oc-mail: Manage multiple CN restriction

By ignoring <, =< and = operators and simplifying the following
request:

    MODSEQ >= x || MODSEQ >= y || MODSEQ >= z  --> MODSEQ >= min(x, y, z)

This hack will reduce the number of current retrieved UID keys
from the IMAP server. Current status is to retrieve everything when
the multiple CN restriction is sent as the required restriction
is too complex and it is not defined by the IMAP spec.

The proper implementation for:

    CN > x_1 & CN < x_2 | CN > y_1 & CN < y_2 | CN > z_1

It will be something like this:

    set(MODSEQ >= x_1 + 1) - set(MODSEQ >= x_2)
    U
    set(MODSEQ >= y_1 + 1) - set(MODSEQ >= y_2)
    U
    set(MODSEQ >= z_1)

Assuming x_1 <= x_2 <= y_1 <= y_2 <= z_1.

OpenChange/MAPIStoreMailFolder.m

@@ -74,6 +74,7 @@ static Class SOGoMailFolderK, MAPIStoreMailFolderK, MAPIStoreOutboxFolderK;
 #include <util/attr.h>
 #include <libmapi/libmapi.h>
 #include <libmapiproxy.h>
+#include <limits.h>
 #include <mapistore/mapistore.h>
 #include <mapistore/mapistore_errors.h>
 
@@ -257,6 +258,67 @@ static Class SOGoMailFolderK, MAPIStoreMailFolderK, MAPIStoreOutboxFolderK;
   return MAPISTORE_SUCCESS;
 }
 
+- (EOQualifier *) simplifyQualifier: (EOQualifier *) qualifier
+{
+  /* Hack: Reduce the number of MODSEQ constraints to a single one as
+     we assume the difference among MODSEQs will be small enough to
+     return a small number of UIDs.
+
+     This is the only case we do simplify:
+     MODSEQ >= x | MODSEQ >= y | MODSEQ >= z => MODSEQ >= min(x,y,z)
+  */
+  if (qualifier && [qualifier isKindOfClass: [EOOrQualifier class]])
+    {
+      EOQualifier *simplifiedQualifier;
+      NSArray  *quals;
+      NSNumber *minModseq;
+      NSUInteger i, count;
+
+      quals = [(EOOrQualifier *)qualifier qualifiers];
+      count = [quals count];
+      if (count < 2)
+        return qualifier;
+
+      minModseq = [NSNumber numberWithUnsignedLongLong: ULLONG_MAX];
+
+      for (i = 0; i < count; i++)
+        {
+          EOQualifier *subQualifier;
+
+          subQualifier = [quals objectAtIndex: i];
+          if ([subQualifier isKindOfClass: [EOAndQualifier class]]
+              && [[(EOAndQualifier *)subQualifier qualifiers] count] == 1)
+            subQualifier = [[(EOAndQualifier *)subQualifier qualifiers] objectAtIndex: 0];
+
+          if ([subQualifier isKindOfClass: [EOKeyValueQualifier class]]
+              && [[(EOKeyValueQualifier *)subQualifier key] isEqualToString: @"MODSEQ"])
+            {
+              NSNumber *value;
+
+              value = (NSNumber *)[(EOKeyValueQualifier *)subQualifier value];
+              if ([minModseq compare: value] == NSOrderedDescending
+                  && [value unsignedLongLongValue] > 0)
+                minModseq = (NSNumber *)[(EOKeyValueQualifier *)subQualifier value];
+
+            }
+          else
+            return qualifier;
+        }
+
+      if ([minModseq unsignedLongLongValue] > 0 && [minModseq unsignedLongLongValue] < ULLONG_MAX)
+        {
+          simplifiedQualifier = [[EOKeyValueQualifier alloc]
+                                       initWithKey: @"MODSEQ"
+                                  operatorSelector: EOQualifierOperatorGreaterThanOrEqualTo
+                                             value: minModseq];
+          [simplifiedQualifier autorelease];
+          return simplifiedQualifier;
+        }
+    }
+
+  return qualifier;
+}
+
 - (EOQualifier *) nonDeletedQualifier
 {
   static EOQualifier *nonDeletedQualifier = nil;
@@ -281,7 +343,7 @@ static Class SOGoMailFolderK, MAPIStoreMailFolderK, MAPIStoreOutboxFolderK;
                           andSortOrderings: (NSArray *) sortOrderings
 {
   NSArray *uidKeys;
-  EOQualifier *fetchQualifier;
+  EOQualifier *fetchQualifier, *simplifiedQualifier;
 
   if ([self ensureFolderExists])
     {
@@ -290,9 +352,10 @@ static Class SOGoMailFolderK, MAPIStoreMailFolderK, MAPIStoreOutboxFolderK;
 
       if (qualifier)
         {
+          simplifiedQualifier = [self simplifyQualifier: qualifier];
           fetchQualifier
             = [[EOAndQualifier alloc] initWithQualifiers:
-                                        [self nonDeletedQualifier], qualifier,
+                                        [self nonDeletedQualifier], simplifiedQualifier,
                                       nil];
           [fetchQualifier autorelease];
         }