#!/usr/bin/env ruby

# This script is designed to be launched with cron every n minutes to knock on
# txcatcher's API and check whether new transactions are being picked up by it.
#
# New transactions are being fetched from a third-party source (currently: blockcypher.com)
# and config is read from the same config file as the one txcatcher uses.
#
# If an incosistency is found, reports are sent to email and to the logfile
# placed in your config_dir/txcatcher_monitor_errors.log
# Successful checks are logged into config_dir/txcatcher_monitor.log
#
# To run this script, specify config dir like this:
#
#   txcatcher-monitor -c ~/.txcatcher/
#
# or
#
#   txcatcher-monitor --config-dir ~/.txcatcher/
#
# When you generated an example config file with txcatcher on the first run,
# you should look at "monitor" section for settings related to this script.
#
# Just in case, here they are:
#
# monitor:
#   txcatcher_url: "https://txcatcher-btc-mainnet.mydomain.com"
#   blockchain_source_url: "https://api.blockcypher.com/v1/btc/main/txs"
#   aws_ses:
#     region: 'us-west-2'
#     access_key: YOUR_AWS_KEY
#     secret_access_key: YOUR_AWS_SECRET_ACCESS_KEY
#   alert_mail:
#     from: "alert@email.com"
#     to:
#       - "your@email.com"
#     subject: "TxCatcher Alert"
#
#  However remember, you'll also need a 'logger' section in this file.

require "rubygems"
require "faraday"
require "aws-sdk-ses"
require "yaml"
require 'time'
require_relative "../lib/txcatcher/config"
require_relative "../lib/txcatcher/logger"
require_relative "../lib/txcatcher/initializer"

def send_alert(subject, text)

  return unless TxCatcher::Config["monitor"]["alert_mail"]

  # Do not send emails more often than once in 1 hour
  email_time_file = TxCatcher::Config.config_dir + "/txcatcher_monitor_last_email_time.txt"
  t = Time.parse(File.read(email_time_file)) if File.exists?(email_time_file)
  return if t && t > Time.now - 3600

  ses_config = TxCatcher::Config["monitor"]["aws_ses"]
  ses = Aws::SES::Client.new(
    region: ses_config["region"],
    access_key_id: ses_config["access_key"],
    secret_access_key: ses_config["secret_access_key"]
  )

  resp = ses.send_email({
    destination: { to_addresses: TxCatcher::Config["monitor"]["alert_mail"]["to"] },
    source: TxCatcher::Config["monitor"]["alert_mail"]["from"],
    message: {
      body: { text: { charset: "utf-8", data: text }},
      subject: { charset: "utf-8", data: subject   }
    }
  })

  File.open(email_time_file, 'w') { |f| f.write Time.now.to_s }

end

def latest_output_addr(i=0)

  txs      = nil
  attempts = 0
  until txs || attempts > 10
    attempts += 1
    begin
      response = Faraday.get do |req|
        req.url TxCatcher::Config["monitor"]["blockchain_source_url"]
        req.options.timeout = 5
        req.options.open_timeout = 5
      end
    rescue StandardError => e
      LOGGER.report(e, :error, data: { attempt: attempts })
      if attempts >= 10
        send_alert(
          "TxCatcher monitor error",
          "Tried fetching new txs from #{TxCatcher::Config["monitor"]["blockchain_source_url"]}, got the following error\n\n" +
          "#{e.to_s}\n\n#{e.backtrace.join("\n")}"
        )
        return nil
      else
        sleep 15
      end
    end
    txs = JSON.parse(response.body) if response
  end

  txs.each do |tx|
    if tx["outputs"] && tx["outputs"][i] && tx["outputs"][i]["addresses"]
      tx["outputs"][i]["addresses"].each do |addr|
        # Blockcypher returns old Litecoin P2SH addresses which start with 3, which
        # txcatcher doesn't support. Let's just ignore them.
        if addr[0] != "3" || !TxCatcher::Config["monitor"]["ignore_3_litecoin_addr"]
          return addr
        end
      end
    end
  end

end

def fetch_txcatcher_response(addr, sleep_time:)
  response = {}
  3.times do
    sleep sleep_time # let's wait, perhaps txcatcher hasn't caught up
    response = fetch_txcatcher_for_addr(addr)
    break unless response.empty?
  end
  return response
end

def fetch_txcatcher_for_addr(addr)
  response = Faraday.get do |req|
    req.url TxCatcher::Config["monitor"]["txcatcher_url"] + "/addr/#{addr}/utxo"
    req.options.timeout = 15
    req.options.open_timeout = 15
  end
  JSON.parse(response.body)
end

LOGGER = TxCatcher::Logger.new(log_file: "txcatcher_monitor.log", error_file: "txcatcher_monitor_errors.log", error_log_delimiter: "")
include TxCatcher::Initializer
ConfigFile.set!
read_config_file

response = nil
attempts = 0
addr     = nil
while attempts < 3 && (response.nil? || response.empty?)

  attempts += 1
  begin

    # if address is the same as in the previous attempt, let's try a different address.
    addr_index = 0
    begin
      a = latest_output_addr(addr_index)
      exit unless a # error already sent in latest_output_addr, so just exit.
      addr_index += 1
    end until addr != a || addr_index > 5
    addr = a
    url = TxCatcher::Config["monitor"]["txcatcher_url"] + "/addr/#{addr}/utxo"

    response = fetch_txcatcher_response(addr, sleep_time: TxCatcher::Config["monitor"]["retry_sleep_time"] )

    if response.empty?
      LOGGER.report("Checked #{url}, got empty response, attempt #{attempts}", :error)
      if attempts >= 3
        send_alert("TxCatcher response empty", "TxCatcher returned an empty {} for #{url}")
      end
    else
      LOGGER.report("Checked #{url}, got #{response.size} utxo for addr #{addr}, attempt #{attempts}", :info)
    end

  rescue StandardError => e
    LOGGER.report(e, :error, data: { attempt: attempts, url: url })
    if attempts >= 3
      send_alert(
        "TxCatcher monitor error",
        "While checking #{url} response, got the following error\n\n" +
        "#{e.to_s}\n\n#{e.backtrace.join("\n")}"
      )
    else
      # Let's give some sufficient time before we retry.
      #
      # Greater chance to have new transactions on blockcypher and new addresses to check.
      # This error could simply be due to a long list of tx utxos that's being loaded
      # and connection timeout hitting before that.
      sleep TxCatcher::Config["monitor"]["retry_sleep_time"]
    end
  end # begin/rescue
end #while

# Only report if we actually fetched something. Otherwise another error was probably reported already.