# -*- coding: utf-8 -*-
#
# Copyright (C) 2006 Christopher Lenz
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://markup.cmlenz.net/wiki/License.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://markup.cmlenz.net/log/.

"""Support for "safe" evaluation of Python expressions."""

from __future__ import division

import __builtin__
try:
    import _ast # Python 2.5
except ImportError:
    _ast = None
    import compiler
import operator

from markup.core import Stream

__all__ = ['Expression']


class Expression(object):
    """Evaluates Python expressions used in templates.

    >>> data = dict(test='Foo', items=[1, 2, 3], dict={'some': 'thing'})
    >>> Expression('test').evaluate(data)
    'Foo'
    >>> Expression('items[0]').evaluate(data)
    1
    >>> Expression('items[-1]').evaluate(data)
    3
    >>> Expression('dict["some"]').evaluate(data)
    'thing'
    
    Similar to e.g. Javascript, expressions in templates can use the dot
    notation for attribute access to access items in mappings:
    
    >>> Expression('dict.some').evaluate(data)
    'thing'
    
    This also works the other way around: item access can be used to access
    any object attribute (meaning there's no use for `getattr()` in templates):
    
    >>> class MyClass(object):
    ...     myattr = 'Bar'
    >>> data = dict(mine=MyClass(), key='myattr')
    >>> Expression('mine.myattr').evaluate(data)
    'Bar'
    >>> Expression('mine["myattr"]').evaluate(data)
    'Bar'
    >>> Expression('mine[key]').evaluate(data)
    'Bar'
    
    All of the standard Python operators are available to template expressions.
    Built-in functions such as `len()` are also available in template
    expressions:
    
    >>> data = dict(items=[1, 2, 3])
    >>> Expression('len(items)').evaluate(data)
    3
    """
    __slots__ = ['source', 'ast']
    __visitors = {}

    def __init__(self, source):
        """Create the expression.
        
        @param source: the expression as string
        """
        self.source = source
        self.ast = None

    def __repr__(self):
        return '<Expression "%s">' % self.source

    if _ast is None:

        def evaluate(self, data):
            """Evaluate the expression against the given data dictionary.
            
            @param data: a mapping containing the data to evaluate against
            @return: the result of the evaluation
            """
            if not self.ast:
                self.ast = compiler.parse(self.source, 'eval')
            return self._visit(self.ast.node, data)

        # AST traversal

        def _visit(self, node, data):
            v = self.__visitors.get(node.__class__)
            if not v:
                v = getattr(self, '_visit_%s' % node.__class__.__name__.lower())
                self.__visitors[node.__class__] = v
            return v(node, data)

        def _visit_expression(self, node, data):
            for child in node.getChildNodes():
                return self._visit(child, data)

        # Functions & Accessors

        def _visit_callfunc(self, node, data):
            func = self._visit(node.node, data)
            if func is None:
                return None
            args = [self._visit(arg, data) for arg in node.args
                    if not isinstance(arg, compiler.ast.Keyword)]
            kwargs = dict([(arg.name, self._visit(arg.expr, data)) for arg
                           in node.args if isinstance(arg, compiler.ast.Keyword)])
            return func(*args, **kwargs)

        def _visit_getattr(self, node, data):
            obj = self._visit(node.expr, data)
            if hasattr(obj, node.attrname):
                return getattr(obj, node.attrname)
            try:
                return obj[node.attrname]
            except TypeError:
                return None

        def _visit_slice(self, node, data):
            obj = self._visit(node.expr, data)
            lower = node.lower and self._visit(node.lower, data) or None
            upper = node.upper and self._visit(node.upper, data) or None
            return obj[lower:upper]

        def _visit_subscript(self, node, data):
            obj = self._visit(node.expr, data)
            subs = map(lambda sub: self._visit(sub, data), node.subs)
            if len(subs) == 1:
                subs = subs[0]
            try:
                return obj[subs]
            except (KeyError, IndexError, TypeError):
                try:
                    return getattr(obj, subs)
                except (AttributeError, TypeError):
                    return None

        # Operators

        def _visit_and(self, node, data):
            return reduce(lambda x, y: x and y,
                          [self._visit(n, data) for n in node.nodes])

        def _visit_or(self, node, data):
            return reduce(lambda x, y: x or y,
                          [self._visit(n, data) for n in node.nodes])

        def _visit_bitand(self, node, data):
            return reduce(operator.and_,
                          [self._visit(n, data) for n in node.nodes])

        def _visit_bitor(self, node, data):
            return reduce(operator.or_,
                          [self._visit(n, data) for n in node.nodes])

        _OP_MAP = {'==': operator.eq, '!=': operator.ne,
                   '<':  operator.lt, '<=': operator.le,
                   '>':  operator.gt, '>=': operator.ge,
                   'is': operator.is_, 'is not': operator.is_not,
                   'in': lambda x, y: operator.contains(y, x),
                   'not in': lambda x, y: not operator.contains(y, x)}
        def _visit_compare(self, node, data):
            result = self._visit(node.expr, data)
            ops = node.ops[:]
            ops.reverse()
            for op, rval in ops:
                result = self._OP_MAP[op](result, self._visit(rval, data))
            return result

        def _visit_add(self, node, data):
            return self._visit(node.left, data) + self._visit(node.right, data)

        def _visit_div(self, node, data):
            return self._visit(node.left, data) / self._visit(node.right, data)

        def _visit_floordiv(self, node, data):
            return self._visit(node.left, data) // self._visit(node.right, data)

        def _visit_mod(self, node, data):
            return self._visit(node.left, data) % self._visit(node.right, data)

        def _visit_mul(self, node, data):
            return self._visit(node.left, data) * self._visit(node.right, data)

        def _visit_power(self, node, data):
            return self._visit(node.left, data) ** self._visit(node.right, data)

        def _visit_sub(self, node, data):
            return self._visit(node.left, data) - self._visit(node.right, data)

        def _visit_unaryadd(self, node, data):
            return +self._visit(node.expr, data)

        def _visit_unarysub(self, node, data):
            return -self._visit(node.expr, data)

        def _visit_not(self, node, data):
            return not self._visit(node.expr, data)

        def _visit_invert(self, node, data):
            return ~self._visit(node.expr, data)

        # Identifiers & Literals

        def _visit_name(self, node, data):
            val = data.get(node.name)
            if val is None:
                val = getattr(__builtin__, node.name, None)
            return val

        def _visit_const(self, node, data):
            return node.value

        def _visit_dict(self, node, data):
            return dict([(self._visit(k, data), self._visit(v, data))
                         for k, v in node.items])

        def _visit_tuple(self, node, data):
            return tuple([self._visit(n, data) for n in node.nodes])

        def _visit_list(self, node, data):
            return [self._visit(n, data) for n in node.nodes]

    else:

        def evaluate(self, data):
            """Evaluate the expression against the given data dictionary.
            
            @param data: a mapping containing the data to evaluate against
            @return: the result of the evaluation
            """
            if not self.ast:
                self.ast = compile(self.source, '?', 'eval', 0x400)
            return self._visit(self.ast, data)

        # AST traversal

        def _visit(self, node, data):
            v = self.__visitors.get(node.__class__)
            if not v:
                v = getattr(self, '_visit_%s' % node.__class__.__name__.lower())
                self.__visitors[node.__class__] = v
            return v(node, data)

        def _visit_expression(self, node, data):
            return self._visit(node.body, data)

        # Functions & Accessors

        def _visit_attribute(self, node, data):
            obj = self._visit(node.value, data)
            if hasattr(obj, node.attr):
                return getattr(obj, node.attr)
            try:
                return obj[node.attr]
            except TypeError:
                return None

        def _visit_call(self, node, data):
            func = self._visit(node.func, data)
            if func is None:
                return None
            args = [self._visit(arg, data) for arg in node.args]
            kwargs = dict([(kwarg.arg, self._visit(kwarg.value, data))
                           for kwarg in node.keywords])
            return func(*args, **kwargs)

        def _visit_subscript(self, node, data):
            obj = self._visit(node.value, data)
            if isinstance(node.slice, _ast.Slice):
                try:
                    return obj[self._visit(lower, data):
                               self._visit(upper, data):
                               self._visit(step, data)]
                except (KeyError, IndexError, TypeError):
                    pass
            else:
                index = self._visit(node.slice.value, data)
                try:
                    return obj[index]
                except (KeyError, IndexError, TypeError):
                    try:
                        return getattr(obj, index)
                    except (AttributeError, TypeError):
                        pass
            return None

        # Operators

        _OP_MAP = {_ast.Add: operator.add, _ast.And: lambda l, r: l and r,
                   _ast.BitAnd: operator.and_, _ast.BitOr: operator.or_,
                   _ast.Div: operator.truediv, _ast.Eq: operator.eq,
                   _ast.FloorDiv: operator.floordiv, _ast.Gt: operator.gt,
                   _ast.GtE: operator.ge, _ast.Invert: operator.inv,
                   _ast.In: lambda l, r: operator.contains(r, l),
                   _ast.Is: operator.is_, _ast.IsNot: operator.is_not,
                   _ast.Lt: operator.lt, _ast.LtE: operator.le,
                   _ast.Mod: operator.mod, _ast.Mult: operator.mul,
                   _ast.Not: operator.not_, _ast.NotEq: operator.ne,
                   _ast.NotIn: lambda l, r: not operator.contains(r, l),
                   _ast.Or: lambda l, r: l or r, _ast.Pow: operator.pow,
                   _ast.Sub: operator.sub, _ast.UAdd: operator.pos,
                   _ast.USub: operator.neg}

        def _visit_unaryop(self, node, data):
            return self._OP_MAP[node.op.__class__](self._visit(node.operand, data))

        def _visit_binop(self, node, data):
            return self._OP_MAP[node.op.__class__](self._visit(node.left, data),
                                                   self._visit(node.right, data))

        def _visit_boolop(self, node, data):
            return reduce(self._OP_MAP[node.op.__class__],
                          [self._visit(n, data) for n in node.values])

        def _visit_compare(self, node, data):
            result = self._visit(node.left, data)
            ops = node.ops[:]
            ops.reverse()
            for op, rval in zip(ops, node.comparators):
                result = self._OP_MAP[op.__class__](result,
                                                     self._visit(rval, data))
            return result

        # Identifiers & Literals

        def _visit_dict(self, node, data):
            return dict([(self._visit(k, data), self._visit(v, data))
                         for k, v in zip(node.keys, node.values)])

        def _visit_list(self, node, data):
            return [self._visit(n, data) for n in node.elts]

        def _visit_name(self, node, data):
            val = data.get(node.id)
            if val is None:
                val = getattr(__builtin__, node.id, None)
            return val

        def _visit_num(self, node, data):
            return node.n

        def _visit_str(self, node, data):
            return node.s

        def _visit_tuple(self, node, data):
            return tuple([self._visit(n, data) for n in node.elts])