feat(share): short /share/<code> links with a compact versioned view format (#1418)

* feat(share): add compact versioned share-view codec

Add a standalone codec for `#s=<base64url>` share links: a version byte
followed by protobuf-style tag-length-value fields. Settings equal to
their default are omitted and refilled from the same table on decode;
unknown fields are skipped by wire type, so new fields never break
older apps. Views are a place (camera) or a thing (an aircraft,
military aircraft, vessel or satellite to follow, with camera offset
and last-known fix); an unknown kind falls back to the camera.

The decoder bounds its input and rejects malformed payloads with a
reason instead of throwing. A converter maps the long form's parsed
state to and from the codec state; the long form is unchanged.

* fix(share): tighten codec decoding after review

Unknown detection mode and allocation names now fall back to their
defaults instead of reaching the lenient long-form migration. Future
panel values and style-parameter tokens are skipped rather than applied
or rejected, and layer options are accepted only under their owner
layer. Wrap longitudes before scaling, normalize negative zero, reuse
the layer-state tracking ID grammar, and align the format doc with the
decoder.

* feat(share): let a host share the link its own way

ShareLinkManager.buildLink() returns the current share link without
copying it, and copyLink() now copies exactly that. The share button
passes the link to an optional services.shareLink(url), which resolves
to 'shared', 'copied', 'cancelled' or false; 'cancelled' shows no toast
and 'shared' shows the new "Link shared" (es, ru, zh-CN). Without the
service the button copies as before.

* feat(share): open and make short /share/<code> links

The share button now makes `<app>/share/<code>` links with the compact
share-view code, and the app opens them at start-up through the same
restore pipeline as long links. Once the app next writes the address, the
share path is replaced (no new history entry) by the app's own address and
the live long-form hash, so a reload follows the live view. A host can pass
the code as `initialShareCode` instead. A code that fails to decode restores
nothing and shows "This share link can't be opened".

The code gains a trailing CRC-8 check byte, so any single mistyped
character is rejected instead of opening a different view. Thing views no
longer store a camera: it is derived from the entity's last-known fix and
the follow offset on a sphere, the entity kind is implied by the id's
field, and the followed entity's layer bit is implied; an aircraft followed
from the app's own camera is a 42-character code. The `#s=` hash form is
gone.

While the camera follows an aircraft, military aircraft or satellite, the
link is a thing view with the camera's offset and the entity's position.
Opening one turns the layer on and follows the entity through the existing
shared-follow restore, then swings the camera round to the shared offset; a
vessel view selects the vessel once the vessel feed has it. If the entity
is not reporting within its window, the view stays at its last-known fix
and says so. The panel and style-parameter tables now come from the codec,
and a host share hook that returns a plain value or throws still gets a
toast.

* fix(share): encode style settings against the style's own look

Settings a style applies when selected (bloom, sharpen, HUD, detection,
celestial ring and the style's shader parameters) now default, per field,
to what that style applies in a fresh session, read from the tables the
app applies (the first-load baseline, the style presets and the shader
defaults). The encoder compares against the view's style and the decoder
fills omitted settings from the decoded style, so a view that keeps its
style's look costs only its camera and style. The previous defaults did not
match a fresh session (sharpen, HUD and detection were off), so every link
paid for them, and a style's own shader parameters were always written.

A test pins the per-style defaults as frozen v1 meanings. A followed
aircraft in Noir is now 44 characters and the real long-link example 39.

* docs: changelog for #1418

src/sharelink.js

@@ -11,12 +11,30 @@ import {
   encodeLayerStateParams,
 } from './data/layerState.js';
 import { STYLE_URL_NAMES } from './view/index.js';
+import {
+  SHARE_VIEW_PANELS,
+  SHARE_VIEW_STYLE_PARAMS,
+  decodeShareView,
+  encodeShareView,
+} from './share/viewCodec.js';
+import {
+  fromLegacyShareState,
+  toLegacyShareState,
+} from './share/legacyShareState.js';
+import {
+  appRootUrl,
+  parseSharePath,
+  shareLinkUrl,
+} from './share/shareLinkPath.js';
 
 /**
  * Share Links — URL Hash State Management
  *
- * Encodes camera position + style into the URL hash so links can be shared.
- * Format: #lat=37.77&lon=-122.42&alt=800&heading=0&pitch=-35&style=nvg&bloom=1&bi=84&bv=2&sharpen=0&si=65&hud=tactical&hv=1&dm=BALANCED&dd=50&da=elastic&kf=16&ko=0&cr=0&map=photoreal
+ * The address bar follows the live view in the long hash form:
+ * #lat=37.77&lon=-122.42&alt=800&heading=0&pitch=-35&style=nvg&bloom=1&bi=84&bv=2&sharpen=0&si=65&hud=tactical&hv=1&dm=BALANCED&dd=50&da=elastic&kf=16&ko=0&cr=0&map=photoreal
+ *
+ * A shared link is the short form, `<app>/share/<code>`, with the code from
+ * src/share/viewCodec.js (docs/SHARE-LINK-FORMAT.md). Both forms open here.
  */
 
 const DEBOUNCE_MS = 500;
@@ -29,20 +47,9 @@ const SHARE_UI_STATE_PARAM = 'ui';
 const SHARE_STYLE_PARAMS_PARAM = 'sp';
 const SHARE_CREATED_AT_PARAM = 'at';
 
-const SHARE_PANEL_STATE_REGISTRY = Object.freeze([
-  { id: 'control-panel', token: 'c', pinnable: true },
-  { id: 'location-bar', token: 'l', pinnable: true },
-  { id: 'data-panel', token: 'd', pinnable: false },
-  { id: 'cctv-panel', token: 'v', pinnable: false },
-  { id: 'recent-imagery-panel', token: 'i', pinnable: false },
-  { id: 'street-level-panel', token: 't', pinnable: false },
-  { id: 'radio-panel', token: 'r', pinnable: false },
-  { id: 'scene-panel', token: 's', pinnable: false },
-  { id: 'global-context-panel', token: 'g', pinnable: false },
-  { id: 'pp-toggles', token: 'p', pinnable: false },
-  { id: 'param-slider-panel', token: 'm', pinnable: false },
-]);
-
+// The panel and visual-preset parameter tables are the share format's own
+// (src/share/viewCodec.js); the long form spells their entries by token.
+const SHARE_PANEL_STATE_REGISTRY = SHARE_VIEW_PANELS;
 const SHARE_PANEL_STATE_BY_TOKEN = Object.freeze(
   new Map(SHARE_PANEL_STATE_REGISTRY.map((entry) => [entry.token, entry])),
 );
@@ -51,46 +58,25 @@ const URL_TO_STYLE = Object.fromEntries(
   Object.entries(STYLE_TO_URL).map(([k, v]) => [v, k]),
 );
 
-const SHARE_STYLE_PARAM_REGISTRY = Object.freeze({
-  retro: Object.freeze([
-    { key: 'pixelation', token: 'p', min: 1, max: 10 },
-    { key: 'distortion', token: 'd', min: 0, max: 1 },
-    { key: 'instability', token: 'i', min: 0, max: 1 },
-  ]),
-  surveillance: Object.freeze([
-    { key: 'gain', token: 'g', min: 0, max: 1 },
-    { key: 'bloom', token: 'b', min: 0, max: 1 },
-    { key: 'scanlineStr', token: 's', min: 0, max: 1 },
-    { key: 'pixelation', token: 'p', min: 1, max: 6 },
-  ]),
-  thermal: Object.freeze([
-    { key: 'sensitivity', token: 's', min: 0, max: 1 },
-    { key: 'bloom', token: 'b', min: 0, max: 1 },
-    { key: 'mode', token: 'm', min: 0, max: 1 },
-    { key: 'pixelation', token: 'p', min: 1, max: 6 },
-    { key: 'palette', token: 'a', min: 0, max: 1 },
-  ]),
-  anime: Object.freeze([
-    { key: 'saturation', token: 's', min: 0, max: 2 },
-    { key: 'edgeThick', token: 'e', min: 0, max: 1 },
-  ]),
-  noir: Object.freeze([
-    { key: 'contrastAmt', token: 'c', min: 0, max: 2 },
-    { key: 'grainAmt', token: 'g', min: 0, max: 1 },
-    { key: 'vignetteAmt', token: 'v', min: 0, max: 1 },
-  ]),
-  snow: Object.freeze([
-    { key: 'density', token: 'd', min: 0, max: 1 },
-    { key: 'wind', token: 'w', min: 0, max: 1 },
-  ]),
-});
+const SHARE_STYLE_PARAM_REGISTRY = SHARE_VIEW_STYLE_PARAMS;
 
 export class ShareLinkManager {
   constructor(
     viewer,
-    { onRestore, isNavigationCurrent, cancelOwnedNavigation } = {},
+    {
+      onRestore,
+      isNavigationCurrent,
+      cancelOwnedNavigation,
+      initialShareCode = null,
+    } = {},
   ) {
     this.viewer = viewer;
+    // A host may hand over the share code to open instead of the address.
+    this._initialShareCode =
+      typeof initialShareCode === 'string' ? initialShareCode : null;
+    // Why the share code this page opened with was refused, if it was.
+    this.rejectedShareCode = null;
+    this._followSubjectProvider = null;
     this._onRestore = onRestore; // callback: ({ style, bloom, sharpen }) => void
     this._debounceTimer = null;
     this._currentStyle = 'normal';
@@ -155,17 +141,42 @@ export class ShareLinkManager {
   }
 
   /**
-   * Parse URL hash on page load. Returns parsed state or null.
+   * Parse the share this page opened with: the host's `initialShareCode`, a
+   * `/share/<code>` address, or a long-form hash. Returns the parsed state, or
+   * null for none. A share code that cannot be opened is recorded in
+   * `rejectedShareCode` and restores nothing.
    */
   parseInitialHash() {
     const hash = window.location.hash.slice(1);
     this._knownHash = hash;
-    const state = this._parseShareHash(hash);
+    const code =
+      this._initialShareCode ??
+      parseSharePath(window.location.pathname)?.code ??
+      null;
+    this._initialShareCode = null;
+    const state =
+      code === null ? this._parseShareHash(hash) : this._parseShareCode(code);
     if (!state) return null;
     this._beginIncomingRestore(state);
     return state;
   }
 
+  /**
+   * The restore state for a share code, in the long form's parsed shape plus
+   * `shareView` (what the view follows, with its offset and last-known fix),
+   * or null when the code is refused.
+   */
+  _parseShareCode(code) {
+    const result = decodeShareView(code);
+    if (!result.ok) {
+      this.rejectedShareCode = result.reason;
+      return null;
+    }
+    const state = toLegacyShareState(result.state);
+    state.shareView = result.state.view;
+    return state;
+  }
+
   /** Parse one hash without side effects. Returns null unless it is a share. */
   _parseShareHash(hash) {
     if (!hash) return null;
@@ -459,6 +470,16 @@ export class ShareLinkManager {
     this._layerStateProvider = typeof provider === 'function' ? provider : null;
   }
 
+  /**
+   * Install the source of the entity the camera follows, used for share links:
+   * `({ nowMs }) => ({ kind, id, offset, lastKnown }) | null`, in the share
+   * format's terms (src/share/follow.js), with the fix as of `nowMs`.
+   */
+  setFollowSubjectProvider(provider) {
+    this._followSubjectProvider =
+      typeof provider === 'function' ? provider : null;
+  }
+
   /** Install the finalized panel-state source used by URL generation. */
   setPanelStateProvider(provider) {
     this._panelStateProvider = typeof provider === 'function' ? provider : null;
@@ -559,17 +580,41 @@ export class ShareLinkManager {
     this._scheduleUpdate();
   }
 
+  /**
+   * The share link for the current state, `<app>/share/<code>`, stamped with
+   * its creation time, or null before the camera has a position. While the
+   * camera follows an entity, the link follows it too.
+   */
+  buildLink({ nowMs = Date.now() } = {}) {
+    const params = this._buildHashParams();
+    if (!params) return null;
+    // The long form is the one description of the live state; the code is
+    // that state in the share format.
+    const state = fromLegacyShareState(this._parseShareHash(params.toString()));
+    state.sharedAtMs = Math.floor(nowMs / 1000) * 1000;
+    let subject = null;
+    try {
+      subject = this._followSubjectProvider?.({ nowMs }) ?? null;
+    } catch {
+      subject = null;
+    }
+    if (subject) {
+      state.view = {
+        kind: 'thing',
+        entity: { kind: subject.kind, id: subject.id },
+        offset: subject.offset ?? null,
+        lastKnown: subject.lastKnown ?? null,
+      };
+    }
+    return shareLinkUrl(encodeShareView(state), window.location.href);
+  }
+
   /** Copy a current-state snapshot with a copy-time timestamp. Returns true on success. */
   async copyLink({ nowMs = Date.now() } = {}) {
-    const params = this._buildHashParams();
-    if (!params) return false;
-    params.set(SHARE_CREATED_AT_PARAM, String(Math.floor(nowMs / 1000)));
-    const copiedUrl = new URL(window.location.href);
-    // ?lang is the sender's language override; the recipient keeps their own.
-    copiedUrl.searchParams.delete('lang');
-    copiedUrl.hash = params.toString();
     try {
-      await navigator.clipboard.writeText(copiedUrl.href);
+      const href = this.buildLink({ nowMs });
+      if (!href) return false;
+      await navigator.clipboard.writeText(href);
       return true;
     } catch {
       return false;
@@ -587,8 +632,13 @@ export class ShareLinkManager {
     const params = this._buildHashParams();
     if (!params) return;
     // The hash belongs to this page's address, not the document base the
-    // app may load under.
-    const url = new URL(`#${params.toString()}`, window.location.href);
+    // app may load under. A `/share/<code>` address gives way to the app's
+    // own address, so a reload follows the live view; replacing it adds no
+    // history entry.
+    const url = parseSharePath(new URL(window.location.href).pathname)
+      ? appRootUrl(window.location.href)
+      : new URL(window.location.href);
+    url.hash = params.toString();
     this._knownHash = url.hash.slice(1);
     history.replaceState(null, '', url.href);
   }
@@ -649,8 +699,8 @@ export class ShareLinkManager {
       this._styleParamStateProvider?.(this._currentStyle),
     );
 
-    // Copy-time metadata is intentionally absent here. `copyLink()` adds a
-    // fresh timestamp to its ephemeral URL without aging the live address.
+    // Creation-time metadata is intentionally absent here. `buildLink()`
+    // stamps its own link without aging the live address.
     params.delete(SHARE_CREATED_AT_PARAM);
     return params;
   }
@@ -677,6 +727,7 @@ export class ShareLinkManager {
     this._layerStateProvider = null;
     this._panelStateProvider = null;
     this._styleParamStateProvider = null;
+    this._followSubjectProvider = null;
     this._onRestore = null;
   }
 }