Myx
85eef74bf7
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60 lines
2.3 KiB
TypeScript
60 lines
2.3 KiB
TypeScript
/** Behaviour the message list should apply when new messages arrive. */
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export type AutoScrollBehavior = 'smooth' | 'instant' | 'none';
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export interface AutoScrollDecisionInput {
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/** Whether the message count grew since the last render. */
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readonly newMessages: boolean;
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/** Forced jump for the local user's own just-sent message. */
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readonly forceLocalSend: boolean;
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/** Pixels from the bottom of the scroll container. */
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readonly distanceFromBottom: number;
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/**
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* True while the conversation is still settling after a channel/server
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* switch (initial scroll + async embed/image height changes). During this
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* window we jump instantly so we never animate to the wrong position.
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*/
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readonly withinInitialGrace: boolean;
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/** Distance threshold under which the list is considered stuck to bottom. */
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readonly stickyThreshold?: number;
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}
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/**
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* Decides how the message list should react when the message count changes.
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*
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* - No new messages -> `none`.
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* - Local user's own send -> `instant` (never animate your own message).
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* - Near bottom during the post-switch settle window -> `instant` (so loading
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* a channel always lands at the bottom without a mid-chat smooth animation).
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* - Near bottom afterwards -> `smooth` (live messages animate into view).
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* - Far from bottom -> `none` (show the new-messages indicator instead).
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*/
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export function resolveAutoScrollBehavior(input: AutoScrollDecisionInput): AutoScrollBehavior {
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if (!input.newMessages)
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return 'none';
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if (input.forceLocalSend)
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return 'instant';
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const threshold = input.stickyThreshold ?? 300;
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if (input.distanceFromBottom > threshold)
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return 'none';
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return input.withinInitialGrace ? 'instant' : 'smooth';
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}
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/** Default pixel distance under which the list is considered stuck to bottom. */
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export const STICKY_BOTTOM_THRESHOLD = 300;
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/**
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* Whether the scroll position is close enough to the bottom that the list
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* should keep auto-pinning to the latest message. Negative distances (rubber
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* band / overscroll) count as stuck.
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*
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* This is the predicate the message list uses to decide whether a content
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* height change (late image/embed/plugin render) should re-pin to bottom.
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*/
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export function isStuckToBottom(distanceFromBottom: number, threshold: number = STICKY_BOTTOM_THRESHOLD): boolean {
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return distanceFromBottom <= threshold;
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}
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