#include <istream>
#include <string>
#include <vector>
#include <stdexcept>
#include "parse_csv.h"
using namespace std;

/*************

Format defined:
  https://tools.ietf.org/html/rfc4180
See also:
  https://en.wikipedia.org/wiki/Comma-separated_values

We depart from the RFC by ignoring \r, so that lines can
end with either \r\n (dos style) or simply \n (unix style).

We check for malformed quoted fields and throw exceptions.

The last line of the input .csv file may or may not
contain a newline:
:; echo -en "xxx\n" | ./parse_csv_demo - | od -b -Anone
 170 170 170 012
:; echo -en "xxx" | ./parse_csv_demo - | od -b -Anone
 170 170 170 012

A line containing nothing but the newline has one field
with a zero-length datum:
:; echo -en "\n" | ./parse_csv_demo - | od -b -Anone
 012

A line containing no data /and/ no newline isn't a line
at all.  No line, no fields, no data:
:; echo -en "" | ./parse_csv_demo - | wc
      0       0       0

************/

string const Q("\"");

enum class CSVState {
    Start,
    UnquotedField,
    QuotedField,
    QuoteInQuote
};

// Read one row of .csv table.
// Return a zero-length vector if we encounter EoF
//   before seeing any data.
// Note that a table row can extend across multiple .csv file lines,
//   if there are embedded newlines.
//
// Within quoted fields, we accept commas, quotes, and newlines,
//   e.g "Hughie, ""Louie"", Dewey".
template <class datum = qstring>
vector<datum> readCSVRow(istream& input) {
  using namespace std;
  if (input.eof()) return vector<datum>(0);
  CSVState state = CSVState::Start;
  vector<datum> fields(0);
  char c;
  for (;;) {
    input.read(&c, 1);
    if (input.eof()) {
      if (state == CSVState::QuotedField)
        throw runtime_error("Unterminated quote in .csv file in field# "
                               + to_string(fields.size())
                    + "\n... namely <"
                    + Q + fields.back() + ">");
      break;
    }
    if (!input.good()) throw runtime_error("input error in .csv file");

// if we made it this far, the line contains at least one datum:
    if (fields.size() == 0) fields.push_back(datum());
    switch (state) {
      case CSVState::Start:
        switch (c) {
          case ',':     // zero-length field
            fields.push_back(datum());
            break;
          case '"':
            state = CSVState::QuotedField;
// This is no-op if the datum is not of type qstring:
            set_q(fields.back(), 1);
            break;
          case '\r':
            break;
          case '\n':
            goto EndRecord;
          default:
            state = CSVState::UnquotedField;
            fields.back().push_back(c);
            break;
        }
        break;
      case CSVState::UnquotedField:
        switch (c) {
          case ',': // start a new field:
            state = CSVState::Start;
            fields.push_back(datum());
            break;
          case '"': throw runtime_error
            ("Stray quote in .csv file in field# "
               + to_string(fields.size())
               + "\n... namely <"
               + fields.back() + Q + ">"
            );
            break;
          case '\r': break;
          case '\n': goto EndRecord;
          default:  fields.back().push_back(c);
            break;
        }
        break;
      case CSVState::QuotedField:
        switch (c) {
          case '"': state = CSVState::QuoteInQuote;
            break;
// Accept anything except quote here;
// that includes comma, \r, and \n.
          default:  fields.back().push_back(c);
            break;
        }
        break;
// Previous state saw a quote; we consider what follows:
      case CSVState::QuoteInQuote:
        switch (c) {
          case ',':     // comma after closing quote
            state = CSVState::Start;
            fields.push_back(datum());
            break;
          case '"':     // double ", map to plain "
            fields.back().push_back('"');
            state = CSVState::QuotedField;
            break;
          case '\r': break;
          case '\n': goto EndRecord;
          default:  throw runtime_error
              ("Extraneous verbiage in .csv file after quoted field# "
                    + to_string(fields.size())
                    + "\n... namely <"
                    + Q + fields.back() + Q
                    + string(1,c) +">");
            break;
        }
        break;
    }
  }
  EndRecord:;;;;
  return fields;
}

// Read entire CSV file.
// Within quoted fields, we accept commas, quotes, and newlines,
// e.g "Hughie, ""Louie"", Dewey".
template <class datum = qstring>
vector<vector<datum> > readCSV(istream &in) {
  using namespace std;
  vector<vector<datum> > table;
  datum row;
  while (!in.eof()) {
    auto fields = readCSVRow<datum>(in);
    if (fields.size() == 0) break;
    table.push_back(fields);
  }
  return table;
}

// Explicit instantiation for the <qstring> version.
// If you want some other version, you'll have to instantiate it.
template vector<qstring> readCSVRow<qstring>(istream& input);
template vector<vector<qstring> >readCSV<qstring>(istream &in);
// Apparently it's not necessary to mention get_q() here,
// but probably more portable to do it anyway:
////template int get_q<qstring>(qstring const&);

#if 1
// Explicit instantiation for the <string> version.
template vector<string> readCSVRow<string>(istream& input);
template vector<vector<string> >readCSV<string>(istream &in);
/////template int get_q<string>(string const&);
#endif