// When scroll position is within 10% of edges:
if (scrollRatio < 0.1 || scrollRatio > 0.9) {
  // 1. Calculate how far from center
  const dayDelta = Math.round(scrollDelta / config.dayWidth);
  // 2. Adjust dayOffset to compensate
  setDayOffset(dayOffset - dayDelta);
  // 3. Jump scroll to center
  container.scrollLeft = centerScrollLeft;
}

// Capture anchor before zoom
const anchorPixel = container.scrollLeft + anchorX;
const bufferDayPosition = anchorPixel / currentDayWidth;
const anchorDay = bufferDayPosition + dayOffset;

// After zoom - position so anchor day stays at anchorX
const newBufferPosition = anchorDay - dayOffset;
const newAnchorPixel = newBufferPosition * newDayWidth;
const newScrollLeft = newAnchorPixel - anchorX;

interface DragState {
  cardId: string;
  lane: number;
  title: string;
  startDay: number;
  endDay: number;
  mode: DragMode;
  startX: number;      // Initial pointer position
  startY: number;
  dx: number;          // Current delta from start
  dy: number;
  rect: DOMRect;       // Card rect at drag start
}

// displayCardsAtom computes visual positions during drag
const targetY = drag.rect.top + drag.rect.height / 2 + drag.dy;
const targetLane = findLaneAtY(targetY);  // Uses [data-lane] attributes

if (targetLane !== sourceLane) {
  // Shift cards between source and target lanes
  if (movingDown) {
    // Cards in between shift UP
    for (lane = sourceLane + 1; lane <= targetLane; lane++) {
      card.lane = lane - 1;
    }
  } else {
    // Cards in between shift DOWN
    for (lane = targetLane; lane < sourceLane; lane++) {
      card.lane = lane + 1;
    }
  }
}

// auto-scroll.ts
const SCROLL_EDGE_PX = 60;
const MAX_SCROLL_SPEED = 20;

function tick() {
  if (pointerX < containerRect.left + SCROLL_EDGE_PX) {
    // Scroll left, speed proportional to edge proximity
    deltaX = -(d / SCROLL_EDGE_PX) * MAX_SCROLL_SPEED;
  }
  // Similar for right, top, bottom edges
  container.scrollLeft += deltaX;
  container.scrollTop += deltaY;
}

if (mode === "resize-start" && snappedStartDay >= endDay) {
  // Dragged past: show swapped state
  absoluteLeft = (endDay - dayOffset) * dayWidth;
  width = (snappedStartDay + 1 - endDay) * dayWidth;
  isCrossed = true;
  effectivePosition = "end";  // Handle visually on opposite side
}

interface TimelineConfig {
  dayWidth: number;         // Base width per day (default: 80px)
  laneHeight: number;       // Height per lane (default: 60px)
  scrollBufferDays: number; // Total days in scroll buffer (default: 100)
  recenterThreshold: number;// Edge % to trigger recenter (default: 0.1)
  resizeHandleWidth: number;// Resize handle hit area (default: 12px)
}

interface ZoomConfig {
  minZoom: number;    // Minimum zoom level (default: 0.25)
  maxZoom: number;    // Maximum zoom level (default: 3)
  zoomStep: number;   // Increment per zoom action (default: 0.05)
  defaultZoom: number;// Initial zoom (default: 1)
}

interface BaseCard {
  id: string;        // Unique identifier
  lane: number;      // 0-indexed lane position
  startDay: number;  // Start day (0 = today, negative = past)
  endDay: number;    // End day (exclusive)
}

interface TaskCard extends BaseCard {
  title: string;
  color: string;
  assignee: string;
}