import re
from ..utils.patches import create_patch

class FormatExternalFunction:

    @staticmethod
    def format (slither, patches, elements):
        for element in elements:
            target_contract = slither.get_contract_from_name(element['type_specific_fields']['parent']['name'])
            if target_contract:
                for function in target_contract.functions:
                    if function.name == element['name']:
                        # If function parameters are written to in function body then we cannot convert this function
                        # to external because external function parameters are allocated in calldata region which is
                        # non-modifiable. See https://solidity.readthedocs.io/en/develop/types.html#data-location
                        if not FormatExternalFunction.function_parameters_written(function):
                            FormatExternalFunction.create_patch(slither, patches,
                                                                element['source_mapping']['filename_absolute'],
                                                                element['source_mapping']['filename_relative'],
                                                                "external",
                                                                int(function.parameters_src.source_mapping['start']),
                                                                int(function.returns_src.source_mapping['start']))
                            break

    @staticmethod
    def create_patch(slither, patches, in_file, in_file_relative, replace_text, modify_loc_start, modify_loc_end):
        in_file_str = slither.source_code[in_file].encode('utf-8')
        old_str_of_interest = in_file_str[modify_loc_start:modify_loc_end]
        m = re.search(r'((\spublic)\s+)|(\spublic)$|(\)public)$', old_str_of_interest.decode('utf-8'))
        if m is None:
            # No visibility specifier exists; public by default.
            create_patch(patches,
                         "external-function",
                         in_file_relative,
                         in_file,
                         modify_loc_start + len(old_str_of_interest.decode('utf-8').split(')')[0]) + 1,
                         modify_loc_start + len(old_str_of_interest.decode('utf-8').split(')')[0]) + 1,
                         "",
                         " "+ replace_text)
        else:
            create_patch(patches,
                         "external-function",
                         in_file_relative,
                         in_file,
                         modify_loc_start + m.span()[0] + 1,
                         modify_loc_start + m.span()[0] + 1 + 6,
                         "",
                         " " + replace_text)

    @staticmethod
    def function_parameters_written(function):
        for node in function.nodes:
            if any (var.name == parameter.name for var in node.local_variables_written for parameter in function.parameters):
                return True
        return False