package router

import (
	"context"
	"encoding/json"
	"fmt"

	"gophergate/internal/db"
)

// Decision holds the result of a routing decision.
type Decision struct {
	SelectedModel string `json:"selected_model"`
	Strategy      string `json:"strategy"` // "heuristic" or "classifier"
	Reason        string `json:"reason"`
}

// ClassifierFunc is the callback for classifier-based routing.
type ClassifierFunc func(ctx context.Context, selectorModel, systemPrompt, userMessage string) (string, error)

// Router resolves model groups to concrete models.
type Router struct {
	groups   map[string]db.ModelGroup
	classify ClassifierFunc
}

// New creates a Router. classify may be nil if no classifier groups exist.
func New(groups []db.ModelGroup, classify ClassifierFunc) *Router {
	r := &Router{
		groups:   make(map[string]db.ModelGroup),
		classify: classify,
	}
	for _, g := range groups {
		r.groups[g.ID] = g
	}
	return r
}

// IsGroup returns true if the model name is a group ID.
func (r *Router) IsGroup(modelID string) bool {
	_, ok := r.groups[modelID]
	return ok
}

// Route resolves a group to a concrete model.
func (r *Router) Route(ctx context.Context, groupID string, userMessage string) (*Decision, error) {
	group, ok := r.groups[groupID]
	if !ok {
		return nil, fmt.Errorf("unknown model group: %s", groupID)
	}

	var targets []string
	if err := json.Unmarshal([]byte(group.Targets), &targets); err != nil || len(targets) == 0 {
		return nil, fmt.Errorf("invalid or empty targets for group %s", groupID)
	}

	switch group.Strategy {
	case "heuristic":
		return routeHeuristic(group, targets, userMessage)
	case "classifier":
		if r.classify == nil {
			return routeHeuristic(group, targets, userMessage)
		}
		return routeClassifier(ctx, r.classify, group, targets, userMessage)
	default:
		return nil, fmt.Errorf("unknown strategy: %s", group.Strategy)
	}
}

// Reload replaces the group definitions without recreating the router.
func (r *Router) Reload(groups []db.ModelGroup) {
	r.groups = make(map[string]db.ModelGroup)
	for _, g := range groups {
		r.groups[g.ID] = g
	}
}