defmodule OrgGarden.Transforms.Citations do
  @moduledoc """
  Markdown transform: resolves org-citar citation keys to hyperlinks.

  ## Recognised citation syntax (as output by ox-hugo from org-citar)

      [cite:@key]           → org-cite / citar standard (most common)
      [cite:@key1;@key2]    → multiple citations
      cite:key              → older roam-style bare cite syntax

  ## Resolution chain (in order)

    1. Zotero (live instance via Better BibTeX JSON-RPC)   — preferred
    2. BibTeX file (BIBTEX_FILE env var)                   — fallback
    3. DOI / bare key                                       — always succeeds

  ## Modes (opts.citation_mode)

    :silent  — silently use DOI/bare-key fallback when Zotero+BibTeX fail
    :warn    — (default) emit a Logger.warning for unresolved keys
    :strict  — raise on unresolved keys (aborts pipeline)

  ## Format

  Resolved citations are rendered as:

      [Label](url)       when a URL is available
      [Label]            when no URL could be determined (bare key fallback)

  Multiple semicolon-separated keys become space-separated links:

      [cite:@a;@b]  →  [Author A, 2020](url_a) [Author B, 2019](url_b)

  ## init/1 callback

  Loads the BibTeX file (if configured) once before processing begins,
  and probes Zotero availability, emitting warnings as appropriate.
  """

  @behaviour OrgGarden.Transform

  require Logger

  alias OrgGarden.Resolvers.Zotero
  alias OrgGarden.Resolvers.BibTeX
  alias OrgGarden.Resolvers.DOI

  # Match [cite:@key] and [cite:@key1;@key2;...] (org-cite / citar style)
  @cite_bracket_regex ~r/\[cite:(@[^\]]+)\]/

  # Match bare cite:key or cite:@key (older roam style, no brackets, optional @ prefix)
  @cite_bare_regex ~r/(?<![(\[])cite:@?([a-zA-Z0-9_:-]+)/

  # ------------------------------------------------------------------
  # OrgGarden callbacks
  # ------------------------------------------------------------------

  @doc """
  Called once before processing any files. Loads BibTeX, probes Zotero.
  Returns a state map passed to every `apply/3` call.
  """
  def init(opts) do
    bibtex_entries = load_bibtex(opts)
    zotero_available = probe_zotero(opts)

    if not zotero_available and bibtex_entries == %{} do
      Logger.warning(
        "Citations: neither Zotero nor a BibTeX file is available. " <>
          "All citations will fall back to bare-key rendering. " <>
          "Set BIBTEX_FILE env var or start Zotero with Better BibTeX to resolve citations."
      )
    end

    %{
      bibtex_entries: bibtex_entries,
      zotero_available: zotero_available,
      zotero_url: Map.get(opts, :zotero_url, "http://localhost:23119"),
      citation_mode: Map.get(opts, :citation_mode, :warn)
    }
  end

  @doc """
  Apply citation resolution to a single markdown file's content.
  """
  def apply(content, state, _opts) do
    content
    |> resolve_bracket_citations(state)
    |> resolve_bare_citations(state)
  end

  # ------------------------------------------------------------------
  # Resolution passes
  # ------------------------------------------------------------------

  defp resolve_bracket_citations(content, state) do
    Regex.replace(@cite_bracket_regex, content, fn _full, keys_str ->
      keys_str
      |> String.split(";")
      |> Enum.map(&String.trim/1)
      |> Enum.map(fn "@" <> key -> key end)
      |> Enum.map(&resolve_key(&1, state))
      |> Enum.join(" ")
    end)
  end

  defp resolve_bare_citations(content, state) do
    Regex.replace(@cite_bare_regex, content, fn _full, key ->
      resolve_key(key, state)
    end)
  end

  # ------------------------------------------------------------------
  # Single-key resolution chain
  # ------------------------------------------------------------------

  defp resolve_key(key, state) do
    info =
      with :error <- try_zotero(key, state),
           :error <- try_bibtex(key, state) do
        handle_unresolved(key, state)
      else
        {:ok, citation_info} -> citation_info
      end

    format_result(info)
  end

  defp try_zotero(_key, %{zotero_available: false}), do: :error

  defp try_zotero(key, %{zotero_url: url}) do
    Zotero.resolve(key, url)
  end

  defp try_bibtex(_key, %{bibtex_entries: entries}) when map_size(entries) == 0, do: :error

  defp try_bibtex(key, %{bibtex_entries: entries}) do
    BibTeX.resolve(key, entries)
  end

  defp handle_unresolved(key, %{citation_mode: mode}) do
    case mode do
      :strict ->
        raise "Citations: could not resolve citation key '#{key}' and mode is :strict"

      :warn ->
        Logger.warning("Citations: unresolved citation key '#{key}' — using bare-key fallback")
        {:ok, result} = DOI.resolve(key)
        result

      :silent ->
        {:ok, result} = DOI.resolve(key)
        result
    end
  end

  defp format_result(%{label: label, url: nil}), do: "[#{label}]"
  defp format_result(%{label: label, url: url}), do: "[#{label}](#{url})"

  # ------------------------------------------------------------------
  # Init helpers
  # ------------------------------------------------------------------

  defp load_bibtex(opts) do
    path = Map.get(opts, :bibtex_file) || System.get_env("BIBTEX_FILE")

    cond do
      is_nil(path) ->
        Logger.debug("Citations: BIBTEX_FILE not set — BibTeX resolver disabled")
        %{}

      not File.exists?(path) ->
        Logger.warning("Citations: BIBTEX_FILE=#{path} does not exist — BibTeX resolver disabled")
        %{}

      true ->
        case BibTeX.load(path) do
          {:ok, entries} -> entries
          {:error, reason} ->
            Logger.warning("Citations: failed to load BibTeX file #{path}: #{inspect(reason)}")
            %{}
        end
    end
  end

  defp probe_zotero(opts) do
    url = Map.get(opts, :zotero_url, "http://localhost:23119")

    # Use a no-op JSON-RPC call to probe availability.
    # /better-bibtex/cayw is intentionally avoided — it blocks waiting for
    # user interaction and never returns without a pick.
    payload =
      Jason.encode!(%{
        jsonrpc: "2.0",
        method: "item.search",
        params: [[[]]],
        id: 0
      })

    result =
      try do
        Req.post(url <> "/better-bibtex/json-rpc",
          body: payload,
          headers: [{"content-type", "application/json"}],
          receive_timeout: 3_000,
          finch: OrgGarden.Finch
        )
      rescue
        e -> {:error, e}
      end

    case result do
      {:ok, %{status: 200}} ->
        Logger.info("Citations: Zotero Better BibTeX is available at #{url}")
        true

      {:ok, %{status: status}} ->
        Logger.warning(
          "Citations: Zotero responded HTTP #{status} at #{url} — " <>
            "is Better BibTeX installed?"
        )
        false

      _ ->
        Logger.warning(
          "Citations: Zotero not reachable at #{url} — " <>
            "start Zotero with Better BibTeX or set BIBTEX_FILE as fallback"
        )
        false
    end
  end
end