#!/usr/bin/env python3
"""
issue_evict.py — closed issues leave the store. Offline.

    issue_evict.py                 every closed issue that is not origin: local
    issue_evict.py old-thing …     only these
    issue_evict.py --dry-run       print what would go; touch nothing

The store is a working set, not an archive. A closed issue is not a unit of
work any more, and `pull.py` has kept new ones out of filter mode for a while —
but the files already on disk were nobody's job, so the only way to remove one
was `rm` past every script, followed by rebuilding `INDEX.md` by hand. This is
that job.

WHAT IS EVICTED, and it is two conditions, both read off the file:

    state: closed      the work is done
    origin: <tracker>  the work is somewhere else too

TWO CONDITIONS, AND THE SECOND ONE IS THE WHOLE SAFETY ARGUMENT. `origin:
local` means this file IS the issue — there is no other copy and deleting it
deletes the work. It is therefore never evicted, in any state, not even when
named explicitly on the command line: a closed local issue is reported and
kept. The only files that go are ones whose own metadata says the work can be
fetched back (`pull.py <n>`), which is the same trade `push.py` makes when it
drops a file the tracker has just confirmed.

That parallel is exact except for where the confirmation comes from. Push has
to ask Gitea, because it is Gitea that just changed. Eviction asks the file,
because `state:` and `origin:` are domain fields and the answer is already in
the store — which is why this command lives in the domain layer and needs no
network, no login, and no `tea`. See `skills/sync/scripts/evict.py` for the
variant that refreshes `state:` from the tracker first; it makes the deletion
decision by calling `run()` below, so there is exactly one implementation of
"what may be evicted" and it is this one.

NOT A ONE-OFF MIGRATION. `pull.py <n>` fetches an issue in any state — a number
is an address, not a query — so a closed issue pulled after an eviction lands on
disk again. That is the tracker being asked a direct question, not a regression,
and the answer is to evict again when you are done with it.

`.remote.json` is deliberately NOT pruned. It is the local number -> slug
ledger, its entries outlive the files they name (that is what makes `pull.py
<n>` land on the same slug after a push deleted the file), and an evicted issue
is in exactly that state. `INDEX.md` is rebuilt, because it *is* a view of the
directory.
"""
import argparse
import os
import sys

sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
import issue  # noqa: E402
import issue_index  # noqa: E402

CLOSED = "closed"

# Why an issue was kept, in the receipt. `LOCAL_REASON` is the one that matters:
# it is printed whether or not the issue was named, because "this closed thing
# is still here" needs an answer every time.
LOCAL_REASON = "origin: %s — this file IS the issue" % issue.LOCAL


def classify(issues, ids=None):
    """Split the store into (evict, protected, still_open).

    Pure — it reads the loaded issues and decides; nothing here touches disk.

        evict        closed, and lives in a tracker too: safe to remove
        protected    closed, but `origin: local`: the only copy of the work
        still_open   not closed

    `ids` restricts the question to those issues; without it the whole store is
    considered. A protected issue is returned as such even when it was named
    explicitly — naming a file does not make deleting it safe.
    """
    chosen = list(ids) if ids else sorted(issues)
    evict, protected, still_open = [], [], []
    for id in chosen:
        iss = issues[id]
        if iss.state != CLOSED:
            still_open.append(id)
        elif iss.is_local:
            protected.append(id)
        else:
            evict.append(id)
    return evict, protected, still_open


def remove(root, id):
    """Delete everything the store holds under one slug; return the paths.

    Deliberately dumb, and for the same reason `push.drop_local` is: it takes an
    id, not a decision. Whether an issue may go is settled by `classify` before
    this is reached, so the dangerous half of the operation has no branches in
    it at all. There is exactly one call site.
    """
    gone = []
    for p in issue.slug_files(root, id):
        os.remove(p)
        gone.append(p)
    return gone


def run(root, issues, ids=None, dry_run=False, out=None):
    """Classify, report, remove, rebuild the index. Returns (gone, kept).

    The one implementation of eviction, called both by `main` below and by the
    sync layer's `evict.py` — which does nothing to this decision except hand
    over issues whose `state:` it has just refreshed from the tracker.

    `gone` is {id: [paths]} and is empty on a dry run; `kept` is
    [(id, why)] for everything considered and not removed.
    """
    out = out or sys.stdout
    evict, protected, still_open = classify(issues, ids)

    gone, kept = {}, []
    for id in evict:
        paths = issue.slug_files(root, id) if dry_run else remove(root, id)
        if not dry_run:
            gone[id] = paths
        out.write("%-11s  %s\n" % ("would evict" if dry_run else "evicted", id))
        for p in paths:
            out.write("    %s\n" % p)
    for id in protected:
        kept.append((id, LOCAL_REASON))
        out.write("%-11s  %s  closed, %s\n" % ("kept", id, LOCAL_REASON))
    # An open issue is the normal case and says nothing worth a line — unless
    # the operator named it, in which case they are owed the reason.
    for id in still_open:
        kept.append((id, "state: %s" % issues[id].state))
        if ids:
            out.write("%-11s  %s  state: %s\n" % ("kept", id, issues[id].state))

    if dry_run:
        out.write("%d issue(s) would be evicted, %d kept — nothing was touched\n"
                  % (len(evict), len(kept)))
        return gone, kept

    out.write("%d issue(s) evicted, %d kept\n" % (len(gone), len(kept)))
    # Only when something actually went: the index is a view of the directory,
    # and rewriting it after a run that changed nothing is a write nobody asked
    # for.
    if gone:
        path, n = issue_index.build(root)
        out.write("index: %s — %d issue(s)\n" % (path, n))
    return gone, kept


def main(argv=None):
    ap = argparse.ArgumentParser(
        description="Evict closed issues from the local store (offline)")
    ap.add_argument("ids", nargs="*",
                    help="issue ids (default: every closed issue in the store)")
    ap.add_argument("--dry-run", action="store_true",
                    help="print what would be removed; touch nothing")
    ap.add_argument("--out", default=issue.ISSUE_ROOT,
                    help="store root (default: <repo>/tmp/issues)")
    args = ap.parse_args(argv)

    root = args.out
    if not issue.store_exists(root):
        sys.exit("issue_evict.py: store %s does not exist — nothing to evict" % root)

    issues = issue.load_all(root)
    missing = [i for i in args.ids if i not in issues]
    if missing:
        sys.exit("issue_evict.py: no such issue(s) in the store: %s"
                 % ", ".join(missing))

    run(root, issues, args.ids, args.dry_run)
    return 0


if __name__ == "__main__":
    sys.exit(main())