// https://www.npmjs.com/package/eventsource-parser/v/1.1.1

function createParser(onParse) {
  let isFirstChunk
  let bytes
  let buffer
  let startingPosition
  let startingFieldLength
  let eventId
  let eventName
  let data
  reset()
  return {
    feed,
    reset,
  }
  function reset() {
    isFirstChunk = true
    bytes = []
    buffer = ''
    startingPosition = 0
    startingFieldLength = -1
    eventId = void 0
    eventName = void 0
    data = ''
  }

  function feed(chunk) {
    bytes = bytes.concat(Array.from(chunk))
    buffer = new TextDecoder().decode(new Uint8Array(bytes))
    if (isFirstChunk && hasBom(buffer)) {
      buffer = buffer.slice(BOM.length)
    }
    isFirstChunk = false
    const length = buffer.length
    let position = 0
    let discardTrailingNewline = false
    while (position < length) {
      if (discardTrailingNewline) {
        if (buffer[position] === '\n') {
          ++position
        }
        discardTrailingNewline = false
      }
      let lineLength = -1
      let fieldLength = startingFieldLength
      let character
      for (let index = startingPosition; lineLength < 0 && index < length; ++index) {
        character = buffer[index]
        if (character === ':' && fieldLength < 0) {
          fieldLength = index - position
        } else if (character === '\r') {
          discardTrailingNewline = true
          lineLength = index - position
        } else if (character === '\n') {
          lineLength = index - position
        }
      }
      if (lineLength < 0) {
        startingPosition = length - position
        startingFieldLength = fieldLength
        break
      } else {
        startingPosition = 0
        startingFieldLength = -1
      }
      parseEventStreamLine(buffer, position, fieldLength, lineLength)
      position += lineLength + 1
    }
    if (position === length) {
      bytes = []
      buffer = ''
    } else if (position > 0) {
      bytes = bytes.slice(new TextEncoder().encode(buffer.slice(0, position)).length)
      buffer = buffer.slice(position)
    }
  }

  function parseEventStreamLine(lineBuffer, index, fieldLength, lineLength) {
    if (lineLength === 0) {
      if (data.length > 0) {
        onParse({
          type: 'event',
          id: eventId,
          event: eventName || void 0,
          data: data.slice(0, -1),
          // remove trailing newline
        })

        data = ''
        eventId = void 0
      }
      eventName = void 0
      return
    }
    const noValue = fieldLength < 0
    const field = lineBuffer.slice(index, index + (noValue ? lineLength : fieldLength))
    let step = 0
    if (noValue) {
      step = lineLength
    } else if (lineBuffer[index + fieldLength + 1] === ' ') {
      step = fieldLength + 2
    } else {
      step = fieldLength + 1
    }
    const position = index + step
    const valueLength = lineLength - step
    const value = lineBuffer.slice(position, position + valueLength).toString()
    if (field === 'data') {
      data += value ? ''.concat(value, '\n') : '\n'
    } else if (field === 'event') {
      eventName = value
    } else if (field === 'id' && !value.includes('\0')) {
      eventId = value
    } else if (field === 'retry') {
      const retry = parseInt(value, 10)
      if (!Number.isNaN(retry)) {
        onParse({
          type: 'reconnect-interval',
          value: retry,
        })
      }
    }
  }
}
const BOM = [239, 187, 191]
function hasBom(buffer) {
  return BOM.every((charCode, index) => buffer.charCodeAt(index) === charCode)
}
export { createParser }