defmodule Mix.Tasks.Jetons.Inspect do
  @moduledoc """
  Inspect and debug design tokens.

  Provides four modes for exploring token files and resolver documents.

  ## Token Lookup

      mix jetons.inspect -f tokens.resolver.json --token color.background.brand.default
      mix jetons.inspect -f tokens.resolver.json --token color.background.brand.default --set brand=markant

  ## Reference Tracing

      mix jetons.inspect -f tokens.resolver.json --refs button.primary.color-background.default

  ## List Permutations

      mix jetons.inspect -f tokens.resolver.json --permutations

  ## Diff Contexts

      # Diff defaults vs a specific context
      mix jetons.inspect -f tokens.resolver.json --diff --set theme=dark

      # Diff two explicit contexts
      mix jetons.inspect -f tokens.resolver.json --diff --set brand=acme --vs brand=markant

  ## Options

    * `-f` / `--file` — (required) input JSON or resolver file
    * `--token` — token dot-path to look up across contexts
    * `--refs` — token dot-path for reference chain tracing
    * `--permutations` — list all valid modifier combinations
    * `--diff` — diff resolved tokens between two contexts
    * `--set` — modifier input for context selection (format: `name=value`, repeatable)
    * `--vs` — second context for diff comparison (format: `name=value`, repeatable)
  """

  use Mix.Task

  alias Jetons.DTCG
  alias Jetons.Parser
  alias Jetons.Ref
  alias Jetons.Resolver

  @shortdoc "Inspect and debug design tokens"

  @switches [
    file: :string,
    token: :string,
    refs: :string,
    permutations: :boolean,
    diff: :boolean,
    set: [:string, :keep],
    vs: [:string, :keep]
  ]

  @aliases [f: :file]

  @impl Mix.Task
  def run(args) do
    {opts, _rest} = OptionParser.parse!(args, strict: @switches, aliases: @aliases)

    path = opts[:file] || raise Mix.Error, "--file (-f) is required"
    mode = detect_mode(opts)
    doc = load_doc(path)
    is_resolver = resolver_file?(path)
    base_dir = Path.dirname(Path.expand(path))

    run_mode(mode, doc, is_resolver, base_dir, opts)
  end

  defp detect_mode(opts) do
    modes =
      [
        {:token, opts[:token]},
        {:refs, opts[:refs]},
        {:permutations, opts[:permutations]},
        {:diff, opts[:diff]}
      ]
      |> Enum.filter(fn {_, v} -> v end)

    case modes do
      [{mode, _}] ->
        validate_mode_opts(mode, opts)

      [] ->
        raise Mix.Error, "Specify one of: --token, --refs, --permutations, --diff"

      _ ->
        raise Mix.Error,
              "Only one mode allowed at a time (--token, --refs, --permutations, --diff)"
    end
  end

  defp validate_mode_opts(mode, opts) do
    if Keyword.has_key?(opts, :vs) and mode != :diff do
      raise Mix.Error, "--vs can only be used with --diff"
    end

    mode
  end

  defp run_mode(:token, doc, is_resolver, base_dir, opts),
    do: run_token(doc, is_resolver, base_dir, opts)

  defp run_mode(:refs, doc, is_resolver, base_dir, opts),
    do: run_refs(doc, is_resolver, base_dir, opts)

  defp run_mode(:permutations, doc, is_resolver, _base_dir, _opts),
    do: run_permutations(doc, is_resolver)

  defp run_mode(:diff, doc, is_resolver, base_dir, opts),
    do: run_diff(doc, is_resolver, base_dir, opts)

  # --- Token Lookup ---

  defp run_token(doc, true = _is_resolver, base_dir, opts) do
    token_path = opts[:token]
    set_input = parse_set_opts(opts)
    perms = filter_permutations(doc, set_input)

    if perms == [] do
      raise Mix.Error, "No permutations match the given --set values"
    end

    results =
      Enum.map(perms, fn input ->
        config = Resolver.resolve!(doc, input, base_dir: base_dir)
        raw = config |> Parser.from_config(resolve_refs: false) |> Map.new()

        resolved =
          case Parser.from_config_safe(config) do
            {:ok, tokens} -> tokens |> Map.new() |> Map.get(token_path)
            {:error, _reason} -> nil
          end

        {input, Map.get(raw, token_path), resolved}
      end)

    if Enum.all?(results, fn {_, raw, _} -> is_nil(raw) end) do
      config = Resolver.resolve!(doc, elem(hd(results), 0), base_dir: base_dir)
      raise_token_not_found(token_path, config, base_dir)
    end

    type = lookup_type(doc, hd(perms), base_dir, token_path)
    print_token_header(token_path, type)

    Enum.each(results, fn {input, raw, resolved} ->
      label = format_input(input)
      display = format_token_value(raw, resolved)
      Mix.shell().info("  #{String.pad_trailing(label, 40)} #{display}")
    end)
  end

  defp run_token(doc, false = _is_resolver, _base_dir, opts) do
    token_path = opts[:token]
    tokens = doc |> Parser.from_config() |> Map.new()

    case Map.fetch(tokens, token_path) do
      {:ok, value} ->
        type = DTCG.type_map(doc) |> Map.get(token_path)
        print_token_header(token_path, type)
        Mix.shell().info("  #{format_value(value)}")

      :error ->
        raise_token_not_found(token_path, doc, nil)
    end
  end

  # --- Reference Tracing ---

  defp run_refs(doc, is_resolver, base_dir, opts) do
    token_path = opts[:refs]
    config = resolve_config(doc, is_resolver, base_dir, opts)
    unresolved = config |> Parser.from_config(resolve_refs: false) |> Map.new()

    case Map.fetch(unresolved, token_path) do
      {:ok, _} ->
        chain = trace_refs(token_path, unresolved)
        print_ref_chain(chain)

      :error ->
        raise_token_not_found(token_path, config, base_dir)
    end
  end

  defp trace_refs(token_path, unresolved, visited \\ MapSet.new()) do
    if MapSet.member?(visited, token_path) do
      [{token_path, :cycle}]
    else
      value = Map.get(unresolved, token_path)
      visited = MapSet.put(visited, token_path)

      cond do
        is_nil(value) ->
          [{token_path, :not_found}]

        Ref.ref?(value) ->
          ref_path = Ref.path(value)
          [{token_path, value} | trace_refs(ref_path, unresolved, visited)]

        is_binary(value) and String.contains?(value, "{") ->
          [{token_path, {:embedded, value}}]

        true ->
          [{token_path, {:literal, value}}]
      end
    end
  end

  defp print_ref_chain(chain) do
    chain
    |> Enum.with_index()
    |> Enum.each(fn {{path, value}, depth} ->
      indent = String.duplicate("   ", depth)
      prefix = if depth == 0, do: "", else: "#{indent}\u2514\u2500 "

      case value do
        :cycle ->
          Mix.shell().info("#{prefix}#{path} (circular reference!)")

        :not_found ->
          Mix.shell().info("#{prefix}#{path} (not found!)")

        {:embedded, raw} ->
          Mix.shell().info("#{prefix}#{path}")
          Mix.shell().info("#{indent}   = #{raw} (embedded references)")

        {:literal, raw} ->
          Mix.shell().info(format_literal(path, raw, depth, prefix))

        raw when is_binary(raw) ->
          Mix.shell().info("#{prefix}#{path}")
      end
    end)
  end

  # --- Permutations ---

  defp run_permutations(doc, true = _is_resolver) do
    modifiers = Map.get(doc, "modifiers", %{})
    perms = Resolver.list_permutations(doc)

    Mix.shell().info("Modifiers:")

    modifiers
    |> Enum.sort_by(fn {name, _} -> name end)
    |> Enum.each(fn {name, mod_def} ->
      Mix.shell().info("  #{name}: #{format_modifier_contexts(mod_def)}")
    end)

    Mix.shell().info("\nPermutations (#{length(perms)}):")

    Enum.each(perms, fn input ->
      Mix.shell().info("  #{format_input(input)}")
    end)
  end

  defp run_permutations(_doc, false = _is_resolver) do
    raise Mix.Error, "--permutations requires a .resolver.json file"
  end

  # --- Diff ---

  defp run_diff(doc, true = _is_resolver, base_dir, opts) do
    set_input = parse_set_opts(opts)
    vs_input = parse_vs_opts(opts)

    {left_input, right_input, left_label, right_label} =
      build_diff_inputs(doc, set_input, vs_input)

    left_tokens = resolve_and_flatten_raw(doc, left_input, base_dir)
    right_tokens = resolve_and_flatten_raw(doc, right_input, base_dir)

    all_paths =
      MapSet.union(MapSet.new(Map.keys(left_tokens)), MapSet.new(Map.keys(right_tokens)))

    changes =
      all_paths
      |> Enum.sort()
      |> Enum.filter(fn path -> Map.get(left_tokens, path) != Map.get(right_tokens, path) end)
      |> Enum.map(fn path ->
        {path, Map.get(left_tokens, path), Map.get(right_tokens, path)}
      end)

    Mix.shell().info("Diff: #{left_label} \u2192 #{right_label}")
    Mix.shell().info("#{length(changes)} token(s) changed\n")

    if changes == [] do
      Mix.shell().info("  (no differences)")
    else
      max_path_len = changes |> Enum.map(fn {p, _, _} -> String.length(p) end) |> Enum.max()

      Enum.each(changes, fn {path, left, right} ->
        Mix.shell().info(
          "  #{String.pad_trailing(path, max_path_len)}  #{format_value(left)} \u2192 #{format_value(right)}"
        )
      end)
    end
  end

  defp run_diff(_doc, false = _is_resolver, _base_dir, _opts),
    do: raise(Mix.Error, "--diff requires a .resolver.json file")

  defp build_diff_inputs(doc, set_input, vs_input) do
    modifiers = Map.get(doc, "modifiers", %{})
    defaults = Resolver.default_input(modifiers)

    cond do
      vs_input != %{} ->
        left = Map.merge(defaults, set_input)
        right = Map.merge(defaults, vs_input)
        {left, right, format_input(left), format_input(right)}

      set_input != %{} ->
        left = defaults
        right = Map.merge(defaults, set_input)
        {left, right, format_input(left), format_input(right)}

      true ->
        raise Mix.Error, "--diff requires at least --set to specify what to compare"
    end
  end

  # --- Shared Helpers ---

  defp load_doc(path) do
    case File.read(path) do
      {:ok, contents} ->
        case Jason.decode(contents) do
          {:ok, data} -> data
          {:error, e} -> raise Mix.Error, "Invalid JSON in #{path}: #{Exception.message(e)}"
        end

      {:error, reason} ->
        raise Mix.Error, "Cannot read file #{path}: #{:file.format_error(reason)}"
    end
  end

  defp resolver_file?(path), do: String.ends_with?(path, ".resolver.json")

  defp resolve_config(doc, true = _is_resolver, base_dir, opts) do
    input = parse_set_opts(opts)
    modifiers = Map.get(doc, "modifiers", %{})
    full_input = Map.merge(Resolver.default_input(modifiers), input)
    Resolver.resolve!(doc, full_input, base_dir: base_dir)
  end

  defp resolve_config(doc, false = _is_resolver, _base_dir, _opts), do: doc

  defp resolve_and_flatten_raw(doc, input, base_dir) do
    doc
    |> Resolver.resolve!(input, base_dir: base_dir)
    |> Parser.from_config(resolve_refs: false)
    |> Map.new()
  end

  defp filter_permutations(doc, set_input) do
    modifiers = Map.get(doc, "modifiers", %{})

    Resolver.list_permutations(doc)
    |> Enum.filter(fn perm ->
      Enum.all?(set_input, fn {k, v} -> perm[k] == v end)
    end)
    |> case do
      [] when map_size(set_input) > 0 ->
        # If set doesn't match any permutation, it may specify all modifiers
        defaults = Resolver.default_input(modifiers)
        [Map.merge(defaults, set_input)]

      perms ->
        perms
    end
  end

  defp lookup_type(doc, input, base_dir, token_path) do
    doc
    |> Resolver.resolve!(input, base_dir: base_dir)
    |> DTCG.type_map()
    |> Map.get(token_path)
  rescue
    ArgumentError -> nil
  end

  defp raise_token_not_found(token_path, config, _base_dir) do
    all_paths = config |> Parser.from_config(resolve_refs: false) |> Enum.map(&elem(&1, 0))

    suggestion = Ref.closest(token_path, all_paths)

    message =
      case suggestion do
        nil -> "Token not found: #{token_path}"
        match -> "Token not found: #{token_path}. Did you mean #{inspect(match)}?"
      end

    raise Mix.Error, message
  end

  defp parse_set_opts(opts) do
    opts |> Keyword.get_values(:set) |> parse_kv_pairs("--set")
  end

  defp parse_vs_opts(opts) do
    opts |> Keyword.get_values(:vs) |> parse_kv_pairs("--vs")
  end

  defp parse_kv_pairs(values, flag_name) do
    Enum.reduce(values, %{}, fn value, acc ->
      case String.split(value, "=", parts: 2) do
        [key, val] ->
          Map.put(acc, key, val)

        _ ->
          raise Mix.Error, "Invalid #{flag_name} format: #{inspect(value)}. Expected: name=value"
      end
    end)
  end

  defp format_input(input) do
    input
    |> Enum.sort_by(fn {k, _} -> k end)
    |> Enum.map_join(", ", fn {k, v} -> "#{k}=#{v}" end)
  end

  defp format_modifier_contexts(mod_def) do
    contexts = mod_def["contexts"] |> Map.keys() |> Enum.sort()
    default = mod_def["default"]

    Enum.map_join(contexts, ", ", fn ctx ->
      if ctx == default, do: "#{ctx} (default)", else: ctx
    end)
  end

  defp format_literal(path, raw, 0, _prefix), do: "#{path} = #{format_value(raw)}"
  defp format_literal(_path, raw, _depth, prefix), do: "#{prefix}#{format_value(raw)}"

  defp format_value(nil), do: "(not defined)"
  defp format_value(v) when is_binary(v), do: v
  defp format_value(v), do: inspect(v)

  defp format_token_value(nil, _), do: "(not defined)"

  defp format_token_value(raw, resolved) when is_binary(raw) and is_binary(resolved) do
    if raw == resolved, do: raw, else: "#{resolved}  (via #{raw})"
  end

  defp format_token_value(raw, nil) when is_binary(raw), do: "#{raw}  (unresolved)"

  defp format_token_value(raw, resolved),
    do: "#{format_value(resolved)}  (via #{format_value(raw)})"

  defp print_token_header(token_path, nil) do
    Mix.shell().info("Token: #{token_path}\n")
  end

  defp print_token_header(token_path, type) do
    Mix.shell().info("Token: #{token_path}")
    Mix.shell().info("Type: #{type}\n")
  end
end