const axios = require('axios')
const decode = require('decode-html')
const CHANNEL = '#dev'
const ISSUE_REPO = 'foo/bar'

exports.otochan = (req, res) => {
  console.log('Received request:', req.body)

  // slack challenge
  if (req.body.challenge) {
    res.send(req.body.challenge)
    return
  }

  // slack event
  if (req.body.event) {
    handleSlack(req, res)
    return
  }
}

function handleSlack(req, res) {
  const event = req.body.event

  if (event.type === 'reaction_added') {
    if (event.reaction === 'イシュー') {
      handleReaction(event)
        .then(() => {
          res.send('ok')
        })
        .catch(err => {
          console.error(err)
          res.status(500).send(err.message)
        })

      return
    }
  }

  res.send('ok: no matched handler')
}

async function handleReaction(event) {
  const { channel, ts } = event.item
  const { messages } = await getMessages(channel, ts, 10)
  const message = messages[0]
  const permalink = await getPermalink(channel, message.ts)

  const repo = ISSUE_REPO

  const title = decode(message.text)
  const historyText = messages.reverse()
    .filter(m => m.type === 'message')
    .map(m => decode(m.text))
    .join("\n")

  const body = `${permalink}\n` + '```\n' + historyText + '\n```'

  const issues = await getLatestIssues(repo)
  const foundIssue = issues.find((issue) => {
    return issue.title === title
  })

  if (foundIssue) {
    return
  }

  const issue = await createIssue(repo, { title: title, body: body })
  const slackMessage = `<@${event.user}> ${issue.html_url}`
  await postMessage(channel, slackMessage)
}

function apiHeaders(token) {
  return {
    'Content-Type': 'application/json',
    'Authorization': `Bearer ${token}`
  }
}

async function getMessages (channel, ts, count = 1) {
  const token = process.env.SLACK_USER_TOKEN

  const res = await axios.get('https://slack.com/api/channels.history', {
    params: {
      channel: channel,
      latest: ts,
      count: count,
      inclusive: true,
      token: token
    }
  })

  return res.data
}

async function postMessage (channel, text) {
  const token = process.env.SLACK_TOKEN

  await axios.post('https://slack.com/api/chat.postMessage', {
    channel: channel,
    text: text,
    icon_emoji: ':chicken:'
  }, {
    headers: apiHeaders(token)
  })
}

async function getPermalink (channel, ts) {
  const res = await axios.get('https://slack.com/api/chat.getPermalink', {
    params: {
      channel: channel,
      message_ts: ts,
      token: process.env.SLACK_TOKEN
    }
  })

  return res.data.permalink
}

function githubApiHeaders() {
  return {
    ...apiHeaders(process.env.GITHUB_TOKEN),
    'Accept': 'application/vnd.github.v3+json'
  }
}

async function createIssue(repo, params) {
  const res = await axios.post(`https://api.github.com/repos/${repo}/issues`, params, {
    headers: githubApiHeaders()
  })

  if (res.status > 300) {
    console.error(res.data)
    throw new Error(res.data.message)
  }

  return res.data
}

async function getLatestIssues(repo) {
  const res = await axios.get(`https://api.github.com/repos/${repo}/issues`, {
    params: {
      state: 'all'
    },
    headers: githubApiHeaders()
  })

  if (res.status > 300) {
    console.error(res.data)
    throw new Error(res.data.message)
  }

  return res.data
}