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package algs35;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac Interpreter.java
 *  Execution:    java Interpreter
 *  Dependencies: In.java ST.java
 *
 *  Parses simple arithmetic expressions of the form z = x and
 *  z = x + y, where x and y can be symbolic variables or real
 *  numbers. Uses a symbol table to store the mapping between
 *  variable names and their values.
 *
 *
 *  % java Interpreter
 *  >> x := 34
 *  x = 34.0
 *
 *  >> y := 23 * x
 *  y := 782.0
 *
 *  >> z := x ^ y
 *  z := Infinity
 *
 *  >> z := y ^ 2
 *  z := 611524.0
 *
 *  >> x
 *  x := 34.0
 *
 *  >> x := sqrt 2
 *  x := 1.4142135623730951
 *
 *  >> <Ctrl-d>
 *
 *  Remarks
 *  -------
 *
 *   - Currently allows values on the LHS, e.g., 17 = x + y,
 *     and treats "17" as a variable name.
 *
 *
 *************************************************************************/

public class XInterpreter {

  public static void main(String[] args) {

    ST<String, Double> st = new ST<>();

    // read in one line at a time and parse
    String line;
    StdOut.print(">> ");
    while ((line = StdIn.readLine()) != null) {
      String[] tokens = line.split("\\s");

      // singe variable - just print out its value
      if (tokens.length == 1)  {
        String zvar = tokens[0];
        StdOut.println(zvar + " := " + st.get(zvar));
      }

      // z = x
      else if (tokens.length == 3) {
        String zvar = tokens[0];
        String eq   = tokens[1];
        String xvar = tokens[2];
        if (!eq.equals(":=")) throw new Error("Illegal assignment");
        Double x = st.get(xvar);
        if (x == null) x = Double.parseDouble(xvar);
        st.put(zvar, x);
        StdOut.println(zvar + " := " + st.get(zvar));
      }

      // z = function x
      else if (tokens.length == 4) {
        String zvar = tokens[0];
        String eq   = tokens[1];
        String func = tokens[2];
        String xvar = tokens[3];
        if (!eq.equals(":=")) throw new Error("Illegal assignment");
        Double x = st.get(xvar);
        if (x == null) x = Double.parseDouble(xvar);
        if      (func.equals("sin")) st.put(zvar, Math.sin(x));
        else if (func.equals("cos")) st.put(zvar, Math.cos(x));
        else if (func.equals("sqrt")) st.put(zvar, Math.sqrt(x));
        else if (func.equals("-")) st.put(zvar, -x);
        else throw new Error("Illegal function");
        StdOut.println(zvar + " := " + st.get(zvar));
      }

      // z = x + y
      else if (tokens.length == 5) {
        String zvar = tokens[0];
        String eq   = tokens[1];
        String xvar = tokens[2];
        String op   = tokens[3];
        String yvar = tokens[4];
        if (!eq.equals(":=")) throw new Error("Illegal assignment");
        Double x = st.get(xvar);
        Double y = st.get(yvar);
        if (x == null) x = Double.parseDouble(xvar);
        if (y == null) y = Double.parseDouble(yvar);
        if      (op.equals("+")) st.put(zvar, x + y);
        else if (op.equals("-")) st.put(zvar, x - y);
        else if (op.equals("*")) st.put(zvar, x * y);
        else if (op.equals("/")) st.put(zvar, x / y);
        else if (op.equals("^")) st.put(zvar, Math.pow(x, y));
        else throw new Error("Illegal operator");
        StdOut.println(zvar + " = " + st.get(zvar));
      }

      else throw new Error("Illegal expression");
      StdOut.println();
      StdOut.print(">> ");
    }

  }
}