From 6f8a1bf831e32f10f9304dacc7ecba2958d955d7 Mon Sep 17 00:00:00 2001
From: Reid McKenzie <me@arrdem.com>
Date: Fri, 14 May 2021 11:55:28 -0600
Subject: [PATCH] yamlschema

---
 projects/yamlschema/BUILD         |  12 ++++
 projects/yamlschema/README.md     |   3 +
 projects/yamlschema/yamlschema.py | 111 ++++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+)
 create mode 100644 projects/yamlschema/BUILD
 create mode 100644 projects/yamlschema/README.md
 create mode 100644 projects/yamlschema/yamlschema.py

diff --git a/projects/yamlschema/BUILD b/projects/yamlschema/BUILD
new file mode 100644
index 0000000..03c512d
--- /dev/null
+++ b/projects/yamlschema/BUILD
@@ -0,0 +1,12 @@
+py_library(
+    name = "yamlschema",
+    srcs = [
+        "yamlschema.py",
+    ],
+    imports = [
+        ".",
+    ],
+    deps = [
+        py_requirement("PyYAML"),
+    ]
+)
diff --git a/projects/yamlschema/README.md b/projects/yamlschema/README.md
new file mode 100644
index 0000000..22cf4b2
--- /dev/null
+++ b/projects/yamlschema/README.md
@@ -0,0 +1,3 @@
+# YAML Schema
+
+A pocket library that implements some amount of jsonschema validation against YAML documents.
diff --git a/projects/yamlschema/yamlschema.py b/projects/yamlschema/yamlschema.py
new file mode 100644
index 0000000..ef83795
--- /dev/null
+++ b/projects/yamlschema/yamlschema.py
@@ -0,0 +1,111 @@
+"""
+JSONSchema linting for YAML documents.
+"""
+
+import logging
+import typing as t
+
+from yaml.nodes import MappingNode, Node, ScalarNode, SequenceNode
+
+
+log = logging.getLogger(__name__)
+
+
+def lint_mapping(schema, node: Node) -> t.List[str]:
+  lint: t.List[str] = []
+  if schema["type"] != "object" or not isinstance(node, MappingNode):
+    raise TypeError(
+        f"Expected {schema['type']}, got {node.id} {str(node.start_mark).lstrip()}"
+    )
+
+  additional_allowed: bool = schema.get("additionalProperties", False) != False
+  additional_type: t.Union[dict, bool] = (
+    schema.get("additionalProperties") if additional_allowed
+    else {}
+  )
+  properties: dict = schema.get("properties", {})
+  required: t.List[str] = schema.get("required", [])
+
+  for k in required:
+    if k not in [_k.value for _k, _v in node.value]:
+      raise TypeError(
+          f"Required key {k!r} absent from mapping {str(node.start_mark).lstrip()}"
+      )
+
+  for k, v in node.value:
+    if k.value in properties:
+      lint.extend(lint_document(properties.get(k.value), v))
+
+    elif additional_allowed:
+      # 'true' is a way to encode the any type.
+      if additional_type == True:
+        pass
+      else:
+        lint.extend(lint_document(additional_type, v))
+    else:
+      lint.append(
+          f"Key {k.value!r} is not allowed by schema {str(node.start_mark).lstrip()}"
+      )
+
+  return lint
+
+
+def lint_sequence(schema, node: Node) -> t.List[str]:
+  """"FIXME.
+
+  There aren't sequences we need to lint in the current schema design, punting.
+
+  """
+
+  if schema["type"] != "array" or not isinstance(node, SequenceNode):
+    raise TypeError(
+      f"Expected {schema['type']}, got {node.id} {str(node.start_mark).lstrip()}"
+    )
+
+  lint = []
+  subschema = schema.get("items")
+  if subschema:
+    for item in node.value:
+      lint.extend(lint_document(subschema, item))
+  return lint
+
+
+def lint_scalar(schema, node: Node) -> t.List[str]:
+  """FIXME.
+
+  The only terminal we care about linting in the current schema is {"type": "string"}.
+
+  """
+  if schema["type"] not in ["string", "number"] or not isinstance(node, ScalarNode):
+    raise TypeError(
+      f"Expected {schema['type']}, got {node.id} {str(node.start_mark).lstrip()}"
+    )
+
+  lint = []
+  if schema["type"] == "string":
+    if not isinstance(node.value, str):
+      lint.append(f"Expected string, got {node.id} {str(node.start_mark).lstrip()}")
+  else:
+    log.info(f"Ignoring unlintable scalar, schema {schema!r} {str(node.start_mark).lstrip()}")
+
+  return lint
+
+
+def lint_document(schema, node):
+  """Lint a document.
+
+  Given a Node within a document (or the root of a document!), return a
+  (possibly empty!) list of lint or raise in case of fatal errors.
+
+  """
+
+  if schema == True or schema == {}:
+    return []
+  elif isinstance(node, MappingNode):
+    return lint_mapping(schema, node)
+  elif isinstance(node, SequenceNode):
+    return lint_sequence(schema, node)
+  elif isinstance(node, ScalarNode):
+    return lint_scalar(schema, node)
+  else:
+    return []