weather_app/tests/lib/api/lightning.test.js

import { describe, it, expect, vi, afterEach } from 'vitest'
import { fetchLightningStrikes, projectStrikeToLayer, haversineKm, filterStrikesWithinKm } from '../../../src/lib/api/lightning.js'

afterEach(() => {
  vi.restoreAllMocks()
})

describe('fetchLightningStrikes', () => {
  it('builds the relay URL with lat/lon/radius/limit', async () => {
    const fetchMock = vi.fn().mockResolvedValue({
      ok: true,
      json: async () => ({ source: 'blitzortung', strikes: [] }),
    })
    globalThis.fetch = fetchMock

    await fetchLightningStrikes({ lat: 36.35, lon: -95.81, radiusKm: 100, limit: 50 })

    const [url] = fetchMock.mock.calls[0]
    expect(url).toContain('https://cors.thecookiejar.me/lightning?')
    expect(url).toContain('lat=36.35')
    expect(url).toContain('lon=-95.81')
    expect(url).toContain('radiusKm=100')
    expect(url).toContain('limit=50')
  })

  it('returns the strike list on a valid response', async () => {
    globalThis.fetch = vi.fn().mockResolvedValue({
      ok: true,
      json: async () => ({
        source: 'blitzortung',
        strikes: [
          { lat: 36.3, lon: -95.8, time: 1724671234, strength: -12 },
          { lat: 36.5, lon: -95.9, time: 1724671299 },
        ],
      }),
    })

    const strikes = await fetchLightningStrikes({ lat: 36.35, lon: -95.81 })
    expect(strikes).toHaveLength(2)
    expect(strikes[0]).toMatchObject({ lat: 36.3, lon: -95.8, strength: -12 })
  })

  it('throws on a non-OK relay response', async () => {
    globalThis.fetch = vi.fn().mockResolvedValue({ ok: false, status: 502, statusText: 'Bad Gateway' })
    await expect(fetchLightningStrikes({ lat: 0, lon: 0 })).rejects.toThrow(/Lightning relay error: 502/)
  })

  it('throws on a malformed response (no strikes array)', async () => {
    globalThis.fetch = vi.fn().mockResolvedValue({ ok: true, json: async () => ({ foo: 1 }) })
    await expect(fetchLightningStrikes({ lat: 0, lon: 0 })).rejects.toThrow(/invalid response/)
  })

  it('throws when the relay is unreachable (network failure)', async () => {
    globalThis.fetch = vi.fn().mockRejectedValue(new TypeError('Failed to fetch'))
    await expect(fetchLightningStrikes({ lat: 0, lon: 0 })).rejects.toThrow()
  })
})

describe('projectStrikeToLayer', () => {
  // Center tile is (0.5, 0.5) at zoom 0 (lon=0,lat=0). A strike exactly at the
  // location should land at the center of the 5x5 layer: (2.5, 2.5) tiles.
  it('maps a strike at the center location to the layer center', () => {
    const { x, y } = projectStrikeToLayer(0, 0, { zoom: 0, cx: 0.5, cy: 0.5, tileSize: 256 })
    expect(x).toBeCloseTo(640)
    expect(y).toBeCloseTo(640)
  })

  it('scales with tile size', () => {
    const { x } = projectStrikeToLayer(0, 0, { zoom: 0, cx: 0.5, cy: 0.5, tileSize: 128 })
    expect(x).toBeCloseTo(320)
  })

  it('moves the strike right as lon increases', () => {
    const a = projectStrikeToLayer(0, 1, { zoom: 0, cx: 0.5, cy: 0.5, tileSize: 256 })
    const b = projectStrikeToLayer(0, 5, { zoom: 0, cx: 0.5, cy: 0.5, tileSize: 256 })
    expect(a.x).toBeGreaterThan(640)
    expect(b.x).toBeGreaterThan(a.x)
  })
})

describe('haversineKm', () => {
  it('returns ~0 for identical coords', () => {
    expect(haversineKm(36.35, -95.81, 36.35, -95.81)).toBeCloseTo(0, 5)
  })
  it('~39.66km for 0.3567 deg of latitude', () => {
    expect(haversineKm(36.0, -95.81, 36.3567, -95.81)).toBeCloseTo(39.66, 1)
  })

  it('~111.19km per 1 deg of latitude', () => {
    expect(haversineKm(36.0, -95.81, 37.0, -95.81)).toBeCloseTo(111.19, 1)
  })
})

describe('filterStrikesWithinKm', () => {
  // Distances computed with the real haversine helper (not hardcoded), so the
  // boundary tests are exact regardless of floating-point rounding.
  const R = haversineKm(36.35, -95.81, 37.0, -95.81)
  // A lon at 37.0 N whose distance from the location is just past R.
  let ln = -95.81
  while (haversineKm(36.35, -95.81, 37.0, ln) <= R) ln += 0.001
  const pastLon = ln

  const strikes = [
    { lat: 36.35, lon: -95.81, time: 1, strength: -10 }, // at the location (0 km) -> keep
    { lat: 37.0, lon: -95.81, time: 2, strength: -12 }, // exactly R km north -> keep
    { lat: 37.0, lon: pastLon, time: 3, strength: -9 }, // just past R -> drop
  ]

  it('keeps strikes strictly inside the radius', () => {
    const kept = filterStrikesWithinKm(strikes, 36.35, -95.81, R - 1)
    expect(kept).toHaveLength(1)
    expect(kept[0].strength).toBe(-10)
  })

  it('keeps strikes exactly at the radius boundary (inclusive)', () => {
    const kept = filterStrikesWithinKm(strikes, 36.35, -95.81, R)
    expect(kept).toHaveLength(2)
  })

  it('drops strikes just past the radius', () => {
    const kept = filterStrikesWithinKm(strikes, 36.35, -95.81, R - 0.0001)
    expect(kept).toHaveLength(1)
    expect(kept[0].strength).toBe(-10)
  })

  it('returns an empty array when everything is beyond the radius', () => {
    // Reference point far from any strike, with a tiny radius.
    expect(filterStrikesWithinKm(strikes, 40.0, -95.81, 0.0001)).toHaveLength(0)
  })
})