use gix::bstr::{BString, ByteSlice};
use gix::objs::tree::EntryMode;
use gix::odb::store::RefreshMode;
use gix::prelude::ObjectIdExt;

pub fn tree(
    mut repo: gix::Repository,
    out: &mut dyn std::io::Write,
    old_treeish: BString,
    new_treeish: BString,
) -> anyhow::Result<()> {
    repo.object_cache_size_if_unset(repo.compute_object_cache_size_for_tree_diffs(&**repo.index_or_empty()?));
    repo.objects.refresh = RefreshMode::Never;

    let old_tree_id = repo.rev_parse_single(old_treeish.as_bstr())?;
    let new_tree_id = repo.rev_parse_single(new_treeish.as_bstr())?;

    let old_tree = old_tree_id.object()?.peel_to_tree()?;
    let new_tree = new_tree_id.object()?.peel_to_tree()?;

    let changes = repo.diff_tree_to_tree(&old_tree, &new_tree, None)?;

    writeln!(
        out,
        "Diffing trees `{old_treeish}` ({old_tree_id}) -> `{new_treeish}` ({new_tree_id})\n"
    )?;
    write_changes(&repo, out, changes)?;

    Ok(())
}

fn write_changes(
    repo: &gix::Repository,
    mut out: impl std::io::Write,
    changes: Vec<gix::diff::tree_with_rewrites::Change>,
) -> Result<(), std::io::Error> {
    for change in changes {
        match change {
            gix::diff::tree_with_rewrites::Change::Addition {
                location,
                id,
                entry_mode,
                ..
            } => {
                writeln!(out, "A: {}", typed_location(location, entry_mode))?;
                writeln!(out, "  {}", id.attach(repo).shorten_or_id())?;
                writeln!(out, "  -> {:o}", entry_mode.0)?;
            }
            gix::diff::tree_with_rewrites::Change::Deletion {
                location,
                id,
                entry_mode,
                ..
            } => {
                writeln!(out, "D: {}", typed_location(location, entry_mode))?;
                writeln!(out, "  {}", id.attach(repo).shorten_or_id())?;
                writeln!(out, "  {:o} ->", entry_mode.0)?;
            }
            gix::diff::tree_with_rewrites::Change::Modification {
                location,
                previous_id,
                id,
                previous_entry_mode,
                entry_mode,
            } => {
                writeln!(out, "M: {}", typed_location(location, entry_mode))?;
                writeln!(
                    out,
                    "  {previous_id} -> {id}",
                    previous_id = previous_id.attach(repo).shorten_or_id(),
                    id = id.attach(repo).shorten_or_id()
                )?;
                if previous_entry_mode != entry_mode {
                    writeln!(out, "  {:o} -> {:o}", previous_entry_mode.0, entry_mode.0)?;
                }
            }
            gix::diff::tree_with_rewrites::Change::Rewrite {
                source_location,
                source_id,
                id,
                location,
                source_entry_mode,
                entry_mode,
                ..
            } => {
                writeln!(
                    out,
                    "R: {source} -> {dest}",
                    source = typed_location(source_location, source_entry_mode),
                    dest = typed_location(location, entry_mode)
                )?;
                writeln!(
                    out,
                    "  {source_id} -> {id}",
                    source_id = source_id.attach(repo).shorten_or_id(),
                    id = id.attach(repo).shorten_or_id()
                )?;
                if source_entry_mode != entry_mode {
                    writeln!(out, "  {:o} -> {:o}", source_entry_mode.0, entry_mode.0)?;
                }
            }
        };
    }

    Ok(())
}

fn typed_location(mut location: BString, mode: EntryMode) -> BString {
    if mode.is_tree() {
        location.push(b'/');
    }
    location
}