// https://quuxplusone.github.io/blog/2019/03/06/pythagorean-triples/

#include <stdio.h>
#include <stc/coroutine.h>
#include <stc/algorithm.h>

typedef struct {
    int max_triples;
    int a, b, c;
} Triple;

// Create an iterable generator over Triple with count items.
// Requires coroutine Triple_next() and function Triple_begin() to be defined.
cco_iter_struct(Triple,
    int count;
);

int Triple_next(Triple_iter* it) {
    Triple* g = it->ref; // note: before cco_routine
    cco_routine(it)
    {
        for (g->c = 5;; ++g->c) {
            for (g->a = 1; g->a < g->c; ++g->a) {
                for (g->b = g->a; g->b < g->c; ++g->b) {
                    if (g->a*g->a + g->b*g->b == g->c*g->c) {
                        if (it->count++ == g->max_triples)
                            cco_return;
                        cco_yield();
                    }
                }
            }
        }
        cco_final:
        it->ref = NULL; // stop the iterator
    }
    return 0;
}

Triple_iter Triple_begin(Triple* g) {
    Triple_iter it = {.ref=g};
    Triple_next(&it);
    return it;
}


int main(void)
{
    puts("Pythagorean triples.\nGet max 200 triples with c < 50:");
    Triple triple = {.max_triples=200};

    c_foreach (i, Triple, triple) {
        if (i.ref->c < 50)
            printf("%u: (%d, %d, %d)\n", i.count, i.ref->a, i.ref->b, i.ref->c);
        else
            cco_stop(&i);
    }

    puts("\nGet the 10 first triples with odd a's and a <= 20:");
    c_forfilter (i, Triple, triple,
                    i.ref->a <= 20 &&
                    (i.ref->a & 1) &&
                    c_flt_take(i, 10)
    ){
        printf("%d: (%d, %d, %d)\n", c_flt_getcount(i), i.ref->a, i.ref->b, i.ref->c);
    }
}