table_persistence.lua

-- Internal persistence library

--[[ Provides ]]
-- persistence.store(path, ...): Stores arbitrary items to the file at the given path
-- persistence.load(path): Loads files that were previously stored with store and returns them

--[[ Limitations ]]
-- Does not export userdata, threads or most function values
-- Function export is not portable

--[[ License: MIT (see bottom) ]]

-- Private methods
local write, writeIndent, writers, refCount;

persistence =
{
    store = function (path, ...)
        local file, e;
        if type(path) == "string" then
            -- Path, open a file
            file, e = io.open(path, "w");
            if not file then
                return error(e);
            end
        else
            -- Just treat it as file
            file = path;
        end
        local n = select("#", ...);
        -- Count references
        local objRefCount = {}; -- Stores reference that will be exported
        for i = 1, n do
            refCount(objRefCount, (select(i,...)));
        end;
        -- Export Objects with more than one ref and assign name
        -- First, create empty tables for each
        local objRefNames = {};
        local objRefIdx = 0;
        file:write("-- Persistent Data\n");
        file:write("local multiRefObjects = {\n");
        for obj, count in pairs(objRefCount) do
            if count > 1 then
                objRefIdx = objRefIdx + 1;
                objRefNames[obj] = objRefIdx;
                file:write("{},"); -- table objRefIdx
            end;
        end;
        file:write("\n} -- multiRefObjects\n");
        -- Then fill them (this requires all empty multiRefObjects to exist)
        for obj, idx in pairs(objRefNames) do
            for k, v in pairs(obj) do
                file:write("multiRefObjects["..idx.."][");
                write(file, k, 0, objRefNames);
                file:write("] = ");
                write(file, v, 0, objRefNames);
                file:write(",\n");
            end;
        end;
        -- Create the remaining objects
        for i = 1, n do
            file:write("local ".."obj"..i.." = ");
            write(file, (select(i,...)), 0, objRefNames);
            file:write("\n");
        end
        -- Return them
        if n > 0 then
            file:write("return obj1");
            for i = 2, n do
                file:write(" ,obj"..i);
            end;
            file:write("\n");
        else
            file:write("return\n");
        end;
        file:close();
    end;

    load = function (path)
        local f, e = loadfile(path);
        if f then
            return f();
        else
            return nil, e;
        end;
    end;
}

-- Private methods

-- write thing (dispatcher)
write = function (file, item, level, objRefNames)
    writers[type(item)](file, item, level, objRefNames);
end;

-- write indent
writeIndent = function (file, level)
    for i = 1, level do
        file:write("    ");
    end;
end;

-- recursively count references
refCount = function (objRefCount, item)
    -- only count reference types (tables)
    if type(item) == "table" then
        -- Increase ref count
        if objRefCount[item] then
            objRefCount[item] = objRefCount[item] + 1;
        else
            objRefCount[item] = 1;
            -- If first encounter, traverse
            for k, v in pairs(item) do
                refCount(objRefCount, k);
                refCount(objRefCount, v);
            end;
        end;
    end;
end;

-- Format items for the purpose of restoring
writers = {
    ["nil"] = function (file, item)
            file:write("nil");
        end;
    ["number"] = function (file, item)
            file:write(tostring(item));
        end;
    ["string"] = function (file, item)
            file:write(string.format("%q", item));
        end;
    ["boolean"] = function (file, item)
            if item then
                file:write("true");
            else
                file:write("false");
            end
        end;
    ["table"] = function (file, item, level, objRefNames)
            local refIdx = objRefNames[item];
            if refIdx then
                -- Table with multiple references
                file:write("multiRefObjects["..refIdx.."]");
            else
                -- Single use table
                file:write("{\n");
                for k, v in pairs(item) do
                    writeIndent(file, level+1);
                    file:write("[");
                    write(file, k, level+1, objRefNames);
                    file:write("] = ");
                    write(file, v, level+1, objRefNames);
                    file:write(",\n");
                end
                writeIndent(file, level);
                file:write("}");
            end;
        end;
    ["function"] = function (file, item)
            -- Does only work for "normal" functions, not those
            -- with upvalues or c functions
            local dInfo = debug.getinfo(item, "uS");
            if dInfo.nups > 0 then
                file:write("nil --[[functions with upvalue not supported]]");
            elseif dInfo.what ~= "Lua" then
                file:write("nil --[[non-lua function not supported]]");
            else
                local r, s = pcall(string.dump,item);
                if r then
                    file:write(string.format("loadstring(%q)", s));
                else
                    file:write("nil --[[function could not be dumped]]");
                end
            end
        end;
    ["thread"] = function (file, item)
            file:write("nil --[[thread]]\n");
        end;
    ["userdata"] = function (file, item)
            file:write("nil --[[userdata]]\n");
        end;
}

--[[
 Copyright (c) 2010 Gerhard Roethlin

 Permission is hereby granted, free of charge, to any person
 obtaining a copy of this software and associated documentation
 files (the "Software"), to deal in the Software without
 restriction, including without limitation the rights to use,
 copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the
 Software is furnished to do so, subject to the following
 conditions:

 The above copyright notice and this permission notice shall be
 included in all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 OTHER DEALINGS IN THE SOFTWARE.
]]