/**
 * Unit tests for src/core/state.ts
 *
 * Covers:
 *  - First update creates entry; subsequent updates increment position_count_session
 *  - LRU eviction: with cap=3, after 4 distinct devices the oldest is evicted
 *  - Eviction increments evictedTotal()
 *  - last_seen reflects the position's timestamp (device-reported time)
 *  - Out-of-order positions: last_seen only advances forward (max semantics)
 *  - get() returns undefined for unknown devices
 *  - size() returns the current number of stored devices
 *  - LRU order: most-recently-updated device is not evicted on overflow
 */

import { describe, it, expect, vi } from 'vitest';
import type { Logger } from 'pino';
import type { Config } from '../src/config/load.js';
import type { Position, Metrics } from '../src/core/types.js';
import { createDeviceStateStore } from '../src/core/state.js';

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

function makeSilentLogger(): Logger {
  return {
    debug: vi.fn(),
    info: vi.fn(),
    warn: vi.fn(),
    error: vi.fn(),
    fatal: vi.fn(),
    child: vi.fn().mockReturnThis(),
    trace: vi.fn(),
    level: 'silent',
    silent: vi.fn(),
  } as unknown as Logger;
}

function makeMetrics(): Metrics {
  return {
    inc: vi.fn(),
    observe: vi.fn(),
  };
}

function makeConfig(overrides: Partial<Config> = {}): Config {
  return {
    NODE_ENV: 'test',
    INSTANCE_ID: 'test-processor',
    LOG_LEVEL: 'silent',
    REDIS_URL: 'redis://localhost:6379',
    POSTGRES_URL: 'postgres://localhost:5432/test',
    REDIS_TELEMETRY_STREAM: 'telemetry:t',
    REDIS_CONSUMER_GROUP: 'processor',
    REDIS_CONSUMER_NAME: 'test-consumer',
    METRICS_PORT: 9090,
    BATCH_SIZE: 10,
    BATCH_BLOCK_MS: 100,
    WRITE_BATCH_SIZE: 50,
    DEVICE_STATE_LRU_CAP: 1000,
    ...overrides,
  };
}

function makePosition(deviceId: string, overrides: Partial<Position> = {}): Position {
  return {
    device_id: deviceId,
    timestamp: new Date('2024-05-01T12:00:00.000Z'),
    latitude: 54.6872,
    longitude: 25.2797,
    altitude: 100,
    angle: 90,
    speed: 50,
    satellites: 12,
    priority: 1,
    attributes: {},
    ...overrides,
  };
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

describe('createDeviceStateStore — initial state', () => {
  it('creates a new entry on first update', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const position = makePosition('DEV001');

    const state = store.update(position);

    expect(state.device_id).toBe('DEV001');
    expect(state.last_position).toBe(position);
    expect(state.position_count_session).toBe(1);
    expect(state.last_seen).toEqual(position.timestamp);
  });

  it('increments position_count_session on subsequent updates', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const pos1 = makePosition('DEV001', { timestamp: new Date('2024-05-01T12:00:00.000Z') });
    const pos2 = makePosition('DEV001', { timestamp: new Date('2024-05-01T12:00:01.000Z') });
    const pos3 = makePosition('DEV001', { timestamp: new Date('2024-05-01T12:00:02.000Z') });

    store.update(pos1);
    store.update(pos2);
    const state = store.update(pos3);

    expect(state.position_count_session).toBe(3);
  });

  it('get() returns undefined for an unknown device', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());

    expect(store.get('UNKNOWN')).toBeUndefined();
  });

  it('get() returns the current state for a known device', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const position = makePosition('DEV002');

    store.update(position);
    const state = store.get('DEV002');

    expect(state).toBeDefined();
    expect(state?.device_id).toBe('DEV002');
  });

  it('size() returns 0 before any updates', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    expect(store.size()).toBe(0);
  });

  it('size() returns the number of distinct devices after updates', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());

    store.update(makePosition('DEV001'));
    store.update(makePosition('DEV002'));
    store.update(makePosition('DEV001')); // duplicate device — should not increase size

    expect(store.size()).toBe(2);
  });
});

describe('createDeviceStateStore — last_seen semantics', () => {
  it('last_seen reflects the position timestamp (not wall clock)', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const ts = new Date('2024-03-15T08:30:00.000Z');
    const position = makePosition('DEV010', { timestamp: ts });

    const state = store.update(position);

    expect(state.last_seen).toEqual(ts);
    expect(state.last_seen).not.toBe(new Date()); // not wall clock
  });

  it('last_seen advances on newer timestamps', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const ts1 = new Date('2024-05-01T10:00:00.000Z');
    const ts2 = new Date('2024-05-01T11:00:00.000Z');

    store.update(makePosition('DEV011', { timestamp: ts1 }));
    const state = store.update(makePosition('DEV011', { timestamp: ts2 }));

    expect(state.last_seen).toEqual(ts2);
  });

  it('last_seen does NOT regress on out-of-order (older) timestamps', () => {
    // Devices buffer offline records and replay them in bursts; within a burst
    // consecutive timestamps may decrease. last_seen must mean "highest device
    // timestamp seen so far" — it must never go backward.
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const newer = new Date('2024-05-01T12:00:00.000Z');
    const older = new Date('2024-05-01T10:00:00.000Z');

    store.update(makePosition('DEV012', { timestamp: newer }));
    const state = store.update(makePosition('DEV012', { timestamp: older }));

    // last_seen must remain at the newer timestamp, not regress to older
    expect(state.last_seen).toEqual(newer);
  });

  it('last_seen stays the same when equal timestamps arrive', () => {
    const store = createDeviceStateStore(makeConfig(), makeSilentLogger(), makeMetrics());
    const ts = new Date('2024-05-01T12:00:00.000Z');

    store.update(makePosition('DEV013', { timestamp: ts }));
    const state = store.update(makePosition('DEV013', { timestamp: new Date(ts.getTime()) }));

    expect(state.last_seen).toEqual(ts);
  });
});

describe('createDeviceStateStore — LRU eviction', () => {
  it('evicts the least-recently-updated device when cap is exceeded', () => {
    const store = createDeviceStateStore(makeConfig({ DEVICE_STATE_LRU_CAP: 3 }), makeSilentLogger(), makeMetrics());
    const ts = new Date('2024-05-01T12:00:00.000Z');

    // Insert 3 devices: DEV001, DEV002, DEV003 (DEV001 is oldest)
    store.update(makePosition('DEV001', { timestamp: ts }));
    store.update(makePosition('DEV002', { timestamp: ts }));
    store.update(makePosition('DEV003', { timestamp: ts }));

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

    // Add a 4th device — DEV001 (the oldest / least-recently-updated) should be evicted
    store.update(makePosition('DEV004', { timestamp: ts }));

    expect(store.size()).toBe(3);
    expect(store.get('DEV001')).toBeUndefined(); // evicted
    expect(store.get('DEV002')).toBeDefined();
    expect(store.get('DEV003')).toBeDefined();
    expect(store.get('DEV004')).toBeDefined();
  });

  it('re-using an existing device bumps it to most-recent so it is not evicted next', () => {
    const store = createDeviceStateStore(makeConfig({ DEVICE_STATE_LRU_CAP: 3 }), makeSilentLogger(), makeMetrics());
    const ts1 = new Date('2024-05-01T12:00:00.000Z');
    const ts2 = new Date('2024-05-01T12:00:01.000Z');

    store.update(makePosition('DEV001', { timestamp: ts1 }));
    store.update(makePosition('DEV002', { timestamp: ts1 }));
    store.update(makePosition('DEV003', { timestamp: ts1 }));

    // Re-touch DEV001 — it should now be the most-recently-updated
    store.update(makePosition('DEV001', { timestamp: ts2 }));

    // Add DEV004 — DEV002 should be evicted (it is now the oldest)
    store.update(makePosition('DEV004', { timestamp: ts1 }));

    expect(store.size()).toBe(3);
    expect(store.get('DEV001')).toBeDefined(); // was re-touched
    expect(store.get('DEV002')).toBeUndefined(); // evicted (oldest after DEV001 was re-touched)
    expect(store.get('DEV003')).toBeDefined();
    expect(store.get('DEV004')).toBeDefined();
  });

  it('evictedTotal() increments on each eviction', () => {
    const store = createDeviceStateStore(makeConfig({ DEVICE_STATE_LRU_CAP: 2 }), makeSilentLogger(), makeMetrics());
    const ts = new Date('2024-05-01T12:00:00.000Z');

    expect(store.evictedTotal()).toBe(0);

    store.update(makePosition('DEV001', { timestamp: ts }));
    store.update(makePosition('DEV002', { timestamp: ts }));
    expect(store.evictedTotal()).toBe(0);

    store.update(makePosition('DEV003', { timestamp: ts })); // evicts DEV001
    expect(store.evictedTotal()).toBe(1);

    store.update(makePosition('DEV004', { timestamp: ts })); // evicts DEV002
    expect(store.evictedTotal()).toBe(2);
  });

  it('evictedTotal() stays 0 when cap is never reached', () => {
    const store = createDeviceStateStore(makeConfig({ DEVICE_STATE_LRU_CAP: 1000 }), makeSilentLogger(), makeMetrics());
    const ts = new Date('2024-05-01T12:00:00.000Z');

    for (let i = 0; i < 10; i++) {
      store.update(makePosition(`DEV${i}`, { timestamp: ts }));
    }

    expect(store.evictedTotal()).toBe(0);
  });
});