import { describe, expect, it } from 'vitest'

import {
  QUOTA_PACE_ETA_MAX_WINDOW_SECONDS,
  QUOTA_PACE_MIN_ELAPSED_FRACTION,
  buildPlanQuota,
  computePace,
  mergeQuotaWindows,
  quotaWindowKey,
  type QuotaWindow,
} from '../src/quota.js'

const NOW = new Date('2026-07-18T12:00:00Z')
const WEEK = 7 * 24 * 3600
const FIVE_HOURS = 5 * 3600

function window(overrides: Partial<QuotaWindow> = {}): QuotaWindow {
  return {
    kind: 'weekly',
    label: 'Weekly',
    usedFraction: 0.5,
    windowSeconds: WEEK,
    resetsAt: resetsAfterElapsedFraction(0.5, WEEK),
    source: 'live',
    ...overrides,
  }
}

/** resetsAt such that `fraction` of the window has elapsed at NOW. */
function resetsAfterElapsedFraction(fraction: number, windowSeconds: number): Date {
  return new Date(NOW.getTime() + windowSeconds * (1 - fraction) * 1000)
}

describe('quotaWindowKey', () => {
  it('distinguishes named kinds and custom kinds', () => {
    expect(quotaWindowKey('weekly')).toBe('weekly')
    expect(quotaWindowKey({ custom: 'Codex-Spark' })).toBe('custom:Codex-Spark')
    expect(quotaWindowKey({ custom: 'weekly' })).not.toBe(quotaWindowKey('weekly'))
  })
})

describe('computePace', () => {
  it('reports on-pace at the window midpoint', () => {
    const pace = computePace(window(), NOW)
    expect(pace?.expectedFraction).toBeCloseTo(0.5, 6)
    expect(pace?.deltaFraction).toBeCloseTo(0, 6)
    expect(pace?.projectedAtReset).toBeCloseTo(1, 6)
    expect(pace?.exhaustsAt).toBeUndefined()
  })

  it('computes deficit with an exhaustion ETA strictly before the reset', () => {
    const resetsAt = resetsAfterElapsedFraction(0.5, WEEK)
    const pace = computePace(window({ usedFraction: 0.8, resetsAt }), NOW)
    expect(pace?.deltaFraction).toBeCloseTo(0.3, 6)
    expect(pace?.projectedAtReset).toBeCloseTo(1.6, 6)
    // 80% in 3.5 days → 100% at 4.375 days elapsed.
    const expectedHit = NOW.getTime() + WEEK * (0.5 * (1 / 0.8) - 0.5) * 1000
    expect(pace?.exhaustsAt?.getTime()).toBeCloseTo(expectedHit, -3)
    expect(pace!.exhaustsAt!.getTime()).toBeLessThan(resetsAt.getTime())
  })

  it('reports reserve without an ETA', () => {
    const pace = computePace(window({ usedFraction: 0.2 }), NOW)
    expect(pace?.deltaFraction).toBeCloseTo(-0.3, 6)
    expect(pace?.projectedAtReset).toBeCloseTo(0.4, 6)
    expect(pace?.exhaustsAt).toBeUndefined()
  })

  it('suppresses the ETA on short windows but keeps the deficit', () => {
    const pace = computePace(
      window({
        usedFraction: 0.9,
        windowSeconds: FIVE_HOURS,
        resetsAt: resetsAfterElapsedFraction(0.5, FIVE_HOURS),
      }),
      NOW
    )
    expect(pace?.deltaFraction).toBeCloseTo(0.4, 6)
    expect(pace?.projectedAtReset).toBeGreaterThan(1)
    expect(pace?.exhaustsAt).toBeUndefined()
  })

  it('says nothing early in the window', () => {
    const early = window({ resetsAt: resetsAfterElapsedFraction(0.02, WEEK) })
    expect(computePace(early, NOW)).toBeUndefined()
    expect(0.02).toBeLessThan(QUOTA_PACE_MIN_ELAPSED_FRACTION)
  })

  it('says nothing on skewed or missing inputs', () => {
    expect(computePace(window({ resetsAt: new Date(NOW.getTime() - 60_000) }), NOW)).toBeUndefined()
    expect(
      computePace(window({ resetsAt: new Date(NOW.getTime() + (WEEK + 3600) * 1000) }), NOW)
    ).toBeUndefined()
    expect(computePace(window({ resetsAt: undefined }), NOW)).toBeUndefined()
    expect(computePace(window({ windowSeconds: undefined }), NOW)).toBeUndefined()
    expect(computePace(window({ windowSeconds: 0 }), NOW)).toBeUndefined()
  })

  it('says nothing on an exhausted window, clamping over-range input', () => {
    expect(computePace(window({ usedFraction: 1 }), NOW)).toBeUndefined()
    expect(computePace(window({ usedFraction: 1.3 }), NOW)).toBeUndefined()
  })

  it('treats zero usage mid-window as pure reserve', () => {
    const pace = computePace(window({ usedFraction: 0 }), NOW)
    expect(pace?.deltaFraction).toBeCloseTo(-0.5, 6)
    expect(pace?.projectedAtReset).toBe(0)
    expect(pace?.exhaustsAt).toBeUndefined()
  })

  it('keeps the ETA boundary aligned with the exported constant', () => {
    const boundary = window({
      usedFraction: 0.9,
      windowSeconds: QUOTA_PACE_ETA_MAX_WINDOW_SECONDS,
      resetsAt: resetsAfterElapsedFraction(0.5, QUOTA_PACE_ETA_MAX_WINDOW_SECONDS),
    })
    expect(computePace(boundary, NOW)?.exhaustsAt).toBeUndefined()
    const above = window({
      usedFraction: 0.9,
      windowSeconds: QUOTA_PACE_ETA_MAX_WINDOW_SECONDS + 3600,
      resetsAt: resetsAfterElapsedFraction(0.5, QUOTA_PACE_ETA_MAX_WINDOW_SECONDS + 3600),
    })
    expect(computePace(above, NOW)?.exhaustsAt).toBeInstanceOf(Date)
  })
})

describe('mergeQuotaWindows', () => {
  const liveWeekly = window({ source: 'live', label: 'Weekly (live)' })
  const derivedWeekly = window({ source: 'derived', label: 'Weekly (derived)' })
  const derivedMonthly = window({ kind: 'monthly', source: 'derived', label: 'Monthly' })

  it('prefers live per window kind and lets derived fill gaps', () => {
    const merged = mergeQuotaWindows([liveWeekly], [derivedWeekly, derivedMonthly])
    expect(merged).toHaveLength(2)
    expect(merged[0]).toBe(liveWeekly)
    expect(merged[1]).toBe(derivedMonthly)
  })

  it('keeps distinct custom kinds separate', () => {
    const spark = window({ kind: { custom: 'Spark' }, source: 'live' })
    const review = window({ kind: { custom: 'Review' }, source: 'derived' })
    expect(mergeQuotaWindows([spark], [review])).toHaveLength(2)
  })

  it('is all-derived when nothing live exists, and empty when nothing exists', () => {
    expect(mergeQuotaWindows([], [derivedWeekly])).toEqual([derivedWeekly])
    expect(mergeQuotaWindows([], [])).toEqual([])
  })
})

describe('buildPlanQuota', () => {
  it('merges, attaches pace, and stamps provenance per window', () => {
    const quota = buildPlanQuota({
      provider: 'codex',
      plan: 'pro',
      live: [window({ usedFraction: 0.8 })],
      derived: [window({ kind: 'monthly', source: 'derived', usedFraction: 0.2 })],
      now: NOW,
    })
    expect(quota.windows).toHaveLength(2)
    expect(quota.windows[0].source).toBe('live')
    expect(quota.windows[0].pace?.deltaFraction).toBeCloseTo(0.3, 6)
    expect(quota.windows[1].source).toBe('derived')
    expect(quota.windows[1].pace?.deltaFraction).toBeCloseTo(-0.3, 6)
    expect(quota.asOf).toBe(NOW)
  })

  it('yields an empty windows list when no source has readings — never zeros', () => {
    const quota = buildPlanQuota({ provider: 'claude', now: NOW })
    expect(quota.windows).toEqual([])
  })

  it('leaves pace undefined when the guards say nothing', () => {
    const quota = buildPlanQuota({
      provider: 'codex',
      live: [window({ resetsAt: resetsAfterElapsedFraction(0.01, WEEK) })],
      now: NOW,
    })
    expect(quota.windows[0].pace).toBeUndefined()
  })
})

describe('computePace NaN guard', () => {
  it('returns undefined for a non-finite usedFraction instead of a NaN pace', () => {
    const now = new Date('2026-07-15T00:00:00Z')
    const win = {
      kind: 'weekly' as const,
      usedFraction: NaN,
      resetsAt: new Date('2026-07-18T12:00:00Z'),
      windowSeconds: 7 * 24 * 3600,
      source: 'live' as const,
    }
    expect(computePace(win, now)).toBeUndefined()
    expect(computePace({ ...win, usedFraction: Infinity }, now)).toBeUndefined()
  })
})