--[[
This is used to return an image legend from Wikidata
image is property P18
image legend is property P2096

Call as {{#invoke:Sandbox/RexxS/ImageLegend |getImageLegend | PARAMETER | lang=<ISO-639code> |id=<QID>}}
Returns PARAMETER, unless it is equal to "FETCH_WIKIDATA" from Item QID (expensive call)
If QID is omitted or blank, the current article is used (not expensive call)
If lang is omitted, it uses the local wiki language, otherwise it uses the provided ISO-639 language code
ISO-639: https://docs.oracle.com/cd/E13214_01/wli/docs92/xref/xqisocodes.html#wp1252447

Ranks are: 'preferred' > 'normal'
This returns the label from the first image with 'preferred' rank
Or the label from the first image with 'normal' rank if preferred returns nothing
Ranks: https://www.mediawiki.org/wiki/Extension:Wikibase_Client/Lua

In South Pole Telescope, the structure of P18 is:
    ["P18"] = table#26 {
      table#27 {
        ["id"] = "Q1513315$bc122c22-4da5-8301-9d2f-8a5eb415e9e8",
        ["mainsnak"] = table#28 {
          ["datatype"] = "commonsMedia",
          ["datavalue"] = table#29 {
            ["type"] = "string",
            ["value"] = "South pole telescope nov2009.jpg",
          },
          ["property"] = "P18",
          ["snaktype"] = "value",
        },
        ["qualifiers"] = table#30 {
          ["P2096"] = table#31 {
            table#32 {
              ["datatype"] = "monolingualtext",
              ["datavalue"] = table#33 {
                ["type"] = "monolingualtext",
                ["value"] = table#34 {
                  ["language"] = "en",
                  ["text"] = "The South Pole Telescope in November 2009",
                },
              },
              ["hash"] = "6d87da1d793aa25eed516953ef8ad15e9b030d12",
              ["property"] = "P2096",
              ["snaktype"] = "value",
            },
            table#35 {
              ["datatype"] = "monolingualtext",
              ["datavalue"] = table#36 {
                ["type"] = "monolingualtext",
                ["value"] = table#37 {
                  ["language"] = "lt",
                  ["text"] = "Pietų ašigalio teleskopas 2009 m. lapkritį",
                },
              },
              ["hash"] = "7a04953630950ebf0cce672c30d1b150e74f7003",
              ["property"] = "P2096",
              ["snaktype"] = "value",
            },
          },
        },
        ["qualifiers-order"] = table#38 {
          "P2096",
        },
        ["rank"] = "normal",
        ["type"] = "statement",
      },
    },

]]

local p = {}

p.getImageLegend = function(frame)
	-- look for named parameter id; if it's blank make it nil
	local id = frame.args.id
	if id and (#id == 0) then
		id = nil
	end
	
	-- look for named parameter lang
	-- it should contain a two-character ISO-639 language code
	-- if it's blank fetch the language of the local wiki
	local lang = frame.args.lang
	if (not lang) or (#lang < 2) then
		lang = mw.language.getContentLanguage().code
	end
	
	-- first unnamed parameter is the local parameter, if supplied
	local input_parm = mw.text.trim(frame.args[1] or "")
	if input_parm == "FETCH_WIKIDATA" then
		local ent = mw.wikibase.getEntityObject(id)
		local imgs
		if ent and ent.claims then
			imgs = ent.claims.P18
		end
		local imglbl
		if imgs then
			-- look for an image with 'preferred' rank
			for k1, v1 in pairs(imgs) do
				if v1.rank == "preferred" and v1.qualifiers.P2096 then
					local imglbls = v1.qualifiers.P2096
					for k2, v2 in pairs(imglbls) do
						if v2.datavalue.value.language == lang then
							imglbl = v2.datavalue.value.text
							break
						end
					end
				end
			end
			-- if we don't find one, look for an image with 'normal' rank
			if (not imglbl) then
				for k1, v1 in pairs(imgs) do
					if v1.rank == "normal" and v1.qualifiers.P2096 then
						local imglbls = v1.qualifiers.P2096
						for k2, v2 in pairs(imglbls) do
							if v2.datavalue.value.language == lang then
								imglbl = v2.datavalue.value.text
								break
							end
						end
					end
				end
			end
		end
		return imglbl
	else
		return input_parm
	end
end

return p