feat: allow to leave comment under issue

lib/ex_linear/client.ex

@@ -128,6 +128,14 @@ defmodule ExLinear.Client do
   }
   """
 
+  @create_comment_mutation """
+  mutation CommentCreate($issueId: String!, $body: String!) {
+    commentCreate(input: {issueId: $issueId, body: $body}) {
+      success
+    }
+  }
+  """
+
   @doc """
   Low-level GraphQL request. Uses `config` for API key and endpoint.
 
@@ -248,6 +256,23 @@ defmodule ExLinear.Client do
     end
   end
 
+  @doc """
+  Creates a comment on the given issue.
+  """
+  @spec create_comment(Config.t() | keyword(), String.t(), String.t()) :: :ok | {:error, term()}
+  def create_comment(config, issue_id, body) when is_binary(issue_id) and is_binary(body) do
+    c = normalize_config(config)
+
+    with {:ok, response} <-
+           graphql(c, @create_comment_mutation, %{issueId: issue_id, body: body}),
+         true <- get_in(response, ["data", "commentCreate", "success"]) == true do
+      :ok
+    else
+      false -> {:error, :comment_create_failed}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
   defp normalize_config(opts) when is_list(opts), do: Config.from_opts(opts)
   defp normalize_config(%Config{} = c), do: c
 

test/ex_linear/client_test.exs

@@ -654,6 +654,45 @@ defmodule ExLinear.ClientTest do
     end
   end
 
+  describe "create_comment/3" do
+    test "succeeds when commentCreate.success is true" do
+      set_request_fun(fn _c, payload, _headers ->
+        vars = payload["variables"] || %{}
+        assert vars[:issueId] == "issue-1"
+        assert vars[:body] == "hello"
+        assert payload["query"] =~ "commentCreate"
+        {:ok, %{status: 200, body: %{"data" => %{"commentCreate" => %{"success" => true}}}}}
+      end)
+
+      assert :ok = Client.create_comment(@base_config, "issue-1", "hello")
+    end
+
+    test "returns comment_create_failed when success is false" do
+      set_request_fun(fn _c, _payload, _headers ->
+        {:ok, %{status: 200, body: %{"data" => %{"commentCreate" => %{"success" => false}}}}}
+      end)
+
+      assert {:error, :comment_create_failed} =
+               Client.create_comment(@base_config, "issue-1", "body")
+    end
+
+    test "propagates transport error" do
+      set_request_fun(fn _c, _payload, _headers -> {:error, :timeout} end)
+
+      assert {:error, {:linear_api_request, :timeout}} =
+               Client.create_comment(@base_config, "issue-1", "body")
+    end
+
+    test "returns comment_create_failed when response body is unexpected" do
+      set_request_fun(fn _c, _payload, _headers ->
+        {:ok, %{status: 200, body: %{"data" => %{}}}}
+      end)
+
+      assert {:error, :comment_create_failed} =
+               Client.create_comment(@base_config, "issue-1", "body")
+    end
+  end
+
   describe "ExLinear.Issue" do
     test "label_names returns labels" do
       issue = %Issue{id: "1", labels: ["frontend", "infra"]}