//
//  SubtitleSync.m
//  keyBoard
//
//  Created by Mac on 2026/1/15.
//

#import "SubtitleSync.h"

@implementation SubtitleSync

- (NSString *)visibleTextForFullText:(NSString *)fullText
                         currentTime:(NSTimeInterval)currentTime
                            duration:(NSTimeInterval)duration {

  if (!fullText || fullText.length == 0) {
    return @"";
  }

  NSUInteger visibleCount = [self visibleCountForFullText:fullText
                                              currentTime:currentTime
                                                 duration:duration];

  if (visibleCount >= fullText.length) {
    return fullText;
  }

  return [fullText substringToIndex:visibleCount];
}

- (NSUInteger)visibleCountForFullText:(NSString *)fullText
                          currentTime:(NSTimeInterval)currentTime
                             duration:(NSTimeInterval)duration {

  if (!fullText || fullText.length == 0) {
    return 0;
  }

  // 边界情况处理
  if (duration <= 0) {
    // 如果没有时长信息，直接返回全部
    return fullText.length;
  }

  if (currentTime <= 0) {
    return 0;
  }

  if (currentTime >= duration) {
    return fullText.length;
  }

  // 计算进度比例
  double progress = currentTime / duration;

  // 计算可见字符数
  // 使用略微超前的策略，确保文字不会落后于语音
  double adjustedProgress = MIN(progress * 1.05, 1.0);

  NSUInteger visibleCount =
      (NSUInteger)round(fullText.length * adjustedProgress);

  return MIN(visibleCount, fullText.length);
}

@end