Sets up calendar package with core infrastructure

Adds core calendar package components including:
- Base services for events, resources, and settings
- Calendar app and orchestrator
- Build and bundling configuration
- IndexedDB storage setup

Prepares foundational architecture for calendar functionality

packages/calendar/src/features/event/EventLayoutEngine.ts

@@ -0,0 +1,279 @@
+/**
+ * EventLayoutEngine - Simplified stacking/grouping algorithm
+ *
+ * Supports two layout modes:
+ * - GRID: Events starting at same time rendered side-by-side
+ * - STACKING: Overlapping events with margin-left offset (15px per level)
+ *
+ * No prev/next chains, single-pass greedy algorithm
+ */
+
+import { ICalendarEvent } from '../../types/CalendarTypes';
+import { IGridConfig } from '../../core/IGridConfig';
+import { calculateEventPosition } from '../../utils/PositionUtils';
+import { IColumnLayout, IGridGroupLayout, IStackedEventLayout } from './EventLayoutTypes';
+
+/**
+ * Check if two events overlap (strict - touching at boundary = NOT overlapping)
+ * This matches Scenario 8: end===start is NOT overlap
+ */
+export function eventsOverlap(a: ICalendarEvent, b: ICalendarEvent): boolean {
+  return a.start < b.end && a.end > b.start;
+}
+
+/**
+ * Check if two events are within threshold for grid grouping.
+ * This includes:
+ * 1. Start-to-start: Events start within threshold of each other
+ * 2. End-to-start: One event starts within threshold before another ends
+ */
+function eventsWithinThreshold(a: ICalendarEvent, b: ICalendarEvent, thresholdMinutes: number): boolean {
+  const thresholdMs = thresholdMinutes * 60 * 1000;
+
+  // Start-to-start: both events start within threshold
+  const startToStartDiff = Math.abs(a.start.getTime() - b.start.getTime());
+  if (startToStartDiff <= thresholdMs) return true;
+
+  // End-to-start: one event starts within threshold before the other ends
+  // B starts within threshold before A ends
+  const bStartsBeforeAEnds = a.end.getTime() - b.start.getTime();
+  if (bStartsBeforeAEnds > 0 && bStartsBeforeAEnds <= thresholdMs) return true;
+
+  // A starts within threshold before B ends
+  const aStartsBeforeBEnds = b.end.getTime() - a.start.getTime();
+  if (aStartsBeforeBEnds > 0 && aStartsBeforeBEnds <= thresholdMs) return true;
+
+  return false;
+}
+
+/**
+ * Check if all events in a group start within threshold of each other
+ */
+function allStartWithinThreshold(events: ICalendarEvent[], thresholdMinutes: number): boolean {
+  if (events.length <= 1) return true;
+
+  // Find earliest and latest start times
+  let earliest = events[0].start.getTime();
+  let latest = events[0].start.getTime();
+
+  for (const event of events) {
+    const time = event.start.getTime();
+    if (time < earliest) earliest = time;
+    if (time > latest) latest = time;
+  }
+
+  const diffMinutes = (latest - earliest) / (1000 * 60);
+  return diffMinutes <= thresholdMinutes;
+}
+
+/**
+ * Find groups of overlapping events (connected by overlap chain)
+ * Events are grouped if they overlap with any event in the group
+ */
+function findOverlapGroups(events: ICalendarEvent[]): ICalendarEvent[][] {
+  if (events.length === 0) return [];
+
+  const sorted = [...events].sort((a, b) => a.start.getTime() - b.start.getTime());
+  const used = new Set<string>();
+  const groups: ICalendarEvent[][] = [];
+
+  for (const event of sorted) {
+    if (used.has(event.id)) continue;
+
+    // Start a new group with this event
+    const group: ICalendarEvent[] = [event];
+    used.add(event.id);
+
+    // Expand group by finding all connected events (via overlap)
+    let expanded = true;
+    while (expanded) {
+      expanded = false;
+      for (const candidate of sorted) {
+        if (used.has(candidate.id)) continue;
+
+        // Check if candidate overlaps with any event in group
+        const connects = group.some(member => eventsOverlap(member, candidate));
+
+        if (connects) {
+          group.push(candidate);
+          used.add(candidate.id);
+          expanded = true;
+        }
+      }
+    }
+
+    groups.push(group);
+  }
+
+  return groups;
+}
+
+/**
+ * Find grid candidates within a group - events connected via threshold chain
+ * Uses V1 logic: events are connected if within threshold (no overlap requirement)
+ */
+function findGridCandidates(
+  events: ICalendarEvent[],
+  thresholdMinutes: number
+): ICalendarEvent[][] {
+  if (events.length === 0) return [];
+
+  const sorted = [...events].sort((a, b) => a.start.getTime() - b.start.getTime());
+  const used = new Set<string>();
+  const groups: ICalendarEvent[][] = [];
+
+  for (const event of sorted) {
+    if (used.has(event.id)) continue;
+
+    const group: ICalendarEvent[] = [event];
+    used.add(event.id);
+
+    // Expand by threshold chain (V1 logic: no overlap requirement, just threshold)
+    let expanded = true;
+    while (expanded) {
+      expanded = false;
+      for (const candidate of sorted) {
+        if (used.has(candidate.id)) continue;
+
+        const connects = group.some(member =>
+          eventsWithinThreshold(member, candidate, thresholdMinutes)
+        );
+
+        if (connects) {
+          group.push(candidate);
+          used.add(candidate.id);
+          expanded = true;
+        }
+      }
+    }
+
+    groups.push(group);
+  }
+
+  return groups;
+}
+
+/**
+ * Calculate stack levels for overlapping events using greedy algorithm
+ * For each event: level = max(overlapping already-processed events) + 1
+ */
+function calculateStackLevels(events: ICalendarEvent[]): Map<string, number> {
+  const levels = new Map<string, number>();
+  const sorted = [...events].sort((a, b) => a.start.getTime() - b.start.getTime());
+
+  for (const event of sorted) {
+    let maxOverlappingLevel = -1;
+
+    // Find max level among overlapping events already processed
+    for (const [id, level] of levels) {
+      const other = events.find(e => e.id === id);
+      if (other && eventsOverlap(event, other)) {
+        maxOverlappingLevel = Math.max(maxOverlappingLevel, level);
+      }
+    }
+
+    levels.set(event.id, maxOverlappingLevel + 1);
+  }
+
+  return levels;
+}
+
+/**
+ * Allocate events to columns for GRID layout using greedy algorithm
+ * Non-overlapping events can share a column to minimize total columns
+ */
+function allocateColumns(events: ICalendarEvent[]): ICalendarEvent[][] {
+  const sorted = [...events].sort((a, b) => a.start.getTime() - b.start.getTime());
+  const columns: ICalendarEvent[][] = [];
+
+  for (const event of sorted) {
+    // Find first column where event doesn't overlap with existing events
+    let placed = false;
+    for (const column of columns) {
+      const canFit = !column.some(e => eventsOverlap(event, e));
+      if (canFit) {
+        column.push(event);
+        placed = true;
+        break;
+      }
+    }
+
+    // No suitable column found, create new one
+    if (!placed) {
+      columns.push([event]);
+    }
+  }
+
+  return columns;
+}
+
+/**
+ * Main entry point: Calculate complete layout for a column's events
+ *
+ * Algorithm:
+ * 1. Find overlap groups (events connected by overlap chain)
+ * 2. For each overlap group, find grid candidates (events within threshold chain)
+ * 3. If all events in overlap group form a single grid candidate → GRID mode
+ * 4. Otherwise → STACKING mode with calculated levels
+ */
+export function calculateColumnLayout(
+  events: ICalendarEvent[],
+  config: IGridConfig
+): IColumnLayout {
+  const thresholdMinutes = config.gridStartThresholdMinutes ?? 10;
+
+  const result: IColumnLayout = {
+    grids: [],
+    stacked: []
+  };
+
+  if (events.length === 0) return result;
+
+  // Find all overlapping event groups
+  const overlapGroups = findOverlapGroups(events);
+
+  for (const overlapGroup of overlapGroups) {
+    if (overlapGroup.length === 1) {
+      // Single event - no grouping needed
+      result.stacked.push({
+        event: overlapGroup[0],
+        stackLevel: 0
+      });
+      continue;
+    }
+
+    // Within this overlap group, find grid candidates (threshold-connected subgroups)
+    const gridSubgroups = findGridCandidates(overlapGroup, thresholdMinutes);
+
+    // Check if the ENTIRE overlap group forms a single grid candidate
+    // This happens when all events are connected via threshold chain
+    const largestGridCandidate = gridSubgroups.reduce((max, g) =>
+      g.length > max.length ? g : max, gridSubgroups[0]);
+
+    if (largestGridCandidate.length === overlapGroup.length) {
+      // All events in overlap group are connected via threshold chain → GRID mode
+      const columns = allocateColumns(overlapGroup);
+      const earliest = overlapGroup.reduce((min, e) =>
+        e.start < min.start ? e : min, overlapGroup[0]);
+      const position = calculateEventPosition(earliest.start, earliest.end, config);
+
+      result.grids.push({
+        events: overlapGroup,
+        columns,
+        stackLevel: 0,
+        position: { top: position.top }
+      });
+    } else {
+      // Not all events connected via threshold → STACKING mode
+      const levels = calculateStackLevels(overlapGroup);
+      for (const event of overlapGroup) {
+        result.stacked.push({
+          event,
+          stackLevel: levels.get(event.id) ?? 0
+        });
+      }
+    }
+  }
+
+  return result;
+}