# Reads a locally-downloaded attachment (spreadsheet or plain text/code file) and
# returns its content as text the executor agent can reason over.
# pandas: the standard library for reading tabular data (Excel/CSV) into a
# DataFrame -- a table-like object we then render back out as plain text.
from pathlib import Path

import pandas as pd
from llama_index.core.tools import FunctionTool

MAX_FILE_CHARS = 8000  # keep tool output small enough to fit comfortably in the executor's context
SPREADSHEET_EXTENSIONS = {".xlsx", ".xls", ".csv"}


# Reads every sheet of a spreadsheet file and renders each as a plain-text table.
def _read_spreadsheet(path: Path) -> str:
    if path.suffix == ".csv":
        sheets = {"": pd.read_csv(path)}
    else:
        sheets = pd.read_excel(path, sheet_name=None)  # sheet_name=None -> dict of {sheet_name: DataFrame}

    blocks = []
    for sheet_name, df in sheets.items():
        header = f"Sheet '{sheet_name}':" if sheet_name else "Data:"
        blocks.append(f"{header}\n{df.to_string(index=False)}")
    return "\n\n".join(blocks)


# Reads a text/code file as UTF-8, truncated to a safe length.
def _read_text(path: Path) -> str:
    return path.read_text(encoding="utf-8", errors="replace")


def read_attached_file(file_path: str) -> str:
    """Read a locally attached file (spreadsheet, code, or plain text) and return its content as text."""
    path = Path(file_path)
    if not path.exists():
        return f"File not found: '{file_path}'."

    try:
        content = _read_spreadsheet(path) if path.suffix.lower() in SPREADSHEET_EXTENSIONS else _read_text(path)
    except Exception as e:
        return f"Could not read '{file_path}': {type(e).__name__}: {e}"

    return content[:MAX_FILE_CHARS]


read_attached_file_tool = FunctionTool.from_defaults(
    fn=read_attached_file,
    name="read_attached_file",
    description=(
        "Read the content of a locally attached file by its path -- spreadsheets (.xlsx/.xls/.csv) are "
        "rendered as tables, everything else (.py/.txt/.json/etc.) is read as plain text. "
        "Always use this when the question references an attached file that isn't an image or audio."
    ),
)