'use strict'

const EventEmitter = require('node:events').EventEmitter
const inherits = require('node:util').inherits
const getLimit = require('../../../lib/utils/getLimit')

const B_DCRLF = Buffer.from('\r\n\r\n')
const S_DCRLF = '\r\n\r\n'

function HeaderParser (cfg) {
  EventEmitter.call(this)

  cfg = cfg || {}
  this.nread = 0
  this.maxed = false
  this.npairs = 0
  this.maxHeaderPairs = getLimit(cfg, 'maxHeaderPairs', 2000)
  this.maxHeaderSize = getLimit(cfg, 'maxHeaderSize', 80 * 1024)
  this.buffer = ''
  this.header = Object.create(null)
  this.finished = false
  this.tail = ''
}
inherits(HeaderParser, EventEmitter)

HeaderParser.prototype.push = function (data) {
  if (!Buffer.isBuffer(data)) { data = Buffer.from(data, 'binary') }

  let end = data.length
  let appendEnd = data.length
  let found = false
  let splitTail = 0
  const tail = this.tail

  for (let i = tail.length; i > 0; --i) {
    if (tail.endsWith(S_DCRLF.slice(0, i))) {
      let matched = data.length >= S_DCRLF.length - i
      for (let j = i; matched && j < S_DCRLF.length; ++j) {
        matched = data[j - i] === S_DCRLF.charCodeAt(j)
      }
      if (matched) {
        end = S_DCRLF.length - i
        appendEnd = 0
        splitTail = i
        found = true
        break
      }
    }
  }

  if (!found) {
    const pos = data.indexOf(B_DCRLF)
    if (pos !== -1) {
      end = pos + B_DCRLF.length
      appendEnd = pos
      found = true
    }
  }

  if (!found) {
    this.tail = data.length >= 3
      ? data.toString('binary', data.length - 3)
      : (tail + data.toString('binary')).slice(-3)
  } else { this.tail = '' }

  if (appendEnd !== 0 && !this.maxed) {
    const remaining = this.maxHeaderSize - this.nread
    if (appendEnd >= remaining) {
      this.buffer += data.toString('binary', 0, remaining)
      this.nread = this.maxHeaderSize
      this.maxed = true
    } else {
      this.buffer += data.toString('binary', 0, appendEnd)
      this.nread += appendEnd
    }
  }

  if (found) {
    // A CRLFCRLF header terminator split across pushes left its leading bytes
    // in this.buffer on the previous push; drop them so they do not trail the
    // last header value. splitTail is 0 in the common case, making this a no-op.
    // Skip when maxed: once maxHeaderSize truncation dropped the trailing bytes,
    // the last splitTail bytes are real header content, not the terminator prefix.
    if (!this.maxed) {
      this.buffer = this.buffer.slice(0, this.buffer.length - splitTail)
    }
    this._finish()
    return end
  }
}

HeaderParser.prototype.reset = function () {
  this.finished = false
  this.buffer = ''
  this.header = Object.create(null)
  this.tail = ''
}

HeaderParser.prototype._finish = function () {
  if (this.buffer) { this._parseHeader() }
  const header = this.header
  this.header = Object.create(null)
  this.buffer = ''
  this.tail = ''
  this.finished = true
  this.nread = this.npairs = 0
  this.maxed = false
  this.emit('header', header)
}

HeaderParser.prototype._parseHeader = function () {
  if (this.npairs === this.maxHeaderPairs) { return }

  const buffer = this.buffer
  let h
  let lineStart = 0

  while (lineStart < buffer.length) {
    let lineEnd = buffer.indexOf('\r\n', lineStart)
    if (lineEnd === -1) { lineEnd = buffer.length }

    if (lineEnd === lineStart) {
      lineStart = lineEnd + 2
      continue
    }

    // Reject bare line breaks instead of exposing them in parsed values
    const line = buffer.slice(lineStart, lineEnd)
    if (line.includes('\r') || line.includes('\n')) { return }

    if ((buffer[lineStart] === '\t' || buffer[lineStart] === ' ') && h) {
      // folded header content
      // RFC2822 says to just remove the CRLF and not the whitespace following
      // it, so we follow the RFC and include the leading whitespace ...
      this.header[h][this.header[h].length - 1] += buffer.slice(lineStart, lineEnd)
      lineStart = lineEnd + 2
      continue
    }

    const posColon = buffer.indexOf(':', lineStart)
    if (
      posColon === -1 ||
      posColon === lineStart ||
      posColon > lineEnd
    ) {
      return
    }
    h = buffer.slice(lineStart, posColon).toLowerCase()
    let valueStart = posColon + 1
    if (buffer[valueStart] === ' ' || buffer[valueStart] === '\t') { ++valueStart }
    const values = this.header[h] || (this.header[h] = [])
    values.push(buffer.slice(valueStart, lineEnd))
    if (++this.npairs === this.maxHeaderPairs) { break }

    lineStart = lineEnd + 2
  }
}

module.exports = HeaderParser