learn-languages/src/app/(features)/srt-player/utils/subtitleParser.ts

import { SubtitleEntry } from "../types/subtitle";

export function parseSrt(data: string): SubtitleEntry[] {
  const lines = data.split(/\r?\n/);
  const result: SubtitleEntry[] = [];
  const re = new RegExp(
    "(\\d{2}:\\d{2}:\\d{2},\\d{3})\\s*-->\\s*(\\d{2}:\\d{2}:\\d{2},\\d{3})",
  );
  let i = 0;
  
  while (i < lines.length) {
    if (!lines[i].trim()) {
      i++;
      continue;
    }
    i++;
    if (i >= lines.length) break;
    
    const timeMatch = lines[i].match(re);
    if (!timeMatch) {
      i++;
      continue;
    }
    
    const start = toSeconds(timeMatch[1]);
    const end = toSeconds(timeMatch[2]);
    i++;
    
    let text = "";
    while (i < lines.length && lines[i].trim()) {
      text += lines[i] + "\n";
      i++;
    }
    
    result.push({ 
      start, 
      end, 
      text: text.trim(),
      index: result.length,
    });
    i++;
  }
  
  return result;
}

export function getSubtitleIndex(
  subtitles: SubtitleEntry[],
  currentTime: number,
): number | null {
  for (let i = 0; i < subtitles.length; i++) {
    if (currentTime >= subtitles[i].start && currentTime <= subtitles[i].end) {
      return i;
    }
  }
  return null;
}

export function getNearestIndex(
  subtitles: SubtitleEntry[],
  currentTime: number,
): number | null {
  for (let i = 0; i < subtitles.length; i++) {
    const subtitle = subtitles[i];
    const isBefore = currentTime - subtitle.start >= 0;
    const isAfter = currentTime - subtitle.end >= 0;
    
    if (!isBefore || !isAfter) return i - 1;
    if (isBefore && !isAfter) return i;
  }
  return null;
}

export function getCurrentSubtitle(
  subtitles: SubtitleEntry[],
  currentTime: number,
): SubtitleEntry | null {
  return subtitles.find((subtitle) => 
    currentTime >= subtitle.start && currentTime <= subtitle.end
  ) || null;
}

function toSeconds(timeStr: string): number {
  const [h, m, s] = timeStr.replace(",", ".").split(":");
  return parseFloat(
    (parseInt(h) * 3600 + parseInt(m) * 60 + parseFloat(s)).toFixed(3),
  );
}

export async function loadSubtitle(url: string): Promise<SubtitleEntry[]> {
  try {
    const response = await fetch(url);
    const data = await response.text();
    return parseSrt(data);
  } catch (error) {
    console.error('Failed to load subtitle:', error);
    return [];
  }
}