package server

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"go.uber.org/zap"

	"github.com/Warky-Devs/vecna.git/pkg/adapter"
	"github.com/Warky-Devs/vecna.git/pkg/config"
	"github.com/Warky-Devs/vecna.git/pkg/embedclient"
)

// handler holds shared dependencies for all HTTP handlers.
type handler struct {
	cfg     *config.Config
	clients map[string]embedclient.Client
	adapter adapter.Adapter
	logger  *zap.Logger
}

// resolveClient selects the embed client for the given model name.
// Returns the client, target name, and first endpoint URL for tracing.
func (h *handler) resolveClient(model string) (embedclient.Client, string, string) {
	if c, ok := h.clients[model]; ok {
		url := firstEndpointURL(h.cfg, model)
		return c, model, url
	}
	name := h.cfg.Forward.Default
	c, ok := h.clients[name]
	if !ok {
		// No configured client — return a nil-safe error client
		return &errClient{err: fmt.Errorf("no client configured for model %q and no default", model)}, name, ""
	}
	return c, name, firstEndpointURL(h.cfg, name)
}

func firstEndpointURL(cfg *config.Config, targetName string) string {
	t, ok := cfg.Forward.Targets[targetName]
	if !ok || len(t.Endpoints) == 0 {
		return ""
	}
	return t.Endpoints[0].URL
}

// writeJSON encodes v as JSON and writes it with the given status code.
func writeJSON(w http.ResponseWriter, status int, v interface{}) error {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(v); err != nil {
		return fmt.Errorf("writeJSON: %w", err)
	}
	return nil
}

// writeTraceHeaders writes X-Vecna-* timing headers from the RequestTrace.
func writeTraceHeaders(w http.ResponseWriter, t *RequestTrace) {
	total := time.Since(t.Start)
	w.Header().Set("X-Vecna-Forward-Ms", fmt.Sprintf("%d", t.ForwardDuration.Milliseconds()))
	w.Header().Set("X-Vecna-Translate-Ms", fmt.Sprintf("%d", t.TranslateDuration.Milliseconds()))
	w.Header().Set("X-Vecna-Total-Ms", fmt.Sprintf("%d", total.Milliseconds()))
}

// errClient is a Client that always returns a fixed error (used as safe fallback).
type errClient struct {
	err error
}

func (e *errClient) Embed(_ context.Context, _ embedclient.Request) (embedclient.Response, error) {
	return embedclient.Response{}, e.err
}