Support SharedArrayBuffer; drop isDataView

[Pisces] / binary.js

// ♓🌟 Piscēs ∷ binary.js
// ====================================================================
//
// Copyright © 2020–2023 Lady [@ Lady’s Computer].
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at <https://mozilla.org/MPL/2.0/>.

import { fill, map, reduce } from "./collection.js";
import { bind, call } from "./function.js";
import { ceil, floor } from "./numeric.js";
import { hasOwnProperty, objectCreate } from "./object.js";
import {
  getCodeUnit,
  rawString,
  stringFromCodeUnits,
  stringReplace,
} from "./string.js";
import { ITERATOR } from "./value.js";

const Buffer = ArrayBuffer;
const View = DataView;
const TypedArray = Object.getPrototypeOf(Uint8Array);
const { prototype: arrayPrototype } = Array;
const { prototype: bufferPrototype } = Buffer;
const { prototype: sharedBufferPrototype } = SharedArrayBuffer;
const { prototype: rePrototype } = RegExp;
const { prototype: typedArrayPrototype } = TypedArray;
const { prototype: viewPrototype } = View;

const { [ITERATOR]: arrayIterator } = arrayPrototype;
const {
  next: arrayIteratorNext,
} = Object.getPrototypeOf([][ITERATOR]());
const argumentIterablePrototype = {
  [ITERATOR]() {
    return {
      next: bind(
        arrayIteratorNext,
        call(arrayIterator, this.args, []),
        [],
      ),
    };
  },
};
const binaryCodeUnitIterablePrototype = {
  [ITERATOR]() {
    return {
      next: bind(
        arrayIteratorNext,
        call(arrayIterator, this, []),
        [],
      ),
    };
  },
};

const { exec: reExec } = rePrototype;
const getBufferByteLength =
  Object.getOwnPropertyDescriptor(bufferPrototype, "byteLength").get;
const getSharedBufferByteLength =
  Object.getOwnPropertyDescriptor(sharedBufferPrototype, "byteLength")
    .get;
const getTypedArrayBuffer =
  Object.getOwnPropertyDescriptor(typedArrayPrototype, "buffer").get;
const getTypedArrayByteLength =
  Object.getOwnPropertyDescriptor(typedArrayPrototype, "byteLength")
    .get;
const getTypedArrayByteOffset =
  Object.getOwnPropertyDescriptor(typedArrayPrototype, "byteOffset")
    .get;
const getViewBuffer =
  Object.getOwnPropertyDescriptor(viewPrototype, "buffer").get;
const getViewByteLength =
  Object.getOwnPropertyDescriptor(viewPrototype, "byteLength").get;
const getViewByteOffset =
  Object.getOwnPropertyDescriptor(viewPrototype, "byteOffset").get;
const {
  getUint8: viewGetUint8,
  setUint8: viewSetUint8,
  setUint16: viewSetUint16,
} = viewPrototype;

/**
 * Returns an ArrayBuffer for encoding generated from the provided
 * arguments.
 */
const bufferFromArgs = ($, $s) => {
  try {
    // Try just getting the array buffer associated with the first
    // argument and returning it if possible.
    return toArrayBuffer($);
  } catch {
    // There is no array buffer associated with the first argument.
    //
    // Construct a string and convert it to an array buffer instead.
    return ((string) =>
      call(
        getViewBuffer,
        reduce(
          string,
          (result, ucsCharacter, index) => (
            call(viewSetUint16, result, [
              index * 2,
              getCodeUnit(ucsCharacter, 0),
            ]), result
          ),
          new View(new Buffer(string.length * 2)),
        ),
        [],
      ))(
        typeof $ === "string"
          ? $
          : hasOwnProperty($, "raw")
          ? rawString(
            $,
            ...objectCreate(argumentIterablePrototype, {
              args: { value: $s },
            }),
          )
          : `${$}`,
      );
  }
};

/**
 * Returns the result of decoding the provided base16 string into an
 * ArrayBuffer.
 *
 * ※ This function is not exposed.
 */
const decodeBase16 = (source) => {
  const u4s = map(
    source,
    (ucsCharacter) => {
      const code = getCodeUnit(ucsCharacter, 0);
      const result = code >= 0x30 && code <= 0x39
        ? code - 48
        : code >= 0x41 && code <= 0x46
        ? code - 55
        : code >= 0x61 && code <= 0x66
        ? code - 87
        : -1;
      if (result < 0) {
        // The source contains an invalid character.
        throw new RangeError(
          `Piscēs: Invalid character in Base64: ${ucsCharacter}.`,
        );
      } else {
        // The source contains a valid character with a recognized
        // mapping.
        return result;
      }
    },
  );
  const { length } = u4s;
  if (length % 2 === 1) {
    // The length is such that an entire letter would be dropped during
    // a forgiving decode.
    throw new RangeError(
      `Piscēs: Base16 string has invalid length: ${source}.`,
    );
  } else {
    // Every letter contributes at least some bits to the result.
    const dataView = new View(new Buffer(floor(length / 2)));
    for (let index = 0; index < length - 1;) {
      // Iterate over the characters and assign their bits to the
      // buffer.
      call(viewSetUint8, dataView, [
        floor(index / 2),
        (u4s[index] << 4) | u4s[++index, index++],
      ]);
    }
    return call(getViewBuffer, dataView, []);
  }
};

/**
 * Returns the result of decoding the provided base32 string into an
 * ArrayBuffer.
 *
 * If the second argument is truthy, uses Crockford’s encoding rather
 * than the RFC’s (see <https://www.crockford.com/base32.html>). This
 * is more human‐friendly and tolerant. Check digits are not supported.
 *
 * ※ This function is not exposed.
 */
const decodeBase32 = (source, wrmg) => {
  const u5s = map(
    wrmg
      ? stringReplace(source, /-/gu, "")
      : source.length % 8 === 0
      ? stringReplace(source, /(?:=|={3,4}|={6})$/u, "")
      : source,
    (ucsCharacter) => {
      const code = getCodeUnit(ucsCharacter, 0);
      const result = wrmg
        ? code >= 0x30 && code <= 0x39
          ? code - 48
          : code >= 0x41 && code <= 0x48
          ? code - 55
          : code === 0x49
          ? 1 // I
          : code >= 0x4A && code <= 0x4B
          ? code - 56
          : code === 0x4C
          ? 1 // L
          : code >= 0x4D && code <= 0x4E
          ? code - 57
          : code === 0x4F
          ? 0 // O
          : code >= 0x50 && code <= 0x54
          ? code - 58
          // U is skipped
          : code >= 0x56 && code <= 0x5A
          ? code - 59
          : code >= 0x61 && code <= 0x68
          ? code - 87
          : code === 0x69
          ? 1 // i
          : code >= 0x6A && code <= 0x6B
          ? code - 88
          : code === 0x6C
          ? 1 // l
          : code >= 0x6D && code <= 0x6E
          ? code - 89
          : code === 0x6F
          ? 0 // o
          : code >= 0x70 && code <= 0x74
          ? code - 90
          // u is skipped
          : code >= 0x76 && code <= 0x7A
          ? code - 91
          : -1
        : code >= 0x41 && code <= 0x5A
        ? code - 65
        : code >= 0x61 && code <= 0x7A
        ? code - 97 // same result as above; case insensitive
        : code >= 0x32 && code <= 0x37
        ? code - 24 // digits 2–7 map to 26–31
        : -1;
      if (result < 0) {
        // The source contains an invalid character.
        throw new RangeError(
          `Piscēs: Invalid character in Base32: ${ucsCharacter}.`,
        );
      } else {
        // The source contains a valid character with a recognized
        // mapping.
        return result;
      }
    },
  );
  const { length } = u5s;
  const lengthMod8 = length % 8;
  if (lengthMod8 === 1 || lengthMod8 === 3 || lengthMod8 === 6) {
    // The length is such that an entire letter would be dropped during
    // a forgiving decode.
    throw new RangeError(
      `Piscēs: Base32 string has invalid length: ${source}.`,
    );
  } else {
    // Every letter contributes at least some bits to the result.
    const dataView = new View(new Buffer(floor(length * 5 / 8)));
    for (let index = 0; index < length - 1;) {
      // Iterate over the characters and assign their bits to the
      // buffer.
      //
      // The final index is not handled; if the string is not divisible
      // by 8, some bits might be dropped. This matches the “forgiving
      // decode” behaviour specified by WhatW·G for base64.
      const dataIndex = ceil(index * 5 / 8);
      const remainder = index % 8;
      call(viewSetUint8, dataView, [
        dataIndex,
        remainder === 0
          ? u5s[index] << 3 | u5s[++index] >> 2
          : remainder === 1
          ? u5s[index] << 6 | u5s[++index] << 1 | u5s[++index] >> 4
          : remainder === 3
          ? u5s[index] << 4 | u5s[++index] >> 1
          : remainder === 4
          ? u5s[index] << 7 | u5s[++index] << 2 | u5s[++index] >> 3
          : u5s[index] << 5 | u5s[++index, index++], // remainder === 6
      ]);
    }
    return call(getViewBuffer, dataView, []);
  }
};

/**
 * Returns the result of decoding the provided base64 string into an
 * ArrayBuffer.
 *
 * ※ This function is not exposed.
 */
const decodeBase64 = (source, safe = false) => {
  const u6s = map(
    source.length % 4 === 0
      ? stringReplace(source, /={1,2}$/u, "")
      : source,
    (ucsCharacter) => {
      const code = getCodeUnit(ucsCharacter, 0);
      const result = code >= 0x41 && code <= 0x5A
        ? code - 65
        : code >= 0x61 && code <= 0x7A
        ? code - 71
        : code >= 0x30 && code <= 0x39
        ? code + 4
        : code === (safe ? 0x2D : 0x2B)
        ? 62
        : code === (safe ? 0x5F : 0x2F)
        ? 63
        : -1;
      if (result < 0) {
        // The source contains an invalid character.
        throw new RangeError(
          `Piscēs: Invalid character in Base64: ${ucsCharacter}.`,
        );
      } else {
        // The source contains a valid character with a recognized
        // mapping.
        return result;
      }
    },
  );
  const { length } = u6s;
  if (length % 4 === 1) {
    // The length is such that an entire letter would be dropped during
    // a forgiving decode.
    throw new RangeError(
      `Piscēs: Base64 string has invalid length: ${source}.`,
    );
  } else {
    // Every letter contributes at least some bits to the result.
    const dataView = new View(new Buffer(floor(length * 3 / 4)));
    for (let index = 0; index < length - 1;) {
      // Iterate over the characters and assign their bits to the
      // buffer.
      //
      // The final index is not handled; if the string is not divisible
      // by 4, some bits might be dropped. This matches the “forgiving
      // decode” behaviour specified by WhatW·G for base64.
      const dataIndex = ceil(index * 3 / 4);
      const remainder = index % 4;
      call(viewSetUint8, dataView, [
        dataIndex,
        remainder === 0
          ? u6s[index] << 2 | u6s[++index] >> 4
          : remainder === 1
          ? u6s[index] << 4 | u6s[++index] >> 2
          : u6s[index] << 6 | u6s[++index, index++], // remainder === 2
      ]);
    }
    return call(getViewBuffer, dataView, []);
  }
};

/**
 * Returns the result of encoding the provided ArrayBuffer into a
 * base16 string.
 *
 * ※ This function is not exposed.
 */
const encodeBase16 = (buffer) => {
  const dataView = new View(buffer);
  const byteLength = call(getBufferByteLength, buffer, []);
  const minimumLengthOfResults = byteLength * 2;
  const resultingCodeUnits = fill(
    objectCreate(
      binaryCodeUnitIterablePrototype,
      { length: { value: minimumLengthOfResults } },
    ),
    0x3D,
  );
  for (let index = 0; index < byteLength;) {
    // Iterate over the bytes and generate code units for them.
    const codeUnitIndex = index * 2;
    const datum = call(viewGetUint8, dataView, [index++]);
    const u4s = [datum >> 4, datum & 0xF];
    for (let u4i = 0; u4i < 2; ++u4i) {
      // Handle the high four bits, then the low four bits.
      const u4 = u4s[u4i];
      const result = u4 < 10 ? u4 + 48 : u4 < 16 ? u4 + 55 : -1;
      if (result < 0) {
        // No mapping exists for these four bits.
        //
        // ※ This shouldn’t be possible!
        throw new RangeError(
          `Piscēs: Unexpected Base16 value: ${u4}.`,
        );
      } else {
        // A mapping exists for the bits.
        resultingCodeUnits[codeUnitIndex + u4i] = result;
      }
    }
  }
  return stringFromCodeUnits(...resultingCodeUnits);
};

/**
 * Returns the result of encoding the provided ArrayBuffer into a
 * base32 string.
 *
 * ※ This function is not exposed.
 */
const encodeBase32 = (buffer, wrmg = false) => {
  const dataView = new View(buffer);
  const byteLength = call(getBufferByteLength, buffer, []);
  const minimumLengthOfResults = ceil(byteLength * 8 / 5);
  const fillByte = wrmg ? 0x2D : 0x3D;
  const resultingCodeUnits = fill(
    objectCreate(
      binaryCodeUnitIterablePrototype,
      {
        length: {
          value: minimumLengthOfResults +
            (8 - (minimumLengthOfResults % 8)) % 8,
        },
      },
    ),
    fillByte,
  );
  for (let index = 0; index < byteLength;) {
    // Iterate over the bytes and generate code units for them.
    const codeUnitIndex = ceil(index * 8 / 5);
    const currentIndex = codeUnitIndex + +(
      0b01011 & 1 << index % 5 &&
      resultingCodeUnits[codeUnitIndex] != fillByte
    ); // bytes 0, 1 & 3 handle two letters; this is for the second
    const remainder = currentIndex % 8;
    const currentByte = call(viewGetUint8, dataView, [index]);
    const nextByte =
      0b01011010 & 1 << remainder && ++index < byteLength
        // digits 1, 3, 4 & 6 span multiple bytes
        ? call(viewGetUint8, dataView, [index])
        : 0;
    const u5 = remainder === 0
      ? currentByte >> 3
      : remainder === 1
      ? (currentByte & 0b00000111) << 2 | nextByte >> 6
      : remainder === 2
      ? (currentByte & 0b00111111) >> 1
      : remainder === 3
      ? (currentByte & 0b00000001) << 4 | nextByte >> 4
      : remainder === 4
      ? (currentByte & 0b00001111) << 1 | nextByte >> 7
      : remainder === 5
      ? (currentByte & 0b01111111) >> 2
      : remainder === 6
      ? (currentByte & 0b00000011) << 3 | nextByte >> 5
      : (++index, currentByte & 0b00011111); // remainder === 7
    const result = wrmg
      ? u5 < 10 ? u5 + 48 : u5 < 18
        ? u5 + 55
        // skip I
        : u5 < 20
        ? u5 + 56
        // skip L
        : u5 < 22
        ? u5 + 57
        // skip O
        : u5 < 27
        ? u5 + 58
        // skip U
        : u5 < 32
        ? u5 + 59
        : -1
      : u5 < 26
      ? u5 + 65
      : u5 < 32
      ? u5 + 24
      : -1;
    if (result < 0) {
      // No mapping exists for these five bits.
      //
      // ※ This shouldn’t be possible!
      throw new RangeError(`Piscēs: Unexpected Base32 value: ${u5}.`);
    } else {
      // A mapping exists for the bits.
      resultingCodeUnits[currentIndex] = result;
    }
  }
  const answer = stringFromCodeUnits(...resultingCodeUnits);
  return wrmg ? answer.replace(/-+$/u, "") : answer;
};

/**
 * Returns the result of encoding the provided ArrayBuffer into a
 * base64 string.
 *
 * ※ This function is not exposed.
 */
const encodeBase64 = (buffer, safe = false) => {
  const dataView = new View(buffer);
  const byteLength = call(getBufferByteLength, buffer, []);
  const minimumLengthOfResults = ceil(byteLength * 4 / 3);
  const resultingCodeUnits = fill(
    objectCreate(
      binaryCodeUnitIterablePrototype,
      {
        length: {
          value: minimumLengthOfResults +
            (4 - (minimumLengthOfResults % 4)) % 4,
        },
      },
    ),
    0x3D,
  );
  for (let index = 0; index < byteLength;) {
    // Iterate over the bytes and generate code units for them.
    const codeUnitIndex = ceil(index * 4 / 3);
    const currentIndex = codeUnitIndex + +(
      index % 3 === 0 && resultingCodeUnits[codeUnitIndex] != 0x3D
    ); // every third byte handles two letters; this is for the second
    const remainder = currentIndex % 4;
    const currentByte = call(viewGetUint8, dataView, [index]);
    const nextByte = remainder % 3 && ++index < byteLength
      // digits 1 & 2 span multiple bytes
      ? call(viewGetUint8, dataView, [index])
      : 0;
    const u6 = remainder === 0
      ? currentByte >> 2
      : remainder === 1
      ? (currentByte & 0b00000011) << 4 | nextByte >> 4
      : remainder === 2
      ? (currentByte & 0b00001111) << 2 | nextByte >> 6
      : (++index, currentByte & 0b00111111); // remainder === 3
    const result = u6 < 26
      ? u6 + 65
      : u6 < 52
      ? u6 + 71
      : u6 < 62
      ? u6 - 4
      : u6 < 63
      ? (safe ? 0x2D : 0x2B)
      : u6 < 64
      ? (safe ? 0x5F : 0x2F)
      : -1;
    if (result < 0) {
      // No mapping exists for these six bits.
      //
      // ※ This shouldn’t be possible!
      throw new RangeError(`Piscēs: Unexpected Base64 value: ${u6}.`);
    } else {
      // A mapping exists for the bits.
      resultingCodeUnits[currentIndex] = result;
    }
  }
  return stringFromCodeUnits(...resultingCodeUnits);
};

/**
 * Returns a source string generated from the arguments passed to a
 * tag function.
 *
 * ※ This function is not exposed.
 */
const sourceFromArgs = ($, $s) =>
  stringReplace(
    typeof $ === "string" ? $ : hasOwnProperty($, "raw")
      ? rawString(
        $,
        ...objectCreate(argumentIterablePrototype, {
          args: { value: $s },
        }),
      )
      : `${$}`,
    /[\t\n\f\r ]+/gu,
    "",
  );

/**
 * Returns an ArrayBuffer generated from the provided base16 string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 *
 * ☡ This function throws if the provided string is not a valid base16
 * string.
 */
export const base16Binary = ($, ...$s) =>
  decodeBase16(sourceFromArgs($, $s));

/**
 * Returns a (big‐endian) base16 string created from the provided typed
 * array, buffer, or (16‐bit) string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 */
export const base16String = ($, ...$s) =>
  encodeBase16(bufferFromArgs($, $s));

/**
 * Returns an ArrayBuffer generated from the provided base32 string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 *
 * ☡ This function throws if the provided string is not a valid base32
 * string.
 */
export const base32Binary = ($, ...$s) =>
  decodeBase32(sourceFromArgs($, $s));

/**
 * Returns a (big‐endian) base32 string created from the provided typed
 * array, buffer, or (16‐bit) string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 */
export const base32String = ($, ...$s) =>
  encodeBase32(bufferFromArgs($, $s));

/**
 * Returns an ArrayBuffer generated from the provided base64 string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 *
 * ☡ This function throws if the provided string is not a valid base64
 * string.
 */
export const base64Binary = ($, ...$s) =>
  decodeBase64(sourceFromArgs($, $s));

/**
 * Returns a (big‐endian) base64 string created from the provided typed
 * array, buffer, or (16‐bit) string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 */
export const base64String = ($, ...$s) =>
  encodeBase64(bufferFromArgs($, $s));

/**
 * Returns an ArrayBuffer generated from the provided filename‐safe
 * base64 string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 *
 * ☡ This function throws if the provided string is not a valid
 * filename‐safe base64 string.
 */
export const filenameSafeBase64Binary = ($, ...$s) =>
  decodeBase64(sourceFromArgs($, $s), true);

/**
 * Returns a (big‐endian) filename‐safe base64 string created from the
 * provided typed array, buffer, or (16‐bit) string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 */
export const filenameSafeBase64String = ($, ...$s) =>
  encodeBase64(bufferFromArgs($, $s), true);

/**
 * Returns the byte length for the provided array buffer or array
 * buffer view.
 *
 * ☡ This function throws if the provided value is not an array buffer,
 * data view, or typed array.
 */
export const getByteLength = ($) => {
  try {
    // Attempt to get the byte length from the provided value as an
    // `ArrayBuffer`.
    return call(getBufferByteLength, $, []);
  } catch {
    // The provided value is not an `ArrayBuffer`.
    /* do nothing */
  }
  try {
    // Attempt to get the byte length from the provided value as a
    // `SharedArrayBuffer`.
    return call(getSharedBufferByteLength, $, []);
  } catch {
    // The provided value is not a `SharedArrayBuffer`.
    /* do nothing */
  }
  try {
    // Attempt to get the byte length from the provided value as a
    // data view.
    return call(getViewByteLength, $, []);
  } catch {
    // The provided value is not a data view.
    /* do nothing */
  }
  try {
    // Attempt to get the byte length from the provided value as a
    // typed array.
    return call(getTypedArrayByteLength, $, []);
  } catch {
    // The provided value is not a typed array.
    /* do nothing */
  }
  throw new TypeError(`Piscēs: Not an array buffer or view: ${$}.`);
};

/**
 * Returns the byte offset for the provided array buffer or array
 * buffer view.
 *
 * ※ This function always returns `0` for array buffers.
 *
 * ☡ This function throws if the provided value is not an array buffer,
 * data view, or typed array.
 */
export const getByteOffset = ($) => {
  if (isArrayBuffer($)) {
    // The provided value is an array buffer.
    return 0;
  } else {
    try {
      // Attempt to get the byte offset from the provided value as a
      // data view.
      return call(getViewByteOffset, $, []);
    } catch {
      // The provided value is not a data view.
      /* do nothing */
    }
    try {
      // Attempt to get the byte offset from the provided value as a
      // typed array.
      return call(getTypedArrayByteOffset, $, []);
    } catch {
      // The provided value is not a typed array.
      /* do nothing */
    }
    throw new TypeError(`Piscēs: Not an array buffer or view: ${$}.`);
  }
};

/**
 * Returns whether the provided value is a view on an underlying array
 * buffer.
 *
 * ※ This function returns true for typed arrays and data views.
 */
export const { isView: isArrayBufferView } = Buffer;

/**
 * Returns whether the provided value is an array buffer.
 *
 * ※ This function returns true for both `ArrayBuffer`s and
 * `SharedArrayBuffer`s.
 */
export const isArrayBuffer = ($) => {
  try {
    // Try to see if the provided argument has array buffer internal
    // slots and return true if so.
    return call(getBufferByteLength, $, []), true;
  } catch {
    // The provided argument does not have array buffer internal slots.
    /* do nothing */
  }
  try {
    // Try to see if the provided argument has array buffer internal
    // slots and return true if so.
    return call(getSharedBufferByteLength, $, []), true;
  } catch {
    // The provided argument does not have array buffer internal slots.
    /* do nothing */
  }
  return false;
};

/**
 * Returns whether the provided value is a base16 string.
 *
 * ※ This function returns false if the provided value is not a string
 * primitive.
 */
export const isBase16 = ($) => {
  if (typeof $ !== "string") {
    // The provided value is not a string.
    return false;
  } else {
    // The provided value is a string.
    const source = stringReplace($, /[\t\n\f\r ]+/gu, "");
    return source.length % 2 !== 1 &&
      call(reExec, /[^0-9A-F]/iu, [source]) === null;
  }
};

/**
 * Returns whether the provided value is a base32 string.
 *
 * ※ This function returns false if the provided value is not a string
 * primitive.
 */
export const isBase32 = ($) => {
  if (typeof $ !== "string") {
    // The provided value is not a string.
    return false;
  } else {
    // The provided value is a string.
    const source = stringReplace($, /[\t\n\f\r ]+/gu, "");
    const trimmed = source.length % 8 === 0
      ? stringReplace(source, /(?:=|={3,4}|={6})$/u, "")
      : source;
    return trimmed.length % 8 !== 1 &&
      call(reExec, /[^2-7A-Z/]/iu, [trimmed]) === null;
  }
};

/**
 * Returns whether the provided value is a Base64 string.
 *
 * ※ This function returns false if the provided value is not a string
 * primitive.
 */
export const isBase64 = ($) => {
  if (typeof $ !== "string") {
    // The provided value is not a string.
    return false;
  } else {
    // The provided value is a string.
    const source = stringReplace($, /[\t\n\f\r ]+/gu, "");
    const trimmed = source.length % 4 === 0
      ? stringReplace(source, /={1,2}$/u, "")
      : source;
    return trimmed.length % 4 !== 1 &&
      call(reExec, /[^0-9A-Za-z+\/]/u, [trimmed]) === null;
  }
};

/**
 * Returns whether the provided value is a filename‐safe base64 string.
 *
 * ※ This function returns false if the provided value is not a string
 * primitive.
 */
export const isFilenameSafeBase64 = ($) => {
  if (typeof $ !== "string") {
    // The provided value is not a string.
    return false;
  } else {
    // The provided value is a string.
    const source = stringReplace($, /[\t\n\f\r ]+/gu, "");
    const trimmed = source.length % 4 === 0
      ? stringReplace(source, /={1,2}$/u, "")
      : source;
    return trimmed.length % 4 !== 1 &&
      call(reExec, /[^0-9A-Za-z_-]/u, [trimmed]) === null;
  }
};

/** Returns whether the provided value is a shared array buffer. */
export const isSharedArrayBuffer = ($) => {
  try {
    // Try to see if the provided argument has shared array buffer
    // internal slots and return true if so.
    return call(getSharedBufferByteLength, $, []), true;
  } catch {
    // The provided argument does not have data view internal slots.
    return false;
  }
};

/** Returns whether the provided value is a typed array. */
export const isTypedArray = ($) => {
  try {
    // Try to see if the provided argument has typed array internal
    // slots and return true if so.
    return call(getTypedArrayBuffer, $, []), true;
  } catch {
    // The provided argument does not have typed array internal slots.
    return false;
  }
};

/**
 * Returns whether the provided value is a W·R·M·G (Crockford) base32
 * string. Check digits are not supported.
 *
 * ※ This function returns false if the provided value is not a string
 * primitive.
 */
export const isWRMGBase32 = ($) => {
  if (typeof $ !== "string") {
    // The provided value is not a string.
    return false;
  } else {
    // The provided value is a string.
    const source = stringReplace($, /[\t\n\f\r ]+/gu, "");
    const trimmed = stringReplace(source, /-/gu, "");
    return trimmed.length % 8 !== 1 &&
      call(reExec, /[^0-9A-TV-Z]/iu, [trimmed]) === null;
  }
};

/**
 * Returns the array buffer associated with the provided object.
 *
 * ☡ This function throws if the provided object is not a data view or
 * typed array.
 */
export const toArrayBuffer = ($) => {
  if (isArrayBuffer($)) {
    // The provided argument has array buffer internal slots.
    return $;
  } else {
    // The provided argument does not have array buffer internal slots.
    try {
      // The provided argument has typed array internal slots.
      return call(getTypedArrayBuffer, $, []);
    } catch {
      /* do nothing */
    }
    try {
      // The provided argument has data view internal slots.
      return call(getViewBuffer, $, []);
    } catch {
      /* do nothing */
    }
    throw new TypeError(`Piscēs: Not an array buffer or view: ${$}.`);
  }
};

/**
 * Returns an ArrayBuffer generated from the provided W·R·M·G
 * (Crockford) base32 string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 *
 * ☡ This function throws if the provided string is not a valid W·R·M·G
 * base32 string.
 */
export const wrmgBase32Binary = ($, ...$s) =>
  decodeBase32(sourceFromArgs($, $s), true);

/**
 * Returns a (big‐endian) W·R·M·G (Crockford) base32 string created
 * from the provided typed array, buffer, or (16‐bit) string.
 *
 * This function can also be used as a tag for a template literal. The
 * literal will be interpreted akin to `String.raw`.
 */
export const wrmgBase32String = ($, ...$s) =>
  encodeBase32(bufferFromArgs($, $s), true);