using System;
using System.Linq;
using System.Threading.Tasks;

using Swan;

namespace Unosquare.RaspberryIO.Computer {
  /// <summary>
  /// Settings for audio device.
  /// </summary>
  public class AudioSettings : SingletonBase<AudioSettings> {
    private const String DefaultControlName = "PCM";
    private const Int32 DefaultCardNumber = 0;

    private readonly String[] _errorMess = { "Invalid", "Unable" };

    /// <summary>
    /// Gets the current audio state.
    /// </summary>
    /// <param name="cardNumber">The card number.</param>
    /// <param name="controlName">Name of the control.</param>
    /// <returns>An <see cref="AudioState"/> object.</returns>
    /// <exception cref="InvalidOperationException">Invalid command, card number or control name.</exception>
    public async Task<AudioState> GetState(Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) {
      String volumeInfo = await ProcessRunner.GetProcessOutputAsync("amixer", $"-c {cardNumber} get {controlName}").ConfigureAwait(false);

      String[] lines = volumeInfo.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries);

      if(!lines.Any()) {
        throw new InvalidOperationException("Invalid command.");
      }

      if(this._errorMess.Any(x => lines[0].Contains(x))) {
        throw new InvalidOperationException(lines[0]);
      }

      String volumeLine = lines.FirstOrDefault(x => x.Trim().StartsWith("Mono:", StringComparison.OrdinalIgnoreCase));

      if(volumeLine == null) {
        throw new InvalidOperationException("Unexpected output from 'amixer'.");
      }

      String[] sections = volumeLine.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

      Int32 level = Int32.Parse(sections[3][1..^2], System.Globalization.NumberFormatInfo.InvariantInfo);

      Single decibels = Single.Parse(sections[4][1..^3], System.Globalization.NumberFormatInfo.InvariantInfo);

      Boolean isMute = sections[5].Equals("[off]", StringComparison.CurrentCultureIgnoreCase);

      return new AudioState(cardNumber, controlName, level, decibels, isMute);
    }

    /// <summary>
    /// Sets the volume percentage.
    /// </summary>
    /// <param name="level">The percentage level.</param>
    /// <param name="cardNumber">The card number.</param>
    /// <param name="controlName">Name of the control.</param>
    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
    /// <exception cref="InvalidOperationException">Invalid card number or control name.</exception>
    public Task SetVolumePercentage(Int32 level, Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) => SetAudioCommand($"{level}%", cardNumber, controlName);

    /// <summary>
    /// Sets the volume by decibels.
    /// </summary>
    /// <param name="decibels">The decibels.</param>
    /// <param name="cardNumber">The card number.</param>
    /// <param name="controlName">Name of the control.</param>
    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
    /// <exception cref="InvalidOperationException">Invalid card number or control name.</exception>
    public Task SetVolumeByDecibels(Single decibels, Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) => SetAudioCommand($"{decibels}dB", cardNumber, controlName);

    /// <summary>
    /// Increments the volume by decibels.
    /// </summary>
    /// <param name="decibels">The decibels to increment or decrement.</param>
    /// <param name="cardNumber">The card number.</param>
    /// <param name="controlName">Name of the control.</param>
    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
    /// <exception cref="InvalidOperationException">Invalid card number or control name.</exception>
    public Task IncrementVolume(Single decibels, Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) => SetAudioCommand($"{decibels}dB{(decibels < 0 ? "-" : "+")}", cardNumber, controlName);

    /// <summary>
    /// Toggles the mute state.
    /// </summary>
    /// <param name="mute">if set to <c>true</c>, mutes the audio.</param>
    /// <param name="cardNumber">The card number.</param>
    /// <param name="controlName">Name of the control.</param>
    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
    /// <exception cref="InvalidOperationException">Invalid card number or control name.</exception>
    public Task ToggleMute(Boolean mute, Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) => SetAudioCommand(mute ? "mute" : "unmute", cardNumber, controlName);

    private static async Task<String> SetAudioCommand(String command, Int32 cardNumber = DefaultCardNumber, String controlName = DefaultControlName) {
      String taskResult = await ProcessRunner.GetProcessOutputAsync("amixer", $"-q -c {cardNumber} -- set {controlName} {command}").ConfigureAwait(false);

      if(!String.IsNullOrWhiteSpace(taskResult)) {
        throw new InvalidOperationException(taskResult.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries).First());
      }

      return taskResult;
    }
  }
}