local M, bin = {}, require("casc.bin")
local assert, loadstring, smatch = assert, loadstring or load, string.match

local uint32_le, int32_le, float32_le = bin.uint32_le, bin.int32_le, bin.float32_le

local function unpacker(data, format, rows, stride, hsize, sbase, tfunc)
	tfunc = type(tfunc) == "function" and tfunc or nil
	
	local skip, p, pe = 0, [=[-- casc.dbc:iterator
		local smatch, uint32_le, int32_le, float32_le, tfunc, data, rows, stride, sbase, rpos, i = ...
		return function()
			if i < rows then
				rpos, i = rpos + stride, i + 1
				return ]=] .. (tfunc and "tfunc(i" or "i"), (tfunc and ")" or "") .. '\nend\nend'
	
	for r, t in format:gmatch("(%d*)(.)") do
		r = tonumber(r) or 1
		for i=1,r do
			if t == '.' then
				skip = skip + 4 * r
				break
			elseif t == 'u' then
				p, skip = p .. ', uint32_le(data, rpos+' .. skip .. ')', skip + 4
			elseif t == 'i' then
				p, skip = p .. ', int32_le(data, rpos+' .. skip .. ')', skip + 4
			elseif t == 'f' then
				p, skip = p .. ', float32_le(data, rpos+' .. skip .. ')', skip + 4
			elseif t == 's' then
				assert(sbase, "invalid signature: 's' requires a string block")
				p, skip = p .. ', smatch(data, "%Z*", sbase + uint32_le(data,rpos+' .. skip .. '))', skip + 4
			else
				error('Unknown signature field type "' .. t .. '"')
			end
		end
	end

	return loadstring(p .. pe)(smatch, uint32_le, int32_le, float32_le,
		tfunc, data, rows, stride, sbase, hsize - stride, 0), skip
end

local header do
	local function dbc(data)
		assert(data:sub(1,4) == "WDBC", "DBC magic signature")
		local rows, fields, stride, stringSize = uint32_le(data, 4), uint32_le(data, 8), uint32_le(data, 12), uint32_le(data, 16)
		assert(20 + rows*stride + stringSize <= #data, "Data too short")
	
		return rows, fields, stride, 20, 21 + rows * stride
	end
	local function db2(data)
		local hsize = 48
		local rows, fields, stride, stringSize = uint32_le(data, 4), uint32_le(data, 8), uint32_le(data, 12), uint32_le(data, 16)
		local build, minId, maxId, locale, rid = uint32_le(data, 24), uint32_le(data, 32), uint32_le(data, 36), uint32_le(data, 40)
	
		if maxId > 0 then
			local n, p = maxId-minId + 1, hsize
			rid, hsize = {}, hsize + 6 * n
			for i=1,n do
				rid[i], p = uint32_le(data, p), p + 6
			end
		end
		assert(hsize + rows*stride + stringSize <= #data, "Data too short")
	
		return rows, fields, stride, hsize, hsize + 1 + rows * stride, rid, minId, maxId, build, locale
	end
	header = {WDBC=dbc, WDB2=db2, WCH2=db2}
end

function M.header(data)
	assert(type(data) == "string", 'Syntax: casc.dbc.header("data")')
	local fourCC = data:sub(1,4)
	return assert(header[fourCC], "Unsupported format")(data)
end

function M.rows(data, sig, loose)
	assert(type(data) == "string" and type(sig) == "string", 'Syntax: casc.dbc.rows("data", "rowSignature"[, loose])')
	
	local rows, _, stride, hsize, sbase, rid = M.header(data)
	local iter, skip = unpacker(data, sig, rows, stride, hsize, sbase, rid and function(i, ...) return rid[i], ... end)
	assert(skip <= stride, 'signature exceeds stride')
	assert(loose or skip == stride, 'signature/stride mismatch')

	return iter
end

return M