import { test } from '@japa/runner'
import type { Overview } from '#lib/nntp/index'
import {
  estimateDate,
  medianDate,
  monotone,
  sampleCount,
  samplePoints,
} from '#services/group_dates'

const now = new Date('2026-10-25T10:00:00Z')
const overview = (n: number, date: string): Overview => [n, { subject: 's', from: 'f', date }]
const day = (d: string) => new Date(`${d}T00:00:00Z`)

test.group('group dates', () => {
  test('the median of the plausible Date headers, or null for too few', ({ assert }) => {
    const slice = [
      overview(1, 'Mon, 02 Mar 2015 10:00:00 +0000'),
      overview(2, 'Tue, 03 Mar 2015 10:00:00 GMT'),
      overview(3, 'Wed, 04 Mar 2015 10:00:00 UTC'),
      // A broken clock, a future one, and junk: left out.
      overview(4, 'Sat, 01 Jan 1980 00:00:00 +0000'),
      overview(5, 'Fri, 01 Jan 2027 00:00:00 +0000'),
      overview(6, 'not a date'),
      overview(7, 'Thu, 05 Mar 2015 10:00:00 +0100'),
    ]
    assert.equal(medianDate(slice, now)!.toISOString(), '2015-03-04T10:00:00.000Z')
    assert.isNull(medianDate(slice.slice(0, 2), now))
    assert.isNull(medianDate([], now))
  })

  test('sample points span low to high, the last slice ending at high', ({ assert }) => {
    assert.deepEqual(samplePoints(100, 1099, 5, 100), [100, 325, 550, 775, 1000])
    assert.deepEqual(samplePoints(100, 150, 5, 100), [100])
    assert.equal(sampleCount(0, 161e9, 500e6), 323)
    assert.equal(sampleCount(0, 1000, 500e6), 16)
    assert.equal(sampleCount(0, 10e12, 500e6), 1000)
  })

  test('the curve drops a spike, raises a dip, and keeps the order', ({ assert }) => {
    const curve = monotone([
      { article: 300, postedAt: day('2015-03-01') },
      { article: 100, postedAt: day('2015-01-01') },
      // One poster's clock in the future for a whole slice.
      { article: 200, postedAt: day('2019-06-01') },
      // Old crossposts: earlier than the sample before.
      { article: 400, postedAt: day('2014-12-01') },
      { article: 500, postedAt: day('2015-05-01') },
    ])
    assert.deepEqual(
      curve.map((s) => [s.article, s.postedAt.toISOString().slice(0, 10)]),
      [
        [100, '2015-01-01'],
        [300, '2015-03-01'],
        [400, '2015-03-01'],
        [500, '2015-05-01'],
      ]
    )
  })

  test('a date is interpolated between the samples around it and clamped beyond them', ({
    assert,
  }) => {
    const curve = [
      { article: 100, postedAt: day('2015-01-01') },
      { article: 300, postedAt: day('2015-03-02') },
      { article: 500, postedAt: day('2015-05-01') },
    ]
    assert.equal(estimateDate(curve, 200)!.toISOString().slice(0, 10), '2015-01-31')
    assert.equal(estimateDate(curve, 300)!.toISOString().slice(0, 10), '2015-03-02')
    assert.equal(estimateDate(curve, 1)!.toISOString().slice(0, 10), '2015-01-01')
    assert.equal(estimateDate(curve, 900)!.toISOString().slice(0, 10), '2015-05-01')
    assert.isNull(estimateDate([], 200))
  })
})