Merge pull request #421 from PureFunctor/caesar-command

Caesar cipher command

2 files changed, 103 insertions, 2 deletions

diff --git a/bot/exts/evergreen/fun.py b/bot/exts/evergreen/fun.py
index b0240c45..2f575c1c 100644
--- a/bot/exts/evergreen/fun.py
+++ b/bot/exts/evergreen/fun.py
@@ -1,14 +1,16 @@
 import functools
+import json
 import logging
 import random
-from typing import Callable, Tuple, Union
+from pathlib import Path
+from typing import Callable, Iterable, Tuple, Union
 
 from discord import Embed, Message
 from discord.ext import commands
 from discord.ext.commands import Bot, Cog, Context, MessageConverter
 
 from bot import utils
-from bot.constants import Emojis
+from bot.constants import Colours, Emojis
 
 log = logging.getLogger(__name__)
 
@@ -26,12 +28,35 @@ UWU_WORDS = {
 }
 
 
+def caesar_cipher(text: str, offset: int) -> Iterable[str]:
+    """
+    Implements a lazy Caesar Cipher algorithm.
+
+    Encrypts a `text` given a specific integer `offset`. The sign
+    of the `offset` dictates the direction in which it shifts to,
+    with a negative value shifting to the left, and a positive
+    value shifting to the right.
+    """
+    for char in text:
+        if not char.isascii() or not char.isalpha() or char.isspace():
+            yield char
+            continue
+
+        case_start = 65 if char.isupper() else 97
+        true_offset = (ord(char) - case_start + offset) % 26
+
+        yield chr(case_start + true_offset)
+
+
 class Fun(Cog):
     """A collection of general commands for fun."""
 
     def __init__(self, bot: Bot) -> None:
         self.bot = bot
 
+        with Path("bot/resources/evergreen/caesar_info.json").open("r", encoding="UTF-8") as f:
+            self._caesar_cipher_embed = json.load(f)
+
     @commands.command()
     async def roll(self, ctx: Context, num_rolls: int = 1) -> None:
         """Outputs a number of random dice emotes (up to 6)."""
@@ -79,6 +104,78 @@ class Fun(Cog):
             converted_text = f">>> {converted_text.lstrip('> ')}"
         await ctx.send(content=converted_text, embed=embed)
 
+    @commands.group(name="caesarcipher", aliases=("caesar", "cc",))
+    async def caesarcipher_group(self, ctx: Context) -> None:
+        """
+        Translates a message using the Caesar Cipher.
+
+        See `decrypt`, `encrypt`, and `info` subcommands.
+        """
+        if ctx.invoked_subcommand is None:
+            await ctx.invoke(self.bot.get_command("help"), "caesarcipher")
+
+    @caesarcipher_group.command(name="info")
+    async def caesarcipher_info(self, ctx: Context) -> None:
+        """Information about the Caesar Cipher."""
+        embed = Embed.from_dict(self._caesar_cipher_embed)
+        embed.colour = Colours.dark_green
+
+        await ctx.send(embed=embed)
+
+    @staticmethod
+    async def _caesar_cipher(ctx: Context, offset: int, msg: str, left_shift: bool = False) -> None:
+        """
+        Given a positive integer `offset`, translates and sends the given `msg`.
+
+        Performs a right shift by default unless `left_shift` is specified as `True`.
+
+        Also accepts a valid Discord Message ID or link.
+        """
+        if offset < 0:
+            await ctx.send(":no_entry: Cannot use a negative offset.")
+            return
+
+        if left_shift:
+            offset = -offset
+
+        def conversion_func(text: str) -> str:
+            """Encrypts the given string using the Caesar Cipher."""
+            return "".join(caesar_cipher(text, offset))
+
+        text, embed = await Fun._get_text_and_embed(ctx, msg)
+
+        if embed is not None:
+            embed = Fun._convert_embed(conversion_func, embed)
+
+        converted_text = conversion_func(text)
+
+        if converted_text:
+            converted_text = f">>> {converted_text.lstrip('> ')}"
+
+        await ctx.send(content=converted_text, embed=embed)
+
+    @caesarcipher_group.command(name="encrypt", aliases=("rightshift", "rshift", "enc",))
+    async def caesarcipher_encrypt(self, ctx: Context, offset: int, *, msg: str) -> None:
+        """
+        Given a positive integer `offset`, encrypt the given `msg`.
+
+        Performs a right shift of the letters in the message.
+
+        Also accepts a valid Discord Message ID or link.
+        """
+        await self._caesar_cipher(ctx, offset, msg, left_shift=False)
+
+    @caesarcipher_group.command(name="decrypt", aliases=("leftshift", "lshift", "dec",))
+    async def caesarcipher_decrypt(self, ctx: Context, offset: int, *, msg: str) -> None:
+        """
+        Given a positive integer `offset`, decrypt the given `msg`.
+
+        Performs a left shift of the letters in the message.
+
+        Also accepts a valid Discord Message ID or link.
+        """
+        await self._caesar_cipher(ctx, offset, msg, left_shift=True)
+
     @staticmethod
     async def _get_text_and_embed(ctx: Context, text: str) -> Tuple[str, Union[Embed, None]]:
         """
diff --git a/bot/resources/evergreen/caesar_info.json b/bot/resources/evergreen/caesar_info.json
new file mode 100644
index 00000000..8229c4f3
--- /dev/null
+++ b/bot/resources/evergreen/caesar_info.json
@@ -0,0 +1,4 @@
+{
+    "title": "Caesar Cipher",
+    "description": "**Information**\nThe Caesar Cipher, named after the Roman General Julius Caesar, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter given a specific position offset in the alphabet, with the letters wrapping around both sides.\n\n**Examples**\n1) `Hello World` <=> `Khoor Zruog` where letters are shifted forwards by `3`.\n2) `Julius Caesar` <=> `Yjaxjh Rpthpg` where letters are shifted backwards by `11`."
+}