RebasePath.lua

--TODO: add redirections to accomodate common repository paths
--[[--
	Returns a modified version of a pacakge path string
	@param table|nil opt a table with options
	options:
		path: package path to use, defaults to pacakge.path
		target: the new path component to use
		base: search for this in paths, interpreted as a string pattern, defaults to './'
		limit: limit number of substitutions to this number, defaults to 1
		anchor: anchor at beginning of path, defaults to true
		mode: defaults to 'replace'
			append: mix the original and the rebased in place
			replace: replace base in place
			new: return only the modified paths
	simple example: package.path = package.path .. dofile "<pathToThisFile>" {
		base = '../MyLibraries/',--mind the trailing slash
		mode = 'new',
	}
]]
return function ( opt )
	opt = opt or {}
	
	local function Escape ( str )
		return str:gsub ( '%W', '%%%1' )
	end
	
	local Path = opt.path or package.path
	local Base = opt.base or './'
	local Target = assert ( opt.target, 'No target given' )
	local Limit = opt.limit or 1
	local Separator = package.config and package.config:match'.\n(.)' or ';'
	local BaseSafe = Escape ( Base )
	local Anchor = opt.anchor
	if Anchor == nil then
		Anchor = true
	end
	if Anchor then
		BaseSafe = '^' .. BaseSafe
	end
	local SeparatorSafe = Escape ( Separator )
	local PathPattern = '[^' .. SeparatorSafe ..']+'
	
	local Rebaser
	local mode = opt.mode or 'replace'
	if mode == 'append' then
		function Rebaser ( path )
			return path:gsub ( BaseSafe, Target, Limit ) .. Separator .. path
		end
	elseif mode == 'replace' or mode == 'new' then
		function Rebaser ( path )
			return path:gsub ( BaseSafe, Target, Limit )
		end
	end
	
	if mode == 'new' then
		local newPaths, i = {}, 1
		for path in Path:gmatch ( PathPattern ) do
			newPaths [ i ], i = Rebaser ( path ), i + 1
		end
		return Separator .. table.concat ( newPaths, Separator )
	else
		return Path:gsub (
			PathPattern,
			Rebaser
		)
	end
end