Ilia Mashkov
22 lines
744 B
TypeScript
22 lines
744 B
TypeScript
/**
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* The id one step from `currentId` in board order, wrapping at both ends.
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*
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* @param orderedIds - Pairing ids in board order.
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* @param currentId - The currently focal id to step from.
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* @param direction - +1 for next, -1 for previous.
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* @returns The neighbouring id (wrapped), `currentId` unchanged if it isn't in
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* the list, or null for an empty list.
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*/
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export function nextFocalId(orderedIds: string[], currentId: string, direction: 1 | -1): string | null {
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if (orderedIds.length === 0) {
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return null;
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}
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const i = orderedIds.indexOf(currentId);
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if (i === -1) {
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return currentId;
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}
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const len = orderedIds.length;
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const next = (i + direction + len) % len;
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return orderedIds[next];
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}
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