feat: add config loading with env var substitution

config.yaml.example

@@ -0,0 +1,40 @@
+# config.yaml.example
+
+# ============================================================
+# Token Generation:
+#   python -c "import secrets; print(secrets.token_urlsafe(32))"
+#   openssl rand -base64 32
+# ============================================================
+
+# Document definitions (each is self-contained)
+documents:
+  budget-2024:
+    url: https://work.getgrist.com
+    doc_id: mK7xB2pQ9mN4v
+    api_key: ${GRIST_WORK_API_KEY}
+
+  expenses:
+    url: https://work.getgrist.com
+    doc_id: nL8yC3qR0oO5w
+    api_key: ${GRIST_WORK_API_KEY}
+
+  personal-tracker:
+    url: https://docs.getgrist.com
+    doc_id: pN0zE5sT2qP7x
+    api_key: ${GRIST_PERSONAL_API_KEY}
+
+# Agent tokens with access scopes
+tokens:
+  - token: REPLACE_WITH_GENERATED_TOKEN
+    name: finance-agent
+    scope:
+      - document: budget-2024
+        permissions: [read, write]
+      - document: expenses
+        permissions: [read]
+
+  - token: REPLACE_WITH_ANOTHER_TOKEN
+    name: analytics-agent
+    scope:
+      - document: personal-tracker
+        permissions: [read, write, schema]

src/grist_mcp/config.py

@@ -0,0 +1,99 @@
+"""Configuration loading and parsing."""
+
+import os
+import re
+from dataclasses import dataclass
+from pathlib import Path
+
+import yaml
+
+
+@dataclass
+class Document:
+    """A Grist document configuration."""
+    url: str
+    doc_id: str
+    api_key: str
+
+
+@dataclass
+class TokenScope:
+    """Access scope for a single document."""
+    document: str
+    permissions: list[str]
+
+
+@dataclass
+class Token:
+    """An agent token with its access scopes."""
+    token: str
+    name: str
+    scope: list[TokenScope]
+
+
+@dataclass
+class Config:
+    """Full server configuration."""
+    documents: dict[str, Document]
+    tokens: list[Token]
+
+
+def _substitute_env_vars(value: str) -> str:
+    """Replace ${VAR} patterns with environment variable values."""
+    pattern = r'\$\{([^}]+)\}'
+
+    def replacer(match: re.Match) -> str:
+        var_name = match.group(1)
+        env_value = os.environ.get(var_name)
+        if env_value is None:
+            raise ValueError(f"Environment variable not set: {var_name}")
+        return env_value
+
+    return re.sub(pattern, replacer, value)
+
+
+def _substitute_env_vars_recursive(obj):
+    """Recursively substitute env vars in a data structure."""
+    if isinstance(obj, str):
+        return _substitute_env_vars(obj)
+    elif isinstance(obj, dict):
+        return {k: _substitute_env_vars_recursive(v) for k, v in obj.items()}
+    elif isinstance(obj, list):
+        return [_substitute_env_vars_recursive(item) for item in obj]
+    return obj
+
+
+def load_config(config_path: str) -> Config:
+    """Load and parse configuration from YAML file."""
+    path = Path(config_path)
+    raw = yaml.safe_load(path.read_text())
+
+    # Substitute environment variables
+    raw = _substitute_env_vars_recursive(raw)
+
+    # Parse documents
+    documents = {}
+    for name, doc_data in raw.get("documents", {}).items():
+        documents[name] = Document(
+            url=doc_data["url"],
+            doc_id=doc_data["doc_id"],
+            api_key=doc_data["api_key"],
+        )
+
+    # Parse tokens
+    tokens = []
+    for token_data in raw.get("tokens", []):
+        scope = [
+            TokenScope(
+                document=s["document"],
+                permissions=s["permissions"],
+            )
+            for s in token_data.get("scope", [])
+        ]
+        tokens.append(Token(
+            token=token_data["token"],
+            name=token_data["name"],
+            scope=scope,
+        ))
+
+    return Config(documents=documents, tokens=tokens)

tests/test_config.py

@@ -0,0 +1,86 @@
+import pytest
+from grist_mcp.config import load_config, Config, Document, Token, TokenScope
+
+
+def test_load_config_parses_documents(tmp_path):
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text("""
+documents:
+  my-doc:
+    url: https://grist.example.com
+    doc_id: abc123
+    api_key: secret-key
+
+tokens: []
+""")
+
+    config = load_config(str(config_file))
+
+    assert "my-doc" in config.documents
+    doc = config.documents["my-doc"]
+    assert doc.url == "https://grist.example.com"
+    assert doc.doc_id == "abc123"
+    assert doc.api_key == "secret-key"
+
+
+def test_load_config_parses_tokens(tmp_path):
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text("""
+documents:
+  budget:
+    url: https://grist.example.com
+    doc_id: abc123
+    api_key: key123
+
+tokens:
+  - token: my-secret-token
+    name: test-agent
+    scope:
+      - document: budget
+        permissions: [read, write]
+""")
+
+    config = load_config(str(config_file))
+
+    assert len(config.tokens) == 1
+    token = config.tokens[0]
+    assert token.token == "my-secret-token"
+    assert token.name == "test-agent"
+    assert len(token.scope) == 1
+    assert token.scope[0].document == "budget"
+    assert token.scope[0].permissions == ["read", "write"]
+
+
+def test_load_config_substitutes_env_vars(tmp_path, monkeypatch):
+    monkeypatch.setenv("TEST_API_KEY", "env-secret-key")
+
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text("""
+documents:
+  my-doc:
+    url: https://grist.example.com
+    doc_id: abc123
+    api_key: ${TEST_API_KEY}
+
+tokens: []
+""")
+
+    config = load_config(str(config_file))
+
+    assert config.documents["my-doc"].api_key == "env-secret-key"
+
+
+def test_load_config_raises_on_missing_env_var(tmp_path):
+    config_file = tmp_path / "config.yaml"
+    config_file.write_text("""
+documents:
+  my-doc:
+    url: https://grist.example.com
+    doc_id: abc123
+    api_key: ${MISSING_VAR}
+
+tokens: []
+""")
+
+    with pytest.raises(ValueError, match="MISSING_VAR"):
+        load_config(str(config_file))