//! 401 attribution callback hook for the sampling client.
//!
//! Every 401 response site can optionally emit an attribution event so
//! a downstream observer can split production 401s into "client sent a
//! stale snapshot bearer that the server rejected" vs. "client sent
//! the live token from its auth source and the server still rejected
//! it" buckets.
//!
//! `kigi-sampler` is intentionally decoupled from `kigi-shell`
//! (no shell types, no logging crate, no auth-manager dependency). The
//! caller wires an implementation of [`Auth401AttributionCallback`]
//! into [`crate::SamplerConfig::attribution_callback`]; the sampler
//! invokes the callback at each UNAUTHORIZED arm with the bearer that
//! was actually sent on the wire. The implementation is free to join
//! the bearer with whatever live credential source it owns and emit
//! the attribution however it wants.
//!
//! When the callback is `None` (the default), the 401 sites are silent
//! and return the same `SamplingError::Auth` they would otherwise.

use std::sync::Arc;

/// A logical 401-emitting site inside the sampling client. The string
/// identifier ends up in the consumer field of the attribution event
/// so downstream queries can break down 401s by API path.
///
/// # Scope: sampler endpoints only
///
/// This enum enumerates the six HTTP endpoints owned by
/// `SamplingClient` (chat completions, responses, messages -- each in
/// streaming and non-streaming form). It does *not* cover image
/// generation, video generation, web search, or embedding -- those
/// tools live in `kigi-tools`
/// (`crates/codegen/kigi-tools/src/implementations/`), have their
/// own HTTP clients that do not flow through `SamplingClient`, and
/// hook into the `kigi_tools::ApiKeyProvider` trait rather than
/// this enum.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SamplingConsumer {
    /// `chat_completion_stream`: OpenAI-compatible streaming OpenAI Chat Completions API.
    ChatCompletionsStream,
    /// `chat_completion`: OpenAI-compatible non-streaming OpenAI Chat Completions API.
    ChatCompletions,
    /// `create_response_stream`: Responses API streaming.
    ResponsesStream,
    /// `create_response`: Responses API non-streaming.
    Responses,
    /// `messages_stream`: Anthropic Messages API streaming.
    MessagesStream,
    /// `messages`: Anthropic Messages API non-streaming.
    Messages,
}

impl SamplingConsumer {
    /// Stable string identifier for this emit site. Callbacks
    /// typically combine this with a fixed prefix (e.g. the client
    /// type) when building the consumer field of the attribution
    /// event.
    pub fn as_endpoint(self) -> &'static str {
        match self {
            Self::ChatCompletionsStream => "chat_completions_stream",
            Self::ChatCompletions => "chat_completions",
            Self::ResponsesStream => "responses_stream",
            Self::Responses => "responses",
            Self::MessagesStream => "messages_stream",
            Self::Messages => "messages",
        }
    }
}

/// Maximum prefix length the sampler shares with attribution
/// callbacks across the crate boundary. Mirrors
/// `kigi_shell::auth::token_suffix` (which truncates to 12 chars
/// before any sink) so the two crates stay in lock-step on the
/// "bearers leaving the sampler are 12-char prefixes only" invariant.
///
/// The cross-crate boundary is the only place this constant is
/// load-bearing -- changing it requires updating `token_suffix` in
/// `kigi-shell/src/auth/manager.rs` to match, otherwise the
/// shell's local-log payload and the sampler's callback argument
/// will disagree on prefix length.
pub const SENT_BEARER_PREFIX_LEN: usize = 12;
/// Hook invoked by [`crate::SamplingClient`] at every 401 response site.
///
/// Implementations are responsible for joining `sent_bearer_prefix`
/// with whatever live credential source they own (e.g. an auth
/// manager holding the most-recently-refreshed token) and emitting
/// whatever attribution event makes sense for their observability
/// stack.
///
/// Implementations must be cheap to invoke and must not block. They
/// run inside the request's response-handling path and any latency
/// they add is paid by the user-visible 401 error path.
//
// The `Debug` bound is a structural requirement: [`crate::SamplerConfig`]
// derives `Debug` and carries an `Option<Arc<dyn Auth401AttributionCallback>>`
// field, which only compiles when the trait is `Debug`. Do not remove
// the bound when factoring this trait out -- it will break
// `derive(Debug)` on `SamplerConfig`.
pub trait Auth401AttributionCallback: Send + Sync + std::fmt::Debug {
    /// Record a 401 attribution event for one logical 401 response.
    ///
    /// `sent_bearer_prefix` is the **first
    /// [`SENT_BEARER_PREFIX_LEN`] characters** of the bearer that
    /// was actually sent on the wire. The sampler extracts the
    /// bearer from the `Authorization` header (or `x-api-key` for
    /// Anthropic Messages API backends) and truncates it to the prefix
    /// length **before crossing this trait boundary** -- the full
    /// bearer never leaves [`crate::SamplingClient`]. This is the
    /// scrub-at-the-boundary invariant: even a misbehaving callback
    /// implementation that logs `sent_bearer_prefix` directly leaks
    /// only the prefix, never the full credential.
    ///
    /// `None` indicates the request had no bearer header at all
    /// (distinct from "had a bearer that turned out to be stale").
    fn record_401(&self, consumer: SamplingConsumer, sent_bearer_prefix: Option<&str>);
}

/// Shared, cheap-to-clone alias for the attribution callback.
pub type SharedAttributionCallback = Arc<dyn Auth401AttributionCallback>;