//! Single-commit cherry-pick uses Git's CHERRY_PICK_HEAD and MERGE_MSG for continuation.
use crate::{Result, branches, checkout, local, output, repo::error, staging};
use gix::bstr::ByteSlice;

pub(crate) fn merge_trees(
    repo: &gix::Repository,
    base: gix::ObjectId,
    ours: gix::ObjectId,
    theirs: gix::ObjectId,
    current: &str,
    other: &str,
) -> Result<(gix::ObjectId, gix::index::State, Vec<String>)> {
    let local = crate::merge::merge_repository(repo)?;
    let labels = gix::merge::blob::builtin_driver::text::Labels {
        ancestor: None,
        current: Some(current.into()),
        other: Some(other.into()),
    };
    let mut outcome = local
        .merge_trees(
            base,
            ours,
            theirs,
            labels,
            local
                .tree_merge_options()
                .map_err(|e| error("merge options", e))?,
        )
        .map_err(|e| error("merge trees", e))?;
    let tree = outcome
        .tree
        .write()
        .map_err(|e| error("merge tree", e))?
        .detach();
    let mut index = gix::index::State::from_tree(&tree, &repo.objects, Default::default())
        .map_err(|e| error("merge index", e))?;
    outcome.index_changed_after_applying_conflicts(
        &mut index,
        Default::default(),
        gix::merge::tree::apply_index_entries::RemovalMode::Prune,
    );
    index.sort_entries();
    let conflicts = index
        .entries()
        .iter()
        .filter(|e| e.stage_raw() != 0)
        .map(|e| e.path(&index).to_str_lossy().into_owned())
        .collect::<std::collections::BTreeSet<_>>()
        .into_iter()
        .collect();
    Ok((tree, index, conflicts))
}
fn clear(repo: &gix::Repository) -> Result<()> {
    for name in ["CHERRY_PICK_HEAD", "MERGE_MSG"] {
        let path = repo.git_dir().join(name);
        if path.exists() {
            std::fs::remove_file(path).map_err(|e| error("cherry-pick cleanup", e))?;
        }
    }
    Ok(())
}
pub(crate) fn run(
    repo: &gix::Repository,
    revision: Option<String>,
    resume: bool,
    abort: bool,
    quiet: bool,
) -> Result<i32> {
    if abort {
        if !repo.git_dir().join("CHERRY_PICK_HEAD").exists() {
            return Err(error("cherry-pick abort", "no cherry-pick in progress"));
        }
        let old = std::fs::read_to_string(repo.git_dir().join("ORIG_HEAD"))
            .map_err(|e| error("cherry-pick abort", e))?;
        local::reset(repo, old.trim(), &[], false, true, true)?;
        clear(repo)?;
        return Ok(0);
    }
    let id = if resume {
        let id = std::fs::read_to_string(repo.git_dir().join("CHERRY_PICK_HEAD"))
            .map_err(|e| error("cherry-pick continue", e))?;
        branches::resolve(repo, id.trim())?
    } else {
        crate::merge::ensure_idle(repo)?;
        crate::merge::clean(repo)?;
        branches::resolve(repo, &crate::required(revision, "cherry-pick revision")?)?
    };
    let old = branches::resolve(repo, "HEAD")?;
    let original = repo
        .find_commit(id)
        .map_err(|e| error("cherry-pick commit", e))?;
    let decoded = original
        .decode()
        .map_err(|e| error("cherry-pick decode", e))?;
    let subject = decoded
        .message
        .to_str_lossy()
        .lines()
        .next()
        .unwrap_or("")
        .to_owned();
    let tree = if resume {
        staging::tree_from_index(repo, &staging::load(repo)?)?
    } else {
        let base = match decoded.parents.first() {
            Some(id) => local::tree(repo, &id.to_string())?,
            None => repo
                .write_object(&gix::objs::Tree { entries: vec![] })
                .map_err(|e| error("empty tree", e))?
                .detach(),
        };
        let ours = local::tree(repo, "HEAD")?;
        let (tree, index, conflicts) = merge_trees(
            repo,
            base,
            ours,
            decoded.tree(),
            "HEAD",
            &format!("{} ({subject})", &id.to_string()[..7]),
        )?;
        checkout::write_tree_to_worktree(repo, Some(ours), tree, false)?;
        staging::publish(repo, index)?;
        if !conflicts.is_empty() {
            std::fs::write(repo.git_dir().join("CHERRY_PICK_HEAD"), format!("{id}\n"))
                .map_err(|e| error("cherry-pick state", e))?;
            std::fs::write(repo.git_dir().join("ORIG_HEAD"), format!("{old}\n"))
                .map_err(|e| error("cherry-pick state", e))?;
            std::fs::write(repo.git_dir().join("MERGE_MSG"), decoded.message.as_bytes())
                .map_err(|e| error("cherry-pick state", e))?;
            output::conflicts(&conflicts, false);
            return Ok(1);
        }
        tree
    };
    let commit = gix::objs::Commit {
        tree,
        parents: vec![old].into_iter().collect(),
        author: decoded
            .author()
            .map_err(|e| error("pick author", e))?
            .to_owned()
            .map_err(|e| error("pick author", e))?,
        committer: staging::signature(None, None)?,
        encoding: decoded.encoding.map(ToOwned::to_owned),
        message: decoded.message.to_owned(),
        extra_headers: vec![],
    };
    let new = repo
        .write_object(&commit)
        .map_err(|e| error("cherry-pick write", e))?
        .detach();
    staging::update_head(
        repo,
        Some(old),
        new,
        &staging::signature(None, None)?,
        &format!("cherry-pick: {subject}"),
    )?;
    clear(repo)?;
    if !quiet {
        let head = crate::head_info(repo)?;
        println!(
            "[{} {}] {subject}",
            head.branch
                .unwrap_or_else(|| "detached HEAD".into())
                .trim_start_matches("refs/heads/"),
            &new.to_string()[..7]
        );
        output::author_date(&repo.find_commit(new).map_err(|e| error("pick output", e))?)?;
        output::commit_stat(&crate::changes::diff(crate::changes::DiffParams {
            repo: repo.workdir().unwrap().to_string_lossy().into_owned(),
            from: Some(old.to_string()),
            to: Some(new.to_string()),
            staged: None,
            path: None,
            context: None,
        })?);
    }
    Ok(0)
}