nvim/lua/netrw-preview.lua

local M = {}

local uv = vim.uv
local states = {}
local preview_buffers = {}
local preview_group = vim.api.nvim_create_augroup('netrw_live_preview', { clear = true })

local DEBOUNCE_MS = 90
local MAX_ENTRIES = 200
local PREVIEW_BUFFER_CLEANUP_MS = 2000

local function is_valid_buffer(buf)
  return type(buf) == 'number' and buf > 0 and vim.api.nvim_buf_is_valid(buf)
end

local function is_valid_window(win)
  return type(win) == 'number' and win > 0 and vim.api.nvim_win_is_valid(win)
end

local function is_valid_tab(tab)
  return type(tab) == 'number' and tab > 0 and vim.api.nvim_tabpage_is_valid(tab)
end

local function is_remote_path(path)
  return type(path) == 'string' and path:match('^%a[%w+.-]*://') ~= nil
end

local function netrw_call(name, ...)
  return pcall(vim.fn['netrw#Call'], name, ...)
end

local function find_preview_window(tab)
  if not is_valid_tab(tab) then
    return nil
  end

  for _, win in ipairs(vim.api.nvim_tabpage_list_wins(tab)) do
    if is_valid_window(win) and vim.wo[win].previewwindow then
      return win
    end
  end
end

local function close_timer(state, key)
  key = key or 'timer'
  local timer = state and state[key]
  if not timer then
    return
  end

  pcall(timer.stop, timer)
  if not timer:is_closing() then
    pcall(timer.close, timer)
  end
  state[key] = nil
end

local function indent_guides_enabled(buf)
  local ok, config = pcall(require, 'ibl.config')
  if not ok or not config.config then
    return nil
  end
  return config.get_config(buf).enabled
end

local function set_indent_guides(buf, enabled)
  if enabled == nil then
    return
  end

  local ok, ibl = pcall(require, 'ibl')
  if ok and ibl.initialized then
    ibl.setup_buffer(buf, { enabled = enabled })
  end
end

local function restore_preview_buffer(buf, for_editing)
  local metadata = preview_buffers[buf]
  if not metadata or not is_valid_buffer(buf) then
    return
  end

  vim.b[buf].netrw_live_preview_buffer = nil
  vim.bo[buf].bufhidden = metadata.bufhidden
  vim.bo[buf].buflisted = for_editing or metadata.buflisted
  vim.bo[buf].syntax = metadata.syntax
  vim.diagnostic.enable(metadata.diagnostics_enabled, { bufnr = buf })
  set_indent_guides(buf, metadata.indent_guides_enabled)
  if metadata.treesitter_active then
    pcall(vim.treesitter.start, buf)
  end
  preview_buffers[buf] = nil
end

local function schedule_preview_buffer_cleanup(state)
  if not state or state.preview_cleanup_scheduled then
    return
  end

  state.preview_cleanup_scheduled = true
  vim.defer_fn(function()
    state.preview_cleanup_scheduled = false

    for buf, metadata in pairs(preview_buffers) do
      local is_preview = is_valid_buffer(buf) and vim.b[buf].netrw_live_preview_buffer == true
      local is_visible = is_valid_buffer(buf) and #vim.fn.win_findbuf(buf) > 0
      if not is_preview or not is_visible then
        if is_preview and metadata.loaded then
          restore_preview_buffer(buf, false)
        end
        if not is_preview then
          preview_buffers[buf] = nil
        end
      end
    end
  end, PREVIEW_BUFFER_CLEANUP_MS)
end

local function close_preview(state)
  if not state then
    return
  end

  local preview = find_preview_window(state.tab)
  if preview then
    pcall(vim.api.nvim_win_close, preview, false)
    schedule_preview_buffer_cleanup(state)
  end
end

local function normalize_local_path(path)
  if type(path) ~= 'string' or path == '' then
    return nil
  end

  local trimmed = path:gsub('/+$', '')
  if trimmed == '' and path:sub(1, 1) == '/' then
    trimmed = '/'
  end
  return vim.fs.normalize(trimmed)
end

local function selected_entry(buf, win)
  if not is_valid_buffer(buf) or not is_valid_window(win) then
    return nil, 'netrw buffer or window is no longer valid'
  end

  return vim.api.nvim_win_call(win, function()
    local curdir = vim.b[buf].netrw_curdir
    local ok_word, word = netrw_call('NetrwGetWord')
    if not ok_word or type(word) ~= 'string' or word == '' then
      return nil, 'netrw could not identify the selected entry'
    end

    if is_remote_path(curdir) then
      return {
        remote = true,
        word = word,
      }
    end

    local path
    if vim.w[win].netrw_liststyle == 3 and type(vim.w[win].netrw_treetop) == 'string' then
      local ok_tree, tree_path = netrw_call('NetrwTreePath', vim.w[win].netrw_treetop)
      if not ok_tree or type(tree_path) ~= 'string' or tree_path == '' then
        return nil, 'netrw could not resolve the selected tree path'
      end

      if word == '../' then
        path = vim.fs.dirname(normalize_local_path(tree_path))
      elseif word:sub(-1) == '/' then
        path = tree_path
      else
        path = vim.fs.joinpath(tree_path, (word:gsub('[@*]$', '')))
      end
    else
      local name = word:gsub('/$', ''):gsub('[@*]$', '')
      path = vim.fs.isabs(name) and name or vim.fs.joinpath(curdir, name)
    end

    return {
      path = normalize_local_path(path),
      remote = false,
      word = word,
    }
  end)
end

local function human_size(bytes)
  if type(bytes) ~= 'number' then
    return '—'
  end

  local units = { 'B', 'K', 'M', 'G', 'T' }
  local value = bytes
  local unit = 1
  while value >= 1024 and unit < #units do
    value = value / 1024
    unit = unit + 1
  end

  if unit == 1 then
    return ('%d%s'):format(value, units[unit])
  end

  local formatted = ('%.1f'):format(value):gsub('%.0$', '')
  return formatted .. units[unit]
end

local function modified_time(stat)
  local seconds = stat and stat.mtime and stat.mtime.sec
  if type(seconds) ~= 'number' then
    return '—'
  end

  return os.date('%Y-%m-%d %H:%M', seconds)
end

local function visible_in_netrw(name, entry_type)
  local hide_mode = tonumber(vim.g.netrw_hide) or 0
  local pattern = vim.g.netrw_list_hide
  if hide_mode == 0 or type(pattern) ~= 'string' or pattern == '' then
    return true
  end

  local candidate = name .. (entry_type == 'directory' and '/' or '')
  local hidden = vim.fn.match(candidate, pattern) >= 0
  return (hide_mode == 1 and not hidden) or (hide_mode == 2 and hidden)
end

local function entry_details(directory, name, hinted_type)
  local path = vim.fs.joinpath(directory, name)
  local stat = uv.fs_lstat(path)
  local entry_type = stat and stat.type or hinted_type or 'unknown'
  local display_name = name
  local size = '—'

  if entry_type == 'directory' then
    display_name = display_name .. '/'
  elseif entry_type == 'file' then
    size = human_size(stat and stat.size)
  elseif entry_type == 'link' then
    local target = uv.fs_readlink(path)
    display_name = display_name .. '@'
    if target then
      display_name = display_name .. ' -> ' .. target
    end
  end

  return {
    name = name,
    display_name = display_name,
    path = path,
    type = entry_type,
    size = size,
    bytes = entry_type == 'file' and stat and stat.size or 0,
    modified = modified_time(stat),
  }
end

local function plural(count, singular, plural_form)
  return ('%d %s'):format(count, count == 1 and singular or plural_form)
end

local function directory_lines(path)
  local scan, scan_error = uv.fs_scandir(path)
  if not scan then
    return {
      path .. '/',
      '',
      'Unable to read directory:',
      tostring(scan_error or 'unknown error'),
    }
  end

  local entries = {}
  local counts = { directory = 0, file = 0, link = 0, other = 0 }
  local total_file_size = 0

  while true do
    local name, hinted_type = uv.fs_scandir_next(scan)
    if not name then
      break
    end

    if visible_in_netrw(name, hinted_type) then
      local entry = entry_details(path, name, hinted_type)
      if entry.type == 'directory' then
        counts.directory = counts.directory + 1
      elseif entry.type == 'file' then
        counts.file = counts.file + 1
        total_file_size = total_file_size + (entry.bytes or 0)
      elseif entry.type == 'link' then
        counts.link = counts.link + 1
      else
        counts.other = counts.other + 1
      end
      table.insert(entries, entry)
    end
  end

  local ranks = { directory = 1, file = 2, link = 3 }
  table.sort(entries, function(a, b)
    local a_rank = ranks[a.type] or 4
    local b_rank = ranks[b.type] or 4
    if a_rank ~= b_rank then
      return a_rank < b_rank
    end
    return a.name:lower() < b.name:lower()
  end)

  local lines = {
    path == '/' and '/' or path .. '/',
    '',
    ('%-5s %8s  %-16s  %s'):format('Type', 'Size', 'Modified', 'Name'),
    ('%-5s %8s  %-16s  %s'):format('-----', '--------', '----------------', '----'),
  }

  for index, entry in ipairs(entries) do
    if index > MAX_ENTRIES then
      break
    end
    local label = entry.type == 'directory' and 'dir'
      or entry.type == 'file' and 'file'
      or entry.type == 'link' and 'link'
      or 'other'
    table.insert(lines, ('%-5s %8s  %-16s  %s'):format(
      label,
      entry.size,
      entry.modified,
      entry.display_name
    ))
  end

  if #entries == 0 then
    table.insert(lines, '(empty)')
  elseif #entries > MAX_ENTRIES then
    table.insert(lines, ('… showing first %d of %d entries'):format(MAX_ENTRIES, #entries))
  end

  table.insert(lines, '')
  local summary = {
    plural(counts.directory, 'directory', 'directories'),
    plural(counts.file, 'file', 'files'),
  }
  if counts.link > 0 then
    table.insert(summary, plural(counts.link, 'link', 'links'))
  end
  if counts.other > 0 then
    table.insert(summary, plural(counts.other, 'other entry', 'other entries'))
  end
  table.insert(lines, table.concat(summary, ', ') .. ', ' .. human_size(total_file_size) .. ' in immediate files')

  return lines
end

local function symlink_lines(path, stat)
  local target, read_error = uv.fs_readlink(path)
  return {
    path .. '@',
    '',
    'Type:      symbolic link',
    'Target:    ' .. tostring(target or read_error or 'unavailable'),
    'Modified:  ' .. modified_time(stat),
    '',
    'The target is not traversed in directory previews.',
  }
end

local function unavailable_lines(path, error_message)
  return {
    tostring(path or '(unknown entry)'),
    '',
    'Preview unavailable:',
    tostring(error_message or 'entry no longer exists'),
  }
end

local function ensure_summary_buffer(state)
  if is_valid_buffer(state.summary_buf) then
    return state.summary_buf
  end

  local buf = vim.api.nvim_create_buf(false, true)
  vim.bo[buf].buftype = 'nofile'
  vim.bo[buf].bufhidden = 'wipe'
  vim.bo[buf].swapfile = false
  vim.bo[buf].filetype = 'netrw-preview'
  vim.b[buf].netrw_directory_preview = true
  state.summary_buf = buf
  return buf
end

local function set_summary_lines(buf, lines)
  vim.bo[buf].readonly = false
  vim.bo[buf].modifiable = true
  vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
  vim.bo[buf].modified = false
  vim.bo[buf].modifiable = false
  vim.bo[buf].readonly = true
end

local function configure_summary_window(win)
  vim.wo[win].previewwindow = true
  vim.wo[win].number = false
  vim.wo[win].relativenumber = false
  vim.wo[win].cursorline = false
  vim.wo[win].wrap = false
  vim.wo[win].list = false
  vim.wo[win].spell = false
  vim.wo[win].signcolumn = 'no'
end

local function show_summary(state, netrw_win, lines)
  local buf = ensure_summary_buffer(state)
  set_summary_lines(buf, lines)

  local preview = find_preview_window(state.tab)
  if preview then
    local ok = pcall(vim.api.nvim_win_set_buf, preview, buf)
    if not ok then
      return false
    end
  else
    local ok, created = pcall(vim.api.nvim_open_win, buf, false, {
      split = 'below',
      win = netrw_win,
      noautocmd = true,
    })
    if not ok then
      return false
    end
    preview = created
  end

  configure_summary_window(preview)
  vim.api.nvim_win_set_cursor(preview, { 1, 0 })
  return true
end

local function native_preview(entry)
  local path = entry.path
  if entry.remote then
    -- Match netrw's own `p` mapping arguments for local and remote listings.
    local ok_path, resolved = netrw_call('NetrwBrowseChgDir', 1, entry.word, 1, 1)
    if not ok_path then
      return false
    end
    path = resolved
  end

  if type(path) ~= 'string' or path == '' then
    return false
  end

  local ok = netrw_call('NetrwPreview', path)
  return ok
end

local function show_native_preview(state, entry)
  state.native_preview_active = true

  local existing_buf = entry.path and vim.fn.bufnr(entry.path) or -1
  local existing = is_valid_buffer(existing_buf) and {
    buf = existing_buf,
    loaded = vim.api.nvim_buf_is_loaded(existing_buf),
    buflisted = vim.bo[existing_buf].buflisted,
    bufhidden = vim.bo[existing_buf].bufhidden,
    syntax = vim.bo[existing_buf].syntax,
    treesitter_active = vim.treesitter.highlighter.active[existing_buf] ~= nil,
    diagnostics_enabled = vim.diagnostic.is_enabled({ bufnr = existing_buf }),
    indent_guides_enabled = indent_guides_enabled(existing_buf),
  } or nil

  local ok, shown = pcall(native_preview, entry)

  local preview = find_preview_window(state.tab)
  if preview then
    local preview_buf = vim.api.nvim_win_get_buf(preview)
    local preview_only = #vim.fn.win_findbuf(preview_buf) == 1
    if vim.bo[preview_buf].buftype == '' and preview_only then
      preview_buffers[preview_buf] = preview_buffers[preview_buf] or {
        loaded = existing ~= nil and existing.buf == preview_buf and existing.loaded,
        buflisted = existing ~= nil and existing.buf == preview_buf and existing.buflisted or false,
        bufhidden = existing ~= nil and existing.buf == preview_buf and existing.bufhidden or '',
        syntax = existing ~= nil and existing.buf == preview_buf and existing.syntax or '',
        treesitter_active = existing ~= nil
            and existing.buf == preview_buf
            and existing.loaded
            and existing.treesitter_active
          or vim.treesitter.highlighter.active[preview_buf] ~= nil,
        diagnostics_enabled = existing ~= nil
            and existing.buf == preview_buf
            and existing.diagnostics_enabled
          or vim.diagnostic.is_enabled({ bufnr = preview_buf }),
        indent_guides_enabled = existing ~= nil
            and existing.buf == preview_buf
            and existing.indent_guides_enabled
          or indent_guides_enabled(preview_buf),
      }

      vim.bo[preview_buf].bufhidden = 'hide'
      vim.bo[preview_buf].buflisted = preview_buffers[preview_buf].buflisted
      vim.b[preview_buf].netrw_live_preview_buffer = true
      pcall(vim.treesitter.stop, preview_buf)
      vim.diagnostic.enable(false, { bufnr = preview_buf })
      vim.bo[preview_buf].syntax = ''
      set_indent_guides(preview_buf, false)
    end
  end

  if is_valid_window(state.win) then
    pcall(vim.api.nvim_set_current_win, state.win)
  end
  state.native_preview_active = false
  return ok and shown
end

local function preview_selected(state, allow_create)
  if not state or not is_valid_buffer(state.buf) or not is_valid_window(state.win) then
    return
  end

  if vim.api.nvim_win_get_buf(state.win) ~= state.buf then
    return
  end

  if not find_preview_window(state.tab) and not allow_create then
    return
  end

  local entry, resolve_error = selected_entry(state.buf, state.win)
  if not entry then
    show_summary(state, state.win, unavailable_lines(nil, resolve_error))
    return
  end

  if entry.remote then
    show_native_preview(state, entry)
    return
  end

  local stat, stat_error = uv.fs_lstat(entry.path)
  if not stat then
    show_summary(state, state.win, unavailable_lines(entry.path, stat_error))
    return
  end

  if stat.type == 'directory' then
    show_summary(state, state.win, directory_lines(entry.path))
  elseif stat.type == 'link' then
    show_summary(state, state.win, symlink_lines(entry.path, stat))
  elseif stat.type == 'file' then
    show_native_preview(state, entry)
  else
    show_summary(state, state.win, unavailable_lines(entry.path, 'unsupported entry type: ' .. stat.type))
  end
end

local function schedule_preview(state)
  if not state then
    return
  end

  if not find_preview_window(state.tab) then
    schedule_preview_buffer_cleanup(state)
    return
  end

  if not state.timer then
    state.timer = uv.new_timer()
  end

  state.timer:stop()
  state.timer:start(DEBOUNCE_MS, 0, vim.schedule_wrap(function()
    preview_selected(state, false)
  end))
end

vim.api.nvim_create_autocmd('BufEnter', {
  group = preview_group,
  desc = 'Restore normal editing behavior for a file previously used as a netrw preview',
  callback = function(args)
    local buf = args.buf
    if not is_valid_buffer(buf) or vim.b[buf].netrw_live_preview_buffer ~= true then
      return
    end

    local win = vim.api.nvim_get_current_win()
    if is_valid_window(win) and vim.wo[win].previewwindow then
      return
    end

    if preview_buffers[buf] then
      restore_preview_buffer(buf, true)
    end
  end,
})

local function state_for(buf)
  local state = states[buf]
  if not state then
    state = { buf = buf }
    states[buf] = state
  end
  return state
end

local function schedule_leave_cleanup(state)
  close_timer(state, 'leave_timer')
  state.leave_timer = uv.new_timer()
  state.leave_timer:start(20, 0, vim.schedule_wrap(function()
    close_timer(state, 'leave_timer')

    if state.native_preview_active then
      return
    end

    local current_win = vim.api.nvim_get_current_win()
    local still_in_explorer = is_valid_window(current_win)
      and current_win == state.win
      and vim.api.nvim_win_get_buf(current_win) == state.buf
    if not still_in_explorer then
      close_preview(state)
    end
  end))
end

local function scroll_preview(direction, count)
  local preview = find_preview_window(vim.api.nvim_get_current_tabpage())
  if not preview then
    return
  end

  local key = vim.keycode(direction > 0 and '<C-e>' or '<C-y>')
  pcall(vim.api.nvim_win_call, preview, function()
    vim.cmd.normal({ args = { tostring(count) .. key }, bang = true })
  end)
end

function M.setup(buf)
  if vim.fn.has('nvim-0.12') == 0 or not is_valid_buffer(buf) then
    return false
  end

  if vim.b[buf].netrw_live_preview_configured then
    return true
  end

  if vim.fn.exists('*netrw#Call') ~= 1 then
    return false
  end

  vim.b[buf].netrw_live_preview_configured = true
  local state = state_for(buf)

  vim.keymap.set('n', 'p', function()
    state.win = vim.api.nvim_get_current_win()
    state.tab = vim.api.nvim_get_current_tabpage()
    preview_selected(state, true)
  end, {
    buffer = buf,
    desc = 'Netrw: Preview selection and enable live updates',
    nowait = true,
    silent = true,
  })

  vim.keymap.set('n', '<M-j>', function()
    scroll_preview(1, vim.v.count1)
  end, {
    buffer = buf,
    desc = 'Netrw: Scroll preview down',
    nowait = true,
    silent = true,
  })

  vim.keymap.set('n', '<M-k>', function()
    scroll_preview(-1, vim.v.count1)
  end, {
    buffer = buf,
    desc = 'Netrw: Scroll preview up',
    nowait = true,
    silent = true,
  })

  vim.api.nvim_create_autocmd('CursorMoved', {
    group = preview_group,
    buffer = buf,
    desc = 'Update an existing netrw preview after cursor movement',
    callback = function()
      state.win = vim.api.nvim_get_current_win()
      state.tab = vim.api.nvim_get_current_tabpage()
      schedule_preview(state)
    end,
  })

  vim.api.nvim_create_autocmd({ 'BufLeave', 'WinLeave' }, {
    group = preview_group,
    buffer = buf,
    desc = 'Close the netrw preview when leaving the explorer',
    callback = function()
      close_timer(state)
      schedule_leave_cleanup(state)
    end,
  })

  vim.api.nvim_create_autocmd('BufWipeout', {
    group = preview_group,
    buffer = buf,
    once = true,
    desc = 'Release netrw preview resources',
    callback = function()
      close_timer(state)
      close_timer(state, 'leave_timer')
      close_preview(state)
      states[buf] = nil
    end,
  })

  return true
end

return M