48 lines
1.8 KiB
TypeScript
48 lines
1.8 KiB
TypeScript
|
// Block-level streaming reveal.
|
||
|
|
//
|
||
|
|
// Token-by-token streaming mutates the trailing paragraph in place on every
|
||
|
|
// tick: words rewrap, the last line jitters, and the reader's eye fights the
|
||
|
|
// motion. Committing only up to the last COMPLETE line keeps every rendered
|
||
|
|
// block immutable once it appears — prose arrives a paragraph at a time (a
|
||
|
|
// markdown paragraph is one logical line), code fences reveal line by line,
|
||
|
|
// tables row by row — and the only remaining motion is the follow scroll.
|
||
|
|
//
|
||
|
|
// A paragraph with no newline for a long stretch must not stall the stream,
|
||
|
|
// so once the held tail outgrows a threshold it is committed at the last
|
||
|
|
// sentence boundary (falling back to the last word boundary).
|
||
|
|
|
||
|
|
const HOLD_MAX_CHARS = 320;
|
||
|
|
|
||
|
|
const SENTENCE_END = /[.!?…][)"'»”’]?\s/g;
|
||
|
|
|
||
|
|
export const commitStreamedText = (text: string): string => {
|
||
|
|
if (text.length === 0) return text;
|
||
|
|
|
||
|
|
const lastNewline = text.lastIndexOf('\n');
|
||
|
|
const committed = lastNewline === -1 ? '' : text.slice(0, lastNewline + 1);
|
||
|
|
const held = text.slice(committed.length);
|
||
|
|
|
||
|
|
if (held.length <= HOLD_MAX_CHARS) {
|
||
|
|
return committed;
|
||
|
|
}
|
||
|
|
|
||
|
|
// The held paragraph got long: release it up to the last finished
|
||
|
|
// sentence so the block still never mutates mid-sentence.
|
||
|
|
let lastSentenceEnd = -1;
|
||
|
|
for (const match of held.matchAll(SENTENCE_END)) {
|
||
|
|
lastSentenceEnd = match.index + match[0].length;
|
||
|
|
}
|
||
|
|
if (lastSentenceEnd > 0) {
|
||
|
|
return committed + held.slice(0, lastSentenceEnd);
|
||
|
|
}
|
||
|
|
|
||
|
|
// No sentence boundary either (a URL, a very long token run): release up
|
||
|
|
// to the last word boundary, keeping only the incomplete word held.
|
||
|
|
const lastSpace = held.lastIndexOf(' ');
|
||
|
|
if (lastSpace > 0) {
|
||
|
|
return committed + held.slice(0, lastSpace + 1);
|
||
|
|
}
|
||
|
|
|
||
|
|
return text;
|
||
|
|
};
|