feat: add simple todo list module

.envrc

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+use flake

.gitignore

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+### direnv ###
+.direnv
+.envrc
+
+### Elixir ###
+/_build
+/cover
+/deps
+/doc
+/.fetch
+erl_crash.dump
+*.ez
+*.beam
+/config/*.secret.exs
+.elixir_ls/
+
+### Elixir Patch ###

flake.lock

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+{
+  "nodes": {
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1719994518,
+        "narHash": "sha256-pQMhCCHyQGRzdfAkdJ4cIWiw+JNuWsTX7f0ZYSyz0VY=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "9227223f6d922fee3c7b190b2cc238a99527bbb7",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1722185531,
+        "narHash": "sha256-veKR07psFoJjINLC8RK4DiLniGGMgF3QMlS4tb74S6k=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "52ec9ac3b12395ad677e8b62106f0b98c1f8569d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1719876945,
+        "narHash": "sha256-Fm2rDDs86sHy0/1jxTOKB1118Q0O3Uc7EC0iXvXKpbI=",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/5daf0514482af3f97abaefc78a6606365c9108e2.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/5daf0514482af3f97abaefc78a6606365c9108e2.tar.gz"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-parts": "flake-parts",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "Description for the project";
+
+  inputs = {
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [
+        # To import a flake module
+        # 1. Add foo to inputs
+        # 2. Add foo as a parameter to the outputs function
+        # 3. Add here: foo.flakeModule
+
+      ];
+      systems = [ "x86_64-linux" "aarch64-linux" "aarch64-darwin" "x86_64-darwin" ];
+      perSystem = { config, self', inputs', pkgs, system, ... }: {
+        # Per-system attributes can be defined here. The self' and inputs'
+        # module parameters provide easy access to attributes of the same
+        # system.
+
+        # Equivalent to  inputs'.nixpkgs.legacyPackages.hello;
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = with pkgs; [ elixir-ls elixir_1_17];
+        };
+      };
+      flake = {
+        # The usual flake attributes can be defined here, including system-
+        # agnostic ones like nixosModule and system-enumerating ones, although
+        # those are more easily expressed in perSystem.
+
+      };
+    };
+}

todo_list.csv

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+2024-12-19,Dentist
+2024-12-20,Shopping
+2024-12-19,Movies

todo_list.ex

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+defmodule TodoList do
+  defstruct entries: %{}, next_id: 1
+
+  def new(entries \\ []) do
+    Enum.reduce(entries, %__MODULE__{}, &add(&2, &1))
+  end
+
+  def add(
+        %__MODULE__{entries: entries, next_id: next_id} = todo_list,
+        %{date: _, title: _} = entry
+      ) do
+    new_entry = Map.put(entry, :id, next_id)
+
+    new_entries = Map.put(entries, next_id, new_entry)
+
+    %__MODULE__{todo_list | entries: new_entries, next_id: next_id + 1}
+  end
+
+  def entries(%__MODULE__{entries: entries}, date) do
+    entries
+    |> Map.filter(fn {_, entry} -> entry.date == date end)
+    |> Map.values()
+  end
+
+  def update(%__MODULE__{entries: entries} = todo_list, id, update_fun)
+      when is_function(update_fun, 1) do
+    case Map.fetch(entries, id) do
+      :error ->
+        todo_list
+
+      {:ok, entry} ->
+        new_entry = update_fun.(entry)
+        new_entries = Map.put(entries, id, new_entry)
+        %__MODULE__{todo_list | entries: new_entries}
+    end
+  end
+
+  def delete(%__MODULE__{entries: entries} = todo_list, id) when is_number(id) do
+    new_entries = Map.delete(entries, id)
+
+    %__MODULE__{todo_list | entries: new_entries}
+  end
+end
+
+defmodule TodoList.CSVImporter do
+  def import(path) do
+    path
+    |> File.stream!()
+    |> Stream.map(&parse_line/1)
+    |> TodoList.new()
+  end
+
+  defp parse_line(line) do
+    line
+    |> String.trim()
+    |> String.split(",")
+    |> create_entry()
+  end
+
+  defp create_entry([date, title]) do
+    final_date = parse_date(date)
+
+    %{date: final_date, title: title}
+  end
+
+  defp parse_date(string) do
+    [year, month, day] = string |> String.split("-") |> Enum.map(&String.to_integer/1)
+
+    Date.new!(year, month, day)
+  end
+end