commit 0dd22bd7bc35f530c5b3b757e6db0b2077716091
Author: Kristóf Tóth <mrtoth@strongds.hu>
Date:   Thu Feb 10 00:43:17 2022 +0100

    Implement OpenSSH style identicon calculation

diff --git a/identicon/__init__.py b/identicon/__init__.py
new file mode 100644
index 0000000..84d3068
--- /dev/null
+++ b/identicon/__init__.py
@@ -0,0 +1 @@
+from .identicon import Identicon
diff --git a/identicon/identicon.py b/identicon/identicon.py
new file mode 100644
index 0000000..bc785e0
--- /dev/null
+++ b/identicon/identicon.py
@@ -0,0 +1,89 @@
+from dataclasses import dataclass
+from copy import deepcopy
+
+
+@dataclass
+class Coordinate:
+    x: int
+    y: int
+
+    def __add__(self, other):
+        return self.__class__(
+            self.x+other.x,
+            self.y+other.y
+        )
+
+
+class Identicon:
+    WIDTH = 17
+    HEIGHT = 9
+    SYMBOLS = ' .o+=*BOX@%&#/^'
+    START_SYMBOL = 'S'
+    END_SYMBOL = 'E'
+    BISHOP_START = Coordinate(8, 4)
+
+    MOVES = {
+        0: Coordinate(-1, -1),  # 00 ↖
+        1: Coordinate( 1, -1),  # 01 ↗
+        2: Coordinate(-1,  1),  # 10 ↙
+        3: Coordinate( 1,  1),  # 11 ↘
+    }
+
+    def __init__(self, data):
+        self._data = data
+        self._grid = [[0] * self.WIDTH for _ in range(self.HEIGHT)]
+        self._bishop_position = deepcopy(self.BISHOP_START)
+        self._end_position = None
+
+    def calculate(self):
+        for command in self._get_commands():
+            self._execute(command)
+        self._end_position = self._bishop_position
+
+    def _get_commands(self):
+        commands = []
+        for octet in self._data:
+            commands.extend([
+                octet        & 0b11,  #  00   00   00  [00]
+                (octet >> 2) & 0b11,  #  00   00  [00]  00
+                (octet >> 4) & 0b11,  #  00  [00]  00   00
+                (octet >> 6) & 0b11,  # [00]  00   00   00
+            ])
+        return commands
+
+    def _execute(self, command):
+        move = self.MOVES[command]
+        self._bishop_position = self._ensure_within_grid_borders(self._bishop_position + move)
+        self._increment_current_position()
+
+    def _ensure_within_grid_borders(self, coordinate: Coordinate):
+        coordinate.x = max(0, min(self.WIDTH-1, coordinate.x))
+        coordinate.y = max(0, min(self.HEIGHT-1, coordinate.y))
+        return coordinate
+
+    def _increment_current_position(self):
+        self._grid[self._bishop_position.y][self._bishop_position.x] += 1
+
+    def __str__(self):
+        icon = self._header+'\n'
+        for y, row in enumerate(self._grid):
+            icon += '|'
+            for x, cell in enumerate(row):
+                icon += self._determine_symbol(Coordinate(x, y), cell)
+            icon += '|\n'
+        icon += self._header
+
+        return icon
+
+    @property
+    def _header(self):
+        return f'+{self.WIDTH*"-"}+'
+
+    def _determine_symbol(self, coordinate, cell):
+        symbol = self.SYMBOLS[min(cell, len(self.SYMBOLS)-1)]
+        if coordinate == self.BISHOP_START:
+            symbol = self.START_SYMBOL
+        elif coordinate == self._end_position:
+            symbol = self.END_SYMBOL
+
+        return symbol
diff --git a/identicon/test_identicon.py b/identicon/test_identicon.py
new file mode 100644
index 0000000..7165348
--- /dev/null
+++ b/identicon/test_identicon.py
@@ -0,0 +1,89 @@
+from base64 import b64decode
+from dataclasses import dataclass
+from textwrap import dedent
+
+import pytest
+
+from .identicon import Identicon
+
+
+@dataclass
+class ReferenceIcon:
+    fingerprint: bytes
+    icon: str
+
+
+REFERENCE_ICONS = [
+    ReferenceIcon(
+        bytearray.fromhex(''.join('b7:a3:e2:ce:09:06:ad:39:c8:1d:ad:b5:95:48:8f:99'.split(':'))),
+        dedent('''\
+            +-----------------+
+            |                 |
+            |                 |
+            |     .           |
+            |   .o * .        |
+            |  ...E +S .      |
+            |...++ o  . .     |
+            |..+oo.    o      |
+            |   o o.. . .     |
+            |     o=..        |
+            +-----------------+'''
+        )
+    ),
+    ReferenceIcon(
+        b64decode('sX58LC41tVlsctG1+H5PrkbMDfG374yghEg96KlnFZA=='),
+        dedent('''\
+            +-----------------+
+            |       .       .o|
+            |      E       + o|
+            |       ..    o = |
+            |       o.o  o B o|
+            |      o S. . X +o|
+            |     o +.+o.o =..|
+            |      +.o.=.+. .+|
+            |     .o .+ + ..=+|
+            |    .o   .o  .oo=|
+            +-----------------+'''
+        )
+    ),
+    ReferenceIcon(
+        bytearray.fromhex(''.join('9b:cf:42:fd:25:ff:ce:83:e9:e0:f1:d4:10:c3:ae:a8'.split(':'))),
+        dedent('''\
+            +-----------------+
+            |                 |
+            |            .    |
+            |             +   |
+            |            . o  |
+            |        S.   o   |
+            |        .oo o +  |
+            |       .o. = =o. |
+            |        oo. *o.o |
+            |       E .o..o o=|
+            +-----------------+'''
+        )
+    ),
+    ReferenceIcon(
+        b64decode('5/WozN6loc0G8DxxrJhV8+aG/6Dvz1/gTBVipWU9nb0='),
+            dedent('''\
+            +-----------------+
+            |             o.==|
+            |            + =o=|
+            |           o +  +|
+            |        . o o oE |
+            |        SB.+.+o  |
+            |        oo*..*o. |
+            |          .ooo* .|
+            |         o *.=.o.|
+            |         .*.*ooo*|
+            +-----------------+'''
+        )
+    )
+]
+
+
+@pytest.mark.parametrize("reference", REFERENCE_ICONS)
+def test_identicon(reference):
+    icon = Identicon(reference.fingerprint)
+    icon.calculate()
+
+    assert str(icon) == reference.icon