#!/usr/bin/env lua

--- This script provides an interface to upgrade or downgrade the Doodle3D wifibox.
-- It can both be used as a standalone command-line tool and as a Lua library.

-- TODO/NOTES:
-- add to status: validImage: none|<version> (can use checkValidImage for this)
-- any more TODO's across this file?
-- max 1 image tegelijk (moet api doen), en rekening houden met printbuffer (printen blokkeren?)

-- MAYBE/LATER:
-- add API calls to retrieve a list of all versions with their info (i.e., the result of getAvailableVersions)
-- wget: add provision (in verbose mode?) to use '-v' instead of '-q' and disable output redirection
-- document index file format (Version first, then in any order: Files: sysup; factory, FileSize: sysup; factory, MD5: sysup; factory, ChangelogStart:, ..., ChangelogEnd:)
-- copy improved fileSize back to utils (add unit tests!)
-- create new utils usable by updater as well as api? (remove dependencies on uci and logger etc)
-- note: take care not to print any text in module functions, as this breaks http responses
-- change representation of sysupgrade/factory info in versionInfo? (and also in image index?) <- create api call to get all info on all versions?

local M = {}

--- Possible states the updater can be in, they are stored in @{STATE_FILE}.
-- @table STATE
M.STATE = {
	NONE = 1, -- @{STATE_FILE} does not exist
	DOWNLOADING = 2, -- downloading is started but not finished yet
	DOWNLOAD_FAILED = 3, -- download failed (often occurs when the wifibox is not connected to internet)
	IMAGE_READY = 4, -- download succeeded and the image is valid
	INSTALLING = 5, -- image is being installed (this state will probably never be returned since the box is flashing/rebooting)
	INSTALLED = 6, -- image has been installed successfully (this state will never be returned since the box will reboot)
	INSTALL_FAILED = 7 -- installation failed
}

-- Names for the states in @{STATE}, these are returned through the REST API.
M.STATE_NAMES = {
	[M.STATE.NONE] = 'none', [M.STATE.DOWNLOADING] = 'downloading', [M.STATE.DOWNLOAD_FAILED] = 'download_failed', [M.STATE.IMAGE_READY] = 'image_ready',
	[M.STATE.INSTALLING] = 'installing', [M.STATE.INSTALLED] = 'installed', [M.STATE.INSTALL_FAILED] = 'install_failed'
}

--- The base URL to use for finding update files.
-- This URL will usually contain both an OpenWRT feed directory and an `images`-directory.
-- This script uses only the latter, and expects to find the file @{IMAGE_INDEX_FILE} there.
M.DEFAULT_BASE_URL = 'http://doodle3d.com/updates'
--M.DEFAULT_BASE_URL = 'http://localhost/~USERNAME/wifibox/updates'

--- The index file containing metadata on update images.
M.IMAGE_INDEX_FILE = 'wifibox-image.index'

--- Path to the updater cache.
M.CACHE_PATH = '/tmp/d3d-updater'

--- Name of the file to store current state in, this file resides in @{CACHE_PATH}.
M.STATE_FILE = 'update-state'

M.WGET_OPTIONS = "-q -t 1 -T 30"
--M.WGET_OPTIONS = "-v -t 1 -T 30"

local verbosity = 0 -- set by parseCommandlineArguments()
local log = nil -- wifibox API can use M.setLogger to enable this module to use its logger
local useCache = true -- default, can be overwritten using M.setUseCache()
local baseUrl = M.DEFAULT_BASE_URL -- default, can be overwritten by M.setBaseUrl()



---------------------
-- LOCAL FUNCTIONS --
---------------------

--- Log a message with the given level, if logging is enabled for that level.
-- Messages will be written to [stdout](http://www.cplusplus.com/reference/cstdio/stdout/), or logged using the logger set with @{setLogger}.
-- @number lvl Level to log to, use 1 for important messages, 0 for regular messages and -1 for less important messages.
-- @string msg The message to log.
local function P(lvl, msg)
	if log then
		if lvl == -1 then log:debug(msg)
		elseif lvl == 0 or lvl == 1 then log:info(msg)
		end
	else
		if (-lvl <= verbosity) then print(msg) end
	end
end

--- Log a debug message, this function wraps @{P}.
-- The message will be logged with level -1 and be prefixed with '(DBG)'.
-- @string msg The message to log.
local function D(msg) P(-1, (log and msg or "(DBG) " .. msg)) end

--- Log an error.
-- Messages will be written to [stderr](http://www.cplusplus.com/reference/cstdio/stderr/), or logged using the logger set with @{setLogger}.
-- @string msg The message to log.
local function E(msg)
	if log then log:error(msg)
	else io.stderr:write(msg .. '\n')
	end
end

--- Splits the return status from `os.execute`, which consists of two bytes.
--
-- `os.execute` internally calls [system](http://linux.die.net/man/3/system),
-- which usually returns the command exit status as high byte (see [WEXITSTATUS](http://linux.die.net/man/2/wait)).
-- Furthermore, see [shifting bits in Lua](http://stackoverflow.com/questions/16158436/how-to-shift-and-mask-bits-from-integer-in-lua).
-- @number exitStatus The combined exit status.
-- @treturn number The command exit status.
-- @treturn number The `os.execute`/[system](http://linux.die.net/man/3/system) return status.
local function splitExitStatus(exitStatus)
	if exitStatus == -1 then return -1,-1 end
	local cmdStatus = math.floor(exitStatus / 256)
	local systemStatus = exitStatus - cmdStatus * 256
	return cmdStatus, systemStatus
end

--- Returns a human-readable message for a [wget exit status](http://www.gnu.org/software/wget/manual/wget.html#Exit-Status).
-- @number exitStatus An exit status from wget.
-- @treturn string|number Either the status followed by a description, or a message indicating the call was interrupted, or just the status if it was not recognized.
local function wgetStatusToString(exitStatus)
	local wgetStatus,systemStatus = splitExitStatus(exitStatus)

	if systemStatus ~= 0 then
		return "interrupted:" .. systemStatus
	end

	-- adapted from man(1) wget on OSX
	local statusTexts = {
		['0'] = 'Ok',
		['1'] = 'Generic error',
		['2'] = 'Parse error', -- for instance, when parsing command-line options, the .wgetrc or .netrc...
		['3'] = 'File I/O error',
		['4'] = 'Network failure',
		['5'] = 'SSL verification failure',
		['6'] = 'Username/password authentication failure',
		['7'] = 'Protocol error',
		['8'] = 'Server issued an error response'
	}
	local result = statusTexts[tostring(wgetStatus)]

	if result then return exitStatus .. ": " .. result
	else return exitStatus
	end
end

--- Creates the updater cache directory.
-- @return bool|nil True, or nil on error.
-- @return ?string A message in case of error.
local function createCacheDirectory()
	if os.execute('mkdir -p ' .. M.CACHE_PATH) ~= 0 then
		return nil,"Error: could not create cache directory '" .. M.CACHE_PATH .. "'"
	end
	return true
end

--- Retrieves the current updater state code and message from @{STATE_FILE}.
-- @treturn STATE The current state code (@{STATE}.NONE if no state has been set).
-- @treturn string The current state message (empty string if no state has been set).
local function getState()
	local file,msg = io.open(M.CACHE_PATH .. '/' .. M.STATE_FILE, 'r')
	if not file then return M.STATE.NONE,"" end

	local state = file:read('*a')
	file:close()
	local code,msg = string.match(state, '([^|]+)|+(.*)')
	return code,msg
end

--- Trims whitespace from both ends of a string.
-- See [this Lua snippet](http://snippets.luacode.org/?p=snippets/trim_whitespace_from_string_76).
-- @string s The text to trim.
-- @treturn string s, with whitespace trimmed.
local function trim(s)
	if type(s) ~= 'string' then return s end
	return (s:find('^%s*$') and '' or s:match('^%s*(.*%S)'))
end

--- Read the contents of a file.
--
-- TODO: this file has been copied from @{util.utils}.lua and should be merged again.
-- @string filePath The file to read.
-- @bool trimResult Whether or not to trim the read data.
-- @treturn bool|nil True, or nil on error.
-- @treturn ?string A descriptive message on error.
-- @treturn ?number TODO: find out why this value is returned.
local function readFile(filePath, trimResult)
	local f, msg, nr = io.open(filePath, 'r')
	if not f then return nil,msg,nr end

	local res = f:read('*all')
	f:close()

	if trimResult then
		res = trim(res)
	end

	return res
end

--- Reports whether or not a file exists.
--
-- TODO: this file has been copied from @{util.utils}.lua and should be merged again.
-- @string file The file to report about.
-- @treturn bool True if the file exists, false otherwise.
local function exists(file)
	if not file or type(file) ~= 'string' or file:len() == 0 then
		return nil, "file must be a non-empty string"
	end

	local r = io.open(file, 'r') -- ignore returned message
	if r then r:close() end
	return r ~= nil
end

--- Reports the size of a file or file handle.
--
-- TODO: this file has been copied from @{util.utils}.lua and should be merged again.
-- @param file A file path or open file handle.
-- @treturn number Size of the file.
local function fileSize(file)
	local size = nil
	if type(file) == 'file' then
		local current = file:seek()
		size = file:seek('end')
		file:seek('set', current)
	elseif type(file) == 'string' then
		local f = io.open(file)
		if f then
			size = f:seek('end')
			f:close()
		end
	end

	return size
end

--- Runs an arbitrary shell command.
-- @string command The command to run.
-- @bool dryRun Only log a message if true, otherwise run the command and log a message.
-- @treturn number Exit status of of command or -1 if dryRun is true.
local function runCommand(command, dryRun)
	D("about to run: '" .. command .. "'")
	return (not dryRun) and os.execute(command) or -1
end

--- Removes a file.
-- @string filePath The file to remove.
local function removeFile(filePath)
	return runCommand('rm ' .. filePath)
end

--- Downloads a file and stores it locally.
-- @string url The full URL to download.
-- @string saveDir The path at which to save the downloaded file.
-- @string[opt] filename File name to save as, note that leaving this out has issues with files not being overwritten but suffixed with '.1', '.2',etc instead.
-- @treturn number|nil Exit status of wget command or nil on error.
-- @treturn ?string Descriptive message if saveDir is nil or empty.
local function downloadFile(url, saveDir, filename)
	if not saveDir or saveDir:len() == 0 then return nil, "saveDir must be non-empty" end
	local outArg = (filename:len() > 0) and (' -O' .. filename) or ''
	if filename:len() > 0 then
		return runCommand('wget ' .. M.WGET_OPTIONS .. ' -O ' .. saveDir .. '/' .. filename .. ' ' .. url .. ' 2> /dev/null')
	else
		return runCommand('wget ' .. M.WGET_OPTIONS .. ' -P ' .. saveDir .. ' ' .. url .. ' 2> /dev/null')
	end
end

--- Parses command-line arguments and returns a table containing information distilled from them.
-- @tparam table arglist A table in the same form as the [arg table](http://www.lua.org/pil/1.4.html) created by Lua.
-- @treturn table|nil A table containing information on what to do, or nil if invalid arguments were specified.
-- @treturn ?string Descriptive message on error.
local function parseCommandlineArguments(arglist)
	local result = { verbosity = 0, baseUrl = M.DEFAULT_BASE_URL, action = nil }
	local nextIsVersion, nextIsUrl = false, false
	for index,argument in ipairs(arglist) do
		if nextIsVersion then
			result.version = argument; nextIsVersion = false
		elseif nextIsUrl then
			result.baseUrl = argument; nextIsUrl = false
		else
			if argument == '-h' then result.action = 'showHelp'
			elseif argument == '-q' then result.verbosity = -1
			elseif argument == '-V' then result.verbosity = 1
			elseif argument == '-c' then result.useCache = true
			elseif argument == '-C' then result.useCache = false
			elseif argument == '-u' then nextIsUrl = true
			elseif argument == '-v' then result.action = 'showCurrentVersion'
			elseif argument == '-s' then result.action = 'showStatus'
			elseif argument == '-l' then result.action = 'showAvailableVersions'
			elseif argument == '-i' then result.action = 'showVersionInfo'; nextIsVersion = true
			elseif argument == '-d' then result.action = 'imageDownload'; nextIsVersion = true
			elseif argument == '-f' then result.action = 'imageInstall'; nextIsVersion = true
			elseif argument == '-r' then result.action = 'clear'
			else return nil,"unrecognized argument '" .. argument .. "'"
			end
		end
	end

	if result.version then
		result.version = M.parseVersion(result.version)
		if not result.version then
			return nil,"error parsing specified version"
		end
	end

	if nextIsVersion then return nil, "missing required version argument" end
	if nextIsUrl then return nil, "missing required URL argument" end

	return result
end

--- Returns the [MD5](http://en.wikipedia.org/wiki/MD5) hash for a given file.
--
-- NOTE: this function is not implemented, and a better hash function should probably be chosen anyway.
-- @string filepath The path of which to calculate the MD5-sum.
-- @treturn nil
local function md5sum(filepath)
	return nil
	-- TODO [osx: md5 -q <file>], [linux: ?]
end




----------------------
-- MODULE FUNCTIONS --
----------------------

--- Enables use of the given @{util.logger} object, otherwise `stdout`/`stderr` will be used.
-- @tparam util.logger logger The logger to log future messages to.
function M.setLogger(logger)
	log = logger
end

--- Controls whether or not to use pre-existing files over (re-)downloading them.
--
-- Note that the mechanism is currently naive, (e.g., there are no mechanisms like maximum cache age).
-- @bool use If true, try not to download anything unless necessary.
function M.setUseCache(use)
	useCache = use
end

--- Sets the base URL to use for finding update images, defaults to @{DEFAULT_BASE_URL}.
-- @string url The new base URL to use.
function M.setBaseUrl(url)
	baseUrl = url
end

--- Returns a table with information about current update status of the wifibox.
--
-- The result table will contain at least the current version, current state code and text.
-- If the box has internet access, it will also include the newest version available.
-- If an image is currently being downloaded, progress information will also be included.
--
-- @treturn bool True if status has been determined fully, false if not.
-- @treturn table The result table.
-- @treturn ?string Descriptive message in case the result table is not complete.
function M.getStatus()
	if not baseUrl then baseUrl = M.DEFAULT_BASE_URL end
	local unknownVersion = { major = 0, minor = 0, patch = 0 }
	local result = {}

	result.currentVersion = M.getCurrentVersion()
	result.stateCode, result.stateText = getState()
	result.stateCode = tonumber(result.stateCode)

	local verTable,msg = M.getAvailableVersions()
	if not verTable then
		D("could not obtain available versions (" .. msg .. ")")
		-- TODO: set an error state in result to signify we probably do not have internet access?
		return false, result, msg
	end

	local newest = verTable and verTable[#verTable]
	result.newestVersion = newest and newest.version or unknownVersion

	if result.stateCode == M.STATE.DOWNLOADING then
		result.progress = fileSize(M.CACHE_PATH .. '/' .. newest.sysupgradeFilename)
		if not result.progress then result.progress = 0 end -- in case the file does not exist yet (which yields nil)
		result.imageSize = newest.sysupgradeFileSize
	end

	return true, result
end

--- Turns a plain-text version as returned by @{formatVersion} into a table.
-- @tparam string|table versionText The version string to parse, if it is already a table, it is returned as-is.
-- @treturn table A parse version.
function M.parseVersion(versionText)
	if type(versionText) == 'table' then return versionText end
	if not versionText or versionText:len() == 0 then return nil end

	local major,minor,patch = versionText:match("^%s*(%d+)%.(%d+)%.(%d+)%s*$")
	if not major or not minor or not patch then return nil end

	return { ['major'] = major, ['minor'] = minor, ['patch'] = patch }
end

--- Formats a version as returned by @{parseVersion}.
-- @tparam table|string version The version to format, if it is already a string, that will be returned unmodified.
-- @treturn string A formatted version.
function M.formatVersion(version)
	if type(version) == 'string' then return version end
	return version.major .. "." .. version.minor .. "." .. version.patch
end

--- Compares two versions.
-- @tparam table versionA A version as returned by @{parseVersion}.
-- @tparam table versionB A version as returned by @{parseVersion}.
-- @treturn number -1 if versionA is smaller than versionB, 0 if versions are equal or 1 if versionA is larger than versionB.
function M.compareVersions(versionA, versionB)
	if type(versionA) ~= 'table' or type(versionB) ~= 'table' then return nil end
	local diff = versionA.major - versionB.major
	if diff == 0 then diff = versionA.minor - versionB.minor end
	if diff == 0 then diff = versionA.patch - versionB.patch end
	return diff > 0 and 1 or (diff < 0 and -1 or 0)
end

--- Returns information on a version if it can be found in a collection of versions as returned by @{getAvailableVersions}.
-- @tparam table version The version to look for.
-- @tparam table[opt] verTable A table containing a collection of versions, if not passed in, it will be obtained using @{getAvailableVersions}.
-- @treturn table|nil Version information table found in the collection, or nil on error or if not found.
-- @treturn string Descriptive message in case of error or if the version could not be found.
function M.findVersion(version, verTable)
	local msg = nil
	version = M.parseVersion(version)
	if not verTable then verTable,msg = M.getAvailableVersions() end

	if not verTable then return nil,msg end

	for _,ent in pairs(verTable) do
		if M.compareVersions(ent.version, version) == 0 then return ent end
	end
	return nil,"no such version"
end

--- Creates an image file name based on given properties.
-- The generated name has the following form: `doodle3d-wifibox-<version>-<deviceType>-<'factory'|'sysupgrade'>.bin`.
-- @tparam table|string version The version of the image.
-- @string[opt] devType Openwrt device identifier (defaults to 'tl-mr3020').
-- @bool[opt] isFactory Switches between factory or sysupgrade image name.
-- @treturn string The constructed file name.
function M.constructImageFilename(version, devType, isFactory)
	local sf = isFactory and 'factory' or 'sysupgrade'
	local v = M.formatVersion(version)
	local dt = devType and devType or 'tl-mr3020'
	return 'doodle3d-wifibox-' .. M.formatVersion(v) .. '-' .. dt .. '-' .. sf .. '.bin'
end

--- Checks whether a valid image file is present in @{CACHE_PATH} for the given image properties.
-- The versionEntry table will be augmented with an `isValid` key.
--
-- NOTE: currently, this function only checks the image exists and has the correct size.
-- Sysupgrade will perform integrity checks, so this is not a major issue.
--
-- @tparam table versionEntry A version information table.
-- @string[opt] devType Image device type, see @{constructImageFilename}.
-- @bool[opt] isFactory Image type, see @{constructImageFilename}.
-- @treturn bool True if a valid image is present, false otherwise.
function M.checkValidImage(versionEntry, devType, isFactory)
	local filename = M.constructImageFilename(versionEntry.version, devType, isFactory)
	--return versionEntry.md5 == md5sum(M.CACHE_PATH .. '/' .. filename)
	local size = fileSize(M.CACHE_PATH .. '/' .. filename)
	versionEntry.isValid = versionEntry.sysupgradeFileSize == size
	return versionEntry.isValid
end

--- Returns the current wifibox version text, extracted from `/etc/wifibox-version`.
-- @treturn string Current version as plain-text.
function M.getCurrentVersionText()
	local res,msg,nr = readFile('/etc/wifibox-version', true)
	if res then return res else return nil,msg,nr end
end

--- Returns the current wifibox version as a table with major, minor and patch as keys.
-- @treturn table Current version as version table.
function M.getCurrentVersion()
	local vt,msg = M.getCurrentVersionText()
	return vt and M.parseVersion(vt) or nil,msg
end

--- Returns an indexed and sorted table containing version information tables.
-- The information is obtained from the either cached or downloaded image index (@{IMAGE_INDEX_FILE}).
-- @treturn table A table with a collection of version information tables.
function M.getAvailableVersions()
	if not baseUrl then baseUrl = M.DEFAULT_BASE_URL end
	local indexFilename = M.CACHE_PATH .. '/' .. M.IMAGE_INDEX_FILE

	local ccRv,ccMsg = createCacheDirectory()
	if not ccRv then return nil,ccMsg end

	if not useCache or not exists(indexFilename) then
		local rv = downloadFile(baseUrl .. '/images/' .. M.IMAGE_INDEX_FILE, M.CACHE_PATH, M.IMAGE_INDEX_FILE)
		if rv ~= 0 then return nil,"could not download image index file (" .. wgetStatusToString(rv) .. ")" end
	end

	local status,idxLines = pcall(io.lines, indexFilename)

	if not status then return nil,"could not open image index file '" .. indexFilename .. "'" end --do not include io.lines error message

	local result,entry = {}, nil
	local lineno,changelogMode = 1, false
	for line in idxLines do
		local k,v = line:match('^(.-):(.*)$')
		k,v = trim(k), trim(v)
		if not log then D("#" .. lineno .. ": considering '" .. line .. "' (" .. (k or '<nil>') .. " / " .. (v or '<nil>') .. ")") end
		if not changelogMode and (not k or not v) then return nil,"incorrectly formatted line in index file (line " .. lineno .. ")" end

		if k == 'ChangelogEnd' then
			changelogMode = false
		elseif changelogMode then
			entry.changelog = entry.changelog .. line .. '\n'
		else
			if k == 'Version' then
				if entry ~= nil then table.insert(result, entry) end

				local pv = M.parseVersion(v)
				if not pv then return nil,"incorrect version text in index file (line " .. lineno .. ")" end
				entry = { version = pv }
			elseif k == 'ChangelogStart' then
				changelogMode = true
				entry.changelog = ""
			elseif k == 'Files' then
				local sName,fName = v:match('^(.-);(.*)$')
				sName,fName = trim(sName), trim(fName)
				if sName then entry.sysupgradeFilename = sName end
				if fName then entry.factoryFilename = fName end
			elseif k == 'FileSize' then
				local sSize,fSize = v:match('^(.-);(.*)$')
				sSize,fSize = trim(sSize), trim(fSize)
				if sSize then entry.sysupgradeFileSize = tonumber(sSize) end
				if fSize then entry.factoryFileSize = tonumber(fSize) end
			elseif k == 'MD5' then
				local sSum,fSum = v:match('^(.-);(.*)$')
				sSum,fSum = trim(sSum), trim(fSum)
				if sSum then entry.sysupgradeMD5 = sSum end
				if fSum then entry.factoryMD5 = fSum end
			else
				P(-1, "ignoring unrecognized field in index file '" .. k .. "' (line " .. lineno .. ")")
			end
		end
		lineno = lineno + 1
	end

	if entry ~= nil then table.insert(result, entry) end

	table.sort(result, function(a,b)
		return M.compareVersions(a.version,b.version) < 0
	end)

	return result
end

--- Attempts to download an image file with the requested properties.
-- @tparam table versionEntry A version information table.
-- @string[opt] devType Image device type, see @{constructImageFilename}.
-- @bool[opt] isFactory Image type, see @{constructImageFilename}.
-- @treturn bool|nil True if successful, or nil on error.
-- @treturn ?string|number (optional) Descriptive message on general error, or wget exit status.
function M.downloadImageFile(versionEntry, devType, isFactory)
	if not baseUrl then baseUrl = M.DEFAULT_BASE_URL end
	local filename = M.constructImageFilename(versionEntry.version, devType, isFactory)
	local doDownload = not useCache

	local ccRv,ccMsg = createCacheDirectory()
	if not ccRv then return nil,ccMsg end

	if versionEntry.isValid == false then
		doDownload = true
	elseif versionEntry.isValid == nil then
		M.checkValidImage(versionEntry, devType, isFactory)
		if versionEntry.isValid == false then doDownload = true end
	end

	local rv = 0
	if doDownload then
		M.setState(M.STATE.DOWNLOADING, "Downloading image (" .. filename .. ")")
		rv = downloadFile(baseUrl .. '/images/' .. filename, M.CACHE_PATH, filename)
	end

	if rv == 0 then
		if M.checkValidImage(versionEntry, devType, isFactory) then
			M.setState(M.STATE.IMAGE_READY, "Image downloaded, ready to install (image name: " .. filename .. ")")
			return true
		else
			removeFile(M.CACHE_PATH .. '/' .. filename)
			local ws = "Image download failed (invalid image)"
			M.setState(M.STATE.DOWNLOAD_FAILED, ws)
			return nil,ws
		end
	else
		local ws = wgetStatusToString(rv)
		removeFile(M.CACHE_PATH .. '/' .. filename)
		M.setState(M.STATE.DOWNLOAD_FAILED, "Image download failed (wget error: " .. ws .. ")")
		return nil,ws
	end
end

--- Issues a [sysupgrade](http://wiki.openwrt.org/doc/howto/generic.sysupgrade) command with a wifibox image file.
--
-- This function will not return if it does its job successfully, the device will flash and reboot instead.
-- @tparam table versionEntry A version information table.
-- @bool[opt] noRetain If true, do not keep files in overlay filesystem (i.e., the '-n' switch in sysupgrade).
-- @string[opt] devType Image device type, see @{constructImageFilename}.
-- @bool[opt] isFactory Image type, see @{constructImageFilename}.
-- @treturn bool|nil True on success (with the 'exception' as noted above) or nil on error.
-- @treturn ?string|number (optional) Descriptive message or sysupgrade exit status on error.
function M.flashImageVersion(versionEntry, noRetain, devType, isFactory)
	log:info("flashImageVersion")
	local imgName = M.constructImageFilename(versionEntry.version, devType, isFactory)
	local cmd = noRetain and 'sysupgrade -n ' or 'sysupgrade '
	cmd = cmd .. M.CACHE_PATH .. '/' .. imgName

	local ccRv,ccMsg = createCacheDirectory()
	if not ccRv then return nil,ccMsg end

	if not M.checkValidImage(versionEntry) then
		return nil,"no valid image for requested version present"
	end

	M.setState(M.STATE.INSTALLING, "Installing new image (" .. imgName .. ")") -- yes this is rather pointless
	local rv = runCommand(cmd) -- if everything goes to plan, this will not return

	if rv == 0 then
		M.setState(M.STATE.INSTALLED, "Image installed")
	else
		-- NOTE: if cmdrv == 127, this means the command was not found
		local cmdrv,sysrv = splitExitStatus(rv)
		M.setState(M.STATE.INSTALL_FAILED, "Image installation failed (sysupgrade returned " .. cmdrv .. ", execution status: " .. sysrv .. ")")
	end

	return (rv == 0) and true or nil,rv
end

--- Clears '*.bin' in the @{CACHE_PATH} directory.
-- @treturn bool|nil True on success, or nil on error.
-- @treturn ?string Descriptive message on error.
function M.clear()
	local ccRv,ccMsg = createCacheDirectory()
	if not ccRv then return nil,ccMsg end

	D("Removing " .. M.CACHE_PATH .. "/doodle3d-wifibox-*.bin")
	M.setState(M.STATE.NONE, "")
	local rv = os.execute('rm -f ' .. M.CACHE_PATH .. '/doodle3d-wifibox-*.bin')
	return (rv == 0) and true or nil,"could not remove image files"
end

--- Set updater state.
--
-- NOTE: make sure the cache directory  @{CACHE_PATH} exists before calling this function or it will fail.
--
-- NOTE: this function _can_ fail but this is not expected to happen so the return value is mostly ignored for now.
--
-- @number code The @{STATE} code to set.
-- @string msg The accompanying state message to set.
-- @treturn bool True on success or false if the state file could not be opened for writing.
function M.setState(code, msg)
	local s = code .. '|' .. msg
	D("set update state: " .. M.STATE_NAMES[code] .. " ('" .. s .. "')")
	local file,msg = io.open(M.CACHE_PATH .. '/' .. M.STATE_FILE, 'w')

	if not file then
		E("error: could not open state file for writing (" .. msg .. ")")
		return false
	end

	file:write(s)
	file:close()
	return true
end



----------
-- MAIN --
----------

--- The main function which will be called in standalone mode.
-- At the end of the file, this function will be invoked only if `arg` is defined,
-- so this file can also be used as a library.
-- Command-line arguments are expected to be present in the global `arg` variable.
local function main()
	local argTable,msg = parseCommandlineArguments(arg)

	if not argTable then
		E("error interpreting command-line arguments, try '-h' for help (".. msg ..")")
		os.exit(1)
	end

	verbosity = argTable.verbosity
	if argTable.useCache ~= nil then useCache = argTable.useCache end

	P(0, "Doodle3D Wifibox firmware updater")
	local cacheCreated,msg = createCacheDirectory()
	if not cacheCreated then
		E(msg)
		os.exit(1)
	end

	if argTable.action == 'showHelp' then
		P(1, "\t-h\t\tShow this help message")
		P(1, "\t-q\t\tquiet mode")
		P(1, "\t-V\t\tverbose mode")
		P(1, "\t-c\t\tUse cache as much as possible")
		P(1, "\t-C\t\tDo not use the cache")
		P(1, "\t-u <base_url>\tUse specified base URL (default: " .. M.DEFAULT_BASE_URL .. ")")
		P(1, "\t-v\t\tShow current image version")
		P(1, "\t-s\t\tShow current update status")
		P(1, "\t-l\t\tShow list of available image versions (and which one has been downloaded, if any)")
		P(1, "\t-i <version>\tShow information (changelog) about the requested image version")
		P(1, "\t-d <version>\tDownload requested image version")
		P(1, "\t-f <version>\tFlash to requested image version (by means of sysupgrade)")
		P(1, "\t-r\t\tClear downloaded images and reset state")
		os.exit(10)

	elseif argTable.action == 'showCurrentVersion' then
		local vText,msg,nr = M.getCurrentVersionText()
		if not vText then E("error reading firmware version (" .. nr .. ": " .. msg .. ")"); os.exit(1) end
		local v = M.parseVersion(vText)
		if not v then E("error parsing version '" .. vText .. "'"); os.exit(2) end
		P(1, "version: " .. M.formatVersion(v))

	elseif argTable.action == 'showStatus' then
		local status = M.getStatus()
		P(0, "Current update status:")
		P(1, "  currentVersion:\t" .. (M.formatVersion(status.currentVersion) or '?'))
		P(1, "  newestVersion:\t" .. (M.formatVersion(status.newestVersion) or '?'))

		if status.stateText and status.stateText:len() > 0 then
			P(1, "  state:\t\t" .. M.STATE_NAMES[status.stateCode] .. " (" .. status.stateText .. ")")
		else
			P(1, "  state:\t\t" .. M.STATE_NAMES[status.stateCode])
		end

		if status.stateCode == M.STATE.DOWNLOADING then
			local percent = (status.imageSize > 0) and (math.ceil(status.progress / status.imageSize * 1000) / 10) or 0
			P(1, "  download progress:\t" .. status.progress .. "/" .. status.imageSize .. " (" .. percent .. "%)")
		end

	elseif argTable.action == 'showAvailableVersions' then
		local verTable,msg = M.getAvailableVersions()
		if not verTable then
			E("error collecting version information (" .. msg .. ")")
			os.exit(2)
		end

		P(0, "Available versions:")
		for _,ent in ipairs(verTable) do P(1, M.formatVersion(ent.version)) end

	elseif argTable.action == 'showVersionInfo' then
		local vEnt,msg = M.findVersion(argTable.version)

		if vEnt then
			P(0, "Information on version:")
			P(1, "  version:\t\t" .. M.formatVersion(vEnt.version))
			P(1, "  sysupgradeFilename:\t" .. (vEnt.sysupgradeFilename or '-'))
			P(1, "  sysupgradeFileSize:\t" .. (vEnt.sysupgradeFileSize or '-'))
			P(1, "  sysupgradeMD5:\t" .. (vEnt.sysupgradeMD5 or '-'))
			P(1, "  factoryFilename:\t" .. (vEnt.factoryFilename or '-'))
			P(1, "  factoryFileSize:\t" .. (vEnt.factoryFileSize or '-'))
			P(1, "  factoryMD5:\t\t" .. (vEnt.factoryMD5 or '-'))
			if vEnt.changelog then
				P(1, "\n--- Changelog ---\n" .. vEnt.changelog .. '---')
			else
				P(1, "  changelog:\t\t-")
			end
		elseif vEnt == false then
			P(1, "no such version")
			os.exit(4)
		elseif vEnt == nil then
			E("error searching version index (" .. msg .. ")")
			os.exit(2)
		end

	elseif argTable.action == 'imageDownload' then
		local vEnt,msg = M.findVersion(argTable.version)
		if vEnt == false then
			P(1, "no such version")
			os.exit(4)
		elseif vEnt == nil then
			E("error searching version index (" .. msg .. ")")
			os.exit(2)
		end

		local rv,msg = M.downloadImageFile(vEnt)
		if not rv then E("could not download file (" .. msg .. ")")
		else P(1, "success")
		end

	elseif argTable.action == 'clear' then
		local rv,msg = M.clear()
		if not rv then P(1, "error (" .. msg .. ")")
		else P(1, "success")
		end

	elseif argTable.action == 'imageInstall' then
		local vEnt, msg = nil, nil
		vEnt,msg = M.findVersion(argTable.version)
		if vEnt == false then
			P(1, "no such version")
			os.exit(4)
		elseif vEnt == nil then
			E("error searching version index (" .. msg .. ")")
			os.exit(2)
		end

		local rv
		rv,msg = M.flashImageVersion(vEnt)
		E("error: failed to flash image to device (" .. msg .. ")")
		os.exit(3)

	else
		P(0, "usage: d3d-updater [-hqVcCvslr] [-u base_url] [-i version] [-d version] [-f version]")
	end

	os.exit(0)
end

--- Only execute the main function if an arg table is present, this enables usage both as module and as standalone script.
if arg ~= nil then main() end

return M