defmodule Mix.Tasks.Firebird.Target.Report do
  @moduledoc """
  Generate a compilation report for the WASM target.

  Compiles all WASM sources and produces a detailed report with
  per-module statistics, aggregate totals, and timing information.

  ## Usage

      # Generate report to stdout
      mix firebird.target.report

      # Save report as JSON
      mix firebird.target.report --json --output build_report.json

      # Compare with previous report
      mix firebird.target.report --compare previous_report.json

      # Quick summary only
      mix firebird.target.report --summary

  ## Output

  The report includes:
  - Per-module WAT/WASM sizes
  - Export counts
  - Compression ratio
  - Compilation timing
  - Configuration used
  """

  use Mix.Task

  @shortdoc "Generate a WASM compilation report"

  @switches [
    output: :string,
    json: :boolean,
    compare: :string,
    summary: :boolean,
    dirs: :string,
    files: :string,
    optimize: :boolean,
    tco: :boolean,
    inline: :boolean,
    wat_only: :boolean
  ]

  @aliases [
    o: :output,
    d: :dirs,
    f: :files
  ]

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

    json_mode = Keyword.get(opts, :json, false)
    summary_only = Keyword.get(opts, :summary, false)

    config = Mix.Tasks.Firebird.Target.Compile.build_config(opts)

    # Discover and compile
    sources = Firebird.Target.discover_sources(config)

    if Enum.empty?(sources) do
      Mix.shell().info("No compilable sources found.")
      :ok
    else
      start = System.monotonic_time(:millisecond)
      {:ok, results} = Firebird.Target.compile(config)
      elapsed = System.monotonic_time(:millisecond) - start

      # Handle partial failure
      results =
        case results do
          list when is_list(list) -> list
          _ -> []
        end

      report = Firebird.Target.Report.generate(results, config, elapsed)

      # Output
      cond do
        json_mode ->
          json = Firebird.Target.Report.to_json(report)

          if output = Keyword.get(opts, :output) do
            File.write!(output, json)
            Mix.shell().info("📋 Report saved to #{output}")
          else
            Mix.shell().info(json)
          end

        summary_only ->
          print_summary(report)

        true ->
          Mix.shell().info(Firebird.Target.Report.format(report))
      end

      # Compare with previous if requested
      if compare_path = Keyword.get(opts, :compare) do
        compare_with(report, compare_path)
      end

      :ok
    end
  end

  defp print_summary(report) do
    t = report.totals
    Mix.shell().info("📊 WASM Compilation Summary")
    Mix.shell().info("   Modules: #{t.module_count}")
    Mix.shell().info("   WAT: #{format_bytes(t.total_wat_bytes)}")
    Mix.shell().info("   WASM: #{format_bytes(t.total_wasm_bytes)}")

    if t.compression_ratio do
      Mix.shell().info("   Ratio: #{t.compression_ratio}%")
    end

    Mix.shell().info("   Time: #{report.elapsed_ms}ms")
  end

  defp compare_with(current, path) do
    case File.read(path) do
      {:ok, json} ->
        case Jason.decode(json) do
          {:ok, prev_data} ->
            prev_report = normalize_report(prev_data)
            diff = Firebird.Target.Report.diff(prev_report, current)

            Mix.shell().info("")
            Mix.shell().info("📊 Comparison with #{path}:")
            Mix.shell().info("   Modules: #{format_change(diff.module_count_change)}")

            Mix.shell().info(
              "   WAT: #{format_bytes_change(diff.wat_bytes_change, diff.wat_percent_change)}"
            )

            Mix.shell().info(
              "   WASM: #{format_bytes_change(diff.wasm_bytes_change, diff.wasm_percent_change)}"
            )

            Mix.shell().info("   Time: #{format_time_change(diff.time_change_ms)}")

          _ ->
            Mix.shell().error("Could not parse #{path}")
        end

      {:error, _} ->
        Mix.shell().error("Could not read #{path}")
    end
  end

  defp normalize_report(data) when is_map(data) do
    %{
      timestamp: data["timestamp"] || "",
      elapsed_ms: data["elapsed_ms"] || 0,
      modules: data["modules"] || [],
      totals: %{
        module_count: get_in(data, ["totals", "module_count"]) || 0,
        total_wat_bytes: get_in(data, ["totals", "total_wat_bytes"]) || 0,
        total_wasm_bytes: get_in(data, ["totals", "total_wasm_bytes"]) || 0,
        compression_ratio: get_in(data, ["totals", "compression_ratio"])
      },
      config: data["config"] || %{}
    }
  end

  defp format_change(0), do: "no change"
  defp format_change(n) when n > 0, do: "+#{n}"
  defp format_change(n), do: "#{n}"

  defp format_bytes_change(bytes, pct) do
    sign = if bytes >= 0, do: "+", else: ""
    pct_str = if pct, do: " (#{sign}#{pct}%)", else: ""
    "#{sign}#{format_bytes(abs(bytes))}#{pct_str}"
  end

  defp format_time_change(0), do: "no change"
  defp format_time_change(ms) when ms > 0, do: "+#{ms}ms (slower)"
  defp format_time_change(ms), do: "#{ms}ms (faster)"

  defp format_bytes(0), do: "0 B"
  defp format_bytes(bytes) when bytes < 1024, do: "#{bytes} B"
  defp format_bytes(bytes) when bytes < 1_048_576, do: "#{Float.round(bytes / 1024, 1)} KB"
  defp format_bytes(bytes), do: "#{Float.round(bytes / 1_048_576, 1)} MB"
end