116 lines
4.6 KiB
Python
116 lines
4.6 KiB
Python
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import logging
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import re
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from ...util import levenshtein
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from ...workflow import WorkflowException
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logger = logging.getLogger('spiff.dmn')
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class DMNEngine:
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"""
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Handles the processing of a decision table.
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"""
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def __init__(self, decision_table):
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self.decision_table = decision_table
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def decide(self, task):
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for rule in self.decision_table.rules:
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if self.__check_rule(rule, task):
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return rule
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def __check_rule(self, rule, task):
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for input_entry in rule.inputEntries:
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for lhs in input_entry.lhs:
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if lhs is not None:
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input_val = DMNEngine.__get_input_val(input_entry, task.data)
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else:
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input_val = None
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try:
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if not self.evaluate(input_val, lhs, task):
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return False
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except NameError as e:
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# Add a bit of info, re-raise as Name Error
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raise NameError(str(e) + "Failed to execute "
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"expression: '%s' is '%s' in the "
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"Row with annotation '%s'")
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except WorkflowException as we:
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raise we
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except Exception as e:
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raise Exception("Failed to execute "
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"expression: '%s' is '%s' in the "
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"Row with annotation '%s', %s" % (
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input_val, lhs, rule.description, str(e)))
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else:
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# Empty means ignore decision value
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continue # Check the other operators/columns
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return True
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def needs_eq(self, script_engine, text):
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try:
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# this should work if we can just do a straight equality
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script_engine.validate(text)
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return True
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except SyntaxError:
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# if we have problems parsing, then we introduce a variable on the left hand side
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# and try that and see if that parses. If so, then we know that we do not need to
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# introduce an equality operator later in the dmn
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script_engine.validate(f'v {text}')
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return False
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def evaluate(self, input_expr, match_expr, task):
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"""
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Here we need to handle a few things such as if it is an equality or if
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the equality has already been taken care of. For now, we just assume
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it is equality.
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An optional task can be included if this is being executed in the
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context of a BPMN task.
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"""
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if match_expr is None:
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return True
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script_engine = task.workflow.script_engine
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# NB - the question mark allows us to do a double ended test - for
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# example - our input expr is 5 and the match expr is 4 < ? < 6 -
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# this should evaluate as 4 < 5 < 6 and it should evaluate as 'True'
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# NOTE: It should only do this replacement outside of quotes.
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# for example, provided "This thing?" in quotes, it should not
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# do the replacement.
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match_expr = re.sub('(\?)(?=(?:[^\'"]|[\'"][^\'"]*[\'"])*$)', 'dmninputexpr', match_expr)
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if 'dmninputexpr' in match_expr:
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external_methods = {
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'dmninputexpr': script_engine.evaluate(task, input_expr)
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}
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return script_engine.evaluate(task, match_expr,
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external_methods=external_methods)
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# The input expression just has to be something that can be parsed as is by the engine.
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try:
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script_engine.validate(input_expr)
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except Exception as e:
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raise WorkflowException(f"Input Expression '{input_expr}' is malformed. " + str(e))
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# If we get here, we need to check whether the match expression includes
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# an operator or if can use '=='
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needs_eq = self.needs_eq(script_engine, match_expr)
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expr = input_expr + ' == ' + match_expr if needs_eq else input_expr + match_expr
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return script_engine.evaluate(task, expr)
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@staticmethod
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def __get_input_val(input_entry, context):
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"""
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The input of the decision method should be an expression, but will
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fallback to the likely very bad idea of trying to use the label.
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:param inputEntry:
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:param context: # A dictionary that provides some context/local vars.
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:return:
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"""
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if input_entry.input.expression:
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return input_entry.input.expression
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else:
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# Backwards compatibility
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return "%r" % context[input_entry.input.label]
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