"""Application configuration via environment variables / .env file.

All settings are read from the environment (or a .env file in the project
root).  Import :func:`get_settings` wherever you need configuration; the
returned object is cached after the first call.
"""

from __future__ import annotations

from functools import lru_cache

from pydantic import AliasChoices, Field
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    """Centralised, env-driven configuration for the codex application."""

    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        case_sensitive=False,
        extra="ignore",
    )

    # ------------------------------------------------------------------
    # Database
    # ------------------------------------------------------------------
    database_url: str = Field(
        default="postgresql://researcher:change_me@localhost:5432/papers",
        description=(
            "libpq-compatible connection string consumed by psycopg. "
            "Example: postgresql://user:pass@host:5432/dbname"
        ),
    )

    # ------------------------------------------------------------------
    # External services
    # ------------------------------------------------------------------
    grobid_url: str = Field(
        default="http://localhost:8070",
        description="Base URL of the GROBID HTTP API (containerised).",
    )

    nougat_url: str = Field(
        default="http://localhost:8080",
        validation_alias=AliasChoices("NOUGAT_URL", "nougat_url"),
        description="Base URL of the Nougat OCR HTTP API (containerised).",
    )

    ollama_base_url: str = Field(
        default="http://localhost:11434",
        description="Base URL of the local Ollama endpoint (optional Q&A layer).",
    )

    # ------------------------------------------------------------------
    # Embeddings
    # ------------------------------------------------------------------
    embedding_model: str = Field(
        default="BAAI/bge-m3",
        description=(
            "sentence-transformers model identifier. "
            "Must match EMBEDDING_DIM. Default: BAAI/bge-m3 (1024 dims)."
        ),
    )

    embedding_dim: int = Field(
        default=1024,
        gt=0,
        description=(
            "Dimension of the dense embedding vectors. "
            "Must match the output dimension of EMBEDDING_MODEL."
        ),
    )

    # ------------------------------------------------------------------
    # API etiquette
    # ------------------------------------------------------------------
    openalex_mailto: str = Field(
        default="",
        description=(
            "E-mail address for the OpenAlex Polite Pool (faster rate limits). "
            "Required by OpenAlex ToS for automated access."
        ),
    )


@lru_cache(maxsize=1)
def get_settings() -> Settings:
    """Return the cached application settings singleton."""
    return Settings()