package api

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/http"
	"strings"
	"time"
)

// Local-password sessions (spec §B). The remote face authenticates statelessly
// with a Cloudflare-Access JWT and sets no cookie; local-password auth, used on
// op.console when Zero Trust is not configured (and as the demo's primary web
// login), needs a server-minted session. We store only the sha-256 of the opaque
// cookie value, mirroring how service tokens are stored, so a database read never
// yields a usable cookie.

const (
	// sessionCookieName is the host-only session cookie. It carries no Domain
	// attribute, so an op.console session is never sent to the player console.
	sessionCookieName = "felis_session"
	// sessionTTL bounds a local-password session. Staff re-authenticate after it.
	sessionTTL = 12 * time.Hour
)

// LocalAuthEnabledKey is the platform_settings key that gates whether
// local-password sessions are honored. It is flipped on by `felis breakGlass`
// direct-to-Postgres at first-run and read live per-request, so enabling local
// auth needs no pod roll. Exported so the break-glass writer and this
// per-request reader share one source of truth instead of drifting copies.
const LocalAuthEnabledKey = "local_auth_enabled"

// newSessionToken returns a fresh opaque session value (256 bits, URL-safe). It
// is the cookie value; only its hash is persisted.
func newSessionToken() (string, error) {
	var b [32]byte
	if _, err := rand.Read(b[:]); err != nil {
		return "", fmt.Errorf("generate session token: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(b[:]), nil
}

// hashCookie maps a cookie value to its storage key (sha-256 hex), so the raw
// cookie is never written to the database.
func hashCookie(value string) string {
	sum := sha256.Sum256([]byte(value))
	return hex.EncodeToString(sum[:])
}

// setSessionCookie writes the session cookie: HttpOnly + Secure + SameSite=Lax,
// host-only (no Domain), rooted at "/". Secure means the console must be served
// over HTTPS — already a hard requirement, since WebAuthn and Zero Trust both
// demand a secure context.
func setSessionCookie(w http.ResponseWriter, value string, expires time.Time) {
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    value,
		Path:     "/",
		Expires:  expires,
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteLaxMode,
	})
}

// clearSessionCookie expires the session cookie (logout). The attributes must
// match setSessionCookie for the browser to overwrite it.
func clearSessionCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    "",
		Path:     "/",
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteLaxMode,
	})
}

// hostIsAdminConsole reports whether the request arrived on the configured
// operator console host. The session cookie is host-only, so a session minted on
// the admin host is structurally unable to reach the player console. If older
// configs omit [auth].admin_hostname, fall back to op.console.<root_domain>.
// Local bootstrap may also use the node's private/loopback IP directly when
// wildcard DNS is unavailable; that is treated as the local admin face.
func hostIsAdminConsole(r *http.Request, rootDomain, adminHostname string) bool {
	want := strings.TrimSpace(adminHostname)
	if want == "" {
		if rootDomain == "" {
			return false
		}
		want = "op.console." + rootDomain
	}
	host := r.Host
	if h, _, err := net.SplitHostPort(host); err == nil {
		host = h
	}
	if ip := net.ParseIP(strings.Trim(host, "[]")); ip != nil {
		return ip.IsLoopback() || ip.IsPrivate()
	}
	return strings.EqualFold(strings.TrimSuffix(host, "."), strings.TrimSuffix(want, "."))
}

// SessionAuth is the composite ExternalAuth for the web face. It prefers a
// local-password session cookie and otherwise delegates to the remote JWT
// verifier, so both auth models coexist on one face:
//
//   - No cookie  → delegate to Delegate (the Cloudflare-Access JWT path).
//   - Cookie set → local auth MUST be enabled (a missing or non-true
//     local_auth_enabled setting is treated as disabled — fail closed); the
//     session hash must resolve to a live user. On any failure the request is
//     rejected and does NOT fall through to the JWT delegate, so a stale or
//     forged cookie can never be laundered into a JWT attempt.
type SessionAuth struct {
	Repo          Repo
	Delegate      ExternalAuth
	RootDomain    string
	AdminHostname string
	Now           func() time.Time
}

func (s SessionAuth) now() time.Time {
	if s.Now != nil {
		return s.Now()
	}
	return time.Now()
}

// Authenticate resolves the caller from a session cookie or delegates to the JWT
// verifier (see the type comment for the fail-closed rules).
func (s SessionAuth) Authenticate(r *http.Request) (*Principal, error) {
	cookie, err := r.Cookie(sessionCookieName)
	if err != nil || cookie.Value == "" {
		// No usable session cookie: this is the remote JWT path.
		if s.Delegate == nil {
			return nil, fmt.Errorf("external auth not configured")
		}
		return s.Delegate.Authenticate(r)
	}

	ctx := r.Context()
	if !localAuthEnabled(ctx, s.Repo) {
		// A cookie was presented but local auth is off: reject, never fall through.
		return nil, fmt.Errorf("local auth disabled")
	}

	u, err := s.Repo.SessionUser(ctx, hashCookie(cookie.Value), s.now())
	if err != nil {
		return nil, fmt.Errorf("invalid session: %w", err)
	}
	return &Principal{
		UserID:             u.ID,
		Email:              u.Email,
		Role:               u.Role,
		ViaAdminAccess:     u.Role == "admin" && hostIsAdminConsole(r, s.RootDomain, s.AdminHostname),
		MustChangePassword: u.MustChangePassword,
	}, nil
}

// localAuthEnabled reports whether the runtime local_auth_enabled toggle is true.
// A missing setting, a read error, or a non-true value all read as disabled — the
// gate fails closed so local sessions are honored, and new ones minted, only on an
// explicit opt-in. Both SessionAuth (honoring a cookie) and the login handler
// (minting one) consult it, so the two never disagree about whether local auth is
// live.
func localAuthEnabled(ctx context.Context, repo Repo) bool {
	raw, err := repo.GetSetting(ctx, LocalAuthEnabledKey)
	if err != nil {
		return false // ErrNotFound (never enabled) or a transient read error → closed
	}
	var enabled bool
	if err := json.Unmarshal(raw, &enabled); err != nil {
		return false
	}
	return enabled
}

// ensure SessionAuth satisfies ExternalAuth at compile time.
var _ ExternalAuth = SessionAuth{}

// errIsNotFound is a small helper so handlers can branch on the repo's sentinel
// without importing errors at every call site.
func errIsNotFound(err error) bool { return errors.Is(err, ErrNotFound) }