--[[ md
@name lua/util
Various utilities that aren't big enough for their own module, but are still
used in more than one place.
]]


local config = require("config")
local db = require("db")
local queries = require("queries")

local util = {}


local stmnt_comments
local oldconfigure = configure
function configure(...)
	stmnt_comments = assert(db.conn:prepare(queries.select_comments))
	return oldconfigure(...)
end

--[[ md
@name doc/url_spec

URLs generated from smr use letters and numbers to encode a monotonically
increasing post id into a url that can easily be shared (and ends up
considerably shorter). The characters used in url generation are:
[a-z][A-Z][0-9], and numbers are encoded to use the second available 1-character
permuation, then the first available 2-character permutation, and so on.

For example, the first post is encoded as 'b', the second as 'c', the thrid
as 'd', and so on. The off-by-one nature is to simplify implementation of
2-character and 3-character combinations with Lua's 1-indexed arrays.

see https://perishablepress.com/stop-using-unsafe-characters-in-urls/
no underscore because we use that for our operative pages

A set of legacy characters that are no longer in use (because they were invalid
to use in URL's) is also defined, but unused as long as
{{config/legacy_url_cutoff}} is set to 0.
]]
local url_characters =
	[[abcdefghijklmnopqrstuvwxyz]]..
	[[ABCDEFGHIJKLMNOPQRSTUVWXYZ]]..
	[[0123456789]]

local url_characters_legacy =
	url_characters ..
	[[$-+!*'(),]]

local function str2set(str)
	local tbl = {}
	for i = 1, #str do
		tbl[string.sub(str,i,i)] = i
	end
	return tbl
end
local url_characters_rev = str2set(url_characters)
local url_characters_rev_legacy = str2set(url_characters_legacy)

--[[ md
@name lua/util/encode_id
Encode a number to a shorter HTML-safe url path. Url paths are generated
according to the {{doc/url_spec}
]]
function util.encode_id(number)
        local result = {}
	repeat
                local pos = (number % #url_characters) + 1
		number = math.floor(number / #url_characters)
                table.insert(result,string.sub(url_characters,pos,pos))
	until number == 0
        return table.concat(result)
end
--[[
Legacy code, try to encode with invalid characters in the url first
]]
local new_encode = util.encode_id
function util.encode_id(number)
	if number >= config.legacy_url_cutoff then
		return new_encode(number)
	else
		local result = {}
		repeat
			local pos = (number % #url_characters_legacy) + 1
			number = math.floor(number / #url_characters_legacy)
			table.insert(result,string.sub(url_characters_legacy,pos,pos))
		until number == 0
		return table.concat(result)
	end
end

--[[
Given a short HTML-safe url path, convert it to a storyid
]]
function util.decode_id(s)
	local res, id = pcall(function()
		local n = 0
		for i = 1,string.len(s) do
			local char = string.sub(s,i,i)
			local pos = url_characters_rev[char] - 1
			n = n + (pos*math.pow(#url_characters,i-1))
		end
		return n
	end)
	if res then
		return id
	else
		return false,"Failed to decode id:" .. s
	end
end

--[[
Legacy code, try to decode with invalid characters in the url first
]]
local new_decode = util.decode_id
function util.decode_id(s)
	local res, id = pcall(function()
		local n = 0
		for i = 1,string.len(s) do
			local char = string.sub(s,i,i)
			local pos = url_characters_rev_legacy[char] - 1
			n = n + (pos * math.pow(#url_characters_legacy,i-1))
		end
		return n
	end)
	if res then
		if id > config.legacy_url_cutoff then
			return new_decode(s)
		else
			return id
		end
	else
		return false,"Failed to decode id:" .. s
	end
end

--arbitary data to hex encoded string
function util.encode_unlisted(str)
	assert(type(str) == "string","Tried to encode something not a string:" .. type(str))
	local safe = {}
	for i = 1,#str do
		local byte = str:byte(i)
		table.insert(safe,string.format("%02x",byte))
	end
	return table.concat(safe)
end

--hex encoded string to arbitrary data
function util.decode_unlisted(str)
	local output = {}
	for byte in str:gmatch("%x%x") do
		table.insert(output, string.char(tonumber(byte,16)))
	end
	return table.concat(output)
end

--[[
Parses a semicolon seperated string into it's parts:
1. seperates by semicolon
2. trims whitespace
3. lowercases
4. capitalizes the first letter.
Returns an array of zero or more strings.
There is no blank tag, parsing "one;two;;three" will yield
{"one","two","three"}
]]
function util.parse_tags(str)
	local tags = {}
	for tag in string.gmatch(str,"([^;]+)") do
		assert(tag, "Found a nil or false tag in:" .. str)
		local tag_fmt = tag:match("%s*(.*)%s*"):lower():gsub("^.",string.upper)
		assert(tag_fmt, "After processing tag:" .. tag .. " it was falsey.")
		if string.len(tag_fmt) > 0 then
			table.insert(tags, tag_fmt)
		end
	end
	return tags
end

--[[
Get the comments for a story

Comments are a table with the structure:
comment :: table {
	author :: string - The author's text name
	isanon :: boolean - True if the author is anon (author string will be "Anonymous")
	text :: string - The text of the comment
}
]]
function util.get_comments(sid)
	stmnt_comments:bind_names{id = sid}
	local comments = {}
	for com_author, com_isanon, com_text in db.sql_rows(stmnt_comments) do
		table.insert(comments,{
			author = com_author,
			isanon = com_isanon == 1, --int to boolean
			text = com_text
		})
	end
	return comments
end


if config.debugging then
	function util.checktypes(...)
		local args = {...}
		if #args == 1 then
			args = table.unpack(args)
		end
		assert(
			#args % 3 == 0,
			"Arguments to checktypes() must be triplets of " ..
			"<variable>, <lua type>, <type check function> "
		)
		for i = 1,#args,3 do
			local var, ltype, veri_f = args[i+0], args[i+1], args[i+2]
			assert(
				type(var) == ltype,
				string.format(
					"Expected argument %d (%q) to be type %s, but was %s",
					i/3
				)
			)
			if veri_f then
				assert(veri_f(var))
			end
		end
	end
else
	function util.checktypes()
	end
end

local function decodeentity(capture)
	return string.char(tonumber(capture,16)) --Decode base 16 and conver to character
end
function util.decodeentities(str)
	return string.gsub(str,"%%(%x%x)",decodeentity)
end

return util