Align text lines along occurrences of a pattern

// Align selected text lines along occurrences of a given pattern or substring
// During the alignment process, all the pattern occurrences will be deleted

/* global  UltraEdit, selectedLines, lineEnd */

/* eslint no-shadow:0 */

var alignAt        = UltraEdit.getString("Align at pattern (e.g. \\t)",1)
var alignAtPattern = new RegExp( alignAt )

// Cut array "selectedLines" into clipboard,
// determine "lineEnd" byte sequence of this document:
// include cutSelection.js

var cells = selectedLines.map( function(line) { return line.split(alignAtPattern) } )

var colwidths = cells.reduce( function( widths, row ) {
  row.forEach( function(cell,i) {
    if (widths.length < i+1) widths.push(0)
    widths[i] = Math.max(widths[i],cell.length)
    })
  return widths
  }, [])

var resultLines = cells.map(
  pad_to( colwidths )
  )

// Output - and done
UltraEdit.activeDocument.write( resultLines.join(lineEnd) )

//-----------------------------------------------------------------------------------

 function pad_to( colwidths ) {
  var spaces = new Array( Math.max.apply(null,colwidths)+1).join(' ')
  return function( row ) {
    return row.map( function(cell,i){
      return cell+spaces.substr(0,colwidths[i]-cell.length)
      }).join(' ')
    }
  }