add flag to enable telescope preview and to choose picker (#97)

* Flags to enable telescope preview and to choose picker

* 4 spaces -> 2 space lua

* changes to align with repo code-style

vim/lua/himalaya/mbox.lua

@@ -0,0 +1,57 @@
+local M = {}
+
+local actions = require('telescope.actions')
+local action_state = require('telescope.actions.state')
+local finders = require('telescope.finders')
+local pickers = require('telescope.pickers')
+local sorters = require('telescope.sorters')
+local previewers = require('telescope.previewers')
+
+local function preview_command(entry, bufnr)
+  vim.api.nvim_buf_call(bufnr, function()
+    local page = 0 -- page 0 for preview
+    local success, output = pcall(vim.fn['himalaya#msg#list_with'], entry.value, page, true)
+    if not (success) then
+      vim.cmd('redraw')
+      vim.bo.modifiable = true
+      local errors = vim.fn.split(output, '\n')
+      errors[1] = "Errors: "..errors[1]
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, errors)
+    end
+  end)
+end
+
+local function entry_maker(entry)
+  return {
+    value = entry,
+    display = entry,
+    ordinal = entry,
+    preview_command = preview_command,
+  }
+end
+
+M.mbox_picker = function(mboxes)
+  local finder_opts = {results = mboxes}
+  local previewer = nil
+  if vim.g.himalaya_telescope_preview_enabled then
+    finder_opts.entry_maker = entry_maker
+    previewer = previewers.display_content.new({})
+  end
+  pickers.new {
+    results_title = 'Mailboxes',
+    finder = finders.new_table(finder_opts),
+    sorter = sorters.fuzzy_with_index_bias(),
+    attach_mappings = function(prompt_bufnr)
+      actions.select_default:replace(function()
+        local selection = action_state.get_selected_entry()
+        actions.close(prompt_bufnr)
+        vim.fn['himalaya#mbox#post_input'](selection.display)
+      end)
+
+      return true
+    end,
+    previewer = previewer,
+  }:find()
+end
+
+return M