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

namespace Unosquare.RaspberryIO.Gpio {
  /// <summary>
  /// Represents a singleton of the Raspberry Pi GPIO controller
  /// as an IReadOnlyCollection of GpioPins
  /// Low level operations are accomplished by using the Wiring Pi library.
  /// Use the Instance property to access the singleton's instance
  /// </summary>
  public sealed class GpioController : SingletonBase<GpioController>, IReadOnlyCollection<GpioPin> {
    #region Private Declarations

    private const String WiringPiCodesEnvironmentVariable = "WIRINGPI_CODES";
    private static readonly Object SyncRoot = new Object();
    private readonly Dictionary<WiringPiPin, GpioPin> _pinsByWiringPiPinNumber = new Dictionary<WiringPiPin, GpioPin>();

    #endregion

    #region Constructors and Initialization

    /// <summary>
    /// Prevents a default instance of the <see cref="GpioController" /> class from being created.
    /// It in turn initializes the controller and registers the pin -- in that order.
    /// </summary>
    /// <exception cref="Exception">Unable to initialize the GPIO controller.</exception>
    private GpioController() {
      if(this.Pins != null) {
        return;
      }

      if(IsInitialized == false) {
        Boolean initResult = this.Initialize(ControllerMode.DirectWithWiringPiPins);
        if(initResult == false) {
          throw new Exception("Unable to initialize the GPIO controller.");
        }
      }

      #region Pin Registration (32 WiringPi Pins)

      this.RegisterPin(GpioPin.Pin00.Value);
      this.RegisterPin(GpioPin.Pin01.Value);
      this.RegisterPin(GpioPin.Pin02.Value);
      this.RegisterPin(GpioPin.Pin03.Value);
      this.RegisterPin(GpioPin.Pin04.Value);
      this.RegisterPin(GpioPin.Pin05.Value);
      this.RegisterPin(GpioPin.Pin06.Value);
      this.RegisterPin(GpioPin.Pin07.Value);
      this.RegisterPin(GpioPin.Pin08.Value);
      this.RegisterPin(GpioPin.Pin09.Value);
      this.RegisterPin(GpioPin.Pin10.Value);
      this.RegisterPin(GpioPin.Pin11.Value);
      this.RegisterPin(GpioPin.Pin12.Value);
      this.RegisterPin(GpioPin.Pin13.Value);
      this.RegisterPin(GpioPin.Pin14.Value);
      this.RegisterPin(GpioPin.Pin15.Value);
      this.RegisterPin(GpioPin.Pin16.Value);
      this.RegisterPin(GpioPin.Pin17.Value);
      this.RegisterPin(GpioPin.Pin18.Value);
      this.RegisterPin(GpioPin.Pin19.Value);
      this.RegisterPin(GpioPin.Pin20.Value);
      this.RegisterPin(GpioPin.Pin21.Value);
      this.RegisterPin(GpioPin.Pin22.Value);
      this.RegisterPin(GpioPin.Pin23.Value);
      this.RegisterPin(GpioPin.Pin24.Value);
      this.RegisterPin(GpioPin.Pin25.Value);
      this.RegisterPin(GpioPin.Pin26.Value);
      this.RegisterPin(GpioPin.Pin27.Value);
      this.RegisterPin(GpioPin.Pin28.Value);
      this.RegisterPin(GpioPin.Pin29.Value);
      this.RegisterPin(GpioPin.Pin30.Value);
      this.RegisterPin(GpioPin.Pin31.Value);

      #endregion

      this.Pins = new ReadOnlyCollection<GpioPin>(this._pinsByWiringPiPinNumber.Values.ToArray());
      Dictionary<Int32, GpioPin> headerP1 = new Dictionary<Int32, GpioPin>(this.Pins.Count);
      Dictionary<Int32, GpioPin> headerP5 = new Dictionary<Int32, GpioPin>(this.Pins.Count);
      foreach(GpioPin pin in this.Pins) {
        Dictionary<Int32, GpioPin> target = pin.Header == GpioHeader.P1 ? headerP1 : headerP5;
        target[pin.HeaderPinNumber] = pin;
      }

      this.HeaderP1 = new ReadOnlyDictionary<Int32, GpioPin>(headerP1);
      this.HeaderP5 = new ReadOnlyDictionary<Int32, GpioPin>(headerP5);
    }

    /// <summary>
    /// Determines if the underlying GPIO controller has been initialized properly.
    /// </summary>
    /// <value>
    /// <c>true</c> if the controller is properly initialized; otherwise, <c>false</c>.
    /// </value>
    public static Boolean IsInitialized {
      get {
        lock(SyncRoot) {
          return Mode != ControllerMode.NotInitialized;
        }
      }
    }

    /// <summary>
    /// Gets the number of registered pins in the controller.
    /// </summary>
    public Int32 Count => this.Pins.Count;

    #endregion

    #region Pin Addressing

    /// <summary>
    /// Gets the PWM base frequency (in Hz).
    /// </summary>
    public Int32 PwmBaseFrequency => 19200000;

    /// <summary>
    /// Gets a red-only collection of all registered pins.
    /// </summary>
    public ReadOnlyCollection<GpioPin> Pins {
      get;
    }

    /// <summary>
    /// Provides all the pins on Header P1 of the Pi as a lookup by physical header pin number.
    /// This header is the main header and it is the one commonly used.
    /// </summary>
    public ReadOnlyDictionary<Int32, GpioPin> HeaderP1 {
      get;
    }

    /// <summary>
    /// Provides all the pins on Header P5 of the Pi as a lookup by physical header pin number.
    /// This header is the secondary header and it is rarely used.
    /// </summary>
    public ReadOnlyDictionary<Int32, GpioPin> HeaderP5 {
      get;
    }

    #endregion

    #region Individual Pin Properties

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 00.
    /// </summary>
    public GpioPin Pin00 => GpioPin.Pin00.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 01.
    /// </summary>
    public GpioPin Pin01 => GpioPin.Pin01.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 02.
    /// </summary>
    public GpioPin Pin02 => GpioPin.Pin02.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 03.
    /// </summary>
    public GpioPin Pin03 => GpioPin.Pin03.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 04.
    /// </summary>
    public GpioPin Pin04 => GpioPin.Pin04.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 05.
    /// </summary>
    public GpioPin Pin05 => GpioPin.Pin05.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 06.
    /// </summary>
    public GpioPin Pin06 => GpioPin.Pin06.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 07.
    /// </summary>
    public GpioPin Pin07 => GpioPin.Pin07.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 08.
    /// </summary>
    public GpioPin Pin08 => GpioPin.Pin08.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 09.
    /// </summary>
    public GpioPin Pin09 => GpioPin.Pin09.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 10.
    /// </summary>
    public GpioPin Pin10 => GpioPin.Pin10.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 11.
    /// </summary>
    public GpioPin Pin11 => GpioPin.Pin11.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 12.
    /// </summary>
    public GpioPin Pin12 => GpioPin.Pin12.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 13.
    /// </summary>
    public GpioPin Pin13 => GpioPin.Pin13.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 14.
    /// </summary>
    public GpioPin Pin14 => GpioPin.Pin14.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 15.
    /// </summary>
    public GpioPin Pin15 => GpioPin.Pin15.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 16.
    /// </summary>
    public GpioPin Pin16 => GpioPin.Pin16.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 17.
    /// </summary>
    public GpioPin Pin17 => GpioPin.Pin17.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 18.
    /// </summary>
    public GpioPin Pin18 => GpioPin.Pin18.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 19.
    /// </summary>
    public GpioPin Pin19 => GpioPin.Pin19.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 20.
    /// </summary>
    public GpioPin Pin20 => GpioPin.Pin20.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 21.
    /// </summary>
    public GpioPin Pin21 => GpioPin.Pin21.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 22.
    /// </summary>
    public GpioPin Pin22 => GpioPin.Pin22.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 23.
    /// </summary>
    public GpioPin Pin23 => GpioPin.Pin23.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 24.
    /// </summary>
    public GpioPin Pin24 => GpioPin.Pin24.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 25.
    /// </summary>
    public GpioPin Pin25 => GpioPin.Pin25.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 26.
    /// </summary>
    public GpioPin Pin26 => GpioPin.Pin26.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 27.
    /// </summary>
    public GpioPin Pin27 => GpioPin.Pin27.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 28.
    /// </summary>
    public GpioPin Pin28 => GpioPin.Pin28.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 29.
    /// </summary>
    public GpioPin Pin29 => GpioPin.Pin29.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 30.
    /// </summary>
    public GpioPin Pin30 => GpioPin.Pin30.Value;

    /// <summary>
    /// Provides direct access to Pin known to Wiring Pi (not the pin header number) as Pin 31.
    /// </summary>
    public GpioPin Pin31 => GpioPin.Pin31.Value;

    #endregion

    #region Indexers

    /// <summary>
    /// Gets or sets the initialization mode.
    /// </summary>
    private static ControllerMode Mode { get; set; } = ControllerMode.NotInitialized;

    /// <summary>
    /// Gets the <see cref="GpioPin"/> with the specified Wiring Pi pin number.
    /// </summary>
    /// <value>
    /// The <see cref="GpioPin"/>.
    /// </value>
    /// <param name="pinNumber">The pin number.</param>
    /// <returns>A reference to the GPIO pin</returns>
    public GpioPin this[WiringPiPin pinNumber] => this._pinsByWiringPiPinNumber[pinNumber];

    /// <summary>
    /// Gets the <see cref="GpioPin"/> with the specified pin number.
    /// </summary>
    /// <value>
    /// The <see cref="GpioPin"/>.
    /// </value>
    /// <param name="pinNumber">The pin number.</param>
    /// <returns>A reference to the GPIO pin</returns>
    public GpioPin this[P1 pinNumber] => this.HeaderP1[(Int32)pinNumber];

    /// <summary>
    /// Gets the <see cref="GpioPin"/> with the specified pin number.
    /// </summary>
    /// <value>
    /// The <see cref="GpioPin"/>.
    /// </value>
    /// <param name="pinNumber">The pin number.</param>
    /// <returns>A reference to the GPIO pin</returns>
    public GpioPin this[P5 pinNumber] => this.HeaderP5[(Int32)pinNumber];

    /// <summary>
    /// Gets the <see cref="GpioPin"/> with the specified Wiring Pi pin number.
    /// Use the HeaderP1 and HeaderP5 lookups if you would like to retrieve pins by physical pin number.
    /// </summary>
    /// <value>
    /// The <see cref="GpioPin"/>.
    /// </value>
    /// <param name="wiringPiPinNumber">The pin number as defined by Wiring Pi. This is not the header pin number as pin number in headers are obvoisly repeating.</param>
    /// <returns>A reference to the GPIO pin</returns>
    /// <exception cref="IndexOutOfRangeException">When the pin index is not found</exception>
    public GpioPin this[Int32 wiringPiPinNumber] {
      get {
        if(Enum.IsDefined(typeof(WiringPiPin), wiringPiPinNumber) == false) {
          throw new IndexOutOfRangeException($"Pin {wiringPiPinNumber} is not registered in the GPIO controller.");
        }

        return this._pinsByWiringPiPinNumber[(WiringPiPin)wiringPiPinNumber];
      }
    }

    #endregion

    #region Pin Group Methods (Read, Write, Pad Drive)

    /// <summary>
    /// This sets the “strength” of the pad drivers for a particular group of pins.
    /// There are 3 groups of pins and the drive strength is from 0 to 7.
    /// Do not use this unless you know what you are doing.
    /// </summary>
    /// <param name="group">The group.</param>
    /// <param name="value">The value.</param>
    public void SetPadDrive(Int32 group, Int32 value) {
      lock(SyncRoot) {
        _ = WiringPi.SetPadDrive(group, value);
      }
    }

    /// <summary>
    /// This sets the “strength” of the pad drivers for a particular group of pins.
    /// There are 3 groups of pins and the drive strength is from 0 to 7.
    /// Do not use this unless you know what you are doing.
    /// </summary>
    /// <param name="group">The group.</param>
    /// <param name="value">The value.</param>
    /// <returns>The awaitable task</returns>
    public Task SetPadDriveAsync(Int32 group, Int32 value) => Task.Run(() => this.SetPadDrive(group, value));

    /// <summary>
    /// This writes the 8-bit byte supplied to the first 8 GPIO pins.
    /// It’s the fastest way to set all 8 bits at once to a particular value,
    /// although it still takes two write operations to the Pi’s GPIO hardware.
    /// </summary>
    /// <param name="value">The value.</param>
    /// <exception cref="InvalidOperationException">PinMode</exception>
    public void WriteByte(Byte value) {
      lock(SyncRoot) {
        if(this.Skip(0).Take(8).Any(p => p.PinMode != GpioPinDriveMode.Output)) {
          throw new InvalidOperationException(
              $"All firts 8 pins (0 to 7) need their {nameof(GpioPin.PinMode)} to be set to {GpioPinDriveMode.Output}");
        }

        WiringPi.DigitalWriteByte(value);
      }
    }

    /// <summary>
    /// This writes the 8-bit byte supplied to the first 8 GPIO pins.
    /// It’s the fastest way to set all 8 bits at once to a particular value,
    /// although it still takes two write operations to the Pi’s GPIO hardware.
    /// </summary>
    /// <param name="value">The value.</param>
    /// <returns>The awaitable task</returns>
    public Task WriteByteAsync(Byte value) => Task.Run(() => this.WriteByte(value));

    /// <summary>
    /// This reads the 8-bit byte supplied to the first 8 GPIO pins.
    /// It’s the fastest way to get all 8 bits at once to a particular value.
    /// Please note this function is undocumented and unsopported
    /// </summary>
    /// <returns>A byte from the GPIO</returns>
    /// <exception cref="InvalidOperationException">PinMode</exception>
    public Byte ReadByte() {
      lock(SyncRoot) {
        if(this.Skip(0).Take(8).Any(p =>
           p.PinMode != GpioPinDriveMode.Input && p.PinMode != GpioPinDriveMode.Output)) {
          throw new InvalidOperationException(
              $"All firts 8 pins (0 to 7) need their {nameof(GpioPin.PinMode)} to be set to {GpioPinDriveMode.Input} or {GpioPinDriveMode.Output}");
        }

        return (Byte)WiringPi.DigitalReadByte();
      }
    }

    /// <summary>
    /// This reads the 8-bit byte supplied to the first 8 GPIO pins.
    /// It’s the fastest way to get all 8 bits at once to a particular value.
    /// Please note this function is undocumented and unsopported
    /// </summary>
    /// <returns>A byte from the GPIO</returns>
    public Task<Byte> ReadByteAsync() => Task.Run(() => this.ReadByte());

    #endregion

    #region IReadOnlyCollection Implementation

    /// <summary>
    /// Returns an enumerator that iterates through the collection.
    /// </summary>
    /// <returns>
    /// A <see cref="T:System.Collections.Generic.IEnumerator`1" /> that can be used to iterate through the collection.
    /// </returns>
    public IEnumerator<GpioPin> GetEnumerator() => this.Pins.GetEnumerator();

    /// <summary>
    /// Returns an enumerator that iterates through the collection.
    /// </summary>
    /// <returns>
    /// An <see cref="T:System.Collections.IEnumerator" /> object that can be used to iterate through the collection.
    /// </returns>
    IEnumerator IEnumerable.GetEnumerator() => this.Pins.GetEnumerator();

    #endregion

    #region Helper and Init Methods

    /// <summary>
    /// Gets the GPIO pin by BCM pin number.
    /// </summary>
    /// <param name="bcmPinNumber">The BCM pin number.</param>
    /// <returns>The GPIO pin</returns>
    public GpioPin GetGpioPinByBcmPinNumber(Int32 bcmPinNumber) => this.First(pin => pin.BcmPinNumber == bcmPinNumber);

    /// <summary>
    /// Converts the Wirings Pi pin number to the BCM pin number.
    /// </summary>
    /// <param name="wiringPiPinNumber">The wiring pi pin number.</param>
    /// <returns>The converted pin</returns>
    internal static Int32 WiringPiToBcmPinNumber(Int32 wiringPiPinNumber) {
      lock(SyncRoot) {
        return WiringPi.WpiPinToGpio(wiringPiPinNumber);
      }
    }

    /// <summary>
    /// Converts the Physical (Header) pin number to BCM pin number.
    /// </summary>
    /// <param name="headerPinNumber">The header pin number.</param>
    /// <returns>The converted pin</returns>
    internal static Int32 HaderToBcmPinNumber(Int32 headerPinNumber) {
      lock(SyncRoot) {
        return WiringPi.PhysPinToGpio(headerPinNumber);
      }
    }

    /// <summary>
    /// Short-hand method of registering pins
    /// </summary>
    /// <param name="pin">The pin.</param>
    private void RegisterPin(GpioPin pin) {
      if(this._pinsByWiringPiPinNumber.ContainsKey(pin.WiringPiPinNumber) == false) {
        this._pinsByWiringPiPinNumber[pin.WiringPiPinNumber] = pin;
      } else {
        throw new InvalidOperationException($"Pin {pin.WiringPiPinNumber} has been registered");
      }
    }

    /// <summary>
    /// Initializes the controller given the initialization mode and pin numbering scheme
    /// </summary>
    /// <param name="mode">The mode.</param>
    /// <returns>True when successful.</returns>
    /// <exception cref="PlatformNotSupportedException">
    /// This library does not support the platform
    /// </exception>
    /// <exception cref="InvalidOperationException">Library was already Initialized</exception>
    /// <exception cref="ArgumentException">The init mode is invalid</exception>
    private Boolean Initialize(ControllerMode mode) {
      if(Runtime.OS != Swan.OperatingSystem.Unix) {
        throw new PlatformNotSupportedException("This library does not support the platform");
      }

      lock(SyncRoot) {
        if(IsInitialized) {
          throw new InvalidOperationException($"Cannot call {nameof(Initialize)} more than once.");
        }

        Environment.SetEnvironmentVariable(WiringPiCodesEnvironmentVariable, "1", EnvironmentVariableTarget.Process);
        Int32 setpuResult;

        switch(mode) {
          case ControllerMode.DirectWithWiringPiPins: {
            setpuResult = WiringPi.WiringPiSetup();
            break;
          }

          case ControllerMode.DirectWithBcmPins: {
            setpuResult = WiringPi.WiringPiSetupGpio();
            break;
          }

          case ControllerMode.DirectWithHeaderPins: {
            setpuResult = WiringPi.WiringPiSetupPhys();
            break;
          }

          case ControllerMode.FileStreamWithHardwarePins: {
            setpuResult = WiringPi.WiringPiSetupSys();
            break;
          }

          default: {
            throw new ArgumentException($"'{mode}' is not a valid initialization mode.");
          }
        }

        Mode = setpuResult == 0 ? mode : ControllerMode.NotInitialized;
        return IsInitialized;
      }
    }

    #endregion

  }
}