"""
Batch Aggregation Service - College-level macro analysis
Aggregates individual student scores into batch-level reports
"""
import logging
import numpy as np
from typing import Dict, List, Any, Optional
from dataclasses import dataclass, asdict
from datetime import datetime
from collections import Counter

logger = logging.getLogger(__name__)


@dataclass
class AggregateMetrics:
    """Batch-level aggregate metrics"""
    total_students: int
    avg_employability_score: float
    median_score: float
    std_dev: float
    placement_ready_pct: float  # % with score >= 0.6
    skill_diversity_index: int  # Unique skills count
    avg_cgpa: float
    avg_internship_months: float


@dataclass
class AspectDistribution:
    """Distribution stats for an aspect"""
    aspect: str
    avg: float
    std: float
    min: float
    max: float
    top_10_pct_avg: float  # Avg of top 10%
    bottom_10_pct_avg: float


@dataclass  
class DomainBreakdown:
    """Domain-wise student distribution"""
    domain_id: str
    display_name: str
    count: int
    percentage: float
    avg_score: float


@dataclass
class SkillGap:
    """Skill gap analysis result"""
    skill: str
    demand_score: float
    students_with_skill: int
    students_pct: float
    gap_severity: str  # 'critical', 'moderate', 'low'


@dataclass
class BatchRecommendation:
    """Recommendation for batch improvement"""
    category: str  # 'curriculum', 'training', 'industry'
    priority: str  # 'high', 'medium', 'low'
    recommendation: str
    impact: str


class BatchAggregationService:
    """
    Aggregates individual student data into college-level macro reports
    """
    
    # Thresholds
    PLACEMENT_READY_THRESHOLD = 0.60
    CRITICAL_GAP_THRESHOLD = 0.30  # < 30% students have skill
    MODERATE_GAP_THRESHOLD = 0.50
    
    def __init__(self):
        # Industry demand mapping (can be loaded from external source)
        self.industry_demands = {
            'python': 0.90,
            'sql': 0.85,
            'java': 0.80,
            'javascript': 0.75,
            'machine_learning': 0.70,
            'cloud': 0.85,
            'devops': 0.75,
            'data_analysis': 0.70,
            'system_design': 0.65,
            'communication': 0.80,
            'leadership': 0.60,
            'teamwork': 0.75
        }
    
    def aggregate_batch(self, 
                        students: List[Dict[str, Any]],
                        college_name: str = "Unknown College",
                        batch_year: int = None) -> Dict[str, Any]:
        """
        Generate comprehensive batch report from student data
        
        Args:
            students: List of student score packets (from scoring endpoint)
            college_name: Name of the college
            batch_year: Graduation year
        
        Returns:
            Complete macro analysis report
        """
        if not students:
            return self._empty_report(college_name, batch_year)
        
        batch_year = batch_year or datetime.now().year
        
        # Extract scores and features
        scores = []
        cgpas = []
        internship_months = []
        all_skills = []
        domain_counts = Counter()
        aspect_scores = {
            'technical_skills': [],
            'problem_solving': [],
            'leadership': [],
            'communication': [],
            'teamwork': [],
            'learning_agility': []
        }
        
        for student in students:
            # Final score
            final_score = student.get('final_score', 0)
            scores.append(final_score)
            
            # Features
            features = student.get('detailed_features', {})
            universal = features.get('universal', {})
            text = features.get('text', {})
            
            cgpas.append(universal.get('cgpa_norm', 0) * 10)  # Denormalize
            internship_months.append(universal.get('internship_exposure', 0) * 12)
            
            # Domain
            domain = student.get('domain_type') or student.get('detected_domain', 'general')
            domain_counts[domain] += 1
            
            # Aspect scores
            for aspect in aspect_scores:
                if aspect in text:
                    aspect_scores[aspect].append(text[aspect])
                elif aspect in universal:
                    aspect_scores[aspect].append(universal[aspect])
            
            # Skills (from raw student data if available)
            if 'skills' in student:
                skills = student['skills']
                if isinstance(skills, str):
                    skills = [s.strip().lower() for s in skills.split(',')]
                all_skills.extend(skills)
        
        # Compute aggregates
        aggregate = self._compute_aggregate_metrics(
            scores, cgpas, internship_months, all_skills
        )
        
        # Aspect distributions
        aspects = self._compute_aspect_distributions(aspect_scores)
        
        # Domain breakdown
        domains = self._compute_domain_breakdown(domain_counts, students)
        
        # Skill gaps
        skill_gaps = self._analyze_skill_gaps(all_skills, len(students))
        
        # Recommendations
        recommendations = self._generate_recommendations(
            aggregate, aspects, skill_gaps
        )
        
        # Build report
        report = {
            'report_id': f"BATCH_{batch_year}_{college_name[:3].upper()}",
            'college_name': college_name,
            'batch_year': batch_year,
            'generated_at': datetime.utcnow().isoformat() + 'Z',
            'total_students': len(students),
            
            'aggregate_metrics': asdict(aggregate),
            
            'score_distribution': self._compute_score_distribution(scores),
            
            'aspect_analysis': [asdict(a) for a in aspects],
            
            'domain_breakdown': [asdict(d) for d in domains],
            
            'skill_gap_analysis': [asdict(g) for g in skill_gaps],
            
            'recommendations': [asdict(r) for r in recommendations],
            
            'percentile_bands': self._compute_percentile_bands(scores)
        }
        
        return report
    
    def _compute_aggregate_metrics(self, scores, cgpas, internship_months, 
                                   skills) -> AggregateMetrics:
        """Compute high-level aggregate metrics"""
        scores_arr = np.array(scores)
        
        placement_ready = sum(1 for s in scores if s >= self.PLACEMENT_READY_THRESHOLD)
        placement_pct = (placement_ready / len(scores)) * 100 if scores else 0
        
        return AggregateMetrics(
            total_students=len(scores),
            avg_employability_score=round(float(np.mean(scores_arr)), 3),
            median_score=round(float(np.median(scores_arr)), 3),
            std_dev=round(float(np.std(scores_arr)), 3),
            placement_ready_pct=round(placement_pct, 1),
            skill_diversity_index=len(set(skills)),
            avg_cgpa=round(float(np.mean(cgpas)) if cgpas else 0, 2),
            avg_internship_months=round(float(np.mean(internship_months)) if internship_months else 0, 1)
        )
    
    def _compute_aspect_distributions(self, aspect_scores) -> List[AspectDistribution]:
        """Compute distribution stats for each aspect"""
        distributions = []
        
        for aspect, scores in aspect_scores.items():
            if not scores:
                continue
            
            arr = np.array(scores)
            top_10_idx = int(len(arr) * 0.1) or 1
            bottom_10_idx = int(len(arr) * 0.1) or 1
            
            sorted_arr = np.sort(arr)
            
            distributions.append(AspectDistribution(
                aspect=aspect,
                avg=round(float(np.mean(arr)), 3),
                std=round(float(np.std(arr)), 3),
                min=round(float(np.min(arr)), 3),
                max=round(float(np.max(arr)), 3),
                top_10_pct_avg=round(float(np.mean(sorted_arr[-top_10_idx:])), 3),
                bottom_10_pct_avg=round(float(np.mean(sorted_arr[:bottom_10_idx])), 3)
            ))
        
        return distributions
    
    def _compute_domain_breakdown(self, domain_counts, students) -> List[DomainBreakdown]:
        """Compute domain-wise breakdown"""
        breakdowns = []
        total = len(students)
        
        for domain, count in domain_counts.most_common():
            # Calculate avg score for this domain
            domain_scores = [
                s.get('final_score', 0) for s in students
                if (s.get('domain_type') or s.get('detected_domain', 'general')) == domain
            ]
            avg_score = np.mean(domain_scores) if domain_scores else 0
            
            breakdowns.append(DomainBreakdown(
                domain_id=domain,
                display_name=domain.replace('_', ' ').title(),
                count=count,
                percentage=round((count / total) * 100, 1),
                avg_score=round(float(avg_score), 3)
            ))
        
        return breakdowns
    
    def _analyze_skill_gaps(self, all_skills, total_students) -> List[SkillGap]:
        """Analyze skill gaps against industry demand"""
        skill_counts = Counter(all_skills)
        gaps = []
        
        for skill, demand in self.industry_demands.items():
            count = skill_counts.get(skill, 0)
            pct = (count / total_students) * 100 if total_students else 0
            
            # Determine severity
            if pct < self.CRITICAL_GAP_THRESHOLD * 100:
                severity = 'critical'
            elif pct < self.MODERATE_GAP_THRESHOLD * 100:
                severity = 'moderate'
            else:
                severity = 'low'
            
            gaps.append(SkillGap(
                skill=skill,
                demand_score=demand,
                students_with_skill=count,
                students_pct=round(pct, 1),
                gap_severity=severity
            ))
        
        # Sort by demand * (1 - coverage)
        gaps.sort(key=lambda g: g.demand_score * (1 - g.students_pct/100), reverse=True)
        
        return gaps[:10]  # Top 10 gaps
    
    def _generate_recommendations(self, aggregate, aspects, 
                                  skill_gaps) -> List[BatchRecommendation]:
        """Generate actionable recommendations"""
        recommendations = []
        
        # Critical skill gaps
        critical_gaps = [g for g in skill_gaps if g.gap_severity == 'critical']
        for gap in critical_gaps[:3]:
            recommendations.append(BatchRecommendation(
                category='curriculum',
                priority='high',
                recommendation=f"Add {gap.skill.replace('_', ' ').title()} training to curriculum",
                impact=f"Only {gap.students_pct}% students have this in-demand skill"
            ))
        
        # Low placement readiness
        if aggregate.placement_ready_pct < 60:
            recommendations.append(BatchRecommendation(
                category='training',
                priority='high',
                recommendation="Implement intensive placement preparation program",
                impact=f"Only {aggregate.placement_ready_pct}% students are placement-ready"
            ))
        
        # Low internship exposure
        if aggregate.avg_internship_months < 3:
            recommendations.append(BatchRecommendation(
                category='industry',
                priority='medium',
                recommendation="Establish mandatory internship partnerships with industry",
                impact=f"Average internship exposure is only {aggregate.avg_internship_months} months"
            ))
        
        # Weak aspects
        for aspect in aspects:
            if aspect.avg < 0.5:
                recommendations.append(BatchRecommendation(
                    category='training',
                    priority='medium',
                    recommendation=f"Conduct workshops on {aspect.aspect.replace('_', ' ').title()}",
                    impact=f"Average score is {aspect.avg:.0%}, below acceptable threshold"
                ))
        
        return recommendations[:8]  # Limit to 8 recommendations
    
    def _compute_score_distribution(self, scores) -> Dict[str, int]:
        """Compute score distribution by grade bands"""
        distribution = {
            'A+ (90-100%)': 0,
            'A (80-90%)': 0,
            'B+ (70-80%)': 0,
            'B (60-70%)': 0,
            'C (50-60%)': 0,
            'D (<50%)': 0
        }
        
        for score in scores:
            pct = score * 100
            if pct >= 90:
                distribution['A+ (90-100%)'] += 1
            elif pct >= 80:
                distribution['A (80-90%)'] += 1
            elif pct >= 70:
                distribution['B+ (70-80%)'] += 1
            elif pct >= 60:
                distribution['B (60-70%)'] += 1
            elif pct >= 50:
                distribution['C (50-60%)'] += 1
            else:
                distribution['D (<50%)'] += 1
        
        return distribution
    
    def _compute_percentile_bands(self, scores) -> Dict[str, float]:
        """Compute percentile thresholds"""
        if not scores:
            return {}
        
        arr = np.array(scores)
        return {
            'p10': round(float(np.percentile(arr, 10)), 3),
            'p25': round(float(np.percentile(arr, 25)), 3),
            'p50': round(float(np.percentile(arr, 50)), 3),
            'p75': round(float(np.percentile(arr, 75)), 3),
            'p90': round(float(np.percentile(arr, 90)), 3)
        }
    
    def _empty_report(self, college_name: str, batch_year: int) -> Dict[str, Any]:
        """Generate empty report for no data"""
        return {
            'report_id': f"BATCH_{batch_year or 'UNKNOWN'}_{college_name[:3].upper()}",
            'college_name': college_name,
            'batch_year': batch_year,
            'generated_at': datetime.utcnow().isoformat() + 'Z',
            'total_students': 0,
            'error': 'No student data provided',
            'aggregate_metrics': None,
            'recommendations': []
        }


# Singleton
_batch_service: Optional[BatchAggregationService] = None


def get_batch_aggregation_service() -> BatchAggregationService:
    """Get singleton batch aggregation service"""
    global _batch_service
    if _batch_service is None:
        _batch_service = BatchAggregationService()
    return _batch_service