base POC python

.gitignore

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+python/.venv

python/config.py

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+import yaml
+import yaql
+from os import getenv, getcwd, putenv
+from os.path import exists,isfile,isdir
+from typing import Any
+
+class FileReference:
+    """
+    !FileReference should simply refer to a file that exists.
+    The file is not loaded as part of the configuration.
+    """
+    yaml_tag = '!FileReference'
+    yaml_loader = yaml.SafeLoader
+    yaml_dumper = yaml.SafeDumper
+    filename: str = None
+    def __init__(self, filename: str):
+        self.filename = filename
+    @property
+    def scalar_value(self):
+        return self.filename
+    def __repr__(self):
+        fn = self.filename
+        exists = isfile(fn)
+        return ("(reference to '{}')" if exists else "(invalid reference to '{}')").format(fn)
+
+class FileData(yaml.YAMLObject):
+    """
+    !FileData should refer to a file that exists.
+    The file's contents are then loaded as a string
+    and available for reference.
+    """
+    yaml_tag = '!FileData'
+    yaml_loader = yaml.SafeLoader
+    yaml_dumper = yaml.SafeDumper
+    filename: str = None
+    data: Any = None
+    def __init__(self, filename: str):
+        self.filename = filename
+    @property
+    def scalar_value(self):
+        return self.filename
+    def read_data(self):
+        if self.data is not None: return self.data
+        with open(self.filename,'r') as file:
+            self.data = file.read()
+        return self.data
+    def calculate_data_hash(self):
+        # to-do: actually hash the data
+        return self.data[:10] if isinstance(self.data,str) else 'DATA HASH'
+    def __repr__(self):
+        hashdata = self.calculate_data_hash()
+        return '(filename:{filename:}, data hash: {hashdata:})'.format(filename=self.filename,hashdata=hashdata)
+
+class EncryptedFileData(FileData):
+    yaml_tag = '!EncryptedFileData'
+    yaml_loader = yaml.SafeLoader
+    yaml_dumper = yaml.SafeDumper
+    def __init__(self, filename: str, key: str | FileData):
+        self.filename = filename
+        self.key = key
+    def key_data(self):
+        if isinstance(self.key, str): return self.key
+        if isinstance(self.key, FileData):
+            return self.key.read_data()
+    def decrypt(self, data, key):
+        return data
+    def read_data(self):
+        base_data = super().read_data()
+        key_data = self.key_data()
+        return self.decrypt(base_data, key_data)
+    def __repr__(self):
+        return '(encrypted file: {:})'.format(self.filename)
+
+def generic_representer(dumper, data):
+    return dumper.represent_scalar(type(data).yaml_tag, data.scalar_value)
+
+def filedata_constructor(loader, node):
+    filename = loader.construct_scalar(node)
+    return FileData(filename)
+
+def fileref_constructor(loader, node):
+    filename = loader.construct_scalar(node)
+    return FileReference(filename)
+
+yaml.add_representer(FileData, generic_representer)
+yaml.add_constructor(FileData.yaml_tag, filedata_constructor, yaml.SafeLoader)
+yaml.add_representer(FileReference, generic_representer)
+yaml.add_constructor(FileReference.yaml_tag, fileref_constructor, yaml.SafeLoader)
+
+class Configuration:
+    appname: str = ''
+    document: Any = None
+    engine: Any = None
+    def __init__(self):
+        self.engine = yaql.factory.YaqlFactory().create()
+    @property
+    def specified_configfile_variable_name(self):
+        return self.appname+"_CONFIG_FILE"
+    def find_config_file(self) -> str:
+        specified_file = getenv(self.specified_configfile_variable_name)
+        if specified_file is not None:
+            return specified_file
+        home = getenv('HOME')
+        pwd = getcwd()
+        populate_template = lambda base:base.format(appname=self.appname,pwd=pwd,home=home)
+        paths = map(populate_template,[
+            "{pwd:}/.config.yaml",
+            "{home:}/.config/{appname:}/.config.yaml",
+            "/etc/{appname:}/.config.yaml"
+        ])
+        for path in paths:
+            if isfile(path):
+                return path
+    def specify_config_file(self, fn):
+        putenv(self.specified_configfile_variable_name, fn)
+    def load_data(self, config_source=None):
+        if isinstance(config_source, str):
+            self.document = yaml.safe_load(config_source)
+            return
+        filename_to_load = self.find_config_file()
+        with open(filename_to_load,'r') as config_file:
+            self.document = yaml.safe_load(filename_to_load)
+    def save_config(self):
+        filename_to_load = self.find_config_file()
+        with open(filename_to_load,'w') as config_file:
+            yaml.safe_dump(self.document, config_file, default_flow_style=False)
+    def dump_config(self):
+        return yaml.safe_dump(self.document)
+    def query(self,query):
+        expression = self.engine(query)
+        return expression.evaluate(data=self.document)
+
+def query_property(query, unpack_filedata=True, null_invalid_file_references=True):
+    def run_query(config):
+        results = config.query(query)
+        if not (unpack_filedata or null_invalid_file_references):
+            return results
+    return property(run_query)

python/encrypted_file.txt

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+SOON MAY THE WEATHER MAN COME

python/key.txt

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+ThereOnceWasAShip

python/plain_file.txt

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+WE'LL TAKE OUR LEAVE AND GO

python/sample.py

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+from config import Configuration, query_property
+
+class SampleConfiguration(Configuration):
+    plain_file = query_property("$.plain")
+    reference = query_property("$.working_reference")
+    broken_reference = query_property("$.broken_reference")
+    encrypted_file = query_property("$.encrypted_file")
+
+
+sample_config="""
+plain: !FileData plain_file.txt
+working_reference: !FileReference plain_file.txt
+broken_reference: !FileReference fake_file.txt
+encrypted_file: !EncryptedFileData
+    filename: encrypted_file.txt
+    key: !FileReference key.txt
+"""
+
+config = SampleConfiguration()
+config.load_data(config_source=sample_config)
+
+from pprint import pprint
+
+pprint([config.reference, config.broken_reference, config.plain_file.read_data(),config.encrypted_file.read_data()])

readme.md

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+# Priorities:
+
+1. Runtime Settings
+1. `$($(appname))_CONFIG_FILE`
+1. `$PWD/.config.yaml`
+1. `$HOME/.config/$appname/.config.yaml`
+1. `/etc/$appname/.config.yaml`