from enum import Enum
from token_agl import Token, TokenType


class State(Enum):
    looking = 1
    zero = 2
    integer = 3
    string = 4


def scan(program):
    tokens = []     # list of tokens to return
    accum = ''      # for building multi-character tokens

    # the state machine
    state = State.looking
    pos = 0
    while pos < len(program):
        # print(pos, ' ', state)           # trace flow
        if state == State.looking:
            if program[pos].isspace():
                pass
            elif program[pos] == ';':
                tokens.append(Token(TokenType.terminator))
            elif program[pos] in '0':
                accum = program[pos]
                state = State.zero
            elif program[pos] in '123456789':
                accum = program[pos]
                state = State.integer
            else:     # I decided to accept any character!
                accum = program[pos]
                state = State.string
            pos += 1
        elif state == State.zero:
            if program[pos].isspace():
                tokens.append(Token(TokenType.int_token, 0))
            elif program[pos] == ';':
                tokens.append(Token(TokenType.int_token, 0))
                tokens.append(Token(TokenType.terminator))
            elif program[pos].isdigit():
                error_msg = 'Integers do not have leading zeros: 0{}'
                raise ValueError(error_msg.format(program[pos]))
            else:
                error_msg = 'Invalid character after a 0: 0{}'
                raise ValueError(error_msg.format(program[pos]))
            accum = ''
            state = State.looking
            pos += 1
        elif state == State.integer:
            if program[pos].isdigit():
                accum += program[pos]
            elif program[pos].isspace():
                tokens.append(Token(TokenType.int_token, int(accum)))
                accum = ''
                state = State.looking
            elif program[pos] == ';':
                tokens.append(Token(TokenType.int_token, int(accum)))
                tokens.append(Token(TokenType.terminator))
                accum = ''
                state = State.looking
            else:
                error_msg = 'Invalid character in integer {}*{}*'
                raise ValueError(error_msg.format(accum, program[pos]))
            pos += 1
        elif state == State.string:
            if program[pos].isspace():
                tokens.append(Token(TokenType.str_token, accum))
            elif program[pos] == ';':
                tokens.append(Token(TokenType.str_token, accum))
                tokens.append(Token(TokenType.terminator))
            else:
                error_msg = 'All strings are single character {}*{}*'
                raise ValueError(error_msg.format(accum, program[pos]))
            accum = ''
            state = State.looking
            pos += 1
        else:
            error_msg = 'Invalid state {}.  How did that happen?'
            raise TypeError(error_msg.format(state))

    # handle accumulator at the end of the file    (I had a bug...)
    if accum:
        if state == State.zero:
            tokens.append(Token(TokenType.int_token, 0))
        elif state == State.integer:
            tokens.append(Token(TokenType.int_token, int(accum)))
        elif state == State.string:
            tokens.append(Token(TokenType.str_token, accum))
        else:
            error_msg = 'Invalid state {} with this accum {}'
            raise TypeError(error_msg.format(state, accum))

    # return list of tokens
    return tokens


# ----------------------------------------------------------
# a function that demonstrates the scanner on class example
# ----------------------------------------------------------

def demo_scanner():
    file = open('demo.agl', 'r')
    program = file.read()
    #     4 12 X;
    #     8 4 b 4 X 4 b;
    #     4 12 X;
    print(scan(program))
    #     [integer = 4, integer = 12, string  = X, terminator, ...]


# ----------------------------------------------------------
# a main "function" that demonstrates several simple cases
# ----------------------------------------------------------

if __name__ == "__main__":
    programs = ['',          # empty program
                ' ',         # empty program with whitespace
                ';',         # one empty line
                '0 x;',      # one chunk on a line, count 0
                '16 x;',     # one chunk on a line, count >0
                '01 x;']     # illegal token: leading zero
    for p in programs:
        print('PROGRAM\n*{}*'.format(p))
        try:
            print('SCANNED\n{}\n'.format(scan(p)))
        except ValueError as e:
            print('ILLEGAL TOKEN\n{}\n'.format(e))