// Package pages provides server-side HTML rendering via Go templates.
//
// Templates are embedded in the binary via //go:embed and organized as:
//
//	templates/base.html          — outer shell (banner + surface block + scripts)
//	templates/login.html         — standalone login page
//	templates/components/*.html  — reusable partials (model-select, team-select, chat-pane, etc.)
//	templates/surfaces/*.html    — one per surface (chat, editor, notes, admin, etc.)
//	templates/admin/*.html       — admin sub-pages (roles, routing, providers, etc.)
package pages

import (
	"context"
	"crypto/rand"
	"embed"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"strings"
	"sync"

	"github.com/gin-gonic/gin"

	"git.gobha.me/xcaliber/chat-switchboard/config"
	"git.gobha.me/xcaliber/chat-switchboard/store"
)

//go:embed templates/*.html templates/components/*.html templates/surfaces/*.html templates/admin/*.html
var templateFS embed.FS

// Engine holds parsed templates and rendering state.
type Engine struct {
	mu        sync.RWMutex
	templates *template.Template
	cfg       *config.Config
	stores    store.Stores
	loaders   map[string]DataLoaderFunc
	devMode   bool
}

// BannerConfig holds environment banner settings.
type BannerConfig struct {
	Text       string `json:"text"`
	Color      string `json:"color"`
	Background string `json:"background"`
	Visible    bool   `json:"visible"`
}

// PageData is passed to every template render.
type PageData struct {
	Banner      BannerConfig
	Surface     string // active surface ID
	Section     string // sub-section (for admin pages)
	CSPNonce    string
	BasePath    string
	Version     string
	Environment string
	User        *UserContext
	Data        any // surface-specific data from loader

	// v0.22.7: Theme + settings injection
	Theme           string // "dark", "light", or "" (= use default)
	SurfaceSettings any    // JSON-serialized to window.__SETTINGS__

	// v0.22.7: Login/splash page fields
	InstanceName     string // branding: instance display name
	LogoURL          string // branding: custom logo URL
	Tagline          string // branding: tagline under instance name
	RegistrationOpen bool   // whether self-registration is enabled
}

// UserContext is the authenticated user's info available to templates.
type UserContext struct {
	ID          string `json:"id"`
	Username    string `json:"username"`
	DisplayName string `json:"display_name"`
	Role        string `json:"role"`
	Email       string `json:"email"`
}

// DataLoaderFunc loads surface-specific data for template rendering.
type DataLoaderFunc func(c *gin.Context, stores store.Stores) (any, error)

// New creates a template engine. Call after config and stores are ready.
func New(cfg *config.Config, stores store.Stores) *Engine {
	e := &Engine{
		cfg:     cfg,
		stores:  stores,
		loaders: make(map[string]DataLoaderFunc),
		devMode: gin.Mode() == gin.DebugMode,
	}
	e.parseTemplates()
	e.registerLoaders()
	return e
}

// parseTemplates compiles all embedded templates with the custom FuncMap.
func (e *Engine) parseTemplates() {
	funcMap := template.FuncMap{
		"toJSON":         toJSON,
		"eq":             func(a, b string) bool { return a == b },
		"contains":       stringContains,
		"roleFilterType": roleFilterType,
		"esc":            template.HTMLEscapeString,
		"safeHTML":       func(s string) template.HTML { return template.HTML(s) },
		"join":           strings.Join,
		"dict":           dict,
		"or":             tmplOr,
	}

	tmpl, err := template.New("").Funcs(funcMap).ParseFS(templateFS,
		"templates/*.html",
		"templates/components/*.html",
		"templates/surfaces/*.html",
		"templates/admin/*.html",
	)
	if err != nil {
		log.Fatalf("❌ Failed to parse templates: %v", err)
	}

	e.mu.Lock()
	e.templates = tmpl
	e.mu.Unlock()

	var names []string
	for _, t := range tmpl.Templates() {
		if t.Name() != "" {
			names = append(names, t.Name())
		}
	}
	log.Printf("[pages] Parsed %d templates", len(names))
}

// RegisterLoader adds a named data loader for a surface.
func (e *Engine) RegisterLoader(name string, fn DataLoaderFunc) {
	e.loaders[name] = fn
}

// Render renders a named template into the response.
func (e *Engine) Render(c *gin.Context, name string, data PageData) {
	data.BasePath = e.cfg.BasePath
	data.Version = Version
	data.Environment = e.cfg.Environment
	data.CSPNonce = generateNonce()
	data.Banner = e.loadBanner()

	// v0.22.7: Default theme if not set
	if data.Theme == "" {
		data.Theme = "dark"
	}

	e.mu.RLock()
	tmpl := e.templates
	e.mu.RUnlock()

	c.Header("Content-Type", "text/html; charset=utf-8")
	c.Status(http.StatusOK)

	if err := tmpl.ExecuteTemplate(c.Writer, name, data); err != nil {
		log.Printf("[pages] Template render error (%s): %v", name, err)
	}
}

// RenderSurface is a Gin handler factory for surface routes.
func (e *Engine) RenderSurface(surfaceID string) gin.HandlerFunc {
	return func(c *gin.Context) {
		user := e.getUserContext(c)

		var data any
		if loader, ok := e.loaders[surfaceID]; ok {
			var err error
			data, err = loader(c, e.stores)
			if err != nil {
				log.Printf("[pages] Data loader error (%s): %v", surfaceID, err)
				c.String(http.StatusInternalServerError, "Failed to load page data")
				return
			}
		}

		section := c.Param("section")
		if section == "" && surfaceID == "admin" {
			section = "overview"
		}
		if section == "" && surfaceID == "settings" {
			section = "general"
		}

		e.Render(c, "base.html", PageData{
			Surface: surfaceID,
			Section: section,
			User:    user,
			Data:    data,
		})
	}
}

// RenderLogin serves the standalone login page.
func (e *Engine) RenderLogin() gin.HandlerFunc {
	return func(c *gin.Context) {
		// v0.22.7: Populate splash/login fields from global config
		instanceName, logoURL, tagline := e.loadBranding()
		regOpen := e.isRegistrationOpen()

		e.Render(c, "login.html", PageData{
			Surface:          "login",
			InstanceName:     instanceName,
			LogoURL:          logoURL,
			Tagline:          tagline,
			RegistrationOpen: regOpen,
		})
	}
}

// getUserContext extracts user info from gin context (set by auth middleware).
func (e *Engine) getUserContext(c *gin.Context) *UserContext {
	userID, exists := c.Get("user_id")
	if !exists {
		return nil
	}
	return &UserContext{
		ID:   userID.(string),
		Role: c.GetString("role"),
	}
}

// loadBanner reads banner config from global settings.
func (e *Engine) loadBanner() BannerConfig {
	if e.stores.GlobalConfig == nil {
		return BannerConfig{}
	}
	raw, err := e.stores.GlobalConfig.Get(context.Background(), "banner")
	if err != nil || raw == nil {
		return BannerConfig{}
	}
	b := BannerConfig{}
	if v, ok := raw["enabled"].(bool); ok {
		b.Visible = v
	}
	if v, ok := raw["text"].(string); ok {
		b.Text = v
	}
	if v, ok := raw["fg"].(string); ok {
		b.Color = v
	}
	if v, ok := raw["bg"].(string); ok {
		b.Background = v
	}
	return b
}

// loadBranding reads instance branding from global settings.
func (e *Engine) loadBranding() (name, logoURL, tagline string) {
	name = "Chat Switchboard" // default
	if e.stores.GlobalConfig == nil {
		return
	}
	raw, err := e.stores.GlobalConfig.Get(context.Background(), "branding")
	if err != nil || raw == nil {
		return
	}
	if v, ok := raw["instance_name"].(string); ok && v != "" {
		name = v
	}
	if v, ok := raw["logo_url"].(string); ok {
		logoURL = v
	}
	if v, ok := raw["tagline"].(string); ok {
		tagline = v
	}
	return
}

// isRegistrationOpen checks if self-registration is enabled.
func (e *Engine) isRegistrationOpen() bool {
	if e.stores.GlobalConfig == nil {
		return false
	}
	raw, err := e.stores.GlobalConfig.Get(context.Background(), "registration")
	if err != nil || raw == nil {
		return false
	}
	if v, ok := raw["enabled"].(bool); ok {
		return v
	}
	return false
}

// Version is injected at build time via ldflags.
var Version = "dev"

// SetVersion allows main.go to inject the build version.
func SetVersion(v string) {
	Version = v
}

// WriteError writes an error page directly to the response.
func (e *Engine) WriteError(w http.ResponseWriter, status int, msg string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	fmt.Fprintf(w, `<!DOCTYPE html><html><head><title>Error</title></head><body><h1>%d</h1><p>%s</p></body></html>`, status, template.HTMLEscapeString(msg))
}

// ── Template FuncMap helpers ─────────────────

func toJSON(v any) template.JS {
	b, err := json.Marshal(v)
	if err != nil {
		return template.JS("null")
	}
	return template.JS(b)
}

func stringContains(haystack []string, needle string) bool {
	for _, s := range haystack {
		if s == needle {
			return true
		}
	}
	return false
}

// roleFilterType returns the model_type filter for a given role name.
func roleFilterType(role string) string {
	switch role {
	case "embedding":
		return "embedding"
	case "utility":
		return "chat"
	default:
		return ""
	}
}

// dict creates a map from alternating key/value pairs for template use.
func dict(pairs ...any) map[string]any {
	m := make(map[string]any, len(pairs)/2)
	for i := 0; i < len(pairs)-1; i += 2 {
		key, ok := pairs[i].(string)
		if !ok {
			continue
		}
		m[key] = pairs[i+1]
	}
	return m
}

// tmplOr returns the first non-empty string argument.
func tmplOr(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}

func generateNonce() string {
	b := make([]byte, 16)
	if _, err := io.ReadFull(rand.Reader, b); err != nil {
		return "fallback-nonce"
	}
	return hex.EncodeToString(b)
}