defmodule Ragex.Analysis.DeadCode do
  @moduledoc """
  Dead code detection for identifying unused functions and code.

  Provides two complementary approaches:

  ## Interprocedural Analysis (Graph-based)
  Analyzes the knowledge graph to find:
  - Unused public functions (exported but never called externally)
  - Unused private functions (never called within module)
  - Functions with low confidence of being dead (potential entry points, callbacks)

  ## Intraprocedural Analysis (AST-based via Metastatic)
  Analyzes individual files for:
  - Unreachable code after early returns
  - Constant conditionals with unreachable branches
  - Other dead code patterns within function bodies

  Provides confidence scores to help distinguish between truly dead code and
  potential entry points (callbacks, GenServer handlers, etc.).
  """

  alias Metastatic.Analysis.DeadCode, as: MetaDeadCode
  alias Ragex.{Analysis.DeadCode.AIRefiner, Analysis.MetastaticBridge, Graph.Store}

  require Logger

  @type function_ref ::
          {:function, module(), atom(), non_neg_integer()}
          | %{type: :function, module: module(), name: atom(), arity: non_neg_integer()}
  @type confidence :: float()
  @type dead_function :: %{
          function: function_ref(),
          confidence: confidence(),
          reason: String.t(),
          visibility: :public | :private,
          module: module(),
          metadata: map()
        }
  @type suggestion :: %{
          type: :remove_function | :review_function | :potential_callback,
          confidence: confidence(),
          target: function_ref(),
          description: String.t(),
          metadata: map()
        }

  # Known callback patterns that should not be flagged as dead code
  @callback_patterns [
    # GenServer callbacks
    {:init, 1},
    {:handle_call, 3},
    {:handle_cast, 2},
    {:handle_info, 2},
    {:terminate, 2},
    {:code_change, 3},
    # GenStage callbacks
    {:handle_demand, 2},
    {:handle_events, 3},
    {:handle_subscribe, 4},
    {:handle_cancel, 3},
    # Supervisor callbacks
    {:start_link, 1},
    # Phoenix callbacks
    {:mount, 3},
    {:handle_event, 3},
    {:handle_params, 3},
    {:render, 1},
    # Test callbacks
    {:setup, 1},
    {:setup_all, 1},
    # Mix tasks
    {:run, 1},
    # Application callbacks
    {:start, 2},
    {:stop, 1}
  ]

  # Entry point detection patterns
  # Note: These are defined as a function to avoid Elixir 1.18 attribute escaping issues
  defp entry_point_patterns do
    [
      ~r/^main$/,
      ~r/^run$/,
      ~r/^start/,
      ~r/^handle_/,
      ~r/^mount$/,
      ~r/^render$/,
      ~r/^test_/
    ]
  end

  @doc """
  Finds unused public (exported) functions.

  Public functions with no callers are potentially dead code, but may be:
  - Entry points (main, CLI commands)
  - Callbacks (GenServer, Supervisor, Phoenix)
  - API functions not yet used
  - Test helpers

  Returns functions with confidence scores indicating likelihood of being dead.

  ## Parameters
  - `opts`: Keyword list of options
    - `:min_confidence` - Minimum confidence threshold (0.0-1.0, default: 0.5)
    - `:exclude_tests` - Exclude test modules (default: true)
    - `:include_callbacks` - Include potential callbacks (default: false)
    - `:ai_refine` - Use AI to refine confidence scores (default: from config)

  ## Returns
  - `{:ok, [dead_function]}` - List of potentially unused functions with confidence scores
  - `{:error, reason}` - Error if analysis fails

  ## Examples

      # Find unused exports with high confidence
      {:ok, dead} = find_unused_exports(min_confidence: 0.8)

      # Include potential callbacks
      {:ok, all} = find_unused_exports(include_callbacks: true, min_confidence: 0.3)
  """
  @spec find_unused_exports(keyword()) :: {:ok, [dead_function()]} | {:error, term()}
  def find_unused_exports(opts \\ []) do
    min_confidence = Keyword.get(opts, :min_confidence, 0.5)
    exclude_tests = Keyword.get(opts, :exclude_tests, true)
    include_callbacks = Keyword.get(opts, :include_callbacks, false)
    ai_refine = Keyword.get(opts, :ai_refine)

    try do
      functions = Store.list_nodes(:function, :infinity)

      dead_functions =
        functions
        |> Enum.filter(fn func ->
          public_function?(func) && should_check_module?(func, exclude_tests)
        end)
        |> Enum.map(&analyze_function/1)
        |> Enum.filter(fn result ->
          result != nil &&
            (include_callbacks || result.confidence >= min_confidence) &&
            result.confidence >= min_confidence
        end)
        |> maybe_refine_with_ai(ai_refine, opts)
        |> Enum.sort_by(& &1.confidence, :desc)

      {:ok, dead_functions}
    rescue
      e ->
        Logger.error("Failed to find unused exports: #{inspect(e)}")
        {:error, {:analysis_failed, Exception.message(e)}}
    end
  end

  @doc """
  Finds unused private functions.

  Private functions with no callers within their module are likely dead code.
  Higher confidence than public functions since private functions are not part of the API.

  ## Parameters
  - `opts`: Keyword list of options
    - `:min_confidence` - Minimum confidence threshold (default: 0.7)
    - `:exclude_tests` - Exclude test modules (default: true)
    - `:ai_refine` - Use AI to refine confidence scores (default: from config)

  ## Returns
  - `{:ok, [dead_function]}` - List of unused private functions
  - `{:error, reason}` - Error if analysis fails

  ## Examples

      {:ok, dead} = find_unused_private()
  """
  @spec find_unused_private(keyword()) :: {:ok, [dead_function()]} | {:error, term()}
  def find_unused_private(opts \\ []) do
    min_confidence = Keyword.get(opts, :min_confidence, 0.7)
    exclude_tests = Keyword.get(opts, :exclude_tests, true)
    ai_refine = Keyword.get(opts, :ai_refine)

    try do
      functions = Store.list_nodes(:function, :infinity)

      dead_functions =
        functions
        |> Enum.filter(fn func ->
          private_function?(func) && should_check_module?(func, exclude_tests)
        end)
        |> Enum.map(&analyze_function/1)
        |> Enum.filter(fn result ->
          result != nil && result.confidence >= min_confidence
        end)
        |> maybe_refine_with_ai(ai_refine, opts)
        |> Enum.sort_by(& &1.confidence, :desc)

      {:ok, dead_functions}
    rescue
      e ->
        Logger.error("Failed to find unused private functions: #{inspect(e)}")
        {:error, {:analysis_failed, Exception.message(e)}}
    end
  end

  @doc """
  Finds all unused functions (both public and private).

  Combines results from `find_unused_exports/1` and `find_unused_private/1`.

  ## Parameters
  - `opts`: Keyword list of options (same as individual functions)

  ## Returns
  - `{:ok, [dead_function]}` - Combined list of unused functions

  ## Examples

      {:ok, all_dead} = find_all_unused(min_confidence: 0.6)
  """
  @spec find_all_unused(keyword()) :: {:ok, [dead_function()]} | {:error, term()}
  def find_all_unused(opts \\ []) do
    with {:ok, exports} <- find_unused_exports(opts),
         {:ok, private} <- find_unused_private(opts) do
      all = (exports ++ private) |> Enum.sort_by(& &1.confidence, :desc)
      {:ok, all}
    end
  end

  @doc """
  Finds unused functions within a specific module.

  Analyzes all functions (public and private) in the specified module to identify
  potentially dead code. This is useful for focused refactoring of a single module.

  ## Parameters
  - `module`: Module name atom
  - `opts`: Keyword list of options
    - `:min_confidence` - Minimum confidence threshold (default: 0.5)
    - `:include_callbacks` - Include potential callbacks (default: false)
    - `:visibility` - Filter by `:public`, `:private`, or `:all` (default: `:all`)

  ## Returns
  - `{:ok, [dead_function]}` - List of unused functions in the module
  - `{:error, reason}` - Error if module not found or analysis fails

  ## Examples

      # Find all dead code in MyModule
      {:ok, dead} = find_in_module(MyModule)

      # Find only dead private functions with high confidence
      {:ok, dead_private} = find_in_module(MyModule, visibility: :private, min_confidence: 0.8)

      # Include potential callbacks
      {:ok, all} = find_in_module(MyModule, include_callbacks: true, min_confidence: 0.3)
  """
  @spec find_in_module(module(), keyword()) :: {:ok, [dead_function()]} | {:error, term()}
  def find_in_module(module, opts \\ []) do
    min_confidence = Keyword.get(opts, :min_confidence, 0.5)
    include_callbacks = Keyword.get(opts, :include_callbacks, false)
    visibility_filter = Keyword.get(opts, :visibility, :all)

    # Verify module exists
    case Store.find_node(:module, module) do
      nil ->
        {:error, {:module_not_found, module}}

      _node ->
        try do
          # Get all functions in the module
          functions =
            Store.list_nodes(:function, :infinity)
            |> Enum.filter(fn %{id: {mod, _name, _arity}} -> mod == module end)

          # Filter by visibility if specified
          functions =
            case visibility_filter do
              :public -> Enum.filter(functions, &public_function?/1)
              :private -> Enum.filter(functions, &private_function?/1)
              :all -> functions
              _ -> functions
            end

          # Analyze each function
          dead_functions =
            functions
            |> Enum.map(&analyze_function/1)
            |> Enum.filter(fn result ->
              result != nil &&
                (include_callbacks || result.confidence >= min_confidence) &&
                result.confidence >= min_confidence
            end)
            |> Enum.sort_by(& &1.confidence, :desc)

          {:ok, dead_functions}
        rescue
          e ->
            Logger.error("Failed to find dead code in module #{module}: #{inspect(e)}")
            {:error, {:analysis_failed, Exception.message(e)}}
        end
    end
  end

  @doc """
  Analyzes a file for intraprocedural dead code patterns.

  Uses Metastatic's AST-level analysis to detect:
  - Unreachable code after early returns
  - Constant conditionals (if true/false) with unreachable branches
  - Other dead code patterns within function bodies

  This is complementary to the interprocedural analysis (`find_unused_exports/1`, etc.)
  which detects unused functions based on the call graph.

  ## Parameters
  - `file_path` - Path to the file to analyze
  - `opts` - Keyword list of options
    - `:min_confidence` - Minimum confidence level (`:high`, `:medium`, `:low`, default: `:low`)

  ## Returns
  - `{:ok, result}` - Metastatic.Analysis.DeadCode.Result struct
  - `{:error, reason}` - Error if analysis fails

  ## Examples

      iex> {:ok, result} = analyze_file("lib/my_module.ex")
      iex> result.has_dead_code?
      true
  """
  @spec analyze_file(String.t(), keyword()) ::
          {:ok, Metastatic.Analysis.DeadCode.Result.t()} | {:error, term()}
  def analyze_file(file_path, opts \\ []) do
    min_confidence = Keyword.get(opts, :min_confidence, :low)

    case MetastaticBridge.parse_file(file_path) do
      {:ok, document} ->
        # Use Metastatic's dead code analysis
        MetaDeadCode.analyze(document, min_confidence: min_confidence)

      {:error, reason} ->
        Logger.warning("Failed to parse file #{file_path}: #{inspect(reason)}")
        {:error, reason}
    end
  end

  @doc """
  Analyzes multiple files for intraprocedural dead code patterns.

  Batch version of `analyze_file/2` that processes multiple files in parallel.

  ## Parameters
  - `file_paths` - List of file paths to analyze
  - `opts` - Keyword list of options (same as `analyze_file/2`)

  ## Returns
  - `{:ok, results_map}` - Map of file_path => result
  - `{:error, reason}` - Error if analysis fails

  ## Examples

      iex> {:ok, results} = analyze_files(["lib/a.ex", "lib/b.ex"])
      iex> is_map(results)
      true
  """
  @spec analyze_files([String.t()], keyword()) :: {:ok, %{String.t() => any()}} | {:error, term()}
  def analyze_files(file_paths, opts \\ []) when is_list(file_paths) do
    results =
      file_paths
      |> Task.async_stream(
        fn path ->
          case analyze_file(path, opts) do
            {:ok, result} -> {path, result}
            {:error, reason} -> {path, {:error, reason}}
          end
        end,
        max_concurrency: System.schedulers_online() * 2,
        timeout: 30_000
      )
      |> Enum.map(fn {:ok, result} -> result end)
      |> Map.new()

    {:ok, results}
  rescue
    e ->
      Logger.error("Failed to analyze files: #{inspect(e)}")
      {:error, {:analysis_failed, Exception.message(e)}}
  end

  @doc """
  Finds unused modules (modules with no external references).

  Delegates to `DependencyGraph.find_unused/1` for consistency.

  ## Parameters
  - `opts`: Keyword list of options (passed to DependencyGraph)

  ## Returns
  - `{:ok, [module_name]}` - List of unused modules
  - `{:error, reason}` - Error if analysis fails
  """
  @spec find_unused_modules(keyword()) :: {:ok, [module()]} | {:error, term()}
  def find_unused_modules(opts \\ []) do
    # Delegate to DependencyGraph for consistency
    alias Ragex.Analysis.DependencyGraph
    DependencyGraph.find_unused(opts)
  end

  @doc """
  Generates removal suggestions based on dead code analysis.

  Categorizes dead code into:
  - Safe to remove (high confidence)
  - Review recommended (medium confidence)
  - Potential callbacks (low confidence, may be entry points)

  ## Parameters
  - `opts`: Keyword list of options
    - `:min_confidence` - Minimum confidence for suggestions (default: 0.5)
    - `:group_by_module` - Group suggestions by module (default: true)

  ## Returns
  - `{:ok, [suggestion]}` - List of removal suggestions
  - `{:error, reason}` - Error if analysis fails

  ## Examples

      {:ok, suggestions} = removal_suggestions()
      # Process suggestions...
  """
  @spec removal_suggestions(keyword()) :: {:ok, [suggestion()]} | {:error, term()}
  def removal_suggestions(opts \\ []) do
    min_confidence = Keyword.get(opts, :min_confidence, 0.5)
    group_by_module = Keyword.get(opts, :group_by_module, true)

    with {:ok, dead_functions} <- find_all_unused(opts) do
      suggestions =
        dead_functions
        |> Enum.map(&create_suggestion/1)
        |> Enum.filter(fn s -> s.confidence >= min_confidence end)

      suggestions =
        if group_by_module do
          suggestions
          |> Enum.group_by(fn s -> extract_module(s.target) end)
          |> Enum.flat_map(fn {_module, module_suggestions} ->
            if length(module_suggestions) > 1 do
              # Create a summary suggestion for the module
              create_module_summary_suggestion(module_suggestions)
            else
              module_suggestions
            end
          end)
        else
          suggestions
        end

      {:ok, suggestions}
    end
  end

  @doc """
  Calculates a confidence score for dead code detection.

  Takes into account:
  - Function name patterns (callbacks, entry points)
  - Visibility (public vs private)
  - Number of callers
  - Module characteristics (test, Mix task, etc.)

  ## Returns
  - Float between 0.0 (definitely not dead) and 1.0 (definitely dead)
  """
  @spec confidence_score(function_ref(), map()) :: confidence()
  def confidence_score(func_ref, metadata) do
    {module, name, arity} = extract_func_parts(func_ref)

    # Base confidence based on callers
    caller_count = count_callers(func_ref)
    base_confidence = if caller_count == 0, do: 1.0, else: 0.0

    # Adjust for visibility
    visibility = Map.get(metadata, :visibility, :public)
    visibility_modifier = if visibility == :private, do: 0.0, else: -0.2

    # Adjust for callback patterns
    callback_modifier =
      if callback_pattern?(name, arity) do
        -0.7
      else
        0.0
      end

    # Adjust for entry point patterns
    entry_point_modifier =
      if entry_point_pattern?(name) do
        -0.5
      else
        0.0
      end

    # Adjust for module type
    module_modifier =
      cond do
        test_module?(module) -> -0.3
        mix_task?(module) -> -0.4
        true -> 0.0
      end

    # Calculate final confidence
    confidence =
      base_confidence + visibility_modifier + callback_modifier + entry_point_modifier +
        module_modifier

    # Clamp to [0.0, 1.0]
    max(0.0, min(1.0, confidence))
  end

  # Private functions

  # Analyze a function to determine if it's dead code
  defp analyze_function(%{id: {module, name, arity}, data: metadata}) do
    # func_ref = {:function, module, name, arity}
    func_ref = %{type: :function, module: module, name: name, arity: arity}
    caller_count = count_callers(func_ref)

    if caller_count == 0 do
      confidence = confidence_score(func_ref, metadata)
      visibility = Map.get(metadata, :visibility, :public)

      reason =
        cond do
          confidence > 0.8 -> "No callers found, likely dead code"
          confidence > 0.5 -> "No callers found, but may be entry point or callback"
          true -> "Potential callback or entry point with no callers"
        end

      %{
        function: func_ref,
        confidence: confidence,
        reason: reason,
        visibility: visibility,
        module: module,
        metadata: metadata
      }
    else
      nil
    end
  end

  # Count the number of callers for a function
  defp count_callers(func_ref) do
    # Convert to tuple format for Store lookup
    {module, name, arity} = extract_func_parts(func_ref)
    tuple_ref = {:function, module, name, arity}

    Store.get_incoming_edges(tuple_ref, :calls)
    |> length()
  end

  # Check if function is public
  defp public_function?(%{data: metadata}) do
    Map.get(metadata, :visibility, :public) == :public
  end

  # Check if function is private
  defp private_function?(%{data: metadata}) do
    Map.get(metadata, :visibility, :public) == :private
  end

  # Check if we should analyze this module
  defp should_check_module?(%{id: {module, _name, _arity}}, exclude_tests) do
    if exclude_tests do
      !test_module?(module)
    else
      true
    end
  end

  # Check if function matches callback patterns
  defp callback_pattern?(name, arity) do
    {name, arity} in @callback_patterns
  end

  # Check if function name matches entry point patterns
  defp entry_point_pattern?(name) do
    name_str = Atom.to_string(name)

    Enum.any?(entry_point_patterns(), fn pattern ->
      Regex.match?(pattern, name_str)
    end)
  end

  # Check if module is a test module
  defp test_module?(module) do
    module_str = to_string(module)
    String.ends_with?(module_str, "Test") || String.contains?(module_str, ".Test.")
  end

  # Check if module is a Mix task
  defp mix_task?(module) do
    module_str = to_string(module)
    String.starts_with?(module_str, "Mix.Tasks.")
  end

  # Extract module, name, arity from function reference
  defp extract_func_parts({:function, module, name, arity}), do: {module, name, arity}

  defp extract_func_parts(%{type: :function, module: module, name: name, arity: arity}),
    do: {module, name, arity}

  # Create a suggestion from a dead function
  defp create_suggestion(%{function: func_ref, confidence: confidence} = dead_func) do
    {module, name, arity} = extract_func_parts(func_ref)

    {type, description} =
      cond do
        confidence > 0.8 ->
          {:remove_function,
           "Function #{module}.#{name}/#{arity} appears to be dead code and can be removed"}

        confidence > 0.5 ->
          {:review_function,
           "Function #{module}.#{name}/#{arity} has no callers - review whether it's still needed"}

        true ->
          {:potential_callback,
           "Function #{module}.#{name}/#{arity} may be a callback or entry point - verify before removing"}
      end

    %{
      type: type,
      confidence: confidence,
      target: func_ref,
      description: description,
      metadata: Map.get(dead_func, :metadata, %{})
    }
  end

  # Extract module from function reference
  defp extract_module({:function, module, _name, _arity}), do: module
  defp extract_module(%{type: :function, module: module}), do: module
  defp extract_module({:module, module}), do: module

  # Conditionally refine confidence scores with AI
  defp maybe_refine_with_ai(dead_functions, ai_refine, opts) do
    # Only use AI if explicitly enabled or if config enables it
    use_ai =
      case ai_refine do
        true -> true
        false -> false
        nil -> AIRefiner.enabled?(opts)
      end

    if use_ai && !Enum.empty?(dead_functions) do
      Logger.info("Refining #{length(dead_functions)} dead code results with AI")

      case AIRefiner.refine_batch(dead_functions, opts) do
        {:ok, refined} ->
          Logger.info("AI refinement complete")
          refined

          # {:error, reason} ->
          #   Logger.warning("AI refinement failed: #{inspect(reason)}, using original results")
          #   dead_functions
      end
    else
      dead_functions
    end
  end

  # Create a module-level summary suggestion
  defp create_module_summary_suggestion(module_suggestions) do
    module = extract_module(List.first(module_suggestions).target)

    avg_confidence =
      Enum.sum(Enum.map(module_suggestions, & &1.confidence)) / length(module_suggestions)

    function_count = length(module_suggestions)

    high_confidence = Enum.count(module_suggestions, fn s -> s.confidence > 0.8 end)

    medium_confidence =
      Enum.count(module_suggestions, fn s -> s.confidence > 0.5 && s.confidence <= 0.8 end)

    low_confidence = Enum.count(module_suggestions, fn s -> s.confidence <= 0.5 end)

    description =
      """
      Module #{module} has #{function_count} potentially unused functions:
      - #{high_confidence} with high confidence (can be removed)
      - #{medium_confidence} requiring review
      - #{low_confidence} potential callbacks/entry points
      """
      |> String.trim()

    [
      %{
        type: :review_function,
        confidence: avg_confidence,
        target: {:module, module},
        description: description,
        metadata: %{
          function_count: function_count,
          functions: Enum.map(module_suggestions, & &1.target),
          breakdown: %{
            high_confidence: high_confidence,
            medium_confidence: medium_confidence,
            low_confidence: low_confidence
          }
        }
      }
    ]
  end

  @doc """
  Finds all dead code in the knowledge graph.

  Convenience function combining unused exports and private functions.

  ## Examples

      {:ok, dead_functions} = DeadCode.find_dead_code()
  """
  @spec find_dead_code() :: {:ok, [map()]} | {:error, term()}
  def find_dead_code do
    with {:ok, exports} <- find_unused_exports(),
         {:ok, private} <- find_unused_private() do
      {:ok, exports ++ private}
    end
  end
end