import torch
import sys
import ast
import inspect
import string
from textwrap import dedent
from torch._C._jit_tree_views import (
    ClassDef, Ident, Stmt, Decl, Def, Var,
    EmptyTypeAnnotation, Param, ExprStmt, Assign,
    Delete, Return, Raise, Assert, AugAssign, While,
    For, If, Pass, Break, Continue, Apply, Dots, Select,
    TrueLiteral, FalseLiteral, NoneLiteral, Starred,
    ListLiteral, TupleLiteral, DictLiteral, Const,
    StringLiteral, ListComp, Attribute, BinOp, UnaryOp,
    SliceExpr, Subscript, TernaryIf, With, WithItem, Property,
)
from torch._utils_internal import get_source_lines_and_file

from torch._jit_internal import SourceContext, should_drop, is_static_fn
import torch.jit.annotations

# Borrowed from cPython implementation
# https://github.com/python/cpython/blob/561612d8456cfab5672c9b445521113b847bd6b3/Lib/textwrap.py#L411#

_reserved_prefix = '__jit'
_reserved_names = {'print'}
_identifier_chars = set(string.ascii_lowercase + string.ascii_uppercase + string.digits)


def is_reserved_name(name):
    return name.startswith(_reserved_prefix) or name in _reserved_names


pretty_node_names = {
    ast.FunctionDef: "function definitions",
    ast.For: "for loops",
    ast.Delete: "del statements",
    ast.ClassDef: "class definitions",
    ast.With: "with statements",
    ast.Raise: "raise statements",
    ast.Assert: "assertions",
    ast.Import: "import statements",
    ast.ImportFrom: "import statements",
    ast.Global: "global variables",
    ast.Break: "break statements",
    ast.Continue: "continue statements",
}

node_start_tokens = {
    ast.FunctionDef: "def",
    ast.For: "for",
    ast.Delete: "del",
    ast.ClassDef: "class",
    ast.With: "with",
    ast.Raise: "raise",
    ast.Assert: "assert",
    ast.Import: "import",
    ast.ImportFrom: "from",
    ast.Global: "global",
    ast.Break: "break",
    ast.Continue: "continue",
}

pretty_node_names.update({
    ast.AsyncFunctionDef: "async function definitions",
    ast.AsyncFor: "async for loops",
    ast.AsyncWith: "async with statements",
    ast.Try: "try blocks",
    ast.Nonlocal: "nonlocal variables",
})

node_start_tokens.update({
    ast.AsyncFunctionDef: "async def",
    ast.AsyncFor: "async for",
    ast.AsyncWith: "async with",
    ast.Try: "try",
    ast.Nonlocal: "nonlocal",
})

if sys.version_info >= (3, 6):
    pretty_node_names.update({
        ast.AnnAssign: "annotated assignments",
    })
    # NB: no specific token for AnnAssign


class FrontendError(Exception):
    def __init__(self, source_range, msg):
        self.source_range = source_range
        self.msg = msg

        # This has to be instantiated here so the ErrorReport is accurate to the
        # call stack when the FrontendError was raised
        self.error_report = torch._C.ErrorReport(self.source_range)

    def __str__(self):
        return self.msg + self.error_report.what().lstrip()


class NotSupportedError(FrontendError):
    pass


class UnsupportedNodeError(NotSupportedError):
    def __init__(self, ctx, offending_node, reason=''):
        # If we don't have a specific token, we default to length of 1
        node_type = type(offending_node)
        range_len = len(node_start_tokens.get(node_type, ' '))
        source_range = ctx.make_range(offending_node.lineno,
                                      offending_node.col_offset,
                                      offending_node.col_offset + range_len)
        feature_name = pretty_node_names.get(node_type, node_type.__name__)
        msg = "{} {}aren't supported".format(feature_name, reason + ' ' if reason else '')
        super(UnsupportedNodeError, self).__init__(source_range, msg)


class FrontendTypeError(FrontendError):
    pass


def build_withitems(ctx, items):
    items = [build_withitem(ctx, i) for i in items]
    return list(items)


def build_stmts(ctx, stmts):
    stmts = [build_stmt(ctx, s) for s in stmts]
    return list(filter(None, stmts))


def get_class_properties(cls, self_name):
    """
    Get a list of Property objects representing the properties of a class.

    Arguments:
        cls:  The class to get properties of.
        self_name: The name of the class that the properties should belong to.
    Returns:
        A list of Property objects corresponding to the properties of cls. Property
        here refers to the subclass of TreeView.
    """
    props = inspect.getmembers(
        cls, predicate=lambda m: isinstance(m, property))
    # Any property that should not compiled must be in this list on the Module.
    unused_properties = getattr(cls, "__jit_unused_properties__", [])

    # Create Property TreeView objects from inspected property objects.
    properties = []
    for prop in props:
        if prop[0] not in unused_properties and not should_drop(prop[1].fget):
            getter = get_jit_def(prop[1].fget, f"__{prop[0]}_getter", self_name=self_name)
            setter = get_jit_def(prop[1].fset, f"__{prop[0]}_setter", self_name=self_name) if prop[1].fset else None
            properties.append(Property(getter.range(), Ident(getter.range(), prop[0]), getter, setter))

    return properties


def get_jit_class_def(cls, self_name):
    # Get defs for each method within the current class independently
    # TODO: proper overriding analysis when implementing class inheritance
    methods = inspect.getmembers(
        cls,
        predicate=lambda m: (inspect.ismethod(m) or inspect.isfunction(m))
        and not is_static_fn(cls, m.__name__)
        and m.__name__ in cls.__dict__
    )
    methods = [get_jit_def(method[1],
                           method[0],
                           self_name=self_name) for method in methods]

    properties = get_class_properties(cls, self_name)

    sourcelines, file_lineno, filename = get_source_lines_and_file(cls, torch._C.ErrorReport.call_stack())
    source = ''.join(sourcelines)
    dedent_src = dedent(source)
    py_ast = ast.parse(dedent_src)
    leading_whitespace_len = len(source.split('\n', 1)[0]) - len(dedent_src.split('\n', 1)[0])
    ctx = SourceContext(source, filename, file_lineno, leading_whitespace_len, False)
    return build_class_def(ctx, py_ast.body[0], methods, properties, self_name)

def check_and_indent_multiline_strings(sourcelines):
    """
    This is a helper function which checks for multiline strings and
    indents the strings by calculating the leading space and appending
    the spaces to each line of the multiline string.The failure to indent
    multiline strings causes failures during downstream dedent
    Arguments:
        sourcelines: This is an array of source lines of the function
    Returns:
        This function returns the updated indented sources,i.e,sourcelines
    """
    indices = []
    triple_quotes = '\"\"\"'
    # Extract the start and end line number of the multiline string
    for index, source in enumerate(sourcelines):
        if triple_quotes in source and source.find(triple_quotes) == source.rfind(triple_quotes):
            indices.append(index)

    # Adding leading space for every line of the multiline string
    indices_length = len(indices)
    for i in range(0, indices_length, 2):
        if i + 1 < indices_length:
            start = indices[i]
            end = indices[i + 1]
            leading_space = len(sourcelines[start]) - len(sourcelines[start].lstrip())
            for lines in range(start + 1, end + 1):
                sourcelines[lines] = ' ' * leading_space + sourcelines[lines]
    return sourcelines

def get_jit_def(fn, def_name, self_name=None):
    """
    Build a JIT AST (TreeView) from the given function.

    Arguments:
        fn: A function object to compile
        def_name: The name to give to the resulting AST object. This is not
            always the same as `fn.__name__`, for example:
                def _forward(self):
                    ...
                forward = _forward
            In this case, the `__name__` attribute of the function object is "_forward",
            but we want the result AST to have the name "forward".
        self_name: If this function is a method, what the type name of `self` is.
    """
    sourcelines, file_lineno, filename = get_source_lines_and_file(fn, torch._C.ErrorReport.call_stack())
    sourcelines = check_and_indent_multiline_strings(sourcelines)
    source = ''.join(sourcelines)
    dedent_src = dedent(source)
    py_ast = ast.parse(dedent_src)
    if len(py_ast.body) != 1 or not isinstance(py_ast.body[0], ast.FunctionDef):
        raise RuntimeError("Expected a single top-level function")
    leading_whitespace_len = len(source.split('\n', 1)[0]) - len(dedent_src.split('\n', 1)[0])
    type_line = torch.jit.annotations.get_type_line(source)
    ctx = SourceContext(source, filename, file_lineno, leading_whitespace_len, True)
    fn_def = py_ast.body[0]

    # Swap out the function signature and body if it is unused
    if should_drop(fn):
        unused_fn_def = ast.parse("def unused_fn(self: Any):\n\traise RuntimeError(\"Cannot call @unused methods\")")
        if len(unused_fn_def.body) != 1 or not isinstance(unused_fn_def.body[0], ast.FunctionDef):
            raise RuntimeError("Expected a single top-level function")
        unused_def = unused_fn_def.body[0]
        fn_def.body = unused_def.body
        # kwarg/vararg not supported by `build_def`
        fn_def.args.kwarg = fn_def.args.vararg = None
        for arg in fn_def.args.args + fn_def.args.kwonlyargs:
            # Replace potentially unsupported type annotations by "Any"
            arg.annotation = unused_def.args.args[0].annotation

    return build_def(ctx, fn_def, type_line, def_name, self_name=self_name)


class Builder(object):
    def __call__(self, ctx, node):
        method = getattr(self, 'build_' + node.__class__.__name__, None)
        if method is None:
            raise UnsupportedNodeError(ctx, node)
        return method(ctx, node)


def build_class_def(ctx, py_def, methods, properties, self_name):
    r = ctx.make_range(py_def.lineno, py_def.col_offset,
                       py_def.col_offset + len("class"))
    return ClassDef(Ident(r, self_name), [Stmt(method) for method in methods], properties)


def build_def(ctx, py_def, type_line, def_name, self_name=None):
    body = py_def.body
    r = ctx.make_range(py_def.lineno + len(py_def.decorator_list),
                       py_def.col_offset,
                       py_def.col_offset + len("def"))
    param_list = build_param_list(ctx, py_def.args, self_name)
    return_type = None
    if getattr(py_def, 'returns', None) is not None:
        return_type = build_expr(ctx, py_def.returns)
    decl = Decl(r, param_list, return_type)
    is_method = self_name is not None
    if type_line is not None:
        type_comment_decl = torch._C.parse_type_comment(type_line)
        decl = torch._C.merge_type_from_type_comment(decl, type_comment_decl, is_method)

    return Def(Ident(r, def_name),
               decl,
               build_stmts(ctx, body))


_vararg_kwarg_err = ("Compiled functions can't take variable number of arguments "
                     "or use keyword-only arguments with defaults")


def build_param_list(ctx, py_args, self_name):
    if py_args.kwarg is not None:
        expr = py_args.kwarg
        ctx_range = ctx.make_range(expr.lineno, expr.col_offset - 1, expr.col_offset + len(expr.arg))
        raise NotSupportedError(ctx_range, _vararg_kwarg_err)
    if py_args.vararg is not None:
        expr = py_args.vararg
        ctx_range = ctx.make_range(expr.lineno, expr.col_offset - 1, expr.col_offset + len(expr.arg))
        raise NotSupportedError(ctx_range, _vararg_kwarg_err)
    if len(py_args.kw_defaults) > 0:
        # kw_defaults is a list of the values for the kwargs (which default to None),
        # so they don't actually have line numbers.
        for arg in py_args.kw_defaults:
            if arg is not None:
                ctx_range = build_expr(ctx, arg).range()
                raise NotSupportedError(ctx_range, _vararg_kwarg_err)
    result = [build_param(ctx, arg, self_name, False) for arg in py_args.args]
    result += [build_param(ctx, arg, self_name, True) for arg in py_args.kwonlyargs]
    return result


def build_param(ctx, py_arg, self_name, kwarg_only):
    # NB: In Python3 py_arg is a pair of (str arg, expr? annotation)
    name = py_arg.arg
    r = ctx.make_range(py_arg.lineno, py_arg.col_offset, py_arg.col_offset + len(name))
    if getattr(py_arg, 'annotation', None) is not None:
        annotation_expr = build_expr(ctx, py_arg.annotation)
    elif self_name is not None and name == 'self':
        annotation_expr = Var(Ident(r, self_name))
    else:
        annotation_expr = EmptyTypeAnnotation(r)
    return Param(annotation_expr, Ident(r, name), kwarg_only)


def get_default_args(fn):
    if fn is None:
        return {}

    signature = inspect.signature(fn)
    return {
        k: v.default
        for k, v in signature.parameters.items()
        if v.default is not inspect.Parameter.empty
    }


def get_default_args_for_class(cls):
    """
    Get default arguments for all methods in a class (except for static methods).

    Args:
        cls: type - The class type to inspect for default arguments.
    Returns:
        A Dict[str, Dict[str, Any]] which maps each method name to a Dict[str, Any]
        that maps each argument name to its default value.
    """
    # Get methods (except static methods because those are compiled separately as
    # if they were independent script functions).
    methods = inspect.getmembers(
        cls,
        predicate=lambda m: (inspect.ismethod(m) or inspect.isfunction(m))
        and not is_static_fn(cls, m.__name__)
        and m.__name__ in cls.__dict__
    )

    # Get method defaults. Property defaults do not need to be considered
    # because setters cannot be invoked without a value.
    defaults = {method_name: get_default_args(method_impl) for method_name, method_impl in methods}

    return defaults


class WithItemBuilder(Builder):
    @staticmethod
    def build_withitem(ctx, item):
        lineno = item.context_expr.lineno
        start = item.context_expr.col_offset
        end = start + len(pretty_node_names[ast.With])
        op_vars = item.optional_vars
        r = ctx.make_range(lineno, start, end)

        return WithItem(r, build_expr(ctx, item.context_expr), build_expr(ctx, op_vars) if op_vars else None)


class StmtBuilder(Builder):
    augassign_map = {
        ast.Add: '+',
        ast.Sub: '-',
        ast.Mult: '*',
        ast.Div: '/',
        ast.Mod: '%',
    }

    @staticmethod
    def build_Expr(ctx, stmt):
        value = stmt.value
        if value.__class__.__name__ == 'Str':
            # If a statement is a string literal expression,
            # then it is a docstring. Just ignore it.
            return None
        else:
            return ExprStmt(build_expr(ctx, value))

    @staticmethod
    def build_Assign(ctx, stmt):
        rhs = build_expr(ctx, stmt.value)
        lhs = list(map(lambda x: build_expr(ctx, x), stmt.targets))
        return Assign(lhs, rhs)

    @staticmethod
    def build_AnnAssign(ctx, stmt):
        if stmt.value is None:
            raise UnsupportedNodeError(ctx, stmt, reason='without assigned value')
        rhs = build_expr(ctx, stmt.value)
        lhs = build_expr(ctx, stmt.target)
        the_type = build_expr(ctx, stmt.annotation)
        return Assign([lhs], rhs, the_type)

    @staticmethod
    def build_Delete(ctx, stmt):
        if len(stmt.targets) > 1:
            source_range = ctx.make_range(stmt.lineno, stmt.col_offset,
                                          stmt.col_offset + len("del"))
            raise NotSupportedError(
                source_range, 'del with more than one operand is not supported')
        return Delete(build_expr(ctx, stmt.targets[0]))

    @staticmethod
    def build_Return(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("return"))
        return Return(r, None if stmt.value is None else build_expr(ctx, stmt.value))

    @staticmethod
    def build_Raise(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("raise"))
        expr = build_expr(ctx, stmt.exc)
        return Raise(r, expr)

    @staticmethod
    def build_Assert(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("assert"))
        test = build_expr(ctx, stmt.test)
        msg = build_expr(ctx, stmt.msg) if stmt.msg is not None else None
        return Assert(r, test, msg)

    @staticmethod
    def build_AugAssign(ctx, stmt):
        lhs = build_expr(ctx, stmt.target)
        rhs = build_expr(ctx, stmt.value)
        op = type(stmt.op)
        if op in StmtBuilder.augassign_map:
            op_token = StmtBuilder.augassign_map[op]
        else:
            raise NotSupportedError(
                find_before(ctx, rhs.range().start, '=', offsets=(-1, 0)),
                "unsupported kind of augumented assignment: " + op.__name__)
        return AugAssign(lhs, op_token, rhs)

    @staticmethod
    def build_While(ctx, stmt):
        if stmt.orelse:
            # TODO: try to recover the location of else:? Python doesn't give us useful
            # annotations in this case
            raise NotSupportedError(None, "else branches of while loops aren't supported")
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("while"))
        return While(r, build_expr(ctx, stmt.test),
                     build_stmts(ctx, stmt.body))

    @staticmethod
    def build_For(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("for"))
        return For(
            r, [build_expr(ctx, stmt.target)],
            [build_expr(ctx, stmt.iter)], build_stmts(ctx, stmt.body))

    @staticmethod
    def build_If(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("if"))
        return If(r, build_expr(ctx, stmt.test),
                  build_stmts(ctx, stmt.body),
                  build_stmts(ctx, stmt.orelse))

    @staticmethod
    def build_Print(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("print"))
        if stmt.dest:
            raise NotSupportedError(r, "print statements with non-default destinations aren't supported")
        args = [build_expr(ctx, val) for val in stmt.values]
        return ExprStmt(Apply(Var(Ident(r, "print")), args, []))

    @staticmethod
    def build_Pass(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("pass"))
        return Pass(r)

    @staticmethod
    def build_Break(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("break"))
        return Break(r)

    @staticmethod
    def build_Continue(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("continue"))
        return Continue(r)

    @staticmethod
    def build_With(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset + len("with"))
        return With(r, build_withitems(ctx, stmt.items), build_stmts(ctx, stmt.body))

class ExprBuilder(Builder):
    binop_map = {
        ast.Add: '+',
        ast.Sub: '-',
        ast.Mult: '*',
        ast.Div: '/',
        ast.Pow: '**',
        ast.Mod: '%',
        ast.FloorDiv: '//',
        ast.BitAnd: '&',
        ast.BitXor: '^',
        ast.BitOr: '|',
        ast.LShift: '<<',
        ast.RShift: '>>',
    }

    binop_map[ast.MatMult] = '@'

    unop_map = {
        ast.Not: 'not',
        ast.USub: '-',
        ast.Invert: '~',
    }

    boolop_map = {
        ast.And: 'and',
        ast.Or: 'or',
    }

    cmpop_map = {
        ast.Eq: '==',
        ast.NotEq: '!=',
        ast.LtE: '<=',
        ast.Lt: '<',
        ast.GtE: '>=',
        ast.Gt: '>',
        ast.Is: 'is',
        ast.IsNot: 'is not',
        ast.In: 'in',
        ast.NotIn: 'not in',
    }

    @staticmethod
    def build_Attribute(ctx, expr):
        base = build_expr(ctx, expr.value)
        # expr.attr is just a string, so it's not annotated in any way, so we have
        # to build the range manually
        source = ctx.source.encode('utf-8')

        def get_char(index):
            return chr(source[index])

        start_pos = base.range().end + 1
        while get_char(start_pos) in string.whitespace:  # Skip whitespace
            start_pos += 1
        end_pos = start_pos + len(expr.attr)
        name_range = ctx.make_raw_range(start_pos, end_pos)
        return Select(base, Ident(name_range, expr.attr))

    @staticmethod
    def build_Call(ctx, expr):
        func = build_expr(ctx, expr.func)
        args = [build_expr(ctx, py_arg) for py_arg in expr.args]
        if hasattr(expr, 'starargs') and expr.starargs:
            stararg_expr = build_expr(ctx, expr.starargs)
            args += [Starred(stararg_expr.range(), stararg_expr)]
        kwargs = []
        for kw in expr.keywords:
            kw_expr = build_expr(ctx, kw.value)
            # XXX: we could do a better job at figuring out the range for the name here
            if not kw.arg:
                raise NotSupportedError(kw_expr.range(), 'keyword-arg expansion is not supported')
            kwargs.append(Attribute(Ident(kw_expr.range(), kw.arg), kw_expr))
        return Apply(func, args, kwargs)

    @staticmethod
    def build_Ellipsis(ctx, expr):
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 3)  # len("...") == 3
        return Dots(r)

    @staticmethod
    def build_Name(ctx, expr):
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + len(expr.id))
        if expr.id.startswith(_reserved_prefix):
            raise NotSupportedError(r, "names of variables used in JIT-ed functions "
                                       "can't start with " + _reserved_prefix)
        if expr.id == "True":
            return TrueLiteral(r)
        elif expr.id == "False":
            return FalseLiteral(r)
        elif expr.id == "None":
            return NoneLiteral(r)
        return Var(Ident(r, expr.id))

    @staticmethod
    def build_NameConstant(ctx, expr):
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + len(str(expr.value)))
        if expr.value is True:
            return TrueLiteral(r)
        elif expr.value is False:
            return FalseLiteral(r)
        elif expr.value is None:
            return NoneLiteral(r)
        else:
            raise ValueError("Name constant value unsupported: " + str(expr.value))

    @staticmethod
    def build_BinOp(ctx, expr):
        lhs = build_expr(ctx, expr.left)
        rhs = build_expr(ctx, expr.right)
        op = type(expr.op)

        if op == ast.Div and not ctx.uses_true_division:
            err_range = ctx.make_raw_range(lhs.range().end, rhs.range().start)
            raise FrontendError(err_range, 'Division of ints in TorchScript uses Python 3 true '
                                'division semantics. Please put `from __future__ '
                                'import division` at the top of your file')
        op_token = ExprBuilder.binop_map.get(op)
        if op_token is None:
            err_range = ctx.make_raw_range(lhs.range().end, rhs.range().start)
            raise NotSupportedError(err_range, "unsupported binary operator: " + op.__name__)
        return BinOp(op_token, lhs, rhs)

    @staticmethod
    def build_UnaryOp(ctx, expr):
        sub_expr = build_expr(ctx, expr.operand)
        op = type(expr.op)
        op_token = ExprBuilder.unop_map.get(op)
        if op_token is None:
            raise NotSupportedError(expr.range(), "unsupported unary operator: " + op.__name__)
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + len(op_token))
        return UnaryOp(r, op_token, sub_expr)

    @staticmethod
    def build_BoolOp(ctx, expr):
        if len(expr.values) < 2:
            raise AssertionError("expected at least 2 values in BoolOp, but got " + str(len(expr.values)))
        sub_exprs = [build_expr(ctx, sub_expr) for sub_expr in expr.values]
        op = type(expr.op)
        op_token = ExprBuilder.boolop_map.get(op)
        if op_token is None:
            err_range = ctx.make_raw_range(sub_exprs[0].range().end, sub_exprs[1].range().start)
            raise NotSupportedError(err_range, "unsupported boolean operator: " + op.__name__)
        lhs = sub_exprs[0]
        for rhs in sub_exprs[1:]:
            lhs = BinOp(op_token, lhs, rhs)
        return lhs

    @staticmethod
    def build_IfExp(ctx, expr):
        return TernaryIf(build_expr(ctx, expr.test),
                         build_expr(ctx, expr.body),
                         build_expr(ctx, expr.orelse))

    @staticmethod
    def build_Compare(ctx, expr):
        operands = [build_expr(ctx, e) for e in [expr.left] + list(expr.comparators)]
        result = None
        for lhs, op_, rhs in zip(operands, expr.ops, operands[1:]):
            op = type(op_)
            op_token = ExprBuilder.cmpop_map.get(op)
            r = ctx.make_raw_range(lhs.range().end, rhs.range().start)
            if op_token is None:
                raise NotSupportedError(r, "unsupported comparison operator: " + op.__name__)

            if op == ast.NotIn:
                # NB: `not in` is just `not( in )`, so we don't introduce new tree view
                # but just make it a nested call in our tree view structure
                in_expr = BinOp('in', lhs, rhs)
                cmp_expr = UnaryOp(r, 'not', in_expr)
            else:
                cmp_expr = BinOp(op_token, lhs, rhs)

            if result is None:
                result = cmp_expr
            else:
                result = BinOp('and', result, cmp_expr)
        return result

    @staticmethod
    def build_Subscript(ctx, expr):
        def build_SliceExpr(ctx, base, slice_expr):
            lower = build_expr(ctx, slice_expr.lower) if slice_expr.lower is not None else None
            upper = build_expr(ctx, slice_expr.upper) if slice_expr.upper is not None else None
            step = build_expr(ctx, slice_expr.step) if slice_expr.step is not None else None
            return SliceExpr(base.range(), lower, upper, step)

        def build_Index(ctx, base, index_expr):
            if isinstance(index_expr.value, ast.Tuple) or \
                    isinstance(index_expr.value, ast.List):
                raise NotSupportedError(base.range(),
                                        "slicing multiple dimensions with "
                                        "sequences not supported yet")
            return build_expr(ctx, index_expr.value)

        def build_ExtSlice(ctx, base, extslice):
            sub_exprs = []
            for expr in extslice.dims:
                sub_type = type(expr)
                if sub_type is ast.Index:
                    sub_exprs.append(build_Index(ctx, base, expr))
                elif sub_type is ast.Slice:
                    sub_exprs.append(build_SliceExpr(ctx, base, expr))
                elif sub_type is ast.Ellipsis:
                    sub_exprs.append(Dots(base.range()))
                else:
                    raise NotSupportedError(base.range(),
                                            "slicing multiple dimensions with "
                                            "{} not supported".format(sub_type))
            return sub_exprs

        base = build_expr(ctx, expr.value)
        sub_type = type(expr.slice)
        if sub_type is ast.Index:
            if isinstance(expr.slice.value, ast.Tuple):
                # N-dimensional indexing using Tuple: x[(i, j, k)] is equivalent to x[i, j, k]
                # XXX: Indexing using a list is **different**! It triggers advanced indexing.
                indices = []
                for index_expr in expr.slice.value.elts:
                    indices.append(build_expr(ctx, index_expr))
                return Subscript(base, indices)
            else:
                return Subscript(base, [build_expr(ctx, expr.slice.value)])
        elif sub_type is ast.Slice:
            return Subscript(base, [build_SliceExpr(ctx, base, expr.slice)])
        elif sub_type is ast.ExtSlice:
            return Subscript(base, build_ExtSlice(ctx, base, expr.slice))
        else:  # Ellipsis (can only happen in Python 2)
            raise NotSupportedError(base.range(), "ellipsis is not supported")

    @staticmethod
    def build_List(ctx, expr):
        return ListLiteral(ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1),
                           [build_expr(ctx, e) for e in expr.elts])

    @staticmethod
    def build_Tuple(ctx, expr):
        return TupleLiteral(ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1),
                            [build_expr(ctx, e) for e in expr.elts])

    @staticmethod
    def build_Dict(ctx, expr):
        return DictLiteral(ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1),
                           [build_expr(ctx, e) for e in expr.keys], [build_expr(ctx, e) for e in expr.values])

    @staticmethod
    def build_Num(ctx, expr):
        value = str(expr.n)
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + len(value))
        return Const(r, value)

    @staticmethod
    def build_Constant(ctx, expr):
        value = expr.value
        if value is None or isinstance(value, bool):
            # NB: this check has to happen before the int check because bool is
            # a subclass of int
            return ExprBuilder.build_NameConstant(ctx, expr)
        if isinstance(value, (int, float)):
            return ExprBuilder.build_Num(ctx, expr)
        elif isinstance(value, str):
            return ExprBuilder.build_Str(ctx, expr)
        elif isinstance(value, type(Ellipsis)):
            return ExprBuilder.build_Ellipsis(ctx, expr)
        else:
            error_range = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + len(str(value)))
            raise FrontendError(error_range, "Unknown Constant expression type")

    @staticmethod
    def build_Str(ctx, expr):
        value = str(expr.s)
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1)
        return StringLiteral(r, value)

    @staticmethod
    def build_JoinedStr(ctx, expr):
        s = ''
        args = []
        for value in expr.values:
            r = ctx.make_range(value.lineno, value.col_offset, value.col_offset + 1)
            if isinstance(value, ast.FormattedValue):
                if value.conversion != -1:
                    raise NotSupportedError(r, 'Don\'t support conversion in JoinedStr')
                if value.format_spec is not None:
                    raise NotSupportedError(r, 'Don\'t support formatting in JoinedStr')
                s += '{}'
                args.append(build_expr(ctx, value.value))
            elif isinstance(value, ast.Str):
                s += value.s
            else:
                raise NotSupportedError(r, 'Unsupported value in JoinedStr')

        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1)
        return Apply(Select(StringLiteral(r, s), Ident(r, 'format')), args, [])

    @staticmethod
    def build_ListComp(ctx, stmt):
        r = ctx.make_range(stmt.lineno, stmt.col_offset, stmt.col_offset)
        if (len(stmt.generators) > 1):
            raise NotSupportedError(r, "multiple comprehension generators not supported yet")

        if (len(stmt.generators[0].ifs) != 0):
            raise NotSupportedError(r, "comprehension ifs not supported yet")

        elt_expr = build_expr(ctx, stmt.elt)
        target_expr = build_expr(ctx, stmt.generators[0].target)

        iter_expr = build_expr(ctx, stmt.generators[0].iter)
        return ListComp(r, elt_expr, target_expr, iter_expr)

    @staticmethod
    def build_Starred(ctx, expr):
        r = ctx.make_range(expr.lineno, expr.col_offset, expr.col_offset + 1)
        return Starred(r, build_expr(ctx, expr.value))

build_expr = ExprBuilder()
build_stmt = StmtBuilder()
build_withitem = WithItemBuilder()

def find_before(ctx, pos, substr, offsets=(0, 0)):
    new_pos = ctx.source[:pos].rindex(substr)
    return ctx.make_raw_range(new_pos + offsets[0], new_pos + len(substr) + offsets[1])