import { Asset } from '@/types/asset-management';
import { AssetAssignment } from '@/types/asset-management';
import { RequestedAssetItem, AssetAvailabilityStatus } from '@/types/asset-request';

/**
 * Calculate available quantity for a specific asset type
 * @param assetType - The type of asset to check
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns Available quantity
 */
export function calculateAvailableQuantity(
  assetType: string,
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): number {
  // Count total assets of this type
  const totalAssets = allAssets.filter(asset => asset.assetType === assetType).length;
  
  // Count how many are currently assigned (active assignments only)
  const assignedCount = activeAssignments.filter(assignment => {
    const asset = allAssets.find(a => a.assetID === assignment.assetID);
    return asset && asset.assetType === assetType;
  }).length;
  
  // Calculate available
  const available = totalAssets - assignedCount;
  
  return Math.max(0, available); // Ensure non-negative
}

/**
 * Calculate availability status for multiple requested asset items
 * @param requestedAssets - List of requested asset items
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns Array of availability status for each requested asset type
 */
export function calculateAvailabilityStatus(
  requestedAssets: RequestedAssetItem[],
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): AssetAvailabilityStatus[] {
  return requestedAssets.map(requestedItem => {
    const available = calculateAvailableQuantity(
      requestedItem.assetType,
      allAssets,
      activeAssignments
    );
    
    return {
      assetType: requestedItem.assetType,
      requested: requestedItem.quantity,
      available,
      canFulfill: available >= requestedItem.quantity
    };
  });
}

/**
 * Check if all requested assets can be fulfilled
 * @param requestedAssets - List of requested asset items
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns True if all requested assets can be fulfilled
 */
export function canFulfillRequest(
  requestedAssets: RequestedAssetItem[],
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): boolean {
  const availabilityStatus = calculateAvailabilityStatus(
    requestedAssets,
    allAssets,
    activeAssignments
  );
  
  return availabilityStatus.every(status => status.canFulfill);
}

/**
 * Get available assets of a specific type (not currently assigned)
 * @param assetType - The type of asset to filter
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns Array of available assets
 */
export function getAvailableAssetsByType(
  assetType: string,
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): Asset[] {
  // Get all assets of this type
  const assetsOfType = allAssets.filter(asset => asset.assetType === assetType);
  
  // Get IDs of assets that are currently assigned
  const assignedAssetIds = new Set(
    activeAssignments.map(assignment => assignment.assetID)
  );
  
  // Filter out assigned assets
  return assetsOfType.filter(asset => !assignedAssetIds.has(asset.assetID));
}

/**
 * Check if inventory is low for a specific asset type
 * @param assetType - The type of asset to check
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @param threshold - Threshold percentage (default 20%)
 * @returns True if inventory is below threshold
 */
export function isLowStock(
  assetType: string,
  allAssets: Asset[],
  activeAssignments: AssetAssignment[],
  threshold: number = 0.2
): boolean {
  const totalAssets = allAssets.filter(asset => asset.assetType === assetType).length;
  
  // If no assets exist, it's definitely low stock
  if (totalAssets === 0) return true;
  
  const available = calculateAvailableQuantity(assetType, allAssets, activeAssignments);
  const availabilityRatio = available / totalAssets;
  
  return availabilityRatio <= threshold;
}

/**
 * Get inventory summary for all asset types
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns Map of asset type to inventory summary
 */
export function getInventorySummary(
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): Map<string, { total: number; assigned: number; available: number; lowStock: boolean }> {
  const summary = new Map<string, { total: number; assigned: number; available: number; lowStock: boolean }>();
  
  // Get unique asset types
  const assetTypes = new Set(allAssets.map(asset => asset.assetType));
  
  assetTypes.forEach(assetType => {
    const total = allAssets.filter(asset => asset.assetType === assetType).length;
    const available = calculateAvailableQuantity(assetType, allAssets, activeAssignments);
    const assigned = total - available;
    const lowStock = isLowStock(assetType, allAssets, activeAssignments);
    
    summary.set(assetType, {
      total,
      assigned,
      available,
      lowStock
    });
  });
  
  return summary;
}

/**
 * Validate that requested assets can be assigned without over-assignment
 * @param requestedAssets - List of requested asset items
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active (not returned) assignments
 * @returns Validation result with error messages if any
 */
export function validateAssignmentAvailability(
  requestedAssets: RequestedAssetItem[],
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): { valid: boolean; errors: string[] } {
  const errors: string[] = [];
  
  requestedAssets.forEach(requestedItem => {
    const available = calculateAvailableQuantity(
      requestedItem.assetType,
      allAssets,
      activeAssignments
    );
    
    if (available < requestedItem.quantity) {
      errors.push(
        `Insufficient ${requestedItem.assetType}: requested ${requestedItem.quantity}, only ${available} available`
      );
    }
  });
  
  return {
    valid: errors.length === 0,
    errors
  };
}

/**
 * Audit log entry for inventory changes
 */
export interface InventoryAuditLog {
  timestamp: string;
  action: 'assignment' | 'return' | 'adjustment';
  assetType: string;
  assetId: number;
  assetCode: string;
  employeeId: number;
  employeeName: string;
  performedBy: number;
  previousState: 'available' | 'assigned';
  newState: 'available' | 'assigned';
  requestId?: number;
  remarks?: string;
}

/**
 * Create an audit log entry for an inventory change
 * @param params - Audit log parameters
 * @returns Audit log entry
 */
export function createInventoryAuditLog(params: {
  action: 'assignment' | 'return' | 'adjustment';
  assetType: string;
  assetId: number;
  assetCode: string;
  employeeId: number;
  employeeName: string;
  performedBy: number;
  previousState: 'available' | 'assigned';
  newState: 'available' | 'assigned';
  requestId?: number;
  remarks?: string;
}): InventoryAuditLog {
  return {
    timestamp: new Date().toISOString(),
    ...params
  };
}

/**
 * Log inventory change to console (can be extended to send to backend)
 * @param log - Audit log entry
 */
export function logInventoryChange(log: InventoryAuditLog): void {
  console.log('[INVENTORY AUDIT]', {
    timestamp: log.timestamp,
    action: log.action,
    asset: `${log.assetType} (${log.assetCode})`,
    employee: `${log.employeeName} (ID: ${log.employeeId})`,
    stateChange: `${log.previousState} → ${log.newState}`,
    requestId: log.requestId,
    performedBy: log.performedBy,
    remarks: log.remarks
  });
}

/**
 * Validate assignment request against current inventory
 * @param assignedAssets - Assets being assigned
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active assignments
 * @returns Validation result with detailed errors
 */
export function validateAssignmentRequest(
  assignedAssets: Array<{ assetID: number; assetCode: string; assetType: string }>,
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): { valid: boolean; errors: string[]; warnings: string[] } {
  const errors: string[] = [];
  const warnings: string[] = [];
  
  // Get currently assigned asset IDs
  const assignedAssetIds = new Set(activeAssignments.map(a => a.assetID));
  
  // Validate each asset
  assignedAssets.forEach(assignedAsset => {
    // Check if asset exists
    const asset = allAssets.find(a => a.assetID === assignedAsset.assetID);
    if (!asset) {
      errors.push(`Asset ${assignedAsset.assetCode} (ID: ${assignedAsset.assetID}) does not exist`);
      return;
    }
    
    // Check if asset is already assigned
    if (assignedAssetIds.has(assignedAsset.assetID)) {
      errors.push(`Asset ${assignedAsset.assetCode} is already assigned to another employee`);
      return;
    }
    
    // Check asset condition
    if (asset.assetCondition === 'Damaged' || asset.assetCondition === 'Under Repair') {
      warnings.push(
        `Asset ${assignedAsset.assetCode} is in ${asset.assetCondition} condition. ` +
        'Consider selecting a different asset.'
      );
    }
    
    // Verify asset type matches
    if (asset.assetType !== assignedAsset.assetType) {
      errors.push(
        `Asset type mismatch for ${assignedAsset.assetCode}: ` +
        `expected ${assignedAsset.assetType}, found ${asset.assetType}`
      );
    }
  });
  
  return {
    valid: errors.length === 0,
    errors,
    warnings
  };
}

/**
 * Calculate inventory impact of an assignment
 * @param assignedAssets - Assets being assigned
 * @param allAssets - All assets in the system
 * @param activeAssignments - All active assignments before the new assignment
 * @returns Inventory impact summary
 */
export function calculateInventoryImpact(
  assignedAssets: Array<{ assetType: string }>,
  allAssets: Asset[],
  activeAssignments: AssetAssignment[]
): Map<string, { before: number; after: number; percentageUsed: number }> {
  const impact = new Map<string, { before: number; after: number; percentageUsed: number }>();
  
  // Group assigned assets by type
  const assignmentsByType = new Map<string, number>();
  assignedAssets.forEach(asset => {
    const count = assignmentsByType.get(asset.assetType) || 0;
    assignmentsByType.set(asset.assetType, count + 1);
  });
  
  // Calculate impact for each asset type
  assignmentsByType.forEach((assignedCount, assetType) => {
    const totalAssets = allAssets.filter(a => a.assetType === assetType).length;
    const beforeAvailable = calculateAvailableQuantity(assetType, allAssets, activeAssignments);
    const afterAvailable = beforeAvailable - assignedCount;
    const percentageUsed = totalAssets > 0 ? ((totalAssets - afterAvailable) / totalAssets) * 100 : 0;
    
    impact.set(assetType, {
      before: beforeAvailable,
      after: afterAvailable,
      percentageUsed: Math.round(percentageUsed)
    });
  });
  
  return impact;
}