import pandas as pd
import plotly.graph_objects as go

def plot_metric_tool(file_path: str, date_col: str, value_col: str):
    """
    Generic interactive line chart for any numeric metric.
    Returns a Plotly Figure or error message string.
    """
    df = pd.read_csv(file_path)

    if date_col not in df.columns or value_col not in df.columns:
        return f"❌ '{date_col}' or '{value_col}' column missing."

    df[date_col] = pd.to_datetime(df[date_col], errors="coerce")
    if df[date_col].isna().all():
        return f"❌ '{date_col}' could not be parsed as dates."

    fig = go.Figure(
        go.Scatter(
            x=df[date_col],
            y=df[value_col],
            mode="lines+markers",
            line=dict(width=2),
        )
    )
    fig.update_layout(title=f"{value_col} Trend", template="plotly_dark")
    fig.write_image("metric_plot.png")
    return fig