import msal
import requests
import json
import os
import atexit
from dotenv import load_dotenv
from datetime import datetime

# --- Configuration ---
# Load environment variables from .env file
load_dotenv()

# Application (client) ID from Azure AD App Registration (read from .env)
CLIENT_ID = os.getenv("CLIENT_ID")
# SCOPES: Tasks.Read is sufficient to read all tasks and lists the user has access to.
SCOPES = ["Tasks.Read"]
AUTHORITY = "https://login.microsoftonline.com/common"
GRAPH_API_ENDPOINT = "https://graph.microsoft.com/v1.0"

# Cache file for MSAL tokens
CACHE_FILENAME = "ms_todo_token_cache.bin"
OUTPUT_FILENAME = "todo.txt"
# --- End Configuration ---


def get_access_token():
    """Authenticates the user and returns an access token."""
    cache = msal.SerializableTokenCache()
    if os.path.exists(CACHE_FILENAME):
        cache.deserialize(open(CACHE_FILENAME, "r").read())

    atexit.register(
        lambda: open(CACHE_FILENAME, "w").write(cache.serialize())
        if cache.has_state_changed
        else None
    )

    app = msal.PublicClientApplication(
        CLIENT_ID, authority=AUTHORITY, token_cache=cache
    )

    accounts = app.get_accounts()
    result = None

    if accounts:
        print("Attempting to acquire token silently...")
        result = app.acquire_token_silent(SCOPES, account=accounts[0])

    if not result:
        print(
            "No cached token found or silent acquisition failed. Starting interactive login."
        )
        flow = app.initiate_device_flow(scopes=SCOPES)
        if "user_code" not in flow:
            raise ValueError(
                "Failed to create device flow. Err: %s" % json.dumps(flow.get("error"))
            )

        print(flow["message"])
        result = app.acquire_token_by_device_flow(flow)

    if "access_token" in result:
        return result["access_token"]
    else:
        print("Error acquiring token:")
        print(result.get("error"))
        print(result.get("error_description"))
        print(result.get("correlation_id"))
        raise Exception("Authentication failed.")


def get_date_from_graph_datetime(graph_datetime_str: str | None) -> str | None:
    """
    Parses a datetime string from Graph API (ISO 8601 format) and returns YYYY-MM-DD.
    Handles potential variations in microsecond precision for wider Python compatibility.
    """
    if not graph_datetime_str:
        return None
    try:
        dt_str = graph_datetime_str
        # Truncate microseconds to 6 digits if they are longer, for Python < 3.11 compatibility
        if "." in dt_str:
            main_part, fractional_part = dt_str.split(".", 1)

            micro_digits = ""
            idx = 0
            while idx < len(fractional_part) and fractional_part[idx].isdigit():
                micro_digits += fractional_part[idx]
                idx += 1

            suffix = fractional_part[idx:]  # e.g., "Z", "+01:00", or ""

            if len(micro_digits) > 6:
                micro_digits = micro_digits[:6]  # Truncate

            if micro_digits:  # Only add dot and microseconds if they exist
                dt_str = f"{main_part}.{micro_digits}{suffix}"
            else:  # No microsecond digits after dot, or dot was followed by non-digits
                dt_str = f"{main_part}{suffix}"

        # datetime.fromisoformat in Python 3.7+ handles 'Z' by parsing it as UTC.
        dt_obj = datetime.fromisoformat(dt_str)

        return dt_obj.strftime("%Y-%m-%d")

    except Exception as e:
        print(
            f"Warning: Could not parse date from '{graph_datetime_str}' (Error: {e}). Trying direct extraction."
        )
        # Fallback: try to extract YYYY-MM-DD directly if full parsing fails
        if (
            len(graph_datetime_str) >= 10
            and graph_datetime_str[4] == "-"
            and graph_datetime_str[7] == "-"
        ):
            return graph_datetime_str[:10]
        print(f"Error: Failed to parse date: {graph_datetime_str}. Full error: {e}")
        return None


def format_task_for_todotxt(task_obj: dict, list_name: str) -> str | None:
    """Formats a Microsoft To-Do task object into a todo.txt string."""
    parts = []
    is_completed = task_obj.get("status") == "completed"
    title = task_obj.get("title", "").strip()

    if not title:
        print(
            f"Warning: Skipping task without a title in list '{list_name}'. Task ID: {task_obj.get('id')}"
        )
        return None

    if is_completed:
        parts.append("x")
        completion_date = get_date_from_graph_datetime(
            task_obj.get("completedDateTime", {}).get("dateTime")
        )
        if completion_date:
            parts.append(completion_date)

        # Add creation date after completion date for completed tasks, if available
        creation_date_completed = get_date_from_graph_datetime(
            task_obj.get("createdDateTime")
        )
        if creation_date_completed:
            parts.append(creation_date_completed)

        parts.append(title)
    else:  # Incomplete task
        # Priority
        priority_str = None
        importance = task_obj.get("importance")
        if importance == "high":
            priority_str = "(A)"
        elif importance == "normal":
            priority_str = "(B)"
        elif importance == "low":
            priority_str = "(C)"

        if priority_str:
            parts.append(priority_str)

        # Creation Date
        creation_date_incomplete = get_date_from_graph_datetime(
            task_obj.get("createdDateTime")
        )
        if creation_date_incomplete:
            parts.append(creation_date_incomplete)

        parts.append(title)

    # Project (from list name, sanitized)
    if list_name:
        # Remove spaces and common separators to make it a single "word" for todo.txt project tag
        project_name_sanitized = "".join(char for char in list_name if char.isalnum())
        if project_name_sanitized:  # Ensure not empty after sanitizing
            parts.append(f"+{project_name_sanitized}")

    # Due Date (key:value)
    due_date_obj = task_obj.get("dueDateTime")
    if due_date_obj and due_date_obj.get("dateTime"):
        due_date = get_date_from_graph_datetime(due_date_obj.get("dateTime"))
        if due_date:
            parts.append(f"due:{due_date}")

    return " ".join(filter(None, parts))


def get_all_task_lists(access_token: str) -> list:
    """Fetches all To-Do task lists from Microsoft Graph API."""
    headers = {"Authorization": "Bearer " + access_token}
    all_lists = []
    url = f"{GRAPH_API_ENDPOINT}/me/todo/lists?$top=100"  # Max 100 lists per page

    print("Fetching task lists...")
    while url:
        response = requests.get(url, headers=headers)
        response.raise_for_status()
        data = response.json()
        fetched_lists = data.get("value", [])
        all_lists.extend(fetched_lists)
        for lst in fetched_lists:
            print(f"  Found list: {lst.get('displayName', 'Unknown List')}")
        url = data.get("@odata.nextLink")
    print(f"Found {len(all_lists)} task list(s).")
    return all_lists


def get_tasks_from_list(access_token: str, list_id: str, list_name: str) -> list:
    """Gets all tasks from the specified list, handling pagination."""
    headers = {"Authorization": "Bearer " + access_token}
    all_tasks = []

    url = f"{GRAPH_API_ENDPOINT}/me/todo/lists/{list_id}/tasks?$top=100"

    print(f"Fetching tasks from list: '{list_name}'...")
    while url:
        response = requests.get(url, headers=headers)
        response.raise_for_status()
        data = response.json()
        all_tasks.extend(data.get("value", []))
        url = data.get("@odata.nextLink")
    print(f"  Fetched {len(all_tasks)} tasks from '{list_name}'.")
    return all_tasks


def main():
    """Main function to authenticate, fetch tasks, format, and export."""
    if not CLIENT_ID:
        print("Error: CLIENT_ID not found. Make sure it's set in your .env file.")
        return

    token = get_access_token()
    print("Successfully obtained access token.\n")

    task_lists = get_all_task_lists(token)
    if not task_lists:
        print("No task lists found.")
        return

    all_formatted_tasks = []
    for lst in task_lists:
        list_id = lst["id"]
        # Use displayName as it's user-visible; 'wellknownListName' is for special lists
        list_name = lst.get("displayName", f"List_{list_id}")

        tasks = get_tasks_from_list(token, list_id, list_name)
        for task_obj in tasks:
            formatted_task = format_task_for_todotxt(task_obj, list_name)
            if formatted_task:
                all_formatted_tasks.append(formatted_task)

    if not all_formatted_tasks:
        print("\nNo tasks found to export.")
        return

    with open(OUTPUT_FILENAME, "w", encoding="utf-8") as f:
        for task_line in all_formatted_tasks:
            f.write(task_line + "\n")

    print(
        f"\nSuccessfully exported {len(all_formatted_tasks)} tasks to {OUTPUT_FILENAME}"
    )


if __name__ == "__main__":
    main()