//
// This is example code from Chapter 23.4 "Maps" of
// "Programming -- Principles and Practice Using C++" by Bjarne Stroustrup
//

#include<string>
#include<vector>
#include<map>
#include<fstream>
#include<iostream>

using namespace std;

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

// We define a Message as a pair of iterators into a vector<string> (our vector of lines):
typedef vector<string>::const_iterator Line_iter;

class Message {  // a Message points to the first and the last line of a message
    Line_iter first;
    Line_iter last;
public:
    Message(Line_iter p1, Line_iter p2) :first(p1), last(p2) { }
    Line_iter begin() const { return first; }
    Line_iter end() const { return last; }
    // ...
};

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

typedef vector<Message>::const_iterator Mess_iter;

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

// We define a Mail_file as a structure holding lines of text and messages:
struct Mail_file {        // a Mail_file holds all the lines from a file
                          // and simplifies access to messages
    string name;          // file name
    vector<string> lines; // the lines in order
    vector<Message> m;    // Messages in order

    Mail_file(const string& n);  // read file n into lines

    Mess_iter begin() const { return m.begin(); }
    Mess_iter end() const { return m.end(); }
};

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

// find the name of the sender in a Message;
// return true if found
// if found, place the sender's name in s:
bool find_from_addr(const Message* m, string& s);

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

// return the subject of the Message, if any, otherwise "":
string find_subject(const Message* m);

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

int main()
{
    Mail_file mfile("my-mail-file.txt");        // initialize mfile from a file

    // first gather messages from each sender together in a multimap:

    multimap<string, const Message*> sender;

    for (Mess_iter p = mfile.begin(); p!=mfile.end(); ++p) {
        const Message& m = *p;
        string s;
        if (find_from_addr(&m,s))
            sender.insert(make_pair(s,&m));
    }

    // now iterate through the multimap
    // and extract the subjects of Goofy's messages:
    typedef multimap<string, const Message*>::const_iterator MCI;
    pair<MCI,MCI> pp = sender.equal_range("John Doe");
    for(MCI p = pp.first; p!=pp.second; ++p)
        cout << find_subject(p->second) << '\n';
}

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