lib/src/utils.dart

// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:math' as math;

/// Pads [source] to [length] by adding spaces at the end.
String padRight(String source, int length) =>
    source + ' ' * (length - source.length);

/// Wraps a block of text into lines no longer than [length].
///
/// Tries to split at whitespace, but if that's not good enough to keep it
/// under the limit, then it splits in the middle of a word.
///
/// Preserves indentation (leading whitespace) for each line (delimited by '\n')
/// in the input, and indents wrapped lines the same amount.
///
/// If [hangingIndent] is supplied, then that many spaces are added to each
/// line, except for the first line. This is useful for flowing text with a
/// heading prefix (e.g. "Usage: "):
///
/// ```dart
/// var prefix = "Usage: ";
/// print(prefix + wrapText(invocation, hangingIndent: prefix.length, length: 40));
/// ```
///
/// yields:
/// ```
/// Usage: app main_command <subcommand>
///        [arguments]
/// ```
///
/// If [length] is not specified, then no wrapping occurs, and the original
/// [text] is returned unchanged.
String wrapText(String text, {int length, int hangingIndent}) {
  if (length == null) return text;
  hangingIndent ??= 0;
  var splitText = text.split('\n');
  var result = <String>[];
  for (var line in splitText) {
    var trimmedText = line.trimLeft();
    final leadingWhitespace =
        line.substring(0, line.length - trimmedText.length);
    var notIndented;
    if (hangingIndent != 0) {
      // When we have a hanging indent, we want to wrap the first line at one
      // width, and the rest at another (offset by hangingIndent), so we wrap
      // them twice and recombine.
      var firstLineWrap = wrapTextAsLines(trimmedText,
          length: length - leadingWhitespace.length);
      notIndented = [firstLineWrap.removeAt(0)];
      trimmedText = trimmedText.substring(notIndented[0].length).trimLeft();
      if (firstLineWrap.isNotEmpty) {
        notIndented.addAll(wrapTextAsLines(trimmedText,
            length: length - leadingWhitespace.length - hangingIndent));
      }
    } else {
      notIndented = wrapTextAsLines(trimmedText,
          length: length - leadingWhitespace.length);
    }
    String hangingIndentString;
    result.addAll(notIndented.map<String>((String line) {
      // Don't return any lines with just whitespace on them.
      if (line.isEmpty) return '';
      var result = '${hangingIndentString ?? ''}$leadingWhitespace$line';
      hangingIndentString ??= ' ' * hangingIndent;
      return result;
    }));
  }
  return result.join('\n');
}

/// Wraps a block of text into lines no longer than [length],
/// starting at the [start] column, and returns the result as a list of strings.
///
/// Tries to split at whitespace, but if that's not good enough to keep it
/// under the limit, then splits in the middle of a word. Preserves embedded
/// newlines, but not indentation (it trims whitespace from each line).
///
/// If [length] is not specified, then no wrapping occurs, and the original
/// [text] is returned after splitting it on newlines. Whitespace is not trimmed
/// in this case.
List<String> wrapTextAsLines(String text, {int start = 0, int length}) {
  assert(start >= 0);

  /// Returns true if the code unit at [index] in [text] is a whitespace
  /// character.
  ///
  /// Based on: https://en.wikipedia.org/wiki/Whitespace_character#Unicode
  bool isWhitespace(String text, int index) {
    var rune = text.codeUnitAt(index);
    return rune >= 0x0009 && rune <= 0x000D ||
        rune == 0x0020 ||
        rune == 0x0085 ||
        rune == 0x1680 ||
        rune == 0x180E ||
        rune >= 0x2000 && rune <= 0x200A ||
        rune == 0x2028 ||
        rune == 0x2029 ||
        rune == 0x202F ||
        rune == 0x205F ||
        rune == 0x3000 ||
        rune == 0xFEFF;
  }

  if (length == null) return text.split('\n');

  var result = <String>[];
  var effectiveLength = math.max(length - start, 10);
  for (var line in text.split('\n')) {
    line = line.trim();
    if (line.length <= effectiveLength) {
      result.add(line);
      continue;
    }

    var currentLineStart = 0;
    var lastWhitespace;
    for (var i = 0; i < line.length; ++i) {
      if (isWhitespace(line, i)) lastWhitespace = i;

      if (i - currentLineStart >= effectiveLength) {
        // Back up to the last whitespace, unless there wasn't any, in which
        // case we just split where we are.
        if (lastWhitespace != null) i = lastWhitespace;

        result.add(line.substring(currentLineStart, i).trim());

        // Skip any intervening whitespace.
        while (isWhitespace(line, i) && i < line.length) {
          i++;
        }

        currentLineStart = i;
        lastWhitespace = null;
      }
    }
    result.add(line.substring(currentLineStart).trim());
  }
  return result;
}