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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *   http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.calculator2;
     18 
     19 import android.content.Context;
     20 import android.text.SpannableStringBuilder;
     21 import android.text.TextUtils;
     22 
     23 public class CalculatorExpressionBuilder extends SpannableStringBuilder {
     24 
     25     private final CalculatorExpressionTokenizer mTokenizer;
     26     private boolean mIsEdited;
     27 
     28     public CalculatorExpressionBuilder(
     29             CharSequence text, CalculatorExpressionTokenizer tokenizer, boolean isEdited) {
     30         super(text);
     31 
     32         mTokenizer = tokenizer;
     33         mIsEdited = isEdited;
     34     }
     35 
     36     @Override
     37     public SpannableStringBuilder replace(int start, int end, CharSequence tb, int tbstart,
     38             int tbend) {
     39         if (start != length() || end != length()) {
     40             mIsEdited = true;
     41             return super.replace(start, end, tb, tbstart, tbend);
     42         }
     43 
     44         String appendExpr =
     45                 mTokenizer.getNormalizedExpression(tb.subSequence(tbstart, tbend).toString());
     46         if (appendExpr.length() == 1) {
     47             final String expr = mTokenizer.getNormalizedExpression(toString());
     48             switch (appendExpr.charAt(0)) {
     49                 case '.':
     50                     // don't allow two decimals in the same number
     51                     final int index = expr.lastIndexOf('.');
     52                     if (index != -1 && TextUtils.isDigitsOnly(expr.substring(index + 1, start))) {
     53                         appendExpr = "";
     54                     }
     55                     break;
     56                 case '+':
     57                 case '*':
     58                 case '/':
     59                     // don't allow leading operator
     60                     if (start == 0) {
     61                         appendExpr = "";
     62                         break;
     63                     }
     64 
     65                     // don't allow multiple successive operators
     66                     while (start > 0 && "+-*/".indexOf(expr.charAt(start - 1)) != -1) {
     67                         --start;
     68                     }
     69                     // fall through
     70                 case '-':
     71                     // don't allow -- or +-
     72                     if (start > 0 && "+-".indexOf(expr.charAt(start - 1)) != -1) {
     73                         --start;
     74                     }
     75 
     76                     // mark as edited since operators can always be appended
     77                     mIsEdited = true;
     78                     break;
     79                 default:
     80                     break;
     81             }
     82         }
     83 
     84         // since this is the first edit replace the entire string
     85         if (!mIsEdited && appendExpr.length() > 0) {
     86             start = 0;
     87             mIsEdited = true;
     88         }
     89 
     90         appendExpr = mTokenizer.getLocalizedExpression(appendExpr);
     91         return super.replace(start, end, appendExpr, 0, appendExpr.length());
     92     }
     93 }
     94