josh-changes 26.4.19

use anyhow::anyhow;
use josh_core::Change;

#[derive(PartialEq, Clone, Debug)]
pub enum PushMode {
    Normal,
    Stack(String),
    Split(String),
}

#[derive(Debug, Clone)]
pub struct PushRef {
    pub ref_name: String,
    pub oid: git2::Oid,
    pub change_id: String,
}

pub fn baseref_and_options(
    refname: &str,
    author: &str,
) -> anyhow::Result<(String, String, Vec<String>, PushMode)> {
    let mut split = refname.splitn(2, '%');
    let push_to = split.next().ok_or(anyhow!("no next"))?.to_owned();

    let options = if let Some(options) = split.next() {
        options.split(',').map(|x| x.to_string()).collect()
    } else {
        vec![]
    };

    let mut baseref = push_to.to_owned();
    let mut push_mode = PushMode::Normal;

    if baseref.starts_with("refs/for") {
        baseref = baseref.replacen("refs/for", "refs/heads", 1)
    }
    if baseref.starts_with("refs/drafts") {
        baseref = baseref.replacen("refs/drafts", "refs/heads", 1)
    }
    if baseref.starts_with("refs/stack/for") {
        push_mode = PushMode::Stack(author.to_string());
        baseref = baseref.replacen("refs/stack/for", "refs/heads", 1)
    }
    if baseref.starts_with("refs/split/for") {
        push_mode = PushMode::Split(author.to_string());
        baseref = baseref.replacen("refs/split/for", "refs/heads", 1)
    }
    Ok((baseref, push_to, options, push_mode))
}

fn add_base_refs(repo: &git2::Repository, refs: &mut Vec<PushRef>) -> anyhow::Result<()> {
    let original_refs = std::mem::take(refs);
    for push_ref in original_refs.into_iter() {
        let base_ref = push_ref
            .ref_name
            .replacen("refs/heads/@changes", "refs/heads/@base", 1);

        let oid = push_ref.oid;
        let change_id = push_ref.change_id.clone();
        refs.push(push_ref);

        if let Some(parent_sha) = repo.find_commit(oid)?.parent_ids().next() {
            refs.push(PushRef {
                ref_name: base_ref,
                oid: parent_sha,
                change_id,
            });
        }
    }

    Ok(())
}

fn split_changes(
    repo: &git2::Repository,
    changes: &mut [PushRef],
    base: git2::Oid,
) -> anyhow::Result<()> {
    if base == git2::Oid::zero() {
        return Ok(());
    }

    for push_ref in changes.iter_mut() {
        push_ref.oid = downstack(repo, base, push_ref.oid)?;
    }

    Ok(())
}

pub fn downstack(
    repo: &git2::Repository,
    base: git2::Oid,
    change: git2::Oid,
) -> anyhow::Result<git2::Oid> {
    if !repo.graph_descendant_of(change, base)? {
        return Err(anyhow!(
            "change {} is not a descendant of base {}",
            change,
            base
        ));
    }

    // Collect commits from base to change (exclusive of base, inclusive of change)
    let mut walk = repo.revwalk()?;
    walk.simplify_first_parent()?;
    walk.set_sorting(git2::Sort::REVERSE | git2::Sort::TOPOLOGICAL)?;
    walk.push(change)?;
    walk.hide(base)?;

    let oids: Vec<git2::Oid> = walk.collect::<Result<Vec<_>, _>>()?;

    if oids.is_empty() {
        return Ok(change);
    }

    let mut commits: Vec<git2::Commit> = oids
        .into_iter()
        .map(|oid| repo.find_commit(oid))
        .collect::<Result<Vec<_>, _>>()?;

    // The last commit is `change`; split it off from the intermediates
    let change_commit = commits.pop().unwrap();
    let change_parent = change_commit.parent(0)?;

    // Compute d_change: the diff introduced by the change commit itself
    let change_diff = repo.diff_tree_to_tree(
        Some(&change_parent.tree()?),
        Some(&change_commit.tree()?),
        None,
    )?;

    // Walk through intermediates, including only those needed for d_change to apply
    let mut current_base = repo.find_commit(base)?;

    for intermediate in &commits {
        // If d_change already applies to the current base tree, we can stop
        if repo
            .apply_to_tree(&current_base.tree()?, &change_diff, None)
            .is_ok()
        {
            break;
        }

        // d_change does not apply yet; we need this intermediate commit.
        // Rebase it onto current_base by applying its diff.
        let inter_parent = intermediate.parent(0)?;
        let inter_diff = repo.diff_tree_to_tree(
            Some(&inter_parent.tree()?),
            Some(&intermediate.tree()?),
            None,
        )?;

        let mut index = repo.apply_to_tree(&current_base.tree()?, &inter_diff, None)?;
        let new_tree = repo.find_tree(index.write_tree_to(repo)?)?;

        let new_oid = josh_core::history::rewrite_commit(
            repo,
            intermediate,
            &[&current_base],
            josh_core::filter::Rewrite::from_tree(new_tree),
            josh_core::history::GpgsigMode::Preserve,
        )?;
        current_base = repo.find_commit(new_oid)?;
    }

    // Apply d_change on top of the minimal base and create the new change commit
    let mut index = repo.apply_to_tree(&current_base.tree()?, &change_diff, None)?;
    let new_tree = repo.find_tree(index.write_tree_to(repo)?)?;

    josh_core::history::rewrite_commit(
        repo,
        &change_commit,
        &[&current_base],
        josh_core::filter::Rewrite::from_tree(new_tree),
        josh_core::history::GpgsigMode::Preserve,
    )
}

pub fn changes_to_refs(
    baseref: &str,
    change_author: &str,
    changes: Vec<Change>,
) -> anyhow::Result<Vec<PushRef>> {
    if !change_author.contains('@') {
        return Err(anyhow!(
            "Push option 'author' needs to be set to a valid email address",
        ));
    };

    let changes: Vec<Change> = changes
        .into_iter()
        .filter(|change| change.author == change_author)
        .collect();

    let mut seen = std::collections::HashSet::new();
    for change in changes.iter() {
        if let Some(id) = &change.id {
            if id.contains('@') {
                return Err(anyhow!("Change id must not contain '@'"));
            }
            if !seen.insert(id) {
                return Err(anyhow!(
                    "rejecting to push {:?} with duplicate label",
                    change.commit
                ));
            }
            seen.insert(id);
        }
    }

    Ok(changes
        .into_iter()
        .filter_map(|change| {
            change.id.map(|change_id| PushRef {
                ref_name: format!(
                    "refs/heads/@changes/{}/{}/{}",
                    baseref.replacen("refs/heads/", "", 1),
                    change.author,
                    change_id,
                ),
                oid: change.commit,
                change_id,
            })
        })
        .collect())
}

fn get_changes(
    repo: &git2::Repository,
    tip: git2::Oid,
    base: git2::Oid,
) -> anyhow::Result<Vec<Change>> {
    let mut walk = repo.revwalk()?;
    walk.set_sorting(git2::Sort::REVERSE | git2::Sort::TOPOLOGICAL)?;
    walk.simplify_first_parent()?;
    walk.push(tip)?;
    if base != git2::Oid::zero() {
        walk.hide(base)?;
    }

    let mut changes = vec![];
    for rev in walk {
        let commit = repo.find_commit(rev?)?;
        changes.push(josh_core::get_change_id(&commit));
    }

    Ok(changes)
}

pub fn build_to_push(
    repo: &git2::Repository,
    push_mode: &PushMode,
    baseref: &str,
    ref_with_options: &str,
    oid_to_push: git2::Oid,
    base_oid: git2::Oid,
) -> anyhow::Result<Vec<PushRef>> {
    match push_mode {
        PushMode::Stack(author) | PushMode::Split(author) => {
            let changes = get_changes(repo, oid_to_push, base_oid)?;
            let mut push_refs = changes_to_refs(baseref, author, changes)?;

            if matches!(push_mode, PushMode::Split(_)) {
                split_changes(repo, &mut push_refs, base_oid)?;
            }

            add_base_refs(repo, &mut push_refs)?;

            push_refs.push(PushRef {
                ref_name: format!(
                    "refs/heads/@heads/{}/{}",
                    baseref.replacen("refs/heads/", "", 1),
                    author,
                ),
                oid: oid_to_push,
                change_id: baseref.replacen("refs/heads/", "", 1),
            });

            Ok(push_refs)
        }
        PushMode::Normal => Ok(vec![PushRef {
            ref_name: ref_with_options.to_string(),
            oid: oid_to_push,
            change_id: "JOSH_PUSH".to_string(),
        }]),
    }
}