package surf

import (
	"bytes"
	"fmt"
	"math"
	"net/http"
	"strings"
	"time"

	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/cabana"
	"git.golem15.com/golem15/summercms/modules/pact"
	"git.golem15.com/golem15/summercms/modules/party"
	"git.golem15.com/golem15/summercms/modules/towel"
	"git.golem15.com/golem15/summercms/modules/wire"
)

// Use names a middleware list for Group, matching PHP ->middleware().
func Use(names ...string) []string {
	return names
}

type namedMiddleware struct {
	pluginID    string
	fn          pact.Middleware
	houseTagged bool
}

type namedMiddlewareFactory struct {
	pluginID    string
	fn          func(param string) pact.Middleware
	houseTagged bool
}

type route struct {
	pluginID    string
	method      string
	path        string
	handler     http.Handler
	middleware  []string
	constraints []Constraint
	raw         bool
}

// Router compiles group declarations onto net/http ServeMux.
type Router struct {
	pluginID     string
	prefix       string
	middleware   []string
	named        map[string]namedMiddleware
	factories    map[string]namedMiddlewareFactory
	routes       []route
	seen         map[string]string
	origins      []string
	compileErr   error
	limiter      *FixedWindowLimiter
	corsCfg      CORSConfig
	defaultBytes int64
	uploadBytes  int64
	built        map[string]pact.Middleware
}

var (
	_ pact.Router = (*Router)(nil)
	_ pact.Router = (*Group)(nil)
)

// Group is a prefixed route collection.
type Group struct {
	router     *Router
	pluginID   string
	prefix     string
	middleware []string
	raw        bool
}

// New returns an empty router.
func New(origins []string) *Router {
	return &Router{
		named:     make(map[string]namedMiddleware),
		factories: make(map[string]namedMiddlewareFactory),
		seen:      make(map[string]string),
		built:     make(map[string]pact.Middleware),
		origins:   origins,
	}
}

// RegisterMiddleware stores a named wrapper. Duplicate names fail.
func (r *Router) RegisterMiddleware(pluginID, name string, fn pact.Middleware) error {
	return r.registerNamed(pluginID, name, false, fn)
}

// RegisterHouseMiddleware stores a named wrapper tagged as house-envelope/error
// handling. Raw groups refuse these names at wrap/Assemble time. Called only
// from BuildRouter's HasHouseMiddleware plugin loop.
func (r *Router) RegisterHouseMiddleware(pluginID, name string, fn pact.Middleware) error {
	return r.registerNamed(pluginID, name, true, fn)
}

func (r *Router) registerNamed(pluginID, name string, tagged bool, fn pact.Middleware) error {
	if r == nil {
		return fmt.Errorf("surf: router is nil")
	}
	if name == "" || fn == nil {
		return fmt.Errorf("surf: plugin %q registered empty middleware", pluginID)
	}
	if existing, ok := r.named[name]; ok {
		return fmt.Errorf("surf: middleware %q already registered by %s", name, existing.pluginID)
	}
	r.named[name] = namedMiddleware{pluginID: pluginID, fn: fn, houseTagged: tagged}
	return nil
}

// RegisterMiddlewareFactory stores a parameterized middleware builder.
// At wrap time a name not found in r.named is split on the first ':' and
// the base is looked up here. Duplicate factory names fail.
func (r *Router) RegisterMiddlewareFactory(pluginID, name string, fn func(param string) pact.Middleware) error {
	return r.registerNamedFactory(pluginID, name, false, fn)
}

// RegisterHouseMiddlewareFactory stores a parameterized house-envelope/error
// factory. No plugin-facing capability wires this yet; it exists as
// infrastructure for a future house-tagged parameterized consumer.
func (r *Router) RegisterHouseMiddlewareFactory(pluginID, name string, fn func(param string) pact.Middleware) error {
	return r.registerNamedFactory(pluginID, name, true, fn)
}

func (r *Router) registerNamedFactory(pluginID, name string, tagged bool, fn func(param string) pact.Middleware) error {
	if r == nil {
		return fmt.Errorf("surf: router is nil")
	}
	if name == "" || fn == nil {
		return fmt.Errorf("surf: plugin %q registered empty middleware factory", pluginID)
	}
	if existing, ok := r.factories[name]; ok {
		return fmt.Errorf("surf: middleware factory %q already registered by %s", name, existing.pluginID)
	}
	r.factories[name] = namedMiddlewareFactory{pluginID: pluginID, fn: fn, houseTagged: tagged}
	return nil
}

// BindPlugin records the plugin declaring subsequent routes.
func (r *Router) BindPlugin(id string) {
	if r != nil {
		r.pluginID = id
	}
}

func (r *Router) Group(prefix string, middleware []string, fn func(pact.Router)) {
	r.openGroup(prefix, middleware, false, fn)
}

func (r *Router) GroupRaw(prefix string, middleware []string, fn func(pact.Router)) {
	r.openGroup(prefix, middleware, true, fn)
}

func (r *Router) openGroup(prefix string, middleware []string, raw bool, fn func(pact.Router)) {
	if r == nil || fn == nil {
		return
	}
	g := &Group{
		router:     r,
		pluginID:   r.pluginID,
		prefix:     joinPath(r.prefix, prefix),
		middleware: append([]string{}, r.middleware...),
		raw:        raw,
	}
	g.middleware = append(g.middleware, middleware...)
	fn(g)
}

func (r *Router) Get(path string, handler http.HandlerFunc, middleware ...string) {
	if r == nil {
		return
	}
	r.add(r.pluginID, r.prefix, r.middleware, http.MethodGet, path, handler, middleware, false)
}

func (r *Router) Post(path string, handler http.HandlerFunc, middleware ...string) {
	if r == nil {
		return
	}
	r.add(r.pluginID, r.prefix, r.middleware, http.MethodPost, path, handler, middleware, false)
}

func (r *Router) Put(path string, handler http.HandlerFunc, middleware ...string) {
	if r == nil {
		return
	}
	r.add(r.pluginID, r.prefix, r.middleware, http.MethodPut, path, handler, middleware, false)
}

func (r *Router) Patch(path string, handler http.HandlerFunc, middleware ...string) {
	if r == nil {
		return
	}
	r.add(r.pluginID, r.prefix, r.middleware, http.MethodPatch, path, handler, middleware, false)
}

func (r *Router) Delete(path string, handler http.HandlerFunc, middleware ...string) {
	if r == nil {
		return
	}
	r.add(r.pluginID, r.prefix, r.middleware, http.MethodDelete, path, handler, middleware, false)
}

func (g *Group) Group(prefix string, middleware []string, fn func(pact.Router)) {
	g.openGroup(prefix, middleware, g.raw, fn)
}

func (g *Group) GroupRaw(prefix string, middleware []string, fn func(pact.Router)) {
	g.openGroup(prefix, middleware, true, fn)
}

func (g *Group) openGroup(prefix string, middleware []string, raw bool, fn func(pact.Router)) {
	if g == nil || g.router == nil || fn == nil {
		return
	}
	next := &Group{
		router:     g.router,
		pluginID:   g.pluginID,
		prefix:     joinPath(g.prefix, prefix),
		middleware: append([]string{}, g.middleware...),
		raw:        raw,
	}
	next.middleware = append(next.middleware, middleware...)
	fn(next)
}

func (g *Group) Get(path string, handler http.HandlerFunc, middleware ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.add(g.pluginID, g.prefix, g.middleware, http.MethodGet, path, handler, middleware, g.raw)
}

func (g *Group) Post(path string, handler http.HandlerFunc, middleware ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.add(g.pluginID, g.prefix, g.middleware, http.MethodPost, path, handler, middleware, g.raw)
}

func (g *Group) Put(path string, handler http.HandlerFunc, middleware ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.add(g.pluginID, g.prefix, g.middleware, http.MethodPut, path, handler, middleware, g.raw)
}

func (g *Group) Patch(path string, handler http.HandlerFunc, middleware ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.add(g.pluginID, g.prefix, g.middleware, http.MethodPatch, path, handler, middleware, g.raw)
}

func (g *Group) Delete(path string, handler http.HandlerFunc, middleware ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.add(g.pluginID, g.prefix, g.middleware, http.MethodDelete, path, handler, middleware, g.raw)
}

// Where attaches a compiled regex constraint to the last route, matching PHP ->where().
func (r *Router) Where(param, pattern string) {
	if r == nil {
		return
	}
	c, err := Regex(param, pattern)
	if err != nil {
		r.compileErr = err
		return
	}
	r.addConstraint(c)
}

func (g *Group) Where(param, pattern string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.Where(param, pattern)
}

// WhereIn attaches an allow-listed enum constraint to the last route.
func (r *Router) WhereIn(param string, values ...string) {
	if r == nil {
		return
	}
	c, err := Enum(param, values...)
	if err != nil {
		r.compileErr = err
		return
	}
	r.addConstraint(c)
}

func (g *Group) WhereIn(param string, values ...string) {
	if g == nil || g.router == nil {
		return
	}
	g.router.WhereIn(param, values...)
}

func (r *Router) addConstraint(c Constraint) {
	if r.compileErr != nil {
		return
	}
	if len(r.routes) == 0 {
		r.compileErr = fmt.Errorf("surf: Where(%q) with no route", c.param)
		return
	}
	last := &r.routes[len(r.routes)-1]
	if !pathHasParam(last.path, c.param) {
		r.compileErr = fmt.Errorf("surf: Where(%q) is not a path parameter of %s", c.param, last.path)
		return
	}
	last.constraints = append(last.constraints, c)
}

func (r *Router) add(pluginID, prefix string, groupMW []string, method, path string, handler http.HandlerFunc, extra []string, raw bool) {
	full := joinPath(prefix, path)
	key := method + " " + full
	if prev, ok := r.seen[key]; ok {
		r.compileErr = fmt.Errorf("surf: duplicate route %s registered by %s and %s", key, prev, pluginID)
		return
	}
	r.seen[key] = pluginID
	mw := append([]string{}, groupMW...)
	mw = append(mw, extra...)
	r.routes = append(r.routes, route{
		pluginID:   pluginID,
		method:     method,
		path:       full,
		handler:    handler,
		middleware: mw,
		raw:        raw,
	})
}

func (r *Router) compile() (http.Handler, error) {
	if r.compileErr != nil {
		return nil, r.compileErr
	}
	mux := http.NewServeMux()
	for _, rt := range r.routes {
		h, err := r.wrap(rt)
		if err != nil {
			return nil, err
		}
		if err := handleRoute(mux, rt, h); err != nil {
			return nil, err
		}
	}
	return pathScopedCORS(r.corsCfg, mux), nil
}

// handleRoute registers a route, converting a ServeMux conflict panic into an error.
func handleRoute(mux *http.ServeMux, rt route, h http.Handler) (err error) {
	defer func() {
		if rec := recover(); rec != nil {
			err = fmt.Errorf("surf: route conflict for %s %s (plugin %q): %v", rt.method, rt.path, rt.pluginID, rec)
		}
	}()
	mux.Handle(rt.method+" "+rt.path, h)
	return nil
}

func (r *Router) wrap(rt route) (http.Handler, error) {
	h := constrain(rt.handler, rt.constraints)
	limit, err := routeBodyLimit(rt, r.defaultBytes)
	if err != nil {
		return nil, fmt.Errorf("surf: plugin %q: %w", rt.pluginID, err)
	}
	h = orgSlot(h)
	for i := len(rt.middleware) - 1; i >= 0; i-- {
		name := rt.middleware[i]
		if named, ok := r.named[name]; ok {
			if rt.raw && named.houseTagged {
				return nil, fmt.Errorf("surf: raw group cannot use house-envelope middleware %q (plugin %q)", name, rt.pluginID)
			}
			h = named.fn(h)
			continue
		}
		base, param, hasParam := strings.Cut(name, ":")
		if hasParam {
			if factory, ok := r.factories[base]; ok {
				if rt.raw && factory.houseTagged {
					return nil, fmt.Errorf("surf: raw group cannot use house-envelope middleware %q (plugin %q)", name, rt.pluginID)
				}
				if base == "throttle" && r.limiter != nil {
					if err := r.limiter.ValidateThrottle(param); err != nil {
						return nil, fmt.Errorf("surf: plugin %q: %w", rt.pluginID, err)
					}
				}
				if base == "body.limit" {
					if _, err := parseBodyLimit(param); err != nil {
						return nil, fmt.Errorf("surf: plugin %q: %w", rt.pluginID, err)
					}
				}
				mw, ok := r.built[name]
				if !ok {
					mw = factory.fn(param)
					r.built[name] = mw
				}
				h = mw(h)
				continue
			}
		}
		return nil, fmt.Errorf("surf: plugin %q references unknown middleware %q", rt.pluginID, name)
	}
	// Body cap wraps every named/factory middleware but stays inside recovery.
	if limit > 0 {
		h = bodyLimit(limit)(h)
	}
	h = locale(h)
	if rt.raw {
		h = recoverBare(h)
	} else {
		h = recoverJSON(h)
	}
	return h, nil
}

// Assemble registers plugin middleware and routes, then compiles ServeMux.
func Assemble(app *backpack.App, plugins []party.Plugin) (http.Handler, error) {
	r, err := BuildRouter(app, plugins)
	if err != nil {
		return nil, err
	}
	return r.compile()
}

// BuildRouter registers plugin middleware and routes without compiling ServeMux,
// so callers (route:list) can inspect Routes() after a successful boot.
func BuildRouter(app *backpack.App, plugins []party.Plugin) (*Router, error) {
	r := New(corsOrigins(app))
	trusted := TrustedProxies(nil)
	if app != nil {
		trusted = TrustedProxies(app.Config)
	}
	// longest bucket decay is 1 minute; sweep at 2x
	lim := NewFixedWindowLimiter(NewMemoryStore(2*time.Minute), trusted)
	r.limiter = lim
	if err := r.RegisterMiddlewareFactory("surf", "throttle", func(param string) pact.Middleware {
		return lim.Middleware(param)
	}); err != nil {
		return nil, err
	}
	if err := r.RegisterMiddlewareFactory("surf", "body.limit", func(param string) pact.Middleware {
		// Limit is applied outermost-inside-recovery in wrap(); the factory only occupies the name.
		return func(next http.Handler) http.Handler { return next }
	}); err != nil {
		return nil, err
	}
	if err := r.RegisterMiddleware("surf", "locale.from-principal", LocaleFromPrincipal); err != nil {
		return nil, err
	}
	if app != nil {
		corsCfg, err := LoadCORSConfig(app.Config)
		if err != nil {
			return nil, err
		}
		r.corsCfg = corsCfg
		if app.Config != nil {
			d, err := requiredBytes(app, "http.body_limits.default_bytes")
			if err != nil {
				return nil, err
			}
			u, err := requiredBytes(app, "http.body_limits.upload_bytes")
			if err != nil {
				return nil, err
			}
			r.defaultBytes, r.uploadBytes = d, u
		}
	}
	for _, p := range plugins {
		if hm, ok := p.(pact.HasMiddleware); ok {
			for name, fn := range hm.Middlewares() {
				if err := r.RegisterMiddleware(p.ID(), name, fn); err != nil {
					return nil, err
				}
			}
		}
	}
	for _, p := range plugins {
		if hf, ok := p.(pact.HasMiddlewareFactories); ok {
			for name, fn := range hf.MiddlewareFactories() {
				if err := r.RegisterMiddlewareFactory(p.ID(), name, fn); err != nil {
					return nil, err
				}
			}
		}
	}
	for _, p := range plugins {
		if hh, ok := p.(pact.HasHouseMiddleware); ok {
			for name, fn := range hh.HouseMiddlewares() {
				if err := r.RegisterHouseMiddleware(p.ID(), name, fn); err != nil {
					return nil, err
				}
			}
		}
	}
	for _, p := range plugins {
		if bp, ok := p.(BucketProvider); ok {
			for name, b := range bp.Buckets() {
				if err := lim.RegisterBucket(p.ID(), name, b); err != nil {
					return nil, err
				}
			}
		}
	}
	for _, p := range plugins {
		r.BindPlugin(p.ID())
		if hr, ok := p.(pact.HasRoutes); ok {
			if err := hr.Routes(r); err != nil {
				return nil, fmt.Errorf("surf: routes %s: %w", p.ID(), err)
			}
		}
	}
	admin, err := cabana.Activate(app, plugins)
	if err != nil {
		return nil, err
	}
	if admin != nil {
		if err := r.RegisterMiddleware("summercms.cabana", "backend", admin.Middleware); err != nil {
			return nil, err
		}
		r.BindPlugin("summercms.cabana")
		admin.Mount(r)
		if err := r.checkAdminPrefix(admin.Prefix); err != nil {
			return nil, err
		}
	}
	for _, rt := range r.routes {
		if _, err := r.wrap(rt); err != nil {
			return nil, err
		}
	}
	return r, nil
}

// checkAdminPrefix fails boot when a plugin other than cabana owns a route at
// or under the admin prefix: the admin SPA and API own that whole subtree.
func (r *Router) checkAdminPrefix(prefix string) error {
	if prefix == "" {
		return nil
	}
	for _, rt := range r.routes {
		if rt.pluginID == "summercms.cabana" {
			continue
		}
		if rt.path == prefix || strings.HasPrefix(rt.path, prefix+"/") {
			return fmt.Errorf("surf: route %s %s (plugin %q) is under the admin prefix backend.uri %s", rt.method, rt.path, rt.pluginID, prefix)
		}
	}
	return nil
}

func requiredBytes(app *backpack.App, key string) (int64, error) {
	raw, ok := app.Config.Lookup(key)
	if !ok {
		return 0, fmt.Errorf("surf: config %s is required", key)
	}
	var n int64
	switch v := raw.(type) {
	case int:
		n = int64(v)
	case int64:
		n = v
	case uint64:
		if v > math.MaxInt64 {
			return 0, fmt.Errorf("surf: config %s out of range", key)
		}
		n = int64(v)
	case float64:
		if v != math.Trunc(v) || v > 9007199254740992 {
			return 0, fmt.Errorf("surf: config %s must be a whole number", key)
		}
		n = int64(v)
	default:
		return 0, fmt.Errorf("surf: config %s must be numeric, got %T", key, raw)
	}
	if n < 1 {
		return 0, fmt.Errorf("surf: config %s must be >= 1", key)
	}
	return n, nil
}

func corsOrigins(app *backpack.App) []string {
	if app == nil || app.Config == nil {
		return nil
	}
	raw, ok := app.Config.Lookup("http.cors.allowed_origins")
	if !ok {
		return nil
	}
	switch v := raw.(type) {
	case []string:
		return v
	case []any:
		out := make([]string, 0, len(v))
		for _, item := range v {
			s, _ := item.(string)
			if s != "" {
				out = append(out, s)
			}
		}
		return out
	default:
		return nil
	}
}

func recoverJSON(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		buffered := newBufferedResponse()
		defer func() {
			if rec := recover(); rec != nil {
				wire.WriteOpaque500(w)
				return
			}
			buffered.commit(w)
		}()
		next.ServeHTTP(buffered, r)
	})
}

func recoverBare(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		buffered := newBufferedResponse()
		defer func() {
			if rec := recover(); rec != nil {
				w.WriteHeader(http.StatusInternalServerError)
				return
			}
			buffered.commit(w)
		}()
		next.ServeHTTP(buffered, r)
	})
}

type bufferedResponse struct {
	header http.Header
	status int
	body   bytes.Buffer
}

func newBufferedResponse() *bufferedResponse {
	return &bufferedResponse{header: make(http.Header)}
}

func (w *bufferedResponse) Header() http.Header { return w.header }

func (w *bufferedResponse) WriteHeader(status int) {
	if w.status == 0 {
		w.status = status
	}
}

func (w *bufferedResponse) Write(p []byte) (int, error) {
	if w.status == 0 {
		w.status = http.StatusOK
	}
	return w.body.Write(p)
}

// Flush deliberately does not expose or commit the destination writer. Route
// output becomes visible only after the handler returns successfully.
func (*bufferedResponse) Flush() {}

func (w *bufferedResponse) commit(dst http.ResponseWriter) {
	for key, values := range w.header {
		dst.Header()[key] = append([]string(nil), values...)
	}
	status := w.status
	if status == 0 {
		status = http.StatusOK
	}
	dst.WriteHeader(status)
	_, _ = dst.Write(w.body.Bytes())
}

func locale(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(w, r.WithContext(towel.WithLocale(r.Context(), r.Header.Get("Accept-Language"))))
	})
}

func orgSlot(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(w, r.WithContext(towel.WithOrganization(r.Context(), "")))
	})
}

// Limiter wraps handlers. It is a retained Phase 3 seam with no implementer
// after Phase 6; rate limiting is provided by FixedWindowLimiter through
// the parameterized throttle middleware.
type Limiter interface {
	Wrap(http.Handler) http.Handler
}

func joinPath(prefix, path string) string {
	prefix = strings.TrimSuffix(prefix, "/")
	path = strings.TrimSpace(path)
	if path == "" || path == "/" {
		if prefix == "" {
			return "/"
		}
		return prefix
	}
	if !strings.HasPrefix(path, "/") {
		path = "/" + path
	}
	if prefix == "" {
		return path
	}
	return prefix + path
}