import dash_mantine_components as dmc
from dash import html, dcc, Input, Output, State, clientside_callback, ALL

_TOC_CB_REGISTERED = False


def _indent_px_by_level(level: int, base_px: int = 14) -> int:
    try:
        lvl = int(level or 1)
    except Exception:
        lvl = 1

    if lvl <= 1:
        return 0              # H1
    elif lvl == 2:
        return base_px        # H2
    else:
        return base_px * 2    # H3 以上


def make_toc(
    titles,
    *,
    top_offset: int = 80,
    col_span=None,
    visible_from: str = "md",
):
    global _TOC_CB_REGISTERED

    if not _TOC_CB_REGISTERED:
        clientside_callback(
            """
            function(n_list, id_list, topOffset) {
                if (!n_list || !Array.isArray(n_list) || !id_list) {
                    return window.dash_clientside.no_update;
                }
                const ctx = dash_clientside.callback_context;
                if (!ctx.triggered.length) {
                    return window.dash_clientside.no_update;
                }
                const propId = ctx.triggered[0].prop_id;
                const m = propId.match(/\\[(\\d+)\\]\\.n_clicks$/);
                let idx = -1;
                if (m) {
                    idx = parseInt(m[1]);
                } else {
                    idx = n_list.findIndex(v => v);
                }
                if (idx < 0 || !id_list[idx]) {
                    return window.dash_clientside.no_update;
                }
                const targetId = id_list[idx].target;
                const el = document.getElementById(targetId);
                if (el) {
                    const y = el.getBoundingClientRect().top + window.scrollY - (parseInt(topOffset) || 0);
                    window.scrollTo({ top: y, behavior: 'smooth' });
                }
                return new Array(n_list.length).fill(null);
            }
            """,
            Output({"type": "toc-btn", "target": ALL}, "n_clicks"),
            Input({"type": "toc-btn", "target": ALL}, "n_clicks"),
            State({"type": "toc-btn", "target": ALL}, "id"),
            State({"type": "toc-offset"}, "data"),
            prevent_initial_call=True,
        )
        _TOC_CB_REGISTERED = True

    if titles and isinstance(titles, (list, tuple)) and titles[0]:
        first_label = titles[0].get("label") or ""
    else:
        first_label = ""

    if first_label:
        toc_title = f"目錄({first_label})"
        iter_titles = titles[1:]
    else:
        toc_title = "目錄"
        iter_titles = titles

    buttons = []
    for t in iter_titles:
        lvl = int(t.get("level", 1))
        pad_left = _indent_px_by_level(lvl, base_px=14)

        wrapper = html.Div(
            dmc.Button(
                t["label"],
                id={"type": "toc-btn", "target": t["id"]},
                variant="subtle",
                fullWidth=True,
                fw=400,
                className="toc-button",
                style={
                    "justifyContent": "flex-start",
                    "textAlign": "left",
                    "fontWeight": 400,
                    "fontSize": "16px",
                    "width": "100%",
                    "padding": "6px 0",
                    "display": "flex",
                },
            ),
            style={"paddingLeft": f"{pad_left}px"},
            **{
                "data-level": str(lvl),
                "data-target": t["id"],
            },
            className="toc-item",
        )
        buttons.append(wrapper)

    scroll_box = html.Div(
        dmc.Stack(
            children=[
                dmc.Title(toc_title, order=3),
                dcc.Store(id={"type": "toc-offset"}, data=int(top_offset)),
                *buttons,
            ],
            gap="xs",
        ),
        className="toc-scroll",
        id="toc-root",
        **{"data-toc-offset": int(top_offset)},
    )

    return dmc.Stack(
        [scroll_box],
        gap="xs",
        className="toc-container",
        style={
            "textAlign": "left",
        },
    )