# 必要なパッケージ
library(dplyr)
library(xml2)
library(rvest)
library(readr)

# 対応しているWebサイトと関数
# 1. retest_qt... qiita.com
# 2. retest_gh... github.com
# 3. retest_so... stackoverflow.com

retest_qt <- function(url, rank)
{
  # 1. qiita.com でのコードまでのCSSパス
  path <- 'div .code-frame .highlight pre'

  # 2. コード部分を指定して.Rファイルを一時フォルダ内に作る
  cat(html_text(
    html_nodes(read_html(x = url),
               css = path)[rank]),
    file = tempfile(pattern = paste(rank, "retest", sep = "_"), fileext = ".r"))

  # 3. 2.で作成した一時ファイルまでのパス
  tmp.file.path <- paste(tempdir(), grep(pattern = paste(rank, "retest", sep = "_"), ".r$",
                                    x = list.files(tempdir()),
                                    value = TRUE), sep = "/")
  # 4. Rファイルをsourceとして実行。実行後は削除する
    tryCatch(
    {
      source(file = tmp.file.path, echo = TRUE)
    }, error = function()
      {
      file.remove(tmp.file.path)
      },
    finally = file.remove(tmp.file.path)
    )
}

retest_gh <- function(url, rank, lang = c("R", "plain"), execute = TRUE)
{

  if (lang == "R") {
    path <- 'div .highlight.highlight-R'
  } else if (lang == "plain") {
    path <- 'pre code'
  }
  cat(html_text(
      html_nodes(read_html(x = url),
                 css = path)[rank]),
      file = tempfile(pattern = paste(rank, "retest", sep = "_"), fileext = ".r"))
  tmp.file.path <- paste(tempdir(), grep(pattern = paste(rank, "retest", sep = "_"), ".r$",
                                         x = list.files(tempdir()),
                                         value = TRUE), sep = "/")
  tryCatch(
    {
      source(file = tmp.file.path, echo = TRUE)
    }, error = function()
    {
      file.remove(tmp.file.path)
    },
    finally = file.remove(tmp.file.path)
  )
}

retest_so <- function(url, rank)
{
  path <- 'pre code'
  cat(html_text(
      html_nodes(read_html(x = url), css = path)[rank]),
    file = tempfile(pattern = paste(rank, "retest", sep = "_"), fileext = ".r"))
  tmp.file.path <- paste(tempdir(), grep(pattern = paste(rank, "retest", sep = "_"), ".r$",
                                         x = list.files(tempdir()),
                                         value = TRUE), sep = "/")
  tryCatch(
    {
      source(file = tmp.file.path, echo = TRUE)
    }, error = function()
    {
      file.remove(tmp.file.path)
    },
    finally = file.remove(tmp.file.path)
  )
}