homebridge-mqttthing codec for IKEA bulbs

IKEA_Bulb.js

let states = []

module.exports = {
    init: function () {
        return {
            encode(message, info) {
                let { topic } = info
                let state = states.find(_state => _state.topic === topic.replace(/\/set$/, ''))
                if (!state) return
                switch (info.property) {
                    case 'on':
                        state.state = message
                        return JSON.stringify({ state: message })
                    case 'brightness':
                        state.brightness = brightnessToZigbee(message)
                        return JSON.stringify({
                            state: state.state,
                            brightness: state.brightness,
                        })
                    case 'HSV':
                        let [hue, saturation, brightness] = message.split(',').map(Number)
                        Object.assign(state, { hue, saturation, brightness: brightnessToZigbee(brightness) })
                        return JSON.stringify({
                            state: state.state,
                            brightness: state.brightness,
                            color: { hue, saturation },
                        })
                }
            },
            decode(message, info) {
                let { topic } = info
                let { state, color, brightness } = JSON.parse(message)
                let hue = color?.hue || 0
                let saturation = color?.saturation || 0
                let decodedBrightness = brightnessFromZigbee(brightness)
                upsertState({ topic: topic.replace(/\/set$/, ''), state, hue, saturation, brightness: decodedBrightness })
                switch (info.property) {
                    case 'on':
                        return state
                    case 'brightness':
                        return decodedBrightness
                    case 'HSV':
                        return `${hue},${saturation},${decodedBrightness}`
                }
            }
        }
    }
}

function upsertState(state) {
    let savedState = states.find(_state => _state.topic === state.topic)
    savedState ? Object.assign(savedState, state) : states.push(state)
}

function brightnessToZigbee(brightness) {
    return Math.round(parseInt(brightness) / 100 * 254)
}

function brightnessFromZigbee(brightness) {
    return Math.round(parseInt(brightness) / 254 * 100)
}

This codec is intended to be used with an IKEA bulb paired with zigbee2MQTT. Make sure to go into the device settings tab for the bulb in zigbee2MQTT and check the "retain" check box.