from typing import Optional, List
from pydantic import BaseModel

class TaskCard(BaseModel):
    """Pydantic model representing a task card.

    Attributes:
        title: The main title of the task.
        subject: Optional subject or domain of the task.
        deadline: Optional due date in ISO format or human readable string.
        deliverable: Optional description of what should be produced.
        criteria: List of acceptance criteria strings.
    """

    title: str
    subject: Optional[str] = None
    deadline: Optional[str] = None
    deliverable: Optional[str] = None
    criteria: List[str]

    def to_markdown(self) -> str:
        """Return a Markdown representation of the task card.

        The format follows a simple, readable structure that can be used in
        documentation or issue trackers.  Empty optional fields are omitted.
        """
        lines = [f"# {self.title}"]
        if self.subject:
            lines.append(f"**Subject:** {self.subject}")
        if self.deadline:
            lines.append(f"**Deadline:** {self.deadline}")
        if self.deliverable:
            lines.append(f"**Deliverable:** {self.deliverable}")
        if self.criteria:
            lines.append("## Acceptance Criteria")
            for idx, crit in enumerate(self.criteria, 1):
                lines.append(f"{idx}. {crit}")
        return "\n\n".join(lines)