local base = _G
local io = require("io")
local string = require("string")
local cjson = require "cjson.safe"
local glob = require "posix.glob"
local time = require "posix.time"
local unistd = require "posix.unistd"

local _M = {}
local _internal_ = {}
_internal_.setup = {}

-- ############# i2c ###########

function _internal_.write_to_file(path, data)
    -- base.print(string.format("writing '%s' to '%s'", data, path))
    local f, err = io.open(path, "w")
    if not f then return nil, err end

    ret, err = f:write(data)
    f:close()
    return ret, err
end

function _internal_.read_from_file(path)
    local f, err = io.open(path, "r")
    if not f then return nil, err end

    data, err = f:read("*a")
    f:close()
    return data, err
end

-- ############# i2c ###########

function _M.i2c_bus_path(bus)
    return string.format("/sys/bus/i2c/devices/i2c-%d", bus)
end

function _M.i2c_device_name(bus, address)
    return string.format("%d-%04X", bus, address)
end

function _M.i2c_device_path(bus, address)
    return string.format("/sys/bus/i2c/devices/" .. _M.i2c_device_name(bus, address))
end

function _M.i2c_add_device(bus, address, name)
    return _internal_.write_to_file(_M.i2c_bus_path(bus) .. "/new_device", string.format("%s 0x%02X", name, address))
end

function _M.i2c_delete_device(bus, address)
    return _internal_.write_to_file(_M.i2c_bus_path(bus) .. "/delete_device", string.format("0x%02X", address))
end

function _M.i2c_get_mux_channels(parent, address)
    local channel_paths, glob_result = glob.glob(_M.i2c_device_path(parent, address) .. "/channel-*", 0)
    if not channel_paths then
        if glob_result == glob.GLOB_NOMATCH then return {} end
        if glob_result == glob.GLOB_ABORTED then return nil, "glob(): aborted" end
        if glob_result == glob.GLOB_NOSPACE then return nil, "glob(): no space" end
        return nil, "glob(): unknown error"
    end

    local channels = {}
    for _, channel_path in base.pairs(channel_paths) do
        local channel = string.match(channel_path, '/channel%-(%d+)$')
        if not channel then return nil, "unable to parse channel number from path: " .. channel_path end

        local bus_path, err = unistd.readlink(channel_path)
        if not bus_path then return nil, err end
        local bus = string.match(bus_path, '/i2c%-(%d+)$')
        if not bus then return nil, "unable to parse bus number from path: " .. bus_path end

        channels[tonumber(channel)] = tonumber(bus)
    end
    return channels
end

function _M.i2c_add_devices_recursive(bus, devices)
    local num_devices = 0
    local device
    for _, device in base.ipairs(devices) do
        -- base.print(string.format("i2c_add_device(%d, 0x%02X, %s)", bus, device.address, device.driver))
        _M.i2c_add_device(bus, device.address, device.driver)
        num_devices = num_devices + 1

        local setup_function = _internal_.setup[device.driver]
        if setup_function ~= nil then
            time.nanosleep({tv_sec = 0, tv_nsec = 100000000})
            setup_function(bus, device.address)
        end

        if device.channels then
            time.nanosleep({tv_sec = 0, tv_nsec = 100000000})
            local mux_channels, err = _M.i2c_get_mux_channels(bus, device.address)
            if not mux_channels then return nil, error end
            local channel
            for _, channel in base.ipairs(device.channels) do
                if not mux_channels[channel.number] then return nil, string.format("i2c-mux %s has no channel %d", _M.i2c_device_name(bus, device.address), channel.number) end
                local tmp, err = _M.i2c_add_devices_recursive(mux_channels[channel.number], channel.devices)
                if not tmp then return nil, err end
                num_devices = num_devices + tmp
            end
        end
    end

    return num_devices
end


-- ############# II0 ###########

function _M.iio_device_path_from_i2c_device(bus, address)
    local device_paths, glob_result = glob.glob(_M.i2c_device_path(bus, address) .. "/iio:device*", 0)
    if not device_paths then
        if glob_result == glob.GLOB_NOMATCH then return nil, "couldn't find IIO device handle for i2c device " .. _M.i2c_device_name(bus, address) end
        if glob_result == glob.GLOB_ABORTED then return nil, "glob(): aborted" end
        if glob_result == glob.GLOB_NOSPACE then return nil, "glob(): no space" end
        return nil, "glob(): unknown error"
    end
    if #device_paths ~= 1 then return nil, "found more than one IIO device for i2c device " .. _M.i2c_device_name(bus, address) end
    return device_paths[1]
end

function _M.iio_setup_bmp280(bus, address)
    local iio_device, err = _M.iio_device_path_from_i2c_device(bus, address)
    if not iio_device then return nil, err end

    local ret, err = _internal_.write_to_file(iio_device .. '/in_pressure_oversampling_ratio', '1')
    if not ret then return nil, err end
    return _internal_.write_to_file(iio_device .. '/in_temp_oversampling_ratio', '1')
end
_internal_.setup['bmp280'] = _M.iio_setup_bmp280

function _M.iio_setup_bme280(bus, address)
    local iio_device, err = _M.iio_device_path_from_i2c_device(bus, address)
    if not iio_device then return nil, err end

    local ret, err = _internal_.write_to_file(iio_device .. '/in_humidityrelative_oversampling_ratio', '1')
    if not ret then return nil, err end
    local ret, err = _internal_.write_to_file(iio_device .. '/in_pressure_oversampling_ratio', '1')
    if not ret then return nil, err end
    return _internal_.write_to_file(iio_device .. '/in_temp_oversampling_ratio', '1')
end
_internal_.setup['bme280'] = _M.iio_setup_bme280


-- ############# config ###########

function _M.read_config(path)
    sensors_json, err = _internal_.read_from_file(path)
    if not sensors_json then return nil, err end

    return cjson.decode(sensors_json)
end

function _M.setup(config)
    local num_devices = 0
    if config.i2c then
        local i2c_bus
        for _, i2c_bus in ipairs(config.i2c) do
            local tmp, err = _M.i2c_add_devices_recursive(i2c_bus.number, i2c_bus.devices)
            if not tmp then return nil, err end
            num_devices = num_devices + tmp
        end
    end
end


-- ################################

return _M