From e0be339280fb18230017dcb91d72a6a1e8538549 Mon Sep 17 00:00:00 2001
From: Ken Celenza <ken@celenza.org>
Date: Fri, 4 Aug 2023 19:13:40 -0400
Subject: [PATCH] Add int_to_asn function (#332)

* Add int_to_asn function

* add tests
---
 docs/user/include_jinja_list.md |  1 +
 netutils/asn.py                 | 28 ++++++++++++++++++++++++++++
 netutils/utils.py               |  1 +
 tests/unit/test_asn.py          | 32 ++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+)

diff --git a/docs/user/include_jinja_list.md b/docs/user/include_jinja_list.md
index 4be27d36..a2901448 100644
--- a/docs/user/include_jinja_list.md
+++ b/docs/user/include_jinja_list.md
@@ -1,6 +1,7 @@
 | Filter name | Function |
 | ---------- | ------ |
 | asn_to_int | netutils.asn.asn_to_int |
+| int_to_asn | netutils.asn.int_to_asn |
 | bits_to_name | netutils.bandwidth.bits_to_name |
 | bytes_to_name | netutils.bandwidth.bytes_to_name |
 | name_to_bits | netutils.bandwidth.name_to_bits |
diff --git a/netutils/asn.py b/netutils/asn.py
index 04323b4e..f3833908 100644
--- a/netutils/asn.py
+++ b/netutils/asn.py
@@ -24,3 +24,31 @@ def asn_to_int(asplain: str) -> int:
         asn = int(f"{int(asn_list[0]):016b}{int(asn_list[1]):016b}", 2)
         return asn
     return int(asplain)
+
+
+def int_to_asn(asn_int: int) -> str:
+    """Convert integer to standardized asplain notation for BGP ASN.
+
+    Args:
+        asn_int: Integer value of the BGP ASN.
+
+    Returns:
+        `asplain` notated BGP ASN as a string.
+
+    Examples:
+        >>> from netutils.asn import int_to_asn
+        >>> int_to_asn(65000)
+        '65000'
+        >>> int_to_asn(4259840111)
+        '65000.111'
+        >>>
+    """
+    if isinstance(asn_int, str):
+        asn_int = int(asn_int)
+    if asn_int > 2**32 - 1 or asn_int < 1:
+        raise ValueError(f"`{str(asn_int)}` is not within range of 1 - 2^32-1")
+    if asn_int >= 2**16:
+        asn1 = asn_int >> 16
+        asn2 = asn_int & ((1 << 16) - 1)
+        return f"{asn1}.{asn2}"
+    return str(asn_int)
diff --git a/netutils/utils.py b/netutils/utils.py
index 9580c278..9eefd912 100644
--- a/netutils/utils.py
+++ b/netutils/utils.py
@@ -5,6 +5,7 @@
 
 _JINJA2_FUNCTION_MAPPINGS = {
     "asn_to_int": "asn.asn_to_int",
+    "int_to_asn": "asn.int_to_asn",
     "name_to_bits": "bandwidth.name_to_bits",
     "name_to_bytes": "bandwidth.name_to_bytes",
     "bits_to_name": "bandwidth.bits_to_name",
diff --git a/tests/unit/test_asn.py b/tests/unit/test_asn.py
index 045110c2..b73a8aa8 100644
--- a/tests/unit/test_asn.py
+++ b/tests/unit/test_asn.py
@@ -12,7 +12,39 @@
     {"sent": {"asplain": "0.65526"}, "received": 65526},
 ]
 
+int_to_asn = [
+    {"sent": {"asn_int": 6500}, "received": "6500"},
+    {"sent": {"asn_int": 425985111}, "received": "6500.1111"},
+    {"sent": {"asn_int": 425984001}, "received": "6500.1"},
+    {"sent": {"asn_int": 65546}, "received": "1.10"},
+    {"sent": {"asn_int": 65526}, "received": "65526"},
+    {"sent": {"asn_int": "65526"}, "received": "65526"},
+    {"sent": {"asn_int": "65535"}, "received": "65535"},
+    {"sent": {"asn_int": "65536"}, "received": "1.0"},
+    {"sent": {"asn_int": "425985111"}, "received": "6500.1111"},
+    {"sent": {"asn_int": 4294967295}, "received": "65535.65535"},
+]
+
+int_to_asn_exceptions = [
+    {"asn_int": "one22"},
+    {"asn_int": "not_an_int"},
+    {"asn_int": "4294967296"},
+    {"asn_int": "0"},
+    {"asn_int": -1},
+]
+
 
 @pytest.mark.parametrize("data", asn_to_int)
 def test_asn_to_int(data):
     assert asn.asn_to_int(**data["sent"]) == data["received"]
+
+
+@pytest.mark.parametrize("data", int_to_asn)
+def test_int_to_asn(data):
+    assert asn.int_to_asn(**data["sent"]) == data["received"]
+
+
+@pytest.mark.parametrize("data", int_to_asn_exceptions)
+def test_int_to_asn_exceptions(data):
+    with pytest.raises(ValueError):
+        assert asn.int_to_asn(**data)