Master Serverless APIs: Azure Functions HTTP Triggers Deep Dive

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;

namespace CertHTTPFunctionApp
{
    public class CertificationFunctions
    {
        private readonly ILogger<CertificationFunctions> _logger;

        public CertificationFunctions(ILogger<CertificationFunctions> logger)
        {
            _logger = logger;
        }

        // Static list to simulate a database
        private static readonly List<Certification> _certifications = new()
        {
            new Certification { Id = 1, Name = "Azure Fundamentals", Category = "Fundamentals", Fee = 165, AvailableSlots = 150 },
            new Certification { Id = 2, Name = "AWS Certified Cloud Practitioner", Category = "Fundamentals", Fee = 100, AvailableSlots = 45 },
            new Certification { Id = 3, Name = "Azure Solutions Architect Expert", Category = "Architecture", Fee = 150, AvailableSlots = 80 },
            new Certification { Id = 4, Name = "AWS Certified SysOps Administrator – Associate", Category = "Administrator", Fee = 150, AvailableSlots = 200 }
        };

        // 1. DEMO: Query Strings
        // URL Example: GET /api/cert?category=Fundamentals&minFee=100
        [Function("GetCertificates")]
        public IActionResult GetCertificates(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "cert")] HttpRequest req)
        {
            _logger.LogInformation("Processing GetCertificates request.");
            
            string? category = req.Query["category"];
            string? minFeeStr = req.Query["minFee"];
            decimal? minFee = decimal.TryParse(minFeeStr, out decimal parsedFee) ? parsedFee : null;

            var query = _certifications.AsQueryable();

            if (!string.IsNullOrEmpty(category))
            {
                query = query.Where(p => p.Category.Equals(category, StringComparison.OrdinalIgnoreCase));
            }

            if (minFee.HasValue)
            {
                query = query.Where(p => p.Fee >= minFee.Value);
            }

            return new OkObjectResult(query.ToList());
        }

        // 2. DEMO: Route Parameters
        // URL Example: GET /api/cert/3
        [Function("GetCertificateById")]
        public IActionResult GetCertificateById(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "cert/{id:int}")] HttpRequest req,
            int id)
        {
            var cert = _certifications.FirstOrDefault(p => p.Id == id);
            if (cert == null)
            {
                return new NotFoundObjectResult(new { Message = $"Certificate with ID {id} not found." });
            }

            return new OkObjectResult(cert);
        }

        // 3. DEMO: Request Body
        // URL Example: POST /api/cert
        [Function("CreateCertificate")]
        public IActionResult CreateCertificate(
            [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = "cert")] HttpRequest req,
            [FromBody] Certification newCertificate)
        {
            if (newCertificate == null)
            {
                return new BadRequestObjectResult("Certificate data cannot be null.");
            }

            newCertificate.Id = _certifications.Max(p => p.Id) + 1;
            _certifications.Add(newCertificate);

            return new CreatedResult($"/api/cert/{newCertificate.Id}", newCertificate);
        }

        // 4. DEMO: MIXED SOURCES (Route + Body)
        // URL Example: PATCH /api/cert/2/slot
        [Function("UpdateStock")]
        public IActionResult UpdateStock(
            [HttpTrigger(AuthorizationLevel.Anonymous, "patch", Route = "cert/{id:int}/slot")] HttpRequest req,
            int id,
            [FromBody] UpdateSlotQuantity slotDto)
        {
            var cert = _certifications.FirstOrDefault(p => p.Id == id);
            if (cert == null)
            {
                return new NotFoundObjectResult(new { Message = $"Certificate with ID {id} not found." });
            }

            cert.AvailableSlots += slotDto.NewQuantity;

            return new OkObjectResult(new { Message = $"Slot for cert {id} updated successfully.", Certificate = cert });
        }

        // 5. DEMO: Route Parameter (DELETE)
        // URL Example: DELETE /api/cert/3
        [Function("DeleteCertificate")]
        public IActionResult DeleteCertificate(
            [HttpTrigger(AuthorizationLevel.Anonymous, "delete", Route = "cert/{id:int}")] HttpRequest req,
            int id)
        {
            var cert = _certifications.FirstOrDefault(p => p.Id == id);
            
            if (cert == null)
            {
                return new NotFoundObjectResult(new { Message = $"Certificate with ID {id} not found." });
            }

            _certifications.Remove(cert);

            return new OkObjectResult(new { Message = $"Certificate with ID {id} deleted successfully." });
        }
    }

    public class Certification
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Category { get; set; }
        public decimal Fee { get; set; }
        public int AvailableSlots { get; set; }
    }

    public class UpdateSlotQuantity
    {
        public int NewQuantity { get; set; }
    }
}