#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <errno.h>
#include "tree.h"

/* alokuje nový uzel */
static struct expr_node *alloc_node(void) {
    return malloc(sizeof(struct expr_node));
}

struct expr_node *node_create_const(double val) {
    struct expr_node *node = alloc_node();
    if (!node) return NULL;
    node->type = EXPR_CONST;
    node->vals.num = val;
    return node;
}

struct expr_node *node_create_neg(struct expr_node *unop) {
    struct expr_node *node = alloc_node();
    if (!node) return NULL;
    node->type = EXPR_NEG;
    node->vals.unop = unop;
    return node;
}

/* vytvoří uzel binární operace */
static struct expr_node *create_binary_node(enum expr_type type, struct expr_node *left, struct expr_node *right) {
    struct expr_node *node = alloc_node();
    if (!node) return NULL;
    node->type = type;
    node->vals.binop.left = left;
    node->vals.binop.right = right;
    return node;
}

struct expr_node *node_create_add(struct expr_node *left, struct expr_node *right) {
    return create_binary_node(EXPR_ADD, left, right);
}

struct expr_node *node_create_sub(struct expr_node *left, struct expr_node *right) {
    return create_binary_node(EXPR_SUB, left, right);
}

struct expr_node *node_create_mult(struct expr_node *left, struct expr_node *right) {
    return create_binary_node(EXPR_MULT, left, right);
}

struct expr_node *node_create_div(struct expr_node *left, struct expr_node *right) {
    return create_binary_node(EXPR_DIV, left, right);
}

struct expr_node *node_create_pow(struct expr_node *base, struct expr_node *power) {
    return create_binary_node(EXPR_POW, base, power);
}

struct expr_node *node_create_x(void) {
    struct expr_node *node = alloc_node();
    if (!node) return NULL;
    node->type = EXPR_X;
    return node;
}

struct expr_node *node_create_fn(size_t fn_idx, struct expr_node **args) {
    size_t i, num_args;
    struct expr_node *node = alloc_node();
    if (!node) return NULL;
    node->type = EXPR_FN;
    node->vals.fn.fn_idx = fn_idx;

    num_args = fns_get()[fn_idx].num_args;
    for (i = 0; i < num_args; ++i) {
        node->vals.fn.args[i] = args[i];
    }

    return node;
}

/* pro naše účely definované "nekonečno" */
#define INF (1.0e256)

/* zkontroluje, zda je číslo reálné */
static int is_real(double x) {
    return x == x && x < INF && x > -INF;
}

/* vrátí výsledek vyhodnocení na základě hodnoty x */
static enum eval_result check_real(double x) {
    if (is_real(x))
        return EVAL_OK;
    else
        return EVAL_ERROR;
}

#define EVAL_CHECK(node, x, y) if (node_eval((node), (x), (y)) != EVAL_OK) return EVAL_ERROR;

enum eval_result node_eval(const struct expr_node *node, double x, double *y) {
    double tmp1, tmp2;

    switch (node->type) {
        case EXPR_CONST:
            *y = node->vals.num;
            return check_real(*y);

        case EXPR_X:
            *y = x;
            return check_real(*y);

        case EXPR_NEG:
            EVAL_CHECK(node->vals.unop, x, &tmp1);
            *y = -tmp1;
            return EVAL_OK;

        case EXPR_ADD:
            EVAL_CHECK(node->vals.binop.left, x, &tmp1);
            EVAL_CHECK(node->vals.binop.right, x, &tmp2);
            *y = tmp1 + tmp2;
            return check_real(*y);

        case EXPR_SUB:
            EVAL_CHECK(node->vals.binop.left, x, &tmp1);
            EVAL_CHECK(node->vals.binop.right, x, &tmp2);
            *y = tmp1 - tmp2;
            return check_real(*y);

        case EXPR_MULT:
            EVAL_CHECK(node->vals.binop.left, x, &tmp1);
            EVAL_CHECK(node->vals.binop.right, x, &tmp2);
            *y = tmp1 * tmp2;
            return check_real(*y);

        case EXPR_DIV:
            EVAL_CHECK(node->vals.binop.left, x, &tmp1);
            EVAL_CHECK(node->vals.binop.right, x, &tmp2);
            
            if (tmp2 == 0.0)
                return EVAL_ERROR;
            
            *y = tmp1 / tmp2;
            return check_real(*y);

        case EXPR_POW:
            EVAL_CHECK(node->vals.binop.left, x, &tmp1);
            EVAL_CHECK(node->vals.binop.right, x, &tmp2);
            
            errno = 0;
            *y = pow(tmp1, tmp2);
            
            if (errno) 
                return EVAL_ERROR;
            
            return check_real(*y);

        case EXPR_FN:
        {
            double inner_results[MAX_MATH_FUNCTION_ARGS];
            size_t i;
            const struct math_function *fn = &fns_get()[node->vals.fn.fn_idx];

            for (i = 0; i < fn->num_args; ++i) {
                EVAL_CHECK(node->vals.fn.args[i], x, &inner_results[i]);
            }

            return fn->ptr(y, inner_results);
        }
    }

    return 0.0;
}

#ifdef ENABLE_GRAPHVIZ_EXPORT

static void debug_print_gv(const struct expr_node *node, FILE *output);

static void debug_print_binop_gv(const struct expr_node *node, FILE *output, const char *name) {
    fprintf(output, "node%p [label=\"%s\"]\n", (void*)node, name);
    debug_print_gv(node->vals.binop.left, output);
    debug_print_gv(node->vals.binop.right, output);
    fprintf(output, "node%p -> node%p [label=left]\n", (void*)node, (void*)node->vals.binop.left);
    fprintf(output, "node%p -> node%p [label=right]\n", (void*)node, (void*)node->vals.binop.right);
}

static void debug_print_gv(const struct expr_node *node, FILE *output) {

    switch (node->type) {
        case EXPR_ADD:
            debug_print_binop_gv(node, output, "ADD");
            break;

        case EXPR_SUB:
            debug_print_binop_gv(node, output, "SUB");
            break;

        case EXPR_MULT:
            debug_print_binop_gv(node, output, "MULT");
            break;

        case EXPR_DIV:
            debug_print_binop_gv(node, output, "DIV");
            break;

        case EXPR_POW:
            debug_print_binop_gv(node, output, "POW");
            break;

        case EXPR_NEG:
            fprintf(output, "node%p [label=\"NEG\"]\n", (void*)node);
            debug_print_gv(node->vals.unop, output);
            fprintf(output, "node%p -> node%p [label=unop]\n", (void*)node, (void*)node->vals.unop);
            break;

        case EXPR_CONST:
            fprintf(output, "node%p [label=\"CONST: %.2f\"]\n", (void*)node, node->vals.num);
            break;

        case EXPR_X:
            fprintf(output, "node%p [label=\"X\"]\n", (void*)node);
            break;

        case EXPR_FN:
        {
            size_t i;
            const struct math_function *fn = &fns_get()[node->vals.fn.fn_idx];

            fprintf(output, "node%p [label=\"FN: %s\"]\n", (void*)node, fn->name);

            for (i = 0; i < fn->num_args; ++i) {
                struct expr_node *arg = node->vals.fn.args[i];
                debug_print_gv(arg, output);
                fprintf(output, "node%p -> node%p [label=arg%d]\n", (void*)node, (void*)arg, (int)i + 1);
            }

            break;
        }

        default:
            break;
    }
}

void node_debug_print_gv(const struct expr_node *node, FILE *output) {
    fprintf(output, "digraph G {\n");
    debug_print_gv(node, output);
    fprintf(output, "}\n");
}

#endif /* ENABLE_GRAPHVIZ_EXPORT */

void node_free(struct expr_node *node) {
    if (!node) return;

    switch (node->type) {
        case EXPR_ADD:
        case EXPR_SUB:
        case EXPR_MULT:
        case EXPR_DIV:
        case EXPR_POW:
            node_free(node->vals.binop.left);
            node_free(node->vals.binop.right);
            break;

        case EXPR_NEG:
            node_free(node->vals.unop);
            break;

        case EXPR_FN:
            {
                size_t i, num_args = fns_get()[node->vals.fn.fn_idx].num_args;
                for (i = 0; i < num_args; ++i) {
                    node_free(node->vals.fn.args[i]);
                }
            }
            break;

        default:
            break;
    }

    free(node);
}