using Unosquare.RaspberryIO.Native;
using Unosquare.Swan.Abstractions;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System;

namespace Unosquare.RaspberryIO.Gpio {
  /// <summary>
  /// A simple wrapper for the I2c bus on the Raspberry Pi
  /// </summary>
  public class I2CBus : SingletonBase<I2CBus> {
    // TODO: It would be nice to integrate i2c device detection.
    private static readonly Object SyncRoot = new Object();
    private readonly Dictionary<Int32, I2CDevice> _devices = new Dictionary<Int32, I2CDevice>();

    /// <summary>
    /// Prevents a default instance of the <see cref="I2CBus"/> class from being created.
    /// </summary>
    private I2CBus() {
      // placeholder
    }

    /// <summary>
    /// Gets the registered devices as a read only collection.
    /// </summary>
    public ReadOnlyCollection<I2CDevice> Devices => new ReadOnlyCollection<I2CDevice>(this._devices.Values.ToArray());

    /// <summary>
    /// Gets the <see cref="I2CDevice"/> with the specified device identifier.
    /// </summary>
    /// <value>
    /// The <see cref="I2CDevice"/>.
    /// </value>
    /// <param name="deviceId">The device identifier.</param>
    /// <returns>A reference to an I2C device</returns>
    public I2CDevice this[Int32 deviceId] => this.GetDeviceById(deviceId);

    /// <summary>
    /// Gets the device by identifier.
    /// </summary>
    /// <param name="deviceId">The device identifier.</param>
    /// <returns>The device reference</returns>
    public I2CDevice GetDeviceById(Int32 deviceId) {
      lock(SyncRoot) {
        return this._devices[deviceId];
      }
    }

    /// <summary>
    /// Adds a device to the bus by its Id. If the device is already registered it simply returns the existing device.
    /// </summary>
    /// <param name="deviceId">The device identifier.</param>
    /// <returns>The device reference</returns>
    /// <exception cref="KeyNotFoundException">When the device file descriptor is not found</exception>
    public I2CDevice AddDevice(Int32 deviceId) {
      lock(SyncRoot) {
        if(this._devices.ContainsKey(deviceId)) {
          return this._devices[deviceId];
        }

        Int32 fileDescriptor = SetupFileDescriptor(deviceId);
        if(fileDescriptor < 0) {
          throw new KeyNotFoundException($"Device with id {deviceId} could not be registered with the I2C bus. Error Code: {fileDescriptor}.");
        }

        I2CDevice device = new I2CDevice(deviceId, fileDescriptor);
        this._devices[deviceId] = device;
        return device;
      }
    }

    /// <summary>
    /// This initializes the I2C system with your given device identifier.
    /// The ID is the I2C number of the device and you can use the i2cdetect program to find this out.
    /// wiringPiI2CSetup() will work out which revision Raspberry Pi you have and open the appropriate device in /dev.
    /// The return value is the standard Linux filehandle, or -1 if any error – in which case, you can consult errno as usual.
    /// </summary>
    /// <param name="deviceId">The device identifier.</param>
    /// <returns>The Linux file handle</returns>
    private static Int32 SetupFileDescriptor(Int32 deviceId) {
      lock(SyncRoot) {
        return WiringPi.WiringPiI2CSetup(deviceId);
      }
    }
  }
}