import io, base64
import matplotlib.pyplot as plt

def _b64(fig):
    buf = io.BytesIO()
    fig.savefig(buf, format="png", bbox_inches="tight")
    plt.close(fig)
    return "data:image/png;base64," + base64.b64encode(buf.getvalue()).decode("utf-8")

def line_chart_base64(xs, ys, xlabel="", ylabel="", title=""):
    fig, ax = plt.subplots()
    ax.plot(xs, ys)
    ax.set(xlabel=xlabel, ylabel=ylabel, title=title)
    return _b64(fig)

def materiality_base64(labels, x_vals, y_vals, title="Materiality Matrix"):
    fig, ax = plt.subplots()
    ax.scatter(x_vals, y_vals)
    for lbl, x, y in zip(labels, x_vals, y_vals):
        ax.annotate(lbl, (x, y), xytext=(5,5), textcoords="offset points")
    ax.set(xlabel="Stakeholder Importance", ylabel="Business Impact", title=title)
    ax.grid(True, alpha=0.3)
    return _b64(fig)