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）。
    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
            ));
        }
        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()
}

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