import sys
import ast


# Large float and imaginary literals get turned into infinities in the AST.
# We unparse those infinities to INFSTR.
INFSTR = "1e" + repr(sys.float_info.max_10_exp + 1)


def _interleave(inter, f, seq):
    """Call f on each item in seq, calling inter() in between.
    """
    seq = iter(seq)
    try:
        f(next(seq))
    except StopIteration:
        pass
    else:
        for x in seq:
            inter()
            f(x)


class _Unparser:
    """Methods in this class recursively traverse an AST and
    output source code for the abstract syntax; original formatting
    is disregarded. """

    def __init__(self, tree):
        """Print the source for tree to the "result" string."""
        self.result = ""
        self._indent = 0
        self.dispatch(tree)
        self.result += "\n"

    def fill(self, text=""):
        "Indent a piece of text, according to the current indentation level"
        self.result += "\n"+"    "*self._indent + text

    def write(self, text):
        "Append a piece of text to the current line."
        self.result += text

    def enter(self):
        "Print ':', and increase the indentation."
        self.write(":")
        self._indent += 1

    def leave(self):
        "Decrease the indentation level."
        self._indent -= 1

    def dispatch(self, tree):
        "Dispatcher function, dispatching tree type T to method _T."
        if isinstance(tree, list):
            for t in tree:
                self.dispatch(t)
            return
        meth = getattr(self, "_"+tree.__class__.__name__)
        meth(tree)

    #  Unparsing methods
    #
    # There should be one method per concrete grammar type
    # Constructors should be grouped by sum type. Ideally,
    # this would follow the order in the grammar, but
    # currently doesn't.

    def _Module(self, tree):
        for stmt in tree.body:
            self.dispatch(stmt)

    # stmt
    def _Expr(self, tree):
        self.fill()
        self.dispatch(tree.value)

    def _Import(self, t):
        self.fill("import ")
        _interleave(lambda: self.write(", "), self.dispatch, t.names)

    def _ImportFrom(self, t):
        self.fill("from ")
        self.write("." * t.level)
        if t.module:
            self.write(t.module)
        self.write(" import ")
        _interleave(lambda: self.write(", "), self.dispatch, t.names)

    def _Assign(self, t):
        self.fill()
        for target in t.targets:
            self.dispatch(target)
            self.write(" = ")
        self.dispatch(t.value)

    def _AugAssign(self, t):
        self.fill()
        self.dispatch(t.target)
        self.write(" "+self.binop[t.op.__class__.__name__]+"= ")
        self.dispatch(t.value)

    def _Return(self, t):
        self.fill("return")
        if t.value:
            self.write(" ")
            self.dispatch(t.value)

    def _Pass(self, t):
        self.fill("pass")

    def _Break(self, t):
        self.fill("break")

    def _Continue(self, t):
        self.fill("continue")

    def _Delete(self, t):
        self.fill("del ")
        _interleave(lambda: self.write(", "), self.dispatch, t.targets)

    def _Assert(self, t):
        self.fill("assert ")
        self.dispatch(t.test)
        if t.msg:
            self.write(", ")
            self.dispatch(t.msg)

    def _Global(self, t):
        self.fill("global ")
        _interleave(lambda: self.write(", "), self.write, t.names)

    def _Nonlocal(self, t):
        self.fill("nonlocal ")
        _interleave(lambda: self.write(", "), self.write, t.names)

    def _Yield(self, t):
        self.write("(")
        self.write("yield")
        if t.value:
            self.write(" ")
            self.dispatch(t.value)
        self.write(")")

    def _YieldFrom(self, t):
        self.write("(")
        self.write("yield from")
        if t.value:
            self.write(" ")
            self.dispatch(t.value)
        self.write(")")

    def _Raise(self, t):
        self.fill("raise")
        if not t.exc:
            assert not t.cause
            return
        self.write(" ")
        self.dispatch(t.exc)
        if t.cause:
            self.write(" from ")
            self.dispatch(t.cause)

    def _Try(self, t):
        self.fill("try")
        self.enter()
        self.dispatch(t.body)
        self.leave()
        for ex in t.handlers:
            self.dispatch(ex)
        if t.orelse:
            self.fill("else")
            self.enter()
            self.dispatch(t.orelse)
            self.leave()
        if t.finalbody:
            self.fill("finally")
            self.enter()
            self.dispatch(t.finalbody)
            self.leave()

    def _ExceptHandler(self, t):
        self.fill("except")
        if t.type:
            self.write(" ")
            self.dispatch(t.type)
        if t.name:
            self.write(" as ")
            self.write(t.name)
        self.enter()
        self.dispatch(t.body)
        self.leave()

    def _ClassDef(self, t):
        self.write("\n")
        for deco in t.decorator_list:
            self.fill("@")
            self.dispatch(deco)
        self.fill("class "+t.name)
        self.write("(")
        comma = False
        for e in t.bases:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.dispatch(e)
        for e in t.keywords:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.dispatch(e)
        if t.starargs:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.write("*")
            self.dispatch(t.starargs)
        if t.kwargs:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.write("**")
            self.dispatch(t.kwargs)
        self.write(")")

        self.enter()
        self.dispatch(t.body)
        self.leave()

    def _FunctionDef(self, t):
        self.write("\n")
        for deco in t.decorator_list:
            self.fill("@")
            self.dispatch(deco)
        self.fill("def "+t.name + "(")
        self.dispatch(t.args)
        self.write(")")
        if t.returns:
            self.write(" -> ")
            self.dispatch(t.returns)
        self.enter()
        self.dispatch(t.body)
        self.leave()

    def _For(self, t):
        self.fill("for ")
        self.dispatch(t.target)
        self.write(" in ")
        self.dispatch(t.iter)
        self.enter()
        self.dispatch(t.body)
        self.leave()
        if t.orelse:
            self.fill("else")
            self.enter()
            self.dispatch(t.orelse)
            self.leave()

    def _If(self, t):
        self.fill("if ")
        self.dispatch(t.test)
        self.enter()
        self.dispatch(t.body)
        self.leave()
        # collapse nested ifs into equivalent elifs.
        while (t.orelse and len(t.orelse) == 1 and
               isinstance(t.orelse[0], ast.If)):
            t = t.orelse[0]
            self.fill("elif ")
            self.dispatch(t.test)
            self.enter()
            self.dispatch(t.body)
            self.leave()
        # final else
        if t.orelse:
            self.fill("else")
            self.enter()
            self.dispatch(t.orelse)
            self.leave()

    def _While(self, t):
        self.fill("while ")
        self.dispatch(t.test)
        self.enter()
        self.dispatch(t.body)
        self.leave()
        if t.orelse:
            self.fill("else")
            self.enter()
            self.dispatch(t.orelse)
            self.leave()

    def _With(self, t):
        self.fill("with ")
        _interleave(lambda: self.write(", "), self.dispatch, t.items)
        self.enter()
        self.dispatch(t.body)
        self.leave()

    # expr
    def _Bytes(self, t):
        self.write(repr(t.s))

    def _Str(self, tree):
        self.write(repr(tree.s))

    def _Name(self, t):
        self.write(t.id)

    def _NameConstant(self, t):
        self.write(repr(t.value))

    def _Num(self, t):
        # Substitute overflowing decimal literal for AST infinities.
        self.write(repr(t.n).replace("inf", INFSTR))

    def _List(self, t):
        self.write("[")
        _interleave(lambda: self.write(", "), self.dispatch, t.elts)
        self.write("]")

    def _ListComp(self, t):
        self.write("[")
        self.dispatch(t.elt)
        for gen in t.generators:
            self.dispatch(gen)
        self.write("]")

    def _GeneratorExp(self, t):
        self.write("(")
        self.dispatch(t.elt)
        for gen in t.generators:
            self.dispatch(gen)
        self.write(")")

    def _SetComp(self, t):
        self.write("{")
        self.dispatch(t.elt)
        for gen in t.generators:
            self.dispatch(gen)
        self.write("}")

    def _DictComp(self, t):
        self.write("{")
        self.dispatch(t.key)
        self.write(": ")
        self.dispatch(t.value)
        for gen in t.generators:
            self.dispatch(gen)
        self.write("}")

    def _comprehension(self, t):
        self.write(" for ")
        self.dispatch(t.target)
        self.write(" in ")
        self.dispatch(t.iter)
        for if_clause in t.ifs:
            self.write(" if ")
            self.dispatch(if_clause)

    def _IfExp(self, t):
        self.write("(")
        self.dispatch(t.body)
        self.write(" if ")
        self.dispatch(t.test)
        self.write(" else ")
        self.dispatch(t.orelse)
        self.write(")")

    def _Set(self, t):
        assert(t.elts)  # should be at least one element
        self.write("{")
        _interleave(lambda: self.write(", "), self.dispatch, t.elts)
        self.write("}")

    def _Dict(self, t):
        self.write("{")

        def write_pair(pair):
            (k, v) = pair
            self.dispatch(k)
            self.write(": ")
            self.dispatch(v)
        _interleave(lambda: self.write(", "), write_pair, zip(t.keys, t.values))
        self.write("}")

    def _Tuple(self, t):
        self.write("(")
        if len(t.elts) == 1:
            (elt,) = t.elts
            self.dispatch(elt)
            self.write(",")
        else:
            _interleave(lambda: self.write(", "), self.dispatch, t.elts)
        self.write(")")

    unop = {"Invert": "~", "Not": "not", "UAdd": "+", "USub": "-"}

    def _UnaryOp(self, t):
        self.write("(")
        self.write(self.unop[t.op.__class__.__name__])
        self.write(" ")
        self.dispatch(t.operand)
        self.write(")")

    binop = {"Add": "+", "Sub": "-", "Mult": "*", "Div": "/", "Mod": "%",
             "LShift": "<<", "RShift": ">>",
             "BitOr": "|", "BitXor": "^", "BitAnd": "&",
             "FloorDiv": "//", "Pow": "**"}

    def _BinOp(self, t):
        self.write("(")
        self.dispatch(t.left)
        self.write(" " + self.binop[t.op.__class__.__name__] + " ")
        self.dispatch(t.right)
        self.write(")")

    cmpops = {"Eq": "==", "NotEq": "!=",
              "Lt": "<", "LtE": "<=", "Gt": ">", "GtE": ">=",
              "Is": "is", "IsNot": "is not", "In": "in", "NotIn": "not in"}

    def _Compare(self, t):
        self.write("(")
        self.dispatch(t.left)
        for o, e in zip(t.ops, t.comparators):
            self.write(" " + self.cmpops[o.__class__.__name__] + " ")
            self.dispatch(e)
        self.write(")")

    boolops = {ast.And: "and", ast.Or: "or"}

    def _BoolOp(self, t):
        self.write("(")
        s = " %s " % self.boolops[t.op.__class__]
        _interleave(lambda: self.write(s), self.dispatch, t.values)
        self.write(")")

    def _Attribute(self, t):
        self.dispatch(t.value)
        # Special case: 3.__abs__() is a syntax error, so if t.value
        # is an integer literal then we need to either parenthesize
        # it or add an extra space to get 3 .__abs__().
        if isinstance(t.value, ast.Num) and isinstance(t.value.n, int):
            self.write(" ")
        self.write(".")
        self.write(t.attr)

    def _Call(self, t):
        self.dispatch(t.func)
        self.write("(")
        comma = False
        for e in t.args:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.dispatch(e)
        for e in t.keywords:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.dispatch(e)
        if t.starargs:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.write("*")
            self.dispatch(t.starargs)
        if t.kwargs:
            if comma:
                self.write(", ")
            else:
                comma = True
            self.write("**")
            self.dispatch(t.kwargs)
        self.write(")")

    def _Subscript(self, t):
        self.dispatch(t.value)
        self.write("[")
        self.dispatch(t.slice)
        self.write("]")

    def _Starred(self, t):
        self.write("*")
        self.dispatch(t.value)

    # slice
    def _Ellipsis(self, t):
        self.write("...")

    def _Index(self, t):
        self.dispatch(t.value)

    def _Slice(self, t):
        if t.lower:
            self.dispatch(t.lower)
        self.write(":")
        if t.upper:
            self.dispatch(t.upper)
        if t.step:
            self.write(":")
            self.dispatch(t.step)

    def _ExtSlice(self, t):
        _interleave(lambda: self.write(', '), self.dispatch, t.dims)

    # argument
    def _arg(self, t):
        self.write(t.arg)
        if t.annotation:
            self.write(": ")
            self.dispatch(t.annotation)

    # others
    def _arguments(self, t):
        first = True
        # normal arguments
        defaults = [None] * (len(t.args) - len(t.defaults)) + t.defaults
        for a, d in zip(t.args, defaults):
            if first:
                first = False
            else:
                self.write(", ")
            self.dispatch(a)
            if d:
                self.write("=")
                self.dispatch(d)

        # varargs, or bare '*' if no varargs but keyword-only arguments present
        if t.vararg or t.kwonlyargs:
            if first:
                first = False
            else:
                self.write(", ")
            self.write("*")
            if t.vararg:
                self.write(t.vararg.arg)
                if t.vararg.annotation:
                    self.write(": ")
                    self.dispatch(t.vararg.annotation)

        # keyword-only arguments
        if t.kwonlyargs:
            for a, d in zip(t.kwonlyargs, t.kw_defaults):
                if first:
                    first = False
                else:
                    self.write(", ")
                self.dispatch(a),
                if d:
                    self.write("=")
                    self.dispatch(d)

        # kwargs
        if t.kwarg:
            if first:
                first = False
            else:
                self.write(", ")
            self.write("**"+t.kwarg.arg)
            if t.kwarg.annotation:
                self.write(": ")
                self.dispatch(t.kwarg.annotation)

    def _keyword(self, t):
        self.write(t.arg)
        self.write("=")
        self.dispatch(t.value)

    def _Lambda(self, t):
        self.write("(")
        self.write("lambda ")
        self.dispatch(t.args)
        self.write(": ")
        self.dispatch(t.body)
        self.write(")")

    def _alias(self, t):
        self.write(t.name)
        if t.asname:
            self.write(" as "+t.asname)

    def _withitem(self, t):
        self.dispatch(t.context_expr)
        if t.optional_vars:
            self.write(" as ")
            self.dispatch(t.optional_vars)


def unparse(tree):
    unparser = _Unparser(tree)
    return unparser.result