//TODO - A reader MUST check that the signature is valid (see the n tagged field)
//TODO - Tagged part of type f: the fallback on-chain address should be decoded into an address format
//TODO - A reader MUST check that the SHA-2 256 in the h field exactly matches the hashed description.
//TODO - A reader MUST use the n field to validate the signature instead of performing signature recovery if a valid n field is provided.

function decode(paymentRequest) {
  let input = paymentRequest.toLowerCase()
  let splitPosition = input.lastIndexOf('1')
  let humanReadablePart = input.substring(0, splitPosition)
  let data = input.substring(splitPosition + 1, input.length - 6)
  let checksum = input.substring(input.length - 6, input.length)
  if (
    !verify_checksum(humanReadablePart, bech32ToFiveBitArray(data + checksum))
  ) {
    throw 'Malformed request: checksum is incorrect' // A reader MUST fail if the checksum is incorrect.
  }
  return {
    human_readable_part: decodeHumanReadablePart(humanReadablePart),
    data: decodeData(data, humanReadablePart),
    checksum: checksum
  }
}

function decodeHumanReadablePart(humanReadablePart) {
  let prefixes = ['lnbc', 'lntb', 'lnbcrt', 'lnsb', 'lntbs']
  let prefix
  prefixes.forEach(value => {
    if (humanReadablePart.substring(0, value.length) === value) {
      prefix = value
    }
  })
  if (prefix == null) throw 'Malformed request: unknown prefix' // A reader MUST fail if it does not understand the prefix.
  let amount = decodeAmount(
    humanReadablePart.substring(prefix.length, humanReadablePart.length)
  )
  return {
    prefix: prefix,
    amount: amount
  }
}

function decodeData(data, humanReadablePart) {
  let date32 = data.substring(0, 7)
  let dateEpoch = bech32ToInt(date32)
  let signature = data.substring(data.length - 104, data.length)
  let tagData = data.substring(7, data.length - 104)
  let decodedTags = decodeTags(tagData)
  let value = bech32ToFiveBitArray(date32 + tagData)
  value = fiveBitArrayTo8BitArray(value, true)
  value = textToHexString(humanReadablePart).concat(byteArrayToHexString(value))
  return {
    time_stamp: dateEpoch,
    tags: decodedTags,
    signature: decodeSignature(signature),
    signing_data: value
  }
}

function decodeSignature(signature) {
  let data = fiveBitArrayTo8BitArray(bech32ToFiveBitArray(signature))
  let recoveryFlag = data[data.length - 1]
  let r = byteArrayToHexString(data.slice(0, 32))
  let s = byteArrayToHexString(data.slice(32, data.length - 1))
  return {
    r: r,
    s: s,
    recovery_flag: recoveryFlag
  }
}

function decodeAmount(str) {
  let multiplier = str.charAt(str.length - 1)
  let amount = str.substring(0, str.length - 1)
  if (amount.substring(0, 1) === '0') {
    throw 'Malformed request: amount cannot contain leading zeros'
  }
  amount = Number(amount)
  if (amount < 0 || !Number.isInteger(amount)) {
    throw 'Malformed request: amount must be a positive decimal integer' // A reader SHOULD fail if amount contains a non-digit
  }

  switch (multiplier) {
    case '':
      return 'Any amount' // A reader SHOULD indicate if amount is unspecified
    case 'p':
      return amount / 10
    case 'n':
      return amount * 100
    case 'u':
      return amount * 100000
    case 'm':
      return amount * 100000000
    default:
      // A reader SHOULD fail if amount is followed by anything except a defined multiplier.
      throw 'Malformed request: undefined amount multiplier'
  }
}

function decodeTags(tagData) {
  let tags = extractTags(tagData)
  let decodedTags = []
  tags.forEach(value =>
    decodedTags.push(decodeTag(value.type, value.length, value.data))
  )
  return decodedTags
}

function extractTags(str) {
  let tags = []
  while (str.length > 0) {
    let type = str.charAt(0)
    let dataLength = bech32ToInt(str.substring(1, 3))
    let data = str.substring(3, dataLength + 3)
    tags.push({
      type: type,
      length: dataLength,
      data: data
    })
    str = str.substring(3 + dataLength, str.length)
  }
  return tags
}

function decodeTag(type, length, data) {
  switch (type) {
    case 'p':
      if (length !== 52) break // A reader MUST skip over a 'p' field that does not have data_length 52
      return {
        type: type,
        length: length,
        description: 'payment_hash',
        value: byteArrayToHexString(
          fiveBitArrayTo8BitArray(bech32ToFiveBitArray(data))
        )
      }
    case 'd':
      return {
        type: type,
        length: length,
        description: 'description',
        value: bech32ToUTF8String(data)
      }
    case 'n':
      if (length !== 53) break // A reader MUST skip over a 'n' field that does not have data_length 53
      return {
        type: type,
        length: length,
        description: 'payee_public_key',
        value: byteArrayToHexString(
          fiveBitArrayTo8BitArray(bech32ToFiveBitArray(data))
        )
      }
    case 'h':
      if (length !== 52) break // A reader MUST skip over a 'h' field that does not have data_length 52
      return {
        type: type,
        length: length,
        description: 'description_hash',
        value: data
      }
    case 'x':
      return {
        type: type,
        length: length,
        description: 'expiry',
        value: bech32ToInt(data)
      }
    case 'c':
      return {
        type: type,
        length: length,
        description: 'min_final_cltv_expiry',
        value: bech32ToInt(data)
      }
    case 'f':
      let version = bech32ToFiveBitArray(data.charAt(0))[0]
      if (version < 0 || version > 18) break // a reader MUST skip over an f field with unknown version.
      data = data.substring(1, data.length)
      return {
        type: type,
        length: length,
        description: 'fallback_address',
        value: {
          version: version,
          fallback_address: data
        }
      }
    case 'r':
      data = fiveBitArrayTo8BitArray(bech32ToFiveBitArray(data))
      let pubkey = data.slice(0, 33)
      let shortChannelId = data.slice(33, 41)
      let feeBaseMsat = data.slice(41, 45)
      let feeProportionalMillionths = data.slice(45, 49)
      let cltvExpiryDelta = data.slice(49, 51)
      return {
        type: type,
        length: length,
        description: 'routing_information',
        value: {
          public_key: byteArrayToHexString(pubkey),
          short_channel_id: byteArrayToHexString(shortChannelId),
          fee_base_msat: byteArrayToInt(feeBaseMsat),
          fee_proportional_millionths: byteArrayToInt(
            feeProportionalMillionths
          ),
          cltv_expiry_delta: byteArrayToInt(cltvExpiryDelta)
        }
      }
    default:
    // reader MUST skip over unknown fields
  }
}

function polymod(values) {
  let GEN = [0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3]
  let chk = 1
  values.forEach(value => {
    let b = chk >> 25
    chk = ((chk & 0x1ffffff) << 5) ^ value
    for (let i = 0; i < 5; i++) {
      if (((b >> i) & 1) === 1) {
        chk ^= GEN[i]
      } else {
        chk ^= 0
      }
    }
  })
  return chk
}

function expand(str) {
  let array = []
  for (let i = 0; i < str.length; i++) {
    array.push(str.charCodeAt(i) >> 5)
  }
  array.push(0)
  for (let i = 0; i < str.length; i++) {
    array.push(str.charCodeAt(i) & 31)
  }
  return array
}

function verify_checksum(hrp, data) {
  hrp = expand(hrp)
  let all = hrp.concat(data)
  let bool = polymod(all)
  return bool === 1
}

const bech32CharValues = 'qpzry9x8gf2tvdw0s3jn54khce6mua7l'

function byteArrayToInt(byteArray) {
  let value = 0
  for (let i = 0; i < byteArray.length; ++i) {
    value = (value << 8) + byteArray[i]
  }
  return value
}

function bech32ToInt(str) {
  let sum = 0
  for (let i = 0; i < str.length; i++) {
    sum = sum * 32
    sum = sum + bech32CharValues.indexOf(str.charAt(i))
  }
  return sum
}

function bech32ToFiveBitArray(str) {
  let array = []
  for (let i = 0; i < str.length; i++) {
    array.push(bech32CharValues.indexOf(str.charAt(i)))
  }
  return array
}

function fiveBitArrayTo8BitArray(int5Array, includeOverflow) {
  let count = 0
  let buffer = 0
  let byteArray = []
  int5Array.forEach(value => {
    buffer = (buffer << 5) + value
    count += 5
    if (count >= 8) {
      byteArray.push((buffer >> (count - 8)) & 255)
      count -= 8
    }
  })
  if (includeOverflow && count > 0) {
    byteArray.push((buffer << (8 - count)) & 255)
  }
  return byteArray
}

function bech32ToUTF8String(str) {
  let int5Array = bech32ToFiveBitArray(str)
  let byteArray = fiveBitArrayTo8BitArray(int5Array)

  let utf8String = ''
  for (let i = 0; i < byteArray.length; i++) {
    utf8String += '%' + ('0' + byteArray[i].toString(16)).slice(-2)
  }
  return decodeURIComponent(utf8String)
}

function byteArrayToHexString(byteArray) {
  return Array.prototype.map
    .call(byteArray, function (byte) {
      return ('0' + (byte & 0xff).toString(16)).slice(-2)
    })
    .join('')
}

function textToHexString(text) {
  let hexString = ''
  for (let i = 0; i < text.length; i++) {
    hexString += text.charCodeAt(i).toString(16)
  }
  return hexString
}

function epochToDate(int) {
  let date = new Date(int * 1000)
  return date.toUTCString()
}

function isEmptyOrSpaces(str) {
  return str === null || str.match(/^ *$/) !== null
}

function toFixed(x) {
  if (Math.abs(x) < 1.0) {
    var e = parseInt(x.toString().split('e-')[1])
    if (e) {
      x *= Math.pow(10, e - 1)
      x = '0.' + new Array(e).join('0') + x.toString().substring(2)
    }
  } else {
    var e = parseInt(x.toString().split('+')[1])
    if (e > 20) {
      e -= 20
      x /= Math.pow(10, e)
      x += new Array(e + 1).join('0')
    }
  }
  return x
}