"""FluentGerman.ai — Instruction assembly service."""

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.models import Instruction, InstructionType


async def get_system_prompt(db: AsyncSession, user_id: int) -> str:
    """Assemble the full system prompt from global + personal + homework instructions."""

    # Global instructions (no user_id)
    result = await db.execute(
        select(Instruction).where(
            Instruction.user_id.is_(None),
            Instruction.type == InstructionType.GLOBAL,
        )
    )
    global_instructions = result.scalars().all()

    # Personal + homework for this user
    result = await db.execute(
        select(Instruction).where(Instruction.user_id == user_id)
    )
    user_instructions = result.scalars().all()

    parts: list[str] = []

    if global_instructions:
        parts.append("=== TEACHING METHOD ===")
        for inst in global_instructions:
            parts.append(f"[{inst.title}]\n{inst.content}")

    personal = [i for i in user_instructions if i.type == InstructionType.PERSONAL]
    if personal:
        parts.append("\n=== PERSONAL INSTRUCTIONS ===")
        for inst in personal:
            parts.append(f"[{inst.title}]\n{inst.content}")

    homework = [i for i in user_instructions if i.type == InstructionType.HOMEWORK]
    if homework:
        parts.append("\n=== CURRENT HOMEWORK ===")
        for inst in homework:
            parts.append(f"[{inst.title}]\n{inst.content}")

    if not parts:
        return (
            "You are a helpful German language tutor. Help the student learn German "
            "through conversation, corrections, and explanations."
        )

    return "\n\n".join(parts)