feat: add CDP session and BrowserClient factory

2 files changed, 303 insertions, 0 deletions

diff --git a/src/cdp/session.ts b/src/cdp/session.ts
new file mode 100644
index 0000000..71f7a76
--- /dev/null
+++ b/src/cdp/session.ts
@@ -0,0 +1,123 @@
+import { type Result, err, ok } from "../util/result";
+import { type CdpError, cdpError } from "./errors";
+import type { DialogInfo } from "./types";
+import { isInternalUrl } from "./types";
+import type { CdpTransport } from "./transport";
+
+export type CdpSession = {
+  attachFirstPage(): Promise<Result<{ readonly targetId: string; readonly sessionId: string }, CdpError>>;
+  switchTo(targetId: string): Promise<Result<void, CdpError>>;
+  current(): { readonly sessionId: string; readonly targetId: string } | null;
+  call(method: string, params?: Record<string, unknown>, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  callOnTarget(method: string, params: Record<string, unknown>, sessionId: string, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  callBrowser(method: string, params?: Record<string, unknown>, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  takeDialog(): DialogInfo | null;
+  drainPageInfoInvalidations(): boolean;
+};
+
+export const createCdpSession = (transport: CdpTransport): CdpSession => {
+  let sessionId: string | null = null;
+  let targetId: string | null = null;
+  let dialog: DialogInfo | null = null;
+  let pageInfoDirty = false;
+
+  const consumeEvents = async (): Promise<void> => {
+    for await (const ev of transport.events()) {
+      if (ev.method === "Page.javascriptDialogOpening") {
+        const params = ev.params as Partial<DialogInfo> | undefined;
+        dialog = {
+          type: (params?.type as DialogInfo["type"]) ?? "alert",
+          message: params?.message ?? "",
+          ...(params?.defaultPrompt !== undefined ? { defaultPrompt: params.defaultPrompt } : {}),
+        };
+        continue;
+      }
+      if (ev.method === "Page.javascriptDialogClosed") {
+        dialog = null;
+        continue;
+      }
+      if (ev.method === "Page.frameNavigated" || ev.method === "Page.loadEventFired") {
+        pageInfoDirty = true;
+      }
+    }
+  };
+
+  void consumeEvents();
+  transport.onClose(() => {
+    sessionId = null;
+    targetId = null;
+    dialog = null;
+    pageInfoDirty = false;
+    void consumeEvents();
+  });
+
+  const enableDomains = async (sid: string): Promise<void> => {
+    for (const d of ["Page", "DOM", "Runtime", "Network"]) {
+      await transport.request(`${d}.enable`, {}, { sessionId: sid });
+    }
+  };
+
+  // CDP response shapes are documented in chromedevtools.github.io but not
+  // available as TypeScript types. We cast `as` from `unknown` only in this
+  // file (the CDP boundary). Each cast is paired with the CDP method that
+  // produced the response. Adding runtime guards for every shape would be
+  // noise — Chrome's protocol is stable enough that a wrong cast surfaces
+  // as a clear Error in normal use.
+  return {
+    async attachFirstPage() {
+      const targets = await transport.request("Target.getTargets", {}, { sessionId: null });
+      if (!targets.success) return targets;
+      const data = targets.data as { targetInfos: ReadonlyArray<{ targetId: string; type: string; url: string }> };
+      let pages = data.targetInfos.filter((t) => t.type === "page" && !isInternalUrl(t.url));
+      if (pages.length === 0) {
+        const created = await transport.request("Target.createTarget", { url: "about:blank" }, { sessionId: null });
+        if (!created.success) return created;
+        const c = created.data as { targetId: string };
+        pages = [{ targetId: c.targetId, type: "page", url: "about:blank" }];
+      }
+      const first = pages[0];
+      if (!first) return err(cdpError("invalid_response", "no page targets after creation"));
+      const attached = await transport.request("Target.attachToTarget", { targetId: first.targetId, flatten: true }, { sessionId: null });
+      if (!attached.success) return attached;
+      const a = attached.data as { sessionId: string };
+      sessionId = a.sessionId;
+      targetId = first.targetId;
+      await enableDomains(a.sessionId);
+      return ok({ targetId: first.targetId, sessionId: a.sessionId });
+    },
+    async switchTo(tid) {
+      const activated = await transport.request("Target.activateTarget", { targetId: tid }, { sessionId: null });
+      if (!activated.success) return activated;
+      const attached = await transport.request("Target.attachToTarget", { targetId: tid, flatten: true }, { sessionId: null });
+      if (!attached.success) return attached;
+      const a = attached.data as { sessionId: string };
+      sessionId = a.sessionId;
+      targetId = tid;
+      pageInfoDirty = true;
+      await enableDomains(a.sessionId);
+      return ok(undefined);
+    },
+    current() {
+      return sessionId && targetId ? { sessionId, targetId } : null;
+    },
+    call(method, params = {}, opts = {}) {
+      return transport.request(method, params, { sessionId, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    callOnTarget(method, params, sid, opts = {}) {
+      return transport.request(method, params, { sessionId: sid, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    callBrowser(method, params = {}, opts = {}) {
+      return transport.request(method, params, { sessionId: null, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    takeDialog() {
+      const d = dialog;
+      dialog = null;
+      return d;
+    },
+    drainPageInfoInvalidations() {
+      const dirty = pageInfoDirty;
+      pageInfoDirty = false;
+      return dirty;
+    },
+  };
+};
diff --git a/src/client.ts b/src/client.ts
new file mode 100644
index 0000000..637114b
--- /dev/null
+++ b/src/client.ts
@@ -0,0 +1,180 @@
+import { type Result, err, ok } from "./util/result";
+import { safeJs } from "./util/js-template";
+import { discoverWsUrl } from "./cdp/discovery";
+import { type CdpError, cdpError } from "./cdp/errors";
+import type { CdpTransport } from "./cdp/transport";
+import { createCdpTransport } from "./cdp/transport";
+import { type CdpSession, createCdpSession } from "./cdp/session";
+import type { DaemonStatus, DialogInfo, PageInfo, TabInfo } from "./cdp/types";
+
+export type BrowserClientOptions = {
+  readonly namespace: string;
+  readonly remote?: { readonly cdpUrl: string; readonly browserId: string };
+};
+
+export type BrowserClient = {
+  readonly namespace: string;
+  ensureAlive(): Promise<Result<void, CdpError>>;
+  status(): DaemonStatus;
+  start(): Promise<Result<void, CdpError>>;
+  stop(): Promise<void>;
+  evaluateJs(expression: string, sessionId?: string): Promise<Result<unknown, CdpError>>;
+  pageInfo(): Promise<Result<PageInfo | { readonly dialog: DialogInfo }, CdpError>>;
+  takeDialog(): DialogInfo | null;
+  listTabs(includeInternal?: boolean): Promise<Result<ReadonlyArray<TabInfo>, CdpError>>;
+  switchTab(targetId: string): Promise<Result<void, CdpError>>;
+  newTab(url?: string): Promise<Result<string, CdpError>>;
+  current(): { readonly sessionId: string; readonly targetId: string } | null;
+  session(): CdpSession;
+  transport(): CdpTransport;
+};
+
+const HEALTH_TTL_MS = 30_000;
+const PAGE_INFO_TTL_MS = 1_000;
+
+export const createBrowserClient = (opts: BrowserClientOptions): BrowserClient => {
+  const transport = createCdpTransport();
+  const session = createCdpSession(transport);
+  let lastHealth = 0;
+  let pageCache: { readonly info: PageInfo; readonly at: number } | null = null;
+  let remote: BrowserClientOptions["remote"] | null = opts.remote ?? null;
+
+  const start = async (): Promise<Result<void, CdpError>> => {
+    if (transport.state() === "open" && session.current()) return ok(undefined);
+    const envUrl = process.env["BU_CDP_WS"];
+    let wsUrl: string;
+    if (remote?.cdpUrl) {
+      wsUrl = remote.cdpUrl;
+    } else if (envUrl) {
+      wsUrl = envUrl;
+    } else {
+      const discovered = await discoverWsUrl();
+      if (!discovered.success) return discovered;
+      wsUrl = discovered.data;
+    }
+    const connected = await transport.connect(wsUrl, { timeoutMs: 10_000 });
+    if (!connected.success) return connected;
+    if (!remote) {
+      remote = { cdpUrl: wsUrl, browserId: wsUrl.split("/").pop() ?? "unknown" };
+    }
+    const attached = await session.attachFirstPage();
+    if (!attached.success) {
+      await transport.close();
+      return attached;
+    }
+    lastHealth = Date.now();
+    pageCache = null;
+    return ok(undefined);
+  };
+
+  const stop = async (): Promise<void> => {
+    await transport.close();
+    pageCache = null;
+    lastHealth = 0;
+  };
+
+  const ensureAlive = async (): Promise<Result<void, CdpError>> => {
+    if (transport.state() !== "open" || !session.current()) {
+      await stop();
+      return start();
+    }
+    if (Date.now() - lastHealth < HEALTH_TTL_MS) return ok(undefined);
+    const probe = await transport.request("Target.getTargets", {}, { sessionId: null, timeoutMs: 2_000 });
+    if (probe.success) {
+      lastHealth = Date.now();
+      return ok(undefined);
+    }
+    await stop();
+    return start();
+  };
+
+  const evaluateJs = async (expression: string, sessionId?: string): Promise<Result<unknown, CdpError>> => {
+    const wrapped = expression.includes("return ") && !expression.trim().startsWith("(")
+      ? `(function(){${expression}})()`
+      : expression;
+    const r = sessionId
+      ? await session.callOnTarget("Runtime.evaluate", { expression: wrapped, returnByValue: true, awaitPromise: true }, sessionId)
+      : await session.call("Runtime.evaluate", { expression: wrapped, returnByValue: true, awaitPromise: true });
+    if (!r.success) return r;
+    const data = r.data as { result?: { value?: unknown }; exceptionDetails?: unknown };
+    if (data.exceptionDetails) {
+      return err(cdpError("remote_error", `JS evaluation failed: ${JSON.stringify(data.exceptionDetails)}`, "Runtime.evaluate"));
+    }
+    return ok(data.result?.value);
+  };
+
+  const readPageInfo = async (): Promise<Result<PageInfo, CdpError>> => {
+    const dirty = session.drainPageInfoInvalidations();
+    if (pageCache && !dirty && Date.now() - pageCache.at < PAGE_INFO_TTL_MS) return ok(pageCache.info);
+    const expr = safeJs`JSON.stringify({url:location.href,title:document.title,w:innerWidth,h:innerHeight,sx:scrollX,sy:scrollY,pw:document.documentElement.scrollWidth,ph:document.documentElement.scrollHeight})`;
+    const raw = await evaluateJs(expr);
+    if (!raw.success) return raw;
+    if (typeof raw.data !== "string") return err(cdpError("invalid_response", "page info evaluation did not return a string"));
+    const parsedRaw = JSON.parse(raw.data) as { url: string; title: string; w: number; h: number; sx: number; sy: number; pw: number; ph: number };
+    const info: PageInfo = {
+      url: parsedRaw.url, title: parsedRaw.title,
+      width: parsedRaw.w, height: parsedRaw.h,
+      scrollX: parsedRaw.sx, scrollY: parsedRaw.sy,
+      pageWidth: parsedRaw.pw, pageHeight: parsedRaw.ph,
+    };
+    pageCache = { info, at: Date.now() };
+    return ok(info);
+  };
+
+  const pageInfo = async (): Promise<Result<PageInfo | { readonly dialog: DialogInfo }, CdpError>> => {
+    const d = session.takeDialog();
+    if (d) return ok({ dialog: d });
+    return readPageInfo();
+  };
+
+  const listTabs = async (includeInternal = true): Promise<Result<ReadonlyArray<TabInfo>, CdpError>> => {
+    const r = await session.callBrowser("Target.getTargets");
+    if (!r.success) return r;
+    const data = r.data as { targetInfos: ReadonlyArray<{ targetId: string; type: string; title: string; url: string }> };
+    const tabs = data.targetInfos
+      .filter((t) => t.type === "page")
+      .filter((t) => includeInternal || !t.url.startsWith("chrome://"))
+      .map((t): TabInfo => ({ targetId: t.targetId, title: t.title, url: t.url }));
+    return ok(tabs);
+  };
+
+  const switchTab = async (targetId: string): Promise<Result<void, CdpError>> => {
+    const r = await session.switchTo(targetId);
+    if (!r.success) return r;
+    pageCache = null;
+    await session.call("Runtime.evaluate", { expression: safeJs`if(!document.title.startsWith('🟢'))document.title='🟢 '+document.title` });
+    return ok(undefined);
+  };
+
+  const newTab = async (url?: string): Promise<Result<string, CdpError>> => {
+    const created = await session.callBrowser("Target.createTarget", { url: "about:blank" });
+    if (!created.success) return created;
+    const c = created.data as { targetId: string };
+    const switched = await switchTab(c.targetId);
+    if (!switched.success) return switched;
+    if (url && url !== "about:blank") {
+      const nav = await session.call("Page.navigate", { url });
+      if (!nav.success) return nav;
+      pageCache = null;
+    }
+    return ok(c.targetId);
+  };
+
+  const status = (): DaemonStatus => ({
+    alive: transport.state() === "open" && session.current() !== null,
+    sessionId: session.current()?.sessionId ?? null,
+    namespace: opts.namespace,
+    ...(remote?.browserId !== undefined ? { remoteBrowserId: remote.browserId } : {}),
+  });
+
+  return {
+    namespace: opts.namespace,
+    ensureAlive, status, start, stop,
+    evaluateJs, pageInfo,
+    takeDialog: () => session.takeDialog(),
+    listTabs, switchTab, newTab,
+    current: () => session.current(),
+    session: () => session,
+    transport: () => transport,
+  };
+};