defmodule Yog.Render.DOT do
  @moduledoc """
  DOT (Graphviz) format export for visualizing graphs.

  This module exports graphs to the [DOT language](https://graphviz.org/doc/info/lang.html),
  which is the native format for [Graphviz](https://graphviz.org/) - a powerful open-source
  graph visualization tool. The exported files can be rendered to PNG, SVG, PDF, and other
  formats using the `dot`, `neato`, `circo`, or other Graphviz layout engines.

  ## Quick Start

      # Export with default styling
      dot_string = Yog.Render.DOT.to_dot(my_graph, Yog.Render.DOT.default_options())

      # Write to file and render with Graphviz CLI
      # $ dot -Tpng output.dot -o graph.png

  ## Customization

  Use `t:options/0` to customize:
  - Node labels and shapes
  - Edge labels and styles
  - **Per-node and per-edge attributes** (custom colors, shapes, etc.)
  - **Subgraphs/clusters** for visual grouping
  - Highlight specific nodes or paths
  - Graph direction (LR, TB, etc.)

  ## Generic Data Types

  The `to_dot` function works with any node and edge data types. Use
  `default_options_with_edge_formatter/1` when your edge data is not a String.

  ## Per-Element Styling

  Provide custom attribute functions for fine-grained control:

      options = %{
        Yog.Render.DOT.default_options() |
        node_attributes: fn id, data ->
          case id do
            1 -> [{:fillcolor, "green"}, {:shape, "diamond"}]
            _ -> []
          end
        end,
        edge_attributes: fn from, to, weight ->
          if weight > 10 do
            [{:color, "red"}, {:penwidth, 2}]
          else
            []
          end
        end
      }

  ## Subgraphs and Clusters

  Group nodes visually using subgraphs:

      options = %{
        Yog.Render.DOT.default_options() |
        subgraphs: [
          %{
            name: "cluster_0",
            label: "Cluster A",
            node_ids: [1, 2, 3],
            style: :filled,
            fillcolor: "lightgrey",
            color: nil
          }
        ]
      }

  ## Rendering Options

  | Engine | Best For |
  |--------|----------|
  | `dot` | Hierarchical layouts (DAGs, trees) |
  | `neato` | Spring-based layouts (undirected) |
  | `circo` | Circular layouts |
  | `fdp` | Force-directed layouts |
  | `sfdp` | Large graphs |

  ## References

  - [Graphviz Documentation](https://graphviz.org/documentation/)
  - [DOT Language Guide](https://graphviz.org/doc/info/lang.html)
  - [Node Shapes](https://graphviz.org/doc/info/shapes.html)
  - [Arrow Styles](https://graphviz.org/doc/info/arrows.html)
  - [Cluster/Subgraph Syntax](https://graphviz.org/docs/attrs/cluster/)

  > **Migration Note:** Enhanced in v0.53.0 with full Gleam parity: subgraphs,
  > per-element attributes, layout engines, advanced styling options.
  """

  # =============================================================================
  # TYPES
  # =============================================================================

  @typedoc "Graphviz layout engine"
  @type layout ::
          :dot
          | :neato
          | :circo
          | :fdp
          | :sfdp
          | :twopi
          | :osage
          | {:custom, String.t()}

  @typedoc "Graph direction (rank direction)"
  @type rank_dir :: :tb | :lr | :bt | :rl

  @typedoc "Node shapes"
  @type node_shape ::
          :box
          | :circle
          | :ellipse
          | :diamond
          | :hexagon
          | :pentagon
          | :octagon
          | :triangle
          | :rectangle
          | :square
          | :rect
          | :invtriangle
          | :house
          | :invhouse
          | :parallelogram
          | :trapezoid
          | {:custom, String.t()}

  @typedoc "Visual style"
  @type style ::
          :solid
          | :dashed
          | :dotted
          | :bold
          | :filled
          | :rounded
          | :diagonals
          | :striped
          | :wedged

  @typedoc "Edge routing style"
  @type splines :: :line | :polyline | :curved | :ortho | :spline | :none

  @typedoc "Arrow head/tail style"
  @type arrow_style ::
          :normal
          | :dot
          | :diamond
          | :odiamond
          | :box
          | :crow
          | :vee
          | :inv
          | :tee
          | :none
          | {:custom, String.t()}

  @typedoc "Overlap handling"
  @type overlap :: true | false | :scale | :scalexy | :prism | {:custom, String.t()}

  @typedoc """
  A subgraph (cluster) for grouping nodes visually in the diagram.

  In Graphviz, subgraphs with names starting with "cluster_" are rendered
  as bounded rectangles around the contained nodes.
  """
  @type subgraph :: %{
          name: String.t(),
          label: String.t() | nil,
          node_ids: [Yog.node_id()],
          style: style() | nil,
          fillcolor: String.t() | nil,
          color: String.t() | nil
        }

  @typedoc "Options for customizing DOT (Graphviz) diagram rendering"
  @type options :: %{
          node_label: (Yog.node_id(), any() -> String.t()),
          edge_label: (any() -> String.t()),
          highlighted_nodes: [Yog.node_id()] | nil,
          highlighted_edges: [{Yog.node_id(), Yog.node_id()}] | nil,
          # Per-element styling
          node_attributes: (Yog.node_id(), any() -> [{atom(), String.t()}]),
          edge_attributes: (Yog.node_id(), Yog.node_id(), any() -> [{atom(), String.t()}]),
          # Subgraphs
          subgraphs: [subgraph()] | nil,
          # Graph-level attributes
          graph_name: String.t(),
          layout: layout() | nil,
          rankdir: rank_dir() | nil,
          bgcolor: String.t() | nil,
          splines: splines() | nil,
          overlap: overlap() | nil,
          nodesep: float() | nil,
          ranksep: float() | nil,
          # Node styling
          node_shape: node_shape(),
          node_color: String.t(),
          node_style: style(),
          node_fontname: String.t(),
          node_fontsize: integer(),
          node_fontcolor: String.t(),
          # Edge styling
          edge_color: String.t(),
          edge_style: style(),
          edge_fontname: String.t(),
          edge_fontsize: integer(),
          edge_penwidth: float(),
          arrowhead: arrow_style() | nil,
          arrowtail: arrow_style() | nil,
          # Highlighting
          highlight_color: String.t(),
          highlight_penwidth: float()
        }

  @doc """
  Creates default DOT options with simple labeling and sensible styling.

  Default configuration:
  - Layout: Auto-detected by Graphviz
  - Direction: Top-to-bottom
  - Node shape: Ellipse
  - Colors: Light blue nodes, black edges
  - Font: Helvetica 12pt

  ## Examples

      iex> opts = Yog.Render.DOT.default_options()
      iex> opts.graph_name
      "G"
      iex> opts.node_shape
      :ellipse
      iex> opts.node_color
      "lightblue"
  """
  @spec default_options() :: options()
  def default_options do
    %{
      node_label: fn id, _data -> Integer.to_string(id) end,
      edge_label: fn weight -> to_string(weight) end,
      highlighted_nodes: nil,
      highlighted_edges: nil,
      # Per-element styling defaults
      node_attributes: fn _, _ -> [] end,
      edge_attributes: fn _, _, _ -> [] end,
      # Subgraphs default to none
      subgraphs: nil,
      # Graph-level
      graph_name: "G",
      layout: nil,
      rankdir: :tb,
      bgcolor: nil,
      splines: nil,
      overlap: nil,
      nodesep: nil,
      ranksep: nil,
      # Node styling
      node_shape: :ellipse,
      node_color: "lightblue",
      node_style: :filled,
      node_fontname: "Helvetica",
      node_fontsize: 12,
      node_fontcolor: "black",
      # Edge styling
      edge_color: "black",
      edge_style: :solid,
      edge_fontname: "Helvetica",
      edge_fontsize: 10,
      edge_penwidth: 1.0,
      arrowhead: nil,
      arrowtail: nil,
      # Highlighting
      highlight_color: "red",
      highlight_penwidth: 2.0
    }
  end

  @doc """
  Creates default DOT options with a custom edge formatter.

  Use this when your graph has non-String edge data (e.g., Int, Float, custom types).

  ## Example

      # For a graph with Int edge weights
      options = Yog.Render.DOT.default_options_with_edge_formatter(fn weight ->
        Integer.to_string(weight)
      end)
  """
  @spec default_options_with_edge_formatter((any() -> String.t())) :: options()
  def default_options_with_edge_formatter(edge_formatter) do
    %{default_options() | edge_label: edge_formatter}
  end

  @doc """
  Creates default DOT options with custom label formatters for both nodes and edges.

  ## Example

      options = Yog.Render.DOT.default_options_with(
        node_label: fn id, data -> "\#{data} (\#{id})" end,
        edge_label: fn weight -> "\#{weight} ms" end
      )
  """
  @spec default_options_with(
          node_label: (Yog.node_id(), any() -> String.t()),
          edge_label: (any() -> String.t())
        ) :: options()
  def default_options_with(node_label: node_label, edge_label: edge_label) do
    %{default_options() | node_label: node_label, edge_label: edge_label}
  end

  @doc """
  Converts a graph to DOT (Graphviz) syntax.

  Works with any node data type and edge data type. Use the options
  to customize labels, styling, and to define subgraphs.

  **Time Complexity:** O(V + E + S) where S is the total number of nodes
  across all subgraphs.

  ## Example

      graph =
        Yog.directed()
        |> Yog.add_node(1, "Start")
        |> Yog.add_node(2, "Process")
        |> Yog.add_edge!(from: 1, to: 2, with: "5")

      diagram = Yog.Render.DOT.to_dot(graph, Yog.Render.DOT.default_options())
  """
  @spec to_dot(Yog.graph(), options()) :: String.t()
  def to_dot(graph, options) do
    nodes = extract_nodes(graph)
    edges = extract_edges(graph)
    kind = extract_kind(graph)

    {graph_type, arrow} =
      if kind == :directed do
        {"digraph", "->"}
      else
        {"graph", "--"}
      end

    header = "#{graph_type} #{options.graph_name} {\n"
    graph_attrs = build_graph_attrs(options)
    node_defaults = build_node_defaults(options)
    edge_defaults = build_edge_defaults(options)

    # Generate nodes with per-element attributes
    nodes_str = build_node_lines(nodes, options)

    # Generate subgraphs
    subgraphs_str = build_subgraphs(options.subgraphs)

    # Generate edges with per-element attributes
    edges_str = build_edge_lines(edges, options, arrow, kind)

    # Combine all parts
    [
      header,
      graph_attrs,
      node_defaults,
      edge_defaults,
      "\n",
      nodes_str,
      "\n",
      subgraphs_str,
      edges_str,
      "\n}"
    ]
    |> Enum.reject(&(&1 == ""))
    |> Enum.join("")
  end

  @doc """
  Converts a shortest path result to highlighted DOT options.

  Creates a copy of the base options with the path's nodes and edges
  set to be highlighted. This is useful for visualizing algorithm results.

  ## Example

      case Yog.Pathfinding.Dijkstra.shortest_path(...) do
        {:some, path} ->
          options = Yog.Render.DOT.path_to_options(path, Yog.Render.DOT.default_options())
          dot_string = Yog.Render.DOT.to_dot(graph, options)
        :none ->
          ""
      end
  """
  @spec path_to_options(map(), options()) :: options()
  def path_to_options(path, base_options) do
    nodes = Map.get(path, :nodes, [])
    edges = path_to_edges(nodes)

    %{base_options | highlighted_nodes: nodes, highlighted_edges: edges}
  end

  # =============================================================================
  # PRIVATE HELPERS
  # =============================================================================

  defp extract_nodes(graph) do
    case graph do
      %{nodes: n} when is_map(n) -> n
      _ -> %{}
    end
  end

  defp extract_edges(graph) do
    case graph do
      %{out_edges: e} when is_map(e) -> e
      _ -> %{}
    end
  end

  defp extract_kind(graph) do
    case graph do
      %{kind: k} -> k
      _ -> :directed
    end
  end

  defp build_graph_attrs(options) do
    attrs =
      [
        options.layout && "layout=#{layout_to_string(options.layout)}",
        options.rankdir && "rankdir=#{rankdir_to_string(options.rankdir)}",
        options.bgcolor && "bgcolor=\"#{options.bgcolor}\"",
        options.splines && "splines=#{splines_to_string(options.splines)}",
        options.overlap && "overlap=#{overlap_to_string(options.overlap)}",
        options.nodesep && "nodesep=#{options.nodesep}",
        options.ranksep && "ranksep=#{options.ranksep}"
      ]
      |> Enum.reject(&is_nil/1)

    if attrs != [] do
      "  graph [#{Enum.join(attrs, ", ")}];\n"
    else
      ""
    end
  end

  defp build_node_defaults(options) do
    attrs = [
      "shape=#{node_shape_to_string(options.node_shape)}",
      "style=#{style_to_string(options.node_style)}",
      "fillcolor=\"#{options.node_color}\"",
      "fontname=\"#{options.node_fontname}\"",
      "fontsize=#{options.node_fontsize}",
      "fontcolor=\"#{options.node_fontcolor}\""
    ]

    "  node [#{Enum.join(attrs, ", ")}];\n"
  end

  defp build_edge_defaults(options) do
    base_attrs = [
      "color=\"#{options.edge_color}\"",
      "style=#{style_to_string(options.edge_style)}",
      "fontname=\"#{options.edge_fontname}\"",
      "fontsize=#{options.edge_fontsize}",
      "penwidth=#{options.edge_penwidth}"
    ]

    attrs =
      case {options.arrowhead, options.arrowtail} do
        {nil, nil} ->
          base_attrs

        {head, nil} ->
          ["arrowhead=#{arrow_style_to_string(head)}" | base_attrs]

        {nil, tail} ->
          ["arrowtail=#{arrow_style_to_string(tail)}" | base_attrs]

        {head, tail} ->
          [
            "arrowhead=#{arrow_style_to_string(head)}",
            "arrowtail=#{arrow_style_to_string(tail)}" | base_attrs
          ]
      end

    "  edge [#{Enum.join(attrs, ", ")}];\n"
  end

  defp build_node_lines(nodes, options) do
    Enum.map_join(nodes, "", fn {id, data} ->
      label = options.node_label.(id, data)
      id_str = Integer.to_string(id)

      # Build attribute list starting with label
      attrs = [{:label, label}]

      # Add highlighting if applicable
      attrs =
        if options.highlighted_nodes && id in options.highlighted_nodes do
          [{:fillcolor, options.highlight_color} | attrs]
        else
          attrs
        end

      # Merge custom attributes (these override highlighting and defaults)
      custom_attrs = options.node_attributes.(id, data)
      attrs = merge_attributes_list(attrs, custom_attrs)

      # Format attributes
      attr_str = format_attributes_list(attrs)

      "  #{id_str} [#{attr_str}];\n"
    end)
  end

  defp build_subgraphs(nil), do: ""

  defp build_subgraphs(subgraph_list) do
    Enum.map_join(subgraph_list, "", fn sub ->
      header = "  subgraph #{sub.name} {\n"

      label =
        if sub.label do
          "    label=\"#{sub.label}\";\n"
        else
          ""
        end

      style =
        if sub.style do
          "    style=#{style_to_string(sub.style)};\n"
        else
          ""
        end

      fillcolor =
        if sub.fillcolor do
          "    fillcolor=\"#{sub.fillcolor}\";\n"
        else
          ""
        end

      color =
        if sub.color do
          "    color=\"#{sub.color}\";\n"
        else
          ""
        end

      node_list =
        case sub.node_ids do
          [] ->
            ""

          ids ->
            Enum.map_join(ids, ";\n", &("    " <> Integer.to_string(&1))) <> ";\n"
        end

      header <> label <> style <> fillcolor <> color <> node_list <> "  }\n"
    end)
  end

  defp build_edge_lines(edges, options, arrow, kind) do
    edges
    |> Enum.flat_map(fn {from_id, targets} ->
      targets
      |> Enum.filter(fn {to_id, _weight} ->
        # Handle undirected deduplication
        case kind do
          :undirected -> from_id <= to_id
          :directed -> true
        end
      end)
      |> Enum.map(fn {to_id, weight} ->
        # Build attribute list starting with label
        label = options.edge_label.(weight)
        attrs = [{:label, label}]

        # Add highlighting if applicable
        is_highlighted =
          options.highlighted_edges &&
            ({from_id, to_id} in options.highlighted_edges ||
               {to_id, from_id} in options.highlighted_edges)

        attrs =
          if is_highlighted do
            [
              {:penwidth, options.highlight_penwidth},
              {:color, options.highlight_color} | attrs
            ]
          else
            attrs
          end

        # Merge custom attributes (these override highlighting)
        custom_attrs = options.edge_attributes.(from_id, to_id, weight)
        attrs = merge_attributes_list(attrs, custom_attrs)

        # Format attributes
        attr_str = format_attributes_list(attrs)

        "  #{from_id} #{arrow} #{to_id} [#{attr_str}];\n"
      end)
    end)
    |> Enum.join("")
  end

  # Merge two attribute lists, with override taking precedence
  defp merge_attributes_list(base, override) do
    Enum.reduce(override, base, fn pair, acc ->
      filtered = Enum.reject(acc, fn existing -> elem(existing, 0) == elem(pair, 0) end)
      [pair | filtered]
    end)
  end

  # Format a list of attributes as key="value", key2="value2"
  defp format_attributes_list(attrs) do
    attrs
    |> Enum.reverse()
    |> Enum.map_join(", ", fn {key, value} -> "#{key}=\"#{value}\"" end)
  end

  # Helper to convert a list of nodes to a list of edges
  defp path_to_edges([]), do: []
  defp path_to_edges([_]), do: []

  defp path_to_edges([first, second | rest]) do
    [{first, second} | path_to_edges([second | rest])]
  end

  # =============================================================================
  # ENUM TO STRING CONVERSIONS
  # =============================================================================

  defp layout_to_string(:dot), do: "dot"
  defp layout_to_string(:neato), do: "neato"
  defp layout_to_string(:circo), do: "circo"
  defp layout_to_string(:fdp), do: "fdp"
  defp layout_to_string(:sfdp), do: "sfdp"
  defp layout_to_string(:twopi), do: "twopi"
  defp layout_to_string(:osage), do: "osage"
  defp layout_to_string({:custom, s}), do: s

  defp rankdir_to_string(:tb), do: "TB"
  defp rankdir_to_string(:lr), do: "LR"
  defp rankdir_to_string(:bt), do: "BT"
  defp rankdir_to_string(:rl), do: "RL"

  defp node_shape_to_string(:box), do: "box"
  defp node_shape_to_string(:circle), do: "circle"
  defp node_shape_to_string(:ellipse), do: "ellipse"
  defp node_shape_to_string(:diamond), do: "diamond"
  defp node_shape_to_string(:hexagon), do: "hexagon"
  defp node_shape_to_string(:pentagon), do: "pentagon"
  defp node_shape_to_string(:octagon), do: "octagon"
  defp node_shape_to_string(:triangle), do: "triangle"
  defp node_shape_to_string(:rectangle), do: "rectangle"
  defp node_shape_to_string(:square), do: "square"
  defp node_shape_to_string(:rect), do: "rect"
  defp node_shape_to_string(:invtriangle), do: "invtriangle"
  defp node_shape_to_string(:house), do: "house"
  defp node_shape_to_string(:invhouse), do: "invhouse"
  defp node_shape_to_string(:parallelogram), do: "parallelogram"
  defp node_shape_to_string(:trapezoid), do: "trapezoid"
  defp node_shape_to_string({:custom, s}), do: s

  defp style_to_string(:solid), do: "solid"
  defp style_to_string(:dashed), do: "dashed"
  defp style_to_string(:dotted), do: "dotted"
  defp style_to_string(:bold), do: "bold"
  defp style_to_string(:filled), do: "filled"
  defp style_to_string(:rounded), do: "rounded"
  defp style_to_string(:diagonals), do: "diagonals"
  defp style_to_string(:striped), do: "striped"
  defp style_to_string(:wedged), do: "wedged"

  defp splines_to_string(:line), do: "line"
  defp splines_to_string(:polyline), do: "polyline"
  defp splines_to_string(:curved), do: "curved"
  defp splines_to_string(:ortho), do: "ortho"
  defp splines_to_string(:spline), do: "spline"
  defp splines_to_string(:none), do: "none"

  defp arrow_style_to_string(:normal), do: "normal"
  defp arrow_style_to_string(:dot), do: "dot"
  defp arrow_style_to_string(:diamond), do: "diamond"
  defp arrow_style_to_string(:odiamond), do: "odiamond"
  defp arrow_style_to_string(:box), do: "box"
  defp arrow_style_to_string(:crow), do: "crow"
  defp arrow_style_to_string(:vee), do: "vee"
  defp arrow_style_to_string(:inv), do: "inv"
  defp arrow_style_to_string(:tee), do: "tee"
  defp arrow_style_to_string(:none), do: "none"
  defp arrow_style_to_string({:custom, s}), do: s

  defp overlap_to_string(true), do: "true"
  defp overlap_to_string(false), do: "false"
  defp overlap_to_string(:scale), do: "scale"
  defp overlap_to_string(:scalexy), do: "scalexy"
  defp overlap_to_string(:prism), do: "prism"
  defp overlap_to_string({:custom, s}), do: s
end