--- A single selection primitive. Uses built-in `vim.ui.select` so headless e2e
--- needs no plugins; auto-upgrades to Telescope when it is installed and not
--- explicitly disabled. Tests set `vim.g.heph_force_ui_select` and stub
--- `vim.ui.select`, so a picker never blocks in `--headless`.

local M = {}

local function telescope_available()
  return pcall(require, "telescope")
end

--- Select one of `items`. `opts.prompt`, `opts.format(item)->string`, and an
--- optional `opts.preview(item)->lines` (Telescope only; markdown-rendered).
--- `on_choice(item|nil, index|nil)` — nil when cancelled.
function M.select(items, opts, on_choice)
  opts = opts or {}
  if not vim.g.heph_force_ui_select and telescope_available() then
    -- Telescope path: a thin wrapper so fuzzy UX is available when present.
    local pickers = require("telescope.pickers")
    local finders = require("telescope.finders")
    local conf = require("telescope.config").values
    local actions = require("telescope.actions")
    local action_state = require("telescope.actions.state")
    local previewer = nil
    if opts.preview then
      previewer = require("telescope.previewers").new_buffer_previewer({
        define_preview = function(self, entry)
          vim.api.nvim_buf_set_lines(self.state.bufnr, 0, -1, false, opts.preview(entry.value) or {})
          vim.bo[self.state.bufnr].filetype = "markdown"
        end,
      })
    end
    pickers
      .new({}, {
        prompt_title = opts.prompt or "heph",
        finder = finders.new_table({
          results = items,
          entry_maker = function(item)
            local display = opts.format and opts.format(item) or tostring(item)
            return { value = item, display = display, ordinal = display }
          end,
        }),
        sorter = conf.generic_sorter({}),
        previewer = previewer,
        attach_mappings = function(bufnr)
          actions.select_default:replace(function()
            actions.close(bufnr)
            local sel = action_state.get_selected_entry()
            on_choice(sel and sel.value or nil)
          end)
          return true
        end,
      })
      :find()
    return
  end

  vim.ui.select(items, {
    prompt = opts.prompt,
    format_item = opts.format,
  }, function(choice, idx)
    on_choice(choice, idx)
  end)
end

return M