defmodule GitCli.Worktree.Default do
  @moduledoc """
  Real implementation of the `GitCli.Worktree` behaviour: git worktree
  operations via `System.cmd("git", ...)`. See `GitCli.Worktree` for the
  public contract and per-function documentation.

  Calls to public siblings go back through the `GitCli.Worktree` facade
  (and repo-root resolution through the `GitCli` facade) rather than
  locally, so a test double installed on the corresponding Globals key
  intercepts nested calls, not just top-level entry points.
  """

  @behaviour GitCli.Worktree

  alias GitCli.Worktree

  @impl Worktree
  def default_root(project) when is_binary(project) do
    Path.join([Settings.get_user_home(), ".fnord", "projects", project, "worktrees"])
  end

  @impl Worktree
  def conversation_path(project, conversation_id)
      when is_binary(project) and is_binary(conversation_id) do
    Path.join([Worktree.default_root(project), conversation_id])
  end

  @impl Worktree
  def list(nil), do: {:error, :not_a_repo}

  def list(root) when is_binary(root) do
    with {:ok, worktrees} <- git_worktree_list(root) do
      {:ok, Enum.map(worktrees, &enrich_worktree(root, &1))}
    end
  end

  @impl Worktree
  def list_raw(nil), do: {:error, :not_a_repo}

  def list_raw(root) when is_binary(root) do
    git_worktree_list(root)
  end

  @impl Worktree
  def enrich(root, entry) when is_binary(root) and is_map(entry) do
    enrich_worktree(root, entry)
  end

  @impl Worktree
  def create(project, conversation_id, branch) do
    branch = branch || "fnord-#{conversation_id}"

    with {:ok, root} <- Worktree.project_root(),
         {:ok, base_branch} <- resolve_default_base_branch(root),
         {:ok, path} <- ensure_conversation_path(project, conversation_id),
         {:ok, _out} <- git_worktree_add_branch(root, path, branch, base_branch) do
      {:ok, normalize_worktree_entry(path, branch, base_branch, root)}
    end
  end

  @impl Worktree
  def duplicate(project, source_meta, new_conversation_id)
      when is_binary(project) and is_map(source_meta) and is_binary(new_conversation_id) do
    source_path = meta_path(source_meta)
    source_branch = meta_branch(source_meta)
    source_base_branch = meta_base_branch(source_meta)

    cond do
      not is_binary(source_path) or not File.dir?(source_path) ->
        {:error, :source_missing}

      not is_binary(source_branch) ->
        {:error, :source_branch_missing}

      true ->
        new_branch = "fnord-#{new_conversation_id}"

        with {:ok, root} <- Worktree.project_root(),
             {:ok, base_branch} <-
               resolve_duplicate_base_branch(root, source_base_branch),
             {:ok, new_path} <- ensure_conversation_path(project, new_conversation_id),
             {:ok, _out} <-
               git_worktree_add_branch(root, new_path, new_branch, source_branch),
             :ok <- overlay_dirty_state(source_path, new_path) do
          {:ok, normalize_worktree_entry(new_path, new_branch, base_branch, root)}
        else
          {:error, reason} ->
            cleanup_failed_duplicate(new_conversation_id, project, new_branch)
            {:error, reason}
        end
    end
  end

  # Prefer the source's recorded base branch so the duplicate keeps merging
  # into the same target. Fall back to the repo default only when the source
  # didn't carry one, which is the legacy-metadata case.
  defp resolve_duplicate_base_branch(_root, base) when is_binary(base), do: {:ok, base}
  defp resolve_duplicate_base_branch(root, _), do: resolve_default_base_branch(root)

  # Replays the source worktree's uncommitted state into the freshly created
  # destination worktree without touching the source. Three name lists drive
  # three file ops, in order: modified tracked files are copied (covering both
  # staged and unstaged edits, including binaries), deletions are propagated so
  # the destination doesn't silently resurrect removed files, and untracked
  # files (excluding .gitignore'd noise) are copied last.
  defp overlay_dirty_state(source_path, dest_path) do
    with {:ok, modified} <- list_modified_tracked(source_path),
         {:ok, deleted} <- list_deleted_tracked(source_path),
         {:ok, untracked} <- list_untracked(source_path),
         :ok <- copy_files(source_path, dest_path, modified),
         :ok <- delete_files(dest_path, deleted),
         :ok <- copy_files(source_path, dest_path, untracked) do
      :ok
    end
  end

  defp list_modified_tracked(path) do
    case git_cmd(path, ["diff", "--name-only", "--diff-filter=ACMRT", "HEAD"]) do
      {:ok, out} -> {:ok, parse_name_list(out)}
      {:error, reason} -> {:error, reason}
    end
  end

  defp list_deleted_tracked(path) do
    case git_cmd(path, ["ls-files", "--deleted"]) do
      {:ok, out} -> {:ok, parse_name_list(out)}
      {:error, reason} -> {:error, reason}
    end
  end

  defp list_untracked(path) do
    case git_cmd(path, ["ls-files", "--others", "--exclude-standard"]) do
      {:ok, out} -> {:ok, parse_name_list(out)}
      {:error, reason} -> {:error, reason}
    end
  end

  defp parse_name_list(out) do
    out
    |> String.split("\n", trim: true)
    |> Enum.map(&String.trim/1)
    |> Enum.reject(&(&1 == ""))
  end

  defp copy_files(_source_root, _dest_root, []), do: :ok

  defp copy_files(source_root, dest_root, [rel | rest]) do
    src = Path.join(source_root, rel)
    dst = Path.join(dest_root, rel)

    with :ok <- File.mkdir_p(Path.dirname(dst)),
         {:ok, _} <- File.copy(src, dst) do
      copy_files(source_root, dest_root, rest)
    else
      _ -> {:error, :copy_failed}
    end
  end

  defp delete_files(_dest_root, []), do: :ok

  defp delete_files(dest_root, [rel | rest]) do
    dst = Path.join(dest_root, rel)

    case File.rm(dst) do
      :ok -> delete_files(dest_root, rest)
      # Tolerate already-absent destinations: the source recorded a deletion
      # against a file that the destination branch never had, so the desired
      # end state (file gone) already holds.
      {:error, :enoent} -> delete_files(dest_root, rest)
      {:error, _} -> {:error, :delete_failed}
    end
  end

  # Best-effort rollback after a failed duplicate. Ignores errors because the
  # caller is already returning the original failure reason and partial state
  # left behind here is preferable to masking the real cause.
  defp cleanup_failed_duplicate(new_conversation_id, project, new_branch) do
    new_path = Worktree.conversation_path(project, new_conversation_id)

    case Worktree.project_root() do
      {:ok, root} ->
        if File.exists?(new_path) do
          _ = git_cmd(root, ["worktree", "remove", "--force", new_path])
        end

        _ = git_cmd(root, ["branch", "-D", new_branch])
        :ok

      _ ->
        :ok
    end
  end

  @impl Worktree
  def delete(root, path) when is_binary(root) and is_binary(path) do
    with {:ok, _out} <- git_worktree_remove(root, path) do
      {:ok, :ok}
    end
  end

  @impl Worktree
  def merge(root, path) when is_binary(root) and is_binary(path) do
    with {:ok, branch} <- git_worktree_branch(root, path) do
      rebase_and_ff_merge(root, path, branch)
    else
      {:error, :worktree_not_found} -> {:error, :worktree_not_found}
      {:error, :not_a_repo} -> {:error, :not_a_repo}
    end
  end

  # Rebase the worktree branch onto the current root branch, then ff-merge.
  # If the rebase conflicts, abort it and fall back to a regular merge.
  defp rebase_and_ff_merge(root, path, branch) do
    target = Worktree.current_branch(root) || "HEAD"

    case git_cmd(path, ["rebase", target]) do
      {:ok, _} ->
        case git_cmd(root, ["merge", "--ff-only", branch]) do
          {:ok, _out} -> {:ok, :ok}
          _ -> {:error, :merge_failed}
        end

      _ ->
        git_cmd(path, ["rebase", "--abort"])

        case git_cmd(root, ["merge", branch]) do
          {:ok, _out} -> {:ok, :ok}
          _ -> {:error, :merge_failed}
        end
    end
  end

  @impl Worktree
  def recreate_conversation_worktree(project, conversation_id, meta)
      when is_binary(project) and is_binary(conversation_id) and is_map(meta) do
    with {:ok, prepared} <- prepare_recreated_worktree(project, conversation_id, meta),
         {:ok, _out} <- git_worktree_add(prepared.root, prepared.path, prepared.branch) do
      {:ok, prepared.meta}
    end
  end

  @impl Worktree
  def has_uncommitted_changes?(path) when is_binary(path) do
    case git_cmd(path, ["status", "--porcelain"]) do
      {:ok, ""} -> false
      {:ok, _output} -> true
      _ -> false
    end
  end

  @impl Worktree
  def path_ignored?(root, path) when is_binary(root) and is_binary(path) do
    case System.cmd("git", ["check-ignore", "-q", path], cd: root, stderr_to_stdout: true) do
      {_, 0} -> true
      _ -> false
    end
  end

  @impl Worktree
  def has_changes_to_merge?(root, path, branch, base_branch)
      when is_binary(root) and is_binary(path) do
    cond do
      not File.dir?(path) ->
        false

      Worktree.has_uncommitted_changes?(path) ->
        true

      is_binary(branch) and is_binary(base_branch) ->
        branch_ahead_of_base?(root, branch, base_branch)

      true ->
        false
    end
  end

  def has_changes_to_merge?(_root, _path, _branch, _base_branch), do: false

  @impl Worktree
  def copy_ignored_files(source_root, worktree_path, rel_paths)
      when is_binary(source_root) and is_binary(worktree_path) and is_list(rel_paths) do
    Enum.map(rel_paths, fn rel ->
      src = Path.join(worktree_path, rel)
      dest = Path.join(source_root, rel)
      File.mkdir_p!(Path.dirname(dest))

      case File.cp(src, dest) do
        :ok -> {:ok, rel}
        {:error, reason} -> {:error, rel, reason}
      end
    end)
  end

  # Returns true when `branch` has commits that `base_branch` does not. Uses
  # the same fork-point logic as diff_from_fork_point/3 so the answer matches
  # what the merge flow would actually try to land.
  defp branch_ahead_of_base?(root, branch, base_branch) do
    case Worktree.diff_from_fork_point(root, branch, base_branch) do
      {:ok, diff} -> byte_size(diff) > 0
      _ -> false
    end
  end

  @impl Worktree
  def force_delete(root, path) when is_binary(root) and is_binary(path) do
    case File.dir?(path) do
      false ->
        {:error, :worktree_not_found}

      true ->
        case git_cmd(root, ["worktree", "remove", "--force", path]) do
          {:ok, _out} -> {:ok, :ok}
          {:error, :not_a_repo} -> {:error, :not_a_repo}
          _ -> {:error, :git_failed}
        end
    end
  end

  @impl Worktree
  def fnord_managed?(project, path)
      when is_binary(project) and is_binary(path) do
    default_root = Path.expand(Worktree.default_root(project)) |> String.trim_trailing("/")
    candidate = Path.expand(path) |> String.trim_trailing("/")

    candidate == default_root or String.starts_with?(candidate, default_root <> "/")
  end

  @impl Worktree
  def commit_all(path, message) when is_binary(path) and is_binary(message) do
    with {:ok, _} <- git_cmd(path, ["add", "-A"]),
         {:ok, _} <- git_cmd(path, ["commit", "-m", message]) do
      {:ok, :ok}
    else
      {:error, :git_failed} -> {:error, :nothing_to_commit}
      error -> error
    end
  end

  @impl Worktree
  def diff_against_base(root, branch, base_branch)
      when is_binary(root) and is_binary(branch) and is_binary(base_branch) do
    git_cmd(root, ["diff", "#{base_branch}...#{branch}"])
  end

  @impl Worktree
  def diff_from_fork_point(root, branch, base_branch)
      when is_binary(root) and is_binary(branch) and is_binary(base_branch) do
    with {:ok, merge_base} <- git_cmd(root, ["merge-base", base_branch, branch]) do
      git_cmd(root, ["diff", String.trim(merge_base), branch])
    end
  end

  @impl Worktree
  def delete_branch(root, branch) when is_binary(root) and is_binary(branch) do
    with {:ok, _} <- git_cmd(root, ["branch", "-d", branch]) do
      {:ok, :ok}
    end
  end

  @impl Worktree
  def head_sha(root) when is_binary(root) do
    case git_cmd(root, ["rev-parse", "--short", "HEAD"]) do
      {:ok, out} -> String.trim(out)
      _ -> nil
    end
  end

  @impl Worktree
  def head_sha_full(root) when is_binary(root) do
    case git_cmd(root, ["rev-parse", "HEAD"]) do
      {:ok, out} -> String.trim(out)
      _ -> nil
    end
  end

  @impl Worktree
  def log_oneline(root, from, to) when is_binary(root) and is_binary(from) and is_binary(to) do
    case git_cmd(root, ["log", "--oneline", "#{from}..#{to}"]) do
      {:ok, ""} -> []
      {:ok, out} -> String.split(out, "\n", trim: true)
      _ -> []
    end
  end

  @impl Worktree
  def reset_hard(root, target) when is_binary(root) and is_binary(target) do
    with {:ok, _} <- git_cmd(root, ["reset", "--hard", target]) do
      {:ok, :ok}
    end
  end

  @impl Worktree
  def force_delete_branch(root, branch) when is_binary(root) and is_binary(branch) do
    with {:ok, _} <- git_cmd(root, ["branch", "-D", branch]) do
      {:ok, :ok}
    end
  end

  @impl Worktree
  def project_root do
    case GitCli.repo_root() do
      nil -> {:error, :not_a_repo}
      root -> {:ok, root}
    end
  end

  @impl Worktree
  def normalize_worktree_meta(meta) when is_map(meta) do
    %{path: meta_path(meta), branch: meta_branch(meta), base_branch: meta_base_branch(meta)}
  end

  @impl Worktree
  def normalize_worktree_meta_in_parent(meta) when is_map(meta) do
    raw = Map.get(meta, :worktree) || Map.get(meta, "worktree")

    case raw do
      nil -> meta
      m when is_map(m) -> Map.put(meta, :worktree, Worktree.normalize_worktree_meta(m))
    end
  end

  @impl Worktree
  def recursive_size(path) when is_binary(path) do
    path
    |> recursive_entries()
    |> Enum.reduce(0, fn entry, acc -> acc + file_size(entry) end)
  end

  defp resolve_default_base_branch(root) do
    case Worktree.default_base_branch(root) do
      branch when is_binary(branch) -> {:ok, branch}
      nil -> {:error, :invalid_branch}
    end
  end

  defp ensure_conversation_path(project, conversation_id) do
    path = Worktree.conversation_path(project, conversation_id)

    case File.mkdir_p(Worktree.default_root(project)) do
      :ok -> {:ok, path}
      _ -> {:error, :git_failed}
    end
  end

  defp ensure_parent_dir(path) do
    case File.mkdir_p(Path.dirname(path)) do
      :ok -> :ok
      _ -> {:error, :git_failed}
    end
  end

  @spec prepare_recreated_worktree(String.t(), String.t(), Worktree.worktree_meta()) ::
          {:ok, Worktree.recreation_result()} | {:error, atom()}
  # Preserves the stored worktree path when one exists in metadata, falling
  # back to the default conversation path only for worktrees that were created
  # without an explicit location.
  defp prepare_recreated_worktree(project, conversation_id, meta) do
    stored_path = meta_path(meta)

    target_path =
      if is_binary(stored_path),
        do: stored_path,
        else: Worktree.conversation_path(project, conversation_id)

    branch = meta_branch(meta)
    base_branch = meta_base_branch(meta)

    with {:ok, root} <- Worktree.project_root(),
         :ok <- ensure_parent_dir(target_path),
         {:ok, resolved_base_branch} <- resolve_default_base_branch(root),
         {:ok, branch} <- normalize_branch(branch, base_branch || resolved_base_branch) do
      normalized_meta =
        meta
        |> Map.put(:path, target_path)
        |> Map.put(:branch, branch)
        |> Map.put(:base_branch, base_branch || resolved_base_branch)
        |> Worktree.normalize_worktree_meta()

      {:ok, %{root: root, path: target_path, branch: branch, meta: normalized_meta}}
    end
  end

  defp normalize_worktree_entry(path, branch, base_branch, root) do
    %{
      path: path,
      branch: branch,
      base_branch: base_branch,
      merge_status: Worktree.merge_status(path, root, branch, base_branch),
      size: Worktree.recursive_size(path),
      exists?: true
    }
  end

  defp enrich_worktree(root, %{path: path} = entry) do
    branch = Map.get(entry, :branch) || Map.get(entry, "branch")

    base_branch =
      Map.get(entry, :base_branch) || Map.get(entry, "base_branch") ||
        Worktree.default_base_branch(root)

    Map.merge(entry, %{
      path: path,
      branch: branch,
      base_branch: base_branch,
      merge_status: Worktree.merge_status(path, root, branch, base_branch),
      size: Worktree.recursive_size(path),
      exists?: File.dir?(path)
    })
  end

  @impl Worktree
  def merge_status(path, root, branch, base_branch) do
    cond do
      not File.dir?(path) ->
        :unknown

      is_nil(branch) ->
        :unknown

      is_nil(base_branch) ->
        :unknown

      true ->
        case git_cmd(root, ["merge-base", "--is-ancestor", base_branch, branch]) do
          {:ok, _out} -> :ahead
          _ -> :diverged
        end
    end
  end

  defp git_worktree_list(root) do
    with {:ok, out} <- git_cmd(root, ["worktree", "list", "--porcelain"]) do
      {:ok, parse_worktree_list(out)}
    end
  end

  defp parse_worktree_list(out) do
    out
    |> String.split(~r/\n\s*\n/, trim: true)
    |> Enum.map(&parse_worktree_record/1)
    |> Enum.reject(&is_nil/1)
  end

  defp parse_worktree_record(record) do
    fields =
      record
      |> String.split("\n", trim: true)
      |> Enum.reduce(%{}, fn line, acc -> parse_worktree_line(line, acc) end)

    case Map.fetch(fields, :path) do
      {:ok, path} ->
        %{
          path: path,
          branch: Map.get(fields, :branch),
          base_branch: Map.get(fields, :base_branch)
        }

      :error ->
        nil
    end
  end

  defp parse_worktree_line("worktree " <> path, acc), do: Map.put(acc, :path, path)
  defp parse_worktree_line("branch refs/heads/" <> branch, acc), do: Map.put(acc, :branch, branch)
  defp parse_worktree_line("detached", acc), do: Map.put(acc, :branch, nil)
  defp parse_worktree_line("HEAD " <> _head, acc), do: acc
  defp parse_worktree_line(_, acc), do: acc

  # Creates a worktree with a new branch forked from a start point. Used by
  # create/3 for fresh conversation worktrees.
  defp git_worktree_add_branch(root, path, branch, start_point) do
    case git_cmd(root, ["worktree", "add", "--force", "-b", branch, path, start_point]) do
      {:ok, out} -> {:ok, out}
      {:error, :invalid_branch} -> {:error, :invalid_branch}
      {:error, :not_a_repo} -> {:error, :not_a_repo}
      _ -> {:error, :git_failed}
    end
  end

  # Checks out an existing branch into a worktree. Used by
  # recreate_conversation_worktree/3 to restore a previously created worktree.
  defp git_worktree_add(root, path, branch) do
    case git_cmd(root, ["worktree", "add", "--force", path, branch]) do
      {:ok, out} -> {:ok, out}
      {:error, :invalid_branch} -> {:error, :invalid_branch}
      {:error, :not_a_repo} -> {:error, :not_a_repo}
      _ -> {:error, :git_failed}
    end
  end

  defp git_worktree_remove(root, path) do
    case File.dir?(path) do
      false ->
        {:error, :worktree_not_found}

      true ->
        case git_cmd(root, ["worktree", "remove", path]) do
          {:ok, out} -> {:ok, out}
          {:error, :not_a_repo} -> {:error, :not_a_repo}
          _ -> {:error, :git_failed}
        end
    end
  end

  defp git_worktree_branch(root, path) do
    with true <- File.dir?(path) or {:error, :worktree_not_found},
         {:ok, branch} <- git_cmd(root, ["rev-parse", "--abbrev-ref", "HEAD"], cd: path) do
      {:ok, String.trim(branch)}
    end
  end

  defp normalize_branch(nil, base_branch), do: {:ok, base_branch}
  defp normalize_branch(branch, _base_branch) when is_binary(branch), do: {:ok, branch}
  defp normalize_branch(_, _), do: {:error, :invalid_branch}

  @impl Worktree
  def default_base_branch(root) when is_binary(root) do
    case repo_default_branch(root) do
      branch when is_binary(branch) -> branch
      nil -> Worktree.current_branch(root)
    end
  end

  defp repo_default_branch(root) when is_binary(root) do
    with {:ok, out} <- git_cmd(root, ["symbolic-ref", "--quiet", "refs/remotes/origin/HEAD"]) do
      out
      |> String.trim()
      |> String.replace_prefix("refs/remotes/origin/", "")
      |> case do
        "" -> nil
        branch -> branch
      end
    else
      _ -> nil
    end
  end

  @impl Worktree
  def current_branch(root) when is_binary(root) do
    with {:ok, branch} <- git_cmd(root, ["rev-parse", "--abbrev-ref", "HEAD"]) do
      branch = String.trim(branch)

      case branch do
        "HEAD" -> nil
        "" -> nil
        valid_branch -> valid_branch
      end
    else
      _ -> nil
    end
  end

  defp git_cmd(root, args, opts \\ []) do
    case System.cmd("git", args, Keyword.merge([cd: root, stderr_to_stdout: true], opts)) do
      {out, 0} -> {:ok, out}
      {_, 128} -> {:error, :not_a_repo}
      {_, 129} -> {:error, :invalid_branch}
      {_, 1} -> {:error, :git_failed}
      {_, _} -> {:error, :git_failed}
    end
  end

  defp file_size(path) do
    case File.stat(path) do
      {:ok, %{size: size}} -> size
      _ -> 0
    end
  end

  defp recursive_entries(path) do
    if File.dir?(path) do
      path
      |> Path.join("**/*")
      |> Path.wildcard()
      |> Enum.filter(&File.regular?/1)
    else
      []
    end
  end

  defp meta_path(meta), do: Map.get(meta, :path) || Map.get(meta, "path")
  defp meta_branch(meta), do: Map.get(meta, :branch) || Map.get(meta, "branch")
  defp meta_base_branch(meta), do: Map.get(meta, :base_branch) || Map.get(meta, "base_branch")
end