I'm rebuilding a 10+ year old German e-commerce shop (custom-cut foam products) from CodeIgniter 3 to CodeIgniter 4 as a clean-slate rebuild. 13 detailed specs are already written (5,246 lines), 18 Architecture Decision Records are finalized, the server is provisioned, and a blank CI4 v4.7.2 is running. I need an experienced CI4 developer to implement the specs — not design the architecture. ~200–350h estimated. Fixed-price per spec preferred. No agencies. No Laravel pivots. What's Already Done (So You Can Focus on Code) Most CI4 projects on Freelancer are greenfield or vague. This one is spec-driven and fully documented. You won't have to guess: Already CompletedStatusCI4 v4.7.2 installed via Composer on DomainFactory (PHP 8.3.30)✅ Live at a private GitHub repos (CI4 write, CI3 read-only reference)✅ Access provided after hire13 feature specs (5,246 lines, implementation-ready)✅18 Architecture Decision Records (ADR-001 to ADR-018)✅Contracts: naming conventions, URL map, DB schema, service interfaces✅CI3 reference documentation (35+ files: controller/model/view/route maps)✅Project Constitution (CLAUDE.md) — 10 strict implementation rules✅SFTP deployment workflow documented✅ You do not design, you implement. All 18 ADRs are decided. Specs tell you exactly what to build. The Project Topschaum.de sells custom-cut foam products (mattresses, cushions, acoustic foam). Customers configure dimensions → we cut to order. Live shop, generating revenue. CI3 codebase stats (what we're leaving behind): 42 controllers (Products.php alone: 3,831 LOC, Checkout.php: 2,134 LOC) 950 view files across 9 theme directories (Desktop/Mobile/Tablet variants) 56 DB tables, 21 libraries (Stripe, PayPal, MPDF, Ion Auth, Grocery CRUD) 22 security issues flagged in audit Monolithic controllers with business logic embedded, typos that cannot be renamed (SEO/DB constraints) CI4 target architecture: CodeIgniter 4.7.2 on PHP 8.2+ Tailwind CSS + Alpine.js (NO jQuery, NO Bootstrap) CI4 Shield for auth (NOT Ion Auth) Stripe Payment Intents + Express Checkout (Two-Element Pattern) Mobile-first, ONE responsive template (no device themes) MySQL (existing tables frozen — orders structure stays identical) MPDF via PdfService, Grocery CRUD Enterprise for simple admin tables URLs preserved 1:1 with CI3 (SEO-critical) The 13 Specs (Implementation Order) Phase 1: Foundation Base Config (153 LOC spec) — Environment, DB, Tailwind, Alpine, base layout Layout (245 LOC) — Header, footer, navigation, homepage — single responsive template Auth (251 LOC) — CI4 Shield setup, login, register, password reset, profile Phase 2: Products (the hard part) Products + Configurator (786 LOC) — Most complex spec. 25+ shapes, GeometryService (volume/surface formulas), PriceService (3-layer pricing: foam base + cover + options), real-time configurator UI Catalog & Co. (304 LOC) — Category browse, reviews, wishlist, sample service Phase 3: Checkout Flow Cart (355 LOC) — DB-persistent cart (new carts + cart_items tables), CartService, coupon application Checkout + Stripe (698 LOC) — Second hardest. Two-Element Stripe pattern, webhook-driven order creation, PaymentIntents API Phase 4: Backend & Admin Content Pages (258 LOC) — CMS: static pages + blog + Infothek Admin Panel (781 LOC) — Grocery CRUD Enterprise (19 simple tables) + 7 custom controllers (Orders, Analytics, Commission) Orders + Commission (611 LOC) — OrderModel/Entity, CommissionService (PLZ → Bundesland → commission region), PdfService (invoices, delivery notes, dunning) Email (338 LOC) — MessageService (queue + immediate), 22 templates → CI4 shared layout Contact (226 LOC) — 3 forms (contact, callback, sleep analysis), honeypot spam protection Cron (240 LOC) — Token auth, email dispatch, order cancellation Service Interfaces (Core Architecture) GeometryService → calculateVolume(), calculateSurface(), getShapeFactor() PriceService → calculatePrice(), applyVolumeDiscount(), applyCoupon() CartService → getActiveCart(), addItem(), updateQuantity(), calculateTotals() StripeService → createPaymentIntent(), handleWebhook(), createExpressCheckout() ShippingService → calculateShippingCost(), getFreeThreshold() OrderService → createFromCart(), updateStatus(), getOrderHistory() CommissionService → calculateCommission(), getByRegion(), generateReport() MessageService → queueEmail(), sendImmediately(), processQueue() PdfService → generateInvoice(), generateDeliveryNote(), generateDunning() Critical Business Logic (Must Port 1:1) Price calculation: 3 layers (foam base + cover + options) across 25+ shapes with individual volume/surface formulas Checkout flow: PaymentIntent created on page load, Order created only on "Place Order" click → many PIs without Orders is normal and expected Commission: PLZ → Bundesland → commission region (internal analytics only) PDF hash: md5($orderId . $email . '1789') — must stay identical so old customer links work URL structure: Every CI3 URL must work in CI4 (SEO-critical) Typos that must be preserved: CalculatePercentageDiffrence, calculate_varation_price (DB/SEO constraints) Must-Have Skills ✅ CodeIgniter 4 — real project experience (not "I know Laravel, I'll read the docs") ✅ Stripe Payment Intents + Express Checkout — webhook-driven payments ✅ Tailwind CSS + Alpine.js — clean UI implementation ✅ PHP 8.2+ — named arguments, enums, typed properties, fibers ✅ MySQL — migrations, existing tables, Query Builder + Entity pattern ✅ Git — feature-branch workflow, clean PRs against main Nice-to-Have CI3 → CI4 migration experience MPDF for PDF generation Grocery CRUD Enterprise E-commerce backend experience Disqualifying ❌ No CI4 code on GitHub in the last 12 months ❌ "I know Laravel, CI4 is similar" (it isn't — different kernel, different patterns) ❌ Agency or white-label team (if you bid as an individual, you work as an individual — contract violation if discovered) ❌ Copy-paste proposals that don't answer the screening questions below Screening Questions (Answer All 4 In Your Proposal) Proposals missing any of these will be ignored. 1. CI4 Architecture Explain the difference between CI4 Services (service() / Config\Services) and CI3's $this->load->library(). When would you use a Service vs. a Library in CI4? 2. Routing & Filters How do you implement a CI4 filter chain for routes that need authentication + CSRF + rate limiting? Show the filter registration and route grouping. 3. Stripe Two-Element Pattern We use Stripe's Two-Element Pattern (Card Element on checkout + Express Checkout on cart). How do you handle the case where a customer starts Express Checkout on the cart page but then navigates to the regular checkout? How do you prevent duplicate PaymentIntents? 4. Your CI4 Track Record Link to ONE CI4 project on GitHub (public or private with walkthrough) that you personally built. Tell me what you wrote vs. what was a team effort. Verification Before Contract GitHub profile review — real CI4 commits in the last 12 months Video call with the actual developer (not sales/PM from an agency) Paid test task: Implement Spec 001 (Base Config) — approx. 4–8h, shows whether you can read a spec and respect the contracts. Paid, whether we continue or not. Contract clause: "No agencies, no white-label teams. If discovered, contract is terminated and no further payments are due." Engagement & Budget Fixed-price per spec strongly preferred (quote each phase separately) ~200–350h total estimate, depending on your speed and experience Weekly progress reviews via GitHub PRs SFTP deployment (no CI/CD, no Docker) — developer uploads to dev server, tests, opens PR Long-term potential: If this goes well, ongoing retainer for both shops (topschaum.de + dein-polster.com), 10–20h/month Budget is open and negotiable for the right developer. This is not a $8/hour job. If you're the right person, you'll earn fair rates and have clean specs to work against. How to Apply Your proposal must contain, in this order: Answers to all 4 screening questions above (not one-liners — show you understand) One CI4 project link you built (GitHub URL or screencast walkthrough) Estimated hours per spec phase (Phase 1, 2, 3, 4 separately) Your fixed-price quote per phase OR hourly rate if you prefer T&M Confirmation: "I am an individual freelancer, not an agency, and I will personally write the code." No generic cover letters. No "I can start immediately and deliver in 3 days." Read the specs-driven structure above and respond to it. Skills tags: CodeIgniter 4, PHP 8.2, Stripe Payment Intents, Tailwind CSS, Alpine.js, MySQL, CI4 Shield, MPDF, E-Commerce, CI3 Migration, Spec-driven Development Looking forward to reading your proposal.