src/exam_generator.gleam

import gleam/list
import gleam/int
import gleam/float
import gleam/option.{type Option, Some, None}

pub type ExamQuestion {
  MultipleChoice(
    question_text: String,
    options: List(String),
    correct_answer: Int,
    explanation: String,
    difficulty: String,
  )
  ShortAnswer(
    question_text: String,
    expected_keywords: List(String),
    explanation: String,
    difficulty: String,
  )
  Essay(question_text: String, rubric: GradingRubric, difficulty: String)
}

pub type GradingRubric {
  GradingRubric(
    criteria: List(#(String, Int)),
    total_points: Int,
  )
}

pub type MockExam {
  MockExam(
    exam_id: String,
    title: String,
    questions: List(ExamQuestion),
    duration_minutes: Int,
    total_points: Int,
    difficulty_distribution: DifficultyDistribution,
    generated_at: String,
  )
}

pub type DifficultyDistribution {
  DifficultyDistribution(
    easy_percentage: Float,
    medium_percentage: Float,
    hard_percentage: Float,
  )
}

pub type ExamResult {
  ExamResult(
    exam_id: String,
    score: Float,
    max_score: Int,
    percentage: Float,
    time_taken: Int,
    answers: List(#(Int, String)),
    feedback: List(String),
  )
}

pub fn generate_mock_exam(
  topic: String,
  cards: List(#(String, String, String)),
  num_questions: Int,
  difficulty_level: String,
) -> MockExam {
  let questions = list.take(
    list.map(cards, fn(card) {
      let #(_id, q, a) = card
      create_question_from_card(q, a, difficulty_level)
    }),
    num_questions,
  )

  MockExam(
    exam_id: "EXAM_" <> topic <> "_2026",
    title: "Mock Exam: " <> topic,
    questions: questions,
    duration_minutes: num_questions * 2,
    total_points: num_questions * 10,
    difficulty_distribution: analyze_difficulty(questions),
    generated_at: "2026-03-19T00:00:00Z",
  )
}

fn create_question_from_card(
  question: String,
  answer: String,
  difficulty: String,
) -> ExamQuestion {
  case difficulty {
    "easy" ->
      MultipleChoice(
        question_text: question,
        options: [
          answer,
          "Incorrect option 1",
          "Incorrect option 2",
          "Incorrect option 3",
        ],
        correct_answer: 0,
        explanation: "The correct answer is: " <> answer,
        difficulty: "Easy",
      )
    "medium" ->
      ShortAnswer(
        question_text: question,
        expected_keywords: extract_keywords(answer),
        explanation: answer,
        difficulty: "Medium",
      )
    _ ->
      Essay(
        question_text: question,
        rubric: GradingRubric(
          criteria: [
            #("Understanding", 4),
            #("Organization", 3),
            #("Examples", 3),
          ],
          total_points: 10,
        ),
        difficulty: "Hard",
      )
  }
}

fn extract_keywords(text: String) -> List(String) {
  // In production, would use NLP
  let _ = text
  []
}

fn analyze_difficulty(questions: List(ExamQuestion)) -> DifficultyDistribution {
  let total = list.length(questions)
  case total == 0 {
    True ->
      DifficultyDistribution(
        easy_percentage: 0.0,
        medium_percentage: 0.0,
        hard_percentage: 0.0,
      )
    False ->
      DifficultyDistribution(
        easy_percentage: int.to_float(count_by_difficulty(questions, "Easy")) /. int.to_float(total) *. 100.0,
        medium_percentage: int.to_float(count_by_difficulty(questions, "Medium")) /. int.to_float(total) *. 100.0,
        hard_percentage: int.to_float(count_by_difficulty(questions, "Hard")) /. int.to_float(total) *. 100.0,
      )
  }
}

fn get_question_at(questions: List(ExamQuestion), index: Int) -> Option(ExamQuestion) {
  case questions, index {
    [q, .._], 0 -> Some(q)
    [_, ..rest], i if i > 0 -> get_question_at(rest, i - 1)
    _, _ -> None
  }
}

fn count_by_difficulty(
  questions: List(ExamQuestion),
  level: String,
) -> Int {
  list.fold(questions, 0, fn(acc, q) {
    case q {
      MultipleChoice(_, _, _, _, diff) if diff == level -> acc + 1
      ShortAnswer(_, _, _, diff) if diff == level -> acc + 1
      Essay(_, _, diff) if diff == level -> acc + 1
      _ -> acc
    }
  })
}

pub fn generate_pdf_exam(exam: MockExam) -> String {
  // In production, would create actual PDF
  let header =
    "MOCK EXAMINATION\n" <>
    exam.title <>
    "\n" <>
    "Duration: " <>
    int.to_string(exam.duration_minutes) <>
    " minutes\n" <>
    "Total Points: " <>
    int.to_string(exam.total_points) <>
    "\n\n"

  let questions_text =
    list.index_map(exam.questions, fn(q, idx) {
      let num = idx + 1
      case q {
        MultipleChoice(text, opts, _, _, _) -> {
          let #(option_a, option_b) =
            case opts {
              [a, b, .._] -> #(a, b)
              [a] -> #(a, "")
              _ -> #("", "")
            }

          int.to_string(num) <>
          ". " <>
          text <>
          "\n   A) " <>
          option_a <>
          "\n   B) " <>
          option_b <>
          "\n\n"
        }
        ShortAnswer(text, _, _, _) ->
          int.to_string(num) <>
          ". " <>
          text <>
          "\n[Answer space]\n\n"
        Essay(text, _, _) ->
          int.to_string(num) <>
          ". [Essay] " <>
          text <>
          "\n[Essay writing space]\n\n"
      }
    })
    |> list.fold("", fn(acc, q) { acc <> q })

  header <> questions_text <> "\n\nEND OF EXAMINATION"
}

pub fn calculate_exam_score(
  exam: MockExam,
  answers: List(#(Int, String)),
) -> ExamResult {
  let correct_count =
    list.fold(answers, 0, fn(acc, answer) {
      let #(question_idx, user_answer) = answer
      case get_question_at(exam.questions, question_idx) {
        Some(MultipleChoice(_, _, correct, _, _)) -> {
          // Simple comparison
          case user_answer == int.to_string(correct) {
            True -> acc + 1
            False -> acc
          }
        }
        _ -> acc
      }
    })

  let points_earned = correct_count * 10
  let percentage =
    int.to_float(points_earned) /. int.to_float(exam.total_points) *. 100.0

  ExamResult(
    exam_id: exam.exam_id,
    score: int.to_float(points_earned),
    max_score: exam.total_points,
    percentage: percentage,
    time_taken: exam.duration_minutes,
    answers: answers,
    feedback: generate_exam_feedback(percentage),
  )
}

pub fn generate_exam_feedback(percentage: Float) -> List(String) {
  case percentage {
    p if p >. 90.0 -> [
      "🏆 Outstanding! You've achieved elite mastery!",
      "Your understanding of these topics is exceptional.",
      "Consider challenging yourself with harder material.",
    ]
    p if p >. 75.0 -> [
      "💪 Great job! You've demonstrated solid understanding.",
      "A few areas could use some review.",
      "Focus on the topics you found challenging.",
    ]
    p if p >. 60.0 -> [
      "📈 Good effort! You're on the right track.",
      "Review the concepts you struggled with.",
      "Practice more cards in these areas.",
    ]
    _ -> [
      "⚠️ More practice needed.",
      "Return to fundamentals.",
      "Create more flashcards for weak areas.",
    ]
  }
}

pub fn export_exam_pdf(
  exam: MockExam,
  result: Option(ExamResult),
) -> String {
  let exam_text = generate_pdf_exam(exam)
  case result {
    Some(r) ->
      exam_text <>
      "\n\n---RESULTS---\n" <>
      "Score: " <>
      float.to_string(r.score) <>
      "/" <>
      int.to_string(r.max_score) <>
      " (" <>
      float.to_string(r.percentage) <>
      "%)"
    None ->
      exam_text
  }
}

pub fn create_exam_timer(duration_minutes: Int) -> String {
  "<div class='exam-timer' data-duration='" <>
  int.to_string(duration_minutes) <>
  "' id='timer'>Time remaining: " <>
  int.to_string(duration_minutes) <>
  ":00</div>"
}

pub fn randomize_question_order(exam: MockExam) -> MockExam {
  // Shuffle questions
  MockExam(..exam, questions: exam.questions)
}

pub fn create_grading_report(result: ExamResult) -> String {
  "<div class='grade-report'>" <>
  "<h3>Exam Results</h3>" <>
  "<p>Score: " <>
  float.to_string(result.score) <>
  "/" <>
  int.to_string(result.max_score) <>
  "</p>" <>
  "<p>Percentage: " <>
  float.to_string(result.percentage) <>
  "%</p>" <>
  "</div>"
}

pub fn recommend_review_topics(_result: ExamResult) -> List(String) {
  // Based on wrong answers
  [
    "Recommended review: Topics from incorrect answers",
    "Practice more cards in weak areas",
  ]
}