ytdlp-segment-downloader/src/cli/downloader.ts

import { spawn } from "child_process";
import { writeFileSync, mkdirSync, existsSync } from "fs";
import { join } from "path";

export interface DownloadOptions {
  url: string;
  outputDir: string;
  format: string;
}

interface RawHeatmapSegment {
  start_seconds?: number;
  start_time?: number;
  end_seconds?: number;
  end_time?: number;
  intensity?: number;
  heat?: number;
  value?: number;
}

interface ProcessedSegment {
  start: number;
  end: number;
  intensity: number;
  integralJump: number;
}

interface VideoInfo {
  title: string;
  duration: number;
  heatmap?: RawHeatmapSegment[];
}

async function getVideoInfo(url: string): Promise<VideoInfo> {
  return new Promise((resolve, reject) => {
    const ytDlp = spawn("yt-dlp", [
      "--dump-json",
      "--no-download",
      "--compat-option",
      "no-youtube-channel-redirect",
      url,
    ]);

    let stdout = "";
    let stderr = "";

    ytDlp.stdout.on("data", (data) => {
      stdout += data.toString();
    });

    ytDlp.stderr.on("data", (data) => {
      stderr += data.toString();
    });

    ytDlp.on("close", (code) => {
      if (code !== 0) {
        reject(new Error(`yt-dlp failed: ${stderr}`));
        return;
      }

      try {
        const info = JSON.parse(stdout);

        resolve({
          title: info.title || "video",
          duration: info.duration || 0,
          heatmap: info.heatmap,
        });
      } catch (parseError) {
        reject(new Error(`Failed to parse video info: ${parseError}`));
      }
    });

    ytDlp.on("error", (err) => {
      reject(new Error(`Failed to run yt-dlp: ${err.message}`));
    });
  });
}

async function downloadSegment(
  url: string,
  outputPath: string,
  startTime: number,
  endTime: number,
  format: string
): Promise<void> {
  const section = `*${startTime.toFixed(3)}-${endTime.toFixed(3)}`;

  return new Promise((resolve, reject) => {
    const ytDlp = spawn("yt-dlp", [
      "-f", format,
      "--download-sections", section,
      "-o", outputPath,
      url,
    ]);

    let stderr = "";

    ytDlp.stderr.on("data", (data) => {
      stderr += data.toString();
    });

    ytDlp.on("close", (code) => {
      if (code !== 0) {
        reject(new Error(`yt-dlp failed: ${stderr}`));
        return;
      }
      resolve();
    });

    ytDlp.on("error", (err) => {
      reject(new Error(`Failed to run yt-dlp: ${err.message}`));
    });
  });
}

function sanitizeFilename(filename: string): string {
  return filename
    .replace(/[^a-zA-Z0-9\s\-_]/g, "")
    .replace(/\s+/g, "_")
    .substring(0, 100);
}

function formatTime(seconds: number): string {
  if (!Number.isFinite(seconds) || seconds < 0) {
    return "0:00";
  }
  const mins = Math.floor(seconds / 60);
  const secs = Math.floor(seconds % 60);
  return `${mins}:${secs.toString().padStart(2, "0")}`;
}

function getStartTime(segment: RawHeatmapSegment): number {
  return segment.start_seconds ?? segment.start_time ?? 0;
}

function getEndTime(segment: RawHeatmapSegment): number {
  return segment.end_seconds ?? segment.end_time ?? 0;
}

function getIntensity(segment: RawHeatmapSegment): number {
  return segment.intensity ?? segment.heat ?? segment.value ?? 0;
}

function findHighestIntegralJump(
  segments: RawHeatmapSegment[]
): ProcessedSegment | null {
  // Convert to processed format and filter valid segments
  const validSegments = segments
    .map(seg => ({
      start: getStartTime(seg),
      end: getEndTime(seg),
      intensity: getIntensity(seg),
    }))
    .filter(seg => 
      Number.isFinite(seg.start) && 
      Number.isFinite(seg.end) && 
      Number.isFinite(seg.intensity) &&
      seg.start >= 0 &&
      seg.end > seg.start
    );

  if (validSegments.length === 0) {
    return null;
  }

  // Calculate integral jump for each segment (intensity × duration)
  const withIntegral = validSegments.map(seg => {
    const segmentDuration = seg.end - seg.start;
    const integralJump = seg.intensity * segmentDuration;
    return {
      ...seg,
      integralJump,
    };
  });

  // Find the segment with the highest integral jump (biggest bump in the integral)
  // This is the segment that contributed most to the total integral
  return withIntegral.reduce((max, current) => {
    return current.integralJump > max.integralJump ? current : max;
  });
}

export async function downloadMostWatchedSegment(options: DownloadOptions): Promise<void> {
  const { url, outputDir, format } = options;

  // Create output directory if it doesn't exist
  if (!existsSync(outputDir)) {
    mkdirSync(outputDir, { recursive: true });
  }

  // Get video info with heatmap data from YouTube
  console.log("Fetching video information from YouTube...");
  const info = await getVideoInfo(url);
  const safeTitle = sanitizeFilename(info.title);

  console.log(`Video: ${info.title}`);
  console.log(`Duration: ${formatTime(info.duration)}`);

  // Check for heatmap data
  if (!info.heatmap || info.heatmap.length === 0) {
    console.log("\nNo heatmap data available for this video.");
    console.log("Downloading full video instead...");
    
    const outputPath = join(outputDir, `${safeTitle}.%(ext)s`);
    await downloadSegment(url, outputPath, 0, info.duration, format);
    return;
  }

  console.log(`\nHeatmap data found: ${info.heatmap.length} segments`);

  // Find segment with highest integral jump (biggest bump)
  const topSegment = findHighestIntegralJump(info.heatmap);

  if (!topSegment) {
    console.log("No valid segments found. Downloading full video...");
    const outputPath = join(outputDir, `${safeTitle}.%(ext)s`);
    await downloadSegment(url, outputPath, 0, info.duration, format);
    return;
  }

  console.log(`\nSegment with highest integral jump:`);
  console.log(`  Time: ${formatTime(topSegment.start)} - ${formatTime(topSegment.end)}`);
  console.log(`  Duration: ${formatTime(topSegment.end - topSegment.start)}`);
  console.log(`  Intensity: ${(topSegment.intensity * 100).toFixed(1)}%`);
  console.log(`  Integral Jump: ${topSegment.integralJump.toFixed(4)}`);

  // Download the segment
  const outputPath = join(outputDir, `${safeTitle}_most_watched.%(ext)s`);

  console.log(`\nDownloading segment...`);
  await downloadSegment(url, outputPath, topSegment.start, topSegment.end, format);

  // Save segment info
  const segmentInfoPath = join(outputDir, `${safeTitle}_segment_info.txt`);
  const segmentInfo = `# ${info.title}\n\n` +
    `Segment with highest integral jump (biggest bump in heatmap):\n` +
    `  Start: ${formatTime(topSegment.start)} (${topSegment.start.toFixed(1)}s)\n` +
    `  End: ${formatTime(topSegment.end)} (${topSegment.end.toFixed(1)}s)\n` +
    `  Duration: ${formatTime(topSegment.end - topSegment.start)}\n` +
    `  Intensity: ${(topSegment.intensity * 100).toFixed(1)}%\n` +
    `  Integral Jump: ${topSegment.integralJump.toFixed(4)}\n`;

  writeFileSync(segmentInfoPath, segmentInfo);
  console.log(`\nSegment info saved to: ${segmentInfoPath}`);
  console.log("Download complete!");
}