/* The plan

   1. read the file into an array

   2. read chemical formula from user

   3. be able to search the table

   4. work out total weight

*/

const bool debugging = false;

#include <string>
#include <iostream>
#include <fstream>

using namespace std;

struct element
{ string symbol, name;
  int atnumber;
  double atweight; };

// defined "element" as a new type of variable/constant

void print(element X)
{ cout << X.symbol << "(\"" << X.name << "\", ";
  cout << X.atnumber << ", " << X.atweight << ")\n"; }

void read(element & e, ifstream & f)
{ f >> e.symbol >> e.name >> e.atweight; }

struct nicestream
{ string wholeline;
  int numtaken;
  int length;
  bool ended; };

char readchar(nicestream & ns)
{ char c;
  if (ns.numtaken >= ns.length)
    c = '\n';
  else
    c = ns.wholeline[ns.numtaken];
  ns.numtaken += 1;
  return c; }

char sneakchar(const nicestream & ns)
{ return ns.wholeline[ns.numtaken]; }

void unreadchar(nicestream & ns)
{ if (ns.numtaken > 0)
    ns.numtaken -= 1; }

void refill(nicestream & ns)
{ getline(cin, ns.wholeline);
  if (cin.fail())
  { ns.wholeline = "\n";
    ns.ended = true; }
  else
  { ns.wholeline += '\n';
    ns.ended = false; }
  ns.length = ns.wholeline.length();
  ns.numtaken = 0; }

bool ok(const nicestream & ns)
{ return ! ns.ended; }

element search(string sy, element tab[], int max)
{ for (int i = 1; i <= max; i += 1)
    if (tab[i].symbol == sy)
      return tab[i];
  tab[0].atnumber = 0;
  return tab[0]; }

void prepare_file(ifstream & f, string fname)
{ f.open(fname.c_str());
  if (f.fail())
  { cout << "Can't open file '" << fname << "'\n";
    exit(1); } }

int read_table(ifstream & f, element ptable[])
{ for (int atno = 1; atno < 150; atno += 1)
  { element e;
    read(e, f);
    if (f.fail())
      return atno - 1;
    e.atnumber = atno;
    ptable[atno] = e; } }

void checktable(element ptable[], int numels)
{ cout << "Finished reading " << numels << " elements\n";
  if (debugging)
    for (int i = 1; i <= numels; i += 1)
      print(ptable[i]); 
  if (debugging)
  { while (true)
    { cout << "type a symbol. ";
      string s;
      cin >> s;
      element x = search(s, ptable, numels);
      if (x.atnumber == 0)
        cout << "no such thing\n";
      else
        print(x); } } }

string read_symbol(nicestream & nin)
{ string symbol = "";
  char c = readchar(nin);
  symbol += c;
  c = sneakchar(nin);
  if (c >= 'a' && c <= 'z')
  { c = readchar(nin);
    symbol += c; }
  return symbol; }

int readnumber(nicestream & nin)
{ int num = 0;
  char c = readchar(nin);
  while (c >= '0' && c <= '9')
  { num = num * 10 + c - '0';
     c = readchar(nin); }
  unreadchar(nin);
  return num; }

double process_formula(nicestream & nin, element ptab[], int numels)
{ double total = 0.0, wt;
  char c;
  while (true)
  { c = sneakchar(nin);
    if (c >= 'A' && c <= 'Z')
    { string sym = read_symbol(nin);
      element e = search(sym, ptab, numels);
      if (e.atnumber == 0)
      { cout << "no such thing\n";
        return 0.0; }
      wt = e.atweight;
      cout << "  " << sym << ": " << wt; }
    else if (c == '(')
    { readchar(nin);
      wt = process_formula(nin, ptab, numels);
      cout << "  (...): " << wt; }
    c = sneakchar(nin);
    if (c >= '0' && c <= '9')
    { int value = readnumber(nin);
      cout << " * " << value << " = " << wt*value;
      total += wt * value; }
    else
      total += wt;
    cout << "\n";
    c = sneakchar(nin);
    if ((c < 'A' || c > 'Z') && c != '(')
      break; }
  if (c == '\n' || c == ')')
  { readchar(nin);
    return total; }
  else
  { readchar(nin);
    cout << "bad character '" << c << "'\n";
    return 0.0; } }

int main()
{
  ifstream f;
  prepare_file(f, "/home/www/class/een118/atwt.txt");

  element ptable[150];
  int numels = read_table(f, ptable);
  f.close();
  checktable(ptable, numels);

  nicestream nin;
  while (true)
  { cout << "formula: ";
    refill(nin);
    double molwt = process_formula(nin, ptable, numels);
    cout << "The molecular weight is " << molwt << "\n\n"; }

/* type something like
   NaCl
   H2SO4
   CaCO3
   Ca(NO3)2
*/
}