"""
Course Model - Loads and manages course structure from course.json
"""

import json
from pathlib import Path
from typing import Dict, List, Optional
from app.config import COURSE_JSON, LESSONS_DIR


class Lesson:
    """Represents a single lesson"""

    def __init__(self, data: dict, part_id: str, section_id: str, order: int = 0):
        self.id = data['id']
        self.filename = data['filename']
        self.title = data['title']
        self.estimated_time = data['estimated_time']
        self.difficulty = data['difficulty']
        self.part_id = part_id
        self.section_id = section_id
        self.order = order  # Sequential order in course (1-30)
        self.points = data.get('points', 0)  # Points for completion

        # Construct full path to lesson file
        section_path = LESSONS_DIR / section_id.replace('-', '_').replace('fundamentals', '01-fundamentals').replace('optimization', '02-optimization').replace('spark_physics', '03-spark-physics').replace('advanced_modeling', '04-advanced-modeling')
        self.file_path = section_path / self.filename

    def __repr__(self):
        return f"<Lesson {self.id}: {self.title}>"


class Section:
    """Represents a course section (e.g., 'fundamentals')"""

    def __init__(self, data: dict, part_id: str, lesson_order_start: int = 1):
        self.id = data['id']
        self.title = data['title']
        self.path = data['path']
        self.description = data['description']
        self.part_id = part_id

        # Load lessons with sequential ordering
        self.lessons = []
        for i, lesson_data in enumerate(data['lessons']):
            lesson = Lesson(lesson_data, part_id, self.id, lesson_order_start + i)
            self.lessons.append(lesson)

        self.exercises = data.get('exercises', [])
        self.key_concepts = data.get('key_concepts', [])

    def get_lesson(self, lesson_id: str) -> Optional[Lesson]:
        """Get lesson by ID"""
        for lesson in self.lessons:
            if lesson.id == lesson_id:
                return lesson
        return None

    def __repr__(self):
        return f"<Section {self.id}: {len(self.lessons)} lessons>"


class Part:
    """Represents a course part (e.g., 'Part 1: Fundamentals')"""

    def __init__(self, data: dict, part_number: int, lesson_order_start: int = 1):
        self.id = data['id']
        self.title = data['title']
        self.description = data['description']
        self.estimated_time = data['estimated_time']
        self.number = part_number  # Part number (1-4)

        # Load sections with sequential lesson ordering
        self.sections = []
        current_order = lesson_order_start
        for section_data in data['sections']:
            section = Section(section_data, self.id, current_order)
            self.sections.append(section)
            current_order += len(section.lessons)

        # Create a convenience property for accessing all lessons in this part
        self.lessons = self.get_all_lessons()

    def get_lesson(self, lesson_id: str) -> Optional[Lesson]:
        """Get lesson by ID from any section in this part"""
        for section in self.sections:
            lesson = section.get_lesson(lesson_id)
            if lesson:
                return lesson
        return None

    def get_all_lessons(self) -> List[Lesson]:
        """Get all lessons in this part"""
        lessons = []
        for section in self.sections:
            lessons.extend(section.lessons)
        return lessons

    def __repr__(self):
        return f"<Part {self.id}: {len(self.sections)} sections>"


class LearningPath:
    """Represents a learning path (e.g., 'beginner', 'complete')"""

    def __init__(self, data: dict):
        self.id = data['id']
        self.title = data['title']
        self.description = data['description']
        self.lessons = data.get('lessons', [])
        self.skip = data.get('skip', [])

    def includes_lesson(self, lesson_id: str) -> bool:
        """Check if lesson is included in this path"""
        if self.lessons == 'all':
            return lesson_id not in self.skip
        return lesson_id in self.lessons

    def __repr__(self):
        return f"<LearningPath {self.id}: {self.title}>"


class Course:
    """Main course model - loads and manages entire course structure"""

    def __init__(self, course_json_path: Path = None):
        """
        Load course from course.json

        Args:
            course_json_path: Path to course.json file (default: from config)
        """
        if course_json_path is None:
            course_json_path = COURSE_JSON

        self.json_path = course_json_path
        self._load_course()

    def _load_course(self):
        """Load and parse course.json"""
        try:
            with open(self.json_path, 'r', encoding='utf-8') as f:
                data = json.load(f)

            # Course metadata
            self.title = data['title']
            self.version = data['version']
            self.author = data['author']
            self.description = data['description']
            self.estimated_total_time = data['estimated_total_time']
            self.total_lessons = data['total_lessons']
            self.total_exercises = data['total_exercises']
            self.total_points = data['total_points']

            # Prerequisites
            self.prerequisites_required = data['prerequisites']['required']
            self.prerequisites_recommended = data['prerequisites']['recommended']

            # Load course structure (4 parts) with sequential numbering
            self.parts = []
            current_order = 1
            for i, part_data in enumerate(data['structure']):
                part = Part(part_data, i + 1, current_order)
                self.parts.append(part)
                current_order += len(part.get_all_lessons())

            # Reference materials
            self.reference_materials = data['reference_materials']

            # Worked examples
            self.worked_examples = data['worked_examples']

            # Learning paths
            self.learning_paths = [
                LearningPath(path_data)
                for path_data in data['learning_paths']
            ]

            # Tags
            self.tags = data.get('tags', {})

            # Metadata
            self.metadata = data.get('metadata', {})

            # Build lesson index for quick lookup
            self._build_lesson_index()

            print(f"[Course] Loaded: {self.title}")
            print(f"[Course] {self.total_lessons} lessons across {len(self.parts)} parts")

        except FileNotFoundError:
            print(f"[Course ERROR] course.json not found: {self.json_path}")
            raise
        except json.JSONDecodeError as e:
            print(f"[Course ERROR] Invalid JSON: {e}")
            raise
        except KeyError as e:
            print(f"[Course ERROR] Missing required field: {e}")
            raise

    def _build_lesson_index(self):
        """Build index for fast lesson lookup by ID"""
        self._lesson_index = {}
        for part in self.parts:
            for section in part.sections:
                for lesson in section.lessons:
                    self._lesson_index[lesson.id] = lesson

    def get_lesson(self, lesson_id: str) -> Optional[Lesson]:
        """Get lesson by ID (fast lookup)"""
        return self._lesson_index.get(lesson_id)

    def get_all_lessons(self) -> List[Lesson]:
        """Get all lessons in course order"""
        lessons = []
        for part in self.parts:
            lessons.extend(part.get_all_lessons())
        return lessons

    def get_lesson_by_index(self, index: int) -> Optional[Lesson]:
        """Get lesson by sequential index (0-29)"""
        all_lessons = self.get_all_lessons()
        if 0 <= index < len(all_lessons):
            return all_lessons[index]
        return None

    def get_lesson_index(self, lesson_id: str) -> Optional[int]:
        """Get sequential index of a lesson (0-29)"""
        all_lessons = self.get_all_lessons()
        for i, lesson in enumerate(all_lessons):
            if lesson.id == lesson_id:
                return i
        return None

    def get_next_lesson(self, lesson_id: str) -> Optional[Lesson]:
        """Get next lesson in sequence"""
        index = self.get_lesson_index(lesson_id)
        if index is not None:
            return self.get_lesson_by_index(index + 1)
        return None

    def get_prev_lesson(self, lesson_id: str) -> Optional[Lesson]:
        """Get previous lesson in sequence"""
        index = self.get_lesson_index(lesson_id)
        if index is not None and index > 0:
            return self.get_lesson_by_index(index - 1)
        return None

    def get_part(self, part_id: str) -> Optional[Part]:
        """Get part by ID"""
        for part in self.parts:
            if part.id == part_id:
                return part
        return None

    def get_learning_path(self, path_id: str) -> Optional[LearningPath]:
        """Get learning path by ID"""
        for path in self.learning_paths:
            if path.id == path_id:
                return path
        return None

    def get_lessons_for_path(self, path_id: str) -> List[Lesson]:
        """Get all lessons for a specific learning path"""
        path = self.get_learning_path(path_id)
        if not path:
            return []

        all_lessons = self.get_all_lessons()
        if path.lessons == 'all':
            return [l for l in all_lessons if l.id not in path.skip]
        else:
            return [l for l in all_lessons if l.id in path.lessons]

    def get_lessons_by_tag(self, tag: str) -> List[Lesson]:
        """Get all lessons with a specific tag"""
        if tag not in self.tags:
            return []

        lesson_ids = self.tags[tag]
        return [self.get_lesson(lid) for lid in lesson_ids if self.get_lesson(lid)]

    def get_part_for_lesson(self, lesson_id: str) -> Optional[Part]:
        """Get the part that contains a lesson"""
        for part in self.parts:
            if part.get_lesson(lesson_id):
                return part
        return None

    def search_lessons(self, query: str) -> List[Lesson]:
        """Simple search by lesson title"""
        query = query.lower()
        results = []
        for lesson in self.get_all_lessons():
            if query in lesson.title.lower() or query in lesson.id.lower():
                results.append(lesson)
        return results

    def validate(self) -> bool:
        """Validate that all lesson files exist"""
        all_valid = True
        for lesson in self.get_all_lessons():
            if not lesson.file_path.exists():
                print(f"[Course WARN] Missing lesson file: {lesson.file_path}")
                all_valid = False
        return all_valid

    def __repr__(self):
        return f"<Course: {self.total_lessons} lessons, {len(self.parts)} parts>"


# Global course instance
_course_instance = None

def get_course() -> Course:
    """Get global course instance (singleton)"""
    global _course_instance
    if _course_instance is None:
        _course_instance = Course()
    return _course_instance