use git::context::facade::GitContext;

/// 组装好的模型上下文：提示词正文 + 是否发生截断。
#[derive(Debug, Clone)]
pub struct BuiltContext {
    pub text: String,
    pub truncated: bool,
}

const EMPTY_TREE: &str = "4b825dc642cb6eb9a060e54bf8d69288fbee4904";

impl super::AgentService {
    /// PR 评审上下文：merge-base..head 的三点差异。
    pub async fn build_pull_diff(
        &self,
        space_name: &str,
        repo_name: &str,
        head_sha: &str,
        base_ref: &str,
    ) -> Result<(BuiltContext, String), git::share::errors::GitError> {
        let ctx = self
            .git
            .context(space_name.to_string(), repo_name.to_string())
            .await?;
        let plan = self
            .git
            .merge_plan(&ctx, &format!("refs/heads/{base_ref}"), head_sha)
            .await?;
        let from = plan
            .merge_base
            .clone()
            .unwrap_or_else(|| plan.base_sha.clone());
        let diff = self
            .git
            .diff_raw(
                space_name.to_string(),
                repo_name.to_string(),
                from.clone(),
                plan.head_sha.clone(),
            )
            .await?;
        let label = format!("{}..{}", short(&from), short(&plan.head_sha));
        Ok((self.truncate_diff(diff), label))
    }

    /// Commit 评审上下文：父提交..该提交的差异。
    pub async fn build_commit_diff(
        &self,
        space_name: &str,
        repo_name: &str,
        commit_sha: &str,
    ) -> Result<(BuiltContext, String), git::share::errors::GitError> {
        let ctx = self
            .git
            .context(space_name.to_string(), repo_name.to_string())
            .await?;
        let baby = self.git.baby(&ctx);
        let info = baby
            .get_commit(commit_sha)
            .await
            .map_err(git::share::errors::map_baby)?;
        let parent = info
            .parents
            .first()
            .map(|p| p.to_string())
            .unwrap_or_else(|| EMPTY_TREE.to_string());
        let sha = info.id.to_string();
        let diff = self
            .git
            .diff_raw(
                space_name.to_string(),
                repo_name.to_string(),
                parent.clone(),
                sha.clone(),
            )
            .await?;
        let label = format!("{}..{}", short(&parent), short(&sha));
        Ok((self.truncate_diff(diff), label))
    }

    /// 提交列表（评审用不到，但总结/release 复用同一格式化）。
    ///
    /// 附上正文首段：提交标题往往只有「fix bug」这类动作，真正说明意图、影响面
    /// 与取舍的信息在正文里。总结与 release 文案靠这些内容才能写出实质差别，
    /// 只喂标题时模型只能把标题换个说法复述一遍——那正是输出干瘪的直接原因。
    /// 正文按提交截断，避免一条超长 message 把预算吃光。
    pub(crate) fn format_commits(commits: &[git::service::merge::MergeCommitDto]) -> String {
        let mut out = String::new();
        for commit in commits {
            out.push_str(&format!(
                "- {} {}  ({}, {})\n",
                short(&commit.sha),
                commit.subject.trim(),
                commit.author_name,
                commit.author_at
            ));
            if let Some(body) = commit_body(&commit.message, &commit.subject) {
                out.push_str(&body);
            }
        }
        out
    }

    /// 按字节预算截断差异：超限时逐文件裁剪并标记 truncated。
    pub(crate) fn truncate_diff(&self, diff: String) -> BuiltContext {
        let limit = self.config().ai.context_max_bytes;
        if diff.len() <= limit {
            return BuiltContext {
                text: diff,
                truncated: false,
            };
        }
        let mut text = String::with_capacity(limit);
        let mut truncated = false;
        for file in split_diff_files(&diff) {
            if text.len() + file.len() > limit {
                truncated = true;
                break;
            }
            text.push_str(&file);
        }
        if text.is_empty() {
            // 单个文件本身就超限：按字符边界硬截断。
            text = diff.chars().take(limit).collect();
            truncated = true;
        }
        BuiltContext { text, truncated }
    }
}

/// 按 `diff --git` 切分，保留每段完整补丁文本。
pub fn split_diff_files(diff: &str) -> Vec<String> {
    let mut files: Vec<String> = Vec::new();
    let mut current = String::new();
    for line in diff.split_inclusive('\n') {
        if line.starts_with("diff --git ") && !current.is_empty() {
            files.push(std::mem::take(&mut current));
        }
        current.push_str(line);
    }
    if !current.is_empty() {
        files.push(current);
    }
    files
}

pub(crate) fn short(sha: &str) -> String {
    sha.chars().take(8).collect()
}

/// 单条提交正文进入提示词的字符上限。
const COMMIT_BODY_MAX_CHARS: usize = 400;

/// 提交正文的摘要片段：跳过标题行、去掉签名等尾部噪音、保留首个实质段落。
fn commit_body(message: &str, subject: &str) -> Option<String> {
    let mut lines = message.lines();
    // 第一行是标题，调用方已经输出过。
    lines.next();
    let mut body = String::new();
    for line in lines {
        let trimmed = line.trim();
        if trimmed.is_empty() {
            // 首个空行代表首个段落结束；段落之前的前导空行直接跳过。
            if !body.is_empty() {
                break;
            }
            continue;
        }
        // 「Signed-off-by:」「Co-authored-by:」这类 trailer 不描述变更本身。
        let lower = trimmed.to_ascii_lowercase();
        if lower.starts_with("signed-off-by:") || lower.starts_with("co-authored-by:") {
            continue;
        }
        body.push_str(trimmed);
        body.push(' ');
        if body.chars().count() >= COMMIT_BODY_MAX_CHARS {
            break;
        }
    }
    let body = body.trim();
    if body.is_empty() || body == subject.trim() {
        return None;
    }
    Some(format!(
        "  正文：{}\n",
        truncate_chars(body, COMMIT_BODY_MAX_CHARS)
    ))
}

fn truncate_chars(text: &str, limit: usize) -> String {
    if text.chars().count() <= limit {
        return text.to_string();
    }
    let mut out: String = text.chars().take(limit).collect();
    out.push('…');
    out
}

/// 让 `GitContext` 在本 crate 内可用（避免调用方各自引入 git crate）。
pub type RepoContext = GitContext;

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

    /// 提交正文是总结质量的来源：只喂标题时模型无从区分「一次重构」与
    /// 「一行修复」，输出必然退化成标题复述。这条测试把正文必须进入提示词
    /// 这件事钉住，同时确认签名之类的尾部噪音不会被带上。
    #[test]
    fn commit_body_keeps_prose_and_drops_trailers() {
        let message = "fix: 修正接收器计数\n\nBufferedUdpMetricSink 在批量发送后少记一次，\n对监控口径有影响。\n\nSigned-off-by: Someone <s@example.com>\n";
        let body = commit_body(message, "fix: 修正接收器计数").expect("正文应被保留");
        assert!(body.contains("少记一次"), "正文要点必须保留: {body}");
        assert!(
            !body.contains("Signed-off-by"),
            "trailer 不应进入提示词: {body}"
        );
    }

    /// 没有正文、或正文与标题重复时不必占用预算。
    #[test]
    fn commit_body_is_skipped_when_empty_or_identical() {
        assert!(commit_body("only a subject", "only a subject").is_none());
        assert!(commit_body("subject\n\nsubject", "subject").is_none());
    }

    /// 超长正文按字符截断，避免一条 message 吃掉整段提示词预算。
    #[test]
    fn commit_body_is_bounded() {
        let long = format!("subject\n\n{}", "改".repeat(COMMIT_BODY_MAX_CHARS * 2));
        let body = commit_body(&long, "subject").expect("应有正文");
        assert!(body.chars().count() < COMMIT_BODY_MAX_CHARS + 16);
        assert!(body.ends_with("…\n"));
    }
}