// from Chapter 6 of Usable Forms for the Web, glasshaus (c) 2002
function validate(form)
{
  var returnVal=true;
  var formEls=form.elements;
  var currEl,currName,currType,currVal,currField,minimum,maximum,temp;
  var errMsg="There were problems with the following field(s):\n";
  var firstErr=-1;

  var notWhitespace=/\S/;
  var notAlpha=/[^a-z \-\.\,']/gi;
//  var notAlphaNumeric=/[^a-z0-9]/gi; // doesn't allow spaces or punctuation
  var notAlphaNumeric=/[^a-z0-9 \-\.\,']/gi;
  var notAddress=/[^\w \-#\.\,\/]/gi;
  var hasSpaces=/\s/g;
  var notInt=/\D/g;
  var isDecimal=/^\d+(\.\d+)?$/;
  //var isCC=/^\d{4}(-\d{4}){3}$/;
  var isCC=/^\d{4}([- ]\d{4}){3}$/;  // allow - or space between number groups
  var isUSZip=/^\d{5}(-\d{4})?$/;
  var isCaPost=/^[A-Z][\d][A-Z] [\d][A-Z][\d]$/; // ANA NAN 
  var isUKPost=/[a-zA-Z]{1,2}[\d][1-9a-zA-Z]? [\d][a-zA-Z]{2}/;
  var isUSPhone=/^\d{3}[-\.]\d{3}[-\.]\d{4}$/;
  var isEmail=/^\w(\.?[\w-])*@\w(\.?[\w-])*\.[a-z]{2,6}(\.[a-z]{2})?$/i;
  var isCurrency=/^\d+(\.\d{2})?$/;
  var notComment=/[^a-zA-Z0-9\.\,;:%&#$@!\^-_~`"'\[\]\{\}\*\/\?\(\)]/i;
  
  var requirements=new Array("required","alphabetic","address","alphanumeric","nospace",
                             "integer","decimal","minlength","maxlength","ccnumber","uszip","ukpost",
                             "usphone","email","currency","percent","comment", "capost");



  for(var i=0;i<formEls.length;i++)
  {    
// collect information about the element
    currEl=formEls[i];
    //currName=currEl.name;
    currType=currEl.type;
    currValue=currEl.value;
    currName=currEl.id;
	if (currType === undefined) continue;    // fieldset is useless to us, so skip it


// Get tagname
    currField=currName.indexOf("_")!=-1?currName.split("_")[0]:currName;
    currField=currField.replace(/0/g," ");
    temp=0;

// Get constraints for this element
    var context=new Object;

    for(var j=0;j<requirements.length;j++)
      context[requirements[j]]=currName.indexOf(requirements[j])!=-1;

// Collect min-max values if required
    if(context.minlength)
    {
      minimum=currName.split("minlength")[1];
      minimum=minimum.split("_")[0];
      minimum=parseInt(minimum);
    }

    if(context.maxlength)
    {
      maximum=currName.split("maxlength")[1];
      maximum=maximum.split("_")[0];
      maximum=parseInt(maximum);
    }

// check element against its constraints
    switch(currType.toLowerCase())
    {
      case "text":
      case "textarea":
      case "password":
        if(context.required&&(currValue==""||!notWhitespace.test(currValue)))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The required field \""+currField+"\" was left blank.\n";
          break;
        }
        if(context.alphabetic&&notAlpha.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" contains non-alphabet characters.\n";
        }
        if(context.alphanumeric&&notAlphaNumeric.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" contains illegal characters.\n";
        }
        if(context.address&&notAddress.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" contains illegal characters.\n";
        }
        if(context.nospace&&hasSpaces.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" should not contain any spaces.\n";
        }
        if(context.integer&&notInt.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" should contain only the digits 0-9.\n";
        }
        if(context.decimal&&!isDecimal.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The value you entered in the field \""+currField+"\" is not a number.\n";
        }
        if(context.minlength&&currValue.length<minimum)
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" must contain at least "+minimum+" characters.\n";
        }
        if(context.minlength&&currValue.length>maximum)
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" must contain at most "+maximum+" characters.\n";
        }
        if(context.ccnumber&&!isCC.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The value in the field \""+currField+"\" must be in the form \"XXXX-XXXX-XXXX-XXXX\".\n";
        }
        if(context.uszip&&!isUSZip.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" does not contain a valid 5 or 9 digit ZIP code.\n";
        }
        if(context.ukpost&&!UKPost.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" does not contain a valid UK Postcode.\n";
        }
        if(context.usphone&&!isUSPhone.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" does not contain a valid telephone number.\n";
        }
        if(context.email&&!isEmail.test(currValue))
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="The field \""+currField+"\" does not contain a valid email address.\n";
        }
        if(context.currency&&currValue!="")
        {
          currValue=currValue.replace(/[$£¥\,]/g,"");
          if(!isCurrency.test(CurrValue))
          {
            if(firstErr<0)
              firstErr=i;
            errMsg+="The field \""+currField+"\" does not contain a valid amount.\n";
          }
        }
        else
        {
          form.elements[i].value=currValue;
        }
        break;
      
      case "checkbox":
        if(context.required)
        {
          temp=0;
          for(var n=0;n<form[currName].length;n++)
          {
            if(n<form[currName].length-1)
              i++;
            if(form[currName][n].checked)
            {
              temp++;
            }
          }
          if(!temp&&!context.minlength)
          {
            if(firstErr<0)
              firstErr=i;
            errMsg+="You must check at least one of the \""+currField+"\" checkboxes.\n";
          }
          if(context.minlength&&temp<minimum)
          {
            if(firstErr<0)
              firstErr=i-(form[currName].length-1);
            errMsg+="You must check at least "+minimum+" of the \""+currField+"\" checkboxes.\n";
          }
          if(context.maxlength&&temp>maximum)
          {
            if(firstErr<0)
              firstErr=i-(form[currName].length-1);
            errMsg+="Please check no more than "+maximum+" of the \""+currField+"\" checkboxes.\n";
          }
        }
        break;

      case "radio":
        if(context.required)
        {
          temp=false;
          for(var n=0;n<form[currName].length;n++)
          {
            if(n<form[currName].length-1)
              i++;
            if(form[currName][n].checked)
            {
              temp=true;
            }
          }
          if(!temp)
          {
            if(firstErr<0)
            firstErr=i-(form[currName].length-1);
            errMsg+="You must select one of the \""+currField+"\" radiobuttons.\n";
          }
        }
        break;

      case "select-one":
        if(context.required&&!currEl.selectedIndex)
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="You must select one of the \""+currField+"\" options.\n";
        }
        break;

      case "select-multiple":
        if(context.required||context.minlength||context.maxlength)
        {
          temp=0;
          for(n=0;n<currEl.length;n++)
            if(currEl.options[n].selected)
              temp++;
        }
        else
          break;
        if(!temp&&!context.minlength)
          minimum=1;
        if(context.minlength&&temp<minimum || context.required&&!temp)
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="You must select at least "+minimum+" of the \""+currField+"\" options.\n";
        }
        if(context.maxlength&&temp>minimum)
        {
          if(firstErr<0)
            firstErr=i;
          errMsg+="You must select no more "+maximum+" of the \""+currField+"\" options.\n";
        }
        break;

      case "submit":
      case "reset":
      case "button":
      case "file":
      case "image":
      case "hidden":
      break;
      
      default:
        alert("         ERROR!!\nWe should never get here!");
        break;
    }
  }  // end of for loop
  
  returnVal=firstErr<0;
//  alert("returnVal is: " + returnVal);
  if(!returnVal)
  {
    alert(errMsg);
    form.elements[firstErr].focus();
  }  
  return returnVal;
}