#! lua-5.0.exe
-- ChangeFile.lua
--
-- Apply changes on a given file.
--
-- Take one parameter: the file to convert, used as input and output.
-- Note that the file is processed as binary file, to preserve its EOLs
-- whatever the system default is.
--
-- by Philippe Lhoste <PhiLho(a)GMX.net> http://Phi.Lho.free.fr
-- v. 1.0 -- 2003/10/19 -- Initial code

local filenameIn  = (arg and arg[1]) or "index.html"	-- If absent, use default file

local eol
local fileHandle

-- Process one given line.
function ProcessLine(line)
	if line == nil then
		return nil
	end
	-- Move the link from the end of the header to the start
	line = string.gsub(line, "(%s*)<h2 ([^>]+)>([^<]+)<a ([^/]+)/a></h2>",
		"%1<h2 %2><a %4/a>%3</h2>")
	fileHandle:write(line .. eol)
	return nil
end

-- Get the end of line used in the given string and return it.
-- Check only the first one, as we assume the string is consistent.
function GetEol(str)
	local eol1, eol2, eol, b
	b, _, eol1 = string.find(str, "([\r\n])")
	if b == nil then
		return nil	-- no EOL in this string
	end
	-- Care is taken in case the first line finishes with two EOLs
	eol2 = string.sub(str, b+1, b+1)
	if eol1 == '\r' then
		if eol2 == '\n' then
			-- Windows style
			eol = '\r\n'
		else
			-- Mac style
			eol = '\r'
		end
	else -- eol1 == '\n'
		-- Unix style
		eol = '\n'
	end
	return eol
end

function ConvertFile(filename)
	-- Read the whole file at once, to avoid clash with write
	-- Binary read, to preserve original EOLs, even if not in current system's style
	fileHandle = io.open(filename, "rb")
	if fileHandle == nil then
		return false, "open rb " .. filename
	end
	local file = fileHandle:read("*a")
	if file == nil then
		return false, "read " .. filename
	end
	fileHandle:close()

	-- Get the EOL kind for this file
	eol = GetEol(file)
	if eol == nil then
		-- Avoid to process the file, it can be binary or non-standard
		return false, "no EOL"
	end

	-- Prepare to write in the same file
	fileHandle = io.open(filename, "wb")
	if fileHandle == nil then
		return false, "open wb " .. filename
	end

	-- Loop on the lines and process them
	string.gsub(file, "(.-)" .. eol, ProcessLine)

	fileHandle:close()
	return true, nil
end

local result, op = ConvertFile(filenameIn)
if not result then
	print("Error in operation: " .. (op or 'nil'))
else
	print"Done!"
end