//! embed HTML 渲染。
//!
//! 生成的所有属性值都经过 HTML 转义；`src` 只可能是注册表模板拼接的结果，
//! 或者经过校验的 http(s) 原始 URL，因此不会有脚本或事件属性注入。

use crate::{EmbedKind, Resolved};

/// HTML 属性/文本转义。
pub fn escape_html(value: &str) -> String {
    let mut out = String::with_capacity(value.len() + 8);
    for ch in value.chars() {
        match ch {
            '&' => out.push_str("&"),
            '<' => out.push_str("&lt;"),
            '>' => out.push_str("&gt;"),
            '"' => out.push_str("&quot;"),
            '\'' => out.push_str("&#39;"),
            _ => out.push(ch),
        }
    }
    out
}

fn host_of(url: &str) -> String {
    url::Url::parse(url)
        .ok()
        .and_then(|parsed| parsed.host_str().map(str::to_string))
        .unwrap_or_default()
}

/// 平台标识：`data-*` 上给前端留钩子。
fn data_attrs(resolved: &Resolved) -> String {
    format!(
        " data-platform=\"{}\" data-category=\"{}\"",
        escape_html(resolved.platform),
        resolved.category.as_str(),
    )
}

/// iframe 的尺寸。
///
/// 平台声明了固定像素高时用它（Spotify 单曲 152px、网易云外链 66px、
/// Reddit 500px…），否则才按宽高比撑开。`background:#000` 只给视频类——
/// 推文、音乐、地图这些是浅色卡片，套黑底会在加载前露出一块黑矩形。
fn frame_style(resolved: &Resolved) -> String {
    let base = "width:100%;max-width:640px;border:0;border-radius:12px;display:block";
    let backdrop = if is_dark_player(resolved) {
        ";background:#000"
    } else {
        ""
    };
    match resolved.height {
        Some(height) => format!("{base};height:{height}px{backdrop}"),
        None => format!("{base};aspect-ratio:{}{backdrop}", resolved.aspect.css()),
    }
}

/// 视频类播放器才用黑底：其余嵌入是浅色卡片，不该有黑框。
fn is_dark_player(resolved: &Resolved) -> bool {
    matches!(resolved.kind, EmbedKind::Video | EmbedKind::Audio)
        || matches!(
            resolved.category,
            crate::Category::Video | crate::Category::Live
        )
}

const MEDIA_STYLE: &str =
    "width:100%;max-width:640px;border-radius:12px;background:#000;display:block";
const IMAGE_STYLE: &str =
    "max-width:100%;max-height:480px;border-radius:12px;display:block;object-fit:contain";
const CARD_STYLE: &str = "display:flex;align-items:center;gap:10px;max-width:100%;padding:10px 12px;border:1px solid rgba(127,127,127,.35);border-radius:12px;text-decoration:none;font-size:13px;line-height:1.4;color:inherit";

/// 把一个解析结果渲染成可注入消息流的 HTML 片段。
pub fn render_html(resolved: &Resolved) -> String {
    let attrs = data_attrs(resolved);
    let title = escape_html(&resolved.title);
    match resolved.kind {
        EmbedKind::Iframe => {
            let Some(src) = resolved.src.as_deref() else {
                return render_card(resolved, &attrs);
            };
            format!(
                "<iframe class=\"gd-embed gd-embed-frame\" src=\"{src}\" title=\"{title}\" loading=\"lazy\" \
                 referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen \
                 allow=\"accelerometer;autoplay;clipboard-write;encrypted-media;gyroscope;picture-in-picture;web-share;fullscreen\" \
                 sandbox=\"allow-scripts allow-same-origin allow-popups allow-popups-to-escape-sandbox allow-forms allow-presentation\" \
                style=\"{style}\"{attrs}></iframe>",
                src = escape_html(src),
                style = frame_style(resolved),
            )
        }
        EmbedKind::Video => {
            let src = resolved.src.as_deref().unwrap_or(&resolved.url);
            format!(
                "<video class=\"gd-embed gd-embed-video\" src=\"{src}\" controls preload=\"metadata\" \
                 playsinline style=\"{style}\"{attrs}></video>",
                src = escape_html(src),
                style = MEDIA_STYLE,
            )
        }
        EmbedKind::Audio => {
            let src = resolved.src.as_deref().unwrap_or(&resolved.url);
            format!(
                "<audio class=\"gd-embed gd-embed-audio\" src=\"{src}\" controls preload=\"metadata\" \
                 style=\"width:100%;max-width:640px;display:block\"{attrs}></audio>",
                src = escape_html(src),
            )
        }
        EmbedKind::Image => {
            let src = resolved.src.as_deref().unwrap_or(&resolved.url);
            format!(
                "<img class=\"gd-embed gd-embed-image\" src=\"{src}\" alt=\"{title}\" loading=\"lazy\" \
                 style=\"{style}\"{attrs} />",
                src = escape_html(src),
                style = IMAGE_STYLE,
            )
        }
        EmbedKind::Link => render_card(resolved, &attrs),
    }
}

fn render_card(resolved: &Resolved, attrs: &str) -> String {
    let url = escape_html(&resolved.url);
    let name = escape_html(resolved.platform_name);
    let host = escape_html(&host_of(&resolved.url));
    let raw_title = resolved.title.trim();
    let headline = if raw_title.is_empty() || raw_title == resolved.platform_name {
        name.clone()
    } else {
        escape_html(raw_title)
    };
    let thumb = match resolved.image_url.as_deref() {
        Some(image) if !image.is_empty() => format!(
            "<img class=\"gd-embed-thumb\" src=\"{src}\" alt=\"\" loading=\"lazy\" \
             style=\"width:48px;height:48px;border-radius:8px;object-fit:cover;flex:none\" />",
            src = escape_html(image),
        ),
        _ => String::new(),
    };
    let description = match resolved.description.as_deref().map(str::trim) {
        Some(text) if !text.is_empty() => format!(
            "<span class=\"gd-embed-desc\" style=\"font-size:12px;opacity:.75;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden\">{}</span>",
            escape_html(text),
        ),
        _ => String::new(),
    };
    format!(
        "<a class=\"gd-embed gd-embed-link\" href=\"{url}\" target=\"_blank\" \
         rel=\"noopener noreferrer nofollow\" style=\"{CARD_STYLE}\"{attrs}>\
         {thumb}\
         <span class=\"gd-embed-meta\" style=\"display:flex;flex-direction:column;gap:2px;min-width:0\">\
         <span class=\"gd-embed-title\" style=\"font-weight:600;overflow:hidden;text-overflow:ellipsis;white-space:nowrap\">{headline}</span>\
         {description}\
         <span class=\"gd-embed-host\" style=\"font-size:12px;opacity:.6;overflow:hidden;text-overflow:ellipsis;white-space:nowrap\">{name} · {host}</span>\
         </span>\
         </a>",
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn escapes_attribute_breakers() {
        assert_eq!(escape_html(r#"a"b<c>&'"#), "a&quot;b&lt;c&gt;&amp;&#39;");
    }

    /// 卡片类嵌入不该带黑底，视频类才带；声明了固定高度就用它。
    #[test]
    fn frame_style_matches_the_embed_shape() {
        // X 只出卡片：跨域 iframe 会停在 about:blank，不能再留 520px 的空框。
        let tweet = crate::parse("https://x.com/u/status/1234567890").expect("tweet resolves");
        let html = render_html(&tweet);
        assert!(html.contains("gd-embed-link"), "{html}");
        assert!(!html.contains("<iframe"), "{html}");

        let video = crate::parse("https://www.youtube.com/watch?v=dQw4w9WgXcQ").expect("video");
        let html = render_html(&video);
        assert!(html.contains("aspect-ratio:16 / 9"), "{html}");
        assert!(
            html.contains("background:#000"),
            "视频播放器保留黑底: {html}"
        );

        let song = crate::parse("https://music.163.com/#/song?id=123").expect("song");
        let html = render_html(&song);
        assert!(html.contains("height:66px"), "{html}");

        // 固定高度仍然生效（Reddit oEmbed 声明 500px）。
        let thread =
            crate::parse("https://www.reddit.com/r/rust/comments/abc/title").expect("reddit");
        let html = render_html(&thread);
        assert!(html.contains("height:500px"), "{html}");
    }
}