import { Injectable, ForbiddenException } from '@nestjs/common';
import { Knex } from 'knex';
import { User } from '../models/user.model';
import { ObjectDefinition } from '../models/object-definition.model';
import { FieldDefinition } from '../models/field-definition.model';
import { RecordShare } from '../models/record-share.model';
import { AbilityFactory, AppAbility, Action } from './ability.factory';
import { DynamicModelFactory } from '../object/models/dynamic-model.factory';
import { subject } from '@casl/ability';

@Injectable()
export class AuthorizationService {
  constructor(private abilityFactory: AbilityFactory) {}

  /**
   * Apply authorization scope to a query based on OWD and user permissions
   * This determines which records the user can see
   * Modifies the query in place and returns void
   */
  async applyScopeToQuery<T = any>(
    query: any, // Accept both Knex and Objection query builders
    objectDef: ObjectDefinition,
    user: User & { roles?: any[] },
    action: Action,
    knex: Knex,
  ): Promise<void> {
    // Get user's ability
    const recordShares = await this.getActiveRecordShares(objectDef.id, user.id, knex);
    const ability = await this.abilityFactory.defineAbilityFor(user, recordShares);

    // Check if user has the base permission for this action
    // Use object ID, not API name, since permissions are stored by object ID
    if (!ability.can(action, objectDef.id)) {
      // No permission at all - return empty result
      query.where(knex.raw('1 = 0'));
      return;
    }

    // Check special permissions
    const hasViewAll = ability.can('view_all', objectDef.id);
    const hasModifyAll = ability.can('modify_all', objectDef.id);

    // If user has view_all or modify_all, they can see all records
    if (hasViewAll || hasModifyAll) {
      // No filtering needed
      return;
    }

    // Apply OWD (Org-Wide Default) restrictions
    switch (objectDef.orgWideDefault) {
      case 'public_read_write':
        // Everyone can see all records
        return;

      case 'public_read':
        // Everyone can see all records (write operations checked separately)
        return;

      case 'private':
      default:
        // Only owner and explicitly shared records
        await this.applyPrivateScope(query, objectDef, user, recordShares, knex);
        return;
    }
  }

  /**
   * Apply private scope: owner + shared records
   */
  private async applyPrivateScope<T = any>(
    query: any, // Accept both Knex and Objection query builders
    objectDef: ObjectDefinition,
    user: User,
    recordShares: RecordShare[],
    knex: Knex,
  ): Promise<void> {
    const tableName = this.getTableName(objectDef.apiName);
    
    // Check if table has ownerId column
    const hasOwner = await knex.schema.hasColumn(tableName, 'ownerId');

    if (!hasOwner && recordShares.length === 0) {
      // No ownership and no shares - user can't see anything
      query.where(knex.raw('1 = 0'));
      return;
    }

    // Build conditions: ownerId = user OR record shared with user
    query.where((builder) => {
      if (hasOwner) {
        builder.orWhere(`${tableName}.ownerId`, user.id);
      }

      if (recordShares.length > 0) {
        const sharedRecordIds = recordShares.map(share => share.recordId);
        builder.orWhereIn(`${tableName}.id`, sharedRecordIds);
      }
    });
  }

  /**
   * Check if user can perform action on a specific record
   */
  async canPerformAction(
    action: Action,
    objectDef: ObjectDefinition,
    record: any,
    user: User & { roles?: any[] },
    knex: Knex,
  ): Promise<boolean> {
    const recordShares = await this.getActiveRecordShares(objectDef.id, user.id, knex);
    const ability = await this.abilityFactory.defineAbilityFor(user, recordShares);

    // Check base permission - use object ID not API name
    if (!ability.can(action, objectDef.id)) {
      return false;
    }

    // Check special permissions - use object ID not API name
    const hasViewAll = ability.can('view_all', objectDef.id);
    const hasModifyAll = ability.can('modify_all', objectDef.id);

    // canViewAll only grants read access to all records
    if (action === 'read' && hasViewAll) {
      return true;
    }

    // canModifyAll grants edit/delete access to all records
    if ((action === 'update' || action === 'delete') && hasModifyAll) {
      return true;
    }

    // Check OWD
    switch (objectDef.orgWideDefault) {
      case 'public_read_write':
        return true;

      case 'public_read':
        if (action === 'read') return true;
        // For write actions, check ownership
        return record.ownerId === user.id;

      case 'private':
      default:
        // Check ownership
        if (record.ownerId === user.id) return true;

        // Check if record is shared with user
        const share = recordShares.find(s => s.recordId === record.id);
        if (share) {
          if (action === 'read' && share.accessLevel.canRead) return true;
          if (action === 'update' && share.accessLevel.canEdit) return true;
          if (action === 'delete' && share.accessLevel.canDelete) return true;
        }

        return false;
    }
  }

  /**
   * Filter data based on field-level permissions
   * Removes fields the user cannot read
   */
  async filterReadableFields(
    data: any,
    fields: FieldDefinition[],
    user: User & { roles?: any[] },
  ): Promise<any> {
    const filtered: any = {};

    // Always include id - it's required for navigation and record identification
    if (data.id !== undefined) {
      filtered.id = data.id;
    }

    for (const field of fields) {
      if (this.abilityFactory.canAccessField(field.id, 'read', user)) {
        if (data[field.apiName] !== undefined) {
          filtered[field.apiName] = data[field.apiName];
        }
        
        // For lookup fields, also include the related object (e.g., ownerId -> owner)
        if (field.type === 'LOOKUP') {
          const relationName = DynamicModelFactory.getRelationName(field.apiName);
          if (data[relationName] !== undefined) {
            filtered[relationName] = data[relationName];
          }
        }
      }
    }

    return filtered;
  }

  /**
   * Filter data based on field-level permissions
   * Removes fields the user cannot edit
   */
  async filterEditableFields(
    data: any,
    fields: FieldDefinition[],
    user: User & { roles?: any[] },
  ): Promise<any> {
    const filtered: any = {};

    for (const field of fields) {
      if (this.abilityFactory.canAccessField(field.id, 'edit', user)) {
        if (data[field.apiName] !== undefined) {
          filtered[field.apiName] = data[field.apiName];
        }
      }
    }

    return filtered;
  }

  /**
   * Get active record shares for a user on an object
   */
  private async getActiveRecordShares(
    objectDefinitionId: string,
    userId: string,
    knex: Knex,
  ): Promise<RecordShare[]> {
    const now = new Date();

    return await RecordShare.query(knex)
      .where('objectDefinitionId', objectDefinitionId)
      .where('granteeUserId', userId)
      .whereNull('revokedAt')
      .where((builder) => {
        builder.whereNull('expiresAt').orWhere('expiresAt', '>', now);
      });
  }

  /**
   * Check if user has permission to create records
   */
  async canCreate(
    objectDef: ObjectDefinition,
    user: User & { roles?: any[] },
  ): Promise<boolean> {
    const ability = await this.abilityFactory.defineAbilityFor(user, []);
    return ability.can('create', objectDef.id);
  }

  /**
   * Throw exception if user cannot perform action
   */
  async assertCanPerformAction(
    action: Action,
    objectDef: ObjectDefinition,
    record: any,
    user: User & { roles?: any[] },
    knex: Knex,
  ): Promise<void> {
    const can = await this.canPerformAction(action, objectDef, record, user, knex);
    if (!can) {
      throw new ForbiddenException(`You do not have permission to ${action} this record`);
    }
  }

  /**
   * Get table name from API name
   */
  private getTableName(apiName: string): string {
    // Convert CamelCase to snake_case and pluralize
    const snakeCase = apiName
      .replace(/([A-Z])/g, '_$1')
      .toLowerCase()
      .replace(/^_/, '');
    
    // Simple pluralization
    if (snakeCase.endsWith('y')) {
      return snakeCase.slice(0, -1) + 'ies';
    } else if (snakeCase.endsWith('s')) {
      return snakeCase;
    } else {
      return snakeCase + 's';
    }
  }
}