getTasks.js

/**
 * Lambda Function: GetTasks
 * Purpose: Retrieve all tasks for a user from DynamoDB
 * Trigger: API Gateway GET /tasks
 */

const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');
const { DynamoDBDocumentClient, QueryCommand } = require('@aws-sdk/lib-dynamodb');

// Initialize DynamoDB client
const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

// Table name from environment variable
const TABLE_NAME = process.env.TABLE_NAME || 'TasksTable';

/**
 * Main Lambda handler
 */
exports.handler = async (event) => {
    console.log('Event received:', JSON.stringify(event, null, 2));
    
    try {
        // Extract user ID from Cognito authorizer context
        const userId = event.requestContext.authorizer.claims.sub || 
                      event.requestContext.authorizer.claims['cognito:username'];
        
        if (!userId) {
            return createResponse(401, { message: 'Unauthorized: No user ID found' });
        }
        
        // Query DynamoDB for user's tasks
        const params = {
            TableName: TABLE_NAME,
            KeyConditionExpression: 'userId = :userId',
            ExpressionAttributeValues: {
                ':userId': userId
            },
            ScanIndexForward: false // Sort by most recent first
        };
        
        const result = await docClient.send(new QueryCommand(params));
        
        console.log(`Found ${result.Items.length} tasks for user ${userId}`);
        
        // Return tasks
        return createResponse(200, {
            tasks: result.Items || [],
            count: result.Items.length
        });
        
    } catch (error) {
        console.error('Error retrieving tasks:', error);
        
        return createResponse(500, {
            message: 'Internal server error',
            error: error.message
        });
    }
};

/**
 * Helper function to create API Gateway response
 */
function createResponse(statusCode, body) {
    return {
        statusCode: statusCode,
        headers: {
            'Content-Type': 'application/json',
            'Access-Control-Allow-Origin': '*', // Configure based on your domain
            'Access-Control-Allow-Headers': 'Content-Type,Authorization',
            'Access-Control-Allow-Methods': 'GET,POST,PUT,DELETE,OPTIONS'
        },
        body: JSON.stringify(body)
    };
}

/**
 * DEPLOYMENT INSTRUCTIONS:
 * 
 * 1. Create Lambda function in AWS Console
 * 2. Set runtime to Node.js 18.x or later
 * 3. Add environment variable:
 *    - Key: TABLE_NAME
 *    - Value: TasksTable
 * 
 * 4. Update Lambda execution role with DynamoDB permissions:
 *    {
 *        "Effect": "Allow",
 *        "Action": [
 *            "dynamodb:Query",
 *            "dynamodb:GetItem"
 *        ],
 *        "Resource": "arn:aws:dynamodb:REGION:ACCOUNT_ID:table/TasksTable"
 *    }
 * 
 * 5. Install dependencies (if using deployment package):
 *    npm init -y
 *    npm install @aws-sdk/client-dynamodb @aws-sdk/lib-dynamodb
 *    
 * 6. For Lambda Layer (recommended):
 *    Create layer with node_modules containing the above packages
 * 
 * 7. Configure API Gateway:
 *    - Method: GET
 *    - Resource: /tasks
 *    - Authorization: Cognito User Pool
 *    - Enable CORS
 */