Briven/apps/studio/lib/base64url.ts

/**
 * Avoid modifying this file. It's part of
 * https://github.com/briven-community/base64url-js.  Submit all fixes on
 * that repo!
 */

/**
 * An array of characters that encode 6 bits into a Base64-URL alphabet
 * character.
 */
const TO_BASE64URL = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'.split('')

/**
 * An array of characters that can appear in a Base64-URL encoded string but
 * should be ignored.
 */
const IGNORE_BASE64URL = ' \t\n\r='.split('')

/**
 * An array of 128 numbers that map a Base64-URL character to 6 bits, or if -2
 * used to skip the character, or if -1 used to error out.
 */
const FROM_BASE64URL = (() => {
  const charMap: number[] = new Array(128)

  for (let i = 0; i < charMap.length; i += 1) {
    charMap[i] = -1
  }

  for (let i = 0; i < IGNORE_BASE64URL.length; i += 1) {
    charMap[IGNORE_BASE64URL[i].charCodeAt(0)] = -2
  }

  for (let i = 0; i < TO_BASE64URL.length; i += 1) {
    charMap[TO_BASE64URL[i].charCodeAt(0)] = i
  }

  return charMap
})()

/**
 * Converts a byte to a Base64-URL string.
 *
 * @param byte The byte to convert, or null to flush at the end of the byte sequence.
 * @param state The Base64 conversion state. Pass an initial value of `{ queue: 0, queuedBits: 0 }`.
 * @param emit A function called with the next Base64 character when ready.
 */
export function byteToBase64URL(
  byte: number | null,
  state: { queue: number; queuedBits: number },
  emit: (char: string) => void
) {
  if (byte !== null) {
    state.queue = (state.queue << 8) | byte
    state.queuedBits += 8

    while (state.queuedBits >= 6) {
      const pos = (state.queue >> (state.queuedBits - 6)) & 63
      emit(TO_BASE64URL[pos])
      state.queuedBits -= 6
    }
  } else if (state.queuedBits > 0) {
    state.queue = state.queue << (6 - state.queuedBits)
    state.queuedBits = 6

    while (state.queuedBits >= 6) {
      const pos = (state.queue >> (state.queuedBits - 6)) & 63
      emit(TO_BASE64URL[pos])
      state.queuedBits -= 6
    }
  }
}

/**
 * Converts a String char code (extracted using `string.charCodeAt(position)`) to a sequence of Base64-URL characters.
 *
 * @param charCode The char code of the JavaScript string.
 * @param state The Base64 state. Pass an initial value of `{ queue: 0, queuedBits: 0 }`.
 * @param emit A function called with the next byte.
 */
export function byteFromBase64URL(
  charCode: number,
  state: { queue: number; queuedBits: number },
  emit: (byte: number) => void
) {
  const bits = FROM_BASE64URL[charCode]

  if (bits > -1) {
    // valid Base64-URL character
    state.queue = (state.queue << 6) | bits
    state.queuedBits += 6

    while (state.queuedBits >= 8) {
      emit((state.queue >> (state.queuedBits - 8)) & 0xff)
      state.queuedBits -= 8
    }
  } else if (bits === -2) {
    // ignore spaces, tabs, newlines, =
    return
  } else {
    throw new Error(`Invalid Base64-URL character "${String.fromCharCode(charCode)}"`)
  }
}

/**
 * Converts a JavaScript string (which may include any valid character) into a
 * Base64-URL encoded string. The string is first encoded in UTF-8 which is
 * then encoded as Base64-URL.
 *
 * @param str The string to convert.
 */
export function stringToBase64URL(str: string) {
  const base64: string[] = []

  const emitter = (char: string) => {
    base64.push(char)
  }

  const state = { queue: 0, queuedBits: 0 }

  stringToUTF8(str, (byte: number) => {
    byteToBase64URL(byte, state, emitter)
  })

  byteToBase64URL(null, state, emitter)

  return base64.join('')
}

/**
 * Converts a Base64-URL encoded string into a JavaScript string. It is assumed
 * that the underlying string has been encoded as UTF-8.
 *
 * @param str The Base64-URL encoded string.
 */
export function stringFromBase64URL(str: string) {
  const conv: string[] = []

  const utf8Emit = (codepoint: number) => {
    conv.push(String.fromCodePoint(codepoint))
  }

  const utf8State = {
    utf8seq: 0,
    codepoint: 0,
  }

  const b64State = { queue: 0, queuedBits: 0 }

  const byteEmit = (byte: number) => {
    stringFromUTF8(byte, utf8State, utf8Emit)
  }

  for (let i = 0; i < str.length; i += 1) {
    byteFromBase64URL(str.charCodeAt(i), b64State, byteEmit)
  }

  return conv.join('')
}

/**
 * Converts a Unicode codepoint to a multi-byte UTF-8 sequence.
 *
 * @param codepoint The Unicode codepoint.
 * @param emit      Function which will be called for each UTF-8 byte that represents the codepoint.
 */
export function codepointToUTF8(codepoint: number, emit: (byte: number) => void) {
  if (codepoint <= 0x7f) {
    emit(codepoint)
    return
  } else if (codepoint <= 0x7ff) {
    emit(0xc0 | (codepoint >> 6))
    emit(0x80 | (codepoint & 0x3f))
    return
  } else if (codepoint <= 0xffff) {
    emit(0xe0 | (codepoint >> 12))
    emit(0x80 | ((codepoint >> 6) & 0x3f))
    emit(0x80 | (codepoint & 0x3f))
    return
  } else if (codepoint <= 0x10ffff) {
    emit(0xf0 | (codepoint >> 18))
    emit(0x80 | ((codepoint >> 12) & 0x3f))
    emit(0x80 | ((codepoint >> 6) & 0x3f))
    emit(0x80 | (codepoint & 0x3f))
    return
  }

  throw new Error(`Unrecognized Unicode codepoint: ${codepoint.toString(16)}`)
}

/**
 * Converts a JavaScript string to a sequence of UTF-8 bytes.
 *
 * @param str  The string to convert to UTF-8.
 * @param emit Function which will be called for each UTF-8 byte of the string.
 */
export function stringToUTF8(str: string, emit: (byte: number) => void) {
  for (let i = 0; i < str.length; i += 1) {
    let codepoint = str.charCodeAt(i)

    if (codepoint > 0xd7ff && codepoint <= 0xdbff) {
      // most UTF-16 codepoints are Unicode codepoints, except values in this
      // range where the next UTF-16 codepoint needs to be combined with the
      // current one to get the Unicode codepoint
      const highSurrogate = ((codepoint - 0xd800) * 0x400) & 0xffff
      const lowSurrogate = (str.charCodeAt(i + 1) - 0xdc00) & 0xffff
      codepoint = (lowSurrogate | highSurrogate) + 0x10000
      i += 1
    }

    codepointToUTF8(codepoint, emit)
  }
}

/**
 * Converts a UTF-8 byte to a Unicode codepoint.
 *
 * @param byte  The UTF-8 byte next in the sequence.
 * @param state The shared state between consecutive UTF-8 bytes in the
 *              sequence, an object with the shape `{ utf8seq: 0, codepoint: 0 }`.
 * @param emit  Function which will be called for each codepoint.
 */
export function stringFromUTF8(
  byte: number,
  state: { utf8seq: number; codepoint: number },
  emit: (codepoint: number) => void
) {
  if (state.utf8seq === 0) {
    if (byte <= 0x7f) {
      emit(byte)
      return
    }

    // count the number of 1 leading bits until you reach 0
    for (let leadingBit = 1; leadingBit < 6; leadingBit += 1) {
      if (((byte >> (7 - leadingBit)) & 1) === 0) {
        state.utf8seq = leadingBit
        break
      }
    }

    if (state.utf8seq === 2) {
      state.codepoint = byte & 31
    } else if (state.utf8seq === 3) {
      state.codepoint = byte & 15
    } else if (state.utf8seq === 4) {
      state.codepoint = byte & 7
    } else {
      throw new Error('Invalid UTF-8 sequence')
    }

    state.utf8seq -= 1
  } else if (state.utf8seq > 0) {
    if (byte <= 0x7f) {
      throw new Error('Invalid UTF-8 sequence')
    }

    state.codepoint = (state.codepoint << 6) | (byte & 63)
    state.utf8seq -= 1

    if (state.utf8seq === 0) {
      emit(state.codepoint)
    }
  }
}