ai-usagebar 0.15.0

//! Moonshot / Kimi fetch — reads the account balance from
//! `/v1/users/me/balance` under the shared cache + flock primitives. The host
//! (and therefore the currency) is region-dependent: `api.moonshot.ai` → USD,
//! `api.moonshot.cn` → CNY. The caller passes the matching currency label.

use std::time::Duration;

use crate::cache::{Cache, MAX_STALE, acquire_lock_async};
use crate::error::{AppError, Result};
use crate::usage::{MoonshotSnapshot, finite_amount};
use crate::vendor::{MAX_BODY_BYTES, read_body_capped};

use super::types::{BalanceEnvelope, to_snapshot};

pub const BASE_GLOBAL: &str = "https://api.moonshot.ai";
pub const BASE_CN: &str = "https://api.moonshot.cn";
const HTTP_TIMEOUT: Duration = Duration::from_secs(10);
const LOCK_TIMEOUT: Duration = Duration::from_secs(15);

#[derive(Debug, Clone)]
pub struct Endpoints {
    pub balance: String,
}

impl Endpoints {
    /// Pick the host by region. Returns the endpoints plus the currency label
    /// implied by that host (`"CNY"` for `cn`, `"USD"` otherwise).
    pub fn for_region(region: &str) -> (Self, &'static str) {
        if region.eq_ignore_ascii_case("cn") {
            (
                Self {
                    balance: format!("{BASE_CN}/v1/users/me/balance"),
                },
                "CNY",
            )
        } else {
            (
                Self {
                    balance: format!("{BASE_GLOBAL}/v1/users/me/balance"),
                },
                "USD",
            )
        }
    }
}

impl Default for Endpoints {
    fn default() -> Self {
        Self::for_region("global").0
    }
}

#[derive(Debug, Clone)]
pub struct FetchOutcome {
    pub snapshot: MoonshotSnapshot,
    pub stale: bool,
    pub last_error: Option<(u16, String)>,
    pub cache_age: Option<Duration>,
}

pub async fn fetch_snapshot(
    client: &reqwest::Client,
    api_key: &str,
    cache: &Cache,
    endpoints: &Endpoints,
    cache_ttl: Duration,
    currency: &str,
) -> Result<FetchOutcome> {
    cache.ensure_dir()?;
    let _lock = acquire_lock_async(&cache.lock_path(), LOCK_TIMEOUT).await?;

    let target = target_key(endpoints, currency);

    if let Some(bytes) = cache.fresh_payload(cache_ttl)?
        && let Ok(outcome) = reuse_cache(&bytes, cache, false, &target)
    {
        return Ok(outcome);
    }

    match fetch_live(client, endpoints, api_key, currency).await {
        Ok(snap) => {
            let bytes = serde_json::to_vec(
                &serde_json::json!({ "target": target, "snapshot": serde_repr(&snap) }),
            )?;
            cache.write_payload(&bytes)?;
            Ok(FetchOutcome {
                snapshot: snap,
                stale: false,
                last_error: None,
                cache_age: Some(Duration::ZERO),
            })
        }
        Err(e) if e.is_transient() => fallback_silent(cache, &target, e),
        Err(AppError::Http { status, body }) => {
            cache.mark_stale();
            cache.write_last_error(status, &body);
            let diag = (status, body.clone());
            fallback_with_error(cache, Some(diag), &target, AppError::Http { status, body })
        }
        Err(e) => {
            cache.mark_stale();
            cache.write_last_error(0, &e.to_string());
            let diag = (0, e.to_string());
            fallback_with_error(cache, Some(diag), &target, e)
        }
    }
}

/// Identity of the account+region the cached figure belongs to. `.ai` reports
/// USD and `.cn` reports CNY, so a cached number is meaningless — and actively
/// misleading — once the user points the vendor at the other region.
fn target_key(endpoints: &Endpoints, currency: &str) -> String {
    format!("{}|{}", endpoints.balance, currency)
}

fn fallback_silent(cache: &Cache, target: &str, original: AppError) -> Result<FetchOutcome> {
    let Some(bytes) = cache.fallback_payload(MAX_STALE)? else {
        return Err(original);
    };
    reuse_cache(&bytes, cache, true, target)
}

/// On failure we show the last good figure with the error alongside it. With
/// nothing usable cached there is nothing to show, so the **original** error is
/// returned rather than a generic "no usable cache" that hides what went wrong.
fn fallback_with_error(
    cache: &Cache,
    last_error: Option<(u16, String)>,
    target: &str,
    original: AppError,
) -> Result<FetchOutcome> {
    let Some(bytes) = cache.fallback_payload(MAX_STALE)? else {
        return Err(original);
    };
    // A cache we cannot attribute to this target is no better than no cache.
    let Ok(mut outcome) = reuse_cache(&bytes, cache, true, target) else {
        return Err(original);
    };
    outcome.last_error = last_error;
    Ok(outcome)
}

fn reuse_cache(bytes: &[u8], cache: &Cache, stale: bool, target: &str) -> Result<FetchOutcome> {
    let snap = parse_cache(bytes, target)?;
    Ok(FetchOutcome {
        snapshot: snap,
        stale,
        last_error: cache.read_last_error(),
        cache_age: cache.payload_age(),
    })
}

fn serde_repr(snap: &MoonshotSnapshot) -> serde_json::Value {
    serde_json::json!({
        "available": snap.available,
        "voucher": snap.voucher,
        "cash": snap.cash,
        "currency": snap.currency,
    })
}

fn parse_cache(bytes: &[u8], target: &str) -> Result<MoonshotSnapshot> {
    let v: serde_json::Value = serde_json::from_slice(bytes)?;
    // Payloads written before the target was recorded cannot be attributed to
    // a region/currency, so they are discarded rather than shown against this one.
    let cached_target = v.get("target").and_then(serde_json::Value::as_str);
    if cached_target != Some(target) {
        return Err(AppError::Schema(format!(
            "moonshot cache belongs to a different endpoint/currency ({}); refetching",
            cached_target.unwrap_or("unknown")
        )));
    }
    let s = v
        .get("snapshot")
        .ok_or_else(|| AppError::Schema("moonshot cache missing 'snapshot' field".into()))?;
    let field = |name: &str| -> Result<f64> {
        let v = s[name]
            .as_f64()
            .ok_or_else(|| AppError::Schema(format!("moonshot cache missing '{name}'")))?;
        finite_amount("moonshot cache", name, v)
    };
    Ok(MoonshotSnapshot {
        available: field("available")?,
        voucher: field("voucher")?,
        cash: field("cash")?,
        currency: s["currency"]
            .as_str()
            .ok_or_else(|| AppError::Schema("moonshot cache missing 'currency'".into()))?
            .to_string(),
    })
}

async fn fetch_live(
    client: &reqwest::Client,
    endpoints: &Endpoints,
    api_key: &str,
    currency: &str,
) -> Result<MoonshotSnapshot> {
    let resp = tokio::time::timeout(
        HTTP_TIMEOUT,
        client
            .get(&endpoints.balance)
            .header("Authorization", format!("Bearer {api_key}"))
            .send(),
    )
    .await
    .map_err(|_| AppError::Transport(format!("moonshot timeout: {}", endpoints.balance)))??;

    let status = resp.status();
    let bytes = read_body_capped(resp, MAX_BODY_BYTES).await?;

    if !status.is_success() {
        let body = String::from_utf8_lossy(&bytes).chars().take(200).collect();
        return Err(AppError::Http {
            status: status.as_u16(),
            body,
        });
    }
    let env: BalanceEnvelope = serde_json::from_slice(&bytes)
        .map_err(|e| AppError::Schema(format!("moonshot {}: {e}", endpoints.balance)))?;
    // A 200 can still carry the documented in-band failure indicators.
    env.check_ok()?;
    to_snapshot(env.data, currency)
}

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

    fn cache_fixture() -> (TempDir, Cache) {
        let td = TempDir::new().unwrap();
        let cache = Cache::at(td.path().join("moonshot"));
        cache.ensure_dir().unwrap();
        (td, cache)
    }

    #[test]
    fn region_picks_host_and_currency() {
        let (global, cur) = Endpoints::for_region("global");
        assert!(global.balance.starts_with("https://api.moonshot.ai"));
        assert_eq!(cur, "USD");
        let (cn, cur_cn) = Endpoints::for_region("cn");
        assert!(cn.balance.starts_with("https://api.moonshot.cn"));
        assert_eq!(cur_cn, "CNY");
    }

    #[tokio::test]
    async fn live_fetch_reads_available_balance() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/v1/users/me/balance")
            .match_header("authorization", "Bearer ms-test")
            .with_status(200)
            .with_body(
                r#"{"code":0,"data":{"available_balance":49.58894,
                    "voucher_balance":46.58893,"cash_balance":3.00001},
                    "scode":"0x0","status":true}"#,
            )
            .create_async()
            .await;

        let (_td, cache) = cache_fixture();
        let client = reqwest::Client::new();
        let endpoints = Endpoints {
            balance: format!("{}/v1/users/me/balance", server.url()),
        };
        let out = fetch_snapshot(
            &client,
            "ms-test",
            &cache,
            &endpoints,
            Duration::from_secs(0),
            "USD",
        )
        .await
        .unwrap();
        assert!((out.snapshot.available - 49.58894).abs() < 1e-6);
        assert_eq!(out.snapshot.currency, "USD");
        assert!(!out.stale);
    }

    #[tokio::test]
    async fn http_error_falls_back_to_cache_when_present() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/v1/users/me/balance")
            .with_status(401)
            .with_body(r#"{"error":"auth"}"#)
            .create_async()
            .await;

        let (_td, cache) = cache_fixture();
        let endpoints = Endpoints {
            balance: format!("{}/v1/users/me/balance", server.url()),
        };
        let seed = serde_json::json!({
            "target": target_key(&endpoints, "USD"),
            "snapshot": {
                "available": 49.0, "voucher": 46.0, "cash": 3.0, "currency": "USD"
            },
        });
        cache.write_payload(seed.to_string().as_bytes()).unwrap();

        let client = reqwest::Client::new();
        let out = fetch_snapshot(
            &client,
            "k",
            &cache,
            &endpoints,
            Duration::from_secs(0),
            "USD",
        )
        .await
        .unwrap();
        assert!(out.stale);
        assert_eq!(out.snapshot.available, 49.0);
        assert_eq!(out.last_error.as_ref().map(|(c, _)| *c), Some(401));
    }

    #[tokio::test]
    async fn in_band_failure_on_200_is_not_a_zero_balance() {
        // The documented failure shape: HTTP 200 with status:false.
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/v1/users/me/balance")
            .with_status(200)
            .with_body(r#"{"code":40100,"data":{"available_balance":0.0,"voucher_balance":0.0,"cash_balance":0.0},"status":false,"scode":"0x1"}"#)
            .create_async()
            .await;

        let (_td, cache) = cache_fixture();
        let client = reqwest::Client::new();
        let endpoints = Endpoints {
            balance: format!("{}/v1/users/me/balance", server.url()),
        };
        let out = fetch_snapshot(
            &client,
            "k",
            &cache,
            &endpoints,
            Duration::from_secs(0),
            "USD",
        )
        .await;
        assert!(out.is_err(), "expected a schema error, got {out:?}");
    }

    #[tokio::test]
    async fn switching_region_refetches_instead_of_reusing_the_cache() {
        // A CNY figure cached for .cn must never be shown as the .ai USD balance.
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/v1/users/me/balance")
            .with_status(200)
            .with_body(
                r#"{"code":0,"data":{"available_balance":12.0,"voucher_balance":0.0,
                    "cash_balance":12.0},"status":true}"#,
            )
            .create_async()
            .await;

        let (_td, cache) = cache_fixture();
        let endpoints = Endpoints {
            balance: format!("{}/v1/users/me/balance", server.url()),
        };
        // Fresh, but cached against the CNY target.
        let seed = serde_json::json!({
            "target": target_key(&endpoints, "CNY"),
            "snapshot": {
                "available": 999.0, "voucher": 0.0, "cash": 999.0, "currency": "CNY"
            },
        });
        cache.write_payload(seed.to_string().as_bytes()).unwrap();

        let client = reqwest::Client::new();
        let out = fetch_snapshot(
            &client,
            "k",
            &cache,
            &endpoints,
            Duration::from_secs(3600),
            "USD",
        )
        .await
        .unwrap();
        assert_eq!(out.snapshot.available, 12.0);
        assert_eq!(out.snapshot.currency, "USD");
        assert!(!out.stale);
    }
}