feat: Do basic Shell

Author: MarcellPerger1

src/main/java/net/marcellperger/mathexpr/interactive/Shell.java

@@ -1,13 +1,56 @@
 package net.marcellperger.mathexpr.interactive;
 
+import net.marcellperger.mathexpr.MathSymbol;
+import net.marcellperger.mathexpr.parser.ExprParseException;
+import net.marcellperger.mathexpr.parser.Parser;
+import net.marcellperger.mathexpr.util.Input;
+import net.marcellperger.mathexpr.util.MathUtil;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.io.PrintStream;
 import java.util.Arrays;
 
 import static net.marcellperger.mathexpr.util.Input.input;
 
 public class Shell {
+    Input in;
+    PrintStream out;
+
+    public Shell() {
+        in = new Input();
+        out = System.out;
+    }
+
     public static void main(String[] args) {
-        System.out.println("args = " + Arrays.toString(args));
-        System.out.print("Enter something: ");
-        System.out.println("You entered " + input());
+        new Shell().run();
+    }
+
+    // TODO run() until exit better - parse exit command/Ctrl+C
+    // TODO fails badly with unchecked exception on parsing `12 + (`
+
+    public void run() {
+        //noinspection InfiniteLoopStatement
+        while (true) getAndRunCommand();
+    }
+
+    public void getAndRunCommand() {
+        runCommand(in.getInput(">? "));
+    }
+    public void runCommand(String cmd) {
+        @Nullable MathSymbol sym = parseCmdOrPrintError(cmd);
+        if(sym == null) return;
+        double value = sym.calculateValue();
+        out.println(MathUtil.roundToSigFigs(value, 10));
+    }
+    public @Nullable MathSymbol parseCmdOrPrintError(String cmd) {
+        // No special commands so pass straight to parser
+        Parser p = new Parser(cmd);
+        try {
+            return p.parse();
+        } catch (ExprParseException exc) {
+            out.println(exc);
+            return null;
+        }
     }
 }

src/main/java/net/marcellperger/mathexpr/util/Input.java

@@ -46,7 +46,7 @@ public String getInput() {
         return sc.nextLine();
     }
     public String getInput(String prompt) {
-        Objects.requireNonNull(ps, "An OutputStream is required to use Input.getInput(prompt)").println(prompt);
+        Objects.requireNonNull(ps, "An OutputStream is required to use Input.getInput(prompt)").print(prompt);
         return sc.nextLine();
     }
 

src/main/java/net/marcellperger/mathexpr/util/MathUtil.java

@@ -0,0 +1,20 @@
+package net.marcellperger.mathexpr.util;
+
+import org.jetbrains.annotations.Range;
+
+public class MathUtil {
+    protected MathUtil() {}
+
+    public static double roundToSigFigs(double value, @Range(from=1, to=Integer.MAX_VALUE) int sigFigs) {
+        int mostSignificantDigit = (int)Math.floor(Math.log10(value));
+        int roundToDigit = mostSignificantDigit - sigFigs + 1;
+        return roundToDP(value, roundToDigit);
+    }
+
+    public static double roundToNearest(double value, double nearest) {
+        return Math.round(value / nearest) * nearest;
+    }
+    public static double roundToDP(double value, int decimalPlaces) {
+        return roundToNearest(value, Math.pow(10, decimalPlaces));
+    }
+}