/*
 * rpn.c: evalutor of RPN formulas
 */

#include <syslog.h>
#include <stdlib.h>
#include <string.h>

#include "config.h"
#include "rpn.h"
#include "trie.h"
#include "grow.h"

// Wrapper functions between grow's void*s and our struct trie_retvals
bool stack_push (struct trie_retval val, struct grow *stack) {
	struct trie_retval *p_val = (struct trie_retval *) malloc(sizeof(struct trie_retval));
	if (p_val == NULL) {
		syslog(cfg_log_facility | LOG_ERR, "rpn: stack_push: malloc failed: %m");
		return false;
	}
	*p_val = val;
	return grow_push((void *)p_val, stack);
}

struct trie_retval stack_pop(struct grow *stack) {
	struct trie_retval *p_val = (struct trie_retval *) grow_pop(stack);
	struct trie_retval val = *p_val;
	free(p_val);
	return val;
}

static uint64_t parse_var_name(char str[], char *out[]) {
	uint64_t off;
	for (off = 0;
			('A' <= str[off] && str[off] <= 'Z')
			|| ('0' <= str[off] && str[off] <= '9')
			|| str[off] == '_'
			; off++) {
		if (off < cfg_var_name_max_len) {
			(*out)[off] = str[off];
		} else {
			syslog(cfg_log_facility | LOG_NOTICE, "rpn: variable name too long, trucating char '%c'", str[off]);
		}
	}
	// off is pointing past end of variable name;
	(*out)[off] = '\0';
	return off - 1; //last character of variable name
}

static uint64_t do_cmd(char str[], struct grow *stack) {
	// Check whether a command exists and if so, perform it
	if(0){
		//alignment of others
		//Bonus unconditional jump for compiling with -O0, maybe
	} else if (strncmp("def", str, 3) == 0) {
		struct trie_retval arg = stack_pop(stack);
		if (arg.def) { // true might not be 1, I am not sure.
			stack_push((struct trie_retval) {1, true, NULL}, stack);
		} else {
			stack_push((struct trie_retval) {0, true, NULL}, stack);
		}
		return 2;
	} else if (strncmp("swap", str, 4) == 0) {
		struct trie_retval arg1 = stack_pop(stack);
		struct trie_retval arg2 = stack_pop(stack);
		stack_push(arg1, stack);
		stack_push(arg2, stack);
		return 3;
	} else if (strncmp("dup", str, 3) == 0) {
		struct trie_retval arg = stack_pop(stack);
		stack_push(arg, stack);
		stack_push(arg, stack);
		return 2;
	} else if (strncmp("del", str, 3) == 0) {
		stack_pop(stack);
		return 2;
	} else {
		syslog(cfg_log_facility | LOG_NOTICE, "rpn: Unknown command starting with '%c'", str[0]);
		return 0;
	}
}

static bool rpn_eval_modify (char rpn[], bool modify, bool assoc, uint64_t task) {
	uint64_t rpnoff;
	struct grow *stack = grow_init(true);
	char buf[cfg_var_name_max_len + 1];
	int64_t val = 0;

	// Sign of val==0
	bool val_neg = false;

	//definition of temporary variables, because of switch's goto-y behavior
	struct trie_retval arg;
	struct trie_retval arg1;
	struct trie_retval arg2;
	// this leads to dangerous code -- it is not clear, what are the values.
	// but it has to be done this way due to how C switch works

	// parse the RPN
	for (rpnoff=0; rpn[rpnoff] != '\0' && rpn[rpnoff] != '?'; rpn++) {
		switch (rpn[rpnoff]) {
			case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9':
				; //Label...
				int digit = rpn[rpnoff] - '0';
				val = val * 10 + digit;
				if (val >= 0 && val_neg == true) {
					val *= -1;
				}
				if (rpn[rpnoff+1] < '0' || '9' < rpn[rpnoff+1]) { //ASCII
					// end of number
					stack_push((struct trie_retval) {val, true, NULL}, stack);
					val = 0;
					val_neg = false;
				}
			break;
			case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case 'G':
			case 'H': case 'I': case 'J': case 'K': case 'L': case 'M': case 'N':
			case 'O': case 'P': case 'Q': case 'R': case 'S': case 'T': case 'U':
			case 'V': case 'W': case 'X': case 'Y': case 'Z':
				rpnoff += parse_var_name(rpn + rpnoff, &buf);
				stack_push(trie_lookup(buf),stack);
				if (modify) {
					if (assoc){
						trie_assoc(buf, task);
					} else {
						trie_unassoc(buf, task);
					}
				}
			break;
			case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': case 'g':
			case 'h': case 'i': case 'j': case 'k': case 'l': case 'm': case 'n':
			case 'o': case 'p': case 'q': case 'r': case 's': case 't': case 'u':
			case 'v': case 'w': case 'x': case 'y': case 'z':
				rpnoff += do_cmd(rpn + rpnoff, stack);
			break;
			case '+':
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val + arg2.val, true, NULL}, stack);
			break;
			case '-': // May be unary or binary
				if ('0' <= rpn[rpnoff+1] && rpn[rpnoff] <= '9') {
					// Unary
					// It's shame two's complement doesn't have -0, it would help here
					val_neg = true;
				} else {
					// Binary
					arg1 = stack_pop(stack);
					arg2 = stack_pop(stack);
					stack_push((struct trie_retval) {arg1.val - arg2.val, true, NULL}, stack);
				}
			break;
			case '*':
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val * arg2.val, true, NULL}, stack);
			break;
			case '/':
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val / arg2.val, true, NULL}, stack);
			break;
			case '%': //Modulo
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val % arg2.val, true, NULL}, stack);
			break;
			case '^': //Bit XOR
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val ^ arg2.val, true, NULL}, stack);
			break;
			case '~': //Bit NOT
				; //Label...
				arg = stack_pop(stack);
				stack_push((struct trie_retval) {~(arg.val), true, NULL}, stack);
			break;
			case '!': //Logical NOT
				; //Label...
				arg = stack_pop(stack);
				if (arg.val != 0) {
					stack_push((struct trie_retval) {0,true, NULL}, stack);
				} else {
					stack_push((struct trie_retval) {1,true, NULL}, stack);
				}
			break;
			case '=': //Equality
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val == arg2.val, true, NULL}, stack);
			break;
			case '>': //(mind the operand order)
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val > arg2.val, true, NULL}, stack);
			break;
			case '<': //(mind the operand order)
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				stack_push((struct trie_retval) {arg1.val < arg2.val, true, NULL}, stack);
			break;
			case '|': //Bit or logical OR
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				if (rpn[rpnoff+1] == '|') {
					// Logical OR
					rpnoff++;
					stack_push((struct trie_retval) {arg1.val || arg2.val, true, NULL}, stack);
				} else {
					// Bit OR
					stack_push((struct trie_retval) {arg1.val | arg2.val, true, NULL}, stack);
				}
			break;
			case '&': //Bit or logical AND
				; //Label...
				arg1 = stack_pop(stack);
				arg2 = stack_pop(stack);
				if (rpn[rpnoff+1] == '&') {
					// Logical AND
					rpnoff++;
					stack_push((struct trie_retval) {arg1.val && arg2.val, true, NULL}, stack);
				} else {
					// Bit AND
					stack_push((struct trie_retval) {arg1.val & arg2.val, true, NULL}, stack);
				}
			break;
			case ' ':
			break;
			default:
				syslog(cfg_log_facility | LOG_NOTICE, "rpn: Unexpected char: %c", rpn[rpnoff]);
			break;
		}
	}

	// Return the variable at top of the stack and discard stack
	struct trie_retval retval = stack_pop(stack);
	grow_drop(stack);
	if (retval.def == false || retval.val == 0) {
		return false;
	} else {
		return true;
	}
}

/*
 * Mathematics is the art of giving the same name to different things.
 *                       - Henri Poincaré
 * Programming is the art of giving different names to the same thing.
 *                       - Obvious from the code below.
 *                         (except maybe it is not called art)
 */
bool rpn_eval(char rpn[]) {
	return rpn_eval_modify(rpn, false, false, 0);
}
bool rpn_eval_assoc(char rpn[], uint64_t task) {
	return rpn_eval_modify(rpn, true, true, task);
}
bool rpn_eval_unassoc(char rpn[], uint64_t task) {
	return rpn_eval_modify(rpn, true, false, task);
}