blockString.js.flow

// @flow strict

/**
 * Produces the value of a block string from its parsed raw value, similar to
 * CoffeeScript's block string, Python's docstring trim or Ruby's strip_heredoc.
 *
 * This implements the GraphQL spec's BlockStringValue() static algorithm.
 */
export function dedentBlockStringValue(rawString: string): string {
  // Expand a block string's raw value into independent lines.
  const lines = rawString.split(/\r\n|[\n\r]/g);

  // Remove common indentation from all lines but first.
  const commonIndent = getBlockStringIndentation(lines);

  if (commonIndent !== 0) {
    for (let i = 1; i < lines.length; i++) {
      lines[i] = lines[i].slice(commonIndent);
    }
  }

  // Remove leading and trailing blank lines.
  while (lines.length > 0 && isBlank(lines[0])) {
    lines.shift();
  }
  while (lines.length > 0 && isBlank(lines[lines.length - 1])) {
    lines.pop();
  }

  // Return a string of the lines joined with U+000A.
  return lines.join('\n');
}

// @internal
export function getBlockStringIndentation(
  lines: $ReadOnlyArray<string>,
): number {
  let commonIndent = null;

  for (let i = 1; i < lines.length; i++) {
    const line = lines[i];
    const indent = leadingWhitespace(line);
    if (indent === line.length) {
      continue; // skip empty lines
    }

    if (commonIndent === null || indent < commonIndent) {
      commonIndent = indent;
      if (commonIndent === 0) {
        break;
      }
    }
  }

  return commonIndent === null ? 0 : commonIndent;
}

function leadingWhitespace(str) {
  let i = 0;
  while (i < str.length && (str[i] === ' ' || str[i] === '\t')) {
    i++;
  }
  return i;
}

function isBlank(str) {
  return leadingWhitespace(str) === str.length;
}

/**
 * Print a block string in the indented block form by adding a leading and
 * trailing blank line. However, if a block string starts with whitespace and is
 * a single-line, adding a leading blank line would strip that whitespace.
 */
export function printBlockString(
  value: string,
  indentation?: string = '',
  preferMultipleLines?: boolean = false,
): string {
  const isSingleLine = value.indexOf('\n') === -1;
  const hasLeadingSpace = value[0] === ' ' || value[0] === '\t';
  const hasTrailingQuote = value[value.length - 1] === '"';
  const printAsMultipleLines =
    !isSingleLine || hasTrailingQuote || preferMultipleLines;

  let result = '';
  // Format a multi-line block quote to account for leading space.
  if (printAsMultipleLines && !(isSingleLine && hasLeadingSpace)) {
    result += '\n' + indentation;
  }
  result += indentation ? value.replace(/\n/g, '\n' + indentation) : value;
  if (printAsMultipleLines) {
    result += '\n';
  }

  return '"""' + result.replace(/"""/g, '\\"""') + '"""';
}