import { describe, it, expect } from 'vitest';
import { topologicalLevelSort } from '../../src/core/ingestion/utils/graph-sort.js';

describe('topologicalLevelSort', () => {
  it('returns empty levels for empty graph', () => {
    const importMap = new Map<string, Set<string>>();
    const { levels, cycleCount } = topologicalLevelSort(importMap);
    expect(levels).toEqual([]);
    expect(cycleCount).toBe(0);
  });

  it('returns single level for files with no imports', () => {
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set()],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    expect(levels).toHaveLength(1);
    expect(levels[0]).toContain('a.ts');
    expect(levels[0]).toContain('b.ts');
  });

  it('orders files by dependency depth', () => {
    // b imports a, c imports b → a first, then b, then c
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set(['a.ts'])],
      ['c.ts', new Set(['b.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    expect(levels).toHaveLength(3);
    expect(levels[0]).toContain('a.ts');
    expect(levels[1]).toContain('b.ts');
    expect(levels[2]).toContain('c.ts');
  });

  it('groups independent files at the same level', () => {
    // b and c both import a → a at level 0, b and c at level 1
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set(['a.ts'])],
      ['c.ts', new Set(['a.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    expect(levels).toHaveLength(2);
    expect(levels[0]).toContain('a.ts');
    expect(levels[1]).toContain('b.ts');
    expect(levels[1]).toContain('c.ts');
  });

  it('handles cycles by grouping them in a final level', () => {
    // a imports b, b imports a — circular
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set(['b.ts'])],
      ['b.ts', new Set(['a.ts'])],
    ]);
    const { levels, cycleCount } = topologicalLevelSort(importMap);
    // Both should appear (in a cycle group)
    const allFiles = levels.flat();
    expect(allFiles).toContain('a.ts');
    expect(allFiles).toContain('b.ts');
    expect(cycleCount).toBe(2);
  });

  it('handles disconnected components', () => {
    // Two independent groups with no cross-links
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set(['a.ts'])],
      ['x.ts', new Set()],
      ['y.ts', new Set(['x.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    // Level 0 has both roots, level 1 has both dependents
    expect(levels[0]).toContain('a.ts');
    expect(levels[0]).toContain('x.ts');
    expect(levels[1]).toContain('b.ts');
    expect(levels[1]).toContain('y.ts');
  });

  it('handles diamond dependencies', () => {
    // d imports b and c; b and c both import a
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set(['a.ts'])],
      ['c.ts', new Set(['a.ts'])],
      ['d.ts', new Set(['b.ts', 'c.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    expect(levels).toHaveLength(3);
    expect(levels[0]).toContain('a.ts');
    expect(levels[1]).toContain('b.ts');
    expect(levels[1]).toContain('c.ts');
    expect(levels[2]).toContain('d.ts');
  });

  it('handles a single file with no imports', () => {
    const importMap = new Map<string, Set<string>>([['only.ts', new Set()]]);
    const { levels } = topologicalLevelSort(importMap);
    expect(levels).toHaveLength(1);
    expect(levels[0]).toContain('only.ts');
  });

  it('handles a dependency on a file not explicitly in the map', () => {
    // b imports external.ts which is not itself a key in importMap
    const importMap = new Map<string, Set<string>>([['b.ts', new Set(['external.ts'])]]);
    const { levels } = topologicalLevelSort(importMap);
    // external.ts has in-degree 0 (no one depends on it as a key), appears first
    // b.ts depends on external.ts so appears after
    const allFiles = levels.flat();
    expect(allFiles).toContain('external.ts');
    expect(allFiles).toContain('b.ts');
    const externalLevel = levels.findIndex((l) => l.includes('external.ts'));
    const bLevel = levels.findIndex((l) => l.includes('b.ts'));
    expect(externalLevel).toBeLessThan(bLevel);
  });

  it('handles a cycle mixed with an acyclic dependent', () => {
    // a and b are cyclic; c depends on b (and ends up in cycle group too
    // because b never reaches in-degree 0)
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set(['b.ts'])],
      ['b.ts', new Set(['a.ts'])],
      ['c.ts', new Set(['b.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    // No file has in-degree 0 to start: a needs b, b needs a, c needs b
    // All end up in the cycle group
    const allFiles = levels.flat();
    expect(allFiles).toContain('a.ts');
    expect(allFiles).toContain('b.ts');
    expect(allFiles).toContain('c.ts');
  });

  it('treats a self-edge (file imports itself) as a cycle', () => {
    // A imports A — Kahn's never reduces A's pending-imports count below 1,
    // so A is appended in the cycle group. Preserves prior semantics.
    const importMap = new Map<string, Set<string>>([['a.ts', new Set(['a.ts'])]]);
    const { levels, cycleCount } = topologicalLevelSort(importMap);
    const allFiles = levels.flat();
    expect(allFiles).toContain('a.ts');
    expect(cycleCount).toBe(1);
  });

  it('all files appear exactly once across all levels', () => {
    const importMap = new Map<string, Set<string>>([
      ['a.ts', new Set()],
      ['b.ts', new Set(['a.ts'])],
      ['c.ts', new Set(['a.ts'])],
      ['d.ts', new Set(['b.ts', 'c.ts'])],
    ]);
    const { levels } = topologicalLevelSort(importMap);
    const allFiles = levels.flat();
    const uniqueFiles = new Set(allFiles);
    expect(uniqueFiles.size).toBe(allFiles.length);
    expect(uniqueFiles.size).toBe(4);
  });
});