tt-preview 0.1.0

Cost preview engine — projects cost + savings + route suggestions for an LLM request without calling any model.
Documentation 
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//! Cheaper-equivalent route suggestions.
//!
//! For each candidate cheaper model, compute the cost. Per-task-class
//! whitelists determine acceptability. Quality risk band is `UNKNOWN`
//! by default; cloud-side enrichment may upgrade to LOW/MEDIUM/HIGH.

use crate::classifier::TaskClass;
use crate::pricing::cost_usd;
use crate::types::{QualityRiskBand, RouteSuggestion};

/// Candidate cheaper models per task class, each paired with its provider so
/// pricing is attributed from the RIGHT catalog (avoids the probe-order
/// mis-attribution for any cross-listed model). Ordered by preference.
fn candidates_for(class: TaskClass) -> &'static [(&'static str, &'static str)] {
    match class {
        TaskClass::Classification => &[
            ("claude-haiku-4-5", "anthropic"),
            ("gpt-4o-mini", "openai"),
            ("gemini-3.1-flash-lite", "gemini"),
        ],
        TaskClass::Extraction => &[
            ("claude-haiku-4-5", "anthropic"),
            ("gpt-4o-mini", "openai"),
            ("gemini-3.5-flash", "gemini"),
        ],
        TaskClass::Chat => &[("claude-haiku-4-5", "anthropic"), ("gpt-4o-mini", "openai")],
        TaskClass::Code => &[("claude-haiku-4-5", "anthropic"), ("gpt-4o-mini", "openai")],
        TaskClass::Agent => &[],
    }
}

pub fn suggest(
    current_model: &str,
    current_cost_usd: f64,
    input_tokens: u32,
    output_tokens: u32,
    task_class: TaskClass,
) -> Vec<RouteSuggestion> {
    let mut out = Vec::new();
    for &(candidate, provider) in candidates_for(task_class) {
        if candidate == current_model {
            continue;
        }
        let Ok(hit) = crate::pricing::lookup_with_provider(candidate, provider) else {
            continue;
        };
        let cost = cost_usd(input_tokens, output_tokens, &hit);
        if cost >= current_cost_usd {
            continue;
        }
        out.push(RouteSuggestion {
            route: format!("swap-to-{candidate}"),
            model: candidate.into(),
            cost_usd: cost,
            savings_usd: current_cost_usd - cost,
            quality_risk_band: QualityRiskBand::Unknown,
            rationale: format!(
                "{candidate} is a lower-cost model for {task_class:?}-style tasks by a static \
                 pricing + capability heuristic — not based on your telemetry. Quality \
                 band not yet computed for your org (UNKNOWN); enable Plan engine \
                 quality scoring to upgrade to LOW/MEDIUM/HIGH.",
            ),
            applicable: true,
        });
        if out.len() >= 3 {
            break;
        }
    }
    out
}

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

    #[test]
    fn agent_class_yields_no_suggestions() {
        let v = suggest("claude-opus", 1.0, 100, 100, TaskClass::Agent);
        assert!(v.is_empty());
    }

    #[test]
    fn excludes_current_model() {
        let v = suggest(
            "claude-haiku-4-5",
            0.001,
            100,
            100,
            TaskClass::Classification,
        );
        assert!(!v.iter().any(|s| s.model == "claude-haiku-4-5"));
    }

    #[test]
    fn caps_at_3_suggestions() {
        let v = suggest("claude-opus", 1.0, 1000, 1000, TaskClass::Extraction);
        assert!(v.len() <= 3);
    }

    /// Rationale must not claim telemetry-backed history it doesn't have — the
    /// suggestion is a static pricing/capability heuristic (mirrors the honesty
    /// guard on `find_route_for`).
    #[test]
    fn rationale_makes_no_unsubstantiated_history_claim() {
        let v = suggest("claude-opus-4-7", 1.0, 1000, 1000, TaskClass::Extraction);
        assert!(!v.is_empty(), "expected at least one cheaper suggestion");
        for s in &v {
            let lower = s.rationale.to_lowercase();
            assert!(
                !lower.contains("historically"),
                "rationale must not claim historical/telemetry data: {}",
                s.rationale
            );
            assert!(
                lower.contains("not based on your telemetry"),
                "rationale must disclose it is a heuristic, not telemetry: {}",
                s.rationale
            );
        }
    }
}