1 files changed, 98 insertions, 2 deletions
diff --git a/lib/sql.py b/lib/sql.py
index ae7c4ba..0bd1e31 100644
--- a/lib/sql.py
+++ b/lib/sql.py
@@ -23,6 +23,8 @@
 # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 # License for more details.
 
+import re
+import collections
 from psycopg2 import extensions as ext
 
 
@@ -187,8 +189,102 @@ class Placeholder(Composible):
             return "%s"
 
 
-def compose(sql, args=()):
-    raise NotImplementedError
+re_compose = re.compile("""
+    %                           # percent sign
+    (?:
+        ([%s])                  # either % or s
+        | \( ([^\)]+) \) s      # or a (named)s placeholder (named captured)
+    )
+    """, re.VERBOSE)
+
+
+def compose(sql, args=None):
+    phs = list(re_compose.finditer(sql))
+
+    # check placeholders consistent
+    counts = {'%': 0, 's': 0, None: 0}
+    for ph in phs:
+        counts[ph.group(1)] += 1
+
+    npos = counts['s']
+    nnamed = counts[None]
+
+    if npos and nnamed:
+        raise ValueError(
+            "the sql string contains both named and positional placeholders")
+
+    elif npos:
+        if not isinstance(args, collections.Sequence):
+            raise TypeError(
+                "the sql string expects values in a sequence, got %s instead"
+                % type(args).__name__)
+
+        if len(args) != npos:
+            raise ValueError(
+                "the sql string expects %s values, got %s" % (npos, len(args)))
+
+        return _compose_seq(sql, phs, args)
+
+    elif nnamed:
+        if not isinstance(args, collections.Mapping):
+            raise TypeError(
+                "the sql string expects values in a mapping, got %s instead"
+                % type(args))
+
+        return _compose_map(sql, phs, args)
+
+    else:
+        if not isinstance(args, collections.Sequence) and args:
+            raise TypeError(
+                "the sql string expects no value, got %s instead" % len(args))
+        # If args are a mapping, no placeholder is an acceptable case
+
+        # Convert %% into %
+        return _compose_seq(sql, phs, ())
+
+
+def _compose_seq(sql, phs, args):
+    rv = []
+    j = 0
+    for i, ph in enumerate(phs):
+        if i:
+            rv.append(SQL(sql[phs[i - 1].end():ph.start()]))
+        else:
+            rv.append(SQL(sql[0:ph.start()]))
+
+        if ph.group(1) == 's':
+            rv.append(args[j])
+            j += 1
+        else:
+            rv.append(SQL('%'))
+
+    if phs:
+        rv.append(SQL(sql[phs[-1].end():]))
+    else:
+        rv.append(sql)
+
+    return Composed(rv)
+
+
+def _compose_map(sql, phs, args):
+    rv = []
+    for i, ph in enumerate(phs):
+        if i:
+            rv.append(SQL(sql[phs[i - 1].end():ph.start()]))
+        else:
+            rv.append(SQL(sql[0:ph.start()]))
+
+        if ph.group(2):
+            rv.append(args[ph.group(2)])
+        else:
+            rv.append(SQL('%'))
+
+    if phs:
+        rv.append(SQL(sql[phs[-1].end():]))
+    else:
+        rv.append(sql)
+
+    return Composed(rv)
 
 
 # Alias