defmodule Symbiont.Router do
  @moduledoc """
  Task classifier — routes incoming tasks to the cheapest capable model tier.

  Uses Haiku to classify task complexity, then returns a routing decision:
    - Tier 1 (Haiku):  simple extraction, formatting, classification
    - Tier 2 (Sonnet): content writing, code gen, moderate reasoning
    - Tier 3 (Opus):   complex reasoning, strategy, full-context QA

  The classifier prompt is intentionally concise to minimize routing cost.
  """

  @type tier :: :haiku | :sonnet | :opus
  @type routing :: %{tier: tier, confidence: String.t(), reason: String.t()}

  @tier_costs %{
    haiku: 0.008,
    sonnet: 0.04,
    opus: 0.15
  }

  @classifier_prompt "You are a task complexity classifier. Analyze the task and respond with ONLY valid JSON: " <>
    ~s({"tier": 1|2|3, "confidence": "low"|"medium"|"high", "reason": "brief explanation"}\n\n) <>
    "Tier 1 (Haiku): Simple extraction, formatting, classification, short Q&A\n" <>
    "Tier 2 (Sonnet): Content writing, code generation, analysis, moderate reasoning\n" <>
    "Tier 3 (Opus): Complex multi-step reasoning, strategy, architecture, edge cases\n\n" <>
    "Task: "

  @doc "Classify a task and return the recommended tier."
  @spec classify(String.t()) :: {:ok, routing()} | {:error, term()}
  def classify(task) when is_binary(task) do
    prompt = @classifier_prompt <> task

    case Symbiont.Dispatcher.invoke(:haiku, prompt) do
      {:ok, %{result: result_text} = result} ->
        case parse_classification(result_text) do
          {:ok, classification} ->
            {:ok, Map.merge(classification, %{routing_cost: result.estimated_cost_usd})}

          {:error, _reason} ->
            # If parsing fails, default to Sonnet (safe middle ground)
            {:ok, %{tier: :sonnet, confidence: "low", reason: "classification parse failed"}}
        end

      {:error, reason} ->
        {:error, {:classifier_failed, reason}}
    end
  end

  @doc "Route and execute a task end-to-end."
  @spec route_and_execute(String.t(), keyword()) :: {:ok, map()} | {:error, term()}
  def route_and_execute(task, opts \\ []) do
    force_tier = Keyword.get(opts, :force_tier)

    tier =
      if force_tier do
        normalize_tier(force_tier)
      else
        case classify(task) do
          {:ok, %{tier: tier}} -> tier
          {:error, _} -> :sonnet
        end
      end

    Symbiont.Dispatcher.invoke(tier, task)
  end

  @doc "Return the approximate cost per call for a tier."
  @spec tier_cost(tier()) :: float()
  def tier_cost(tier), do: Map.get(@tier_costs, tier, 0.04)

  # -- Private --

  defp parse_classification(text) do
    # Extract JSON from the response (may have surrounding text)
    case Regex.run(~r/\{[^}]+\}/, text) do
      [json_str] ->
        case Jason.decode(json_str) do
          {:ok, %{"tier" => tier_num} = data} ->
            {:ok,
             %{
               tier: tier_from_number(tier_num),
               confidence: data["confidence"] || "medium",
               reason: data["reason"] || "classified"
             }}

          _ ->
            {:error, :invalid_json}
        end

      nil ->
        {:error, :no_json_found}
    end
  end

  defp tier_from_number(1), do: :haiku
  defp tier_from_number(2), do: :sonnet
  defp tier_from_number(3), do: :opus
  defp tier_from_number(_), do: :sonnet

  defp normalize_tier("haiku"), do: :haiku
  defp normalize_tier("sonnet"), do: :sonnet
  defp normalize_tier("opus"), do: :opus
  defp normalize_tier(tier) when tier in [:haiku, :sonnet, :opus], do: tier
  defp normalize_tier(_), do: :sonnet
end