// Tests for watcher diff logic
// We test the core diffing behaviour by exercising the internals directly
// without needing to spin up a real OGraph server.

import { describe, it, expect, vi, beforeEach } from 'vitest';
import type { DispatcherConfig, PendingEntry } from '../src/types.js';

// ── helpers ──────────────────────────────────────────────────────────────────

function makeConfig(overrides: Partial<DispatcherConfig['intervals']> = {}): DispatcherConfig {
  return {
    ograph: { endpoint: 'http://localhost', token: undefined, projections: [] },
    oc: { statusEndpoint: 'http://localhost', statusToken: 'tok', minAvailable: 2 },
    intervals: {
      watcherIdle: 30_000,
      watcherActive: 5_000,
      schedulerIdle: 60_000,
      schedulerActive: 5_000,
      cooldownAfterPush: 60_000,
      ...overrides,
    },
  };
}

// Minimal inline diff engine extracted from the watcher logic so we can unit-test
// it without I/O dependencies.
function runDiff(
  snapshot: Map<string, unknown>,
  current: Map<string, unknown>,
  pending: Map<string, PendingEntry>,
): { changed: boolean } {
  let changed = false;
  const now = Date.now();

  for (const [name, value] of current.entries()) {
    if (!snapshot.has(name)) {
      // first-run: initialise snapshot, no change
      snapshot.set(name, value);
      continue;
    }

    const prev = snapshot.get(name);
    if (JSON.stringify(prev) !== JSON.stringify(value)) {
      changed = true;
      const existing = pending.get(name);
      if (existing) {
        existing.currentValue = value;
        existing.lastDetectedAt = now;
        existing.changeCount += 1;
      } else {
        pending.set(name, {
          name,
          previousValue: prev,
          currentValue: value,
          firstDetectedAt: now,
          lastDetectedAt: now,
          changeCount: 1,
        });
      }
      snapshot.set(name, value);
    }
  }

  // projections that disappeared
  for (const name of snapshot.keys()) {
    if (!current.has(name)) {
      const prev = snapshot.get(name);
      if (prev !== undefined) {
        changed = true;
        snapshot.set(name, undefined);
        pending.set(name, {
          name,
          previousValue: prev,
          currentValue: undefined,
          firstDetectedAt: now,
          lastDetectedAt: now,
          changeCount: 1,
        });
      }
    }
  }

  return { changed };
}

// ── tests ─────────────────────────────────────────────────────────────────────

describe('watcher diff logic', () => {
  let snapshot: Map<string, unknown>;
  let pending: Map<string, PendingEntry>;

  beforeEach(() => {
    snapshot = new Map();
    pending = new Map();
  });

  it('first run: initialises snapshot without reporting changes', () => {
    const current = new Map([['proj-a', { count: 1 }]]);
    const { changed } = runDiff(snapshot, current, pending);

    expect(changed).toBe(false);
    expect(pending.size).toBe(0);
    expect(snapshot.get('proj-a')).toEqual({ count: 1 });
  });

  it('second run: no diff when value unchanged', () => {
    const current = new Map([['proj-a', { count: 1 }]]);
    runDiff(snapshot, current, pending); // first run — init
    const { changed } = runDiff(snapshot, current, pending); // second run — same value

    expect(changed).toBe(false);
    expect(pending.size).toBe(0);
  });

  it('detects a value change between runs', () => {
    const v1 = new Map([['proj-a', { count: 1 }]]);
    const v2 = new Map([['proj-a', { count: 2 }]]);

    runDiff(snapshot, v1, pending); // init
    const { changed } = runDiff(snapshot, v2, pending);

    expect(changed).toBe(true);
    expect(pending.has('proj-a')).toBe(true);
    expect(pending.get('proj-a')!.previousValue).toEqual({ count: 1 });
    expect(pending.get('proj-a')!.currentValue).toEqual({ count: 2 });
  });

  it('merges multiple changes into one pending entry', () => {
    runDiff(snapshot, new Map([['proj-a', 1]]), pending); // init
    runDiff(snapshot, new Map([['proj-a', 2]]), pending); // change 1
    runDiff(snapshot, new Map([['proj-a', 3]]), pending); // change 2

    expect(pending.get('proj-a')!.changeCount).toBe(2);
    expect(pending.get('proj-a')!.currentValue).toBe(3);
    expect(pending.get('proj-a')!.previousValue).toBe(1); // kept from first change
  });

  it('detects a disappeared projection', () => {
    runDiff(snapshot, new Map([['proj-a', 42]]), pending); // init
    const { changed } = runDiff(snapshot, new Map(), pending); // proj-a gone

    expect(changed).toBe(true);
    expect(pending.get('proj-a')!.currentValue).toBeUndefined();
  });

  it('does not re-fire when a disappeared projection stays absent', () => {
    runDiff(snapshot, new Map([['proj-a', 42]]), pending); // init
    runDiff(snapshot, new Map(), pending);                  // gone → change
    pending.clear();
    const { changed } = runDiff(snapshot, new Map(), pending); // still gone → no change

    expect(changed).toBe(false);
    expect(pending.size).toBe(0);
  });
});