Switch to ref-per-commit approach

This enables single-commit push, and simpler deletion of old snapshots.

lethe/lethe.py

@@ -3,7 +3,7 @@
 Git snapshotting tool
 """
 
-from typing import List, Union, Optional
+from typing import Sequence, Union, Optional
 import subprocess
 import tempfile
 import datetime
@@ -11,18 +11,25 @@ import argparse
 from itertools import chain
 
 
-def _run(command: Union[str, List[str]], **kwargs) -> str:
+def _run(command: Union[str, Sequence[str]], **kwargs) -> str:
     """
     Wrapper for `subprocess.run()`:
 
     - Accepts args as either a list of strings or space-delimited string
     - Captures and returns stdout
+
+    Args:
+        command: A list of strings or a space-delimited string
+        **kwargs: Passed to `subprocess.run()`
+
+    Returns:
+        Captured stdout
     """
+    args: Sequence[str]
     if isinstance(command, str):
         args = command.split()
     else:
         args = command
-#    print('run', ' '.join(args))
     result = subprocess.run(args, stdout=subprocess.PIPE, **kwargs)
     return result.stdout.decode().strip()
 
@@ -33,14 +40,14 @@ def get_latest_commit(short: bool = True, cwd: Optional[str] = None) -> str:
     This includes non-lethe commits.
     """
     fmt = 'h' if short else 'H'
-    return _run('git log --all -1 --format=%{}'.format(fmt), cwd=cwd)
+    return _run(f'git log --all -1 --format=%{fmt}', cwd=cwd)
 
 
 def shorten_hash(sha: str, cwd: Optional[str] = None) -> str:
     """
     Get the short version of a hash
     """
-    return _run('git rev-parse --short {}'.format(sha), cwd=cwd)
+    return _run(f'git rev-parse --short {sha}', cwd=cwd)
 
 
 def get_root(cwd: Optional[str] = None) -> str:
@@ -76,7 +83,7 @@ def get_tree(ref: str, cwd: Optional[str] = None) -> str:
 
 
 def commit_tree(tree: str,
-                parents: List[str],
+                parents: Sequence[str],
                 message: Optional[str] = None,
                 cwd: Optional[str] = None,
                 ) -> str:
@@ -88,13 +95,14 @@ def commit_tree(tree: str,
         message = 'snapshot ' + str(datetime.datetime.now())
 
     pargs = list(chain.from_iterable(('-p', p) for p in parents))
-    commit = _run(['git', 'commit-tree', tree, *pargs, '-m', message], cwd=cwd)            # Create commit
+    commit = _run(['git', 'commit-tree', tree, *pargs, '-m', message], cwd=cwd)   # Create commit
     return commit
 
 
 def update_ref(target_ref: str,
                target_commit: str,
                old_commit: Optional[str] = None,
+               *,
                message: str = 'new snapshot',
                cwd: Optional[str] = None,
                ) -> str:
@@ -111,13 +119,23 @@ def update_ref(target_ref: str,
 
 
 def push_ref(remote: str = 'origin',
-             target_ref: str = 'refs/lethe/HEAD',
+             target_ref: str = 'refs/lethe/LATEST',
              remote_ref: Optional[str] = None,
+             *,
              cwd: Optional[str] = None,
              ) -> str:
     """
     Push `target_ref` to `remote` as `remote_ref`.
     By default, `remote_ref` will be the same as `target_ref`.
+
+    Args:
+        remote: git remote to push to (default 'origin')
+        target_ref: ref to push (default 'refs/lethe/LATEST')
+        remote_ref: ref to push to (default same as `target_ref`)
+        cwd: Repository directory. Default is current working directory.
+
+    Returns:
+        git command stdout
     """
     if remote_ref is None:
         remote_ref = target_ref
@@ -125,29 +143,52 @@ def push_ref(remote: str = 'origin',
 
 
 def fetch_ref(remote: str = 'origin',
-              remote_ref: str = 'refs/lethe/HEAD',
+              remote_ref: str = 'refs/lethe/LATEST',
               target_ref: Optional[str] = None,
+              *,
               cwd: Optional[str] = None,
               ) -> str:
     """
     Fetch `remote_ref` from `remote` as `target_ref`.
     By default, `target_ref` will be the same as `remote_ref`.
+
+    Args:
+        remote: git remote to push to (default 'origin')
+        remote_ref: ref to fetch from (default 'refs/lethe/LATEST')
+        target_ref: ref to fetch to (default same as `remote_ref`)
+        cwd: Repository directory. Default is current working directory.
+
+    Returns:
+        git command stdout
     """
     if target_ref is None:
         target_ref = remote_ref
     return _run(['git', 'fetch', remote, remote_ref + ':' + target_ref], cwd=cwd)
 
 
-def deref_symref(ref: str, cwd: Optional[str] = None) -> str:
+def deref_symref(ref: str,
+                 *,
+                 cwd: Optional[str] = None,
+                 ) -> str:
     """
     Dereference a symbolic ref
     """
     return _run(['git', 'symbolic-ref', '--quiet', ref], cwd=cwd)
 
 
-def find_merge_base(commits: List[str], cwd: Optional[str] = None) -> str:
+def find_merge_base(commits: Sequence[str],
+                    *,
+                    cwd: Optional[str] = None,
+                    ) -> str:
     """
     Find the "best common ancestor" commit.
+
+    Args:
+        commits: Collection of commits to find the best common ancestor for
+        cwd: Repository directory. Default is current working directory.
+
+    Returns:
+        Hash of the best common ancestor commit
     """
     if len(commits) == 0:
         raise Exception('Called find_merge_base with no commits!')
@@ -159,7 +200,7 @@ def find_merge_base(commits: List[str], cwd: Optional[str] = None) -> str:
     return base
 
 
-def snap_tree(cwd: Optional[str] = None) -> str:
+def snap_tree(*, cwd: Optional[str] = None) -> str:
     """
     Create a new tree, consisting of all non-ignored files in the repository.
     Return the hash of the tree.
@@ -173,9 +214,10 @@ def snap_tree(cwd: Optional[str] = None) -> str:
     return tree
 
 
-def snap_ref(parent_refs: List[str],
+def snap_ref(parent_refs: Sequence[str],
-             target_refs: List[str],
+             target_refs: Sequence[str],
              message: Optional[str] = None,
+             *,
              cwd: Optional[str] = None,
              ) -> str:
     """
@@ -185,16 +227,7 @@ def snap_ref(parent_refs: List[str],
     parent_commits = [c for c in [get_commit(p, cwd=cwd) for p in parent_refs] if c]
     old_commits = [get_commit(t, cwd=cwd) for t in target_refs]
 
-    extant_old_commits = list(set(c for c in old_commits if c))
+    commit = commit_tree(new_tree, set(parent_commits), message, cwd=cwd)
-    new_parents = list(set(p for p in parent_commits
-                           if p != find_merge_base([p] + extant_old_commits, cwd=cwd)))
-
-#    if not new_parents:
-#        tree_unchanged = all(new_tree == get_tree(c, cwd=cwd) for c in old_commits)
-#        if tree_unchanged:
-#            return new_tree
-
-    commit = commit_tree(new_tree, extant_old_commits + new_parents, message, cwd=cwd)
 
     for target_ref, old_commit in zip(target_refs, old_commits):
         # update ref to point to commit, or create new ref
@@ -204,41 +237,58 @@ def snap_ref(parent_refs: List[str],
     return commit
 
 
-def snap(parent_refs: Optional[List[str]] = None,
+def snap(parent_refs: Optional[Sequence[str]] = None,
-         target_refs: Optional[List[str]] = None,
+         target_refs: Optional[Sequence[str]] = None,
          message: Optional[str] = None,
+         *,
          cwd: Optional[str] = None,
          ) -> str:
     """
-    Create a new commit of all non-ignored files in the repository.
+    Create a new commit, containing all non-ignored files.
 
-    `parent_refs` default to `['HEAD']`.
+    Args:
-    If there are any symbolic refs in `parent_refs`, the refs
+        parent_refs: Refs in this list are set as parents of the new commit.
-        they point to are added to <parent_refs>.
+            If any symbolic refs are included, the underlying refs they point
+            to are also added to `parent_refs`. Defaults to `['HEAD']`.
+        target_refs: Refs in this list will be updated to point to the new commit.
+            Default is
+                - 'refs/lethe/LATEST', and
+                - 'refs/lethe/path/to/ref/LATEST' and
+                  'refs/lethe/path/to/ref/snap_2020-12-20_18.21.14.281876'
+                  for each parent_ref of the form 'refs/path/to/ref'.
+                  Symbolic refs are dereferenced, so a parent_ref of 'master'
+                  will results in the creation/overwrite of
+                  'refs/lethe/heads/master/LATEST'
+            Note that 'refs/lethe/LATEST' must be specified explicitly if the default
+            is overridden
+        message: The commit message. Default is a simple note containing the current
+            date/time.
+        cwd: Path to the repository. Default is the current working directory.
 
-    All commits pointed to by existing `parent_refs` and `target_refs`,
+    Returns:
-        become parents of the newly created commit.
+        The hash for the new commit.
-
-    `target_refs` are created/updated to point the commit.
-        Default is
-            'refs/lethe/head_name' for each parent ref of the form
-                'refs/heads/head_name', and
-            'refs/lethe/path/to/ref' for each parent ref of the form
-                'refs/path/to/ref'.
-    `message` is used as the commit message.
     """
     if parent_refs is None:
         parent_refs = ['HEAD']
+    else:
+        parent_refs = list(parent_refs)
 
     parent_refs += [r for r in [deref_symref(s, cwd=cwd) for s in parent_refs] if r]
 
-    if target_refs is None:
+    date_str = str(datetime.datetime.now())
-        target_refs = []
+    date_ref = date_str.replace(' ', '_').replace(':', '.')
-        for p in parent_refs:
-            if p.startswith('refs/'):
-                p = p[len('refs/'):]
 
-            target_refs.append('refs/lethe/' + p)
+    if target_refs is None:
+        target_refs = ['refs/lethe/LATEST']
+        for pp in parent_refs:
+            if not pp.startswith('refs/'):
+                continue
+            target_base = 'refs/lethe/' + pp[len('refs/'):]
+            target_refs += [target_base + '/LATEST',
+                            target_base + '/' + date_ref]
+
+    if message is None:
+        message = 'snapshot ' + date_str
 
     commit = snap_ref(parent_refs, target_refs, message=message, cwd=cwd)
     return commit