from typing import List, Dict, Any, Optional
from django.contrib.auth import get_user_model
from django.utils import timezone
from .models import ChangeSet

User = get_user_model()

class ApprovalStage:
    def __init__(self, stage_id: int, name: str, required_roles: List[str]):
        self.id = stage_id
        self.name = name
        self.required_roles = required_roles
        self.approvers: List[Dict[str, Any]] = []
        self.status = 'pending'  # pending, approved, rejected
        self.completed_at = None

    def add_approver(self, user: User, decision: str, comment: str = "") -> None:
        """Add an approver's decision to this stage"""
        self.approvers.append({
            'user_id': user.id,
            'username': user.username,
            'decision': decision,
            'comment': comment,
            'timestamp': timezone.now().isoformat()
        })

    def is_approved(self, policy: str = 'unanimous') -> bool:
        """Check if stage is approved based on policy"""
        if not self.approvers:
            return False

        approve_count = sum(1 for a in self.approvers if a['decision'] == 'approve')
        if policy == 'unanimous':
            return approve_count == len(self.required_roles)
        else:  # majority
            return approve_count > len(self.required_roles) / 2

class ApprovalStateMachine:
    """Manages the state transitions for change approval workflow"""

    def __init__(self, changeset: ChangeSet):
        self.changeset = changeset
        self.stages: List[ApprovalStage] = []
        self.current_stage_index = 0
        self.policy = changeset.approval_policy
        self._load_state()

    def _load_state(self) -> None:
        """Load the current state from changeset approval_state"""
        if not self.changeset.approval_state:
            return

        for stage_data in self.changeset.approval_state:
            stage = ApprovalStage(
                stage_data['id'],
                stage_data['name'],
                stage_data['required_roles']
            )
            stage.approvers = stage_data.get('approvers', [])
            stage.status = stage_data.get('status', 'pending')
            stage.completed_at = stage_data.get('completed_at')
            self.stages.append(stage)

        # Find current stage
        self.current_stage_index = next(
            (i for i, s in enumerate(self.stages) if s.status == 'pending'),
            len(self.stages) - 1
        )

    def initialize_workflow(self, stages_config: List[Dict[str, Any]]) -> None:
        """Set up initial approval workflow stages"""
        self.stages = [
            ApprovalStage(
                i,
                stage['name'],
                stage['required_roles']
            ) for i, stage in enumerate(stages_config)
        ]
        self._save_state()

    def submit_approval(
        self,
        user: User,
        decision: str,
        comment: str = "",
        stage_id: Optional[int] = None
    ) -> bool:
        """
        Submit an approval decision
        Args:
            user: The user submitting approval
            decision: 'approve' or 'reject'
            comment: Optional comment
            stage_id: Optional specific stage ID (for parallel approval)
        Returns:
            bool: True if submission was accepted
        """
        if self.changeset.status != 'pending_approval':
            return False

        if self.policy == 'sequential':
            stage = self.stages[self.current_stage_index]
        else:  # parallel
            if stage_id is None:
                return False
            stage = next((s for s in self.stages if s.id == stage_id), None)
            if not stage:
                return False

        # Check if user has required role
        user_roles = set(user.groups.values_list('name', flat=True))
        if not any(role in user_roles for role in stage.required_roles):
            return False

        # Add decision
        stage.add_approver(user, decision, comment)

        # Update stage status
        if stage.is_approved(self.policy):
            stage.status = 'approved'
            stage.completed_at = timezone.now().isoformat()
            
            if self.policy == 'sequential':
                self._advance_stage()
        elif decision == 'reject':
            stage.status = 'rejected'
            stage.completed_at = timezone.now().isoformat()
            self.changeset.status = 'rejected'
            self.changeset.save()

        self._save_state()
        return True

    def _advance_stage(self) -> None:
        """Move to next stage if available"""
        if self.current_stage_index < len(self.stages) - 1:
            self.current_stage_index += 1
        else:
            # All stages approved
            self.changeset.status = 'approved'
            self.changeset.save()

    def _save_state(self) -> None:
        """Save current state to changeset"""
        self.changeset.approval_state = [
            {
                'id': stage.id,
                'name': stage.name,
                'required_roles': stage.required_roles,
                'approvers': stage.approvers,
                'status': stage.status,
                'completed_at': stage.completed_at
            } for stage in self.stages
        ]
        self.changeset.save()

    def get_current_stage(self) -> Optional[ApprovalStage]:
        """Get the current active stage"""
        if not self.stages:
            return None
        return self.stages[self.current_stage_index]

    def get_stage_by_id(self, stage_id: int) -> Optional[ApprovalStage]:
        """Get a specific stage by ID"""
        return next((s for s in self.stages if s.id == stage_id), None)

    def get_pending_approvers(self) -> List[str]:
        """Get list of roles that still need to approve the current stage"""
        current_stage = self.get_current_stage()
        if not current_stage:
            return []

        approved_by = {a['user_id'] for a in current_stage.approvers}
        return [
            role for role in current_stage.required_roles
            if not any(
                user.id in approved_by
                for user in User.objects.filter(groups__name=role)
            )
        ]

    def can_user_approve(self, user: User) -> bool:
        """Check if user can approve the current stage"""
        current_stage = self.get_current_stage()
        if not current_stage:
            return False

        # Check if user already approved
        if any(a['user_id'] == user.id for a in current_stage.approvers):
            return False

        # Check if user has required role
        user_roles = set(user.groups.values_list('name', flat=True))
        return any(role in user_roles for role in current_stage.required_roles)