#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2019 pavle <pavle.portic@tilda.center>
#
# Distributed under terms of the BSD-3-Clause license.

from constants import (
	NUMBER, EOF,
	PLUS, MINUS, MUL, DIV, IDIV, MOD, POW, SQRT,
	HEX, DEC, BIN,
	SWAP, POP,
)


class InterpreterError(Exception):
	pass


class Interpreter:
	def __init__(self):
		self.stack = []
		self.mode = DEC
		self.mode_func = float

	def init_lexer(self, lexer):
		self.lexer = lexer
		self.current_token = self.lexer.get_next_token()

	def evaluate_binary_operator(self, token):
		if len(self.stack) < 2:
			raise InterpreterError('Needs at least 2 values on the stack')

		right = self.stack.pop()
		left = self.stack.pop()
		self.stack.append(token.value(left, right))

	def evaluate_unary_operator(self, token):
		if len(self.stack) < 1:
			raise InterpreterError('Needs at least 1 value on the stack')

		value = self.stack.pop()
		self.stack.append(token.value(value))

	def set_mode(self, token):
		self.mode = token.type
		self.mode_func = token.value

	def parse(self, lexer):
		self.init_lexer(lexer)

		while self.current_token.type is not EOF:
			if self.current_token.type == NUMBER:
				self.stack.append(self.current_token.value)
			elif self.current_token.type in (PLUS, MINUS, MUL, DIV, IDIV, MOD, POW):
				self.evaluate_binary_operator(self.current_token)
			elif self.current_token.type in (SQRT):
				self.evaluate_unary_operator(self.current_token)
			elif self.current_token.type == SWAP:
				a = self.stack.pop()
				b = self.stack.pop()
				self.stack.append(a)
				self.stack.append(b)
			elif self.current_token.type == POP:
				self.stack.pop()
			elif self.current_token.type in (HEX, DEC, BIN):
				self.set_mode(self.current_token)
			else:
				raise InterpreterError('Unexpected token')

			self.current_token = self.lexer.get_next_token()

		return self.stack