type-from-json/tests/type-inference.test.ts

import { TypeInferrer } from '../src/type-inferrer.js';

describe('TypeInferrer', () => {
  describe('infer', () => {
    it('should infer string type', () => {
      const inferrer = new TypeInferrer({ rootName: 'StringType' });
      const result = inferrer.infer('hello');
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer number type', () => {
      const inferrer = new TypeInferrer({ rootName: 'NumberType' });
      const result = inferrer.infer(42);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer boolean type', () => {
      const inferrer = new TypeInferrer({ rootName: 'BooleanType' });
      const result = inferrer.infer(true);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer null type', () => {
      const inferrer = new TypeInferrer({ rootName: 'NullType' });
      const result = inferrer.infer(null);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer array of primitives', () => {
      const inferrer = new TypeInferrer();
      const result = inferrer.infer([1, 2, 3]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer array of strings', () => {
      const inferrer = new TypeInferrer();
      const result = inferrer.infer(['a', 'b', 'c']);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer empty array', () => {
      const inferrer = new TypeInferrer();
      const result = inferrer.infer([]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should infer simple object', () => {
      const inferrer = new TypeInferrer({ rootName: 'User' });
      const result = inferrer.infer({
        name: 'John',
        age: 30,
        active: true,
      });
      expect(result.types.length).toBeGreaterThan(0);
      expect(result.types[0].name).toBe('User');
    });

    it('should infer nested objects', () => {
      const inferrer = new TypeInferrer({ rootName: 'Company' });
      const result = inferrer.infer({
        name: 'Acme',
        address: {
          street: '123 Main St',
          city: 'Boston',
        },
      });
      expect(result.types.length).toBeGreaterThanOrEqual(1);
      expect(result.types.find(t => t.name === 'Company')).toBeDefined();
    });

    it('should infer array of objects', () => {
      const inferrer = new TypeInferrer({ rootName: 'UserList' });
      const result = inferrer.infer([
        { id: 1, name: 'Alice' },
        { id: 2, name: 'Bob' },
      ]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should handle mixed type arrays', () => {
      const inferrer = new TypeInferrer();
      const result = inferrer.infer([1, 'two', true]);
      expect(result.types.length).toBeGreaterThan(0);
    });
  });

  describe('inferFromMultiple', () => {
    it('should merge compatible objects', () => {
      const inferrer = new TypeInferrer({ rootName: 'User' });
      const result = inferrer.inferFromMultiple([
        { id: 1, name: 'Alice' },
        { id: 2, name: 'Bob' },
      ]);
      expect(result.types.length).toBeGreaterThan(0);
      expect(result.types[0].name).toBe('User');
    });

    it('should detect optional fields', () => {
      const inferrer = new TypeInferrer({ rootName: 'User' });
      const result = inferrer.inferFromMultiple([
        { id: 1, name: 'Alice', email: 'alice@example.com' },
        { id: 2, name: 'Bob' },
      ]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should create union types for field variations', () => {
      const inferrer = new TypeInferrer({ rootName: 'Response' });
      const result = inferrer.inferFromMultiple([
        { id: 1 },
        { id: 'two' },
      ]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should return empty result for empty samples', () => {
      const inferrer = new TypeInferrer();
      const result = inferrer.inferFromMultiple([]);
      expect(result.types.length).toBe(0);
      expect(result.warnings.length).toBeGreaterThan(0);
    });

    it('should handle single sample', () => {
      const inferrer = new TypeInferrer({ rootName: 'Single' });
      const result = inferrer.inferFromMultiple([{ key: 'value' }]);
      expect(result.types.length).toBeGreaterThan(0);
    });

    it('should create literal types for enum-like values', () => {
      const inferrer = new TypeInferrer({ rootName: 'Status' });
      const result = inferrer.inferFromMultiple([
        { status: 'active' },
        { status: 'inactive' },
      ]);
      expect(result.types.length).toBeGreaterThan(0);
    });
  });
});