max / makenotwork

2.8 KB · 93 lines History Blame Raw

1	//! Stripe billing helpers: fee estimation and timestamp conversion.
2
3	/// Convert a Unix timestamp from Stripe into a UTC datetime, falling back to now.
4	pub fn stripe_timestamp(ts: i64) -> chrono::DateTime<chrono::Utc> {
5	chrono::DateTime::from_timestamp(ts, 0).unwrap_or_else(chrono::Utc::now)
6	}
7
8	/// Estimate Stripe's processing fee and the net amount the creator receives.
9	///
10	/// Returns `(fee_cents, creator_receives_cents)`. Uses the standard
11	/// Stripe rate from [`constants`](crate::constants).
12	pub fn estimate_stripe_fee(price_cents: i32) -> (i32, i32) {
13	if price_cents <= 0 {
14	return (0, 0);
15	}
16	let fee = (price_cents as f64 * crate::constants::STRIPE_FEE_PERCENTAGE
17	+ crate::constants::STRIPE_FEE_FIXED_CENTS) as i32;
18	let creator_receives = (price_cents - fee).max(0);
19	(fee.min(price_cents), creator_receives)
20	}
21
22	#[cfg(test)]
23	mod tests {
24	use super::*;
25
26	// ── estimate_stripe_fee ──
27
28	#[test]
29	fn stripe_fee_standard_price() {
30	let (fee, receives) = estimate_stripe_fee(1000);
31	assert_eq!(fee, 59);
32	assert_eq!(receives, 941);
33	}
34
35	#[test]
36	fn stripe_fee_small_price() {
37	let (fee, receives) = estimate_stripe_fee(100);
38	assert_eq!(fee, 32);
39	assert_eq!(receives, 68);
40	}
41
42	#[test]
43	fn stripe_fee_zero_is_free() {
44	let (fee, receives) = estimate_stripe_fee(0);
45	assert_eq!(fee, 0);
46	assert_eq!(receives, 0);
47	}
48
49	#[test]
50	fn stripe_fee_negative_price() {
51	let (fee, receives) = estimate_stripe_fee(-100);
52	assert_eq!(fee, 0);
53	assert_eq!(receives, 0);
54	}
55
56	#[test]
57	fn stripe_fee_plus_receives_equals_price() {
58	for price in [50, 100, 250, 500, 999, 1000, 2500, 5000, 10000, 50000] {
59	let (fee, receives) = estimate_stripe_fee(price);
60	assert_eq!(
61	fee + receives,
62	price,
63	"fee + receives should equal price for {price} cents"
64	);
65	}
66	}
67
68	// ── stripe_timestamp ──
69
70	#[test]
71	fn stripe_timestamp_zero() {
72	assert_eq!(stripe_timestamp(0).timestamp(), 0);
73	}
74
75	#[test]
76	fn stripe_timestamp_valid() {
77	assert_eq!(stripe_timestamp(1_714_400_000).timestamp(), 1_714_400_000);
78	}
79
80	// ── Property-based tests ──
81
82	proptest::proptest! {
83	#[test]
84	fn prop_stripe_fee_invariant(price in 1..=1_000_000i32) {
85	let (fee, receives) = estimate_stripe_fee(price);
86	proptest::prop_assert_eq!(fee + receives, price,
87	"fee ({}) + receives ({}) must equal price ({})", fee, receives, price);
88	proptest::prop_assert!(fee > 0, "Fee should be positive for price {}", price);
89	proptest::prop_assert!(receives >= 0, "Receives should be non-negative");
90	}
91	}
92	}
93