📌 Rate Calculator — Full Development Plan

• Project Description

The Rate Calculator is a modern tool for freelancers and independent professionals to confidently determine their optimal daily rates. It supports both home office (remote) and on-site rates, factoring in all relevant expenses, taxes, and business needs. With integrated AI support, it helps estimate costs, market prices, and even suggests adjustments based on your unique situation. The calculator makes it easy to compare remote and on-site scenarios, ensuring you never undercharge and always understand your true cost basis.

🗝️ Principles

• Simplicity first → flat, feature-based structure
• Functionality over ceremony → no forced layers
• HTMX stays → SPA not needed
• Server-driven logic → secure, predictable
• AI agent → structured, verifiable output
• Paddle handles payments → webhooks link to credits
• Users fully own data → deactivation & deletion possible (GDPR safe)
• Differentiates between home office and on-site rates, using AI to estimate and compare costs for each scenario

This document outlines the complete, ordered development plan for the Rate Calculator project.
Principle: Simplicity first — flat structure, functional organization, minimal layers.

✅ Phase 1 — Initial Setup [MVP]

Est. Duration: 2 days

Goal: Skeleton project starts cleanly with all core tech pieces and translation prep.

• Initialize Go module
• Setup sqlc config
• Setup golang-migrate with /cmd/migrate
• Add air config for live reload
• Create Makefile for common tasks
• Configure Tailwind CLI + DaisyUI
  • Build optimized CSS → embed with go:embed
• Setup .envrc + direnv for local env vars
• Add Sentry, Mailgun, OpenAI placeholders
• Setup Paddle sandbox keys (mock webhooks)
• Setup translation structure:
  • Add go-i18n or similar
  • Base .json or .yaml files for keys
  • Add dummy language toggle
• Deploy minimal server with /health route

🔲 Phase 2 — Database Design [MVP]

Est. Duration: 2 days

Goal: Complete schema with migration and type-safe queries.

• Define tables:
  • Users (Auth0 ID, profile, roles, is_admin, settings)
  • Rates (locations, currency, year, cost basis)
  • Expense Groups & Items (types, descriptions, mandatory/optional)
  • AI chat history
  • Credits (purchased, spent, balance)
  • Shared Rate Snapshots (title, text, fixed date)
  • Audit logs (admin actions)
  • Emails sent
• Write SQL migrations (golang-migrate)
• Generate queries with sqlc

🔲 Phase 3 — Authentication [MVP]

Est. Duration: 2 days

Goal: Secure, tested Auth0 integration.

• Auth0 register, login, logout flows
• Auth0 callback handler & JWT/session management
• Store user info → sync roles → set is_admin
• Data privacy handled by Auth0 consent
• CSRF protection for auth routes
• Secure routes with gorilla/sessions

🔲 Phase 4 — Payments & Credits [MVP]

Est. Duration: 4 days

Goal: Paddle-powered payment flow working with webhooks.

• Integrate Paddle live keys
• Implement webhooks to store purchases → top up credits
• Store invoices/credit transactions for history
• Send Mailgun emails:
  • Credit purchase confirmation + invoice
  • Shared link confirmation
• Handle deletion/refund edge cases
• Deactivation disables shared links

🔲 Phase 5 — User Core [MVP]

Est. Duration: 4 days

Goal: Usable dashboard basics for real work.

• Welcome page:
  • Crisp load, async session check
  • Show sign up/in or dashboard link
• Dashboard:
  • View all rates (private/shared)
  • Create new rate (asks for living/on-site place)
  • CRUD rates
  • Duplicate rates
  • Manage public links
  • Buy credits
  • View credit history
  • Sign out
  • Edit basic profile/settings

🔲 Phase 6 — Rate Editor [MVP]

Est. Duration: 7 days

Goal: Fully interactive calculation flow.

• Show living/on-site locations
• Expense groups:
  • Prefilled groups & items
  • Editable fields
  • Mandatory/optional toggle
  • Remote/on-site toggle
  • Cost type: monthly/yearly/%/per day/night/trip
  • Descriptions
• Table view for 7 rates:
  • Remote min/recommended
  • On-site min/max
  • Manual remote/on-site
  • Market price (AI/manual)
• Live recalculation on any change
• Currency select → backend conversion
• Year tagging
• Export PDF/CSV
• Sharing:
  • Pick which rates to share
  • Add title/text
  • Save frozen snapshot with fixed date
  • Limit active shares or upsell more slots

🔲 Phase 7 — AI Agent [MVP]

Est. Duration: 5 days

Goal: Smart automation for better estimates.

• Integrated AI chat in rate editor
• Send full state → OpenAI → receive structured output
• Replace local state on update
• Store full chat history with each rate
• Admin can adjust system prompt & templates
• Beta: track usage only, enforce limits later

🔲 Phase 8 — Admin Dashboard

Est. Duration: 2 days

Goal: Full operational control and oversight.

• Usage stats: users, rates, credits, AI usage
• User list: lock/unlock, promote/demote, reset (Auth0 API)
• Manual credit adjustments
• Logs / audit trail:
  • Role changes
  • Locks/unlocks
  • AI prompt updates
• Manage all shared rates → take down if needed
• System health: DB, migrations, AI quota
• Trigger system notifications/emails

🔲 Phase 9 — UX & Styling Polish

Est. Duration: 3 days

Goal: Visual consistency, final refinements.

• Final Tailwind & DaisyUI pass
• Clean, clear typography and spacing
• Good enough mobile tweaks (dashboard, editor)
• Smooth HTMX transitions
• Test real device flows

🔲 Phase 10 — Multi-language Support

Est. Duration: 2 days

Goal: Finish full translation layer.

• Use go-i18n for text keys
• Serve localized partials for HTMX
• Add language switcher
• Ensure all policy/legal text localized

smart-software-engineering.com — Rate Calculator Project — 2025