///
/// This is example code from Chapter 6.6 "Trying the
/// first version" of
/// "Software - Principles and Practice using C++"
/// by Bjarne Stroustrup
//

#include "../std_lib_facilities.h"

//------------------------------------------------------------------------------

class Token {
public:
    char kind;        // what kind of token
    double value;     // for numbers: a value
    Token(char ch)    // make a Token from a char
        :kind(ch), value(0) { }
    Token(char ch, double val)     // make a Token from a char and a double
        :kind(ch), value(val) { }
};

//------------------------------------------------------------------------------

Token get_token()    // read a token from cin
{
    char ch;
    cin >> ch;    // note that >> skips whitespace (space, newline, tab, etc.)

    switch (ch) {
 //not yet   case ';':    // for "print"
 //not yet   case 'q':    // for "quit"
    case '(': case ')': case '+': case '-': case '*': case '/':
        return Token(ch);        // let each character represent itself
    case '.':
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
    {
        cin.putback(ch);         // put digit back into the input stream
        double val;
        cin >> val;              // read a floating-point number
        return Token('8',val);   // let '8' represent "a number"
    }
    default:
        error("Bad token");
    }
}

//------------------------------------------------------------------------------

double expression();  /// read and evaluate a Expression

//------------------------------------------------------------------------------

double term();        /// read and evaluate a Term

//------------------------------------------------------------------------------

double primary()     /// read and evaluate a Primary
{
    Token t = get_token();
    switch (t.kind) {
    case '(':    // handle '(' expression ')'
    {
        double d = expression();
        t = get_token();
        if (t.kind != ')') error("')' expected");
        return d;
    }
    case '8':            // we use '8' to represent a number
        return t.value;  // return the number's value
    default:
        error("primary expected");
    }
}
//------------------------------------------------------------------------------

int main()
try {
    while (cin)
        cout << "=" << expression() << '\n';
}
catch (exception& e) {
    cerr << e.what() << endl;
    return 1;
}
catch (...) {
    cerr << "exception \n";
    return 2;
}

//------------------------------------------------------------------------------

double expression()
{
    double left = term();      // read and evaluate a Term
    cout << "\nterm's left = " << left << endl;
    Token t = get_token();     // get the next token
    ///cout << "\nt.kind = " << t.kind << " t.value = " << t.value;
    while(true) {
        switch(t.kind) {
        case '+':
            left += term();    // evaluate Term and add
            t = get_token();
            break;
        case '-':
            left -= term();    // evaluate Term and subtract
            t = get_token();
            break;
        default:
            return left;       // finally: no more + or -: return the answer
        }
    }
}

//------------------------------------------------------------------------------

double term()
{
    double left = primary();
    Token t = get_token();     // get the next token

    while(true) {
        switch (t.kind) {
        case '*':
            left *= primary();
            t = get_token(); ///if expression is 14*2+3
            /// then we'd have left = 28 and t = ('+',0)
            break;
        case '/':
        {
            double d = primary();
            if (d == 0) error("divide by zero");
            left /= d;
            t = get_token();
            break;
        }
        default:
            return left;  /// returns 2 but ate ('+',0)
        }
    }
}

//------------------------------------------------------------------------------