#!/usr/bin/env lua
--
-- Author: Francois Dupoux
-- SPDX-License-Identifier: GPL-3.0-or-later
--
-- SystemRescue configuration processing script
--
-- This script uses the SystemRescue yaml configuration files and the options
-- passed on the boot command line to override the default configuration.
-- It processes yaml configuration files in the alphabetical order, and each option
-- found in a file override the options defined earlier. Options passed on the
-- boot command like take precedence over configuration options defined in files.
-- At the end it writes the effective configuration to a JSON file which is meant
-- to be ready by any initialisation script which needs to know the configuration.
-- Shell scripts can read values from the JSON file using a command such as:
-- jq --raw-output '.global.copytoram' /run/archiso/config/sysrescue-effective-config.json
-- This script requires the following lua packages to run on Arch Linux:
-- sudo pacman -Sy lua lua-yaml lua-dkjson lua-http

-- ==============================================================================
-- Import modules
-- ==============================================================================
local lfs = require('lfs')
local yaml = require('yaml')
local json = require("dkjson")
local request = require("http.request")

-- ==============================================================================
-- Utility functions
-- ==============================================================================
-- Read a file and return all its contents
function read_file_contents(path)
    local file = io.open(path, "rb")
    if not file then
        return nil
    end
    local content = file:read("*a")
    file:close()
    return content
end

-- Return true if the item is present in the list or false otherwise
function item_in_list(item, list)
    for _, curitem in ipairs(list) do
        if (curitem == item) then
            return true
        end
    end
    return false
end

-- Ensure that the given scope exists in the config table, create it if not
function ensure_scope(cfg_table, scopename)
    if (cfg_table == nil) or (type(cfg_table) ~= "table") then
        cfg_table = { }
    end
    if (cfg_table[scopename] == nil) or (type(cfg_table[scopename]) ~= "table") then
        cfg_table[scopename] = { }
    end
end

-- Return the number of items in a table
function get_table_size(mytable)
    size = 0
    for _ in pairs(mytable) do
        size = size + 1
    end
    return size
end

-- Return a list of files with a yaml extension found in the directory 'dirname'
-- If 'filenames' is an empty list then it will return all files which have been found
-- If 'filenames' is not empty then it will only return files with a name present in the list
function list_config_files(dirname, filenames)
    local results = {}
    for curfile in lfs.dir(dirname) do
        fullpath = dirname.."/"..curfile
        filetype = lfs.attributes(fullpath, "mode")
        if (filetype == "file") and curfile:match(".[Yy][Aa][Mm][Ll]$") then
            if (get_table_size(filenames) == 0) or item_in_list(curfile, filenames) then
                table.insert(results, fullpath)
            end
        end
    end
    table.sort(results)
    return results
end

-- Attempt to find the option 'optname' on the boot command line and return its value
-- If 'multiple' is false then it will return the value of the last occurence found or nil
-- If 'multiple' is true then it will return a list of all values passed or an empty list
function search_cmdline_option(optname, multiple)
    local result_single = nil
    local result_multiple = {}
    local cmdline = read_file_contents("/proc/cmdline")
    for curopt in cmdline:gmatch("%S+") do
        optmatch1 = string.match(curopt, "^"..optname.."$")
        _, _, optmatch2 = string.find(curopt, "^"..optname.."=([^%s]+)$")
        if (optmatch1 ~= nil) or (optmatch2 == 'y') or (optmatch2 == 'yes') or (optmatch2 == 'true') then
            result_single = true
            table.insert(result_multiple, true)
        elseif (optmatch2 == 'n') or (optmatch2 == 'no') or (optmatch2 == 'false') then
            result_single = false
            table.insert(result_multiple, false)
        elseif (optmatch2 ~= nil) then
            result_single = optmatch2
            table.insert(result_multiple, optmatch2)
        end
    end
    if multiple == true then
        return result_multiple
    else
        return result_single
    end
end

-- Process a block of yaml configuration and override the current configuration with new values
function process_yaml_config(config_content)
    if (config_content == nil) then
        io.stderr:write(string.format("Error downloading or empty file received\n"))
        return false
    end
    if pcall(function() curconfig = yaml.load(config_content) end) then
        if (curconfig == nil) or (type(curconfig) ~= "table") then
            io.stderr:write(string.format("This is not valid yaml (=no table), it will be ignored\n"))
            return false
        end
        merge_config_table(config, curconfig, "config")
        return true
    else
        io.stderr:write(string.format("Failed parsing yaml, it will be ignored\n"))
        return false
    end
end

-- Recursive merge of a config table
-- config_table: references the current level within the global config
-- new_table: the current level within the new yaml we want to merge right now
-- leveltext: textual representation of the current level used for messages, split by "|"
function merge_config_table(config_table, new_table, leveltext)
    for key, value in pairs(new_table) do
        -- loop through the current level of the new config
        if (config_table[key] == nil) then
            -- a key just existing in the new config, not in current config -> copy it
            print("- Merging "..leveltext.."|"..key.." into the config")
            config_table[key] = value
        else
            -- key of the new config also exisiting in the current config: check value type
            if (type(value) == "nil" or (type(value) == "string" and value == "")) then
                -- remove an existing table entry with an empty value
                print("- Removing "..leveltext.."|"..key)
                config_table[key] = nil
            elseif (type(value) == "table" and type(config_table[key]) == "table") then
                -- old and new values are tables: recurse
                merge_config_table(config_table[key], value, leveltext.."|"..key)
            else
                -- overwrite the old value
                print("- Overriding "..leveltext.."|"..key.." with the value from the yaml file")
                config_table[key] = value
            end
        end
    end
end

-- Download a file over http/https and return the contents of the file or nil if it fails
function download_file(fileurl)
    local req_timeout = 10
    local req = request.new_from_uri(fileurl)
    local headers, stream = req:go(req_timeout)

    if headers == nil then
        io.stderr:write(string.format("Failed to download %s: Could not connect\n", fileurl))
        return nil
    end

    status = headers:get(":status")
    if status ~= '200' then
        io.stderr:write(string.format("Failed to download %s: Received HTTP code %s\n", fileurl, status))
        return nil
    end

    local body, err = stream:get_body_as_string()
    if not body and err then
        io.stderr:write(string.format("Failed to download %s: Error %s\n", fileurl, tostring(err)))
        return nil
    end

    return body
end

-- ==============================================================================
-- Initialisation
-- ==============================================================================
errcnt = 0

-- ==============================================================================
-- We start with an empty global config
-- the default config is usually in the first yaml file parsed (100-defaults.yaml)
-- ==============================================================================
config = { }

-- ==============================================================================
-- Merge one yaml file after the other in lexicographic order
-- ==============================================================================
print ("====> Merging configuration with values from yaml files ...")
confdirs = {"/run/archiso/bootmnt/sysrescue.d", "/run/archiso/copytoram/sysrescue.d"}

-- Process local yaml configuration files
for _, curdir in ipairs(confdirs) do
    if lfs.attributes(curdir, "mode") == "directory" then
        print("Searching for yaml configuration files in "..curdir.." ...")
        for _, curfile in ipairs(list_config_files(curdir, {})) do
            print(string.format("Processing local yaml configuration file: %s ...", curfile))
            if process_yaml_config(read_file_contents(curfile)) == false then
                errcnt = errcnt + 1
            end
        end
    else
        print("Directory "..curdir.." was not found so it has been ignored")
    end
end

-- Process explicitly configured configuration files
-- these are parsed afterwards and in the order given, so they have precedence
conffiles = search_cmdline_option("sysrescuecfg", true)
print("Searching for remote yaml configuration files ...")
for _, curfile in ipairs(conffiles) do
    if string.match(curfile, "^https?://") then
        print(string.format("Processing remote yaml configuration file: %s ...", curfile))
        local contents = download_file(curfile)
        if process_yaml_config(contents) == false then
            errcnt = errcnt + 1
        end
    elseif string.match(curfile, "^/") then
        -- we have a local file with absolute path
        print(string.format("Processing local yaml configuration file: %s ...",curfile))
        if process_yaml_config(read_file_contents(curfile)) == false then
            errcnt = errcnt + 1
        end
    else
        -- we have a local file with relative path, prefix the one existing config dir
        -- this will apply the config again, but later than before, giving it higher priority
        for _, curdir in ipairs(confdirs) do
            if lfs.attributes(curdir, "mode") == "directory" then
                print(string.format("Processing local yaml configuration file: %s ...",curdir.."/"..curfile))
                if process_yaml_config(read_file_contents(curdir.."/"..curfile)) == false then
                    errcnt = errcnt + 1
                end
                -- just try the explicitly configured filename with one dir prefix
                break
            end
        end
    end
end

-- ==============================================================================
-- Override the configuration with values passed on the boot command line
--
-- NOTE: boot command line options are only for legacy compatibility and
--       very common options. Consider carfully before adding new boot 
--       command line options. New features should by default just be 
--       configured through the yaml config.
-- ==============================================================================

cmdline_options = {
    ['copytoram'] = "global",
    ['cow_label'] = "global",
    ['cow_directory'] = "global",
    ['checksum'] = "global",
    ['loadsrm'] = "global",
    ['dostartx'] = "global",
    ['dovnc'] = "global",
    ['noautologin'] = "global",
    ['nofirewall'] = "global",
    ['rootshell'] = "global",
    ['rootpass'] = "global",
    ['rootcryptpass'] = "global",
    ['setkmap'] = "global",
    ['vncpass'] = "global",
    ['ar_disable'] = "autorun",
    ['ar_nowait'] = "autorun",
    ['ar_nodel'] = "autorun",
    ['ar_ignorefail'] = "autorun",
    ['ar_attempts'] = "autorun",
    ['ar_source'] = "autorun",
    ['ar_suffixes'] = "autorun"
}

print ("====> Overriding the configuration with options passed on the boot command line ...")
for option, scope in pairs(cmdline_options) do
    optresult = search_cmdline_option(option, false)
    if optresult == true then
        print("- Option '"..option.."' has been enabled on the boot command line")
        ensure_scope(config, scope)
        config[scope][option] = optresult
    elseif optresult == false then
        print("- Option '"..option.."' has been disabled on the boot command line")
        ensure_scope(config, scope)
        config[scope][option] = optresult
    elseif optresult ~= nil then
        print("- Option '"..option.."' has been defined as '"..optresult.."' on the boot command line")
        ensure_scope(config, scope)
        config[scope][option] = optresult
    end
end

-- ==============================================================================
-- Print the effective configuration
-- ==============================================================================
print ("====> Printing the effective configuration")
local jsoncfgtxt = json.encode (config, { indent = true })
print (jsoncfgtxt)

-- ==============================================================================
-- Write the effective configuration to a JSON file
-- ==============================================================================
print ("====> Writing the effective configuration to a JSON file ...")
output_location = "/run/archiso/config"
output_filename = "sysrescue-effective-config.json"
output_fullpath = output_location.."/"..output_filename
jsoncfgfile = io.open(output_fullpath, "w")
if jsoncfgfile == nil then
    io.stderr:write(string.format("ERROR: Failed to create effective configuration file in %s\n", output_fullpath))
    os.exit(1)
end
jsoncfgfile:write(jsoncfgtxt)
jsoncfgfile:close()
os.execute("chmod 700 "..output_location)
os.execute("chmod 600 "..output_fullpath)
print ("Effective configuration has been written to "..output_fullpath)

-- ==============================================================================
-- Error handling
-- ==============================================================================
if errcnt == 0 then
    print ("SUCCESS: Have successfully completed the processing of the configuration")
    os.exit(0)
else
    io.stderr:write(string.format("FAILURE: Have completed the processing of the configuration with %d errors\n", errcnt))
    os.exit(1)
end