import { describe, it, expect } from 'vitest'
import { buildDiff, makeDiff } from '../src/renderer/src/diff'

describe('buildDiff', () => {
  it('reports no changes for identical text', () => {
    const d = buildDiff('a\nb\nc\n', 'a\nb\nc\n')
    expect(d.add).toBe(0)
    expect(d.del).toBe(0)
    expect(d.rows.every((r) => r.sign === ' ')).toBe(true)
  })

  it('counts a single changed line as one add + one del', () => {
    const d = buildDiff('a\nb\nc', 'a\nB\nc')
    expect(d.add).toBe(1)
    expect(d.del).toBe(1)
    const signs = d.rows.map((r) => r.sign).join('')
    expect(signs).toContain('-')
    expect(signs).toContain('+')
  })

  it('treats an empty original as all additions (new file)', () => {
    const d = buildDiff('', 'x\ny')
    expect(d.add).toBe(2)
    expect(d.del).toBe(0)
    expect(d.left).toHaveLength(0)
    expect(d.right).toHaveLength(2)
  })

  it('treats an empty updated as all deletions (deleted file)', () => {
    const d = buildDiff('x\ny\nz', '')
    expect(d.del).toBe(3)
    expect(d.add).toBe(0)
    expect(d.right).toHaveLength(0)
  })

  it('marks the changed line on both sides', () => {
    const d = buildDiff('keep\nold\nkeep', 'keep\nnew\nkeep')
    expect(d.left.find((l) => l.text === 'old')?.mark).toBe('del')
    expect(d.right.find((l) => l.text === 'new')?.mark).toBe('add')
    expect(d.left.find((l) => l.text === 'keep')?.mark).toBeNull()
  })

  it('aligns split rows: same lines pair, changes stack into the gap', () => {
    const d = buildDiff('a\nold\nb', 'a\nnew\nb')
    // every split row has at least one side
    expect(d.split.every((r) => r.l || r.r)).toBe(true)
    // the matched 'a' and 'b' lines pair on both sides
    const paired = d.split.filter((r) => r.l && r.r && r.l.text === r.r.text)
    expect(paired.map((r) => r.l!.text)).toEqual(['a', 'b'])
  })

  it('ignores a single trailing newline difference', () => {
    const d = buildDiff('a\nb', 'a\nb\n')
    expect(d.add).toBe(0)
    expect(d.del).toBe(0)
  })
})

describe('makeDiff', () => {
  it('flags added / deleted and carries the text pair', () => {
    const added = makeDiff('A', '', 'hi')
    expect(added.added).toBe(true)
    expect(added.deleted).toBe(false)
    expect(added.original).toBe('')
    expect(added.updated).toBe('hi')

    const deleted = makeDiff('D', 'bye', '')
    expect(deleted.deleted).toBe(true)
    expect(deleted.added).toBe(false)
  })
})

describe('buildDiff on large files', () => {
  it('diffs a 60k-line file without exhausting the heap', () => {
    const base = Array.from({ length: 60_000 }, (_, i) => `line ${i}`)
    const changed = base.slice()
    changed[30_000] = 'line 30000 edited'
    const d = buildDiff(base.join('\n'), changed.join('\n'))
    expect(d.add).toBe(1)
    expect(d.del).toBe(1)
    expect(d.right[30_000].mark).toBe('add')
  })

  it('survives a full rewrite of a large file with no shared lines', () => {
    const a = Array.from({ length: 40_000 }, (_, i) => `old ${i}`).join('\n')
    const b = Array.from({ length: 40_000 }, (_, i) => `new ${i}`).join('\n')
    const d = buildDiff(a, b)
    expect(d.del).toBe(40_000)
    expect(d.add).toBe(40_000)
  })

  it('keeps the unchanged head and tail of a large, heavily edited file', () => {
    const head = Array.from({ length: 5_000 }, (_, i) => `head ${i}`)
    const tail = Array.from({ length: 5_000 }, (_, i) => `tail ${i}`)
    const mid = (p: string): string[] => Array.from({ length: 30_000 }, (_, i) => `${p} ${i % 7}`)
    const d = buildDiff([...head, ...mid('x'), ...tail].join('\n'), [...head, ...mid('y'), ...tail].join('\n'))
    expect(d.left.slice(0, 5_000).every((l) => l.mark === null)).toBe(true)
    expect(d.left.slice(-5_000).every((l) => l.mark === null)).toBe(true)
    expect(d.add).toBe(30_000)
  })
})