepted against, not the writer's own.
//
// Phase 18 justified that key by saying an en-US personal word must not silence
// a pt-PT flag once the second pair shipped. Phase 21 shipped it and the
// justification did not survive: under the both-dictionaries rule
// (SUGGESTIONS.md §3a) a word is only ever flagged when *every* loaded
// dictionary rejected it, so there is no such thing as a pt-PT flag an English
// exception could silence. What the key is actually good for is narrower and
// still worth having — the rows say which dictionary each acceptance was made
// against, so a pair that later loses or gains a dictionary keeps a truthful
// record instead of one merged list of unknown provenance. The browser writes a
// row per loaded dictionary when she accepts a word; see useSpellChecker.
package spell

import (
	"encoding/json"
	"net/http"
	"strings"

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

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

// DefaultLang is the dictionary assumed when a caller doesn't name one. English
// is in every pair, so it is the safe assumption; pt-PT is named explicitly by
// the pt-PT pair's second dictionary.
const DefaultLang = "en"

// MaxWordLen bounds a single entry. A personal dictionary holds words, and a
// pasted paragraph is a bug (or an attempt to use the table as storage).
const MaxWordLen = 80

// MaxBatch bounds one request. The only bulk caller is the one-time adoption of
// a browser's pre-Phase-18 list, which is realistically tens of words.
const MaxBatch = 500

// Handler owns the /api/spell routes.
type Handler struct {
	DB *db.DB
}

func New(database *db.DB) *Handler { return &Handler{DB: database} }

// Routes mounts the personal-dictionary endpoints under /api/spell.
func (h *Handler) Routes() chi.Router {
	r := chi.NewRouter()
	r.Get("/words", h.list)
	r.Post("/words", h.add)
	r.Delete("/words", h.remove)
	return r
}

type wordsResponse struct {
	Lang  string   `json:"lang"`
	Words []string `json:"words"`
}

type addRequest struct {
	Lang string `json:"lang"`
	// Word and Words are both accepted so the everyday "add this one word" call
	// stays obvious while the one-shot migration of a browser's old list is a
	// single request rather than one per word.
	Word  string   `json:"word"`
	Words []string `json:"words"`
}

// normLang keeps the dictionary tag in one canonical shape so "EN", "en" and a
// missing value can never split one list into three.
func normLang(lang string) string {
	lang = strings.ToLower(strings.TrimSpace(lang))
	if lang == "" {
		return DefaultLang
	}
	return lang
}

// list returns the caller's words for one dictionary, alphabetically so the
// order is stable between requests.
func (h *Handler) list(w http.ResponseWriter, r *http.Request) {
	lang := normLang(r.URL.Query().Get("lang"))
	words, err := h.fetch(auth.UserID(r.Context()), lang)
	if err != nil {
		httputil.ServerError(w, err)
		return
	}
	httputil.WriteJSON(w, http.StatusOK, wordsResponse{Lang: lang, Words: words})
}

// add inserts one or more words, idempotently, and answers with the resulting
// full list — so the client never has to merge two views of the same set.
func (h *Handler) add(w http.ResponseWriter, r *http.Request) {
	var req addRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		httputil.BadRequest(w, "invalid JSON body")
		return
	}
	lang := normLang(req.Lang)

	incoming := req.Words
	if req.Word != "" {
		incoming = append(incoming, req.Word)
	}
	clean := make([]string, 0, len(incoming))
	for _, word := range incoming {
		word = strings.TrimSpace(word)
		if word == "" || len([]rune(word)) > MaxWordLen {
			continue
		}
		clean = append(clean, word)
	}
	if len(clean) == 0 {
		httputil.BadRequest(w, "no word given")
		return
	}
	if len(clean) > MaxBatch {
		httputil.BadRequest(w, "too many words in one request")
		return
	}

	userID := auth.UserID(r.Context())
	tx, err := h.DB.Begin()
	if err != nil {
		httputil.ServerError(w, err)
		return
	}
	defer func() { _ = tx.Rollback() }()
	for _, word := range clean {
		if _, err := tx.Exec(
			`INSERT INTO personal_words (user_id, lang, word) VALUES (?, ?, ?)
			 ON CONFLICT(user_id, lang, word) DO NOTHING`,
			userID, lang, word,
		); err != nil {
			httputil.ServerError(w, err)
			return
		}
	}
	if err := tx.Commit(); err != nil {
		httputil.ServerError(w, err)
		return
	}

	words, err := h.fetch(userID, lang)
	if err != nil {
		httputil.ServerError(w, err)
		return
	}
	httputil.WriteJSON(w, http.StatusOK, wordsResponse{Lang: lang, Words: words})
}

// remove forgets one word. Deleting something that was never there is a success:
// the caller's intent — "this word is not in my dictionary" — already holds.
func (h *Handler) remove(w http.ResponseWriter, r *http.Request) {
	word := strings.TrimSpace(r.URL.Query().Get("word"))
	if word == "" {
		httputil.BadRequest(w, "no word given")
		return
	}
	lang := normLang(r.URL.Query().Get("lang"))
	userID := auth.UserID(r.Context())
	if _, err := h.DB.Exec(
		`DELETE FROM personal_words WHERE user_id = ? AND lang = ? AND word = ?`,
		userID, lang, word,
	); err != nil {
		httputil.ServerError(w, err)
		return
	}
	words, err := h.fetch(userID, lang)
	if err != nil {
		httputil.ServerError(w, err)
		return
	}
	httputil.WriteJSON(w, http.StatusOK, wordsResponse{Lang: lang, Words: words})
}

// fetch reads one (user, dictionary) list. Both keys are always bound — an
// unscoped read here would hand one writer another's private vocabulary.
func (h *Handler) fetch(userID, lang string) ([]string, error) {
	rows, err := h.DB.Query(
		`SELECT word FROM personal_words WHERE user_id = ? AND lang = ? ORDER BY word`,
		userID, lang,
	)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	words := []string{} // never nil: the client expects a list, not null
	for rows.Next() {
		var word string
		if err := rows.Scan(&word); err != nil {
			return nil, err
		}
		words = append(words, word)
	}
	return words, rows.Err()
}