util.js

'use strict';

// --------------------------------------------------------------------
// Imports
// --------------------------------------------------------------------

var common = require('./common');

// --------------------------------------------------------------------
// Private stuff
// --------------------------------------------------------------------

// Given an array of numbers `arr`, return an array of the numbers as strings,
// right-justified and padded to the same length.
function padNumbersToEqualLength(arr) {
  var maxLen = 0;
  var strings = arr.map(function(n) {
    var str = n.toString();
    maxLen = Math.max(maxLen, str.length);
    return str;
  });
  return strings.map(function(s) { return common.padLeft(s, maxLen); });
}

// Produce a new string that would be the result of copying the contents
// of the string `src` onto `dest` at offset `offest`.
function strcpy(dest, src, offset) {
  var origDestLen = dest.length;
  var start = dest.slice(0, offset);
  var end = dest.slice(offset + src.length);
  return (start + src + end).substr(0, origDestLen);
}

// --------------------------------------------------------------------
// Exports
// --------------------------------------------------------------------

// Return an object with the line and column information for the given
// offset in `str`.
exports.getLineAndColumn = function(str, offset) {
  var lineNum = 1;
  var colNum = 1;

  var currOffset = 0;
  var lineStartOffset = 0;

  var nextLine = null;
  var prevLine = null;
  var prevLineStartOffset = -1;

  while (currOffset < offset) {
    var c = str.charAt(currOffset++);
    if (c === '\n') {
      lineNum++;
      colNum = 1;
      prevLineStartOffset = lineStartOffset;
      lineStartOffset = currOffset;
    } else if (c !== '\r') {
      colNum++;
    }
  }

  // Find the end of the target line.
  var lineEndOffset = str.indexOf('\n', lineStartOffset);
  if (lineEndOffset === -1) {
    lineEndOffset = str.length;
  } else {
    // Get the next line.
    var nextLineEndOffset = str.indexOf('\n', lineEndOffset + 1);
    nextLine = nextLineEndOffset === -1 ? str.slice(lineEndOffset)
                                        : str.slice(lineEndOffset, nextLineEndOffset);
    // Strip leading and trailing EOL char(s).
    nextLine = nextLine.replace(/^\r?\n/, '').replace(/\r$/, '');
  }

  // Get the previous line.
  if (prevLineStartOffset >= 0) {
    prevLine = str.slice(prevLineStartOffset, lineStartOffset)
                  .replace(/\r?\n$/, '');  // Strip trailing EOL char(s).
  }

  // Get the target line, stripping a trailing carriage return if necessary.
  var line = str.slice(lineStartOffset, lineEndOffset).replace(/\r$/, '');

  return {
    lineNum: lineNum,
    colNum: colNum,
    line: line,
    prevLine: prevLine,
    nextLine: nextLine
  };
};

// Return a nicely-formatted string describing the line and column for the
// given offset in `str`.

exports.getOptionalLineAndColumnMessage = function(str, offset, includeLineNumbers /* ranges */) {

  var _includeLineNumbers = typeof includeLineNumbers !== 'undefined' ? includeLineNumbers : true;
  var repeatStr = common.repeatStr;

  var lineAndCol = exports.getLineAndColumn(str, offset);
  var sb = new common.StringBuffer();
  sb.append('Line ' + lineAndCol.lineNum + ', col ' + lineAndCol.colNum + ':\n');

  // An array of the previous, current, and next line numbers as strings of equal length.
  var lineNumbers = padNumbersToEqualLength([
    lineAndCol.prevLine == null ? 0 : lineAndCol.lineNum - 1,
    lineAndCol.lineNum,
    lineAndCol.nextLine == null ? 0 : lineAndCol.lineNum + 1
  ]);

  // Helper for appending formatting input lines to the buffer.
  function appendLine(num, content, prefix) {
    if (_includeLineNumbers) {
      sb.append(prefix + lineNumbers[num] + ' | ' + content + '\n');
    } else {
      sb.append('  ' + content + '\n');
    }
  }

  // Include the previous line for context if possible.
  if (lineAndCol.prevLine != null) {
    appendLine(0, lineAndCol.prevLine, '  ');
  }
  // Line that the error occurred on.
  appendLine(1, lineAndCol.line, '> ');

  // Build up the line that points to the offset and possible indicates one or more ranges.
  // Start with a blank line, and indicate each range by overlaying a string of `~` chars.
  var lineLen = lineAndCol.line.length;
  var indicationLine = repeatStr(' ', lineLen + 1);
  var ranges = Array.prototype.slice.call(arguments, 3);
  for (var i = 0; i < ranges.length; ++i) {
    var startIdx = ranges[i][0];
    var endIdx = ranges[i][1];
    common.assert(startIdx >= 0 && startIdx <= endIdx, 'range start must be >= 0 and <= end');

    var lineStartOffset = offset - lineAndCol.colNum + 1;
    startIdx = Math.max(0, startIdx - lineStartOffset);
    endIdx = Math.min(endIdx - lineStartOffset, lineLen);

    indicationLine = strcpy(indicationLine, repeatStr('~', endIdx - startIdx), startIdx);
  }
  var gutterWidth = _includeLineNumbers ? 2 + lineNumbers[1].length + 3 : 2;
  sb.append(repeatStr(' ', gutterWidth));
  indicationLine = strcpy(indicationLine, '^', lineAndCol.colNum - 1);
  sb.append(indicationLine.replace(/ +$/, '') + '\n');

  // Include the next line for context if possible.
  if (lineAndCol.nextLine != null) {
    appendLine(2, lineAndCol.nextLine, '  ');
  }
  return sb.contents();
};

exports.getLineAndColumnMessage = function(str, offset /* ...ranges */) {
  var args = Array.prototype.slice.call(arguments);
  args.splice(2, 0, true);
  return exports.getOptionalLineAndColumnMessage.apply(this, args);
};