feat(pricing): implement 4-tier pricing engine and migration (#1)

migrations/add_tiered_pricing.sql

@@ -1,6 +1,4 @@
--- Migration: Add tiered pricing support (Issue #1)
--- Idempotent: safe to run multiple times
-
+-- Migration: Add tiered pricing support (Issue #1)
 ALTER TABLE IF EXISTS x402_calls
   ADD COLUMN IF NOT EXISTS tier TEXT DEFAULT 'standard' CHECK (tier IN ('free', 'standard', 'premium', 'priority')),
   ADD COLUMN IF NOT EXISTS price_per_call NUMERIC(10, 6) DEFAULT 0.01,

src/pricing/tier-engine.ts

@@ -1,23 +1,11 @@
-/**
- * Tiered Pricing Engine — Issue #1
- * Implements 4-tier pricing for x402 API calls
- */
-
-export type Tier = 'free' | 'standard' | 'premium' | 'priority';
+export type Tier = 'free' | 'standard' | 'premium' | 'priority';
 
 export interface TierResult {
   tier: Tier;
   pricePerCall: number; // in USDC
   callsInTier: number;
 }
 
-/**
- * Returns the price per call based on total call count and priority flag.
- * - Tier 1 (Free):     calls 1–50     → $0.00
- * - Tier 2 (Standard): calls 51–500  → $0.01
- * - Tier 3 (Premium):  calls 500+    → $0.03
- * - Tier 4 (Priority): priority=true → $0.10
- */
 export function getTierPrice(callCount: number, priorityFlag = false): TierResult {
   if (priorityFlag) {
     return { tier: 'priority', pricePerCall: 0.10, callsInTier: 1 };
@@ -31,13 +19,10 @@ export function getTierPrice(callCount: number, priorityFlag = false): TierResul
   return { tier: 'premium', pricePerCall: 0.03, callsInTier: Infinity };
 }
 
-/**
- * Calculates total cost for a batch of calls.
- */
 export function calculateBatchCost(startCount: number, numCalls: number, priority = false): number {
   let total = 0;
   for (let i = 0; i < numCalls; i++) {
     total += getTierPrice(startCount + i, priority).pricePerCall;
   }
-  return Math.round(total * 1e6) / 1e6; // round to 6 decimals (USDC precision)
+  return Math.round(total * 1e6) / 1e6;
 }

tests/pricing.test.ts

@@ -0,0 +1,29 @@
+import { assertEquals } from 'https://deno.land/std@0.224.0/assert/mod.ts';
+import { getTierPrice, calculateBatchCost } from '../src/pricing/tier-engine.ts';
+
+Deno.test('Tier 1: free for first 50 calls', () => {
+  assertEquals(getTierPrice(1).tier, 'free');
+  assertEquals(getTierPrice(50).tier, 'free');
+  assertEquals(getTierPrice(1).pricePerCall, 0.00);
+});
+
+Deno.test('Tier 2: standard for calls 51-500', () => {
+  assertEquals(getTierPrice(51).tier, 'standard');
+  assertEquals(getTierPrice(500).tier, 'standard');
+  assertEquals(getTierPrice(51).pricePerCall, 0.01);
+});
+
+Deno.test('Tier 3: premium for calls 500+', () => {
+  assertEquals(getTierPrice(501).tier, 'premium');
+  assertEquals(getTierPrice(501).pricePerCall, 0.03);
+});
+
+Deno.test('Tier 4: priority flag overrides all', () => {
+  assertEquals(getTierPrice(1, true).tier, 'priority');
+  assertEquals(getTierPrice(1000, true).pricePerCall, 0.10);
+});
+
+Deno.test('Batch cost calculation', () => {
+  assertEquals(calculateBatchCost(1, 10), 0);
+  assertEquals(calculateBatchCost(51, 1), 0.01);
+});