defmodule OpenAgentsWeb.StackJSON do
  @moduledoc "Renders pull request stacks with their ordered entries."

  def render("index.json", %{stacks: stacks} = assigns),
    do: Enum.map(stacks, &stack(&1, assigns))

  def render("show.json", %{stack: stack} = assigns) do
    json = stack(stack, assigns)

    case Map.get(assigns, :replay_state) do
      nil -> json
      replay_state -> Map.put(json, :replayed, replay_state == :replayed)
    end
  end

  def render("operation.json", %{operation: operation} = assigns) do
    json = %{
      id: operation.id,
      kind: operation.kind,
      state: operation.state,
      expected_stack_version: operation.expected_stack_version,
      target_position: operation.target_position,
      conflict: operation.conflict,
      planned_result: operation.planned_result,
      error: operation.error,
      created_at: operation.inserted_at,
      started_at: operation.started_at,
      completed_at: operation.completed_at
    }

    case Map.get(assigns, :replay_state) do
      nil -> json
      replay_state -> Map.put(json, :replayed, replay_state == :replayed)
    end
  end

  def render("merge_async.json", %{operation: operation} = assigns) do
    base_url = String.trim_trailing(OpenAgentsWeb.Endpoint.url(), "/")

    json = %{
      operation_id: operation.id,
      merge_status: merge_status(operation),
      state: operation.state,
      merge_method: Map.get(operation.request, "merge_method"),
      pull_request: Map.get(operation.request, "pull_request_number"),
      error: operation.error,
      created_at: operation.inserted_at,
      completed_at: operation.completed_at,
      url:
        "#{base_url}/api/v1/repos/#{assigns.owner}/#{assigns.repo}/pulls/#{assigns.pull_number}/merge-async/#{operation.id}"
    }

    case Map.get(assigns, :replay_state) do
      nil -> json
      replay_state -> Map.put(json, :replayed, replay_state == :replayed)
    end
  end

  # The external contract collapses internal operation states into the
  # three the poll surface promises: a submitted merge is pending until
  # it either lands or terminates without landing.
  defp merge_status(%{state: state})
       when state in ~w(pending running waiting_for_conflict_resolution waiting_for_checks),
       do: "pending"

  defp merge_status(%{state: "succeeded"}), do: "merged"
  defp merge_status(_operation), do: "failed"

  defp stack(stack, assigns) do
    base_url = String.trim_trailing(OpenAgentsWeb.Endpoint.url(), "/")
    owner = assigns.owner
    repo = assigns.repo

    %{
      id: stack.id,
      number: stack.number,
      trunk_ref: stack.trunk_ref,
      state: stack.state,
      health: stack.health,
      version: stack.version,
      size: length(stack.entries),
      entries: Enum.map(stack.entries, &entry(&1, owner, repo, base_url)),
      created_at: stack.inserted_at,
      updated_at: stack.updated_at,
      url: "#{base_url}/api/v1/repos/#{owner}/#{repo}/stacks/#{stack.number}"
    }
  end

  defp entry(entry, owner, repo, base_url) do
    pull_request = entry.pull_request

    %{
      position: entry.position,
      boundary_oid: entry.boundary_oid,
      observed_head_oid: entry.observed_head_oid,
      pull_request: %{
        number: pull_request.issue.number,
        state: pull_request.issue.state,
        head: %{ref: pull_request.head_ref, sha: pull_request.head_sha},
        base: %{ref: pull_request.base_ref, sha: pull_request.base_sha},
        url: "#{base_url}/api/v1/repos/#{owner}/#{repo}/pulls/#{pull_request.issue.number}"
      }
    }
  end
end