import { describe, expect, it } from 'vitest'
import { type LaneSubject, previewCascade, resolveLanes } from '@/lib/timetable/lane'
import type { Performance } from '@/types/timetable'

function s(id: string, start: string, end: string, lane: number | null = null, cancelled = false): LaneSubject {
  return { id, start_at: start, end_at: end, lane, cancelled }
}

function p(id: string, start: string, end: string, lane = 0): Performance {
  return {
    id,
    engagement_id: 'e1',
    event_id: 'ev1',
    stage_id: 's1',
    lane,
    lane_resolved: lane,
    start_at: start,
    end_at: end,
    version: 0,
    notes: null,
    warnings: [],
    created_at: null,
    updated_at: null,
    deleted_at: null,
  }
}

describe('resolveLanes (Pass 2 only — implicit lanes)', () => {
  it('places non-overlapping items on lane 0', () => {
    const result = resolveLanes([
      s('a', '2026-07-10T18:00:00Z', '2026-07-10T19:00:00Z'),
      s('b', '2026-07-10T19:00:00Z', '2026-07-10T20:00:00Z'),
    ])

    expect(result.laneOf).toEqual({ a: 0, b: 0 })
    expect(result.laneCount).toBe(1)
  })

  it('stacks overlapping items into separate lanes', () => {
    const result = resolveLanes([
      s('a', '2026-07-10T18:00:00Z', '2026-07-10T19:30:00Z'),
      s('b', '2026-07-10T19:00:00Z', '2026-07-10T20:00:00Z'),
    ])

    expect(result.laneOf.a).toBe(0)
    expect(result.laneOf.b).toBe(1)
    expect(result.laneCount).toBe(2)
  })

  it('Pass 1 — explicit lane is honoured', () => {
    const result = resolveLanes([
      s('a', '2026-07-10T18:00:00Z', '2026-07-10T19:00:00Z', 2),
      s('b', '2026-07-10T19:00:00Z', '2026-07-10T20:00:00Z'),
    ])

    expect(result.laneOf.a).toBe(2)
    expect(result.laneOf.b).toBe(0)
  })

  it('Pass 1 — overlapping explicit lane bumps down', () => {
    const result = resolveLanes([
      s('a', '2026-07-10T18:00:00Z', '2026-07-10T19:30:00Z', 0),
      s('b', '2026-07-10T19:00:00Z', '2026-07-10T20:00:00Z', 0),
    ])

    expect(result.laneOf.a).toBe(0)
    expect(result.laneOf.b).toBe(1)
  })

  it('cancelled items are excluded from collision checks', () => {
    const result = resolveLanes([
      s('a', '2026-07-10T18:00:00Z', '2026-07-10T19:30:00Z'),
      s('b', '2026-07-10T19:00:00Z', '2026-07-10T20:00:00Z', null, true),
    ])

    expect(result.laneOf.b).toBe(0)
  })

  it('handles empty input', () => {
    const result = resolveLanes([])

    expect(result.laneCount).toBe(1)
    expect(result.laneOf).toEqual({})
  })
})

describe('previewCascade (drag preview)', () => {
  it('preserves wanted lane when target is free', () => {
    const cohort = [p('a', '2026-07-10T18:00:00Z', '2026-07-10T19:00:00Z', 0)]

    const result = previewCascade(
      { id: 'dragged', lane: 1, start_at: '2026-07-10T18:30:00Z', end_at: '2026-07-10T19:30:00Z' },
      cohort,
    )

    expect(result.laneOf.dragged).toBe(1)
    expect(result.laneOf.a).toBe(0)
  })

  it('cascades existing item down when wanted lane is busy', () => {
    const cohort = [p('a', '2026-07-10T18:00:00Z', '2026-07-10T19:00:00Z', 0)]

    const result = previewCascade(
      { id: 'dragged', lane: 0, start_at: '2026-07-10T18:30:00Z', end_at: '2026-07-10T19:30:00Z' },
      cohort,
    )

    expect(result.laneOf.dragged).toBe(1)
    expect(result.laneOf.a).toBe(0)
  })
})