-- The loader for individual IO formats for vstruct.
-- Returns the "io function", which is called with:
-- * an IO type, such as 'x' or 'c'
-- * an IO operation, such as 'pack' or 'width'
-- * some (type x operation) specific other arguments
-- upon which it will attempt to load the handler for that operation from the
-- module vstruct.io.<type> and call it.

-- Copyright (c) 2011 Ben "ToxicFrog" Kelly

local defaults = require "vstruct.io.defaults"

local formats = {}

local function iorequire(format)
    local r,v = pcall(require, "vstruct.io."..format)

    if not r then
        error("vstruct: no support for format '"..format.."':\n"..tostring(v))
    end
    
    return v                   
end

local controlnames = {
    seekf   = "+";
    seekb   = "-";
    seekto  = "@";
    bigendian   = ">";
    littleendian= "<";
    hostendian  = "=";
}

for name,symbol in pairs(controlnames) do
    package.preload["vstruct.io."..symbol] = function() return iorequire(name) end
end

return function(format, method, ...)
    local fmt = formats[format]
        or setmetatable(iorequire(format), { __index = defaults })
    
    assert(fmt[method], "No support for method '"..tostring(method).."' in IO module '"..format.."'")
    
    return fmt[method](...)
end