- Move calculateDataOverage, calculateVoiceOverage, calculateSMSOverage, calculateDiscounts, and calculateRecommendedPrice to price_calculation.go
- Remove validation helper methods from pricing_engine.go
- Remove PriceOptimization and CostBreakdown type definitions
- Update Logger interface to use `any` instead of `interface{}`
- Remove inline comments throughout pricing_engine.go
- Add switch statement for discount type handling in calculateDiscounts
- Add PricingEngine struct with repository and logger fields
- Add ValidateRatePlan with comprehensive validation for fields, dates, allowances, overage rates, discounts, and early termination
- Add CalculateOptimalPrice with market analysis and recommended pricing based on competitor data
- Add ValidateSubscription with plan availability, validity dates, and discount validation
- Add CalculateSubscriptionCost with base
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