import { describe, expect, it, vi } from 'vitest'
import { TerminalOutputBuffer } from '../../src/utils/terminalOutputBuffer'

function harness(options: { maxChunkChars?: number; maxPendingChars?: number } = {}) {
  const callbacks: Array<() => void> = []
  const write = vi.fn()
  const buffer = new TerminalOutputBuffer({
    write,
    schedule: (callback) => {
      callbacks.push(callback)
      return callbacks.length
    },
    cancel: vi.fn(),
    ...options,
  })
  return { buffer, callbacks, write }
}

describe('TerminalOutputBuffer', () => {
  it('coalesces events into one write per frame', () => {
    const { buffer, callbacks, write } = harness()
    buffer.enqueue('one')
    buffer.enqueue('two')

    expect(callbacks).toHaveLength(1)
    callbacks.shift()?.()
    expect(write).toHaveBeenCalledWith('onetwo')
  })

  it('preserves UTF-8 characters split across native events', () => {
    const { buffer, callbacks, write } = harness()
    const bytes = new TextEncoder().encode('中文')
    buffer.enqueue(bytes.slice(0, 2))
    buffer.enqueue(bytes.slice(2, 4))
    buffer.enqueue(bytes.slice(4))
    callbacks.shift()?.()

    expect(write).toHaveBeenCalledWith('中文')
  })

  it('limits work per frame and schedules remaining output', () => {
    const { buffer, callbacks, write } = harness({ maxChunkChars: 4 })
    buffer.enqueue('abcdefgh')
    callbacks.shift()?.()
    expect(write).toHaveBeenLastCalledWith('abcd')
    expect(callbacks).toHaveLength(1)
    callbacks.shift()?.()
    expect(write).toHaveBeenLastCalledWith('efgh')
  })

  it('bounds queued output and reports truncation', () => {
    const { buffer, callbacks, write } = harness({ maxPendingChars: 4 })
    buffer.enqueue('abcdefgh')
    callbacks.shift()?.()

    const output = write.mock.calls[0][0] as string
    expect(output).toContain('output truncated')
    expect(output).toContain('efgh')
    expect(output).not.toContain('abcd')
  })
})