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--- Tables mapped to the filing system

-- Only string keys are permitted; package.dirsep characters are

-- converted to underscores.

-- Values are stored as strings (converted by tostring).

-- As with disk operations, a table's elements must be set to nil

-- (deleted) before the table itself can be set to nil.

module ("fstable", package.seeall)

require "io_ext"

require "table_ext"

require "io_ext"

require "lfs"

require "posix"

local function fsnext (dir)

local f

repeat

f = dir:next ()

until f ~= "." and f ~= ".."

return f

end

-- Metamethods for persistent tables

local metatable = {}

metatable.__index =

function (t, k)

local path = io.catfile (getmetatable (t).directory, k)

local attrs = lfs.attributes (path)

if attrs then

if attrs.mode == "file" then

local h = io.open (path)

if h then

local v = h:read ("*a")

h:close ()

return v

end

elseif attrs.mode == "directory" then

return new (path)

end

end

return attrs

end

metatable.__newindex =

function (t, k, v)

local ty = type (v)

if ty == "thread" or ty == "function" or ty == "userdata" then

error ("cannot persist a " .. ty .. "")

elseif type (k) ~= "string" then

error ("keys of persistent tables must be of type string")

else

k = string.gsub (k, package.dirsep, "_")

local path = io.catfile (getmetatable (t).directory, k)

local vm = getmetatable (v)

if v == nil then

os.remove (path)

elseif type (v) ~= "table" then

local h = io.open (path, "w")

h:write (tostring (v))

h:close ()

elseif type (vm) == "table" and vm.metatable == metatable then

-- To match Lua semantics we'd hardlink, but that's not allowed for directories

local ok, errmsg = posix.link (vm.directory, path, true)

else

local ok, errmsg = lfs.mkdir (path)

if not ok then

error (errmsg)

end

new (path, v)

end

end

end

metatable.__pairs =

function (t)

local _, dir = lfs.dir (getmetatable (t).directory)

return function (dir)

local f = fsnext (dir)

if f then

return f, t[f]

end

end,

dir

end

metatable.__ipairs =

function (t)

local _, dir = lfs.dir (getmetatable (t).directory)

return function (dir, i)

local f = fsnext (dir)

if f then

return i + 1, f

end

end,

dir, 0

end

--- Bind a directory to a table

-- @param path directory path

-- @param t table to merge with directory

-- @return table bound to directory

function new (path, t)

if not path:find ("^" .. package.dirsep) then

path = io.catfile (lfs.currentdir (), path)

end

if lfs.attributes (path, "mode") ~= "directory" then

error ("`" .. path .. "' does not exist or is not a directory")

end

local m = table.clone (metatable)

m.directory = path

m.metatable = metatable

local d = setmetatable ({}, m)

if t then

for i, v in pairs (t) do

d[i] = v

end

end

return d

end