MathLearningApp/src/main/java/mathlearning/service/QuestionGenerator/QuestionGenerator.java

package mathlearning.service.QuestionGenerator;

import java.util.Random;

public abstract class   QuestionGenerator{
    protected Random random = new Random();
    public abstract String generateQuestion() ;
    protected String type;

    public String getType() {
        return type;
    }

    QuestionGenerator() {
        type = "无";
    }

    QuestionGenerator(String Type) {
        type = Type;
    }

    protected String  preForOper(int[] operands) {
        StringBuilder question = new StringBuilder();
        String[] operators = {"+", "-", "×", "÷"};
        question.append(operands[0]);

        for (int i = 1; i < operands.length; i++) {
            String op = operators[ random.nextInt (operators.length)];
            question.append(" ").append(op).append(" ").append(operands[i]);
        }
        return question.toString();

    }

    protected boolean Check_num(String expression) {
        if(!(expression.equals("+") || expression.equals("-") || expression.equals("×") || expression.equals("÷"))) {
            return true;
        }
        else{
            return  false;
        }
    }

    protected String addParen(String expression) {
        String[] parts = expression.split(" ");
        StringBuilder result = new StringBuilder();
        boolean r_paren_needed = false;

        for (int i = 0; i < parts.length; i++) {
            if(Check_num ( parts [i]) ) {
                if( !r_paren_needed ) {
                    if(i <= parts.length -3 )
                    {
                        if( random.nextBoolean() )
                        { result.append("(");r_paren_needed = true;}
                    }
                    result.append(parts[i]);
                } else {
                    result.append( parts [i]);
                    if( !random.nextBoolean()) {
                        result.append(")");r_paren_needed = false;
                    }
                }
            } else {
                result.append( parts [i] );
            }
            if( i < parts.length -1 ) {
                result.append(" ");
            }
        }

        if( r_paren_needed ){
            result.append(")");r_paren_needed = false;
        }
        return result.toString();
    }

    protected String add_squs(String expression) {
        String[] parts = expression.split(" ");
        StringBuilder result = new StringBuilder();
        boolean has_squs = false;

        for (int i = 0; i < parts.length; i++) {
            if( Check_num( parts [i] )) {
                double Thres = 0.3;
                if( !has_squs){
                    Thres = 0.7;
                }
                if ( random.nextDouble() < Thres ||(i == parts.length -1 && !has_squs)) {
                    if ( random.nextBoolean() ) {
                        result.append(parts[i]);
                        result.append("²");
                        has_squs = true;
                    } else {
                        result.append("√");
                        result.append(parts[i]);
                        has_squs = true;
                    }
                } else {
                    result.append(parts[i]);
                }
            } else {
                result.append(parts[i]);
            }
            if( i < parts.length -1 ) {
                result.append(" ");
            }
        }
        return result.toString();
    }

    protected String add_sins(String expression) {
        String[] parts = expression.split(" ");
        StringBuilder result = new StringBuilder();
        String[] functions = {"sin", "cos", "tan"};
        boolean has_func = false;

        for (int i = 0; i < parts.length; i++) {
            double Thres = 0.4;
            if(!has_func){Thres = 0.8;}
            if(Check_num(parts[i]))
            {
                if ( random.nextDouble() < Thres ||(i == parts.length-1 && !has_func) ) {
                    String func = functions[random.nextInt(functions.length)];
                    result.append(func).append("(").append(parts[i]).append(")");
                } else {
                    result.append(parts[i]);
                }
            } else {
                result.append(parts[i]);
            }
            if( i < parts.length-1 ) {
                result.append(" ");
            }

        }

        return result.toString();
    }
}