--[[
Implements a simple in-memory cache. The cache has no upper size limit, and
may cause out-of-memory errors. When this happens, the OS will kill the kore
worker process, and the kore parent process will restart with a fresh, empty
cache
]]

local sql = require("lsqlite3")

local queries = require("queries")
local util = require("util")

local ret = {}

local stmnt_cache, stmnt_insert_cache, stmnt_dirty_cache

local oldconfigure = configure
function configure(...)
	local cache = util.sqlassert(sql.open_memory())
	--A cache table to store rendered pages that do not need to be
	--rerendered. In theory this could OOM the program eventually and start
	--swapping to disk. TODO: fixme
	assert(cache:exec([[
	CREATE TABLE IF NOT EXISTS cache (
		path TEXT PRIMARY KEY,
		data BLOB,
		updated INTEGER,
		dirty INTEGER
	);
	]]))
	stmnt_cache = assert(cache:prepare([[
		SELECT data
		FROM cache
		WHERE
			path = :path AND
			((dirty = 0) OR (strftime('%s','now') - updated) < 20)
		;
	]]))
	stmnt_insert_cache = assert(cache:prepare([[
		INSERT OR REPLACE INTO cache (
			path, data, updated, dirty
		) VALUES (
			:path, :data, strftime('%s','now'), 0
		);
	]]))
	stmnt_dirty_cache = assert(cache:prepare([[
		UPDATE OR IGNORE cache
		SET dirty = 1
		WHERE path = :path;
	]]))
	return oldconfigure(...)
end

--Render a page, with cacheing. If you need to dirty a cache, call dirty_cache()
function ret.render(pagename,callback)
	stmnt_cache:bind_names{path=pagename}
	local err = util.do_sql(stmnt_cache)
	if err == sql.DONE then
		stmnt_cache:reset()
		--page is not cached
	elseif err == sql.ROW then
		local data = stmnt_cache:get_values()
		stmnt_cache:reset()
		return data[1]
	else --sql.ERROR or sql.MISUSE
		error("Failed to check cache for page " .. pagename)
	end
	--We didn't have the paged cached, render it
	local text = callback()
	--And save the data back into the cache
	stmnt_insert_cache:bind_names{
		path=pagename,
		data=text,
	}
	err = util.do_sql(stmnt_insert_cache)
	if err == sql.ERROR or err == sql.MISUSE then
		error("Failed to update cache for page " .. pagename)
	end
	stmnt_insert_cache:reset()
	return text
end

function ret.dirty(url)
	stmnt_dirty_cache:bind_names{
		path = url
	}
	util.do_sql(stmnt_dirty_cache)
	stmnt_dirty_cache:reset()
end

function ret.close()
	
end

return ret