gui-video-clipper/src/lib/timeline/interactions.ts

import { type TimelineState, xToTime } from './renderer';

export type { TimelineState };

const MIN_VISIBLE_RANGE = 0.1;
const MIN_ZOOM = 1;

export function clampZoom(zoom: number, duration: number): number {
  const maxZoom = duration / MIN_VISIBLE_RANGE;
  return Math.max(MIN_ZOOM, Math.min(zoom, maxZoom));
}

export function computeZoom(
  state: TimelineState,
  anchorTime: number,
  factor: number,
  duration: number
): { visibleStart: number; visibleEnd: number; zoom: number } {
  const currentRange = state.visibleEnd - state.visibleStart;
  if (currentRange <= 0) {
    return {
      visibleStart: state.visibleStart,
      visibleEnd: state.visibleEnd,
      zoom: state.zoom,
    };
  }
  const newRange = currentRange / factor;
  const clampedRange = Math.max(MIN_VISIBLE_RANGE, Math.min(newRange, duration));

  const anchorRatio = (anchorTime - state.visibleStart) / currentRange;
  let newStart = anchorTime - anchorRatio * clampedRange;
  let newEnd = newStart + clampedRange;

  if (newStart < 0) {
    newStart = 0;
    newEnd = clampedRange;
  }
  if (newEnd > duration) {
    newEnd = duration;
    newStart = Math.max(0, newEnd - clampedRange);
  }

  const newZoom = clampZoom(duration / clampedRange, duration);

  return { visibleStart: newStart, visibleEnd: newEnd, zoom: newZoom };
}

export function panBy(
  state: TimelineState,
  deltaPixels: number,
  duration: number
): { visibleStart: number; visibleEnd: number } {
  const range = state.visibleEnd - state.visibleStart;
  const deltaTime = (deltaPixels / state.width) * range;
  let newStart = state.visibleStart + deltaTime;
  let newEnd = newStart + range;

  if (newStart < 0) {
    newStart = 0;
    newEnd = range;
  }
  if (newEnd > duration) {
    newEnd = duration;
    newStart = Math.max(0, newEnd - range);
  }

  return { visibleStart: newStart, visibleEnd: newEnd };
}

export function handleClick(
  x: number,
  state: TimelineState,
  duration: number
): number {
  const time = xToTime(x, state);
  return Math.max(0, Math.min(time, duration));
}