/**
 * 自定義字母導航欄
 * 
 * 總的來說就四步
 * 1、測量控件尺寸{@link #onMeasure(int, int)}
 * 2、繪制顯示內容（背景以及字符）{@link #onDraw(Canvas)}
 * 3、處理滑動事件{@link #onTouchEvent(MotionEvent)}
 * 4、暴露接口{@link #setOnNavigationScrollerListener(OnNavigationScrollerListener)}
 *
 * @attr customTextColorDefault //導航欄默認文字顏色
 * @attr customTextColorDown //導航欄按下文字顏色
 * @attr customBackgroundColorDown //導航欄按下背景顏色
 * @attr customLetterDivHeight //導航欄內容高度間隔
 * @attr customTextSize //導航欄文字尺寸
 * @attr customBackgroundAngle //導航欄背景角度
 */
public class CustomLetterNavigationView extends View {
  private static final String TAG = "CustomLetterNavigation";
  //導航內容
  private String[] mNavigationContent;
  //導航欄內容間隔
  private float mContentDiv;
  //導航欄文字大小
  private float mContentTextSize;
  //導航欄文字顏色
  private int mContentTextColor;
  //導航欄按下時背景顏色
  private int mBackgroundColor;
  //導航欄按下時圓角度數(shù)
  private int mBackGroundAngle = 0;
  //導航欄按下時文字顏色
  private int mDownContentTextColor;
  private TextPaint mTextPaint;
  private Paint mPaintBackgrount;
  private boolean mEventActionState = false;
  private String mCurrentLetter = "";
  private OnNavigationScrollerListener mOnNavigationScrollerListener;
  private final RectF mRectF = new RectF();
  public CustomLetterNavigationView(Context context) {
    this(context, null);
  }

  public CustomLetterNavigationView(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public CustomLetterNavigationView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initDefaultData();//初始化默認數(shù)據(jù)
    initAttrs(context, attrs);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    /**
     * <P>
     *   這里我們分為兩步
     *
     *   1、繪制背景
     *    這里簡單，直接調用Canvas的drawRoundRect()方法直接繪制
     *   2、繪制顯示文本
     *    繪制文字首先要定位，定位每個字符的坐標
     *    X軸簡單，寬度的一半
     *    Y軸坐標通過每個字符的高heightShould乘以已繪制字符的數(shù)目
     * </P>
     */
    int mViewWidth = getWidth();
    //繪制背景
    mRectF.set(0, 0, mViewWidth, getHeight());
    if (mEventActionState) {
      mTextPaint.setColor(mDownContentTextColor);
      mPaintBackgrount.setColor(mBackgroundColor);
      canvas.drawRoundRect(mRectF, mBackGroundAngle, mBackGroundAngle, mPaintBackgrount);
    } else {
      mTextPaint.setColor(mContentTextColor);
      mPaintBackgrount.setColor(Color.TRANSPARENT);
      Drawable mBackground = getBackground();
      if (mBackground instanceof ColorDrawable) {
        mPaintBackgrount.setColor(((ColorDrawable) mBackground).getColor());
      }
      canvas.drawRoundRect(mRectF, mBackGroundAngle, mBackGroundAngle, mPaintBackgrount);
    }
    //繪制文本
    float textX = mViewWidth / 2;
    //X軸坐標
    int contentLenght = getContentLength();
    //Y軸坐標（這里在測量的時候多加入了兩個間隔高度要減去，同時還有Padding值）
    float heightShould = (getHeight() - mContentDiv * 2 - getPaddingTop() - getPaddingBottom()) / contentLenght;
    for (int i = 0; i < contentLenght; i++) {
      //計算Y軸的坐標
      float startY = ((i + 1) * heightShould) + getPaddingTop();
      //繪制文字
      canvas.drawText(mNavigationContent[i], textX, startY, mTextPaint);
    }
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    /**
     * 這里主要處理手指滑動事件
     */
    float mEventY = event.getY();
    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        //手指按下的時候，修改Enent狀態(tài)、重繪背景、觸發(fā)回調
        mEventActionState = true;
        invalidate();
        if (mOnNavigationScrollerListener != null) {
          mOnNavigationScrollerListener.onDown();
        }
        scrollCount(mEventY);
        break;
      case MotionEvent.ACTION_MOVE:
        scrollCount(mEventY);
        break;
      case MotionEvent.ACTION_CANCEL:
      case MotionEvent.ACTION_UP:
        //手指離開的時候，修改Enent狀態(tài)、重繪背景、觸發(fā)回調
        mEventActionState = false;
        invalidate();
        if (mOnNavigationScrollerListener != null) {
          mOnNavigationScrollerListener.onUp();
        }
        break;
    }
    return true;
  }


  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    /**
     * <p>
     *   這里做了簡單的適應，其目的就是為了能夠正常的顯示我們的內容
     *
     *   不管設置的是真實尺寸或者是包裹內容，都會以內容的最小尺寸為
     *   基礎，如果設置的控件尺寸大于我們內容的最小尺寸，就使用控件
     *   尺寸，反之使用內容的最小尺寸!
     * </p>
     */
    int widhtMode = MeasureSpec.getMode(widthMeasureSpec);
    int heightMode = MeasureSpec.getMode(heightMeasureSpec);
    //獲取控件的尺寸
    int actualWidth = MeasureSpec.getSize(widthMeasureSpec);
    int actualHeight = MeasureSpec.getSize(heightMeasureSpec);
    int contentLegth = getContentLength();
    //計算一個文字的尺寸
    Rect mRect = measureTextSize();
    //內容的最小寬度
    float contentWidth = mRect.width() + mContentDiv * 2;
    //內容的最小高度
    float contentHeight = mRect.height() * contentLegth + mContentDiv * (contentLegth + 3);
    if (MeasureSpec.AT_MOST == widhtMode) {
      //寬度包裹內容
      actualWidth = (int) contentWidth + getPaddingLeft() + getPaddingRight();
    } else if (MeasureSpec.EXACTLY == widhtMode) {
      //寬度限制
      if (actualWidth < contentWidth) {
        actualWidth = (int) contentWidth + getPaddingLeft() + getPaddingRight();
      }
    }
    if (MeasureSpec.AT_MOST == heightMode) {
      //高度包裹內容
      actualHeight = (int) contentHeight + getPaddingTop() + getPaddingBottom();
    } else if (MeasureSpec.EXACTLY == widhtMode) {
      //高度限制
      if (actualHeight < contentHeight) {
        actualHeight = (int) contentHeight + getPaddingTop() + getPaddingBottom();
      }
    }
    setMeasuredDimension(actualWidth, actualHeight);
  }


  /**
   * 初始化默認數(shù)據(jù)
   */
  private void initDefaultData() {
    mNavigationContent = new String[]{"搜", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"};
    mContentDiv = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 5, getResources().getDisplayMetrics());
    mContentTextSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 14, getResources().getDisplayMetrics());
    mContentTextColor = Color.parseColor("#333333");
    mDownContentTextColor = Color.WHITE;
    mBackgroundColor = Color.parseColor("#d7d7d7");
    mBackGroundAngle = 0;
    //繪制文字畫筆
    mTextPaint = new TextPaint();
    mTextPaint.setAntiAlias(true);
    mTextPaint.setTextSize(mContentTextSize);
    mTextPaint.setColor(mContentTextColor);
    mTextPaint.setTextAlign(Paint.Align.CENTER);
    //繪制背景畫筆
    mPaintBackgrount = new Paint();
    mPaintBackgrount.setAntiAlias(true);
    mPaintBackgrount.setStyle(Paint.Style.FILL);
  }

  /**
   * 初始化自定義屬性
   *
   * @param context
   * @param attrs
   */
  private void initAttrs(Context context, AttributeSet attrs) {
    TypedArray mTypedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomLetterNavigationView);
    mContentTextColor = mTypedArray.getColor(R.styleable.CustomLetterNavigationView_customTextColorDefault, mContentTextColor);
    mBackgroundColor = mTypedArray.getColor(R.styleable.CustomLetterNavigationView_customBackgroundColorDown, mBackgroundColor);
    mDownContentTextColor = mTypedArray.getColor(R.styleable.CustomLetterNavigationView_customTextColorDown, mDownContentTextColor);
    mContentTextSize = mTypedArray.getDimension(R.styleable.CustomLetterNavigationView_customTextSize, mContentTextSize);
    mContentDiv = mTypedArray.getFloat(R.styleable.CustomLetterNavigationView_customLetterDivHeight, mContentDiv);
    mBackGroundAngle = mTypedArray.getInt(R.styleable.CustomLetterNavigationView_customBackgroundAngle, mBackGroundAngle);
    mTypedArray.recycle();
  }


  /**
   * 獲取內容長度
   *
   * @return 內容長度
   */
  private int getContentLength() {
    if (mNavigationContent != null) {
      return mNavigationContent.length;
    }
    return 0;
  }

  /**
   * 滑動計算
   *
   * @param mEventY Y軸滑動距離
   */
  private void scrollCount(float mEventY) {
    //滑動的時候利用滑動距離和每一個字符高度進行取整，獲取到Index
    Rect mRect = measureTextSize();
    int index = (int) ((mEventY - getPaddingTop() - getPaddingBottom() - mContentDiv * 2) / (mRect.height() + mContentDiv));
    //防止越界
    if (index >= 0 && index < getContentLength()) {
      String newLetter = mNavigationContent[index];
      //防止重復觸發(fā)回調
      if (!mCurrentLetter.equals(newLetter)) {
        mCurrentLetter = newLetter;
        if (mOnNavigationScrollerListener != null) {
          mOnNavigationScrollerListener.onScroll(mCurrentLetter, index);
        }
      }
    }
  }

  /**
   * 測量文字的尺寸
   *
   * @return 一個漢字的矩陣
   */
  public Rect measureTextSize() {
    Rect mRect = new Rect();
    if (mTextPaint != null) {
      mTextPaint.getTextBounds("田", 0, 1, mRect);
    }
    return mRect;
  }


  /**
   * 設置導航欄滑動監(jiān)聽
   *
   * @param onNavigationScrollerListener
   */
  public void setOnNavigationScrollerListener(OnNavigationScrollerListener onNavigationScrollerListener) {
    this.mOnNavigationScrollerListener = onNavigationScrollerListener;
  }

  /**
   * 設置導航欄顯示內容
   *
   * @param content 需要顯示的內容
   */
  public void setNavigationContent(String content) {
    if (!TextUtils.isEmpty(content)) {
      mNavigationContent = null;
      mNavigationContent = new String[content.length()];
      for (int i = 0; i < content.length(); i++) {
        mNavigationContent[i] = String.valueOf(content.charAt(i));
      }
    }
    //需要重新測量
    requestLayout();
  }

  public interface OnNavigationScrollerListener {
    //按下
    void onDown();

    //滑動
    void onScroll(String letter, int position);

    //離開
    void onUp();

  }
}

<declare-styleable name="CustomLetterNavigationView">
    <attr name="customTextColorDefault" format="color" />
    <attr name="customTextColorDown" format="color" />
    <attr name="customBackgroundColorDown" format="color" />
    <attr name="customLetterDivHeight" format="dimension" />
    <attr name="customTextSize" format="dimension" />
    <attr name="customBackgroundAngle" format="integer" />
</declare-styleable>