@spec fetch(String.t() | URI.t(), Keyword.t() | map()) :: %HTTP.Promise{task: term()}

Performs an HTTP request, similar to global.fetch in web browsers. Uses Erlang's built-in :httpc module asynchronously (sync: false).

Arguments:

• url: The URL to fetch (string or URI struct).
• init: An optional keyword list or map of options for the request.

      Supported options:
        - `:method`: The HTTP method (e.g., "GET", "POST"). Defaults to "GET".
                     Can be a string or an atom (e.g., "GET" or :get).
        - `:headers`: A list of request headers as `{name, value}` tuples (e.g., [{"Content-Type", "application/json"}])
                      or a map that will be converted to the tuple format.
        - `:body`: The request body (should be a binary or a string that can be coerced to binary).
        - `:content_type`: The Content-Type header value. If not provided for methods with body,
                           defaults to "application/octet-stream" in `Request.to_httpc_args`.
        - `:options`: A keyword list of options directly passed as the 3rd argument to `:httpc.request`
                      (e.g., `timeout: 10_000`, `connect_timeout: 5_000`).
        - `:client_opts`: A keyword list of options directly passed as the 4th argument to `:httpc.request`
                          (e.g., `sync: false`, `body_format: :binary`). Overrides `Request` defaults.
        - `:signal`: An `HTTP.AbortController` PID. If provided, the request can be aborted
                     via this controller.

Returns:

• %HTTP.Promise{}: A Promise struct. The caller should HTTP.Promise.await(promise_struct) to get the final

         `%HTTP.Response{}` or `{:error, reason}`. If the request cannot be initiated
         (e.g., invalid URL, bad arguments), the Promise will contain an error result
         when awaited.

Example Usage:

# GET request and awaiting JSON
promise_json = HTTP.fetch("https://jsonplaceholder.typicode.com/todos/1")
case HTTP.Promise.await(promise_json) do
  %HTTP.Response{} = response ->
    case HTTP.Response.json(response) do
      {:ok, json_body} ->
        IO.puts "GET JSON successful! Title: #{json_body["title"]}"
      {:error, reason} ->
        IO.inspect reason, label: "JSON Parse Error"
    end
  {:error, reason} ->
    IO.inspect reason, label: "GET Error for JSON"
end

# GET request and awaiting text
promise_text = HTTP.fetch("https://jsonplaceholder.typicode.com/posts/1")
case HTTP.Promise.await(promise_text) do
  %HTTP.Response{} = response ->
    text_body = HTTP.Response.text(response)
    IO.puts "GET Text successful! First 50 chars: #{String.slice(text_body, 0, 50)}..."
  {:error, reason} ->
    IO.inspect reason, label: "GET Error for Text"
end

# Simple Promise chaining: fetch -> parse JSON -> print title
HTTP.fetch("https://jsonplaceholder.typicode.com/todos/2")
|> HTTP.Promise.then(fn %HTTP.Response{} = response ->
  HTTP.Response.json(response)
end)
|> HTTP.Promise.then(fn {:ok, json_body} ->
  IO.puts "Chained JSON successful! Title: #{json_body["title"]}"
end)
|> HTTP.Promise.await() # Await the final chained promise to ensure execution

# Promise chaining with error handling: fetch -> parse JSON -> handle success or error
HTTP.fetch("https://jsonplaceholder.typicode.com/nonexistent") # This URL will cause an error
|> HTTP.Promise.then(
  fn %HTTP.Response{} = response ->
    IO.puts "This success branch should not be called for a 404!"
    HTTP.Response.json(response)
  end,
  fn reason ->
    IO.inspect reason, label: "Chained Error Handler Caught"
    {:error, :handled_error} # Return an error tuple to propagate rejection
  end
)
|> HTTP.Promise.await() # Await the final chained promise

# Chaining where a callback returns another promise
HTTP.fetch("https://jsonplaceholder.typicode.com/posts/1")
|> HTTP.Promise.then(fn %HTTP.Response{} = response ->
  # Simulate fetching comments for the post
  post_id = case HTTP.Response.json(response) do
    {:ok, %{"id" => id}} -> id
    _ -> nil
  end
  if post_id do
    IO.puts "Fetched post #{post_id}. Now fetching comments..."
    HTTP.fetch("https://jsonplaceholder.typicode.com/posts/#{post_id}/comments")
  else
    # If post_id is nil, we want to reject this branch of the promise chain
    throw {:error, :post_id_not_found}
  end
end)
|> HTTP.Promise.then(fn comments_response ->
  case HTTP.Response.json(comments_response) do
    {:ok, comments} ->
      IO.puts "Successfully fetched #{length(comments)} comments for the post."
    {:error, reason} ->
      IO.inspect reason, label: "Failed to parse comments JSON"
  end
end)
|> HTTP.Promise.await()


# POST request with JSON body and headers
# If you're using Elixir 1.18+, JSON.encode! is built-in. Otherwise, you'd need a library like Poison.
# promise_post = HTTP.fetch("https://jsonplaceholder.typicode.com/posts",
#        method: "POST",
#        headers: [{"Accept", "application/json"}],
#        content_type: "application/json",
#        body: JSON.encode!(%{title: "foo", body: "bar", userId: 1})
#      )
# case HTTP.Promise.await(promise_post) do
#   {:ok, %HTTP.Response{status: 201, body: body}} ->
#     IO.puts "POST successful! Body: #{body}"
#   {:error, reason} ->
#     IO.inspect reason, label: "POST Error"
# end

# Request with custom :httpc options (e.g., longer timeout for request options)
delayed_promise = HTTP.fetch("https://httpbin.org/delay/5", options: [timeout: 10_000])
case HTTP.Promise.await(delayed_promise) do
  %HTTP.Response{status: status} ->
    IO.puts "Delayed request successful! Status: #{status}"
  {:error, reason} ->
    IO.inspect reason, label: "Delayed Request Result"
end

# Abortable request example
controller = HTTP.AbortController.new() # Create a new controller
IO.puts "Fetching a long request that will be aborted..."
abortable_promise = HTTP.fetch("https://httpbin.org/delay/10", signal: controller, options: [timeout: 20_000])

# Simulate some work, then abort after a short delay
Task.start_link(fn ->
  :timer.sleep(2000) # Wait 2 seconds
  IO.puts "Attempting to abort the request after 2 seconds..."
  HTTP.AbortController.abort(controller)
end)

# Await the result of the abortable promise
case HTTP.Promise.await(abortable_promise) do
  %HTTP.Response{status: status} ->
    IO.puts "Abortable request completed successfully! Status: #{status}"
  {:error, reason} ->
    IO.inspect reason, label: "Abortable Request Result"
    if reason == :econnrefused or reason == :nxdomain do # Common errors for aborted :httpc requests
      IO.puts "Request was likely aborted. Reason: #{inspect(reason)}"
    end
end