import re, sys, argparse
import pyyacc
from ppci import Token, CompilerError, SourceLocation
from target import Target
from asmnodes import ALabel, AInstruction, ABinop, AUnop, ASymbol, ANumber

def tokenize(s):
     """
       Tokenizer, generates an iterator that
       returns tokens!

       This GREAT example was taken from python re doc page!
     """
     tok_spec = [
       ('REAL', r'\d+\.\d+'),
       ('HEXNUMBER', r'0x[\da-fA-F]+'),
       ('NUMBER', r'\d+'),
       ('ID', r'[A-Za-z][A-Za-z\d_]*'),
       ('SKIP', r'[ \t]'),
       ('LEESTEKEN', r':=|[\.,=:\-+*\[\]/\(\)]|>=|<=|<>|>|<'),
       ('STRING', r"'.*?'"),
       ('COMMENT', r";.*")
     ]
     tok_re = '|'.join('(?P<%s>%s)' % pair for pair in tok_spec)
     gettok = re.compile(tok_re).match
     line = 1
     pos = line_start = 0
     mo = gettok(s)
     while mo is not None:
       typ = mo.lastgroup
       val = mo.group(typ)
       if typ == 'NEWLINE':
         line_start = pos
         line += 1
       elif typ != 'SKIP':
         if typ == 'LEESTEKEN':
           typ = val
         elif typ == 'NUMBER':
           val = int(val)
         elif typ == 'HEXNUMBER':
           val = int(val[2:], 16)
           typ = 'NUMBER'
         elif typ == 'REAL':
           val = float(val)
         elif typ == 'STRING':
           val = val[1:-1]
         col = mo.start() - line_start
         loc = SourceLocation(line, col, 0)   # TODO retrieve length?
         yield Token(typ, val, loc)
       pos = mo.end()
       mo = gettok(s, pos)
     if pos != len(s):
       col = pos - line_start
       loc = SourceLocation(line, col, 0)
       raise CompilerError('Unexpected character {0}'.format(s[pos]), loc)

class Lexer:
   def __init__(self, src):
      self.tokens = tokenize(src)
      self.curTok = self.tokens.__next__()
   def eat(self):
      t = self.curTok
      self.curTok = self.tokens.__next__()
      return t
   @property
   def Peak(self):
      return self.curTok


class Assembler:
    def __init__(self, target=None):
        self.target = target
        self.restart()
        # Construct a parser given a grammar:
        ident = lambda x: x   # Identity helper function
        g = pyyacc.Grammar(['ID', 'NUMBER', ',', '[', ']', ':', '+', '-', '*', pyyacc.EPS, 'COMMENT'])
        g.add_production('asmline', ['asmline2'])
        g.add_production('asmline', ['asmline2', 'COMMENT'])
        g.add_production('asmline2', ['label', 'instruction'])
        g.add_production('asmline2', ['instruction'])
        g.add_production('asmline2', ['label'])
        g.add_production('asmline2', [])
        g.add_production('optcomment', [])
        g.add_production('optcomment', ['COMMENT'])
        g.add_production('label', ['ID', ':'], self.p_label)
        g.add_production('instruction', ['opcode', 'operands'], self.p_ins_1)
        g.add_production('instruction', ['opcode'], self.p_ins_2)
        g.add_production('opcode', ['ID'], ident)
        g.add_production('operands', ['operand'], self.p_operands_1)
        g.add_production('operands', ['operands', ',', 'operand'], self.p_operands_2)
        g.add_production('operand', ['expression'], ident)
        g.add_production('operand', ['[', 'expression', ']'], self.p_mem_op)
        g.add_production('expression', ['term'], ident)
        g.add_production('expression', ['expression', 'addop', 'term'], self.p_binop)
        g.add_production('addop', ['-'], ident)
        g.add_production('addop', ['+'], ident)
        g.add_production('mulop', ['*'], ident)
        g.add_production('term', ['factor'], ident)
        g.add_production('term', ['term', 'mulop', 'factor'], self.p_binop)
        g.add_production('factor', ['ID'], lambda name: ASymbol(name))
        g.add_production('factor', ['NUMBER'], lambda num: ANumber(int(num)))
        g.start_symbol = 'asmline'
        self.p = g.genParser()

    # Parser handlers:
    def p_ins_1(self, opc, ops):
        ins = AInstruction(opc, ops)
        self.emit(ins)
    def p_ins_2(self, opc):
        self.p_ins_1(opc, [])
    def p_operands_1(self, op1):
        return [op1]
    def p_operands_2(self, ops, comma, op2):
        assert type(ops) is list
        ops.append(op2)
        return ops
    def p_mem_op(self, brace_open, exp, brace_close):
        return AUnop('[]', exp)
    def p_label(self, lname, cn):
        lab = ALabel(lname)
        self.emit(lab)
    def p_binop(self, exp1, op, exp2):
        return ABinop(op, exp1, exp2)

    # Top level interface:
    def restart(self):
        self.output = []
        self.binout = bytearray()
        self.current_section = '.text'

    def emit(self, a):
        """ Emit a parsed instruction """
        self.output.append(a)
        # Determine the bit pattern from a lookup table:
        # TODO

    def parse_line(self, line):
        """ Parse line into asm AST """
        tokens = tokenize(line)
        self.p.parse(tokens)

    def assemble(self, asmsrc):
        """ Assemble this source snippet """
        for line in asmsrc.split('\n'):
            self.assemble_line(line)
        self.back_patch()

    def assemble_line(self, line):
        """ 
            Assemble a single source line. 
            Do not take newlines into account 
        """
        self.parse_line(line)
        self.assemble_aast()

    def assemble_aast(self):
        """ Assemble a parsed asm line """
        # TODO
        if not self.target:
            raise CompilerError('Cannot assemble without target')
        while self.output:
            vi = self.output.pop(0)
            ri = self.target.mapInstruction(vi)
            b = ri.encode()
            assert type(b) is bytes
            self.binout.extend(b)

    def back_patch(self):
        """ Fix references to earlier labels """
        pass


if __name__ == '__main__':
    # When run as main file, try to grab command line arguments:
    parser = argparse.ArgumentParser(description="Assembler")
    parser.add_argument('sourcefile', type=argparse.FileType('r'), help='the source file to assemble')
    args = parser.parse_args()
    a = Assembler()
    obj = a.assemble(args.sourcefile.read())