/**
 * TDD Test Suite for EventStackManager
 *
 * This test suite follows Test-Driven Development principles:
 * 1. Write a failing test (RED)
 * 2. Write minimal code to make it pass (GREEN)
 * 3. Refactor if needed (REFACTOR)
 *
 * @see STACKING_CONCEPT.md for concept documentation
 */

import { describe, it, expect, beforeEach } from 'vitest';
import { EventStackManager, StackLink } from '../../src/managers/EventStackManager';

describe('EventStackManager - TDD Suite', () => {
  let manager: EventStackManager;

  beforeEach(() => {
    manager = new EventStackManager();
  });

  describe('Overlap Detection', () => {
    it('should detect overlap when event A starts before event B ends and event A ends after event B starts', () => {
      // RED - This test will fail initially
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T12:00:00')
      };

      // Expected: true (events overlap from 10:00 to 11:00)
      expect(manager.doEventsOverlap(eventA, eventB)).toBe(true);
    });

    it('should return false when events do not overlap', () => {
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T10:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T11:00:00'),
        end: new Date('2025-01-01T12:00:00')
      };

      expect(manager.doEventsOverlap(eventA, eventB)).toBe(false);
    });

    it('should detect overlap when one event completely contains another', () => {
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T13:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      expect(manager.doEventsOverlap(eventA, eventB)).toBe(true);
    });

    it('should return false when events touch but do not overlap', () => {
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T10:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'), // Exactly when A ends
        end: new Date('2025-01-01T11:00:00')
      };

      expect(manager.doEventsOverlap(eventA, eventB)).toBe(false);
    });
  });

  describe('Find Overlapping Events', () => {
    it('should find all events that overlap with a given event', () => {
      const targetEvent = {
        id: 'target',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const columnEvents = [
        {
          id: 'event-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T10:30:00') // Overlaps
        },
        {
          id: 'event-b',
          start: new Date('2025-01-01T12:00:00'),
          end: new Date('2025-01-01T13:00:00') // Does not overlap
        },
        {
          id: 'event-c',
          start: new Date('2025-01-01T10:30:00'),
          end: new Date('2025-01-01T11:30:00') // Overlaps
        }
      ];

      const overlapping = manager.findOverlappingEvents(targetEvent, columnEvents);

      expect(overlapping).toHaveLength(2);
      expect(overlapping.map(e => e.id)).toContain('event-a');
      expect(overlapping.map(e => e.id)).toContain('event-c');
      expect(overlapping.map(e => e.id)).not.toContain('event-b');
    });

    it('should return empty array when no events overlap', () => {
      const targetEvent = {
        id: 'target',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const columnEvents = [
        {
          id: 'event-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T09:30:00')
        },
        {
          id: 'event-b',
          start: new Date('2025-01-01T12:00:00'),
          end: new Date('2025-01-01T13:00:00')
        }
      ];

      const overlapping = manager.findOverlappingEvents(targetEvent, columnEvents);

      expect(overlapping).toHaveLength(0);
    });
  });

  describe('Create Stack Links', () => {
    it('should create stack links for overlapping events sorted by start time', () => {
      const events = [
        {
          id: 'event-b',
          start: new Date('2025-01-01T10:00:00'),
          end: new Date('2025-01-01T12:00:00')
        },
        {
          id: 'event-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T11:00:00')
        },
        {
          id: 'event-c',
          start: new Date('2025-01-01T11:00:00'),
          end: new Date('2025-01-01T13:00:00')
        }
      ];

      const stackLinks = manager.createStackLinks(events);

      // Should be sorted by start time: event-a, event-b, event-c
      expect(stackLinks.size).toBe(3);

      const linkA = stackLinks.get('event-a');
      expect(linkA).toEqual({
        stackLevel: 0,
        next: 'event-b'
        // no prev
      });

      const linkB = stackLinks.get('event-b');
      expect(linkB).toEqual({
        stackLevel: 1,
        prev: 'event-a',
        next: 'event-c'
      });

      const linkC = stackLinks.get('event-c');
      expect(linkC).toEqual({
        stackLevel: 2,
        prev: 'event-b'
        // no next
      });
    });

    it('should return empty map for empty event array', () => {
      const stackLinks = manager.createStackLinks([]);

      expect(stackLinks.size).toBe(0);
    });

    it('should create single stack link for single event', () => {
      const events = [
        {
          id: 'event-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T10:00:00')
        }
      ];

      const stackLinks = manager.createStackLinks(events);

      expect(stackLinks.size).toBe(1);

      const link = stackLinks.get('event-a');
      expect(link).toEqual({
        stackLevel: 0
        // no prev, no next
      });
    });

    it('should handle events with same start time by sorting by end time', () => {
      const events = [
        {
          id: 'event-b',
          start: new Date('2025-01-01T10:00:00'),
          end: new Date('2025-01-01T12:00:00') // Longer event
        },
        {
          id: 'event-a',
          start: new Date('2025-01-01T10:00:00'),
          end: new Date('2025-01-01T11:00:00') // Shorter event (should come first)
        }
      ];

      const stackLinks = manager.createStackLinks(events);

      // Shorter event should have lower stack level
      expect(stackLinks.get('event-a')?.stackLevel).toBe(0);
      expect(stackLinks.get('event-b')?.stackLevel).toBe(1);
    });
  });

  describe('Calculate Visual Styling', () => {
    it('should calculate marginLeft based on stack level', () => {
      const stackLevel = 0;
      expect(manager.calculateMarginLeft(stackLevel)).toBe(0);

      const stackLevel1 = 1;
      expect(manager.calculateMarginLeft(stackLevel1)).toBe(15);

      const stackLevel2 = 2;
      expect(manager.calculateMarginLeft(stackLevel2)).toBe(30);

      const stackLevel5 = 5;
      expect(manager.calculateMarginLeft(stackLevel5)).toBe(75);
    });

    it('should calculate zIndex based on stack level', () => {
      const stackLevel = 0;
      expect(manager.calculateZIndex(stackLevel)).toBe(100);

      const stackLevel1 = 1;
      expect(manager.calculateZIndex(stackLevel1)).toBe(101);

      const stackLevel2 = 2;
      expect(manager.calculateZIndex(stackLevel2)).toBe(102);
    });
  });

  describe('Stack Link Serialization', () => {
    it('should serialize stack link to JSON string', () => {
      const stackLink: StackLink = {
        stackLevel: 1,
        prev: 'event-a',
        next: 'event-c'
      };

      const serialized = manager.serializeStackLink(stackLink);

      expect(serialized).toBe('{"stackLevel":1,"prev":"event-a","next":"event-c"}');
    });

    it('should deserialize JSON string to stack link', () => {
      const json = '{"stackLevel":1,"prev":"event-a","next":"event-c"}';

      const stackLink = manager.deserializeStackLink(json);

      expect(stackLink).toEqual({
        stackLevel: 1,
        prev: 'event-a',
        next: 'event-c'
      });
    });

    it('should handle stack link without prev/next', () => {
      const stackLink: StackLink = {
        stackLevel: 0
      };

      const serialized = manager.serializeStackLink(stackLink);
      const deserialized = manager.deserializeStackLink(serialized);

      expect(deserialized).toEqual({
        stackLevel: 0
      });
    });

    it('should return null when deserializing invalid JSON', () => {
      const invalid = 'not-valid-json';

      const result = manager.deserializeStackLink(invalid);

      expect(result).toBeNull();
    });
  });

  describe('DOM Integration', () => {
    it('should apply stack link to DOM element', () => {
      const element = document.createElement('div');
      element.dataset.eventId = 'event-a';

      const stackLink: StackLink = {
        stackLevel: 1,
        prev: 'event-b',
        next: 'event-c'
      };

      manager.applyStackLinkToElement(element, stackLink);

      expect(element.dataset.stackLink).toBe('{"stackLevel":1,"prev":"event-b","next":"event-c"}');
    });

    it('should read stack link from DOM element', () => {
      const element = document.createElement('div');
      element.dataset.stackLink = '{"stackLevel":2,"prev":"event-a"}';

      const stackLink = manager.getStackLinkFromElement(element);

      expect(stackLink).toEqual({
        stackLevel: 2,
        prev: 'event-a'
      });
    });

    it('should return null when element has no stack link', () => {
      const element = document.createElement('div');

      const stackLink = manager.getStackLinkFromElement(element);

      expect(stackLink).toBeNull();
    });

    it('should apply visual styling to element based on stack level', () => {
      const element = document.createElement('div');

      manager.applyVisualStyling(element, 2);

      expect(element.style.marginLeft).toBe('30px');
      expect(element.style.zIndex).toBe('102');
    });

    it('should clear stack link from element', () => {
      const element = document.createElement('div');
      element.dataset.stackLink = '{"stackLevel":1}';

      manager.clearStackLinkFromElement(element);

      expect(element.dataset.stackLink).toBeUndefined();
    });

    it('should clear visual styling from element', () => {
      const element = document.createElement('div');
      element.style.marginLeft = '30px';
      element.style.zIndex = '102';

      manager.clearVisualStyling(element);

      expect(element.style.marginLeft).toBe('');
      expect(element.style.zIndex).toBe('');
    });
  });

  describe('Edge Cases', () => {
    it('should optimize stack levels when events do not overlap each other but both overlap a parent event', () => {
      // Visual representation:
      // Event A: 09:00 ════════════════════════════ 14:00
      // Event B:       10:00 ═════ 12:00
      // Event C:                      12:30 ═══ 13:00
      //
      // Expected stacking:
      // Event A: stackLevel 0 (base)
      // Event B: stackLevel 1 (conflicts with A)
      // Event C: stackLevel 1 (conflicts with A, but NOT with B - can share same level!)

      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T14:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T12:00:00')
      };

      const eventC = {
        id: 'event-c',
        start: new Date('2025-01-01T12:30:00'),
        end: new Date('2025-01-01T13:00:00')
      };

      const stackLinks = manager.createOptimizedStackLinks([eventA, eventB, eventC]);

      expect(stackLinks.size).toBe(3);

      // Event A is the base (contains both B and C)
      expect(stackLinks.get('event-a')?.stackLevel).toBe(0);

      // Event B and C should both be at stackLevel 1 (they don't overlap each other)
      expect(stackLinks.get('event-b')?.stackLevel).toBe(1);
      expect(stackLinks.get('event-c')?.stackLevel).toBe(1);

      // Verify they are NOT linked to each other (no prev/next between B and C)
      expect(stackLinks.get('event-b')?.next).toBeUndefined();
      expect(stackLinks.get('event-c')?.prev).toBeUndefined();
    });

    it('should create multiple parallel tracks when events at same level do not overlap', () => {
      // Complex scenario with multiple parallel tracks:
      // Event A: 09:00 ════════════════════════════════════ 15:00
      // Event B:       10:00 ═══ 11:00
      // Event C:                   11:30 ═══ 12:30
      // Event D:                               13:00 ═══ 14:00
      //
      // Expected:
      // - A at level 0 (base)
      // - B, C, D all at level 1 (they don't overlap each other, only with A)

      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T15:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const eventC = {
        id: 'event-c',
        start: new Date('2025-01-01T11:30:00'),
        end: new Date('2025-01-01T12:30:00')
      };

      const eventD = {
        id: 'event-d',
        start: new Date('2025-01-01T13:00:00'),
        end: new Date('2025-01-01T14:00:00')
      };

      const stackLinks = manager.createOptimizedStackLinks([eventA, eventB, eventC, eventD]);

      expect(stackLinks.size).toBe(4);
      expect(stackLinks.get('event-a')?.stackLevel).toBe(0);
      expect(stackLinks.get('event-b')?.stackLevel).toBe(1);
      expect(stackLinks.get('event-c')?.stackLevel).toBe(1);
      expect(stackLinks.get('event-d')?.stackLevel).toBe(1);
    });

    it('should handle nested overlaps with optimal stacking', () => {
      // Scenario:
      // Event A: 09:00 ════════════════════════════════════ 15:00
      // Event B:       10:00 ════════════════════ 13:00
      // Event C:             11:00 ═══ 12:00
      // Event D:                            12:30 ═══ 13:30
      //
      // Expected:
      // - A at level 0 (base, contains all)
      // - B at level 1 (overlaps with A)
      // - C at level 2 (overlaps with A and B)
      // - D at level 2 (overlaps with A and B, but NOT with C - can share level with C)

      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T09:00:00'),
        end: new Date('2025-01-01T15:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T13:00:00')
      };

      const eventC = {
        id: 'event-c',
        start: new Date('2025-01-01T11:00:00'),
        end: new Date('2025-01-01T12:00:00')
      };

      const eventD = {
        id: 'event-d',
        start: new Date('2025-01-01T12:30:00'),
        end: new Date('2025-01-01T13:30:00')
      };

      const stackLinks = manager.createOptimizedStackLinks([eventA, eventB, eventC, eventD]);

      expect(stackLinks.size).toBe(4);
      expect(stackLinks.get('event-a')?.stackLevel).toBe(0);
      expect(stackLinks.get('event-b')?.stackLevel).toBe(1);
      expect(stackLinks.get('event-c')?.stackLevel).toBe(2);
      expect(stackLinks.get('event-d')?.stackLevel).toBe(2); // Can share level with C
    });

    it('should handle events with identical start and end times', () => {
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      expect(manager.doEventsOverlap(eventA, eventB)).toBe(true);

      const stackLinks = manager.createStackLinks([eventA, eventB]);
      expect(stackLinks.size).toBe(2);
    });

    it('should handle events with zero duration', () => {
      const eventA = {
        id: 'event-a',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T10:00:00') // Zero duration
      };

      const eventB = {
        id: 'event-b',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      // Zero-duration event should not overlap
      expect(manager.doEventsOverlap(eventA, eventB)).toBe(false);
    });

    it('should handle large number of overlapping events', () => {
      const events = Array.from({ length: 100 }, (_, i) => ({
        id: `event-${i}`,
        start: new Date('2025-01-01T09:00:00'),
        end: new Date(`2025-01-01T${10 + i}:00:00`)
      }));

      const stackLinks = manager.createStackLinks(events);

      expect(stackLinks.size).toBe(100);
      expect(stackLinks.get('event-0')?.stackLevel).toBe(0);
      expect(stackLinks.get('event-99')?.stackLevel).toBe(99);
    });
  });

  describe('Integration Tests', () => {
    it('should create complete stack for new event with overlapping events', () => {
      // Scenario: Adding new event that overlaps with existing events
      const newEvent = {
        id: 'new-event',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const existingEvents = [
        {
          id: 'existing-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T10:30:00')
        },
        {
          id: 'existing-b',
          start: new Date('2025-01-01T10:30:00'),
          end: new Date('2025-01-01T12:00:00')
        }
      ];

      // Find overlapping
      const overlapping = manager.findOverlappingEvents(newEvent, existingEvents);

      // Create stack links for all events
      const allEvents = [...overlapping, newEvent];
      const stackLinks = manager.createStackLinks(allEvents);

      // Verify complete stack
      expect(stackLinks.size).toBe(3);
      expect(stackLinks.get('existing-a')?.stackLevel).toBe(0);
      expect(stackLinks.get('new-event')?.stackLevel).toBe(1);
      expect(stackLinks.get('existing-b')?.stackLevel).toBe(2);
    });

    it('should handle complete workflow: detect, create, apply to DOM', () => {
      const newEvent = {
        id: 'new-event',
        start: new Date('2025-01-01T10:00:00'),
        end: new Date('2025-01-01T11:00:00')
      };

      const existingEvents = [
        {
          id: 'existing-a',
          start: new Date('2025-01-01T09:00:00'),
          end: new Date('2025-01-01T10:30:00')
        }
      ];

      // Step 1: Find overlapping
      const overlapping = manager.findOverlappingEvents(newEvent, existingEvents);
      expect(overlapping).toHaveLength(1);

      // Step 2: Create stack links
      const allEvents = [...overlapping, newEvent];
      const stackLinks = manager.createStackLinks(allEvents);
      expect(stackLinks.size).toBe(2);

      // Step 3: Apply to DOM
      const elementA = document.createElement('div');
      elementA.dataset.eventId = 'existing-a';

      const elementNew = document.createElement('div');
      elementNew.dataset.eventId = 'new-event';

      manager.applyStackLinkToElement(elementA, stackLinks.get('existing-a')!);
      manager.applyStackLinkToElement(elementNew, stackLinks.get('new-event')!);

      manager.applyVisualStyling(elementA, stackLinks.get('existing-a')!.stackLevel);
      manager.applyVisualStyling(elementNew, stackLinks.get('new-event')!.stackLevel);

      // Verify DOM state
      expect(elementA.dataset.stackLink).toContain('"stackLevel":0');
      expect(elementA.style.marginLeft).toBe('0px');

      expect(elementNew.dataset.stackLink).toContain('"stackLevel":1');
      expect(elementNew.style.marginLeft).toBe('15px');
    });
  });
});