batteries/pretty.lua

--[[
	pretty formatting and printing for nested data structures

	also able to be parsed by lua in many cases, but not always

	circular references and depth limit will cause the string to contain
	things that cannot be parsed.

	this isn't a full serialisation solution, it's for debugging and display to humans

	all exposed functions take a config table, defaults found in pretty.default_config

		indent
			indentation to use for each line, or "" for single-line packed
			can be a number of spaces, boolean, or a string to use verbatim
		depth
			a limit on how deep to explore the table
		per_line
			how many fields to print per line
]]

local path = (...):gsub("pretty", "")
local table = require(path.."tablex") --shadow global table module

local pretty = {}

pretty.default_config = {
	indent = true,
	depth = math.huge,
	per_line = 1,
}

--indentation to use when `indent = true` is provided
pretty.default_indent = "\t"

--pretty-print something directly
function pretty.print(input, config)
	print(pretty.string(input, config))
end

--pretty-format something into a string
function pretty.string(input, config)
	return pretty._process(input, config)
end

--internal
--actual processing part
function pretty._process(input, config, processing_state)
	--if the input is not a table, or it has a tostring metamethod
	--then we can just use tostring directly
	local mt = getmetatable(input)
	if type(input) ~= "table" or mt and mt.__tostring then
		local s = tostring(input)
		--quote strings
		if type(input) == "string" then
			s = '"' .. s .. '"'
		end
		return s
	end

	--pull out config
	config = table.overlay({}, pretty.default_config, config or {})
	
	local per_line = config.per_line
	local depth = config.depth
	local indent = config.indent
	if type(indent) == "number" then
		indent = (" "):rep(indent)
	elseif type(indent) == "boolean" then
		indent = indent and pretty.default_indent or ""
	end

	--dependent vars
	local newline = indent == "" and "" or "\n"

	--init or collect processing state
	processing_state = processing_state or {
		circular_references = {i = 1},
		depth = 0,
	}

	processing_state.depth = processing_state.depth + 1
	if processing_state.depth > depth then
		return "{...}"
	end

	local circular_references = processing_state.circular_references
	local ref = circular_references[input]
	if ref then
		if not ref.string then
			ref.string = string.format("%%%d", circular_references.i)
			circular_references.i = circular_references.i + 1
		end
		return ref.string
	end
	ref = {}
	circular_references[input] = ref

	local function internal_value(v)
		v = pretty._process(v, config, processing_state)
		if indent ~= "" then
			v = v:gsub(newline, newline..indent)
		end
		return v
	end

	--otherwise, we'll build up a table representation of our data
	--collate into member chunks
	local chunks = {}
	--(tracking for already-seen elements from ipairs)
	local seen = {}
	--sequential part first
	--(in practice, pairs already does this, but the order isn't guaranteed)
	for i, v in ipairs(input) do
		seen[i] = true
		table.insert(chunks, internal_value(v))
	end
	--non sequential follows
	for k, v in pairs(input) do
		if not seen[k] then
			--encapsulate anything that's not a string
			--todo: also keywords and strings with spaces
			if type(k) ~= "string" then
				k = "[" .. tostring(k) .. "]"
			end
			table.insert(chunks, k .. " = " .. internal_value(v))
		end
	end

	--resolve number to newline skip after
	if per_line > 1 then
		local line_chunks = {}
		while #chunks > 0 do
			local break_next = false
			local line = {}
			for i = 1, per_line do
				if #chunks == 0 then
					break
				end
				local v = chunks[1]
				--tables split to own line
				if v:find("{") then
					--break line here
					break_next = true
					break
				else
					table.insert(line, table.remove(chunks, 1))
				end
			end
			if #line > 0 then
				table.insert(line_chunks, table.concat(line, ", "))
			end
			if break_next then
				table.insert(line_chunks, table.remove(chunks, 1))
				break_next = false
			end
		end
		chunks = line_chunks
	end

	--drop depth
	processing_state.depth = processing_state.depth - 1

	local multiline = #chunks > 1
	local separator = (indent == "" or not multiline) and ", " or ",\n"..indent

	local prelude = ref.string and (string.format(" <referenced as %s> ",ref.string)) or ""
	if multiline then
		return "{" .. prelude .. newline ..
			indent .. table.concat(chunks, separator) .. newline ..
		"}"
	end
	return "{" .. prelude .. table.concat(chunks, separator) .. "}"
end

return pretty