#include "parser.h"

#define MAXEXP 1000

/* registers */
float reg_a;
float reg_b;
float reg_c;
float reg_ans;

float eval(Tree *t);

int main(void) {
    Tree *t;
    char buf[MAXEXP];

    printf("\n");
    printf("--------------------------------------------\n");
    printf("welcome to calc>, where dreams come true.\n");
    printf("type in your expressions lisp-style.\n");
    printf("press ctrl-D or type (quit) to quit\n");
    printf("--------------------------------------------\n");
    printf("\n");
    printf("calc> ");

    while (fgets(buf, MAXEXP, stdin)) {
        buf[strlen(buf)-1] = '\0';
        if ((t = parse(buf)) == NULL)
            break;
        if ((reg_ans = eval(t)) < 0)
            break;
        printf("%f\n", reg_ans);
        printf("calc> ");
    }
    printf("program quit\n");

    return 0;
}

float eval(Tree *t) {
    List *arglist = List_new();
    Tree *tptr = Tree_first_child(t);
    Node *ptr;
    char *proc;
    float n, result = 0;

    /* fetch the procedure */
    proc = tptr->datum;

    /* replace tree with correct values */
    for (tptr = Tree_next_sibling(tptr); tptr != NULL; tptr = Tree_next_sibling(tptr)) {
        /* find real value if needed */
        if (tptr->datum == NULL)
            n = eval(tptr);
        else {
            if (!(strcmp(tptr->datum, "a")))
                n = reg_a;
            else if (!(strcmp(tptr->datum, "b")))
                n = reg_b;
            else if (!(strcmp(tptr->datum, "c")))
                n = reg_c;
            else if (!(strcmp(tptr->datum, "ans")))
                n = reg_ans;
            else
                n = atof(tptr->datum);
        }
        /* replace tree string with real value */
        free(tptr->datum);
        tptr->datum = malloc(sizeof(float));
        *((float *)(tptr->datum)) = n;
        /* put it in list */
        List_append(arglist, tptr->datum);
    }

    /* assume at least one argument */
    if (proc == NULL) {
        printf("error: missing procedure\n");
        return -1;
    }
    else if (*proc == '*') {
        result = *((float *)(List_first(arglist)->data));
        for (ptr = List_first(arglist)->next; ptr != NULL; ptr = ptr->next)
            result *= *((float *)ptr->data);
    }
    else if (*proc == '+') {
        result = *((float *)(List_first(arglist)->data));
        for (ptr = List_first(arglist)->next; ptr != NULL; ptr = ptr->next)
            result += *((float *)ptr->data);
    }
    else if (*proc == '-') {
        result = *((float *)(List_first(arglist)->data));
        for (ptr = List_first(arglist)->next; ptr != NULL; ptr = ptr->next)
            result /= *((float *)ptr->data);
    }
    else if (*proc == '/') {
        result = *((float *)(List_first(arglist)->data));
        for (ptr = List_first(arglist)->next; ptr != NULL; ptr = ptr->next)
            result /= *((float *)ptr->data);
    }
    else if (*proc == 'a')
        result = reg_a = *((float *)(List_first(arglist)->data));
    else if (*proc == 'b')
        result = reg_b = *((float *)(List_first(arglist)->data));
    else if (*proc == 'c')
        result = reg_c = *((float *)(List_first(arglist)->data));
    else if (!(strcmp(proc, "quit")))
        return -1;
    else {
        printf("error: unsupported procedure\n");
        return -1;
    }

    /* free list */
    List_remove_all(arglist);
    /* free children */
    Tree_remove_children(t);

    return result;
}