Implement log

how_to/Change_17.md

@@ -0,0 +1,12 @@
+- log: Implement
+
+`log` will walk the list of commits and print them.
+
+We will start by implementing `get_commit()` that will parse a commit object by
+OID.
+
+Then in the CLI module we will start from the HEAD commit and walk its parents
+until we reach a commit without a parent.
+
+The result is that the entire commit history is printed to the screen once we
+run `ugit log`.

ugit/base.py

@@ -1,6 +1,10 @@
-from pathlib import Path, PurePath
+import itertools
+import operator
 import os
 
+from collections import namedtuple
+from pathlib import Path, PurePath
+
 from . import data
 
 
@@ -93,5 +97,26 @@ def commit(message):
     return oid
 
 
+Commit = namedtuple("Commit", ["tree", "parent", "message"])
+
+
+def get_commit(oid):
+    parent = None
+
+    commit = data.get_object(oid, "commit").decode()
+    lines = iter(commit.splitlines())
+    for line in itertools.takewhile(operator.truth, lines):
+        key, value = line.split(" ", 1)
+        if key == "tree":
+            tree = value
+        elif key == "parent":
+            parent = value
+        else:
+            assert False, f"Unknown field {key}"
+
+    message = "\n".join(lines)
+    return Commit(tree=tree, parent=parent, message=message)
+
+
 def is_ignored(path):
     return ".ugit" in path.split("/")

ugit/cli.py

@@ -1,7 +1,8 @@
-from pathlib import Path
-
 import argparse
 import sys
+import textwrap
+
+from pathlib import Path
 
 from . import base
 from . import data
@@ -40,6 +41,9 @@ def parse_args():
     commit_parser.set_defaults(func=commit)
     commit_parser.add_argument("-m", "--message", required=True)
 
+    log_parser = commands.add_parser("log")
+    log_parser.set_defaults(func=log)
+
     return parser.parse_args()
 
 
@@ -68,3 +72,15 @@ def read_tree(args):
 
 def commit(args):
     print(base.commit(args.message))
+
+
+def log(args):
+    oid = data.get_HEAD()
+    while oid:
+        commit = base.get_commit(oid)
+
+        print(f"commit {oid}\n")
+        print(textwrap.indent(commit.message, "    "))
+        print("")
+
+        oid = commit.parent