Yet another imgur uploader

lemur.lua

#!/usr/bin/env lua

-- Usage: lemur.lua [filename]
-- If filename is not specified, will output credit information

local os     = require "os"
local io     = require "io"
local string = require "string"
local table  = require "table"
local socket = require "socket"
local ltn12  = require "ltn12"
local http   = require "socket.http"
local url    = require "socket.url"
local json   = require "cjson"

SCRIPT_VERSION = "0.1"
API_HOST = "api.imgur.com"
API_SCHEME = "http"
API_VERSION = 2
API_KEY = "GET_YOUR_OWN_API_KEY"
UA = "LEMURIMGURIMGUPLODR %s <https://github.com/rumia>"

function build_url(action, params)
   if not params then params = {} end
   if not params.key then params.key = API_KEY end

   local queries = {}
   for key, value in pairs(params) do
      queries[#queries + 1] = string.format("%s=%s", url.escape(key), url.escape(value))
   end

   return url.build {
      scheme = API_SCHEME,
      host = API_HOST,
      path = string.format("/%s/%s.json", API_VERSION, action),
      query = table.concat(queries, "&")
   }
end

function show_error(...)
   if arg and #arg > 0 then
      io.stderr:write("ERROR: " .. string.format(unpack(arg)) .. "\n")
   end
end

function get_credit()
   local body, status_code, headers, status_line = http.request(build_url("credits"))

   if status_code ~= 200 then
      show_error(status_line)
   else
      if body and #body > 0 then
         local parsed = json.decode(body)
         if parsed and type(parsed) == "table" then
            if parsed.error then
               show_error(parsed.error.message)
            elseif parsed.credits and type(parsed.credits) == "table" then
               print(string.format(
                  "Information for API key %s\n" ..
                  "\tAvailable credit: %d\n" ..
                  "\tAllocation limit: %d\n" ..
                  "\tNext reset: %s\n" ..
                  "\tRefresh time: %d secs",
                  API_KEY,
                  parsed.credits.remaining,
                  parsed.credits.limit,
                  os.date("!%Y-%m-%d %H:%M:%S %z", parsed.credits.reset),
                  parsed.credits.refresh_in_secs))
            else
               show_error("Unknown response: %s", body)
            end
         end
      else
         show_error("Empty response")
      end
   end
end

function upload(filename, title, caption)
   local body = {}
   local file_handle = assert(io.open(filename, "r"))
   local size = file_handle:seek("end")
   file_handle:seek("set")

   local _, status_code, headers, status_line =
      http.request({
         method   = "PUT",
         url      = build_url("upload", { title = title, caption = caption, name = filename }),
         source   = ltn12.source.file(file_handle),
         sink     = ltn12.sink.table(body),
         headers  = {
            ["content-length"] = size,
            ["user-agent"] = string.format(UA, SCRIPT_VERSION)
         }
      })

   if status_code ~= 200 then
      show_error(status_line)
   else
      if body and type(body) == "table" then
         body = table.concat(body, "")
         if #body > 0 then
            local parsed = json.decode(body)
            if parsed and type(parsed) == "table" then
               if parsed.error then
                  show_error(parsed.error.message)
               elseif parsed.upload then
                  print(string.format(
                     "%s (%ux%u %s)\n" ..
                     "\tPage: %s\n" ..
                     "\tOriginal Size: %s\n" ..
                     "\tSmall Thumbnail: %s\n" ..
                     "\tLarge Thumbnail: %s\n" ..
                     "\tDelete Page: %s",
                     parsed.upload.image.name,
                     parsed.upload.image.width,
                     parsed.upload.image.height,
                     parsed.upload.image.type,
                     parsed.upload.links.imgur_page,
                     parsed.upload.links.original,
                     parsed.upload.links.small_square,
                     parsed.upload.links.large_thumbnail,
                     parsed.upload.links.delete_page))
               else
                  show_error("Unknown response: %s", body)
               end
            else
               show_error("Unable to parse response: %s", body)
            end
         else
            show_error("Empty response")
         end
      end
   end
end

filename = select(1, ...)
if not filename then
   get_credit()
else
   upload(filename, select(2, ...), select(3, ...))
end