// This file contains some examples of using features of C++ that we would
// describe as functional programming, including the use of anonymous functions
// or lambdas.

#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <algorithm>
#include <numeric>

using namespace std;

// used to display the contents of a vector
template<typename T>
string to_string(T t) {
    ostringstream out;
    auto itr = t.begin();
    out << "[";
    if (itr != t.end()) {
        out << *itr;
        itr++;
        while (itr != t.end()) {
            out << ", " << *itr;
            itr++;
        }
    }
    out << "]";
    return out.str();
}

// this defines a named function for comparing two strings and ordering them by
// their length
bool less_length(const string & s1, const string & s2) {
    return s1.length() < s2.length();
}

int main() {
    vector<string> words {"four", "score", "and", "seven", "years", "ago",
            "our", "fathers", "brought", "forth", "on", "this", "continent",
            "a", "new", "nation", "conceived", "in", "liberty", "and",
            "dedicated", "to", "the", "proposition", "that", "all", "men",
            "are", "created", "equal"};
    cout << "words before sort = " << to_string(words) << endl;
    sort(words.begin(), words.end());
    cout << "words after sort = " << to_string(words) << endl;
    stable_sort(words.begin(), words.end(), less_length);
    cout << "words after custom sort = " << to_string(words) << endl;
    cout << endl;

    // lambdas--anonymous functions
    string s = "Hello THerE!";
    for_each(s.begin(), s.end(), [](char ch){cout << ch << endl;});
    for_each(s.begin(), s.end(), [](char & ch){ch = tolower(ch);});
    cout << "s = " << s << endl;
    cout << endl;

    vector<int> numbers1 {3, 18, 7, 22, 3, 10, -2, 23, 52, 7, 9, 6, 14};
    cout << "numbers1 = " << to_string(numbers1) << endl;
    int sum = accumulate(numbers1.begin(), numbers1.end(), 0);
    cout << "sum of numbers1 = " << sum << endl;
    int product =
        accumulate(numbers1.begin(), numbers1.end(), 1, multiplies<int>());
    cout << "product of numbers1 = " << product << endl;
    cout << endl;

    vector<int> numbers2;
    copy_if(numbers1.begin(), numbers1.end(), back_inserter(numbers2),
            [](int n){return n % 3 == 0;});
    cout << "numbers2 = " << to_string(numbers2) << endl;
    int max;
    cout << "max int? ";
    cin >> max;
    vector<int> numbers3;
    auto f = [&max](int n){return n <= max;};
    max = max - 10;
    copy_if(numbers1.begin(), numbers1.end(), back_inserter(numbers3), f);
    cout << "numbers3 = " << to_string(numbers3) << endl;
    cout << endl;

    return 0;
}