package llm

import (
	"context"
	"fmt"
)

// Router calls Primary first; on any error falls back to Fallback, then to
// Tertiary. Fallback and Tertiary may each be nil — a nil tier is skipped and
// the chain returns the errors accumulated so far.
type Router struct {
	Primary  *Client
	Fallback *Client
	Tertiary *Client
}

// Complete implements pipeline.CompleteFunc, routing through Primary, then
// Fallback, then Tertiary — trying each configured tier in order and
// returning the first success.
func (r *Router) Complete(ctx context.Context, system, user string) (string, error) {
	out, err := r.Primary.Complete(ctx, system, user)
	if err == nil {
		return out, nil
	}
	if r.Fallback == nil {
		return "", fmt.Errorf("primary llm: %w", err)
	}
	out, err2 := r.Fallback.Complete(ctx, system, user)
	if err2 == nil {
		return out, nil
	}
	if r.Tertiary == nil {
		return "", fmt.Errorf("primary llm: %w; fallback llm: %v", err, err2)
	}
	out, err3 := r.Tertiary.Complete(ctx, system, user)
	if err3 != nil {
		return "", fmt.Errorf("primary llm: %w; fallback llm: %v; tertiary llm: %v", err, err2, err3)
	}
	return out, nil
}