From 13b5338ae40ed82860e457816300340edbabba00 Mon Sep 17 00:00:00 2001
From: Stephen Bailey <stephen.code@gmail.com>
Date: Fri, 12 Feb 2021 11:40:13 -0800
Subject: [PATCH] add desiutil.depend.mergedep + tests

---
 py/desiutil/depend.py           | 45 +++++++++++++++++++++++++++++++++
 py/desiutil/test/test_depend.py | 43 ++++++++++++++++++++++++++++++-
 2 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/py/desiutil/depend.py b/py/desiutil/depend.py
index 94f2a25e..4d91b867 100644
--- a/py/desiutil/depend.py
+++ b/py/desiutil/depend.py
@@ -174,6 +174,51 @@ def iterdep(header):
             return
     return
 
+def mergedep(srchdr, dsthdr, conflict='src'):
+    '''Merge dependencies from srchdr into dsthdr
+
+    Parameters
+    ----------
+    srchdr : dict-like
+        source dict-like object, *e.g.* :class:`astropy.io.fits.Header`,
+        with dependency keywords DEPNAMnn, DEPVERnn
+    dsthdr : dict-like
+        destination dict-like object
+    conflict : str, optional
+        'src' or 'dst' or 'exception'; see notes
+
+    Notes
+    -----
+    Dependencies in srchdr are added to dsthdr, modifying it in-place,
+    adjusting DEPNAMnn/DEPVERnn numbering as needed.  If the same dependency
+    appears in both headers with different versions, ``conflict``
+    controls the behavior:
+
+      * if 'src', the srchdr value replaces the dsthdr value
+      * if 'dst', the dsthdr value is retained unchanged
+      * if 'exception', raise a ValueError exception
+
+    Raises
+    ------
+    ValueError
+        If `conflict == 'exception'` and the same dependency name appears
+        in both headers with different values; or if `conflict` isn't one
+        of 'src', 'dst', or 'exception'.
+    '''
+    if not conflict in ('src', 'dst', 'exception'):
+        raise ValueError(f"conflict ({conflict}) should be 'src', 'dst', or 'exception'")
+
+    for name, version in iterdep(srchdr):
+        if hasdep(dsthdr, name) and getdep(dsthdr, name) != version:
+            if conflict == 'src':
+                setdep(dsthdr, name, version)
+            elif conflict == 'dst':
+                pass
+            else:
+                v2 = getdep(dsthdr, name)
+                raise ValueError(f'Version conflict for {name}: {version} != {v2}')
+        else:
+            setdep(dsthdr, name, version)
 
 def add_dependencies(header, module_names=None, long_python=False):
     '''Adds ``DEPNAMnn``, ``DEPVERnn`` keywords to header for imported modules.
diff --git a/py/desiutil/test/test_depend.py b/py/desiutil/test/test_depend.py
index 86693ddb..362ba232 100644
--- a/py/desiutil/test/test_depend.py
+++ b/py/desiutil/test/test_depend.py
@@ -5,7 +5,7 @@
 import unittest
 import sys
 from collections import OrderedDict
-from ..depend import (setdep, getdep, hasdep, iterdep, Dependencies,
+from ..depend import (setdep, getdep, hasdep, iterdep, mergedep, Dependencies,
                       add_dependencies)
 from .. import __version__ as desiutil_version
 
@@ -79,6 +79,47 @@ def test_hasdep(self):
         self.assertTrue(hasdep(hdr, 'test010'))
         self.assertFalse(hasdep(hdr, 'test020'))
 
+    def test_mergedep(self):
+        """Test merging dependencies from one header to another
+        """
+        src = dict(
+            DEPNAM00='blat', DEPVER00='1.0',
+            DEPNAM01='foo', DEPVER01='2.0',
+        )
+        dst = dict(
+            DEPNAM00='biz', DEPVER00='3.0',
+            DEPNAM01='bat', DEPVER01='4.0',
+        )
+        #- dependencies from src should be added to dst
+        mergedep(src, dst)
+        self.assertEqual(getdep(src, 'blat'), getdep(dst, 'blat'))
+        self.assertEqual(getdep(src, 'foo'), getdep(dst, 'foo'))
+
+        #- if conflict='src', a src dependency can replace a dst dependency
+        dst = dict(
+            DEPNAM00='biz', DEPVER00='3.0',
+            DEPNAM01='blat', DEPVER01='4.0',
+        )
+        mergedep(src, dst, conflict='src')
+        self.assertEqual(getdep(src, 'blat'), getdep(dst, 'blat'))
+        self.assertEqual(getdep(src, 'foo'), getdep(dst, 'foo'))
+
+        #- if conflict='dst', the dst dependency is kept even if in src
+        dst = dict(
+            DEPNAM00='biz', DEPVER00='3.0',
+            DEPNAM01='blat', DEPVER01='4.0',
+        )
+        mergedep(src, dst, conflict='dst')
+        self.assertEqual(getdep(dst, 'blat'), '4.0')  #- not '1.0'
+
+        #- if conflict='exception', should raise a ValueError
+        dst = dict(
+            DEPNAM00='biz', DEPVER00='3.0',
+            DEPNAM01='blat', DEPVER01='4.0',
+        )
+        with self.assertRaises(ValueError):
+            mergedep(src, dst, conflict='exception')
+
     @unittest.skipUnless(test_fits_header, 'requires astropy.io.fits')
     def test_fits_header(self):
         """Test dependency functions with an actual FITS header.