import type { BlockBox } from './scrollPosition'
import { describe, expect, it } from 'vitest'
import { anchorAt, blockForLine, holdAt, scrollTopFor } from './scrollPosition'

// 页面上的块：顶部有 20px 工具栏，块与块之间 8px 间距
const boxes: BlockBox[] = [
  { line: 0, top: 20, bottom: 60 },
  { line: 3, top: 68, bottom: 108 },
  { line: 4, top: 116, bottom: 196 },
  { line: 10, top: 204, bottom: 244 },
]

describe('anchorAt：视口顶部那块', () => {
  it('视口顶部落在块中间：记这块的起始行和块内偏移', () => {
    expect(anchorAt(boxes, 150)).toEqual({ line: 4, offset: 34, scrollTop: 150 })
  })

  it('视口顶部落在块间空隙：取下面那块，偏移为负', () => {
    expect(anchorAt(boxes, 110)).toEqual({ line: 4, offset: -6, scrollTop: 110 })
  })

  it('还在最顶上：取第一块', () => {
    expect(anchorAt(boxes, 0)).toEqual({ line: 0, offset: -20, scrollTop: 0 })
  })

  it('所有块都滚过去了：取最后一块', () => {
    expect(anchorAt(boxes, 300)).toEqual({ line: 10, offset: 96, scrollTop: 300 })
  })

  it('没有块：没有位置可记', () => {
    expect(anchorAt([], 50)).toBeUndefined()
  })
})

describe('holdAt：页面变了也钉住不动的那块', () => {
  it('视口顶部落在块中间：钉这块', () => {
    expect(holdAt(boxes, 150)).toEqual({ line: 4, offset: 34, scrollTop: 150 })
  })

  it('视口顶部落在块间空隙（或上面那块的问答区）里：钉上面那块，下面那块长高不牵动视口', () => {
    expect(holdAt(boxes, 110)).toEqual({ line: 3, offset: 42, scrollTop: 110 })
  })

  it('还在所有块上面：不钉', () => {
    expect(holdAt(boxes, 0)).toBeUndefined()
  })

  it('起始行相同的外层块和第一个子块：钉靠前的那块，按起始行找回来还是原处', () => {
    const nested = [{ line: 0, top: 20, bottom: 60 }, { line: 4, top: 68, bottom: 100 }, { line: 4, top: 108, bottom: 200 }]
    const anchor = holdAt(nested, 150)!
    expect(anchor).toEqual({ line: 4, offset: 82, scrollTop: 150 })
    expect(scrollTopFor(nested, anchor)).toBe(150)
  })
})

describe('scrollTopFor：按记下的位置恢复', () => {
  it('内容没变：回到原来的 scrollTop', () => {
    expect(scrollTopFor(boxes, anchorAt(boxes, 150)!)).toBe(150)
  })

  it('隐藏期间上面多了一块：跟着那块走，而不是停在原来的像素', () => {
    const anchor = anchorAt(boxes, 150)!
    const edited = [{ line: 0, top: 20, bottom: 60 }, { line: 1, top: 68, bottom: 108 }, ...boxes.slice(1).map(b => ({ ...b, top: b.top + 48, bottom: b.bottom + 48 }))]
    expect(scrollTopFor(edited, anchor)).toBe(198)
  })

  it('那一行已经没有块了：退回原来的 scrollTop', () => {
    expect(scrollTopFor(boxes, { line: 7, offset: 12, scrollTop: 140 })).toBe(140)
  })
})

describe('blockForLine：包含某行的块', () => {
  it('正好是块的起始行', () => {
    expect(blockForLine(boxes, 4)?.line).toBe(4)
  })

  it('落在块中间或块后面的空行：取之前最近的块', () => {
    expect(blockForLine(boxes, 8)?.line).toBe(4)
    expect(blockForLine(boxes, 99)?.line).toBe(10)
  })

  it('在所有块之前：取第一块', () => {
    expect(blockForLine([{ line: 5, top: 20, bottom: 60 }, { line: 9, top: 68, bottom: 108 }], 2)?.line).toBe(5)
  })

  it('没有块：找不到', () => {
    expect(blockForLine([], 3)).toBeUndefined()
  })
})