//Tencent is pleased to support the open source community by making WeDemo available.
//Copyright (C) 2016 THL A29 Limited, a Tencent company. All rights reserved.
//Licensed under the MIT License (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
//http://opensource.org/licenses/MIT
//Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

#import <objc/runtime.h>
#import "UITextView+Placeholder.h"

@implementation UITextView (Placeholder)

#pragma mark - Swizzle Dealloc

+ (void)load {
    [super load];

    // is this the best solution?
    method_exchangeImplementations(class_getInstanceMethod(self.class, NSSelectorFromString(@"dealloc")),
                                   class_getInstanceMethod(self.class, @selector(swizzledDealloc)));
}

- (void)swizzledDealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    UILabel *label = objc_getAssociatedObject(self, @selector(placeholderLabel));
    if (label) {
        for (NSString *key in self.class.observingKeys) {
            @try {
                [self removeObserver:self forKeyPath:key];
            }
            @catch (NSException *exception) {
                // Do nothing
            }
        }
    }
    [self swizzledDealloc];
}


#pragma mark - Class Methods
+ (UIColor *)defaultPlaceholderColor {
    static UIColor *color = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        UITextField *textField = [[UITextField alloc] init];
        textField.placeholder = @" ";
        color = [textField valueForKeyPath:@"_placeholderLabel.textColor"];
    });
    return color;
}

+ (NSArray *)observingKeys {
    return @[@"attributedText",
             @"bounds",
             @"font",
             @"frame",
             @"text",
             @"textAlignment",
             @"textContainerInset"];
}


#pragma mark - Properties
- (UILabel *)placeholderLabel {
    UILabel *label = objc_getAssociatedObject(self, @selector(placeholderLabel));
    if (!label) {
        NSAttributedString *originalText = self.attributedText;
        self.text = @" "; // lazily set font of `UITextView`.
        self.attributedText = originalText;

        label = [[UILabel alloc] init];
        label.textColor = [self.class defaultPlaceholderColor];
        label.numberOfLines = 0;
        label.userInteractionEnabled = NO;
        objc_setAssociatedObject(self, @selector(placeholderLabel), label, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(updatePlaceholderLabel)
                                                     name:UITextViewTextDidChangeNotification
                                                   object:self];

        for (NSString *key in self.class.observingKeys) {
            [self addObserver:self forKeyPath:key options:NSKeyValueObservingOptionNew context:nil];
        }
    }
    return label;
}

- (NSString *)placeholder {
    return self.placeholderLabel.text;
}

- (void)setPlaceholder:(NSString *)placeholder {
    self.placeholderLabel.text = placeholder;
    [self updatePlaceholderLabel];
}

- (NSAttributedString *)attributedPlaceholder {
    return self.placeholderLabel.attributedText;
}

- (void)setAttributedPlaceholder:(NSAttributedString *)attributedPlaceholder {
    self.placeholderLabel.attributedText = attributedPlaceholder;
    [self updatePlaceholderLabel];
}

- (UIColor *)placeholderColor {
    return self.placeholderLabel.textColor;
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor {
    self.placeholderLabel.textColor = placeholderColor;
}


#pragma mark - KVO
- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
    [self updatePlaceholderLabel];
}


#pragma mark - Update
- (void)updatePlaceholderLabel {
    if (self.text.length) {
        [self.placeholderLabel removeFromSuperview];
        return;
    }

    [self insertSubview:self.placeholderLabel atIndex:0];

    self.placeholderLabel.font = self.font;
    self.placeholderLabel.textAlignment = self.textAlignment;

    // `NSTextContainer` is available since iOS 7
    CGFloat lineFragmentPadding;
    UIEdgeInsets textContainerInset;

#pragma deploymate push "ignored-api-availability"
    // iOS 7+
    if (NSFoundationVersionNumber > NSFoundationVersionNumber_iOS_6_1) {
        lineFragmentPadding = self.textContainer.lineFragmentPadding;
        textContainerInset = self.textContainerInset;
    }
#pragma deploymate pop

    // iOS 6
    else {
        lineFragmentPadding = 5;
        textContainerInset = UIEdgeInsetsMake(8, 0, 8, 0);
    }

    CGFloat x = lineFragmentPadding + textContainerInset.left;
    CGFloat y = textContainerInset.top;
    CGFloat width = CGRectGetWidth(self.bounds) - x - lineFragmentPadding - textContainerInset.right;
    CGFloat height = [self.placeholderLabel sizeThatFits:CGSizeMake(width, 0)].height;
    self.placeholderLabel.frame = CGRectMake(x, y, width, height);
}

@end
