void display(Object *root);

void
display_pair(Object *root) {
    display(root->car);
    if (root->cdr->type == OBJ_TYPE_PAIR) {
        printf(" ");
        display_pair(root->cdr);
    } else if (root->cdr->type == OBJ_TYPE_NIL) {
        return;
    } else {
        printf(" . ");
        display(root->cdr);
    }
}

void
display(Object *root) {
    if (root == NULL) {
        return;
    }

    switch (root->type) {
        case OBJ_TYPE_FIXNUM: {
            printf("%zd", root->fixnum);
        } break;
        case OBJ_TYPE_BOOL: {
            if (root->boolean) {
                printf("true");
            } else {
                printf("false");
            }
        } break;
        case OBJ_TYPE_NIL: {
            printf("()");
        } break;
        case OBJ_TYPE_STRING: {
            printf("\"%.*s\"", (int)root->string_n, root->string);
        } break;
        case OBJ_TYPE_SYMBOL: {
            printf(":%.*s", (int)root->symbol_n, root->symbol);
        } break;
        case OBJ_TYPE_PAIR: {
            printf("(");
            display_pair(root);
            printf(")");
        } break;
        case OBJ_TYPE_PROCEDURE: {
            printf("#{procedure}");
        } break;
    }
}

Object *
eval(Object *root) {
    switch (root->type) {
        case OBJ_TYPE_FIXNUM:
        case OBJ_TYPE_BOOL:
        case OBJ_TYPE_NIL:
        case OBJ_TYPE_STRING: {
            return root;
        } break;
        case OBJ_TYPE_SYMBOL: {
            Object *value = find_environment_symbol(root);
            if (value == NULL) {
                printf("error: symbol not found: `");
                display(root);
                printf("`\n");
                return obj_nil;
            }
            return value;
        } break;
        case OBJ_TYPE_PAIR: {
            if (root->car->type == OBJ_TYPE_SYMBOL) {
                Object *value = find_environment_symbol(root->car);
                if (value == NULL) {
                    printf("error: symbol not found: `");
                    display(root->car);
                    printf("`\n");
                    return obj_nil;
                }
                if (value->type == OBJ_TYPE_PROCEDURE) {
                    return value->proc(root->cdr);
                }
            }
        } break;
        default: {
            printf("error: can't eval type %d.\n", root->type);
        } break;
    }
    return obj_nil;
}

Object *
proc_add(Object *args) {
    // Extract first parameter.
    Object *car = eval(args->car);
    if (car == NULL) {
        fprintf(stderr, "error: not enough arguments\n");
        return obj_nil;
    }
    if (car->type != OBJ_TYPE_FIXNUM) {
        fprintf(stderr, "addition not supported for type %d\n", car->type);
        return obj_nil;
    }
    args = args->cdr;
    ssize_t tot = car->fixnum;

    while (args->type == OBJ_TYPE_PAIR) {
        Object *car = eval(args->car);
        if (car == NULL) {
            car = obj_nil;
        }
        if (car->type != OBJ_TYPE_FIXNUM) {
            fprintf(stderr, "addition not supported for type %d\n", car->type);
            return obj_nil;
        }
        tot += car->fixnum;
        args = args->cdr;
    }
    return make_fixnum(tot);
}

Object *
proc_sub(Object *args) {
    // Extract first parameter.
    Object *car = eval(args->car);
    if (car == NULL) {
        fprintf(stderr, "error: not enough arguments\n");
        return obj_nil;
    }
    if (car->type != OBJ_TYPE_FIXNUM) {
        fprintf(stderr, "error: sub not supported for type %d\n", car->type);
        return obj_nil;
    }
    args = args->cdr;
    ssize_t tot = car->fixnum;

    while (args->type == OBJ_TYPE_PAIR) {
        car = eval(args->car);
        if (car == NULL) {
            car = obj_nil;
        }
        if (car->type != OBJ_TYPE_FIXNUM) {
            fprintf(stderr, "error: sub not supported for type %d\n", car->type);
            return obj_nil;
        }
        tot -= car->fixnum;
        args = args->cdr;
    }
    return make_fixnum(tot);
}

Object *
proc_mul(Object *args) {
    // Extract first parameter.
    Object *car = eval(args->car);
    if (car == NULL) {
        fprintf(stderr, "error: not enough arguments\n");
        return obj_nil;
    }
    if (car->type != OBJ_TYPE_FIXNUM) {
        fprintf(stderr, "error: mult not supported for type %d\n", car->type);
        return obj_nil;
    }
    args = args->cdr;
    ssize_t tot = car->fixnum;

    while (args->type == OBJ_TYPE_PAIR) {
        Object *car = eval(args->car);
        if (car == NULL) {
            car = obj_nil;
        }
        if (car->type != OBJ_TYPE_FIXNUM) {
            fprintf(stderr, "error: mult not supported for type %d\n", car->type);
            return obj_nil;
        }
        tot *= car->fixnum;
        args = args->cdr;
    }
    return make_fixnum(tot);
}

Object *
proc_div(Object *args) {
    // Extract first parameter.
    Object *car = eval(args->car);
    if (car == NULL) {
        fprintf(stderr, "error: not enough arguments\n");
        return obj_nil;
    }
    args = args->cdr;
    ssize_t tot = car->fixnum;

    while (args->type == OBJ_TYPE_PAIR) {
        Object *car = eval(args->car);
        if (car == NULL) {
            car = obj_nil;
        }
        if (car->type != OBJ_TYPE_FIXNUM) {
            fprintf(stderr, "error: div not supported for type %d\n", car->type);
            return obj_nil;
        }
        if (car->fixnum == 0) {
            fprintf(stderr, "error: division by zero\n");
            return obj_nil;
        }
        tot /= car->fixnum;
        args = args->cdr;
    }
    return make_fixnum(tot);
}

Object *
proc_display(Object *args) {
    if (args == NULL) {
        return obj_nil;
    }
    if (args->type == OBJ_TYPE_PAIR) {
        display(eval(args->car));
    }
    return obj_nil;
}