deepdrft/DeepDrftPublic.Client/Helpers/EmbedSnippetBuilder.cs

namespace DeepDrftPublic.Client.Helpers;

/// <summary>
/// Builds the iframe embed snippet the share popover copies. Two targets: a single track
/// (<see cref="ForTrack"/> → <c>FramePlayer?TrackEntryKey=...</c>) and a whole release
/// (<see cref="ForRelease"/> → <c>FramePlayer?ReleaseEntryKey=...</c>).
///
/// <para>
/// The two snippets diverge in height by design (Phase 17 §4.1, OQ6): a single-track embed has no
/// queue, so <see cref="ForTrack"/> stays at the compact player height; a release embed renders the
/// always-shown queue panel below the controls, so <see cref="ForRelease"/> is taller to show it
/// without clipping. Other iframe chrome (width, border radius, autoplay permission) is identical and
/// defined once in <see cref="Frame"/>.
/// </para>
///
/// <para>
/// OQ1 Option A — collapse/expand resize handshake. The release snippet carries a tiny host-side
/// listener: the embedded player posts its desired height when the viewer collapses/expands the
/// queue panel, and the listener sizes this specific iframe to match. It is scoped to the snippet's
/// own iframe (matched by id) and ignores any message whose shape does not match, so it cannot be
/// driven by foreign frames. It degrades to Option B's behaviour if the host strips the script: the
/// panel still renders and toggles inside the iframe at its default (expanded) height — only the
/// outer resize is lost. The track snippet needs no script (no panel, no toggle).
/// </para>
///
/// <para>
/// Multi-embed isolation: each <see cref="ForRelease"/> call mints a fresh random token (8 hex
/// chars). The token is used as the iframe id (<c>deepdrft-embed-{token}</c>) and threaded into
/// the iframe src as <c>&amp;EmbedId={token}</c> so the iframe can learn its own id. The host-side
/// resize script matches incoming messages on <c>embedId</c> and resizes only the iframe whose id
/// matches the token — two releases on one host page resize independently without cross-talk. Two
/// calls for the same release still get distinct tokens, ensuring uniqueness even when the same
/// release is pasted twice. Older snippets that lack <c>embedId</c> in their postMessage payload are
/// silently ignored by the script (backward-compatible degradation).
/// </para>
///
/// Pure string composition so the snippet shape is unit-testable without rendering the component.
/// </summary>
public static class EmbedSnippetBuilder
{
    // Compact single-track height (the historical embed height — must not change: UC6/AC6).
    private const int TrackHeight = 196;

    // Release height: the compact player plus the queue panel (fixed, internally scrollable past N
    // rows per OQ6). The panel collapses to the track height via the resize handshake below.
    private const int ReleaseHeight = 384;

    // baseUri carries a trailing slash (NavigationManager.BaseUri), so "FramePlayer" appends cleanly.
    public static string ForTrack(string baseUri, string trackEntryKey)
        => Frame($"{baseUri}FramePlayer?TrackEntryKey={trackEntryKey}", TrackHeight);

    public static string ForRelease(string baseUri, string releaseEntryKey)
    {
        // Mint a fresh random token per call so two embeds on the same host page never share an id,
        // even when they point at the same release.
        var token = Guid.NewGuid().ToString("N")[..8];
        var iframeId = $"deepdrft-embed-{token}";
        var src = $"{baseUri}FramePlayer?ReleaseEntryKey={releaseEntryKey}&EmbedId={token}";
        return Frame(src, ReleaseHeight, iframeId, ResizeScript(iframeId, token));
    }

    private static string Frame(string src, int height, string iframeId = "deepdrft-embed", string trailingScript = "")
        => $"""<iframe id="{iframeId}" src="{src}" width="656" height="{height}" frameborder="0" style="border-radius:8px;" allow="autoplay"></iframe>{trailingScript}""";

    // Host-side listener: resize the matching iframe when the embedded player posts its panel height.
    // The embedId field in the payload is matched against the snippet's own token so only this
    // iframe is driven — foreign frames or other release embeds on the same page cannot interfere.
    // The height is clamped to a sane floor so a bad payload can't collapse the player away.
    // Messages without embedId (older snippets) are silently ignored.
    private static string ResizeScript(string iframeId, string token) =>
        "<script>(function(){var id=\"" + iframeId + "\",tok=\"" + token + "\";" +
        "window.addEventListener(\"message\",function(e){var d=e.data;" +
        "if(!d||d.type!==\"deepdrft-embed-resize\"||d.embedId!==tok)return;" +
        "var f=document.getElementById(id);var h=Number(d.height);" +
        "if(f&&h>=150)f.style.height=h+\"px\";});})();</script>";
}