diff --git a/server/forge.py b/server/forge.py
new file mode 100644
index 0000000..7aba484
--- /dev/null
+++ b/server/forge.py
@@ -0,0 +1,53 @@
+from datetime import datetime, timedelta
+
+
+def get_timefile_exact(time):
+    '''
+    time is of type `datetime`; it is not "rounded" to match the real file;
+    that work is done in get_timefile(time)
+    '''
+    return time.strftime('%Y-%m/%d/rec-%Y-%m-%d-%H-%M-%S-ror.mp3')
+
+
+def round_timefile(exact):
+    '''
+    This will round the datetime, so to match the file organization structure
+    '''
+    return datetime(exact.year, exact.month, exact.day, exact.hour)
+
+
+def get_timefile(exact):
+    return get_timefile_exact(round_timefile(exact))
+
+
+def get_files_and_intervals(start, end, rounder=round_timefile):
+    '''
+    both arguments are datetime objects
+    returns an iterator whose elements are (filename, start_cut, end_cut)
+    Cuts are expressed in seconds
+    '''
+    print '%s < %s' % (start, end)
+    if end <= start:
+        raise ValueError("end < start!")
+
+    while start <= end:
+        begin = rounder(start)
+        start_cut = (start - begin).total_seconds()
+        if end < begin + timedelta(seconds=3599):
+            end_cut = (begin + timedelta(seconds=3599) - end).total_seconds()
+        else:
+            end_cut = 0
+        yield (begin, start_cut, end_cut)
+        start = begin + timedelta(hours=1)
+
+
+def mp3_join(named_intervals):
+    '''
+    Note that these are NOT the intervals returned by get_files_and_intervals,
+    as they do not supply a filename, but only a datetime.
+    What we want in input is basically the same thing, but with get_timefile()
+    applied on the first element
+    '''
+    for (filename, start_cut, end_cut) in named_intervals:
+        pass
+    raise NotImplementedError()
diff --git a/server/test_forge.py b/server/test_forge.py
new file mode 100644
index 0000000..e843ae4
--- /dev/null
+++ b/server/test_forge.py
@@ -0,0 +1,154 @@
+from datetime import datetime, timedelta
+
+from nose.tools import raises, assert_items_equal, eq_
+
+from forge import get_files_and_intervals, get_timefile_exact, round_timefile,\
+    get_timefile
+
+eight = datetime(2014, 5, 30, 20)
+nine = datetime(2014, 5, 30, 21)
+ten = datetime(2014, 5, 30, 22)
+
+
+def minutes(n):
+    return timedelta(minutes=n)
+
+
+def seconds(n):
+    return timedelta(seconds=n)
+
+## timefile
+
+
+def test_timefile_exact():
+    eq_(get_timefile_exact(eight),
+        '2014-05/30/rec-2014-05-30-20-00-00-ror.mp3')
+
+## Rounding
+
+
+def test_rounding_similarity():
+    eq_(round_timefile(eight), round_timefile(eight+minutes(20)))
+    assert round_timefile(eight) != round_timefile(nine)
+
+
+def test_rounding_value():
+    eq_(round_timefile(eight), eight)
+    eq_(round_timefile(eight + minutes(20)), eight)
+
+
+## Rounding + timefile
+
+
+def test_timefile_alreadyround():
+    eq_(get_timefile(eight),
+        '2014-05/30/rec-2014-05-30-20-00-00-ror.mp3')
+
+
+def test_timefile_toround():
+    eq_(get_timefile(eight + minutes(20)),
+        '2014-05/30/rec-2014-05-30-20-00-00-ror.mp3')
+
+## Intervals
+
+
+@raises(ValueError)
+def test_intervals_same():
+    tuple(get_files_and_intervals(eight, eight))
+
+
+@raises(ValueError)
+def test_intervals_before():
+    tuple(get_files_and_intervals(nine, eight))
+
+
+def test_intervals_full_1():
+    res = list(get_files_and_intervals(eight, nine-seconds(1)))
+    eq_(len(res), 1)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+
+
+def test_intervals_partial_1():
+    res = list(get_files_and_intervals(eight, nine-minutes(10)))
+    eq_(len(res), 1)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 10*60 - 1)
+
+
+def test_intervals_exact_2():
+    res = list(get_files_and_intervals(eight, nine))
+    eq_(len(res), 2)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 3599)
+
+
+def test_intervals_partial_2():
+    res = list(get_files_and_intervals(eight, nine + minutes(50)))
+    eq_(len(res), 2)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 599)
+
+
+def test_intervals_full_2():
+    res = list(get_files_and_intervals(eight,
+                                       nine + minutes(59) + seconds(59)))
+    eq_(len(res), 2)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 0)
+
+
+def test_intervals_exact_3():
+    res = list(get_files_and_intervals(eight, ten))
+    eq_(len(res), 3)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 0)
+    eq_(res[2][1], 0)
+    eq_(res[2][2], 3599)
+
+
+def test_intervals_partial_3():
+    res = list(get_files_and_intervals(eight, ten+minutes(50)))
+    eq_(len(res), 3)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 0)
+    eq_(res[2][1], 0)
+    eq_(res[2][2], 599)
+
+
+def test_intervals_full_3():
+    res = list(get_files_and_intervals(eight, ten+minutes(59) + seconds(59)))
+    eq_(len(res), 3)
+    eq_(res[0][1], 0)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 0)
+    eq_(res[2][1], 0)
+    eq_(res[2][2], 0)
+
+
+def test_intervals_middle_1():
+    res = list(get_files_and_intervals(eight + minutes(20),
+                                       nine - minutes(20)))
+    eq_(len(res), 1)
+    eq_(res[0][1], 20*60)
+    eq_(res[0][2], 20*60-1)
+
+
+def test_intervals_left_2():
+    res = list(get_files_and_intervals(eight+minutes(30), nine))
+    eq_(len(res), 2)
+    eq_(res[0][1], 30*60)
+    eq_(res[0][2], 0)
+    eq_(res[1][1], 0)
+    eq_(res[1][2], 3599)