/* The downloads in the phone's shade.

   The Transfers screen is inside the app: the desktop says what a Save is
   doing with its title-bar ring, the phone with a badge on the nav, and
   neither is anywhere to be seen once the app is in the background — which
   is exactly when a Save is left to run on its own. So a running Save says
   so where the phone says things: one notice with how many files are left,
   the one it is on, a bar, Stop all and Open.

   Its own channel, so it can be silenced without silencing the player's
   card, and its own foreground service, so the fetch outlives the playback
   that happened to be keeping the process alive. Everything real is in
   crates/tauri-plugin-transfer-notice; this is the wiring — the mirror of
   transfers.svelte.js, exactly as media.svelte.js mirrors the player. */
import * as api from "../lib/api.js";
import { addPluginListener } from "@tauri-apps/api/core";
import { active, cancelAll } from "./transfers.svelte.js";
import { note } from "./notice.svelte.js";
import { go, push, top, closeSheet } from "./nav.svelte.js";

/* What the phone was last told, and how often. A PLAIN object, not $state:
   nothing renders it, and the effect that drives the post must never read
   what it writes — a self-read in an $effect kills the subtree. The walk
   reads it through __ss.xfn, since a notification is not a thing a headless
   page can be asked about. */
export const xfernote = {
    posted: false,
    updates: 0,
    clears: 0,
    max: 0,
    title: "",
    line: "",
    percent: -1,
    failed: 0,
};

/* a re-post is not free, and progress ticks arrive far faster than anyone
   reads them: the lever is the rate */
const MIN_GAP = 700;
let timer = null;
let lastAt = 0;
let lastKey = "";

/** What is in flight, as the notice would say it — or null when nothing is. */
function shape() {
    const live = active();
    if (!live.length) return null;
    const newest = [...live].sort((a, b) => b.id - a.id);   /* the screen's own order */
    const cur = newest.find((d) => d.state === "transferring") || newest[0];
    let received = 0, total = 0, known = 0;
    for (const d of live) if (d.total) { received += d.received || 0; total += d.total; known++; }
    return {
        count: live.length,
        title: live.length === 1 ? "Saving 1 file" : `Saving ${live.length} files`,
        line: cur.state === "transferring" ? (cur.name || cur.path || "") : "waiting in their queue",
        percent: total ? Math.round((received / total) * 100) : 0,
        indeterminate: !known,
    };
}
const keyOf = (s) => (s ? `${s.count}|${s.title}|${s.line}|${s.percent}` : "");

/** Called from Mobile.svelte's effect: reads the store — so the effect
 *  tracks it — and schedules at most one post per MIN_GAP. */
export function syncShade() {
    const key = keyOf(shape());
    if (key === lastKey || timer) return;
    timer = setTimeout(post, Math.max(0, MIN_GAP - (Date.now() - lastAt)));
}

/** The one place that talks to the plugin. Reads the store again on the way
 *  out, so what lands in the shade is the latest, not the change that
 *  scheduled it. */
async function post() {
    timer = null;
    lastAt = Date.now();
    const s = shape();
    lastKey = keyOf(s);
    if (!s) {
        if (!xfernote.posted) return;
        xfernote.posted = false;
        xfernote.clears++;
        try { await api.clearTransferNotice(); } catch { xfernote.failed++; }
        return;
    }
    xfernote.posted = true;
    xfernote.updates++;
    if (s.count > xfernote.max) xfernote.max = s.count;
    xfernote.title = s.title;
    xfernote.line = s.line;
    xfernote.percent = s.percent;
    try { await api.transferNotice(s); } catch { xfernote.failed++; }
}

let bound = false;
/** The notice's own two buttons. Harmless where there is no plugin. */
export async function bindXferNote() {
    if (bound) return;
    bound = true;
    try {
        await addPluginListener("transfer-notice", "action", (p) => {
            if (p?.action === "cancel") {
                /* the same cancel(id) a row's tap takes, once per live row —
                   never a second path to the same thing */
                void cancelAll();
                note("Downloads stopped.");
            } else if (p?.action === "open") {
                closeSheet();
                go("you");
                if (top().n !== "transfers") push("transfers", {});
            }
        });
    } catch {
        /* not a phone */
    }
}