/*
 * Copyright 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.template.soy.basicfunctions;

import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.template.soy.data.SoyValue;
import com.google.template.soy.data.restricted.FloatData;
import com.google.template.soy.data.restricted.IntegerData;
import com.google.template.soy.data.restricted.NumberData;
import com.google.template.soy.exprtree.Operator;
import com.google.template.soy.internal.targetexpr.TargetExpr;
import com.google.template.soy.jssrc.restricted.JsExpr;
import com.google.template.soy.jssrc.restricted.SoyJsCodeUtils;
import com.google.template.soy.jssrc.restricted.SoyJsSrcFunction;
import com.google.template.soy.pysrc.restricted.PyExpr;
import com.google.template.soy.pysrc.restricted.SoyPySrcFunction;
import com.google.template.soy.shared.restricted.SoyJavaFunction;
import com.google.template.soy.shared.restricted.SoyPureFunction;

import java.util.List;
import java.util.Set;

import javax.inject.Inject;
import javax.inject.Singleton;

/**
 * Soy function that rounds a number to a specified number of digits before or after the decimal
 * point.
 *
 */
@Singleton
@SoyPureFunction
public final class RoundFunction implements SoyJavaFunction, SoyJsSrcFunction, SoyPySrcFunction {


  @Inject
  RoundFunction() {}


  @Override public String getName() {
    return "round";
  }

  @Override public Set<Integer> getValidArgsSizes() {
    return ImmutableSet.of(1, 2);
  }

  @Override public SoyValue computeForJava(List<SoyValue> args) {
    SoyValue value = args.get(0);
    int numDigitsAfterPt = (args.size() == 2) ? args.get(1).integerValue() : 0 /* default */;
    return round(value, numDigitsAfterPt);
  }

  /**
   * Rounds the given value to the closest decimal point left (negative numbers) or right
   * (positive numbers) of the decimal point
   */
  public static NumberData round(SoyValue value, int numDigitsAfterPoint) {
    // NOTE: for more accurate rounding, this should really be using BigDecimal which can do correct
    // decimal arithmetic.  However, for compatibility with js, that probably isn't an option.
    if (numDigitsAfterPoint == 0) {
      return IntegerData.forValue(round(value));
    } else if (numDigitsAfterPoint > 0) {
      double valueDouble = value.numberValue();
      double shift = Math.pow(10, numDigitsAfterPoint);
      return FloatData.forValue(Math.round(valueDouble * shift) / shift);
    } else {
      double valueDouble = value.numberValue();
      double shift = Math.pow(10, -numDigitsAfterPoint);
      return IntegerData.forValue((int) (Math.round(valueDouble / shift) * shift));
    }
  }

  /** Rounds the given value to the closest integer. */
  public static long round(SoyValue value) {
    if (value instanceof IntegerData) {
      return value.longValue();
    } else {
      return Math.round(value.numberValue());
    }
  }

  @Override public JsExpr computeForJsSrc(List<JsExpr> args) {
    JsExpr value = args.get(0);
    JsExpr numDigitsAfterPt = (args.size() == 2) ? args.get(1) : null;

    int numDigitsAfterPtAsInt = convertNumDigits(numDigitsAfterPt);

    if (numDigitsAfterPtAsInt == 0) {
      // Case 1: round() has only one argument or the second argument is 0.
      return new JsExpr("Math.round(" + value.getText() + ")", Integer.MAX_VALUE);

    } else if ((numDigitsAfterPtAsInt >= 0 && numDigitsAfterPtAsInt <= 12) ||
               numDigitsAfterPtAsInt == Integer.MIN_VALUE) {
      String shiftExprText;
      if (numDigitsAfterPtAsInt >= 0 && numDigitsAfterPtAsInt <= 12) {
        shiftExprText = "1" + "000000000000".substring(0, numDigitsAfterPtAsInt);
      } else {
        shiftExprText = "Math.pow(10, " + numDigitsAfterPt.getText() + ")";
      }
      JsExpr shift = new JsExpr(shiftExprText, Integer.MAX_VALUE);
      JsExpr valueTimesShift = SoyJsCodeUtils.genJsExprUsingSoySyntax(
          Operator.TIMES, Lists.newArrayList(value, shift));
      return new JsExpr(
          "Math.round(" + valueTimesShift.getText() + ") / " + shift.getText(),
          Operator.DIVIDE_BY.getPrecedence());

    } else if (numDigitsAfterPtAsInt < 0 && numDigitsAfterPtAsInt >= -12) {
      String shiftExprText = "1" + "000000000000".substring(0, -numDigitsAfterPtAsInt);
      JsExpr shift = new JsExpr(shiftExprText, Integer.MAX_VALUE);
      JsExpr valueDivideByShift = SoyJsCodeUtils.genJsExprUsingSoySyntax(
          Operator.DIVIDE_BY, Lists.newArrayList(value, shift));
      return new JsExpr(
          "Math.round(" + valueDivideByShift.getText() + ") * " + shift.getText(),
          Operator.TIMES.getPrecedence());

    } else {
      throw new IllegalArgumentException(
          "Second argument to round() function is " + numDigitsAfterPtAsInt +
          ", which is too large in magnitude.");
    }
  }

  @Override public PyExpr computeForPySrc(List<PyExpr> args) {
    PyExpr value = args.get(0);
    PyExpr precision = (args.size() == 2) ? args.get(1) : null;

    int precisionAsInt = convertNumDigits(precision);
    boolean isLiteral = precisionAsInt != Integer.MIN_VALUE;

    if (precisionAsInt >= -12 && precisionAsInt <= 12 || !isLiteral) {
      // Python rounds ties away from 0 instead of towards infinity as JS and Java do. So to make
      // the behavior consistent, we add the smallest possible float amount to break ties towards
      // infinity.
      String floatBreakdown = "math.frexp(" + value.getText() + ")";
      String precisionValue = isLiteral ? precisionAsInt + "" : precision.getText();
      StringBuilder roundedValue = new StringBuilder("round(")
          .append("(" + floatBreakdown + "[0]")
          .append(" + sys.float_info.epsilon)*2**" + floatBreakdown + "[1]")
          .append(", ")
          .append(precisionValue)
          .append(")");
      // The precision is less than 1. Convert to an int to prevent extraneous decimals in display.
      return new PyExpr("runtime.simplify_num(" + roundedValue + ", " + precisionValue + ")",
          Integer.MAX_VALUE);
    } else {
      throw new IllegalArgumentException(
          "Second argument to round() function is " + precisionAsInt +
          ", which is too large in magnitude.");
    }
  }

  /**
   * Convert the number of digits after the point from an expression to an int.
   * @param numDigitsAfterPt The number of digits after the point as an expression
   * @return The number of digits after the point and an int.
   */
  private static int convertNumDigits(TargetExpr numDigitsAfterPt) {
    int numDigitsAfterPtAsInt = 0;
    if (numDigitsAfterPt != null) {
      try {
        numDigitsAfterPtAsInt = Integer.parseInt(numDigitsAfterPt.getText());
      } catch (NumberFormatException nfe) {
        numDigitsAfterPtAsInt = Integer.MIN_VALUE;  // indicates it's not a simple integer literal
      }
    }
    return numDigitsAfterPtAsInt;
  }
}