"""Document processing service for PDF, CSV, and Markdown files."""

import os
from typing import List, Optional
from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain_community.document_loaders import (
    PyPDFLoader,
    CSVLoader,
    TextLoader,
)
from langchain.schema import Document
from app.config import settings


class DocumentProcessor:
    """Handles loading and chunking of various document types."""

    def __init__(self):
        self.text_splitter = RecursiveCharacterTextSplitter(
            chunk_size=settings.CHUNK_SIZE,
            chunk_overlap=settings.CHUNK_OVERLAP,
            length_function=len,
            separators=["\n\n", "\n", ". ", " ", ""],
        )

        self.supported_extensions = {
            ".pdf": self._load_pdf,
            ".csv": self._load_csv,
            ".md": self._load_markdown,
            ".txt": self._load_text,
        }

    def get_supported_extensions(self) -> List[str]:
        return list(self.supported_extensions.keys())

    async def process_file(
        self, file_path: str, metadata: Optional[dict] = None
    ) -> List[Document]:
        """Process a file and return chunked documents with metadata."""
        ext = os.path.splitext(file_path)[1].lower()

        if ext not in self.supported_extensions:
            raise ValueError(
                f"Unsupported file type: {ext}. "
                f"Supported: {', '.join(self.supported_extensions.keys())}"
            )

        # Load documents
        loader_fn = self.supported_extensions[ext]
        documents = loader_fn(file_path)

        # Add custom metadata
        filename = os.path.basename(file_path)
        for doc in documents:
            doc.metadata["source"] = filename
            doc.metadata["file_type"] = ext
            if metadata:
                doc.metadata.update(metadata)

        # Split into chunks
        chunks = self.text_splitter.split_documents(documents)

        # Add chunk IDs
        for i, chunk in enumerate(chunks):
            chunk.metadata["chunk_id"] = f"{filename}_chunk_{i}"
            chunk.metadata["chunk_index"] = i
            chunk.metadata["total_chunks"] = len(chunks)

        return chunks

    def _load_pdf(self, file_path: str) -> List[Document]:
        """Load PDF file."""
        loader = PyPDFLoader(file_path)
        return loader.load()

    def _load_csv(self, file_path: str) -> List[Document]:
        """Load CSV file."""
        loader = CSVLoader(file_path, encoding="utf-8")
        return loader.load()

    def _load_markdown(self, file_path: str) -> List[Document]:
        """Load Markdown file."""
        loader = TextLoader(file_path, encoding="utf-8")
        return loader.load()

    def _load_text(self, file_path: str) -> List[Document]:
        """Load plain text file."""
        loader = TextLoader(file_path, encoding="utf-8")
        return loader.load()


document_processor = DocumentProcessor()