package main

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"golang.org/x/crypto/bcrypt"
)

const (
	sessionCookie = "session"
	idleShort     = 24 * time.Hour
	idleRemember  = 30 * 24 * time.Hour
	// Skip the extending UPDATE unless the session has aged at least this much, so a sliding
	// session is not a write on every request.
	extendAfter = time.Minute
)

type member struct {
	ID        int64
	Name      string
	Email     string
	Avatar    *string
	Banned    bool
	CreatedAt time.Time
}

// Initials for the avatar circle: no default image on disk, no identicon generator.
func (m *member) Initials() string {
	out := ""
	for _, f := range strings.Fields(m.Name) {
		out += strings.ToUpper(string([]rune(f)[0]))
		if len(out) == 2 {
			break
		}
	}
	return out
}

type ctxKey int

const memberKey ctxKey = 0

func memberFrom(ctx context.Context) *member {
	m, _ := ctx.Value(memberKey).(*member)
	return m
}

func token() string {
	b := make([]byte, 32)
	rand.Read(b)
	return hex.EncodeToString(b)
}

// A bearer header as well as the cookie, so something that isn't a browser can authenticate
// without a second concept. SameSite=Lax still guards the cookie path, and a cross-origin page
// cannot set Authorization without CORS, which is not enabled.
func sessionToken(r *http.Request) string {
	if h := r.Header.Get("Authorization"); strings.HasPrefix(h, "Bearer ") {
		return strings.TrimPrefix(h, "Bearer ")
	}
	if c, err := r.Cookie(sessionCookie); err == nil {
		return c.Value
	}
	return ""
}

func (a *app) startSession(ctx context.Context, userID int64, remember bool) (string, time.Time, error) {
	ttl := idleShort
	if remember {
		ttl = idleRemember
	}
	tok := token()
	expires := time.Now().Add(ttl)
	_, err := a.pool.Exec(ctx,
		`insert into sessions (token, user_id, idle_ttl, expires_at) values ($1, $2, $3, $4)`,
		tok, userID, ttl, expires)
	return tok, expires, err
}

func (a *app) setSessionCookie(w http.ResponseWriter, tok string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name: sessionCookie, Value: tok, Path: "/", Expires: expires,
		HttpOnly: true, Secure: a.cfg.secureCookies, SameSite: http.SameSiteLaxMode,
	})
}

// session loads the member behind a token, extends the idle timeout, and treats a banned or
// expired session as no session at all.
func (a *app) session(w http.ResponseWriter, r *http.Request) *member {
	tok := sessionToken(r)
	if tok == "" {
		return nil
	}
	var (
		m         member
		expires   time.Time
		ttl       time.Duration
		ttlMicros int64
	)
	err := a.pool.QueryRow(r.Context(), `
		select s.expires_at, extract(epoch from s.idle_ttl) * 1000000,
		       u.id, u.name, u.email, u.avatar, u.banned, u.created_at
		  from sessions s join users u on u.id = s.user_id
		 where s.token = $1 and s.expires_at > now()`, tok).
		Scan(&expires, &ttlMicros, &m.ID, &m.Name, &m.Email, &m.Avatar, &m.Banned, &m.CreatedAt)
	if err != nil {
		if !errors.Is(err, pgx.ErrNoRows) {
			slog.Error("session lookup", "ctx", "auth", "error", err)
		}
		return nil
	}
	if m.Banned {
		// Banning deletes sessions, so this is belt and braces for a row that outlived one.
		a.pool.Exec(r.Context(), `delete from sessions where user_id = $1`, m.ID)
		return nil
	}
	ttl = time.Duration(ttlMicros) * time.Microsecond
	if time.Until(expires) < ttl-extendAfter {
		newExpiry := time.Now().Add(ttl)
		if _, err := a.pool.Exec(r.Context(),
			`update sessions set expires_at = $2 where token = $1`, tok, newExpiry); err == nil {
			a.setSessionCookie(w, tok, newExpiry)
		}
	}
	return &m
}

func (a *app) withMember(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if m := a.session(w, r); m != nil {
			r = r.WithContext(context.WithValue(r.Context(), memberKey, m))
		}
		next.ServeHTTP(w, r)
	})
}

func (a *app) requireMember(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if memberFrom(r.Context()) == nil {
			http.Redirect(w, r, "/login", http.StatusSeeOther)
			return
		}
		next(w, r)
	}
}

// --- pages ---

type authForm struct {
	Name, Email, Code string
	Errors            map[string]string
}

func (a *app) loginPage(w http.ResponseWriter, r *http.Request) {
	a.render(w, r, http.StatusOK, "login.html", page{Title: "Kirjaudu", Narrow: true, Data: authForm{}})
}

func (a *app) login(w http.ResponseWriter, r *http.Request) {
	email := strings.TrimSpace(strings.ToLower(r.FormValue("email")))
	form := authForm{Email: email, Errors: map[string]string{}}

	if a.logins.locked(email) {
		form.Errors["form"] = "Liian monta yritystä. Yritä hetken kuluttua uudelleen."
		a.render(w, r, http.StatusTooManyRequests, "login.html", page{Title: "Kirjaudu", Narrow: true, Data: form})
		return
	}

	var (
		id     int64
		hash   string
		banned bool
	)
	err := a.pool.QueryRow(r.Context(),
		`select id, password_hash, banned from users where email = $1`, email).Scan(&id, &hash, &banned)
	if err != nil || bcrypt.CompareHashAndPassword([]byte(hash), []byte(r.FormValue("password"))) != nil {
		a.logins.fail(email)
		// One message for both cases: a distinct "no such account" tells anyone who asks which
		// addresses are members.
		form.Errors["form"] = "Sähköposti tai salasana ei täsmää."
		a.render(w, r, http.StatusUnauthorized, "login.html", page{Title: "Kirjaudu", Narrow: true, Data: form})
		return
	}
	if banned {
		form.Errors["form"] = "Tunnus on estetty."
		a.render(w, r, http.StatusForbidden, "login.html", page{Title: "Kirjaudu", Narrow: true, Data: form})
		return
	}

	tok, expires, err := a.startSession(r.Context(), id, r.FormValue("remember") != "")
	if err != nil {
		slog.Error("start session", "ctx", "auth", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	a.logins.succeed(email)
	a.setSessionCookie(w, tok, expires)
	slog.Info("login", "ctx", "auth", "user", id)
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func (a *app) logout(w http.ResponseWriter, r *http.Request) {
	if tok := sessionToken(r); tok != "" {
		a.pool.Exec(r.Context(), `delete from sessions where token = $1`, tok)
	}
	http.SetCookie(w, &http.Cookie{
		Name: sessionCookie, Value: "", Path: "/", MaxAge: -1,
		HttpOnly: true, Secure: a.cfg.secureCookies, SameSite: http.SameSiteLaxMode,
	})
	http.Redirect(w, r, "/login", http.StatusSeeOther)
}

func (a *app) registerPage(w http.ResponseWriter, r *http.Request) {
	a.render(w, r, http.StatusOK, "register.html",
		page{Title: "Liity", Narrow: true, Data: authForm{Code: r.URL.Query().Get("code")}})
}

// register spends the invite only when the account is actually created: both statements are in one
// transaction, so a failed signup leaves the code usable.
func (a *app) register(w http.ResponseWriter, r *http.Request) {
	form := authForm{
		Name:   strings.TrimSpace(r.FormValue("name")),
		Email:  strings.TrimSpace(strings.ToLower(r.FormValue("email"))),
		Code:   strings.TrimSpace(r.FormValue("code")),
		Errors: map[string]string{},
	}
	password := r.FormValue("password")

	if form.Name == "" || len([]rune(form.Name)) > 50 {
		form.Errors["name"] = "Nimi on pakollinen, enintään 50 merkkiä."
	}
	if !strings.Contains(form.Email, "@") {
		form.Errors["email"] = "Tarkista sähköpostiosoite."
	}
	// ponytail: no length policy. Invite-only, ten friends, bcrypt, and the admin is the reset
	// path — a minimum buys nothing here and makes dev accounts tedious.
	if password == "" {
		form.Errors["password"] = "Salasana on pakollinen."
	}
	if form.Code == "" {
		form.Errors["code"] = "Kutsukoodi on pakollinen."
	}
	if len(form.Errors) > 0 {
		a.render(w, r, http.StatusUnprocessableEntity, "register.html", page{Title: "Liity", Narrow: true, Data: form})
		return
	}

	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		slog.Error("hash password", "ctx", "auth", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}

	tx, err := a.pool.Begin(r.Context())
	if err != nil {
		slog.Error("begin", "ctx", "auth", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	defer tx.Rollback(r.Context())

	var inviteID int64
	err = tx.QueryRow(r.Context(),
		`update invites set is_valid = false where code = $1 and is_valid returning id`,
		form.Code).Scan(&inviteID)
	if errors.Is(err, pgx.ErrNoRows) {
		form.Errors["code"] = "Kutsukoodi ei kelpaa."
		a.render(w, r, http.StatusUnprocessableEntity, "register.html", page{Title: "Liity", Narrow: true, Data: form})
		return
	} else if err != nil {
		slog.Error("burn invite", "ctx", "invites", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}

	var userID int64
	err = tx.QueryRow(r.Context(),
		`insert into users (name, email, password_hash) values ($1, $2, $3) returning id`,
		form.Name, form.Email, string(hash)).Scan(&userID)
	if isUnique(err) {
		// Rolls back, so the invite is still valid.
		form.Errors["email"] = "Sähköpostiosoite on jo käytössä."
		a.render(w, r, http.StatusUnprocessableEntity, "register.html", page{Title: "Liity", Narrow: true, Data: form})
		return
	} else if err != nil {
		slog.Error("create user", "ctx", "auth", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	if err := tx.Commit(r.Context()); err != nil {
		slog.Error("commit registration", "ctx", "auth", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	slog.Info("registered", "ctx", "auth", "user", userID, "invite", inviteID)

	tok, expires, err := a.startSession(r.Context(), userID, false)
	if err != nil {
		slog.Error("start session", "ctx", "auth", "error", err)
		http.Redirect(w, r, "/login", http.StatusSeeOther)
		return
	}
	a.setSessionCookie(w, tok, expires)
	a.flash(w, "Tervetuloa mukaan!")
	http.Redirect(w, r, "/", http.StatusSeeOther)
}

func isUnique(err error) bool {
	var pgErr interface{ SQLState() string }
	return errors.As(err, &pgErr) && pgErr.SQLState() == "23505"
}