import { describe, it, expect, beforeEach } from 'vitest';
import { CircularityService } from './CircularityService.js';
import { MeldImportError } from '@core/errors/MeldImportError.js';

describe('CircularityService', () => {
  let service: CircularityService;

  beforeEach(() => {
    service = new CircularityService();
  });

  describe('Basic import tracking', () => {
    it('should track imports in stack', () => {
      service.beginImport('fileA.meld');
      expect(service.isInStack('fileA.meld')).toBe(true);
      expect(service.getImportStack()).toEqual(['fileA.meld']);
    });

    it('should remove imports from stack', () => {
      service.beginImport('fileA.meld');
      service.endImport('fileA.meld');
      expect(service.isInStack('fileA.meld')).toBe(false);
      expect(service.getImportStack()).toEqual([]);
    });

    it('should handle multiple imports in LIFO order', () => {
      service.beginImport('fileA.meld');
      service.beginImport('fileB.meld');
      service.beginImport('fileC.meld');

      expect(service.getImportStack()).toEqual([
        'fileA.meld',
        'fileB.meld',
        'fileC.meld'
      ]);

      service.endImport('fileC.meld');
      expect(service.getImportStack()).toEqual([
        'fileA.meld',
        'fileB.meld'
      ]);
    });
  });

  describe('Circular import detection', () => {
    it('should detect direct circular imports', () => {
      service.beginImport('fileA.meld');
      
      expect(() => service.beginImport('fileA.meld'))
        .toThrow(MeldImportError);
    });

    it('should detect indirect circular imports', () => {
      service.beginImport('fileA.meld');
      service.beginImport('fileB.meld');
      
      expect(() => service.beginImport('fileA.meld'))
        .toThrow(MeldImportError);
    });

    it('should include import chain in error', () => {
      service.beginImport('fileA.meld');
      service.beginImport('fileB.meld');
      
      try {
        service.beginImport('fileA.meld');
        fail('Should have thrown');
      } catch (error) {
        expect(error).toBeInstanceOf(MeldImportError);
        if (error instanceof MeldImportError) {
          expect(error.details?.importChain).toEqual([
            'fileA.meld',
            'fileB.meld',
            'fileA.meld'
          ]);
        }
      }
    });

    it('should allow reimporting after file is removed from stack', () => {
      service.beginImport('fileA.meld');
      service.endImport('fileA.meld');
      
      expect(() => service.beginImport('fileA.meld'))
        .not.toThrow();
    });
  });

  describe('Stack management', () => {
    it('should reset the stack', () => {
      service.beginImport('fileA.meld');
      service.beginImport('fileB.meld');
      
      service.reset();
      
      expect(service.getImportStack()).toEqual([]);
      expect(service.isInStack('fileA.meld')).toBe(false);
      expect(service.isInStack('fileB.meld')).toBe(false);
    });

    it('should handle ending import for file not in stack', () => {
      expect(() => service.endImport('nonexistent.meld'))
        .not.toThrow();
    });

    it('should maintain stack order when ending imports out of order', () => {
      service.beginImport('fileA.meld');
      service.beginImport('fileB.meld');
      service.beginImport('fileC.meld');

      service.endImport('fileB.meld');
      
      expect(service.getImportStack()).toEqual([
        'fileA.meld',
        'fileC.meld'
      ]);
    });
  });
});