midenup 1.0.0

use anyhow::{Context, bail};

use crate::{
    channel::UserChannel,
    config::Config,
    paths,
    publish::JournalEntry,
    state::{LocalState, PublicationRef},
};

/// Removes an installed channel.
///
/// Uses the same journalled sequence as install (spec section 9.5), with one difference: the commit
/// point replaces `toolchains/<channel>` with a **tombstone** rather than repointing it. That is
/// what lets recovery tell a removal that was committed and interrupted apart from a toolchain
/// somebody deleted by hand -- the first is completed, the second is reported.
///
/// The publication is removed wholesale. There is no per-component removal pass: the publication
/// directory contains exactly what its receipt says it does and nothing else, so walking components
/// to delete their files individually could only ever remove less than the directory itself.
///
/// `var/` is **kept** unless `purge` is given. It is the user's data -- the client's database lives
/// there -- and removing a toolchain is not a request to delete it. The user is told where it was
/// left.
///
/// What a purge removes is keyed by `requested`, exactly as the user spelled it, because that is
/// how the store is keyed ([`crate::paths::var_dir`]): `uninstall mainnet --purge` removes
/// `var/mainnet`, and `uninstall 0.15.0 --purge` removes `var/0.15.0`. Removing a channel therefore
/// never touches a network's store, which is correct -- the network outlives any channel it names,
/// and its data belongs to the network.
pub fn uninstall(
    config: &Config,
    requested: &UserChannel,
    state: &mut LocalState,
    purge: bool,
) -> anyhow::Result<()> {
    // Resolved against local state, never upstream: a channel that has been withdrawn upstream is
    // precisely one a user needs to be able to remove (spec section 12.3).
    let installed = config.local_channel(requested).and_then(|version| state.get(&version));

    let Some(installation) = installed else {
        bail!("channel {requested} is not installed, nothing to uninstall");
    };
    let channel = installation.channel.clone();
    let publication = match &installation.publication {
        PublicationRef::Managed { id, .. } => Some(id.clone()),
        // Carried over from v1: nothing describes what it owns, so there is no publication to
        // reclaim. The state record still goes.
        PublicationRef::NeedsReinstall => None,
    };

    let home = &config.midenup_home;
    let entry = JournalEntry::uninstall(channel.clone(), publication);
    crate::publish::journal::prepare(home, &entry)?;

    // Network links are derived, so removing them before the commit costs nothing if the operation
    // is discarded: the next install or update recomputes them from upstream.
    //
    // Found by scanning rather than by asking upstream which networks name this channel. Uninstall
    // has to work offline, and a network may have moved upstream since this machine last looked --
    // in which case upstream would not name the link that is actually here.
    //
    // This relies on [`crate::networks::links`] excluding `default`, and that exclusion is load
    // bearing *here* rather than merely tidy: `midenup override <version>` points `default` at a
    // version directly under `toolchains/`, which is the shape of a network link, so only the name
    // tells the two apart. Were `default` to appear in this scan it would be removed before the
    // commit point below, and a discarded uninstall would leave the user without the override it
    // never actually removed -- which is why `default` is handled after the commit instead.
    for (network, linked) in crate::networks::links(home) {
        if linked == channel {
            let link = paths::network_link(home, &network);
            crate::trace!("removing {}", link.display());
            std::fs::remove_file(link)?;
        }
    }

    // The commit point: after this the channel is uninstalled, and an interrupted run is completed
    // rather than rolled back.
    crate::publish::journal::commit_symlink(home, &entry)?;

    // `default` is the user's `midenup override` choice, not a derived link, so nothing would
    // recompute it -- which is why it is removed after the commit point rather than with the
    // network links. Either override form dangles once the channel is gone: one names a network
    // link that has just been removed, the other names the toolchain directory the commit
    // tombstoned. Testing for dangling covers both, and repairs one left over from any earlier
    // cause.
    let default = paths::toolchains_dir(home).join("default");
    if std::fs::symlink_metadata(&default).is_ok() && default.canonicalize().is_err() {
        std::fs::remove_file(&default)?;
        crate::info!(
            "removed the 'default' override, which named {channel}. Set a new one with:\n    \
             midenup override <channel>"
        );
    }

    // Removes the state record, reclaims the publication, clears the tombstone, deletes the
    // journal.
    crate::publish::journal::finish(home, &entry, state)?;

    // Only now, and only if asked. Deliberately after the commit: this is the one part of an
    // uninstall that cannot be undone by reinstalling.
    let var = paths::var_dir(home, requested);
    if var.is_dir() {
        if purge {
            crate::trace!("removing {}", var.display());
            std::fs::remove_dir_all(&var)
                .with_context(|| format!("failed to remove '{}'", var.display()))?;
        } else {
            crate::info!(
                "kept your data for {requested} at {}; remove it with `midenup uninstall \
                 {requested} --purge`",
                var.display()
            );
        }
    }

    crate::info!("uninstalled channel '{channel}'");

    Ok(())
}