# Copyright (c) 2025 Microsoft Corporation.
# Licensed under the MIT Licenses

"""A CSV-based implementation of the Table abstraction for streaming row access."""

from __future__ import annotations

import csv
import inspect
import os
import shutil
import sys
import tempfile
from pathlib import Path
from typing import TYPE_CHECKING, Any

import aiofiles

from graphrag_storage.file_storage import FileStorage
from graphrag_storage.tables.table import RowTransformer, Table

if TYPE_CHECKING:
    from collections.abc import AsyncIterator
    from io import TextIOWrapper

    from graphrag_storage import Storage

try:
    csv.field_size_limit(sys.maxsize)
except OverflowError:
    csv.field_size_limit(100 * 1024 * 1024)


def _identity(row: dict[str, Any]) -> Any:
    """Return row unchanged (default transformer)."""
    return row


def _apply_transformer(transformer: RowTransformer, row: dict[str, Any]) -> Any:
    """Apply transformer to row, handling both callables and classes.

    If transformer is a class (e.g., Pydantic model), calls it with **row.
    Otherwise calls it with row as positional argument.
    """
    if inspect.isclass(transformer):
        return transformer(**row)
    return transformer(row)


class CSVTable(Table):
    """Row-by-row streaming interface for CSV tables."""

    def __init__(
        self,
        storage: Storage,
        table_name: str,
        transformer: RowTransformer | None = None,
        truncate: bool = True,
        encoding: str = "utf-8",
    ):
        """Initialize with storage backend and table name.

        Args:
            storage: Storage instance (File, Blob, or Cosmos)
            table_name: Name of the table (e.g., "documents")
            transformer: Optional callable to transform each row before
                yielding. Receives a dict, returns a transformed dict.
                Defaults to identity (no transformation).
            truncate: If True (default), writes go to a temporary file
                which is moved over the original on close(). This allows
                safe concurrent reads from the original while writes
                accumulate. If False, append to existing file.
            encoding: Character encoding for reading/writing CSV files.
                Defaults to "utf-8".
        """
        self._storage = storage
        self._table_name = table_name
        self._file_key = f"{table_name}.csv"
        self._transformer = transformer or _identity
        self._truncate = truncate
        self._encoding = encoding
        self._write_file: TextIOWrapper | None = None
        self._writer: csv.DictWriter | None = None
        self._header_written = False
        self._temp_path: Path | None = None
        self._final_path: Path | None = None

    def __aiter__(self) -> AsyncIterator[Any]:
        """Iterate through rows one at a time.

        The transformer is applied to each row before yielding.
        If transformer is a Pydantic model, yields model instances.

        Yields
        ------
            Any:
                Each row as dict or transformed type (e.g., Pydantic model).
        """
        return self._aiter_impl()

    async def _aiter_impl(self) -> AsyncIterator[Any]:
        """Implement async iteration over rows."""
        if isinstance(self._storage, FileStorage):
            file_path = self._storage.get_path(self._file_key)
            with Path.open(file_path, "r", encoding=self._encoding) as f:
                reader = csv.DictReader(f)
                for row in reader:
                    yield _apply_transformer(self._transformer, row)

    async def length(self) -> int:
        """Return the number of rows in the table."""
        if isinstance(self._storage, FileStorage):
            file_path = self._storage.get_path(self._file_key)
            count = 0
            async with aiofiles.open(file_path, "rb") as f:
                while True:
                    chunk = await f.read(65536)
                    if not chunk:
                        break
                    count += chunk.count(b"\n")
            return count - 1
        return 0

    async def has(self, row_id: str) -> bool:
        """Check if row with given ID exists."""
        async for row in self:
            # Handle both dict and object (e.g., Pydantic model)
            if isinstance(row, dict):
                if row.get("id") == row_id:
                    return True
            elif getattr(row, "id", None) == row_id:
                return True
        return False

    async def write(self, row: dict[str, Any]) -> None:
        """Write a single row to the CSV file.

        On first write, opens a file handle. When truncate=True, writes
        go to a temporary file in the same directory; the temp file is
        moved over the original in close(), making it safe to read from
        the original while writes are in progress. When truncate=False,
        rows are appended directly to the existing file.

        Args
        ----
            row: Dictionary representing a single row to write.
        """
        if isinstance(self._storage, FileStorage) and self._write_file is None:
            file_path = self._storage.get_path(self._file_key)
            file_path.parent.mkdir(parents=True, exist_ok=True)

            if self._truncate:
                fd, tmp = tempfile.mkstemp(
                    suffix=".csv",
                    dir=file_path.parent,
                )
                os.close(fd)
                self._temp_path = Path(tmp)
                self._final_path = file_path
                self._write_file = Path.open(
                    self._temp_path,
                    "w",
                    encoding=self._encoding,
                    newline="",
                )
                write_header = True
            else:
                file_exists = file_path.exists() and file_path.stat().st_size > 0
                write_header = not file_exists
                self._write_file = Path.open(
                    file_path,
                    "a",
                    encoding=self._encoding,
                    newline="",
                )

            self._writer = csv.DictWriter(
                self._write_file,
                fieldnames=list(row.keys()),
            )
            if write_header:
                self._writer.writeheader()
            self._header_written = write_header

        if self._writer is not None:
            self._writer.writerow(row)

    async def close(self) -> None:
        """Flush buffered writes and release resources.

        When truncate=True, the temp file is moved over the original
        so that readers never see a partially-written file.
        """
        if self._write_file is not None:
            self._write_file.close()
            self._write_file = None
            self._writer = None
            self._header_written = False

        if self._temp_path is not None and self._final_path is not None:
            shutil.move(str(self._temp_path), str(self._final_path))
            self._temp_path = None
            self._final_path = None