//! SyncKit developer billing: pricing formula and constants.
//!
//! Two modes:
//!
//!   bulk     — price = storage_gb_cap × $0.03
//!   per_key  — price = key_cap × gb_per_key × $0.03
//!
//! Both are pure GB-based pricing. Egress and ingress are absorbed by the
//! storage rate's ~2× margin against Cloudflare R2 ($0.015/GB) where SyncKit
//! blobs are hosted.
//!
//! Invoices are floored at a Stripe-fee-cover threshold so we never lose money
//! on a transaction. See `BASE_FLOOR_CENTS` for the math.

/// Storage rate in cents per GB per month. Calibrated to ~2× R2 cost
/// ($0.015/GB storage, $0 egress on R2). The 2× margin spread absorbs any
/// ingress/egress cost variance, so we don't need a separate egress price.
pub const STORAGE_RATE_CENTS_PER_GB: i64 = 3;

/// Stripe-fee-cover floor in cents. Stripe charges 2.9% + $0.30 per
/// successful charge. We pick the smallest invoice `F` (cents) such that the
/// remainder after Stripe fees is non-negative:
///
///   F × (1 − 0.029) − 30 ≥ 0   ⇒   F ≥ 30 / 0.971   ⇒   F ≥ 30.9¢
///
/// Round up to 31¢. At the floor, MNW nets ~$0 — covered, not profitable.
pub const BASE_FLOOR_CENTS: i64 = 31;

/// Warning thresholds (percent of storage cap). Matches CHECK constraint on
/// `sync_app_usage_current.last_warning_pct`. Only storage is enforced, so
/// these thresholds apply to storage usage only.
pub const WARNING_THRESHOLDS_PCT: &[i16] = &[75, 90, 100];

/// Compute the monthly Stripe invoice amount in cents for a given knob set.
///
/// In bulk mode: `storage_gb_cap` is set, others are `None`.
/// In per_key mode: `key_cap` and `gb_per_key` are set, `storage_gb_cap` is `None`.
///
/// Floors at `BASE_FLOOR_CENTS` so we never invoice below the Stripe-fee
/// break-even amount.
pub fn monthly_price_cents(
    enforcement_mode: &str,
    storage_gb_cap: Option<u32>,
    key_cap: Option<u32>,
    gb_per_key: Option<u32>,
) -> i64 {
    // Pure integer-cents arithmetic. The rate is a whole number of cents and
    // the caps are whole GB, so there is no fractional money to round; the old
    // `(gb as f64 * 3.0).ceil()` was an unnecessary trip through f64. Saturating
    // multiplies keep absurd admin-set caps from overflowing i64 instead of
    // wrapping to a negative invoice.
    let gb: i64 = match enforcement_mode {
        "bulk" => i64::from(storage_gb_cap.unwrap_or(0)),
        "per_key" => {
            let k = i64::from(key_cap.unwrap_or(0));
            let g = i64::from(gb_per_key.unwrap_or(0));
            k.saturating_mul(g)
        }
        _ => 0,
    };
    let raw = gb.saturating_mul(STORAGE_RATE_CENTS_PER_GB);
    raw.max(BASE_FLOOR_CENTS)
}

/// Storage cap in bytes for the given GB cap.
pub fn storage_cap_bytes(storage_gb: u32) -> i64 {
    i64::from(storage_gb) * 1024 * 1024 * 1024
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn bulk_mode_pricing() {
        // 100 GB bulk → 100 × 3 = 300 cents.
        assert_eq!(monthly_price_cents("bulk", Some(100), None, None), 300);
        // 1000 GB → $30.
        assert_eq!(monthly_price_cents("bulk", Some(1000), None, None), 3000);
    }

    #[test]
    fn per_key_mode_pricing() {
        // 50 keys × 2 GB = 100 GB equivalent → 300 cents. Matches 100 GB bulk.
        assert_eq!(monthly_price_cents("per_key", None, Some(50), Some(2)), 300);
        // 1000 keys × 1 GB → $30.
        assert_eq!(monthly_price_cents("per_key", None, Some(1000), Some(1)), 3000);
    }

    #[test]
    fn floor_kicks_in_for_small_accounts() {
        // 1 GB bulk → 3¢ raw, floored to 31¢.
        assert_eq!(monthly_price_cents("bulk", Some(1), None, None), 31);
        // 10 GB → 30¢, also floored to 31¢ (one cent short).
        assert_eq!(monthly_price_cents("bulk", Some(10), None, None), 31);
        // 11 GB → 33¢, above floor.
        assert_eq!(monthly_price_cents("bulk", Some(11), None, None), 33);
        // 1 key × 1 GB → 3¢ raw, floored.
        assert_eq!(monthly_price_cents("per_key", None, Some(1), Some(1)), 31);
    }

    #[test]
    fn heavy_workload_pricing() {
        // 10 TB bulk → 10240 × 3 = 30720¢ = $307.20.
        assert_eq!(monthly_price_cents("bulk", Some(10_240), None, None), 30_720);
        // 10k keys × 1 GB → same.
        assert_eq!(monthly_price_cents("per_key", None, Some(10_000), Some(1)), 30_000);
    }

    #[test]
    fn missing_knobs_drop_to_floor() {
        // Mode is set but no knobs provided — should hit the floor.
        assert_eq!(monthly_price_cents("bulk", None, None, None), BASE_FLOOR_CENTS);
        assert_eq!(monthly_price_cents("per_key", None, None, None), BASE_FLOOR_CENTS);
    }

    #[test]
    fn unknown_mode_drops_to_floor() {
        // Defensive: an unrecognized mode shouldn't blow up; it lands at the floor.
        assert_eq!(monthly_price_cents("unknown", Some(100), None, None), BASE_FLOOR_CENTS);
    }

    #[test]
    fn floor_amount_covers_stripe_fee() {
        // 31¢ × 0.971 = 30.10¢, minus 30¢ fixed fee = 0.10¢ net. Verifies the
        // documented math: the floor covers Stripe's fee with ~0 margin.
        let net = (BASE_FLOOR_CENTS as f64) * 0.971 - 30.0;
        assert!(net >= 0.0, "floor must net ≥ 0 after Stripe fees, got {net}");
        assert!(net < 1.0, "floor should be tight, not overshoot — got {net}");
    }

    #[test]
    fn storage_cap_in_bytes() {
        assert_eq!(storage_cap_bytes(10), 10 * 1024 * 1024 * 1024);
    }

    // ── Edge cases (test-fuzz) ──

    #[test]
    fn pricing_at_u32_max_does_not_panic() {
        // u32::MAX GB × 3¢ ≈ 1.3e10 cents, fits in i64. The cast must not panic.
        let p = monthly_price_cents("bulk", Some(u32::MAX), None, None);
        assert!(p > 0, "huge price should be positive, got {p}");
    }

    #[test]
    fn per_key_pricing_at_u32_max_saturates_cleanly() {
        // u32::MAX × u32::MAX overflows f64 precision but Rust's f64-as-i64 cast
        // saturates at i64::MAX rather than UB. Must not panic.
        let p = monthly_price_cents("per_key", None, Some(u32::MAX), Some(u32::MAX));
        assert!(p > 0, "saturated price should still be positive, got {p}");
    }

    #[test]
    fn storage_cap_at_u32_max_fits_in_i64() {
        // u32::MAX × 2^30 = ~4.6e18, well under i64::MAX (~9.2e18).
        let bytes = storage_cap_bytes(u32::MAX);
        assert!(bytes > 0, "u32::MAX GB should produce a positive i64");
        assert_eq!(bytes, (u32::MAX as i64) * 1024 * 1024 * 1024);
    }

    #[test]
    fn bulk_with_zero_gb_drops_to_floor() {
        // Defensive: validate_knobs rejects gb=0 at the route layer, but the
        // pure function should still produce the floor rather than 0.
        assert_eq!(monthly_price_cents("bulk", Some(0), None, None), BASE_FLOOR_CENTS);
    }

    #[test]
    fn per_key_one_dimension_zero_drops_to_floor() {
        // If only one of key_cap/gb_per_key is 0, the product is 0 → floor.
        assert_eq!(monthly_price_cents("per_key", None, Some(0), Some(10)), BASE_FLOOR_CENTS);
        assert_eq!(monthly_price_cents("per_key", None, Some(10), Some(0)), BASE_FLOOR_CENTS);
    }
}