defmodule Syntropy.RuntimeConfig do
  @moduledoc """
  Read and apply runtime provider configuration.

  Provider settings live in the Application environment, seeded from env vars
  at boot (`config/runtime.exs`). `apply_provider/1` validates a candidate
  configuration with `Syntropy.LLMClient.Config` and only then writes it with
  `Application.put_env/3`, so an invalid update never disturbs a working
  provider.

  Applied changes take effect immediately for subsequent LLM calls. When
  persistence is enabled they are also written through to `runtime_settings`
  and rehydrated on boot (`hydrate/0`), so an applied configuration survives
  restarts. Without persistence they are memory-scoped and reset on restart;
  reports include an env-var block (`env_export`) that operators can copy to
  make a configuration permanent either way.
  """

  require Logger

  alias Syntropy.{ClusterInfo, EventRecorder, LLMClient, Persistence, PersistenceHealth, Usage}
  alias Syntropy.LLMClient.Config

  @provider_fields ~w(provider profile model base_url api_key timeout_ms retry_count max_tokens max_concurrency temperature top_p repeat_penalty disable_thinking)

  @clearable_fields ~w(model base_url api_key max_tokens max_concurrency temperature top_p repeat_penalty)

  @probe_timeout_ms 5_000

  @provider_setting_key "provider_overrides"

  @type provider_report :: %{
          provider: String.t(),
          profile: String.t(),
          model: String.t() | nil,
          base_url: String.t() | nil,
          api_key_configured: boolean(),
          timeout_ms: pos_integer(),
          retry_count: non_neg_integer(),
          max_tokens: pos_integer() | nil,
          max_concurrency: pos_integer() | nil,
          temperature: float() | nil,
          top_p: float() | nil,
          repeat_penalty: float() | nil,
          disable_thinking: boolean(),
          valid: boolean(),
          validation_errors: [String.t()],
          applied_scope: String.t(),
          env_export: String.t()
        }

  @doc """
  Full runtime configuration report: effective provider config plus
  persistence, cluster, and source-tool posture. Never includes secrets.
  """
  @spec report() :: map()
  def report do
    %{
      provider: provider_report(),
      persistence: persistence_posture(),
      cluster: cluster_posture(),
      source_tool: source_tool_posture(),
      limits: limits_report()
    }
  end

  @doc """
  Fair-use limits posture: the rolling token budget and its enforcement
  state.
  """
  @spec limits_report() :: map()
  def limits_report do
    %{usage_budget: Usage.budget_report()}
  end

  @doc """
  Effective provider configuration with the API key redacted, plus the env
  block that reproduces it permanently.
  """
  @spec provider_report() :: provider_report()
  def provider_report do
    LLMClient.config() |> describe()
  end

  @doc """
  Validates a candidate provider configuration and applies it to the running
  node when valid.

  Accepts a map with string keys (JSON body). Unknown keys are ignored. Keys
  that are present with `nil` or `""` clear the stored value; absent keys keep
  the current value. Records a redacted `runtime_config_updated` event on
  success.
  """
  @spec apply_provider(map()) :: {:ok, provider_report()} | {:error, [String.t()]}
  def apply_provider(params) when is_map(params) do
    current = Application.get_env(:syntropy, Syntropy.LLMClient, [])
    candidate = merge_params(current, params)
    config = Config.load(candidate)

    case Config.validate(config) do
      :ok ->
        Application.put_env(:syntropy, Syntropy.LLMClient, candidate)
        persist_provider_overrides(candidate)
        record_update(params, config)
        {:ok, describe(config)}

      {:error, errors} ->
        {:error, errors}
    end
  end

  @doc """
  Rehydrates persisted provider overrides into the Application environment.

  Runs at boot (before the endpoint and scheduler start) so an applied
  configuration survives restarts. Persisted overrides layer on top of the
  env-seeded configuration and are ignored when they no longer validate.
  """
  @spec hydrate() :: :ok
  def hydrate do
    case Persistence.get_setting(@provider_setting_key) do
      %{} = overrides ->
        current = Application.get_env(:syntropy, Syntropy.LLMClient, [])
        candidate = merge_params(current, overrides)
        config = Config.load(candidate)

        case Config.validate(config) do
          :ok ->
            Application.put_env(:syntropy, Syntropy.LLMClient, candidate)

          {:error, errors} ->
            Logger.warning("Ignoring persisted provider overrides: #{Enum.join(errors, " / ")}")
        end

      _missing ->
        :ok
    end

    :ok
  end

  @doc """
  Probes the configured provider endpoint without mutating anything.

  Accepts the same params as `apply_provider/1`, layered over the current
  configuration, so a candidate can be tested before it is applied. Mock is
  always reachable; Ollama probes `GET /tags`; OpenAI-compatible providers
  probe `GET /models` with the bearer key.
  """
  @spec test_provider(map()) :: %{
          status: String.t(),
          provider: String.t(),
          model: String.t() | nil,
          base_url: String.t() | nil,
          details: map()
        }
  def test_provider(params) when is_map(params) do
    current = Application.get_env(:syntropy, Syntropy.LLMClient, [])
    config = current |> merge_params(params) |> Config.load()

    base = %{
      provider: Config.provider_name(config),
      model: config.model,
      base_url: config.base_url
    }

    case Config.validate(config) do
      :ok ->
        Map.merge(base, probe(config))

      {:error, errors} ->
        Map.merge(base, %{status: "invalid", details: %{reasons: errors}})
    end
  end

  @doc """
  Env-var block that reproduces the given configuration across restarts.
  The API key is always redacted.
  """
  @spec env_export(Config.t()) :: String.t()
  def env_export(%Config{} = config) do
    [
      {"SYNTROPY_LLM_PROVIDER", Config.provider_name(config)},
      {"SYNTROPY_LLM_PROFILE", config.profile},
      {"SYNTROPY_LLM_MODEL", config.model},
      {"SYNTROPY_LLM_BASE_URL", config.base_url},
      {"SYNTROPY_LLM_API_KEY", if(config.api_key, do: "<your-api-key>")},
      {"SYNTROPY_LLM_TIMEOUT_MS", config.timeout_ms},
      {"SYNTROPY_LLM_RETRY_COUNT", config.retry_count},
      {"SYNTROPY_LLM_MAX_TOKENS", config.max_tokens},
      {"SYNTROPY_LLM_MAX_CONCURRENCY", config.max_concurrency},
      {"SYNTROPY_LLM_TEMPERATURE", config.temperature},
      {"SYNTROPY_LLM_TOP_P", config.top_p},
      {"SYNTROPY_LLM_REPEAT_PENALTY", config.repeat_penalty},
      {"SYNTROPY_LLM_DISABLE_THINKING", if(config.disable_thinking, do: "true")}
    ]
    |> Enum.reject(fn {_name, value} -> is_nil(value) end)
    |> Enum.map_join("\n", fn {name, value} -> "#{name}=#{value}" end)
  end

  defp persistence_posture do
    if Persistence.enabled?() do
      %{enabled: true, status: PersistenceHealth.status()}
    else
      %{enabled: false, status: "disabled"}
    end
  end

  defp cluster_posture do
    %{
      enabled: ClusterInfo.enabled?(),
      node_id: ClusterInfo.node_id(),
      node_name: ClusterInfo.node_name()
    }
  end

  defp source_tool_posture do
    inquiry_mode =
      :syntropy
      |> Application.get_env(Syntropy.SourceReview, [])
      |> Keyword.get(:inquiry_mode, "deterministic")

    %{
      enabled: Application.get_env(:syntropy, :source_tool_enabled, false),
      inquiry_mode: inquiry_mode
    }
  end

  defp describe(%Config{} = config) do
    {valid, errors} =
      case Config.validate(config) do
        :ok -> {true, []}
        {:error, errors} -> {false, errors}
      end

    %{
      provider: Config.provider_name(config),
      profile: config.profile,
      model: config.model,
      base_url: config.base_url,
      api_key_configured: is_binary(config.api_key),
      timeout_ms: config.timeout_ms,
      retry_count: config.retry_count,
      max_tokens: config.max_tokens,
      max_concurrency: config.max_concurrency,
      temperature: config.temperature,
      top_p: config.top_p,
      repeat_penalty: config.repeat_penalty,
      disable_thinking: config.disable_thinking,
      valid: valid,
      validation_errors: errors,
      applied_scope: applied_scope(),
      env_export: env_export(config)
    }
  end

  defp applied_scope do
    if Persistence.enabled?(), do: "runtime_persisted", else: "runtime_memory"
  end

  defp persist_provider_overrides(candidate) do
    overrides =
      candidate
      |> Enum.filter(fn {key, _value} -> Atom.to_string(key) in @provider_fields end)
      |> Map.new(fn {key, value} -> {Atom.to_string(key), value} end)

    @provider_setting_key
    |> Persistence.put_setting(overrides)
    |> Persistence.tolerate_write("runtime_setting_upsert")
  end

  defp merge_params(current, params) do
    Enum.reduce(@provider_fields, current, fn field, acc ->
      case Map.fetch(params, field) do
        {:ok, value} -> put_field(acc, field, value)
        :error -> acc
      end
    end)
  end

  defp put_field(config, field, value) do
    key = String.to_existing_atom(field)

    cond do
      clearable?(field, value) -> Keyword.put(config, key, nil)
      field == "disable_thinking" -> Keyword.put(config, key, value == true or value == "true")
      true -> Keyword.put(config, key, value)
    end
  end

  defp clearable?(field, value) do
    field in @clearable_fields and (is_nil(value) or value == "")
  end

  defp record_update(params, %Config{} = config) do
    EventRecorder.record("runtime_config_updated", %{
      section: "provider",
      provider: Config.provider_name(config),
      profile: config.profile,
      model: config.model,
      base_url: config.base_url,
      api_key_configured: is_binary(config.api_key),
      changed_fields:
        params |> Map.keys() |> Enum.filter(&(&1 in @provider_fields)) |> Enum.sort()
    })
  end

  defp probe(%Config{provider: :mock}) do
    %{status: "ok", details: %{note: "Mock provider is deterministic and always reachable."}}
  end

  defp probe(%Config{provider: :ollama} = config) do
    http_probe("#{config.base_url}/tags", [])
  end

  defp probe(%Config{provider: :openai} = config) do
    http_probe("#{config.base_url}/models", [{"authorization", "Bearer #{config.api_key}"}])
  end

  defp probe(%Config{}) do
    %{status: "invalid", details: %{reasons: ["Unsupported provider."]}}
  end

  defp http_probe(url, headers) do
    case Req.get(url: url, headers: headers, receive_timeout: @probe_timeout_ms, retry: false) do
      {:ok, %{status: status}} when status in 200..299 ->
        %{status: "ok", details: %{http_status: status}}

      {:ok, %{status: status}} ->
        %{status: "unreachable", details: %{http_status: status}}

      {:error, reason} ->
        %{status: "unreachable", details: %{reason: inspect(reason)}}
    end
  end
end