//! 本地图片引用展开(#958 图片入站引用化)
//!
//! 消息持久化只存引用(ContentPart::Image.url = `file://<绝对路径>`,base64 空),
//! 发送请求前在此统一展开为 base64 内嵌——存储面瘦 referencing(一张 5MB 图不再以
//! 6.7MB base64 字符串进 SQLite 随历史全量重放),转换面按需读盘(SSD 毫秒级,
//! 对比 base64 内嵌的每请求全量携带,磁盘读便宜得多)。
//!
//! 展开点是 provider 转换层的入口:主会话/子代理/标题/压缩等全部请求路径在此
//! 单点覆盖,调用方(飞书入站/桌面粘贴图)只管落盘产引用,不关心 provider 差异。
//!
//! 失败语义:引用文件丢失/不可读时降级为 Text 片「[图片文件缺失: path]」——
//! 诚实告知模型图不可用,不让请求 400(空 base64 会被两个协议端点拒绝)。

use crate::provider::ContentPart;
use base64::Engine as _;

/// `file://` 引用前缀。内部引用标识(两端自洽即可,不进端点):落盘方拼
/// `file://<原生绝对路径>`,展开方 strip 后按原生路径读(Windows 盘符路径直接可用)。
pub const LOCAL_FILE_SCHEME: &str = "file://";

/// 判定 Image 片是否为本地引用(base64 空 + url 带本地 scheme)
fn is_local_ref(url: Option<&str>, base64: Option<&str>) -> bool {
    base64.is_none() && url.is_some_and(|u| u.starts_with(LOCAL_FILE_SCHEME))
}

/// 把消息内的本地图片引用展开为 base64 内嵌片;非本地片原样透传。
/// 文件缺失/不可读时该 Image 片降级为 Text 片(请求不炸,模型得到可读的缺失说明)。
pub fn inline_local_image_parts(parts: Vec<ContentPart>) -> Vec<ContentPart> {
    parts.into_iter().map(inline_local_image_part).collect()
}

/// 单片版(provider 转换臂逐片 map 用)
pub fn inline_local_image_part(p: ContentPart) -> ContentPart {
    match p {
        ContentPart::Image { url, base64, media_type, alt }
            if is_local_ref(url.as_deref(), base64.as_deref()) =>
        {
            let path = url.unwrap();
            match std::fs::read(&path[LOCAL_FILE_SCHEME.len()..]) {
                Ok(bytes) => ContentPart::Image {
                    url: None,
                    base64: Some(base64::engine::general_purpose::STANDARD.encode(bytes)),
                    media_type,
                    alt,
                },
                Err(_) => ContentPart::Text {
                    text: format!("[图片文件缺失: {}]", &path[LOCAL_FILE_SCHEME.len()..]),
                },
            }
        }
        other => other,
    }
}

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

    #[test]
    fn local_ref_expands_to_base64() {
        let dir = std::env::temp_dir().join("df-ai-image-ref-test");
        std::fs::create_dir_all(&dir).unwrap();
        let path = dir.join("expands.png");
        std::fs::write(&path, b"\x89PNG fake-bytes").unwrap();

        let out = inline_local_image_parts(vec![ContentPart::Image {
            url: Some(format!("file://{}", path.display())),
            base64: None,
            media_type: Some("image/png".into()),
            alt: None,
        }]);
        match &out[0] {
            ContentPart::Image { url, base64, media_type, .. } => {
                assert!(url.is_none());
                let b = base64.as_deref().expect("base64 应已填充");
                assert_eq!(b, base64::engine::general_purpose::STANDARD.encode(b"\x89PNG fake-bytes"));
                assert_eq!(media_type.as_deref(), Some("image/png"));
            }
            other => panic!("应保持 Image 片, 实际 {other:?}"),
        }
        std::fs::remove_file(&path).ok();
    }

    #[test]
    fn missing_file_degrades_to_text_not_empty_base64() {
        let out = inline_local_image_parts(vec![ContentPart::Image {
            url: Some("file:///nonexistent/df-ai-no-such.png".into()),
            base64: None,
            media_type: Some("image/png".into()),
            alt: None,
        }]);
        match &out[0] {
            ContentPart::Text { text } => {
                assert!(text.contains("[图片文件缺失"), "应降级为缺失说明, 实际 {text}");
                assert!(text.contains("df-ai-no-such.png"));
            }
            other => panic!("缺失文件应降级 Text 片, 实际 {other:?}"),
        }
    }

    #[test]
    fn non_local_parts_pass_through() {
        let passthrough = vec![
            ContentPart::text("hello"),
            ContentPart::image_base64("image/png", "aGVsbG8="),
            ContentPart::image_url("https://x/a.png"),
            // base64 非空的 file:// 不是引用(优先内嵌),原样透传
            ContentPart::Image {
                url: Some("file:///x.png".into()),
                base64: Some("aGVsbG8=".into()),
                media_type: Some("image/png".into()),
                alt: None,
            },
        ];
        let out = inline_local_image_parts(passthrough);
        assert_eq!(out.len(), 4);
        assert!(matches!(&out[0], ContentPart::Text { .. }));
        assert!(matches!(&out[1], ContentPart::Image { base64: Some(_), .. }));
        assert!(matches!(&out[2], ContentPart::Image { url: Some(u), .. } if u.starts_with("https://")));
        assert!(matches!(&out[3], ContentPart::Image { base64: Some(_), .. }));
    }
}