feat: add slack integration (#73)

- add new controller to test slack integration
- create schemas and table for slack integration
- add slack handler module and some changes in schema and migrations
- add controller test cases
- add slack_event schema for validation and use it, improve the test cases
- create slack archives ui, add new ts_utc field, add is_broadcasted field
- add basic text formatting in slack ui, other stylings on the page
- add non-navigable links in the user-settings page
- add module documentation for slack_controller and slack modules, remove comments
- add index for ts_utc column of messages, minor changes in slack ui

Author: maanasb01

config/test.exs

@@ -42,3 +42,5 @@ config :dau, :aws_client, AWSS3.Sandbox
 config :dau, AWSS3, file_prefix: "temp"
 
 config :dau, :gupshup_client, DAU.UserMessage.MessageDelivery.Sandbox
+
+config :dau, :slack_process_async, false

lib/dau/markdown.ex

@@ -0,0 +1,50 @@
+defmodule DAU.Markdown do
+  @moduledoc """
+  This module is used to format the raw text that we receive from slack (during slack integration).
+  """
+  def render(raw) when is_binary(raw) do
+    raw
+    |> preprocess_slack_syntax()
+    |> Earmark.as_html!()
+    |> HtmlSanitizeEx.basic_html()
+    |> add_link_styling()
+    |> Phoenix.HTML.raw()
+  end
+
+  def render(raw) do
+    raw
+  end
+
+  # Add styling to links, preserving existing attributes
+  defp add_link_styling(html) do
+    html
+    |> String.replace(~r/<a(\s+[^>]*)>/, fn match ->
+      # Check if class attribute already exists
+      if String.contains?(match, "class=\"") do
+        # Add to existing class
+        String.replace(match, ~r/class=\"([^\"]*)\"/, "class=\\1 text-blue-600 hover:underline hover:text-blue-800 transition-colors\"")
+      else
+        # Add new class attribute
+        String.replace(match, "<a", "<a class=\"text-blue-600 hover:underline hover:text-blue-800 transition-colors\"")
+      end
+    end)
+  end
+
+  # --- Preprocessing helpers ---
+  defp preprocess_slack_syntax(text) do
+    text
+    |> replace_slack_links()
+    |> replace_single_star_bold()
+  end
+
+  # <url|label>  ->  [label](url)
+  defp replace_slack_links(text) do
+    Regex.replace(~r/<([^>|]+)\|([^>]+)>/, text, "[\\2](\\1)")
+  end
+
+  # Convert Slack-style *bold* (single stars) -> **bold**
+  # Avoid touching **already bold** and skip newlines inside
+  defp replace_single_star_bold(text) do
+    Regex.replace(~r/(?<!\*)\*([^*\n]+)\*(?!\*)/, text, "**\\1**")
+  end
+end