https example in Lua

unfurl-mastodon-thread.lua

-- https://github.com/rxi/json.lua
json = require 'json'
-- https://github.com/brunoos/luasec
https = require 'ssl.https'

-- Construct an URL to query the Mastodon API.
-- I have no idea if ActivityPub carves out the id space between federating
-- hosts (how would it even do that?!) so I'm going to remember two things for
-- each Mastodon link: a host and an id. The host includes the protocol.
function url_from_ml(ml)
  return ('%s/api/v1/statuses/%d'):format(ml.host, ml.id)
end

-- We can parse the Mastodon link from the following formats:
--  https://merveilles.town/users/bd/statuses/109791902220118251
--  https://merveilles.town/@bd/109791902220118251
function ml_from_url(url)
  local host, user, id = url:match('^([^/]*://[^/]*)/@([^/]*)/(%d*)$')
  if host then return {host=host, user=user, id=id} end
  local host, user, id = url:match('^([^/]*://[^/]*)/users/([^/]*)/statuses/(%d*)$')
  if host then return {host=host, user=user, id=id} end
end

-- Given a mastodon link, return all information about it.
function get(ml)
  local url = url_from_ml(ml)
  local response, code, response_headers, status = https.request(url)
  local basic_info = json.decode(response)
  local response, code, response_headers, status = https.request(url..'/context')
  local rels = json.decode(response)
  return {host=ml.host, user=ml.user, id=ml.id, url=basic_info.url, content=basic_info.content, replies_count=basic_info.replies_count, ancestors=rels.ancestors, descendants=rels.descendants}
end

posts = {}
to_process = {}

if #arg == 0 then
  io.stderr:write('provide a Mastodon URL on the command line\n')
  os.exit(1)
end

local result = get(ml_from_url(arg[1]))
if result.ancestors then
  result = get(ml_from_url(result.ancestors[1].url))
end

local filename = os.tmpname()
local f = io.open(filename, 'w')
f:write(json.encode(result))
f:close()
print(filename)

--? os.execute('love . '..filename)
--? os.remove(filename)