"""
Skill system — each skill is a piece of domain knowledge or a capability
that can be attached to an agent to shape its behavior and system prompt.

A Skill is a lightweight object with:
- name        : short identifier (e.g. "media_info")
- description : human-readable summary
- prompt_fragment : extra text injected into the agent's system prompt
"""

from dataclasses import dataclass, field
from typing import Dict


@dataclass
class Skill:
    name: str
    description: str
    prompt_fragment: str = ""


# ---------------------------------------------------------------------------
# Global skill registry — populated at startup / import time
# ---------------------------------------------------------------------------
_skill_registry: Dict[str, Skill] = {}


def register(skill: Skill) -> None:
    """Register a skill so agents can look it up by name."""
    _skill_registry[skill.name] = skill


def get(name: str) -> Skill | None:
    """Return a registered skill by name, or None."""
    return _skill_registry.get(name)


def list_all() -> Dict[str, Skill]:
    """Return a shallow copy of the registry."""
    return dict(_skill_registry)


def get_combined_prompt(skill_names: list[str], base_prompt: str = "") -> str:
    """Build a system prompt from a base prompt + requested skill fragments."""
    parts = [base_prompt] if base_prompt else []
    for name in skill_names:
        s = get(name)
        if s and s.prompt_fragment:
            parts.append(s.prompt_fragment)
    return "\n\n".join(parts)