#include <assert.h>
#include <clingo.h>
#include <stdio.h>
#include <stdlib.h>

bool print_model(clingo_model_t const *model) {
    bool ret = true;
    clingo_symbol_t *atoms = NULL;
    size_t atoms_n;
    clingo_symbol_t const *it, *ie;
    char *str = NULL;
    size_t str_n = 0;

    // determine the number of (shown) symbols in the model
    if (!clingo_model_symbols_size(model, clingo_show_type_shown, &atoms_n)) {
        goto error;
    }

    // allocate required memory to hold all the symbols
    if (!(atoms = (clingo_symbol_t *)malloc(sizeof(*atoms) * atoms_n))) {
        clingo_set_error(clingo_error_bad_alloc, "could not allocate memory for atoms");
        goto error;
    }

    // retrieve the symbols in the model
    if (!clingo_model_symbols(model, clingo_show_type_shown, atoms, atoms_n)) {
        goto error;
    }

    printf("Model:");

    for (it = atoms, ie = atoms + atoms_n; it != ie; ++it) {
        size_t n;
        char *str_new;

        // determine size of the string representation of the next symbol in the model
        if (!clingo_symbol_to_string_size(*it, &n)) {
            goto error;
        }

        if (str_n < n) {
            // allocate required memory to hold the symbol's string
            if (!(str_new = (char *)realloc(str, sizeof(*str) * n))) {
                clingo_set_error(clingo_error_bad_alloc, "could not allocate memory for symbol's string");
                goto error;
            }

            str = str_new;
            str_n = n;
        }

        // retrieve the symbol's string
        if (!clingo_symbol_to_string(*it, str, n)) {
            goto error;
        }

        printf(" %s", str);
    }

    printf("\n");
    goto out;

error:
    ret = false;

out:
    if (atoms) {
        free(atoms);
    }
    if (str) {
        free(str);
    }

    return ret;
}

bool solve(clingo_control_t *ctl, clingo_solve_result_bitset_t *result) {
    bool ret = true;
    clingo_solve_handle_t *handle;
    clingo_model_t const *model;

    // get a solve handle
    if (!clingo_control_solve(ctl, clingo_solve_mode_yield, NULL, 0, NULL, NULL, &handle)) {
        goto error;
    }
    // loop over all models
    while (true) {
        if (!clingo_solve_handle_resume(handle)) {
            goto error;
        }
        if (!clingo_solve_handle_model(handle, &model)) {
            goto error;
        }
        // print the model
        if (model) {
            print_model(model);
        }
        // stop if there are no more models
        else {
            break;
        }
    }
    // close the solve handle
    if (!clingo_solve_handle_get(handle, result)) {
        goto error;
    }

    goto out;

error:
    ret = false;

out:
    // free the solve handle
    return clingo_solve_handle_close(handle) && ret;
}

int main(int argc, char const **argv) {
    char const *error_message;
    int ret = 0;
    size_t offset;
    clingo_solve_result_bitset_t solve_ret;
    clingo_control_t *ctl;
    clingo_symbolic_atoms_t const *atoms;
    clingo_backend_t *backend;
    clingo_atom_t atom_ids[4];
    char const *atom_strings[] = {"a", "b", "c"};
    clingo_literal_t body[2];
    clingo_part_t parts[] = {{"base", NULL, 0}};

    // create a control object and pass command line arguments
    if (!clingo_control_new(argv + 1, argc - 1, NULL, NULL, 20, &ctl) != 0) {
        goto error;
    }

    // add a logic program to the base part
    if (!clingo_control_add(ctl, "base", NULL, 0, "{a; b; c}.")) {
        goto error;
    }

    // ground the base part
    if (!clingo_control_ground(ctl, parts, 1, NULL, NULL)) {
        goto error;
    }

    // get the container for symbolic atoms
    if (!clingo_control_symbolic_atoms(ctl, &atoms)) {
        goto error;
    }
    // get the ids of atoms a, b, and c
    offset = 0;
    for (char const **it = atom_strings, **ie = it + sizeof(atom_strings) / sizeof(*atom_strings); it != ie; ++it) {
        clingo_symbol_t sym;
        clingo_symbolic_atom_iterator_t atom_it, atom_ie;
        clingo_literal_t lit;
        bool equal;

        // lookup the atom
        if (!clingo_symbol_create_id(*it, true, &sym)) {
            goto error;
        }
        if (!clingo_symbolic_atoms_find(atoms, sym, &atom_it)) {
            goto error;
        }
        if (!clingo_symbolic_atoms_end(atoms, &atom_ie)) {
            goto error;
        }
        if (!clingo_symbolic_atoms_iterator_is_equal_to(atoms, atom_it, atom_ie, &equal)) {
            goto error;
        }
        assert(!equal);
        (void)equal;

        // get the atom's id
        if (!clingo_symbolic_atoms_literal(atoms, atom_it, &lit)) {
            goto error;
        }
        atom_ids[offset++] = lit;
    }

    // get the backend
    if (!clingo_control_backend(ctl, &backend)) {
        goto error;
    }

    // prepare the backend for adding rules
    if (!clingo_backend_begin(backend)) {
        goto error;
    }

    // add an additional atom (called d below)
    if (!clingo_backend_add_atom(backend, NULL, &atom_ids[3])) {
        goto error;
    }

    // add rule: d :- a, b.
    body[0] = atom_ids[0];
    body[1] = atom_ids[1];
    if (!clingo_backend_rule(backend, false, &atom_ids[3], 1, body, sizeof(body) / sizeof(*body))) {
        goto error;
    }

    // add rule: :- not d, c.
    body[0] = -(clingo_literal_t)atom_ids[3];
    body[1] = atom_ids[2];
    if (!clingo_backend_rule(backend, false, NULL, 0, body, sizeof(body) / sizeof(*body))) {
        goto error;
    }

    // finalize the backend
    if (!clingo_backend_end(backend)) {
        goto error;
    }

    // solve
    if (!solve(ctl, &solve_ret)) {
        goto error;
    }

    goto out;

error:
    if (!(error_message = clingo_error_message())) {
        error_message = "error";
    }

    printf("%s\n", error_message);
    ret = clingo_error_code();

out:
    if (ctl) {
        clingo_control_free(ctl);
    }

    return ret;
}
