defmodule Mastomation.Delete do
  @moduledoc """
  Deletion-specific CLI logic and status deletion workflow.
  """

  require Logger
  @default_delay_ms 60_000

  @doc """
  Parses delete command options for compatibility with older callers.
  """
  @spec parse_options([String.t()]) :: map()
  def parse_options(args \\ []) do
    case Mastomation.Parser.parse(["delete" | args]) do
      {:ok, [:delete, :all], %{options: options}} ->
        Map.take(options, [:instance_url, :access_token])

      {:ok, [:delete], %{options: options}} ->
        Map.take(options, [:instance_url, :access_token])
    end
  end

  @doc """
  Executes the delete workflow from a parsed CLI result.
  """
  @spec run_delete(map()) :: :ok
  def run_delete(result) do
    options = result.options
    flags = result.flags

    instance =
      options.override_instance_url || options.instance_url ||
        System.get_env("MASTODON_INSTANCE_URL")

    token =
      options.override_access_token || options.access_token ||
        System.get_env("MASTODON_ACCESS_TOKEN")

    delay_ms = options.delay_ms || @default_delay_ms
    thread_source = options.thread_source
    keywords = options.keyword || []
    dry_run = Map.get(flags, :dry_run, false)
    no_backup = Map.get(flags, :no_backup, false)
    frontmatter = Map.get(flags, :frontmatter, false)

    validate_required!(instance, token)

    if is_nil(thread_source) or thread_source == "" do
      delete_all_statuses(instance, token,
        delay_ms: delay_ms,
        dry_run: dry_run,
        keywords: keywords,
        backup: not no_backup,
        frontmatter: frontmatter
      )
    else
      delete_thread_replies(instance, token, thread_source,
        delay_ms: delay_ms,
        dry_run: dry_run,
        keywords: keywords,
        backup: not no_backup,
        frontmatter: frontmatter
      )
    end
  end

  @doc """
  Executes the `delete all` workflow from parsed CLI input.
  """
  @spec run_delete_all(map()) :: :ok
  def run_delete_all(result) do
    options = result.options
    flags = result.flags

    instance =
      options.override_instance_url || options.instance_url ||
        System.get_env("MASTODON_INSTANCE_URL")

    token =
      options.override_access_token || options.access_token ||
        System.get_env("MASTODON_ACCESS_TOKEN")

    validate_required!(instance, token)

    delete_all_statuses(instance, token,
      delay_ms: options.delay_ms || @default_delay_ms,
      dry_run: Map.get(flags, :dry_run, false),
      keywords: options.keyword || [],
      backup: not Map.get(flags, :no_backup, false),
      frontmatter: Map.get(flags, :frontmatter, false)
    )
  end

  @doc """
  Executes the `delete thread` workflow from parsed CLI input.
  """
  @spec run_delete_thread(map()) :: :ok
  def run_delete_thread(result) do
    options = result.options
    flags = result.flags
    source = result.args.source

    instance =
      options.override_instance_url || options.instance_url ||
        System.get_env("MASTODON_INSTANCE_URL")

    token =
      options.override_access_token || options.access_token ||
        System.get_env("MASTODON_ACCESS_TOKEN")

    validate_required!(instance, token)

    delete_thread_replies(instance, token, source,
      delay_ms: options.delay_ms || @default_delay_ms,
      dry_run: Map.get(flags, :dry_run, false),
      keywords: options.keyword || [],
      backup: not Map.get(flags, :no_backup, false),
      frontmatter: Map.get(flags, :frontmatter, false)
    )
  end

  @doc """
  Fetches the authenticated user id from Mastodon.
  """
  @spec get_user_id(String.t(), String.t()) :: String.t()
  def get_user_id(instance, token) do
    %{"id" => id} =
      Mastomation.Client.get_json!("#{instance}/api/v1/accounts/verify_credentials", token)

    id
  end

  @doc """
  Fetches a page of account statuses.
  """
  @spec get_statuses(String.t(), String.t(), String.t()) :: [map()]
  def get_statuses(instance, token, user_id) do
    Mastomation.Client.get_json!(
      "#{instance}/api/v1/accounts/#{user_id}/statuses?limit=40",
      token
    )
  end

  @doc """
  Fetches a paginated page of account statuses using `max_id`.
  """
  @spec get_statuses(String.t(), String.t(), String.t(), String.t()) :: [map()]
  def get_statuses(instance, token, user_id, max_id) do
    Mastomation.Client.get_json!(
      "#{instance}/api/v1/accounts/#{user_id}/statuses?limit=40&max_id=#{max_id}",
      token
    )
  end

  @doc """
  Fetches all statuses for an account by traversing pages.
  """
  @spec get_all_statuses(String.t(), String.t(), String.t()) :: [map()]
  def get_all_statuses(instance, token, user_id) do
    first_batch = get_statuses(instance, token, user_id)

    if first_batch == [] do
      []
    else
      loop_statuses(instance, token, user_id, first_batch)
    end
  end

  @doc """
  Continues paginated status retrieval until exhaustion.
  """
  @spec loop_statuses(String.t(), String.t(), String.t(), [map()]) :: [map()]
  def loop_statuses(instance, token, user_id, accumulated) do
    last_id = get_last_status_id(accumulated)
    next_batch = get_statuses(instance, token, user_id, last_id)

    cond do
      next_batch == [] ->
        accumulated

      get_last_status_id(next_batch) == last_id ->
        accumulated

      true ->
        loop_statuses(instance, token, user_id, accumulated ++ next_batch)
    end
  end

  @doc """
  Filters out pinned/bookmarked/favourited statuses.
  """
  @spec filter_waste([map()]) :: [map()]
  def filter_waste(statuses) do
    Enum.filter(statuses, fn status ->
      status["bookmarked"] == false and
        status["favourited"] == false and
        status["pinned"] == false
    end)
  end

  @doc """
  Returns the id of the last status in a non-empty list.
  """
  @spec get_last_status_id([map()]) :: String.t()
  def get_last_status_id(statuses) do
    %{"id" => id} = List.last(statuses)
    id
  end

  @spec delete_all_statuses(any(), any(), keyword()) :: :ok
  @doc """
  Deletes statuses from the account based on configured filters/options.
  """
  def delete_all_statuses(instance, token, opts \\ []) do
    :telemetry.execute([:mastomation, :delete, :all, :start], %{}, %{})
    delay_ms = Keyword.get(opts, :delay_ms, @default_delay_ms)
    dry_run = Keyword.get(opts, :dry_run, false)
    keywords = Keyword.get(opts, :keywords, [])
    backup? = Keyword.get(opts, :backup, true)
    frontmatter = Keyword.get(opts, :frontmatter, false)
    user_id = get_user_id(instance, token)
    checkpoint = load_checkpoint(:delete_all, user_id)

    statuses =
      get_all_statuses(instance, token, user_id)
      |> filter_waste()
      |> filter_keywords(keywords)
      |> reject_checkpointed(checkpoint)

    Logger.info("found #{Enum.count(statuses)} deletable statuses")

    if backup? do
      backup_statuses_split(statuses, "delete-all", frontmatter: frontmatter)
    end

    Enum.each(statuses, &process_delete_status(&1, instance, token, user_id, delay_ms, dry_run))

    :telemetry.execute([:mastomation, :delete, :all, :stop], %{count: Enum.count(statuses)}, %{})
  end

  @doc """
  Deletes a single status by id.
  """
  @spec delete_status(String.t(), String.t(), String.t()) :: :ok | {:error, term()}
  def delete_status(id, instance, token) do
    Mastomation.Client.delete_status_with_retry(instance, token, id)
  end

  @doc """
  Deletes only same-author statuses in the thread of `thread_source`.
  """
  @spec delete_thread_replies(String.t(), String.t(), String.t(), keyword()) :: :ok
  def delete_thread_replies(instance, token, thread_source, opts \\ []) do
    :telemetry.execute([:mastomation, :delete, :thread, :start], %{}, %{
      thread_source: thread_source
    })

    delay_ms =
      Keyword.get(opts, :delay_ms, @default_delay_ms)
      |> min(2_000)

    dry_run = Keyword.get(opts, :dry_run, false)
    keywords = Keyword.get(opts, :keywords, [])
    backup? = Keyword.get(opts, :backup, true)
    frontmatter = Keyword.get(opts, :frontmatter, false)
    user_id = get_user_id(instance, token)
    source_id = Mastomation.Threads.extract_status_id(thread_source)
    source_status = Mastomation.Threads.get_status(instance, token, source_id)
    context = Mastomation.Threads.get_status_context(instance, token, source_id)
    checkpoint = load_checkpoint({:thread, source_id}, user_id)

    statuses =
      own_thread_statuses(source_status, context, user_id)
      |> filter_keywords(keywords)
      |> reject_checkpointed(checkpoint)

    Logger.info("found #{Enum.count(statuses)} deletable statuses in thread #{source_id}")

    if backup? do
      backup_statuses_joined(statuses, "thread-#{source_id}", thread_source,
        frontmatter: frontmatter
      )
    end

    scope = {:thread, source_id}

    Enum.each(
      statuses,
      &process_delete_status(&1, instance, token, user_id, delay_ms, dry_run, scope)
    )

    :telemetry.execute(
      [:mastomation, :delete, :thread, :stop],
      %{count: Enum.count(statuses)},
      %{thread_source: thread_source}
    )
  end

  @doc """
  Filters statuses to those containing at least one keyword.
  """
  @spec filter_keywords([map()], [String.t()]) :: [map()]
  def filter_keywords(statuses, []), do: statuses

  @spec filter_keywords([map()], [String.t()]) :: [map()]
  def filter_keywords(statuses, keywords) do
    normalized = Enum.map(keywords, &String.downcase/1)

    Enum.filter(statuses, fn status ->
      text =
        status
        |> Map.get("content", "")
        |> String.downcase()

      Enum.any?(normalized, &String.contains?(text, &1))
    end)
  end

  # Ensures the export root folder exists in the current working directory.
  @spec export_folder!() :: String.t()
  defp export_folder! do
    folder = Path.join(File.cwd!(), "export")
    File.mkdir_p!(folder)
    folder
  end

  # Writes one markdown file per status backup.
  @spec backup_statuses_split([map()], String.t(), keyword()) :: :ok
  defp backup_statuses_split(statuses, label, opts) do
    frontmatter = Keyword.get(opts, :frontmatter, false)
    folder = Path.join(export_folder!(), "backups")
    File.mkdir_p!(folder)

    Enum.each(statuses, fn status ->
      id = status["id"]
      path = Path.join(folder, "#{label}-#{id}.md")
      File.write!(path, markdown_for_status(status, frontmatter: frontmatter))
    end)
  end

  # Writes a single combined markdown backup for a thread delete run.
  @spec backup_statuses_joined([map()], String.t(), String.t(), keyword()) :: :ok
  defp backup_statuses_joined(statuses, label, source_reference, opts) do
    frontmatter = Keyword.get(opts, :frontmatter, false)
    folder = Path.join(export_folder!(), "backups")
    File.mkdir_p!(folder)
    path = Path.join(folder, "#{label}.md")

    body =
      statuses
      |> Enum.map_join("\n\n", &markdown_section/1)

    fm =
      if frontmatter do
        """
        ---
        title: Delete Backup
        source_url: #{source_reference}
        exported_at: #{DateTime.utc_now() |> DateTime.to_iso8601()}
        count: #{Enum.count(statuses)}
        ---

        """
      else
        ""
      end

    File.write!(path, fm <> body <> "\n")
  end

  # Builds markdown for a single status backup.
  @spec markdown_for_status(map(), keyword()) :: String.t()
  defp markdown_for_status(status, opts) do
    frontmatter = Keyword.get(opts, :frontmatter, false)

    section = markdown_section(status)

    if frontmatter do
      """
      ---
      title: Status Backup
      status_id: #{status["id"]}
      exported_at: #{DateTime.utc_now() |> DateTime.to_iso8601()}
      ---

      #{section}
      """
    else
      section <> "\n"
    end
  end

  # Renders a markdown section for one status.
  @spec markdown_section(map()) :: String.t()
  defp markdown_section(status) do
    id = status["id"]
    created_at = status["created_at"] || "unknown-time"
    content = status["content"] |> Mastomation.Threads.render_markdown_content()

    """
    ## #{created_at} (#{id})

    #{content}
    """
  end

  # Computes the checkpoint filename for a scope/user pair.
  @spec checkpoint_file(:delete_all | {:thread, String.t()}, String.t()) :: String.t()
  defp checkpoint_file(scope, user_id) do
    key =
      case scope do
        :delete_all -> "delete-all"
        {:thread, source_id} -> "thread-#{source_id}"
      end

    dir = Path.join(export_folder!(), "checkpoints")
    File.mkdir_p!(dir)
    Path.join(dir, "#{key}-#{user_id}.json")
  end

  # Loads deleted ids from checkpoint storage.
  @spec load_checkpoint(:delete_all | {:thread, String.t()}, String.t()) :: MapSet.t(String.t())
  defp load_checkpoint(scope, user_id) do
    path = checkpoint_file(scope, user_id)

    case File.read(path) do
      {:ok, body} ->
        case JSON.decode(body) do
          {:ok, %{"deleted_ids" => ids}} when is_list(ids) -> MapSet.new(ids)
          _ -> MapSet.new()
        end

      _ ->
        MapSet.new()
    end
  end

  # Persists a deleted status id into checkpoint storage.
  @spec append_checkpoint(:delete_all | {:thread, String.t()}, String.t(), String.t()) :: :ok
  defp append_checkpoint(scope, user_id, status_id) do
    path = checkpoint_file(scope, user_id)
    existing = load_checkpoint(scope, user_id) |> ensure_checkpoint_set()
    updated = MapSet.put(existing, status_id) |> MapSet.to_list()
    File.write!(path, JSON.encode!(%{"deleted_ids" => updated}))
  end

  # Removes statuses that have already been checkpointed.
  @spec reject_checkpointed([map()], MapSet.t(String.t()) | [String.t()] | term()) :: [map()]
  defp reject_checkpointed(statuses, checkpoint) do
    checkpoint = ensure_checkpoint_set(checkpoint)
    Enum.reject(statuses, fn status -> MapSet.member?(checkpoint, status["id"]) end)
  end

  # Keeps Dialyzer/ElixirLS happy around MapSet's opaque type.
  @spec ensure_checkpoint_set(MapSet.t(String.t()) | [String.t()] | term()) ::
          MapSet.t(String.t())
  defp ensure_checkpoint_set(%MapSet{} = checkpoint), do: checkpoint
  defp ensure_checkpoint_set(checkpoint) when is_list(checkpoint), do: MapSet.new(checkpoint)
  defp ensure_checkpoint_set(_checkpoint), do: MapSet.new()

  # Handles one status in delete-all mode.
  @spec process_delete_status(
          map(),
          String.t(),
          String.t(),
          String.t(),
          non_neg_integer(),
          boolean()
        ) ::
          :ok
  defp process_delete_status(status, instance, token, user_id, delay_ms, dry_run) do
    process_delete_status(status, instance, token, user_id, delay_ms, dry_run, :delete_all)
  end

  # Handles one status in thread-delete mode.
  @spec process_delete_status(
          map(),
          String.t(),
          String.t(),
          String.t(),
          non_neg_integer(),
          boolean(),
          :delete_all | {:thread, String.t()}
        ) :: :ok
  defp process_delete_status(status, instance, token, user_id, delay_ms, dry_run, scope) do
    content = status["content"] || ""
    id = status["id"]
    action = delete_action_label(dry_run, scope)

    Logger.info("#{action} #{id}")
    Logger.info("status content: #{content}")

    unless dry_run do
      :ok = delete_status(id, instance, token)
      append_checkpoint(scope, user_id, id)
      maybe_sleep(delay_ms)
    end
  end

  @spec delete_action_label(boolean(), :delete_all | {:thread, String.t()}) :: String.t()
  defp delete_action_label(true, :delete_all), do: "dry-run: would delete status"
  defp delete_action_label(true, {:thread, _source_id}), do: "dry-run: would delete thread status"
  defp delete_action_label(false, :delete_all), do: "deleting status"
  defp delete_action_label(false, {:thread, _source_id}), do: "deleting thread status"

  @spec maybe_sleep(non_neg_integer()) :: :ok
  defp maybe_sleep(delay_ms) when delay_ms > 0 do
    Process.sleep(delay_ms)
    :ok
  end

  defp maybe_sleep(_delay_ms), do: :ok

  @doc """
  Returns same-author descendants for a thread, including source when owned.
  """
  @spec own_thread_statuses(map(), map(), String.t()) :: [map()]
  def own_thread_statuses(source_status, context, user_id) do
    descendants =
      Map.get(context, "descendants", [])
      |> Enum.filter(fn status ->
        get_in(status, ["account", "id"]) == user_id
      end)
      |> Enum.sort_by(&Map.get(&1, "created_at", ""), :desc)

    if get_in(source_status, ["account", "id"]) == user_id do
      descendants ++ [source_status]
    else
      descendants
    end
  end

  # Validates required instance/token inputs.
  @spec validate_required!(String.t() | nil, String.t() | nil) :: :ok | no_return()
  defp validate_required!(instance, token) do
    cond do
      is_nil(instance) or instance == "" ->
        raise ArgumentError,
              "missing instance URL (set --instance_url or MASTODON_INSTANCE_URL)"

      is_nil(token) or token == "" ->
        raise ArgumentError,
              "missing access token (set --access_token or MASTODON_ACCESS_TOKEN)"

      true ->
        :ok
    end
  end
end