// utils/duration.util.js

const AVG_WORDS_PER_MINUTE = 200;

function stripHtml(html) {
  // Simple regex strip — no extra dependency needed
  return (html ?? "").replace(/<[^>]*>/g, " ").replace(/\s+/g, " ").trim();
}

/**
 * Estimate seconds for a single lesson block
 * Block shape: { type: 'text'|'image'|'video', content, word_count, video_duration_seconds }
 */
function estimateBlockDuration(block) {
  const videoDuration = Number(block.video_duration_seconds) || 0;

  // Derive word count from HTML content on the fly
  const getWordCount = (html) => {
    const text = stripHtml(html);
    return text ? text.split(" ").filter(Boolean).length : 0;
  };

  const readingSecs = (html) =>
    Math.ceil((getWordCount(html) / AVG_WORDS_PER_MINUTE) * 60);

  switch (block.type) {
    case "text":
      return readingSecs(block.content?.body);

    case "image":
      return 60;

    case "video":
      return videoDuration;

    case "text-image":
    case "text_image":
      return readingSecs(block.content?.body) + 60;

    case "text-video":
    case "text_video":
      return readingSecs(block.content?.body) + videoDuration;

    default:
      return 0;
  }
}

/**
 * Recompute and persist duration_seconds up the chain:
 * blocks → lesson → unit → course
 */
async function recomputeDurations(lessonId) {
  const Lesson = require("../models/courses/lessons.mdl");
  const Unit = require("../models/courses/units.mdl");
  const { Course } = require("../models/courses/courses.mdl");
  const LessonPage = require("../models/courses/lesson_page.mdl");

  // 1. Lesson duration from blocks
  const page = await LessonPage.findOne({ where: { lesson_id: lessonId } });
  const lessonSecs = (page?.blocks ?? []).reduce(
    (sum, block) => sum + estimateBlockDuration(block), 0
  );

  // Guard against NaN before DB write
  const safeLessonSecs = isNaN(lessonSecs) ? 0 : lessonSecs;
  await Lesson.update({ duration_seconds: safeLessonSecs }, { where: { lesson_id: lessonId } });

  // 2. Unit duration — sum of its lessons
  const lesson = await Lesson.findOne({ where: { lesson_id: lessonId } });
  const [unitResult] = await Lesson.sequelize.query(`
    SELECT COALESCE(SUM(duration_seconds), 0) AS total
    FROM lessons
    WHERE unit_id = :unitId AND "deletedAt" IS NULL
  `, { replacements: { unitId: lesson.unit_id }, type: Lesson.sequelize.QueryTypes.SELECT });

  await Unit.update(
    { duration_seconds: unitResult.total },
    { where: { unit_id: lesson.unit_id } }
  );

  // 3. Course duration — sum of its units
  const unit = await Unit.findOne({ where: { unit_id: lesson.unit_id } });
  const [courseResult] = await Lesson.sequelize.query(`
    SELECT COALESCE(SUM(duration_seconds), 0) AS total
    FROM units
    WHERE course_id = :courseId AND "deletedAt" IS NULL
  `, { replacements: { courseId: unit.course_id }, type: Lesson.sequelize.QueryTypes.SELECT });

  await Course.update(
    { duration_seconds: courseResult.total },
    { where: { course_id: unit.course_id } }
  );
}

/**
 * Format seconds → human readable: "1 hr 10 mins", "45 mins", "30 secs"
 */
function formatDuration(seconds) {
  if (!seconds) return "0 mins";
  const h = Math.floor(seconds / 3600);
  const m = Math.floor((seconds % 3600) / 60);
  const s = seconds % 60;

  const parts = [];
  if (h) parts.push(`${h} hour${h !== 1 ? "s" : ""}`);
  if (m) parts.push(`${m} minute${m !== 1 ? "s" : ""}`);
  if (!h && !m && s) parts.push(`${s} second${s !== 1 ? "s" : ""}`);
  return parts.join(" ");
}

module.exports = { estimateBlockDuration, recomputeDurations, formatDuration };