Function createZoomState

src/interaction/createZoomState.ts:80–286

(
  initialStart: number,
  initialEnd: number,
  constraints?: ZoomSpanConstraints,
)

const copyRange = (r: ZoomRange): ZoomRange => ({ start: r.start, end: r.end });

export function createZoomState(
  initialStart: number,
  initialEnd: number,
  constraints?: ZoomSpanConstraints,
): ZoomStateWithConstraints {
  let start = 0;
  let end = 100;
  let lastEmitted: ZoomRange | null = null;

  const listeners = new Set<ZoomRangeChangeCallback>();

  let minSpan = (() => {
    const v = Number.isFinite(constraints?.minSpan) ? (constraints!.minSpan as number) : DEFAULT_MIN_SPAN;
    return clamp(Number.isFinite(v) ? v : 0, 0, 100);
  })();

  let maxSpan = (() => {
    const v = Number.isFinite(constraints?.maxSpan) ? (constraints!.maxSpan as number) : DEFAULT_MAX_SPAN;
    return clamp(Number.isFinite(v) ? v : 100, 0, 100);
  })();

  let normalizedMinSpan = Math.min(minSpan, maxSpan);
  let normalizedMaxSpan = Math.max(minSpan, maxSpan);

  const emit = (): void => {
    const next: ZoomRange = { start, end };
    if (
      lastEmitted !== null &&
      lastEmitted.start === next.start &&
      lastEmitted.end === next.end
    ) {
      return;
    }

    lastEmitted = copyRange(next);

    // Emit to a snapshot so additions/removals during emit don't affect this flush.
    const snapshot = Array.from(listeners);
    for (const cb of snapshot) cb({ start, end });
  };

  const toAnchor = (nextStart: number, nextEnd: number, spec?: ZoomRangeAnchor): { readonly center: number; readonly ratio: number } | undefined => {
    if (!spec) return undefined;
    if (typeof spec === 'string') {
      switch (spec) {
        case 'start':
          return { center: nextStart, ratio: 0 };
        case 'end':
          return { center: nextEnd, ratio: 1 };
        case 'center':
          return { center: (nextStart + nextEnd) * 0.5, ratio: 0.5 };
      }
    }
    if (spec && Number.isFinite(spec.center) && Number.isFinite(spec.ratio)) {
      return { center: spec.center, ratio: spec.ratio };
    }
    return undefined;
  };