--[[
	ast.lua - Generates a structure for use in preprocessing.
]]
-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at https://mozilla.org/MPL/2.0/.

local function nextc(f, c)
	c = c or 1
	return f:read(c)
end

local function peek(f, c)
	c = c or 1
	local z = f:read(c)
	f:seek("cur", -c)
	return z
end

local function skip(f, c)
	c = c or 1
	return f:seek("cur", c)
end

local ws = {
	["\t"] = true,
	[" "] = true
}

local function parse_hex(f)
	local lc = " "
	local hex = ""
	while (48 <= lc:byte() and lc:byte() <= 57) or (97 <= lc:byte() and lc:byte() <= 102) or (65 <= lc:byte() and lc:byte() <= 70) and lc do
		lc = nextc(f)
		if (48 <= lc:byte() and lc:byte()) <= 57 or (97 <= lc:byte() and lc:byte() <= 102) or (65 <= lc:byte() and lc:byte() <= 70) and lc then
			hex = hex .. lc
		end
	end
	return tonumber(hex, 16)
end

local function parse_number(f, c)
	local lc = " "
	local num = c
	while 48 <= lc:byte() and lc:byte() <= 57 and lc do
		lc = nextc(f)
		if (48 <= lc:byte() and lc:byte() <= 57) and lc then
			num = num .. lc
		end
	end
	return tonumber(hex, 10)
end

local esct = {
	["t"] = "\t",
	["n"] = "\n",
	["r"] = "\r",
	["\\"] = "\\\\"
}

for i=0, 9 do
	esct[tostring(i)] = string.char(i)
end

local function parse_dblquote(f)
	local val = ""
	while peek(f) ~= "\"" do
		local c = nextc(f)
		if (peek(f) == "\n" or peek(f) == "\r") then
			return nil, "Unexpected end of line"
		elseif (not peek(f)) then
			return nil, "Unexpected end of file"
		end
		if (c == "\\") then
			if (esct[peek(f)]) then
				c = esct[peek(f)]
				skip(f)
			else
				c = nextc(f)
			end
		end
		val = val .. c
	end
	skip(f)
	return val
end

local function parse_snglquote(f)
	local val = ""
	while peek(f) ~= "\'" do
		local c = nextc(f)
		if (peek(f) == "\n" or peek(f) == "\r") then
			return nil, "Unexpected end of line"
		elseif (not peek(f)) then
			return nil, "Unexpected end of file"
		end
		if (c == "\\") then
			if (esct[peek(f)]) then
				c = esct[peek(f)]
				skip(f)
			else
				c = nextc(f)
			end
		end
		val = val .. c
	end
	skip(f)
	return val
end

local function parse_envarg(f)
	local val = ""
	while peek(f) ~= ")" do
		if (peek(f) == "\n" or peek(f) == "\r") then
			return nil, "Unexpected end of line"
		elseif (not peek(f)) then
			return nil, "Unexpected end of file"
		end
		val = val .. nextc(f)
	end
	skip(f)
	return val
end

local function parse_directive(f)
	local lc = "_"
	local name = ""
	local args = {}
	local carg = ""
	while not ws[lc] do
		lc = nextc(f)
		if (lc == "\n" or lc == "\r") then
			if (lc == "\r" and peek(f) == "\n") then skip(f) end
			return {type="directive", name=name}
		elseif not ws[lc] then
			name = name .. lc
		end
	end
	while true do
		lc = nextc(f)
		if (lc == "\n" or lc == "\r") then
			if (lc == "\r" and peek(f) == "\n") then skip(f) end
			return {type="directive", name=name, args=args}
		elseif lc == "0" and peek(f) == "x" then
			skip(f)
			local val = parse_hex(f)
			args[#args+1] = val
		elseif 48 <= lc:byte() and lc:byte() <= 57 then
			local val = parse_number(f, lc)
			args[#args+1] = val
		elseif lc == "\"" then
			local val, e = parse_dblquote(f)
			if not val then return val, e end
			args[#args+1] = val
		elseif lc == "\'" then
			local val, e = parse_snglquote(f)
			if not val then return val, e end
			args[#args+1] = val
		elseif lc == "$" and peek(f) == "(" then
			skip(f)
			local val = parse_envarg(f)
			if not os.getenv(val) then return nil, "Enviroment variable `"..val.."' does not exist." end
			args[#args+1] = os.getenv(val)
		elseif lc == "@" and peek(f, 2) == "[{" then
			skip(f, 2)
			local val = ""
			while peek(f, 2) ~= "}]" do
				val = val .. nextc(f)
			end
			args[#args+1] = {type="lua_var", val}
			skip(f, 2)
		elseif not ws[lc] then
			return nil, "Syntax error"
		end
	end
end

local function mkast(f, n)
	io.stderr:write("PROC\t",n,"\n")
	local lc = " "
	local lpos = 1
	local ilpos = 1
	local tree = {}
	local code = ""
	local branches = {}
	local function add_code()
		tree[#tree+1] = {type="code", data=code, file=n, line=lpos}
		code = ""
	end
	local function parse_error(e)
		io.stderr:write("ERROR:"..n..":"..lpos..": "..e.."\n")
		os.exit(1)
	end
	while lc and lc ~= "" do
		lc = nextc(f)
		if (lc == "-" and ilpos == 1) then
			if (peek(f, 2) == "-#") then --Directive
				add_code()
				skip(f, 2)
				local d, r = parse_directive(f)
				if not d then
					parse_error(r)
				end
				d.line = lpos
				d.file = n
				lpos = lpos+1
				tree[#tree+1] = d
			else
				code = code .. lc
				ilpos = ilpos+1
			end
		elseif (lc == "/" and ilpos == 1) then
			if (peek(f, 2) == "/#") then --Directive
				add_code()
				skip(f, 2)
				local d, r = parse_directive(f)
				if not d then
					parse_error(r)
				end
				d.line = lpos
				d.file = n
				lpos = lpos+1
				tree[#tree+1] = d
			else
				code = code .. lc
				ilpos = ilpos+1
			end
		elseif (lc == "$" and peek(f) == "(") then
			add_code()
			skip(f)
			local val, e = parse_envarg(f)
			if not val then
				parse_error(e)
			end
			tree[#tree+1] = {type="envvar", var=val, file=n, line=lpos}
		elseif (lc == "@" and peek(f, 2) == "[[") then
			add_code()
			skip(f, 2)
			local val = ""
			while peek(f, 2) ~= "]]" do
				val = val .. nextc(f)
			end
			tree[#tree+1] = {type="lua", code=val, file=n, line=lpos}
			skip(f, 2)
		elseif (lc == "@" and peek(f, 2) == "[{") then
			add_code()
			skip(f, 2)
			local val = ""
			while peek(f, 2) ~= "}]" do
				val = val .. nextc(f)
			end
			tree[#tree+1] = {type="lua_r", code=val, file=n, line=lpos}
			skip(f, 2)
		elseif (lc == "$" and peek(f, 2) == "[[") then
			add_code()
			skip(f, 2)
			local val = ""
			while peek(f, 2) ~= "]]" do
				val = val .. nextc(f)
			end
			tree[#tree+1] = {type="shell", code=val, file=n, line=lpos}
			skip(f, 2)
		elseif (lc == "$" and peek(f, 2) == "[{") then
			add_code()
			skip(f, 2)
			local val = ""
			while peek(f, 2) ~= "}]" do
				val = val .. nextc(f)
			end
			tree[#tree+1] = {type="shell_r", code=val, file=n, line=lpos}
			skip(f, 2)
		elseif (lc == "\r" or lc == "\n") then
			if (lc == "\r" and peek(f) == "\n") then
				skip(f)
			end
			lpos = lpos+1
			ilpos = 1
			code = code .. "\n"
		else
			code = code .. (lc or "")
			ilpos = ilpos+1
		end
	end
	add_code()
	return tree
end