defmodule Systant.HaDiscovery do
  @moduledoc """
  Home Assistant MQTT Discovery integration for Systant.
  
  Publishes device and entity discovery configurations to Home Assistant
  via MQTT following the HA discovery protocol.
  
  Discovery topic format: homeassistant/<component>/<node_id>/<object_id>/config
  """

  require Logger

  @manufacturer "Systant"
  @model "System Monitor"

  @doc """
  Publish all discovery configurations for a host
  """
  def publish_discovery(client_pid, hostname, config \\ nil) do
    app_config = config || Systant.Config.load_config()
    ha_config = Systant.Config.get(app_config, ["homeassistant"]) || %{}
    
    if ha_config["discovery_enabled"] != false do
      discovery_prefix = ha_config["discovery_prefix"] || "homeassistant"
      device_config = build_device_config(hostname)
      
      # Publish device discovery first
      publish_device_discovery(client_pid, hostname, device_config, discovery_prefix)
      
      # Publish sensor discoveries
      publish_sensor_discoveries(client_pid, hostname, device_config, discovery_prefix)
      
      Logger.info("Published Home Assistant discovery for #{hostname}")
    else
      Logger.info("Home Assistant discovery disabled in configuration")
    end
  end

  @doc """
  Remove all discovery configurations for a host
  """
  def remove_discovery(client_pid, hostname, config \\ nil) do
    app_config = config || Systant.Config.load_config()
    ha_config = Systant.Config.get(app_config, ["homeassistant"]) || %{}
    discovery_prefix = ha_config["discovery_prefix"] || "homeassistant"
    
    # Remove by publishing empty payloads to discovery topics
    sensors = get_sensor_definitions(hostname)
    
    Enum.each(sensors, fn {component, object_id, _config} ->
      topic = "#{discovery_prefix}/#{component}/#{hostname}/#{object_id}/config"
      Tortoise.publish(client_pid, topic, "", retain: true)
    end)
    
    Logger.info("Removed Home Assistant discovery for #{hostname}")
  end

  # Private functions

  defp publish_device_discovery(client_pid, hostname, device_config, discovery_prefix) do
    # Use device-based discovery for multiple components
    components_config = %{
      device: device_config,
      components: build_all_components(hostname, device_config)
    }
    
    topic = "#{discovery_prefix}/device/#{hostname}/config"
    payload = Jason.encode!(components_config)
    
    Tortoise.publish(client_pid, topic, payload, retain: true)
  end

  defp publish_sensor_discoveries(client_pid, hostname, device_config, discovery_prefix) do
    sensors = get_sensor_definitions(hostname)
    
    Enum.each(sensors, fn {component, object_id, config} ->
      full_config = Map.merge(config, %{device: device_config})
      topic = "#{discovery_prefix}/#{component}/#{hostname}/#{object_id}/config"
      payload = Jason.encode!(full_config)
      
      Tortoise.publish(client_pid, topic, payload, retain: true)
    end)
  end

  defp build_device_config(hostname) do
    %{
      identifiers: ["systant_#{hostname}"],
      name: "Systant #{hostname}",
      manufacturer: @manufacturer,
      model: @model,
      sw_version: Application.spec(:systant, :vsn) |> to_string()
    }
  end

  defp build_all_components(hostname, device_config) do
    get_sensor_definitions(hostname)
    |> Enum.map(fn {_component, object_id, config} ->
      Map.merge(config, %{device: device_config})
      |> Map.put(:object_id, object_id)
    end)
  end

  defp get_sensor_definitions(hostname) do
    base_topic = "systant/#{hostname}/stats"
    
    [
      # CPU Sensors
      {"sensor", "cpu_load_1m", build_sensor_config("CPU Load 1m", "#{base_topic}", "cpu.avg1", "load", "mdi:speedometer")},
      {"sensor", "cpu_load_5m", build_sensor_config("CPU Load 5m", "#{base_topic}", "cpu.avg5", "load", "mdi:speedometer")},
      {"sensor", "cpu_load_15m", build_sensor_config("CPU Load 15m", "#{base_topic}", "cpu.avg15", "load", "mdi:speedometer")},
      
      # Memory Sensors
      {"sensor", "memory_used_percent", build_sensor_config("Memory Used", "#{base_topic}", "memory.used_percent", "%", "mdi:memory")},
      {"sensor", "memory_used_gb", build_sensor_config("Memory Used GB", "#{base_topic}", "memory.used_kb", "GB", "mdi:memory", "{{ (value_json.memory.used_kb | float / 1024 / 1024) | round(2) }}")},
      {"sensor", "memory_total_gb", build_sensor_config("Memory Total GB", "#{base_topic}", "memory.total_kb", "GB", "mdi:memory", "{{ (value_json.memory.total_kb | float / 1024 / 1024) | round(2) }}")},
      
      # System Sensors
      {"sensor", "uptime_hours", build_sensor_config("Uptime", "#{base_topic}", "system.uptime_seconds", "h", "mdi:clock-outline", "{{ (value_json.system.uptime_seconds | float / 3600) | round(1) }}")},
      {"sensor", "kernel_version", build_sensor_config("Kernel Version", "#{base_topic}", "system.kernel_version", nil, "mdi:linux")},
      
      # Temperature Sensors
      {"sensor", "cpu_temperature", build_sensor_config("CPU Temperature", "#{base_topic}", "temperature.cpu", "°C", "mdi:thermometer")},
      
      # GPU Sensors - NVIDIA
      {"sensor", "gpu_nvidia_utilization", build_sensor_config("NVIDIA GPU Utilization", "#{base_topic}", "gpu.nvidia[0].utilization_percent", "%", "mdi:expansion-card", "{{ value_json.gpu.nvidia[0].utilization_percent if value_json.gpu.nvidia and value_json.gpu.nvidia|length > 0 else 0 }}")},
      {"sensor", "gpu_nvidia_temperature", build_sensor_config("NVIDIA GPU Temperature", "#{base_topic}", "gpu.nvidia[0].temperature_c", "°C", "mdi:thermometer", "{{ value_json.gpu.nvidia[0].temperature_c if value_json.gpu.nvidia and value_json.gpu.nvidia|length > 0 else none }}")},
      {"sensor", "gpu_nvidia_memory", build_sensor_config("NVIDIA GPU Memory", "#{base_topic}", "gpu.nvidia[0].memory_used_mb", "MB", "mdi:memory", "{{ value_json.gpu.nvidia[0].memory_used_mb if value_json.gpu.nvidia and value_json.gpu.nvidia|length > 0 else none }}")},
      
      # GPU Sensors - AMD
      {"sensor", "gpu_amd_utilization", build_sensor_config("AMD GPU Utilization", "#{base_topic}", "gpu.amd[0].utilization_percent", "%", "mdi:expansion-card", "{{ value_json.gpu.amd[0].utilization_percent if value_json.gpu.amd and value_json.gpu.amd|length > 0 else 0 }}")},
      {"sensor", "gpu_amd_temperature", build_sensor_config("AMD GPU Temperature", "#{base_topic}", "gpu.amd[0].temperature_c", "°C", "mdi:thermometer", "{{ value_json.gpu.amd[0].temperature_c if value_json.gpu.amd and value_json.gpu.amd|length > 0 else none }}")},
      
      # Disk Sensors - Main filesystem usage
      {"sensor", "disk_root_usage", build_sensor_config("Root Disk Usage", "#{base_topic}", "disk.disks", "%", "mdi:harddisk", "{{ (value_json.disk.disks | selectattr('mounted_on', 'equalto', '/') | list | first).use_percent if value_json.disk.disks else 0 }}")},
      {"sensor", "disk_home_usage", build_sensor_config("Home Disk Usage", "#{base_topic}", "disk.disks", "%", "mdi:harddisk", "{{ (value_json.disk.disks | selectattr('mounted_on', 'equalto', '/home') | list | first).use_percent if (value_json.disk.disks | selectattr('mounted_on', 'equalto', '/home') | list) else 0 }}")},
      
      # Network Sensors - Primary interface throughput
      {"sensor", "network_rx_throughput", build_sensor_config("Network RX Throughput", "#{base_topic}", "network", "B/s", "mdi:download-network", "{{ value_json.network[0].rx_throughput_bps if value_json.network and value_json.network|length > 0 else 0 }}")},
      {"sensor", "network_tx_throughput", build_sensor_config("Network TX Throughput", "#{base_topic}", "network", "B/s", "mdi:upload-network", "{{ value_json.network[0].tx_throughput_bps if value_json.network and value_json.network|length > 0 else 0 }}")},
      
      # Binary Sensors for status
      {"binary_sensor", "system_online", build_binary_sensor_config("System Online", "#{base_topic}", "mdi:server", "connectivity")}
    ]
  end

  defp build_sensor_config(name, state_topic, value_template_path, unit, icon, custom_template \\ nil) do
    base_config = %{
      name: name,
      state_topic: state_topic,
      value_template: custom_template || "{{ value_json.#{value_template_path} }}",
      icon: icon,
      unique_id: "systant_#{String.replace(state_topic, "/", "_")}_#{String.replace(value_template_path, ".", "_")}",
      origin: %{
        name: "Systant",
        sw_version: Application.spec(:systant, :vsn) |> to_string(),
        support_url: "https://github.com/user/systant"
      }
    }
    
    if unit do
      Map.put(base_config, :unit_of_measurement, unit)
    else
      base_config
    end
  end

  defp build_binary_sensor_config(name, state_topic, icon, device_class) do
    %{
      name: name,
      state_topic: state_topic,
      value_template: "{{ 'ON' if value_json.timestamp else 'OFF' }}",
      device_class: device_class,
      icon: icon,
      unique_id: "systant_#{String.replace(state_topic, "/", "_")}_online",
      origin: %{
        name: "Systant",
        sw_version: Application.spec(:systant, :vsn) |> to_string(),
        support_url: "https://github.com/user/systant"
      }
    }
  end
end