defmodule Mix.Tasks.Ptc.GenDocs do
  @shortdoc "Generate function reference and audit docs from registry"
  @moduledoc """
  Generates documentation from `priv/functions.exs`:

  1. `docs/function-reference.md` — all implemented functions grouped by section
  2. `docs/clojure-core-audit.md` — clojure.core coverage audit
  3. `docs/clojure-string-audit.md` — clojure.string coverage audit
  4. `docs/clojure-set-audit.md` — clojure.set coverage audit
  5. `docs/java-math-audit.md` — java.lang.Math coverage audit

  ## Usage

      mix ptc.gen_docs
  """
  use Mix.Task

  alias PtcRunner.Lisp.Registry

  @function_ref_path "docs/function-reference.md"

  @audits [
    %{
      path: "docs/clojure-core-audit.md",
      title: "Clojure Core Audit for PTC-Lisp",
      description: "Comparison of `clojure.core` vars against PTC-Lisp builtins.",
      fetch: &Registry.clojure_core_audit/0
    },
    %{
      path: "docs/clojure-string-audit.md",
      title: "Clojure String Audit for PTC-Lisp",
      description: "Comparison of `clojure.string` vars against PTC-Lisp builtins.",
      fetch: &Registry.clojure_string_audit/0
    },
    %{
      path: "docs/clojure-set-audit.md",
      title: "Clojure Set Audit for PTC-Lisp",
      description: "Comparison of `clojure.set` vars against PTC-Lisp builtins.",
      fetch: &Registry.clojure_set_audit/0
    },
    %{
      path: "docs/java-math-audit.md",
      title: "Java Math Audit for PTC-Lisp",
      description: "Comparison of `java.lang.Math` methods against PTC-Lisp builtins.",
      fetch: &Registry.java_math_audit/0
    }
  ]

  @interop_path "docs/java-interop.md"

  @impl Mix.Task
  def run(_args) do
    Mix.Task.run("app.start")

    generate_function_reference()
    Enum.each(@audits, &generate_audit/1)
    generate_java_interop()
  end

  defp generate_function_reference do
    entries = Registry.implemented()

    sections =
      entries
      |> Enum.group_by(& &1.section)
      |> Enum.sort_by(fn {section, _} -> section_order(section) end)

    audit_links =
      @audits
      |> Enum.map_join(" | ", fn %{path: path, title: title} ->
        name = title |> String.replace(" for PTC-Lisp", "") |> String.replace(" Audit", "")
        "[#{name}](#{Path.basename(path)})"
      end)

    content = """
    <!-- Auto-generated — do not edit by hand -->
    # PTC-Lisp Function Reference

    > **Warning:** This file is auto-generated by `mix ptc.gen_docs` from `priv/functions.exs`.
    > Manual edits will be overwritten. Edit `priv/functions.exs` instead.

    #{length(entries)} functions and special forms.

    See also: [PTC-Lisp Specification](ptc-lisp-specification.md) | #{audit_links}

    ## Table of Contents

    #{toc(sections)}

    #{Enum.map_join(sections, "\n\n", &render_section/1)}
    """

    File.write!(@function_ref_path, content)
    Mix.shell().info("Generated #{@function_ref_path} (#{length(entries)} entries)")
  end

  defp toc(sections) do
    Enum.map_join(sections, "\n", fn {section, entries} ->
      anchor =
        section |> String.downcase() |> String.replace(~r/[^a-z0-9]+/, "-") |> String.trim("-")

      "- [#{section}](##{anchor}) (#{length(entries)})"
    end)
  end

  defp section_order("Definitions & Bindings"), do: 0
  defp section_order("Conditionals"), do: 1
  defp section_order("Threading Macros"), do: 2
  defp section_order("Control Flow"), do: 3
  defp section_order("Iteration"), do: 4
  defp section_order("Core"), do: 5
  defp section_order("Predicate Builders"), do: 6
  defp section_order("Functional Tools"), do: 7
  defp section_order("Agent Control"), do: 8
  defp section_order("String Functions"), do: 9
  defp section_order("Set Operations"), do: 10
  defp section_order("Regex Functions"), do: 11
  defp section_order("Math Functions"), do: 12
  defp section_order("Interop"), do: 13
  defp section_order(_), do: 99

  defp render_section({section, entries}) do
    rows =
      entries
      |> Enum.sort_by(& &1.name)
      |> Enum.map_join("\n", fn entry ->
        sigs = Enum.join(entry.signatures, ", ")
        ext = if entry.ptc_extension?, do: " *", else: ""
        "| `#{entry.name}`#{ext} | `#{sigs}` | #{entry.description} |"
      end)

    examples =
      entries
      |> Enum.flat_map(fn entry ->
        Enum.map(entry.examples, fn {code, result} -> {entry.name, code, result} end)
      end)

    example_block =
      if examples == [] do
        ""
      else
        examples_text =
          Enum.map_join(examples, "\n", fn {_name, code, result} ->
            "#{code}\n;; => #{result}"
          end)

        "\n```clojure\n#{examples_text}\n```"
      end

    """
    ## #{section}

    | Function | Signature | Description |
    |----------|-----------|-------------|
    #{rows}
    #{example_block}
    """
  end

  defp generate_audit(%{path: path, title: title, description: description, fetch: fetch}) do
    entries = fetch.()

    counts = Enum.frequencies_by(entries, & &1.status)

    rows =
      entries
      |> Enum.sort_by(& &1.name)
      |> Enum.map_join("\n", fn entry ->
        icon = status_icon(entry.status)
        "| `#{entry.name}` | #{icon} #{entry.status} | #{entry.description} | #{entry.notes} |"
      end)

    see_also =
      @audits
      |> Enum.reject(&(&1.path == path))
      |> Enum.map_join(" | ", fn %{path: p, title: t} ->
        name = t |> String.replace(" for PTC-Lisp", "")
        "[#{name}](#{Path.basename(p)})"
      end)

    content = """
    <!-- Auto-generated — do not edit by hand -->
    # #{title}

    > **Warning:** This file is auto-generated by `mix ptc.gen_docs` from `priv/functions.exs`.
    > Manual edits will be overwritten. Edit `priv/functions.exs` instead.

    #{description}

    See also: [Function Reference](function-reference.md) | #{see_also}

    ## Summary

    | Status | Count |
    |--------|-------|
    | Supported | #{counts[:supported] || 0} |
    | Candidate | #{counts[:candidate] || 0} |
    | Not Relevant | #{counts[:not_relevant] || 0} |
    | Not Classified | #{counts[:not_classified] || 0} |
    | **Total** | **#{length(entries)}** |

    ## Details

    | Var | Status | Description | Notes |
    |-----|--------|-------------|-------|
    #{rows}
    """

    File.write!(path, content)
    Mix.shell().info("Generated #{path} (#{length(entries)} entries)")
  end

  defp generate_java_interop do
    entries = Registry.java_interop()

    by_class =
      entries
      |> Enum.group_by(& &1.class)
      |> Enum.sort_by(fn {class, _} -> class end)

    sections =
      Enum.map_join(by_class, "\n\n", fn {class, items} ->
        rows =
          items
          |> Enum.sort_by(& &1.name)
          |> Enum.map_join("\n", fn entry ->
            sigs = Enum.join(entry.signatures, ", ")
            kind = entry.kind |> to_string() |> String.capitalize()
            notes = if entry.notes != "", do: entry.notes, else: ""
            "| `#{entry.name}` | #{kind} | `#{sigs}` | #{entry.description} | #{notes} |"
          end)

        """
        ### #{class}

        | Name | Kind | Signature | Description | Notes |
        |------|------|-----------|-------------|-------|
        #{rows}
        """
      end)

    content = """
    <!-- Auto-generated — do not edit by hand -->
    # Java Interop Reference for PTC-Lisp

    > **Warning:** This file is auto-generated by `mix ptc.gen_docs` from `priv/functions.exs`.
    > Manual edits will be overwritten. Edit `priv/functions.exs` instead.

    PTC-Lisp emulates a subset of Java interop for LLM compatibility. These are **not** real JVM calls — they are BEAM-native implementations that mirror the Java API surface LLMs are trained on.

    #{length(entries)} interop entries across #{length(by_class)} classes.

    See also: [Function Reference](function-reference.md) | [PTC-Lisp Specification](ptc-lisp-specification.md)

    #{sections}
    """

    File.write!(@interop_path, content)
    Mix.shell().info("Generated #{@interop_path} (#{length(entries)} entries)")
  end

  defp status_icon(:supported), do: "✅"
  defp status_icon(:candidate), do: "🔲"
  defp status_icon(:not_relevant), do: "❌"
  defp status_icon(_), do: "❓"
end