package auth

import (
	"database/sql"
	"encoding/json"
	"errors"
	"net/http"
	"strings"

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

// UserStore provisions and reads accounts. Petal has no signup flow: a row
// appears the first time someone Authentik vouches for signs in, and that is
// the only way one is ever created.
type UserStore struct {
	db *sql.DB
}

// NewUserStore returns a store backed by the given database.
func NewUserStore(sqlDB *sql.DB) *UserStore { return &UserStore{db: sqlDB} }

// Upsert records the account behind an OIDC login, keyed by the issuer's
// subject id.
//
// The subject is the id — not the email, which people change and which
// Authentik does not promise is stable. Email and display name are refreshed on
// every login so a rename upstream shows up here; pair_lang is deliberately not
// touched, because it is Petal's own setting rather than the IdP's.
func (u *UserStore) Upsert(sub, email, displayName string) error {
	if sub == "" {
		return errors.New("oidc: empty subject")
	}
	if displayName == "" {
		displayName = email
	}
	_, err := u.db.Exec(
		`INSERT INTO users (id, email, display_name) VALUES (?, ?, ?)
		 ON CONFLICT(id) DO UPDATE SET
		     email        = excluded.email,
		     display_name = excluded.display_name`,
		sub, email, displayName,
	)
	return err
}

// Get loads one account.
func (u *UserStore) Get(id string) (db.User, error) {
	var user db.User
	err := u.db.QueryRow(
		`SELECT id, email, COALESCE(display_name, ''), created_at, pair_lang
		   FROM users WHERE id = ?`, id,
	).Scan(&user.ID, &user.Email, &user.DisplayName, &user.CreatedAt, &user.PairLang)
	return user, err
}

// MeHandler reports who the caller is. The frontend uses it to namespace
// per-account browser state and to show the signed-in writer; it sits behind
// the auth middleware, so reaching it at all already proves a valid session.
func (u *UserStore) MeHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		user, err := u.Get(UserID(r.Context()))
		if err != nil {
			httputil.ErrorJSON(w, http.StatusUnauthorized, "not signed in")
			return
		}
		httputil.WriteJSON(w, http.StatusOK, user)
	}
}

// The pairs a writer may actually choose, in the order the picker offers them.
//
// This is deliberately *not* internal/llm's list of languages. That one names
// every pair the prompts know how to talk about, which is a cheap thing to add;
// this one names the pairs Petal can render itself in, which requires a langpack
// on the frontend. Accepting a code with no pack would leave her looking at
// Chinese with no way back except another guess, so the server refuses it. es
// joins this list on the day its pack lands, not before.
var shippedPairs = []string{"zh", "pt-PT", "fr"}

func pairIsShipped(lang string) bool {
	for _, p := range shippedPairs {
		if p == lang {
			return true
		}
	}
	return false
}

// SetPairLang moves an account to another (English + X) pair.
func (u *UserStore) SetPairLang(id, lang string) error {
	if !pairIsShipped(lang) {
		return errors.New("auth: unshipped pair language " + lang)
	}
	res, err := u.db.Exec(`UPDATE users SET pair_lang = ? WHERE id = ?`, lang, id)
	if err != nil {
		return err
	}
	if n, err := res.RowsAffected(); err == nil && n == 0 {
		return sql.ErrNoRows
	}
	return nil
}

// UpdateMeHandler changes the caller's own settings — today, the one setting
// there is: which language Petal speaks alongside her English.
//
// It answers with the whole updated user rather than an empty 204 so the client
// has one shape to trust: /api/me and this return the same thing, and the app
// re-reads the pair from the response instead of assuming its request took.
//
// The pair language reaches further than the UI copy — it picks her Hunspell
// dictionary, her read-aloud voice, which word-lookup provider answers, and the
// language the prompts ask the model to explain in. All of those read
// `users.pair_lang` at use time, so all of them follow from this one write.
func (u *UserStore) UpdateMeHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var body struct {
			PairLang string `json:"pair_lang"`
		}
		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
			httputil.BadRequest(w, "invalid request body")
			return
		}
		lang := strings.TrimSpace(body.PairLang)
		if !pairIsShipped(lang) {
			// Name the ones that work. A writer who lands here has picked from a
			// stale client, and "not a language" tells her nothing.
			httputil.BadRequest(w, "unsupported language pair — Petal speaks "+strings.Join(shippedPairs, ", "))
			return
		}
		id := UserID(r.Context())
		if err := u.SetPairLang(id, lang); err != nil {
			if errors.Is(err, sql.ErrNoRows) {
				httputil.ErrorJSON(w, http.StatusUnauthorized, "not signed in")
				return
			}
			httputil.ServerError(w, err)
			return
		}
		user, err := u.Get(id)
		if err != nil {
			httputil.ServerError(w, err)
			return
		}
		httputil.WriteJSON(w, http.StatusOK, user)
	}
}

// Allowlist decides which of Authentik's users may write in this Petal.
// Authentik fronts several applications; being a valid user there does not mean
// being a user here.
//
// An entry matches a subject id or an email address, case-insensitively. Both
// are accepted on purpose: a subject is an opaque uuid nobody can know before
// that person's first login, so a subject-only list means the operator must let
// someone in, read a log line, and edit config — whereas an email is knowable in
// advance. An empty list allows everyone the IdP authenticates, which is the
// right default for a single-household instance.
type Allowlist map[string]bool

// ParseAllowlist builds an Allowlist from a comma-separated env value.
func ParseAllowlist(raw string) Allowlist {
	list := Allowlist{}
	for _, part := range strings.Split(raw, ",") {
		if p := strings.ToLower(strings.TrimSpace(part)); p != "" {
			list[p] = true
		}
	}
	return list
}

// Permits reports whether this login may proceed.
func (a Allowlist) Permits(sub, email string) bool {
	if len(a) == 0 {
		return true
	}
	return a[strings.ToLower(sub)] || (email != "" && a[strings.ToLower(email)])
}