/**
 * The `node:events` shim's dispatch semantics. Harness code registers on this
 * class through the module proxy table and branches on what it returns, so the
 * cases below pin the parts a hand-written emitter gets wrong: the boolean
 * `emit` reports, the point at which `once` unregisters, and the listener set an
 * in-flight emit dispatches to.
 */
import { describe, expect, it } from 'vitest'
import { EventEmitter } from '../../src/node/builtin_modules/implemented/events.ts'

describe('emit', () => {
  it('reports whether the event reached a listener', () => {
    const emitter = new EventEmitter()
    expect(emitter.emit('ready')).toBe(false)
    emitter.on('ready', () => {})
    expect(emitter.emit('ready')).toBe(true)
    emitter.removeAllListeners('ready')
    expect(emitter.emit('ready')).toBe(false)
  })

  it('calls the listeners in registration order with every argument', () => {
    const emitter = new EventEmitter()
    const seen: string[] = []
    emitter.on('data', (...args) => { seen.push(`first:${args.join(',')}`) })
    emitter.on('data', (...args) => { seen.push(`second:${args.join(',')}`) })
    emitter.emit('data', 'a', 1, true)
    expect(seen).toEqual(['first:a,1,true', 'second:a,1,true'])
  })

  it('puts a prepended listener ahead of the ones already registered', () => {
    const emitter = new EventEmitter()
    const seen: string[] = []
    emitter.on('data', () => { seen.push('registered') })
    emitter.prependListener('data', () => { seen.push('prepended') })
    emitter.emit('data')
    expect(seen).toEqual(['prepended', 'registered'])
  })

  it('dispatches to the listeners present when the emit began', () => {
    // Node dispatches over a copy, so a removal from inside a listener takes
    // effect on the NEXT emit; a shim that iterated the live list would skip the
    // second listener here.
    const emitter = new EventEmitter()
    const seen: string[] = []
    const second = (): void => { seen.push('second') }
    emitter.on('data', () => {
      seen.push('first')
      emitter.off('data', second)
    })
    emitter.on('data', second)
    emitter.emit('data')
    emitter.emit('data')
    expect(seen).toEqual(['first', 'second', 'first'])
  })
})

describe('once', () => {
  it('unregisters before it calls, so a re-entrant emit does not repeat it', () => {
    const emitter = new EventEmitter()
    let calls = 0
    emitter.once('settled', () => {
      calls += 1
      // A listener that reacts by emitting the same event is the shape that
      // re-enters a once listener whose removal happens after the call.
      emitter.emit('settled')
    })
    emitter.emit('settled')
    expect(calls).toBe(1)
    expect(emitter.listenerCount('settled')).toBe(0)
  })

  it('passes the emit arguments through the wrapper', () => {
    const emitter = new EventEmitter()
    const seen: unknown[][] = []
    emitter.once('exit', (...args) => { seen.push(args) })
    emitter.emit('exit', 3, 'SIGTERM')
    expect(seen).toEqual([[3, 'SIGTERM']])
  })

  it('unregisters through the original listener, not only the wrapper', () => {
    // Node reaches the once wrapper by the listener handed to `once`, so a caller
    // that never saw the wrapper can still cancel its own registration.
    const emitter = new EventEmitter()
    let calls = 0
    const listener = (): void => { calls += 1 }
    emitter.once('ready', listener)
    emitter.off('ready', listener)
    expect(emitter.listenerCount('ready')).toBe(0)
    expect(emitter.emit('ready')).toBe(false)
    expect(calls).toBe(0)
  })
})

describe('registration bookkeeping', () => {
  it('hands out a copy of the listener list', () => {
    const emitter = new EventEmitter()
    emitter.on('data', () => {})
    emitter.listeners('data').length = 0
    expect(emitter.listenerCount('data')).toBe(1)
  })

  it('clears one event by name and every event without one', () => {
    const emitter = new EventEmitter()
    emitter.on('data', () => {})
    emitter.on('error', () => {})
    emitter.removeAllListeners('data')
    expect([emitter.listenerCount('data'), emitter.listenerCount('error')]).toEqual([0, 1])
    emitter.removeAllListeners()
    expect(emitter.listenerCount('error')).toBe(0)
  })

  it('removes only the listener named, and tolerates one that never registered', () => {
    const emitter = new EventEmitter()
    const kept = (): void => {}
    const dropped = (): void => {}
    emitter.on('data', kept).on('data', dropped)
    emitter.removeListener('data', dropped)
    emitter.off('data', (): void => {})
    emitter.off('absent', kept)
    expect(emitter.listeners('data')).toEqual([kept])
  })

  it('removes the last registration of a listener added twice', () => {
    // Removal searches from the tail and stops at one match, as Node does, so
    // the earlier registration is the one that stays — visible here in the order
    // the surviving listeners run.
    const emitter = new EventEmitter()
    const seen: string[] = []
    const repeated = (): void => { seen.push('repeated') }
    emitter.on('data', repeated)
    emitter.on('data', () => { seen.push('other') })
    emitter.on('data', repeated)
    emitter.off('data', repeated)
    emitter.emit('data')
    expect(seen).toEqual(['repeated', 'other'])
  })
})