"""System prompt assembly from a list of source files.

:func:`assemble` concatenates an agent's granules in order. A source is a
path, or a ``(tag, path)`` pair whose content is wrapped in ``<tag>...</tag>``.
"""

from __future__ import annotations

import hashlib
import logging
from pathlib import Path
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from collections.abc import Iterable

__all__ = ["PromptSource", "assemble"]

_log = logging.getLogger("beaver_gateway.agents.prompts")

PromptSource = str | Path | tuple[str, str | Path]


def assemble(sources: Iterable[PromptSource]) -> str:
    """Concatenate ``sources`` in order into one system prompt."""
    parts: list[str] = []
    for source in sources:
        tag, raw = source if isinstance(source, tuple) else (None, source)
        path = Path(raw)
        text = path.read_text(encoding="utf-8").strip()
        digest = hashlib.sha256(text.encode("utf-8")).hexdigest()[:12]
        _log.info(
            "prompt granule %s tag=%s sha=%s bytes=%d", path, tag, digest, len(text)
        )
        if not text:
            continue
        parts.append(f"<{tag}>\n{text}\n</{tag}>" if tag else text)
    return "\n\n".join(parts) + "\n"