my solution

.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Temporary files, for example, from tests.
+/tmp/
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+jump-*.tar
+
+/jump

README.md

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+# Jump
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `jump` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:jump, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at <https://hexdocs.pm/jump>.
+

config/config.exs

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+import Config
+
+config :jump, :base_url, "https://wikimedia.org/api/rest_v1"

lib/cli.ex

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+defmodule Jump.CLI do
+  def main(args \\ []) do
+    parsed_args = parse_args(args)
+
+    parsed_args
+    |> fetch()
+    |> calculate(parsed_args)
+    |> finish()
+  end
+
+  defp parse_args(args) do
+    {opts, _, _} = OptionParser.parse(args, switches: [article: :string, days: :integer])
+    opts
+  end
+
+  defp fetch(args) do
+    the_end = Calendar.strftime(DateTime.utc_now(), "%Y%m%d")
+    {the_end_int, ""} = Integer.parse(the_end)
+
+    start = the_end_int - args[:days]
+
+    Jump.fetch(args[:article], start, the_end)
+  end
+
+  defp calculate(items, args) do
+    total_pageviews = Enum.sum_by(items, &Map.get(&1, "views"))
+    max_views_item = Enum.max_by(items, &Map.get(&1, "views"))
+
+    %{
+      event_name: "campaign_spike_conversion",
+      article: args[:article],
+      window_days: args[:days],
+      total_pageviews: total_pageviews,
+      avg_daily_pageviews: total_pageviews / length(items),
+      top_day: %{
+        date: max_views_item["timestamp"],
+        pageviews: max_views_item["views"]
+      }
+    }
+  end
+
+  defp finish(summary) do
+    Jump.post(summary)
+
+    IO.inspect(summary)
+
+    IO.puts("done.")
+  end
+
+end

lib/jump.ex

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+defmodule Jump do
+
+  @base_url "https://wikimedia.org/api/rest_v1"
+
+  def fetch(article, start, the_end) do
+    url = "/metrics/pageviews/per-article/en.wikipedia.org/all-access/user/#{article}/daily/#{start}/#{the_end}"
+
+    %{body: %{"items" => items}} = Req.get!(req(), url: url)
+    items
+  end
+
+  def post(summary) do
+    Req.post!("https://postman-echo.com/post", body: Jason.encode!(summary))
+  end
+
+  def req do
+    Req.new(base_url: @base_url)
+  end
+end

mix.exs

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+defmodule Jump.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :jump,
+      version: "0.1.0",
+      elixir: "~> 1.19",
+      start_permanent: Mix.env() == :prod,
+      deps: deps(),
+      escript: escript()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  def escript do
+    [main_module: Jump.CLI]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+      {:req, "~> 0.5.17"}
+    ]
+  end
+end

mix.lock

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+%{
+  "finch": {:hex, :finch, "0.21.0", "b1c3b2d48af02d0c66d2a9ebfb5622be5c5ecd62937cf79a88a7f98d48a8290c", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mint, "~> 1.6.2 or ~> 1.7", [hex: :mint, repo: "hexpm", optional: false]}, {:nimble_options, "~> 0.4 or ~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_pool, "~> 1.1", [hex: :nimble_pool, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "87dc6e169794cb2570f75841a19da99cfde834249568f2a5b121b809588a4377"},
+  "hpax": {:hex, :hpax, "1.0.3", "ed67ef51ad4df91e75cc6a1494f851850c0bd98ebc0be6e81b026e765ee535aa", [:mix], [], "hexpm", "8eab6e1cfa8d5918c2ce4ba43588e894af35dbd8e91e6e55c817bca5847df34a"},
+  "jason": {:hex, :jason, "1.4.4", "b9226785a9aa77b6857ca22832cffa5d5011a667207eb2a0ad56adb5db443b8a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "c5eb0cab91f094599f94d55bc63409236a8ec69a21a67814529e8d5f6cc90b3b"},
+  "mime": {:hex, :mime, "2.0.7", "b8d739037be7cd402aee1ba0306edfdef982687ee7e9859bee6198c1e7e2f128", [:mix], [], "hexpm", "6171188e399ee16023ffc5b76ce445eb6d9672e2e241d2df6050f3c771e80ccd"},
+  "mint": {:hex, :mint, "1.7.1", "113fdb2b2f3b59e47c7955971854641c61f378549d73e829e1768de90fc1abf1", [:mix], [{:castore, "~> 0.1.0 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:hpax, "~> 0.1.1 or ~> 0.2.0 or ~> 1.0", [hex: :hpax, repo: "hexpm", optional: false]}], "hexpm", "fceba0a4d0f24301ddee3024ae116df1c3f4bb7a563a731f45fdfeb9d39a231b"},
+  "nimble_options": {:hex, :nimble_options, "1.1.1", "e3a492d54d85fc3fd7c5baf411d9d2852922f66e69476317787a7b2bb000a61b", [:mix], [], "hexpm", "821b2470ca9442c4b6984882fe9bb0389371b8ddec4d45a9504f00a66f650b44"},
+  "nimble_pool": {:hex, :nimble_pool, "1.1.0", "bf9c29fbdcba3564a8b800d1eeb5a3c58f36e1e11d7b7fb2e084a643f645f06b", [:mix], [], "hexpm", "af2e4e6b34197db81f7aad230c1118eac993acc0dae6bc83bac0126d4ae0813a"},
+  "req": {:hex, :req, "0.5.17", "0096ddd5b0ed6f576a03dde4b158a0c727215b15d2795e59e0916c6971066ede", [:mix], [{:brotli, "~> 0.3.1", [hex: :brotli, repo: "hexpm", optional: true]}, {:ezstd, "~> 1.0", [hex: :ezstd, repo: "hexpm", optional: true]}, {:finch, "~> 0.17", [hex: :finch, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:mime, "~> 2.0.6 or ~> 2.1", [hex: :mime, repo: "hexpm", optional: false]}, {:nimble_csv, "~> 1.0", [hex: :nimble_csv, repo: "hexpm", optional: true]}, {:plug, "~> 1.0", [hex: :plug, repo: "hexpm", optional: true]}], "hexpm", "0b8bc6ffdfebbc07968e59d3ff96d52f2202d0536f10fef4dc11dc02a2a43e39"},
+  "telemetry": {:hex, :telemetry, "1.4.1", "ab6de178e2b29b58e8256b92b382ea3f590a47152ca3651ea857a6cae05ac423", [:rebar3], [], "hexpm", "2172e05a27531d3d31dd9782841065c50dd5c3c7699d95266b2edd54c2dafa1c"},
+}

test/jump_test.exs

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+defmodule JumpTest do
+  use ExUnit.Case
+  doctest Jump
+
+  test "greets the world" do
+    assert Jump.hello() == :world
+  end
+end

test/test_helper.exs

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+ExUnit.start()