#include "run.h"
#include "ast.h"

#include <stdio.h>
#include <string.h>

// static int valueof(AstNode *a) {
// 	if (a->ty != AST_NUM) {
// 		printf("i need a number\n");
// 		return -1;
// 	} else {
// 		return a->as.num;
// 	}
// }

// void run_thing(AstNode *a) {
// 	if (a->ty != AST_LIST) 
// 		printf("can only run a list\n");
// 	else if (a->as.list.len < 3)
// 		printf("need at least 3 elements\n");
// 	else {
// 		AstNode *fn = &a->as.list.vals[0];
// 		if (fn->ty != AST_SYMBOL) 
// 			printf("first el needs to be symbol\n");
// 		else if (strcmp(fn->as.str, "+"))
// 			printf("can only run +\n");
// 		else {
// 			int v1 = valueof(&a->as.list.vals[1]);
// 			int v2 = valueof(&a->as.list.vals[2]);
// 			printf("=> %d\n",v1+v2);
// 		}
// 	}
// }

int eval (AstNode a);

// return pointer to nth subnode of AST_LIST node *l.
// doesn't check that l is a list, or that it has at least n elems. 
#define NTH(l,n) (&(l)->as.list.vals[(n)])

// n is max index
#define CK_LEN(s, l, n) do { if(l.len-1 != n) { \
	printf("%s fn requires exactly %d args (%ld provided)",\
	s, n, l.len-1); return 0; } } while(0);
static int func_plus(AstVec l) {
	CK_LEN("+",l,2);
	return eval(l.vals[1]) + eval(l.vals[2]);
}
static int func_id(AstVec l) {
	CK_LEN("id",l,1);
	return eval(l.vals[1]);
}
static int func_minus(AstVec l) {
	CK_LEN("-",l,2);
	return eval(l.vals[1]) - eval(l.vals[2]);
}
static int func_mult(AstVec l) {
	CK_LEN("*",l,2);
	return eval(l.vals[1]) * eval(l.vals[2]);
}
static int func_div(AstVec l) {
	CK_LEN("/",l,2);
	return eval(l.vals[1]) / eval(l.vals[2]);
}
static int func_print(AstVec l) {
	CK_LEN("print",l,1);
	int v = eval(l.vals[1]);
	printf("%d\n",v);
	return v;
}

typedef int (*builtin_func)(AstVec);
typedef struct {
	char *name;
	builtin_func func;
} BuiltinDesc;

BuiltinDesc builtins[] = {
	{ "+", func_plus },
	{ "-", func_minus },
	{ "*", func_mult },
	{ "/", func_div },
	{ "id", func_id },
	{ "print", func_print },
	{ NULL, NULL },
};

static int call_builtin(char *name, AstVec arglist) {
	for (BuiltinDesc *bd = builtins; bd->name != NULL; bd++) {
		if (0 == strcmp(bd->name, name)) {
			return bd->func(arglist);
		}
	}
	printf("couldn't find builtin fn %s\n",name);
	return 0;
}


int eval(AstNode a) {
	switch (a.ty) {
	case AST_SYMBOL:
		printf("cant yet read variable [%s]\n", a.as.str);
		return 0;
		break;
	case AST_NUM:
		return a.as.num;
		break;
	case AST_LIST:;
		AstVec l = a.as.list;
		if (l.len < 1) {
			printf("can't execute empty list\n");
			return 0;
		}
		AstNode *first = &l.vals[0];
		if (first->ty != AST_SYMBOL) {
			printf("first element of list must be symbol\n");
			return 0;
		}
		return call_builtin(first->as.str, l);
		break;
	default:
		printf("???\n");
		return 0;
	}
}