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, direction
		   FROM users WHERE id = ?`, id,
	).Scan(&user.ID, &user.Email, &user.DisplayName, &user.CreatedAt, &user.PairLang, &user.Direction)
	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
// joined on the day its pack landed, not before.
//
// These four are now every pair PairLang names on the frontend, which makes the
// two lists look redundant. They are not: the next pair will exist in the type
// and in the prompts long before it has copy, and this list is the one that
// says a writer may actually be sent there.
var shippedPairs = []string{"zh", "pt-PT", "fr", "es"}

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

// The two directions a pair can be travelled in. `DirectionLearningEn` is the
// original assumption made explicit: the writer is native in X and practising
// English. `DirectionLearningPair` is the other way round.
const (
	DirectionLearningEn   = "learning_en"
	DirectionLearningPair = "learning_pair"
)

// The pairs whose *learner* direction Petal can actually serve, which is a
// narrower thing than a shipped pair and narrower again than a langpack.
//
// Turning a pair around needs data no langpack carries: a word list to segment
// with, and a dictionary that reads from the pair language into English. Chinese
// has both as of Phase 26 (CC-CEDICT + jieba); French, Spanish and Portuguese
// have neither yet, and — unlike a missing pack, which leaves a writer looking
// at copy she cannot read — a missing word list would leave her looking at an
// editor that silently does nothing when she hovers. Both are bad; only one is
// legible as a bug. So the server refuses, for the same reason and by the same
// mechanism as `shippedPairs`.
//
// This list is expected to grow one pair at a time and never to be inferred:
// segmentation is a property of a writing system, and there is no rule that
// derives "has a word list" from a language code.
var learnerPairs = []string{"zh"}

// SupportsLearnerDirection reports whether a pair can be turned around.
func SupportsLearnerDirection(lang string) bool {
	for _, p := range learnerPairs {
		if p == lang {
			return true
		}
	}
	return false
}

func directionIsKnown(d string) bool {
	return d == DirectionLearningEn || d == DirectionLearningPair
}

// SetPair moves an account to another (English + X) pair, in a given direction.
//
// The two are written together because they constrain each other: a direction is
// only meaningful for a pair that can be travelled in it, and validating them a
// field at a time would let a two-step change pass through a state that neither
// step is allowed to leave behind.
func (u *UserStore) SetPair(id, lang, direction string) error {
	if !pairIsShipped(lang) {
		return errors.New("auth: unshipped pair language " + lang)
	}
	if !directionIsKnown(direction) {
		return errors.New("auth: unknown direction " + direction)
	}
	if direction == DirectionLearningPair && !SupportsLearnerDirection(lang) {
		return errors.New("auth: no learner direction for " + lang)
	}
	res, err := u.db.Exec(
		`UPDATE users SET pair_lang = ?, direction = ? WHERE id = ?`, lang, direction, 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: which language Petal
// speaks alongside her English, and which of the two she is learning.
//
// 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.
//
// Both fields are optional and each defaults to what the account already has, so
// the picker can send one without knowing the other. That matters for the
// combination this endpoint exists to prevent: a client that sent only
// `pair_lang: "fr"` while the account sat on `learning_pair` would otherwise ask
// for French-with-segmentation, which does not exist. Here it is one decision
// with one validation, and the answer carries whatever actually landed.
func (u *UserStore) UpdateMeHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var body struct {
			PairLang  *string `json:"pair_lang"`
			Direction *string `json:"direction"`
		}
		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
			httputil.BadRequest(w, "invalid request body")
			return
		}
		id := UserID(r.Context())
		current, err := u.Get(id)
		if err != nil {
			// Only a missing row means "not signed in". A dictionary-file or
			// SQLite fault answered as 401 would trip the client's session
			// interceptor and throw a writer out of an app she is still signed
			// in to — the same distinction SetPair's error branch makes below.
			if errors.Is(err, sql.ErrNoRows) {
				httputil.ErrorJSON(w, http.StatusUnauthorized, "not signed in")
				return
			}
			httputil.ServerError(w, err)
			return
		}

		lang, direction := current.PairLang, current.Direction
		if body.PairLang != nil {
			lang = strings.TrimSpace(*body.PairLang)
		}
		if body.Direction != nil {
			direction = strings.TrimSpace(*body.Direction)
		}

		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
		}
		if !directionIsKnown(direction) {
			httputil.BadRequest(w, "unknown direction — expected "+DirectionLearningEn+" or "+DirectionLearningPair)
			return
		}
		if direction == DirectionLearningPair && !SupportsLearnerDirection(lang) {
			// Refused rather than quietly downgraded to learning_en. A silent
			// downgrade would leave the writer looking at an editor that behaves
			// like the one she just tried to leave, with nothing to read as an
			// explanation — and the caller cannot tell the two outcomes apart
			// without diffing the response it was given.
			httputil.BadRequest(w, "Petal can only be learned toward "+strings.Join(learnerPairs, ", ")+" so far")
			return
		}

		if err := u.SetPair(id, lang, direction); 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)])
}