using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;

using Unosquare.RaspberryIO.Abstractions;

namespace Unosquare.WiringPi {
  /// <inheritdoc />
  /// <summary>
  /// A simple wrapper for the I2c bus on the Raspberry Pi.
  /// </summary>
  public class I2CBus : II2CBus {
    // TODO: It would be nice to integrate i2c device detection.
    private static readonly Object SyncRoot = new Object();
    private readonly Dictionary<Int32, II2CDevice> _devices = new Dictionary<Int32, II2CDevice>();

    /// <inheritdoc />
    public ReadOnlyCollection<II2CDevice> Devices {
      get {
        lock(SyncRoot) {
          return new ReadOnlyCollection<II2CDevice>(this._devices.Values.ToArray());
        }
      }
    }

    /// <inheritdoc />
    public II2CDevice this[Int32 deviceId] => this.GetDeviceById(deviceId);

    /// <inheritdoc />
    public II2CDevice GetDeviceById(Int32 deviceId) {
      lock(SyncRoot) {
        return this._devices[deviceId];
      }
    }

    /// <inheritdoc />
    /// <exception cref="KeyNotFoundException">When the device file descriptor is not found.</exception>
    public II2CDevice 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 Native.WiringPi.WiringPiI2CSetup(deviceId);
      }
    }
  }
}