--[[
 *
 *  Singe 3
 *  Copyright (C) 2006-2026 Scott Duensing <scott@kangaroopunch.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 3
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 *
--]]



-- Talking to the master service without stopping the game.
--
-- Lua in Singe is not threaded, and ssl.https.request blocks until it finishes:  a JSON call would
-- stutter the frame and a several-hundred-megabyte download would look like a hang.  So every
-- request here is a state machine driven a slice at a time from netPump(), which the menu calls
-- once a frame.  A caller hands in a function and gets called back when the answer arrives.
--
-- On trust.  LuaSec's own https.lua ships with verify = "none", which encrypts the connection and
-- authenticates nobody -- anything on the path could read the password going up, the token coming
-- back, and alter the game being downloaded.  Nothing here uses that module.  A connection is
-- verified against a pinned public key:  Singe ships to five platforms and LuaSec can read neither
-- the Windows certificate store nor the macOS keychain, and this client only ever talks to one
-- service, so pinning is both simpler and stronger than carrying a list of every public CA.
--
-- The pin is of the *public key*, not the certificate, so an ordinary renewal that keeps the key
-- does not lock out every cabinet;  two pins are carried so a key can actually be rotated.


local socket = require("socket")
local ssl    = require("ssl")

NET_TIMEOUT      = 30000        -- ms with no progress at all before a request is abandoned
NET_CHUNK        = 65536        -- bytes read per pump slice
NET_REDIRECT_MAX = 5

-- master.singeengine.com.  Two pins: the one in use and its successor, so a key rotation is a
-- release that knows both, then a server that starts using the second.  An empty list means the
-- host's own trust store is used instead, which is what a self-hosted server without a pin gets.
NET_PINS = {}

local active  = {}
local nextId  = 1


-- The SHA-256 of a peer's public key, in the form the pins are written in.
local function keyPin(connection)
	local cert = connection:getpeercertificate()

	if not cert then
		return nil
	end
	local pem = cert:pubkey()
	if not pem then
		return nil
	end
	return utilSha256(pem)
end


local function finish(request, ok, result)
	active[request.id] = nil
	if request.file then
		request.file:close()
		request.file = nil
	end
	if request.socket then
		pcall(function() request.socket:close() end)
		request.socket = nil
	end
	if request.onDone then
		request.onDone(ok, result)
	end
end


local function fail(request, message)
	finish(request, false, { error = message, url = request.url })
end


-- scheme, host, port, path
local function parseUrl(url)
	local scheme, rest = url:match("^(%a[%w+.-]*)://(.*)$")

	if not scheme then
		return nil
	end
	local hostPort, path = rest:match("^([^/]+)(.*)$")
	if not hostPort then
		return nil
	end
	local host, port = hostPort:match("^(.-):(%d+)$")
	host = host or hostPort
	port = tonumber(port) or ((scheme == "https") and 443 or 80)
	return scheme, host, port, (path ~= "" and path or "/")
end


local function beginConnect(request)
	local sock, err = socket.tcp()

	if not sock then
		return fail(request, "no socket: " .. tostring(err))
	end
	sock:settimeout(0)
	request.socket = sock
	-- A non-blocking connect answers "timeout" immediately and finishes in the background; the
	-- socket becoming writable is what says it arrived.
	local ok, connectErr = sock:connect(request.host, request.port)
	if not ok and connectErr ~= "timeout" and connectErr ~= "already connected" then
		return fail(request, "cannot reach " .. request.host .. ": " .. tostring(connectErr))
	end
	request.state = (request.scheme == "https") and "connecting" or "sending"
	request.sent  = 0
end


local function buildRequest(request)
	local lines = {
		string.format("%s %s HTTP/1.1", request.method, request.path),
		"Host: " .. request.host,
		"Connection: close",
		"Accept-Encoding: identity",
		"User-Agent: Singe/" .. SINGE_VERSION_STRING,
	}

	for name, value in pairs(request.headers or {}) do
		lines[#lines + 1] = name .. ": " .. value
	end
	if request.body then
		lines[#lines + 1] = "Content-Length: " .. #request.body
	end
	return table.concat(lines, "\r\n") .. "\r\n\r\n" .. (request.body or "")
end


local function startTls(request)
	local params = {
		mode     = "client",
		protocol = "any",
		options  = { "all", "no_sslv2", "no_sslv3", "no_tlsv1", "no_tlsv1_1" },
		-- With a pin, the chain is checked against the key rather than a CA list, and the pin is
		-- what decides.  Without one, the host's own store is asked -- and if it has nothing to
		-- say, the request fails rather than proceeding unverified.
		verify   = (#NET_PINS > 0) and "none" or "peer",
		capath   = "/etc/ssl/certs",
		cafile   = "/etc/ssl/certs/ca-certificates.crt",
	}
	local wrapped, err = ssl.wrap(request.socket, params)

	if not wrapped then
		return fail(request, "TLS setup failed: " .. tostring(err))
	end
	wrapped:settimeout(0)
	if wrapped.sni then
		wrapped:sni(request.host)
	end
	request.socket = wrapped
	request.state  = "handshake"
end


local function pumpHandshake(request)
	local ok, err = request.socket:dohandshake()

	if ok then
		if #NET_PINS > 0 then
			local seen = keyPin(request.socket)
			local good = false
			for _, pin in ipairs(NET_PINS) do
				if seen == pin then
					good = true
				end
			end
			if not good then
				-- The one failure that must never be shrugged off:  a wrong key is either a
				-- mis-deployed server or somebody in the middle, and both want a person.
				return fail(request, "the server's key is not one this build trusts")
			end
		end
		request.state = "sending"
		return
	end
	if err ~= "wantread" and err ~= "wantwrite" and err ~= "timeout" then
		fail(request, "TLS handshake failed: " .. tostring(err))
	end
end


local function pumpSending(request)
	if not request.outgoing then
		request.outgoing = buildRequest(request)
	end
	local sent, err, partial = request.socket:send(request.outgoing, request.sent + 1)

	if sent then
		request.sent = sent
	elseif err == "timeout" then
		request.sent = partial or request.sent
	else
		return fail(request, "send failed: " .. tostring(err))
	end
	if request.sent >= #request.outgoing then
		request.state = "reading"
	end
end


-- Split the headers off once the blank line arrives, so the body can start going to disk rather
-- than accumulating in memory:  a game is far too big to hold twice.
local function splitHead(request)
	local at = request.buffer:find("\r\n\r\n", 1, true)

	if not at then
		return false
	end
	local head = request.buffer:sub(1, at - 1)
	request.buffer = request.buffer:sub(at + 4)
	request.status = tonumber(head:match("^HTTP/%d%.%d (%d%d%d)")) or 0
	request.responseHeaders = {}
	for name, value in head:gmatch("\r\n([^:\r\n]+):%s*([^\r\n]*)") do
		request.responseHeaders[name:lower()] = value
	end
	request.length = tonumber(request.responseHeaders["content-length"])
	request.got    = 0
	if request.toFile then
		local file, err = io.open(request.toFile, "wb")
		if not file then
			fail(request, "cannot write " .. request.toFile .. ": " .. tostring(err))
			return false
		end
		request.file = file
	end
	return true
end


local function consume(request, data)
	request.got = request.got + #data
	if request.file then
		request.file:write(data)
	else
		request.parts[#request.parts + 1] = data
	end
	if request.onProgress then
		request.onProgress(request.got, request.length)
	end
end


local function complete(request)
	local body = request.file and "" or table.concat(request.parts)

	-- A redirect is followed only for a plain GET, and only within the same scheme and host:  the
	-- point of a pin is lost if a 302 can walk the client somewhere else.
	local location = request.responseHeaders["location"]
	if location and request.status >= 300 and request.status < 400 and request.redirects < NET_REDIRECT_MAX then
		local scheme, host = parseUrl(location)
		if scheme == request.scheme and host == request.host then
			request.redirects = request.redirects + 1
			request.url       = location
			local _, _, port, path = parseUrl(location)
			request.port, request.path = port, path
			request.buffer, request.parts, request.outgoing, request.sent = "", {}, nil, 0
			if request.socket then pcall(function() request.socket:close() end) end
			request.socket = nil
			return beginConnect(request)
		end
	end
	finish(request, true, { status = request.status, body = body, headers = request.responseHeaders,
							bytes = request.got, file = request.toFile })
end


local function pumpReading(request)
	local data, err, partial = request.socket:receive(NET_CHUNK)
	local got = data or partial

	if got and #got > 0 then
		request.lastProgress = singeGetTicks()
		if not request.responseHeaders then
			request.buffer = request.buffer .. got
			if splitHead(request) and #request.buffer > 0 then
				local rest = request.buffer
				request.buffer = ""
				consume(request, rest)
			end
		else
			consume(request, got)
		end
	end
	if request.responseHeaders and request.length and request.got >= request.length then
		return complete(request)
	end
	if err == "closed" then
		if request.responseHeaders then
			return complete(request)
		end
		return fail(request, "the server closed before answering")
	end
	if err and err ~= "timeout" and err ~= "wantread" then
		fail(request, "read failed: " .. tostring(err))
	end
end


-- One slice of work for every request in flight.  Cheap when nothing is happening.
--
-- The list is snapshotted first because a request that finishes calls back into the caller, and the
-- caller very reasonably starts another one from there -- a download that reports itself installed,
-- say.  Adding to a table while pairs() walks it is not allowed, and the failure ("invalid key to
-- 'next'") names neither the table nor the callback that did it.
function netPump()
	local running = {}

	for id in pairs(active) do
		running[#running + 1] = id
	end
	for _, id in ipairs(running) do
		local request = active[id]
		if request then
			if singeGetTicks() - request.lastProgress > NET_TIMEOUT then
				fail(request, "the server stopped responding")
			elseif request.state == "connecting" then
				-- Writable means the connect finished;  LuaSec is wrapped around it only then.
				local _, writable = socket.select(nil, { request.socket }, 0)
				if writable and #writable > 0 then
					request.lastProgress = singeGetTicks()
					startTls(request)
				end
			elseif request.state == "handshake" then
				pumpHandshake(request)
			elseif request.state == "sending" then
				pumpSending(request)
			elseif request.state == "reading" then
				pumpReading(request)
			end
		end
	end
end


-- Start a request.  opts:  url, method, headers, body, toFile, onProgress.  onDone(ok, result) is
-- called once, with result.status/body/headers on success or result.error on failure.
function netRequest(opts, onDone)
	local scheme, host, port, path = parseUrl(opts.url)

	if not scheme or (scheme ~= "http" and scheme ~= "https") then
		onDone(false, { error = "not a URL this understands: " .. tostring(opts.url) })
		return nil
	end
	local request = {
		id = nextId, url = opts.url, scheme = scheme, host = host, port = port, path = path,
		method = opts.method or "GET", headers = opts.headers, body = opts.body,
		toFile = opts.toFile, onProgress = opts.onProgress, onDone = onDone,
		buffer = "", parts = {}, redirects = 0, lastProgress = singeGetTicks(),
	}
	nextId = nextId + 1
	active[request.id] = request
	beginConnect(request)
	return request.id
end


function netCancel(id)
	local request = active[id]

	if request then
		request.onDone = nil
		finish(request, false, { error = "cancelled" })
	end
end


function netBusy()
	return next(active) ~= nil
end