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//! Model selection: `(task_label, complexity_tier) → ordered list of model_ids`.
//! The list serves as both a priority order and a fallback chain. See docs/ROUTING.md.
use crate::config::{Config, TierTargets};
fn to_list(t: &TierTargets) -> Vec<String> {
t.models()
}
/// A task rule, normalized: per-tier model lists ("which model serves this
/// task at each complexity") plus any-tier models that lead regardless.
#[derive(Clone, Default)]
pub struct TaskRule {
pub any: Vec<String>,
pub per: std::collections::HashMap<String, Vec<String>>,
}
pub struct RoutingTable {
tiers: std::collections::HashMap<String, Vec<String>>,
/// Per-task rules — a matching rule's models lead the candidate chain.
tasks: std::collections::HashMap<String, TaskRule>,
default: String,
}
impl RoutingTable {
pub fn from_config(cfg: &Config) -> Self {
Self {
tiers: cfg
.routing
.tiers
.iter()
.map(|(tier, targets)| (tier.clone(), to_list(targets)))
.collect(),
tasks: cfg
.routing
.tasks
.iter()
.map(|(task, targets)| {
let (any, per) = targets.task_rule();
(task.clone(), TaskRule { any, per })
})
.filter(|(_, r)| !r.any.is_empty() || r.per.values().any(|v| !v.is_empty()))
.collect(),
default: cfg.routing.default.clone(),
}
}
/// Candidate chain for `(task, tier)` and whether a task rule shaped it.
///
/// Order of preference:
/// 1. the task's models FOR THIS TIER (the user said exactly which model
/// serves this task at this complexity);
/// 2. at tier=high — the global high chain (escalation: any-tier task
/// models must not undercut it), then the task's any-tier models;
/// otherwise the task's any-tier models, then the global tier chain;
/// 3. `default` as the last resort. Deduplicated, empties dropped.
pub fn candidates_for(&self, task: &str, tier: &str) -> (Vec<String>, bool) {
fn push(out: &mut Vec<String>, id: &str) {
if !id.is_empty() && !out.iter().any(|x| x == id) {
out.push(id.to_string());
}
}
let mut out: Vec<String> = Vec::new();
let rule = self.tasks.get(task);
let tier_chain = self
.tiers
.get(tier)
.cloned()
.unwrap_or_else(|| vec![self.default.clone()]);
if let Some(r) = rule {
if let Some(list) = r.per.get(tier) {
for id in list {
push(&mut out, id);
}
}
}
let escalate = tier == "high" && self.tiers.contains_key("high");
if escalate {
// high verdicts escalate over any-tier task pins
for id in &tier_chain {
push(&mut out, id);
}
if let Some(r) = rule {
for id in &r.any {
push(&mut out, id);
}
}
} else {
if let Some(r) = rule {
for id in &r.any {
push(&mut out, id);
}
}
for id in &tier_chain {
push(&mut out, id);
}
}
let d = self.default.clone();
push(&mut out, &d);
// "task-rule" must mean "the rule chose the head of this chain" — a
// rule that exists but lost to the tier chain (math has a high pick,
// the request came in low) must not claim the credit.
let matched = match (rule, out.first()) {
(Some(r), Some(head)) => {
r.per.get(tier).map(|v| v.contains(head)).unwrap_or(false)
|| r.any.first() == Some(head)
}
_ => false,
};
(out, matched)
}
/// Candidates for the given complexity tier, in preference order.
/// If the tier is not defined, the sole candidate is `default`.
pub fn candidates(&self, tier: &str) -> Vec<String> {
self.candidates_for("", tier).0
}
/// Default model (used when the router is unavailable).
pub fn default_model(&self) -> &str {
&self.default
}
}
// TODO(v0.2): cost_aware mode and circuit breaker — pick the cheapest available
// model no lower than min_class[tier], respecting max_cost_usd_per_request,
// and skip models whose circuit breaker is open.
#[cfg(test)]
mod tests {
use super::*;
fn table(tasks: &[(&str, &[&str])], tiers: &[(&str, &[&str])], default: &str) -> RoutingTable {
RoutingTable {
tiers: tiers
.iter()
.map(|(k, v)| (k.to_string(), v.iter().map(|s| s.to_string()).collect()))
.collect(),
tasks: tasks
.iter()
.map(|(k, v)| {
(
k.to_string(),
TaskRule {
any: v.iter().map(|s| s.to_string()).collect(),
per: Default::default(),
},
)
})
.collect(),
default: default.to_string(),
}
}
fn with_task_tier_models(
mut t: RoutingTable,
task: &str,
tier: &str,
models: &[&str],
) -> RoutingTable {
t.tasks.entry(task.to_string()).or_default().per.insert(
tier.to_string(),
models.iter().map(|s| s.to_string()).collect(),
);
t
}
#[test]
fn task_rule_leads_tier_chain_follows() {
let t = table(
&[("translation", &["local"])],
&[("low", &["cheap", "local"]), ("high", &["big"])],
"cheap",
);
// dedup: rule model already in the tier chain appears once, first
let (c, matched) = t.candidates_for("translation", "low");
assert!(matched);
assert_eq!(c, vec!["local", "cheap"]);
}
#[test]
fn high_tier_escalates_over_task_rule() {
let t = table(
&[("code", &["cheap-coder"])],
&[("low", &["cheap"]), ("high", &["big"])],
"cheap",
);
// medium (no chain defined → default): task rule still leads
let (c, m) = t.candidates_for("code", "medium");
assert!(m);
assert_eq!(c[0], "cheap-coder");
// high: tier chain leads, task rule follows as fallback
let (c, m) = t.candidates_for("code", "high");
// escalation put the global high chain first → the rule did not pick
// the head, so no task-rule credit
assert!(!m);
// default rides along as the very last fallback
assert_eq!(c, vec!["big", "cheap-coder", "cheap"]);
}
#[test]
fn per_tier_models_lead_their_tier() {
let base = table(
&[("code", &["generic-coder"])],
&[("low", &["cheap"]), ("high", &["big"])],
"cheap",
);
let t = with_task_tier_models(base, "code", "high", &["best-coder"]);
// at high: the task's HIGH pick leads, escalation chain next,
// any-tier task models after it, default last
let (c, m) = t.candidates_for("code", "high");
assert!(m);
assert_eq!(c, vec!["best-coder", "big", "generic-coder", "cheap"]);
// at low: any-tier task models lead as before (and the badge is
// honest — the head came from the rule)
let (c, m) = t.candidates_for("code", "low");
assert!(m);
assert_eq!(c, vec!["generic-coder", "cheap"]);
// a tier with an explicit pick but no any-models
let t2 = with_task_tier_models(
table(&[], &[("low", &["cheap"]), ("high", &["big"])], "cheap"),
"legal",
"high",
&["strong"],
);
let (c, m) = t2.candidates_for("legal", "high");
assert!(m);
assert_eq!(c, vec!["strong", "big", "cheap"]);
// the same rule at LOW did not shape the head → no task-rule credit
let (c, m) = t2.candidates_for("legal", "low");
assert!(!m);
assert_eq!(c, vec!["cheap"]);
}
#[test]
fn no_rule_falls_back_to_tier_then_default() {
let t = table(&[], &[("low", &["a"])], "d");
assert_eq!(t.candidates_for("qa", "low").0, vec!["a", "d"]);
let (c, matched) = t.candidates_for("qa", "unknown-tier");
assert!(!matched);
assert_eq!(c, vec!["d"]);
}
}