"""Build a CloudWatch console deep-link for the running Lambda invocation.

Shared by @task_handler and @subtask_handler so both persist the same
`cloud_logs_url` onto the SubTask they run.
"""

import os
from typing import Optional
from urllib.parse import quote


def _console_encode(value: str) -> str:
    return quote(value, safe="").replace("%", "$25")


def cloudwatch_url() -> Optional[str]:
    """Deep-link to this invocation's log stream, or None outside Lambda."""
    region = os.environ.get("AWS_REGION")
    log_group = os.environ.get("AWS_LAMBDA_LOG_GROUP_NAME")
    log_stream = os.environ.get("AWS_LAMBDA_LOG_STREAM_NAME")
    if not (region and log_group and log_stream):
        return None
    return (
        f"https://{region}.console.aws.amazon.com/cloudwatch/home"
        f"?region={region}#logsV2:log-groups/log-group/"
        f"{_console_encode(log_group)}/log-events/{_console_encode(log_stream)}"
    )