//! oEmbed 抓取：把平台声明的端点返回的 JSON 收敛成 [`social::Enrichment`]。
//!
//! 第三方返回的 HTML 不会被注入消息流：只从 `html` 里抠出 iframe 的 `src`，而且
//! `social` 侧还会再校验一次，只有落在该平台自己声明的域名里才会被采用。抓取失败
//! 一律返回 `None`，交给 OpenGraph 兜底，也不会写进 `chat_link_unfurl` 缓存。

use social::Enrichment;

use crate::services::outbound::fetch_following;
use crate::services::outbound::validate_outbound_url;

const MAX_BYTES: usize = 262_144;

/// 抓取 URL 所属平台的 oEmbed 数据；平台没声明端点或抓取失败时返回 `None`。
pub async fn fetch(url: &str) -> Option<Enrichment> {
    let endpoint = social::oembed_endpoint(url)?;
    let body = fetch_following(
        &endpoint.endpoint,
        "application/json",
        Some("json"),
        MAX_BYTES,
    )
    .await
    .ok()?
    .body;
    parse(&body)
}

/// 抓取页面自己声明的 oEmbed 端点。
///
/// 比 [`fetch`] 覆盖面大得多：注册表只硬编码了十几个平台，而页面里的
/// `<link rel="alternate" type="application/json+oembed">` 是平台自己发布的，
/// 新增平台不需要跟着改代码。
pub async fn fetch_endpoint(endpoint: &str) -> Option<Enrichment> {
    if !endpoint.starts_with("http://") && !endpoint.starts_with("https://") {
        return None;
    }
    if validate_outbound_url(endpoint).is_err() {
        return None;
    }
    let body = fetch_following(endpoint, "application/json", Some("json"), MAX_BYTES)
        .await
        .ok()?
        .body;
    parse(&body)
}

fn string_field(value: &serde_json::Value, key: &str) -> Option<String> {
    let text = value.get(key)?.as_str()?.trim();
    (!text.is_empty()).then(|| text.to_string())
}

/// 从 oEmbed 的 `html` 字段里取出 iframe 的 `src`。
fn iframe_src(html: &str) -> Option<String> {
    let start = html.to_ascii_lowercase().find("<iframe")?;
    let tail = &html[start..];
    let index = tail.to_ascii_lowercase().find("src=")? + 4;
    let after = tail[index..].trim_start();
    let quote = after.chars().next()?;
    if quote != '"' && quote != '\'' {
        return None;
    }
    let rest = &after[1..];
    let end = rest.find(quote)?;
    let src = rest[..end].trim();
    (!src.is_empty()).then(|| src.to_string())
}

/// 解析 oEmbed 响应体；没有任何可用字段时返回 `None`。
pub fn parse(body: &str) -> Option<Enrichment> {
    let value: serde_json::Value = serde_json::from_str(body).ok()?;
    if !value.is_object() {
        return None;
    }
    let enrichment = Enrichment {
        title: string_field(&value, "title"),
        description: string_field(&value, "description")
            .or_else(|| string_field(&value, "author_name")),
        image_url: string_field(&value, "thumbnail_url"),
        frame_src: string_field(&value, "html").as_deref().and_then(iframe_src),
    };
    (enrichment.title.is_some()
        || enrichment.description.is_some()
        || enrichment.image_url.is_some()
        || enrichment.frame_src.is_some())
    .then_some(enrichment)
}

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

    #[test]
    fn parses_the_youtube_payload() {
        let body = r#"{"title":"Rick Astley - Never Gonna Give You Up (Official Video)","author_name":"Rick Astley","author_url":"https://www.youtube.com/@RickAstleyYT","thumbnail_url":"https://i.ytimg.com/vi/dQw4w9WgXcQ/hqdefault.jpg","type":"video","version":"1.0"}"#;
        let enrichment = parse(body).unwrap();
        assert_eq!(
            enrichment.title.as_deref(),
            Some("Rick Astley - Never Gonna Give You Up (Official Video)")
        );
        assert_eq!(enrichment.description.as_deref(), Some("Rick Astley"));
        assert_eq!(
            enrichment.image_url.as_deref(),
            Some("https://i.ytimg.com/vi/dQw4w9WgXcQ/hqdefault.jpg")
        );
        assert!(enrichment.frame_src.is_none());
    }

    #[test]
    fn pulls_the_frame_out_of_the_spotify_payload() {
        let body = r#"{"title":"Never Gonna Give You Up","html":"<iframe style=\"border-radius: 12px\" width=\"100%\" height=\"152\" title=\"Spotify Embed: Never Gonna Give You Up\" frameborder=\"0\" allowfullscreen allow=\"autoplay; clipboard-write; encrypted-media; fullscreen; picture-in-picture\" loading=\"lazy\" src=\"https://open.spotify.com/embed/track/4cOdK2wGLETKBW3PvgPWqT?utm_source=oembed\"></iframe>"}"#;
        let enrichment = parse(body).unwrap();
        assert_eq!(
            enrichment.frame_src.as_deref(),
            Some("https://open.spotify.com/embed/track/4cOdK2wGLETKBW3PvgPWqT?utm_source=oembed")
        );
    }

    #[test]
    fn rejects_bodies_without_useful_fields() {
        assert!(parse("<html>nope</html>").is_none());
        assert!(parse("{}").is_none());
        assert!(parse(r#"{"type":"video","html":"<blockquote>quote</blockquote>"}"#).is_none());
    }
}