VBS2004
4406d8ca6a
Extract the resume-scroll decision into lib/pty-scroll (isViewportPinnedToBottom, shouldFollowPtyOutput) and add focused vitest coverage, per review on #59591.
51 lines
2.0 KiB
TypeScript
51 lines
2.0 KiB
TypeScript
/**
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* Dashboard chat resume-scroll helpers.
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*
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* When a chat session is resumed (`/chat?resume=<id>`) the PTY backend replays
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* the entire scrollback over the WebSocket the instant it opens. xterm.js writes
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* those bytes into its buffer but leaves the viewport wherever it was (e.g. the
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* top of a fresh terminal), so the transcript looks truncated until something
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* else forces a re-render. See #59591.
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*
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* The fix pins the viewport to the bottom *as each replayed chunk commits* (via
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* xterm's `write` callback) instead of guessing with a fixed double-rAF delay,
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* and releases that pin the moment the user scrolls up so their manual review of
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* the backlog is never yanked back down.
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*
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* These two decisions are pulled out here as pure functions so they can be
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* unit-tested without a live terminal; `ChatPage` wires them to the real xterm
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* instance (see `term.onScroll` and `ws.onmessage`).
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*/
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/** The subset of xterm's active `IBuffer` these helpers need. */
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export interface TerminalViewportPosition {
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/** Row index of the top of the current viewport. */
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viewportY: number;
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/** Row index of the viewport top when scrolled fully to the bottom. */
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baseY: number;
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}
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/**
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* True when the viewport is scrolled to (or past) the bottom, i.e. the latest
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* output is on screen. xterm reports `viewportY === baseY` at the bottom; the
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* `>=` also covers the transient overshoot while scrollback rows are trimmed.
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*/
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export function isViewportPinnedToBottom(
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buffer: TerminalViewportPosition,
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): boolean {
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return buffer.viewportY >= buffer.baseY;
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}
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/**
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* Whether a freshly written PTY output chunk should scroll the terminal to the
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* bottom afterwards. We only auto-follow while resuming a session (the replay
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* case) and only while the user hasn't scrolled up to read the backlog. A fresh
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* (non-resume) session returns `false` so normal cursor output is never fought.
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*/
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export function shouldFollowPtyOutput(
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resumeParam: string | null,
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stickToBottom: boolean,
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): boolean {
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return Boolean(resumeParam) && stickToBottom;
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}
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