From 52b1d99d0d65cfea9622b23c0d547971eb12e2c4 Mon Sep 17 00:00:00 2001
From: Joe Mou <joe@mou.fo>
Date: Fri, 19 Apr 2019 01:28:00 -0400
Subject: [PATCH] checkout: checkout-index, improve rev-parse, symbolic-ref

---
 checkout       | 15 +++++++++++++++
 checkout-index | 33 +++++++++++++++++++++++++++++++++
 get-sha1-basic | 11 +++++++++++
 rev-parse      | 45 ++++++++++++++++++++++++++++++++++++---------
 symbolic-ref   | 17 +++++++++++------
 5 files changed, 106 insertions(+), 15 deletions(-)
 create mode 100755 checkout
 create mode 100755 checkout-index
 create mode 100755 get-sha1-basic

diff --git a/checkout b/checkout
new file mode 100755
index 0000000..cfe6f3c
--- /dev/null
+++ b/checkout
@@ -0,0 +1,15 @@
+#!/bin/bash -e
+
+if [[ $1 == -b ]]; then
+    ./branch $2
+    shift
+fi
+revision=$1
+tree=$(./rev-parse $revision^{tree})
+./read-tree $tree
+./checkout-index
+if [[ -f .zit/refs/heads/$revision ]]; then
+    ./symbolic-ref HEAD refs/heads/$revision
+else
+    echo "You are in 'detached HEAD' state." >&2
+fi
diff --git a/checkout-index b/checkout-index
new file mode 100755
index 0000000..edd4fb6
--- /dev/null
+++ b/checkout-index
@@ -0,0 +1,33 @@
+#!/usr/bin/python
+
+import os
+import struct
+import subprocess
+
+# TODO dedup w/ write-tree
+index = open('.zit/index').read()
+assert index[0:4] == 'DIRC'
+assert struct.unpack('>I', index[4:8]) == (2,)
+num_entries, = struct.unpack('>I', index[8:12])
+entries = []
+i = 12
+for _ in range(num_entries):
+    # ignore inode heuristics, file/symlink bit, permissions
+    i += 40
+    sha1 = index[i:i+20].encode('hex')
+    # just use NUL-terminated?
+    name_length = struct.unpack('>H', index[i+20:i+22])[0] & 0xfff
+    name = index[i+22:i+22+name_length]
+    i += (22 + name_length + 8) / 8 * 8
+    entries.append((name, sha1))
+
+# entry.c:checkout_entry
+for filename, sha1 in entries:
+    assert not filename.startswith('/')
+    assert '..' not in filename
+    # TODO unlink directories?
+    if os.path.exists(filename):
+        os.unlink(filename)
+    subprocess.check_call(['mkdir', '-p', './' + os.path.dirname(filename)])
+    # TODO git 1.0 doesn't seem to unlink deleted files
+    subprocess.check_call(['./cat-file', 'blob', sha1], stdout=open(filename, 'w'))
diff --git a/get-sha1-basic b/get-sha1-basic
new file mode 100755
index 0000000..901c84d
--- /dev/null
+++ b/get-sha1-basic
@@ -0,0 +1,11 @@
+#!/bin/bash -e
+
+# sha1_name.c:get_sha1_basic
+if [[ ${#1} -eq 40 ]]; then
+    echo $1
+else
+    cat .zit/$(./symbolic-ref $1) 2> /dev/null || \
+        cat .zit/$(./symbolic-ref refs/$1) 2> /dev/null || \
+        cat .zit/$(./symbolic-ref refs/tags/$1) 2> /dev/null || \
+        cat .zit/$(./symbolic-ref refs/heads/$1)
+fi
diff --git a/rev-parse b/rev-parse
index 11ff61f..3f72497 100755
--- a/rev-parse
+++ b/rev-parse
@@ -1,13 +1,40 @@
-#!/bin/bash -e
+#!/usr/bin/python
 # only implements --verify
 
+import subprocess
+import sys
+
 # sha1_name.c:get_sha1
+def get_sha1(name):
+    # TODO ^ and ~?
+    # TODO specialize for tree?
+    if '^' in name:
+        name, type = name.rsplit('^', 1)
+        assert type[0] == '{' and type[-1] == '}'
+        type = type[1:-1]
+        while True:
+            sha1 = get_sha1(name)
+
+            # TODO dedup w/ cat-file
+            import zlib
+            # sha1_file.c:sha1_file_name
+            filename = '.zit/objects/{}/{}'.format(sha1[:2], sha1[2:])
+            decompressed = zlib.decompress(open(filename).read())
+            header, contents = decompressed.split('\0', 1)
+            actual_type, length = header.split(' ')
+
+            if actual_type == type:
+                return sha1
+            elif actual_type == 'commit':
+                assert int(length) == len(contents)
+                tree = next(line for line in contents.split('\n')
+                            if line.startswith('tree '))
+                name = tree.split(' ')[1]
+            # TODO deref tags?
+            else:
+                raise Exception('wrong type')
+    else:
+        return subprocess.check_output(['./get-sha1-basic', name])[:-1]
 
-if [[ ${#1} -eq 40 ]]; then
-    echo $1
-else
-    cat .zit/$(./symbolic-ref $1) 2> /dev/null || \
-        cat .zit/$(./symbolic-ref refs/$1) 2> /dev/null || \
-        cat .zit/$(./symbolic-ref refs/tags/$1) 2> /dev/null || \
-        cat .zit/$(./symbolic-ref refs/heads/$1)
-fi
+_, name = sys.argv
+print get_sha1(name)
diff --git a/symbolic-ref b/symbolic-ref
index 9a72285..907e613 100755
--- a/symbolic-ref
+++ b/symbolic-ref
@@ -1,8 +1,13 @@
 #!/bin/bash -e
 
-# refs.c:resolve_ref
-path=.zit/$1
-while grep -q '^ref: ' $path 2> /dev/null; do
-    path=.zit/$(cut -d' ' -f2 < $path)
-done
-echo $path | cut -d/ -f2-
+if [[ $# == 2 ]]; then
+    # refs.c:create_symref
+    echo "ref: $2" > .zit/$1
+elif [[ $# == 1 ]]; then
+    # refs.c:resolve_ref
+    path=.zit/$1
+    while grep -q '^ref: ' $path 2> /dev/null; do
+        path=.zit/$(cut -d' ' -f2 < $path)
+    done
+    echo $path | cut -d/ -f2-
+fi