Managing Course Content

Course (Top level)
├── Chapter 1 (Section/Module)
│   ├── Lecture 1 (Video content)
│   ├── Lecture 2
│   └── Lecture 3
├── Chapter 2
│   ├── Lecture 1
│   └── Lecture 2
└── Chapter 3
    └── Lecture 1

{
  chapterId: "uuid-v4-format",
  chapterTitle: "Chapter 1: Getting Started",
  chapterOrder: 1,
  chapterContent: [], // Array of lectures
  collapsed: false // UI state (not stored in database)
}

// Edit mode trigger
<button
  onDoubleClick={() => {
    setEditingChapterId(chapter.chapterId)
    setEditingChapterTitle(chapter.chapterTitle)
  }}
>
  {chapter.chapterTitle}
</button>

const removeChapter = (id) => {
  setChapters((prev) => prev.filter((c) => c.chapterId !== id))
}

const lecture = {
  lectureId: "8f4e5d3a-1b2c-4d5e-8f7g-9h0i1j2k3l4m",
  lectureTitle: "Understanding State Management",
  lectureDuration: 22, // minutes
  lectureUrl: "https://youtube.com/watch?v=abc123",
  isPreviewFree: false,
  lectureOrder: 1 // Position within chapter
}

const removeLecture = (chapterId, lectureIndex) => {
  setChapters((prev) =>
    prev.map((chapter) => {
      if (chapter.chapterId !== chapterId) return chapter
      
      const content = [...chapter.chapterContent]
      content.splice(lectureIndex, 1) // Remove at index
      
      return { ...chapter, chapterContent: content }
    })
  )
}

try {
  new URL(details.lectureUrl) // Throws if invalid
  // URL is valid, proceed
} catch {
  toast.error('Please enter a valid URL')
  return
}

// Backend thumbnail processing
const imageUpload = await cloudinary.uploader.upload(imageFile.path)
newCourse.courseThumbnail = imageUpload.secure_url
await newCourse.save()

// Strategic free previews
const courseContent = [
  {
    chapterTitle: "Introduction",
    chapterContent: [
      {
        lectureTitle: "Welcome & Course Overview",
        isPreviewFree: true // ✓ First impression
      }
    ]
  },
  {
    chapterTitle: "Core Concepts",
    chapterContent: [
      {
        lectureTitle: "Component Fundamentals",
        isPreviewFree: true // ✓ Show teaching quality
      }
    ]
  },
  {
    chapterTitle: "Final Project",
    chapterContent: [
      {
        lectureTitle: "Project Demo",
        isPreviewFree: true // ✓ Motivate purchase
      }
    ]
  }
]

// Frontend calculation
const totalLectures = chapters.reduce(
  (sum, chapter) => sum + chapter.chapterContent.length,
  0
)

// Backend verification
let totalLectures = 0
courseContent.forEach((chapter) => {
  if (Array.isArray(chapter.chapterContent)) {
    totalLectures += chapter.chapterContent.length
  }
})

// Sum all lecture durations
let totalDurationMinutes = 0

chapters.forEach((chapter) => {
  chapter.chapterContent.forEach((lecture) => {
    totalDurationMinutes += lecture.lectureDuration
  })
})

// Display formatting
const hours = Math.floor(totalDurationMinutes / 60)
const minutes = totalDurationMinutes % 60
const display = hours > 0 
  ? `${hours}h ${minutes}m`
  : `${minutes}m`

// Section validation
const step3Complete = 
  chapters.length > 0 &&      // At least one chapter
  totalLectures > 0 &&        // At least one lecture
  chapters.every(chapter =>   // All chapters have content
    chapter.chapterContent.length > 0
  )

const createId = () =>
  typeof crypto !== 'undefined' && crypto.randomUUID
    ? crypto.randomUUID() // Modern browsers
    : `${Date.now().toString(36)}-${Math.random().toString(36).slice(2, 10)}` // Fallback

// Example IDs:
// "8f4e5d3a-1b2c-4d5e-8f7g-9h0i1j2k3l4m" (UUID v4)
// "l5x8k9m2-a1b2c3d4" (Fallback)

const courseSchema = new mongoose.Schema({
  // Basic info
  courseTitle: { type: String, required: true },
  courseDescription: { type: String, required: true },
  courseThumbnail: { type: String }, // Cloudinary URL
  coursePrice: { type: Number, required: true },
  discount: { type: Number, required: true, min: 0, max: 100 },
  isPublished: { type: Boolean, default: true },
  
  // Content
  courseContent: [chapterSchema],
  
  // Calculated fields
  totalLectures: { type: Number, default: 0 },
  totalDurationMinutes: { type: Number, default: 0 },
  
  // Relationships
  educatorId: { type: String, ref: 'User', required: true },
  enrolledStudents: [{ type: String, ref: 'User' }],
  
  // Ratings
  courseRatings: [{
    userId: { type: String },
    rating: { type: Number, min: 1, max: 5 }
  }],
  averageRating: { type: Number, default: 0 },
  totalRatings: { type: Number, default: 0 }
}, { timestamps: true })

const chapterSchema = new mongoose.Schema({
  chapterId: { type: String, required: true },
  chapterOrder: { type: Number, required: true },
  chapterTitle: { type: String, required: true },
  chapterContent: [lectureSchema]
}, { _id: false })

const lectureSchema = new mongoose.Schema({
  lectureId: { type: String, required: true },
  lectureTitle: { type: String, required: true },
  lectureDuration: { type: Number, required: true },
  lectureUrl: { type: String, required: true },
  isPreviewFree: { type: Boolean, required: true },
  lectureOrder: { type: Number, required: true }
}, { _id: false })

// Fetch for editing
const { data } = await axios.get(
  `${backendUrl}/api/educator/course/${courseId}`,
  { headers: { Authorization: `Bearer ${token}` } }
)

// Populate form
setCourseTitle(data.course.courseTitle)
setDescription(data.course.courseDescription)
setChapters(data.course.courseContent)
// ... etc

// Update instead of create
const { data } = await axios.put(
  `${backendUrl}/api/educator/course/${courseId}`,
  formData,
  { headers: { Authorization: `Bearer ${token}` } }
)