from __future__ import annotations

import os
from dataclasses import dataclass
from pathlib import Path
from typing import Iterable, Sequence

from dotenv import load_dotenv

# Load .env from repo root when config is used (e.g. for local runs)
_repo_root = Path(__file__).resolve().parent.parent.parent
load_dotenv(_repo_root / ".env")


@dataclass(frozen=True)
class AppConfig:
    repo_path: str
    db_dsn: str
    chunk_size: int
    chunk_overlap: int
    chunk_size_lines: int
    chunk_overlap_lines: int
    embeddings_dim: int
    embeddings_model: str
    llm_model: str
    allowed_extensions: Sequence[str]


def _env_int(name: str, default: int) -> int:
    value = os.getenv(name, "").strip()
    if not value:
        return default
    try:
        return int(value)
    except ValueError as exc:
        raise ValueError(f"Invalid integer for {name}: {value}") from exc


def _env_list(name: str, default: Iterable[str]) -> list[str]:
    value = os.getenv(name, "").strip()
    if not value:
        return list(default)
    return [item.strip() for item in value.split(",") if item.strip()]


def load_config() -> AppConfig:
    repo_path = os.getenv("RAG_REPO_PATH", "").strip()
    if not repo_path:
        raise ValueError("RAG_REPO_PATH is required")

    db_dsn = os.getenv("RAG_DB_DSN", "").strip()
    if not db_dsn:
        raise ValueError("RAG_DB_DSN is required")

    return AppConfig(
        repo_path=repo_path,
        db_dsn=db_dsn,
        chunk_size=_env_int("RAG_CHUNK_SIZE", 400),
        chunk_overlap=_env_int("RAG_CHUNK_OVERLAP", 50),
        chunk_size_lines=_env_int("RAG_CHUNK_SIZE_LINES", 40),
        chunk_overlap_lines=_env_int("RAG_CHUNK_OVERLAP_LINES", 8),
        embeddings_dim=_env_int("RAG_EMBEDDINGS_DIM", 1024),  # GigaChat Embeddings = 1024; OpenAI = 1536
        embeddings_model=os.getenv("RAG_EMBEDDINGS_MODEL", "stub-embeddings"),
        llm_model=os.getenv("RAG_LLM_MODEL", "GigaChat"),
        allowed_extensions=tuple(
            _env_list("RAG_ALLOWED_EXTENSIONS", [".md", ".txt", ".rst"])
        ),
    )