#!/usr/bin/lua


local fs = require('luci.fs')
local nixio = require('nixio')
local platform_info = require('platform_info')
local uci = require('luci.model.uci').cursor()
local util = require('luci.util')

local autoupdater_util = require('autoupdater.util')
local autoupdater_version = require('autoupdater.version')


if not platform_info.get_image_name() then
  io.stderr:write("The autoupdater doesn't support this hardware model.\n")
  os.exit(1)
end


autoupdater_util.randomseed()


local settings = uci:get_all('autoupdater', 'settings')
local branch_name = settings.branch

local old_version = util.trim(fs.readfile(settings.version_file) or '')


-- If force is true the updater will perform an upgrade regardless of
-- the priority and even when it is disabled in uci
local force = false

-- If fallback is true the updater will perform an update only if the
-- timespan given by the priority and another 24h have passed
local fallback = false


local function parse_args()
  local i = 1
  while arg[i] do
    if arg[i] == '-f' then
      force = true
    elseif arg[i] == '--fallback' then
      fallback = true
    elseif arg[i] == '-b' then
      i = i+1

      if not arg[i] then
	io.stderr:write("Error parsing command line: expected branch name\n")
	os.exit(1)
      end

      branch_name = arg[i]
    else
      io.stderr:write("Error parsing command line: unexpected argument '" .. arg[i] .. "'\n")
      os.exit(1)
    end

    i = i+1
  end
end


parse_args()


local branch = uci:get_all('autoupdater', branch_name)
if not branch then
  io.stderr:write("Can't find configuration for branch '" .. branch_name .. "'\n")
  os.exit(1)
end


if settings.enabled ~= '1' and not force then
  io.stderr:write('autoupdater is disabled.\n')
  os.exit(0)
end


-- Verifies a file given as a list of lines with a list of signatures using ecdsaverify
local function verify_lines(lines, sigs)
  local command = string.format('ecdsaverify -n %i', branch.good_signatures)

  -- Build command line from sigs and branch.pubkey
  for _, sig in ipairs(sigs) do
    if sig:match('^' .. string.rep('%x', 128) .. '$') then
      command = command .. ' -s ' .. sig
    end
  end

  for _, key in ipairs(branch.pubkey) do
    if key:match('^' .. string.rep('%x', 64) .. '$') then
      command = command .. ' -p ' .. key
    end
  end


  -- Call ecdsautils
  local pid, f = autoupdater_util.popen(command)

  for _, line in ipairs(lines) do
    f:write(line)
    f:write('\n')
  end

  f:close()


  local wpid, status, code = nixio.waitpid(pid)
  return wpid and status == 'exited' and code == 0
end


-- Downloads, parses and verifies the update manifest from a mirror
-- Returns a table with the fields version, checksum and filename if everything is ok, nil otherwise
local function read_manifest(mirror)
  local sep = false

  local lines = {}
  local sigs = {}

  local branch_ok = false

  local ret = {}

  -- Read all lines from the manifest
  -- The upper part is saves to lines, the lower part to sigs
  for line in io.popen(string.format("wget -T 120 -O- '%s/%s.manifest'", mirror, branch.name), 'r'):lines() do
    if not sep then
      if line == '---' then
	sep = true
      else
	table.insert(lines, line)

	if line == ('BRANCH=' .. branch.name) then
	  branch_ok = true
	end

	local date = line:match('^DATE=(.+)$')
	local priority = line:match('^PRIORITY=([%d%.]+)$')
	local model, version, checksum, filename = line:match('^([^ ]+) ([^ ]+) ([^ ]+) ([^ ]+)$')

	if date then
	  ret.date = autoupdater_util.parse_date(date)
	elseif priority then
	  ret.priority = tonumber(priority)
	elseif model == platform_info.get_image_name() then
	  ret.version = version
	  ret.checksum = checksum
	  ret.filename = filename
	end
      end
    else
      table.insert(sigs, line)
    end
  end

  -- Do some very basic checks before checking the signatures
  -- (as the signature verification is computationally expensive)
  if not sep then
    io.stderr:write('There seems to have gone something wrong downloading the manifest from ' .. mirror .. '\n')
    return nil
  end

  if not ret.date or not ret.priority then
    io.stderr:write('The manifest downloaded from ' .. mirror .. ' is invalid (DATE or PRIORITY missing)\n')
    return nil
  end

  if not branch_ok then
    io.stderr:write('Wrong branch. We are on ', branch.name, '.\n')
    return nil
  end

  if not ret.version then
    io.stderr:write('No matching firmware found (model ' .. platform_info.get_image_name() .. ')\n')
    return nil
  end

  if not verify_lines(lines, sigs) then
    io.stderr:write('Not enough valid signatures!\n')
    return nil
  end

  return ret
end


-- Downloads the firmware image from a mirror to a given output file
local function fetch_firmware(mirror, filename, output)
  if os.execute(string.format("wget -T 120 -O '%s' '%s/%s'", output, mirror, filename)) ~= 0 then
    io.stderr:write('Error downloading the image from ' .. mirror .. '\n')
    return false
  end

  return true
end


-- Returns the computed update probability
local function get_probability(date, priority)
  local seconds = priority * 86400
  local diff = os.difftime(os.time(), date)

  if diff < 0 then
    -- When the difference is negative, there are two possibilities: The manifest contains a wrong date, or our own clock is wrong.
    -- As there isn't anything useful to do for an incorrect manifest, we'll assume the latter case and update anyways as we
    -- can't do anything better
    io.stderr:write('Warning: clock seems to be incorrect.\n')

    if tonumber(fs.readfile('/proc/uptime'):match('^([^ ]+) ')) < 600 then
      -- If the uptime is very low, it's possible we just didn't get the time over NTP yet, so we'll just wait until the next time the updater runs
      return 0
    else
      -- Will give 1 when priority == 0, and lower probabilities the higher the priority value is
      -- (similar to the old static probability system)
      return 0.75^priority
    end

  elseif fallback then
    if diff >= seconds + 86400 then
      return 1
    else
      return 0
    end

  elseif diff >= seconds then
    return 1

  else
    local x = diff/seconds
    -- This is the most simple polynomial with value 0 at 0, 1 at 1, and whose first derivative is 0 at both 0 and 1
    -- (we all love continuously differentiable functions, right?)
    return (-2)*x^3 + 3*x^2
  end
end


-- Tries to perform an update from a given mirror
local function autoupdate(mirror)
  local manifest = read_manifest(mirror)
  if not manifest then
    return false
  end

  if not autoupdater_version.newer_than(manifest.version, old_version) then
    io.stderr:write('No new firmware available.\n')
    return true
  end

  io.stderr:write('New version available.\n')


  if not force and math.random() >= get_probability(manifest.date, manifest.priority) then
    io.stderr:write('No autoupdate this time. Use -f to override.\n')
    return true
  end


  os.execute('sync; sysctl -w vm.drop_caches=3')
  collectgarbage()

  local image = os.tmpname()
  if not fetch_firmware(mirror, manifest.filename, image) then
    return false
  end

  local checksum = util.exec(string.format("sha512sum '%s'", image)):match('^%x+')
  if checksum ~= manifest.checksum then
    io.stderr:write('Invalid image checksum!\n')
    os.remove(image)
    return false
  end

  io.stderr:write('Upgrading firmware...\n')
  local null = nixio.open('/dev/null', 'w+')
  if null then
    nixio.dup(null, nixio.stdin)
    nixio.dup(null, nixio.stderr)
    if null:fileno() > 2 then
      null:close()
    end
  end

  nixio.exec('/sbin/sysupgrade', image)

  -- This should never be reached as nixio.exec replaces the autoupdater process unless /sbin/sysupgrade can't be executed
  -- We output the error message through stdout as stderr isn't available anymore
  io.write('Failed to call sysupgrade?\n')
  os.remove(image)
  os.exit(1)
end


local mirrors = branch.mirror

while #mirrors > 0 do
  local mirror = table.remove(mirrors, math.random(#mirrors))
  if autoupdate(mirror) then
    os.exit(0)
  end
end

io.stderr:write('No usable mirror found.\n')
os.exit(1)