feat: add config loader with validation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/config.py

@@ -0,0 +1,194 @@
+"""Configuration loader and validation for ai-chat-exporter."""
+
+import logging
+import os
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
+from pathlib import Path
+
+import jwt
+from dotenv import load_dotenv
+
+from src.utils import format_token_status
+
+logger = logging.getLogger(__name__)
+
+# Placeholder values from .env.example — reject if still set
+_CHATGPT_PLACEHOLDER = ""
+_CLAUDE_PLACEHOLDER = ""
+
+# Valid OUTPUT_STRUCTURE values
+VALID_STRUCTURES = {"provider/project/year", "provider/project", "provider/year"}
+
+
+class ConfigError(Exception):
+    """Raised when required configuration is missing or invalid."""
+
+
+@dataclass
+class Config:
+    chatgpt_session_token: str | None
+    claude_session_key: str | None
+    export_dir: Path
+    output_structure: str
+    cache_dir: Path
+    log_file: str
+    # Decoded ChatGPT JWT expiry (None if token absent or not a JWT)
+    chatgpt_token_expiry: datetime | None = field(default=None, repr=False)
+
+
+def load_config() -> Config:
+    """Load configuration from environment / .env file.
+
+    Validates all values and logs a startup summary.
+
+    Raises:
+        ConfigError: If a critical config value is missing or invalid.
+    """
+    load_dotenv(override=False)
+
+    chatgpt_token = os.getenv("CHATGPT_SESSION_TOKEN", "").strip() or None
+    claude_key = os.getenv("CLAUDE_SESSION_KEY", "").strip() or None
+    export_dir = Path(os.getenv("EXPORT_DIR", "./exports")).expanduser()
+    output_structure = os.getenv("OUTPUT_STRUCTURE", "provider/project/year").strip()
+    cache_dir = Path(os.getenv("CACHE_DIR", "~/.ai-chat-exporter")).expanduser()
+    log_file = os.getenv("LOG_FILE", "~/.ai-chat-exporter/logs/exporter.log").strip()
+
+    errors: list[str] = []
+
+    # Validate output structure
+    if output_structure not in VALID_STRUCTURES:
+        errors.append(
+            f"OUTPUT_STRUCTURE '{output_structure}' is invalid. "
+            f"Must be one of: {', '.join(sorted(VALID_STRUCTURES))}"
+        )
+
+    # Validate and decode ChatGPT JWT
+    chatgpt_expiry: datetime | None = None
+    if chatgpt_token:
+        chatgpt_expiry = _validate_chatgpt_token(chatgpt_token)
+
+    # Validate Claude key
+    if claude_key:
+        _validate_claude_key(claude_key)
+
+    # Ensure at least one provider is configured (warning only)
+    if not chatgpt_token and not claude_key:
+        logger.warning(
+            "Neither CHATGPT_SESSION_TOKEN nor CLAUDE_SESSION_KEY is set. "
+            "Run 'python -m src.main auth' to configure credentials."
+        )
+
+    # Create and validate output directory
+    try:
+        export_dir.mkdir(parents=True, exist_ok=True)
+        _check_writable(export_dir)
+    except (OSError, PermissionError) as e:
+        errors.append(f"Cannot create/write to EXPORT_DIR '{export_dir}': {e}")
+
+    # Create and validate cache directory
+    try:
+        cache_dir.mkdir(parents=True, exist_ok=True)
+        _check_writable(cache_dir)
+    except (OSError, PermissionError) as e:
+        errors.append(f"Cannot create/write to CACHE_DIR '{cache_dir}': {e}")
+
+    if errors:
+        for err in errors:
+            logger.critical(err)
+        raise ConfigError(
+            "Configuration errors found:\n" + "\n".join(f"  - {e}" for e in errors)
+        )
+
+    config = Config(
+        chatgpt_session_token=chatgpt_token,
+        claude_session_key=claude_key,
+        export_dir=export_dir,
+        output_structure=output_structure,
+        cache_dir=cache_dir,
+        log_file=log_file,
+        chatgpt_token_expiry=chatgpt_expiry,
+    )
+
+    _log_startup_summary(config)
+    return config
+
+
+def _validate_chatgpt_token(token: str) -> datetime | None:
+    """Validate ChatGPT session token (JWT). Returns expiry or None."""
+    if not token.startswith("eyJ"):
+        logger.warning(
+            "CHATGPT_SESSION_TOKEN does not look like a JWT (expected 'eyJ...'). "
+            "It may be expired or incorrectly copied."
+        )
+        return None
+
+    try:
+        payload = jwt.decode(token, options={"verify_signature": False})
+    except jwt.DecodeError as e:
+        logger.warning("CHATGPT_SESSION_TOKEN could not be decoded as JWT: %s", e)
+        return None
+
+    exp = payload.get("exp")
+    if exp is None:
+        logger.warning("CHATGPT_SESSION_TOKEN JWT has no 'exp' claim.")
+        return None
+
+    expiry = datetime.fromtimestamp(exp, tz=timezone.utc)
+    now = datetime.now(tz=timezone.utc)
+    delta = expiry - now
+
+    if delta.total_seconds() < 0:
+        logger.warning(
+            "CHATGPT_SESSION_TOKEN expired at %s. "
+            "Run 'python -m src.main auth' to refresh it.",
+            expiry.strftime("%Y-%m-%d %H:%M UTC"),
+        )
+    elif delta.total_seconds() < 86400:
+        logger.warning(
+            "CHATGPT_SESSION_TOKEN expires in less than 24 hours (%s). "
+            "Consider refreshing it soon.",
+            expiry.strftime("%Y-%m-%d %H:%M UTC"),
+        )
+
+    return expiry
+
+
+def _validate_claude_key(key: str) -> None:
+    """Validate Claude session key (opaque string)."""
+    # Reject if it's the placeholder text from .env.example
+    if not key or key.startswith("CLAUDE_SESSION_KEY="):
+        logger.warning(
+            "CLAUDE_SESSION_KEY appears to be a placeholder. "
+            "Set it to the actual sessionKey cookie value from claude.ai."
+        )
+
+
+def _check_writable(path: Path) -> None:
+    """Raise PermissionError if path is not writable."""
+    test_file = path / ".write_test"
+    try:
+        test_file.touch()
+        test_file.unlink()
+    except OSError as e:
+        raise PermissionError(f"Directory '{path}' is not writable: {e}") from e
+
+
+def _log_startup_summary(cfg: Config) -> None:
+    """Log a single INFO line summarising the active configuration."""
+    chatgpt_status = format_token_status(cfg.chatgpt_session_token, cfg.chatgpt_token_expiry)
+    claude_status = format_token_status(cfg.claude_session_key)
+
+    logger.info(
+        "Config loaded | "
+        "ChatGPT: %s | "
+        "Claude: %s | "
+        "export_dir=%s | "
+        "structure=%s | "
+        "cache_dir=%s",
+        chatgpt_status,
+        claude_status,
+        cfg.export_dir,
+        cfg.output_structure,
+        cfg.cache_dir,
+    )