package gonexapp

import (
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

// AccessGate enforces Required Groups for the Requesting user on ExApp HTTP traffic.
type AccessGate struct {
	Cred           Credentials
	Groups         []string
	CacheTTL       time.Duration // 0 disables cache
	ExtraSkipPaths []string
	Client         *http.Client
	OCS            OCSClient
	Now            func() time.Time

	mu    sync.Mutex
	cache map[string]cacheEntry
}

type cacheEntry struct {
	until time.Time
}

// CheckResult is the outcome of AccessGate.Check.
type CheckResult int

const (
	CheckAllowed CheckResult = iota
	CheckDenied
	CheckUnauthorized
	CheckUnavailable
)

// Wrap returns a handler that applies the Access Gate before next.
func (g AccessGate) Wrap(next http.Handler) http.Handler {
	gate := g.normalized()
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		switch gate.Check(r) {
		case CheckAllowed:
			next.ServeHTTP(w, r)
		case CheckUnauthorized:
			http.Error(w, "unauthorized", http.StatusUnauthorized)
		case CheckUnavailable:
			http.Error(w, "service unavailable", http.StatusServiceUnavailable)
		default:
			gate.writeDenied(w, r)
		}
	})
}

// Check reports whether r may proceed under Required Groups.
func (g *AccessGate) Check(r *http.Request) CheckResult {
	if g.cache == nil {
		g.cache = make(map[string]cacheEntry)
	}
	if g.Now == nil {
		g.Now = time.Now
	}
	if g.shouldSkip(r.URL.Path) || len(g.Groups) == 0 {
		return CheckAllowed
	}
	user, err := UserFromRequest(r)
	if err != nil || user == "" {
		return CheckUnauthorized
	}
	ok, err := g.memberOfRequired(user)
	if err != nil {
		return CheckUnavailable
	}
	if ok {
		return CheckAllowed
	}
	return CheckDenied
}

func (g *AccessGate) memberOfRequired(userID string) (bool, error) {
	key := g.cacheKey(userID)
	if g.CacheTTL > 0 {
		if g.cachedAllowed(key) {
			return true, nil
		}
	}
	groups, err := g.fetchUserGroups(userID)
	if err != nil {
		return false, err
	}
	for _, need := range g.Groups {
		for _, have := range groups {
			if have == need {
				if g.CacheTTL > 0 {
					g.storeAllowed(key)
				}
				return true, nil
			}
		}
	}
	return false, nil
}

func (g *AccessGate) cacheKey(userID string) string {
	return userID + "\x00" + strings.Join(g.Groups, "\x00")
}

func (g *AccessGate) fetchUserGroups(userID string) ([]string, error) {
	ocs := g.ocsClient(userID)
	path := "cloud/users/" + url.PathEscape(userID) + "/groups"
	raw, err := ocs.Call(http.MethodGet, path, nil)
	if err != nil {
		return nil, err
	}
	return decodeUserGroups(raw)
}

func (g *AccessGate) ocsClient(userID string) OCSClient {
	c := g.OCS
	if c.Cred.BaseURL == "" {
		c.Cred = g.Cred
	}
	c.Cred = c.Cred.WithUser(userID)
	if c.Client == nil {
		c.Client = g.Client
	}
	return c
}

func decodeUserGroups(raw []byte) ([]string, error) {
	var parsed struct {
		OCS struct {
			Data struct {
				Groups []string `json:"groups"`
			} `json:"data"`
		} `json:"ocs"`
	}
	if err := json.Unmarshal(raw, &parsed); err != nil {
		return nil, fmt.Errorf("user groups decode: %w", err)
	}
	return parsed.OCS.Data.Groups, nil
}

func (g *AccessGate) cachedAllowed(key string) bool {
	g.mu.Lock()
	defer g.mu.Unlock()
	ent, ok := g.cache[key]
	if !ok {
		return false
	}
	if g.Now().After(ent.until) {
		delete(g.cache, key)
		return false
	}
	return true
}

func (g *AccessGate) storeAllowed(key string) {
	g.mu.Lock()
	defer g.mu.Unlock()
	g.cache[key] = cacheEntry{until: g.Now().Add(g.CacheTTL)}
}

func (g AccessGate) normalized() *AccessGate {
	out := g
	if out.cache == nil {
		out.cache = make(map[string]cacheEntry)
	}
	if out.Now == nil {
		out.Now = time.Now
	}
	return &out
}

func (g *AccessGate) writeDenied(w http.ResponseWriter, r *http.Request) {
	if acceptsHTML(r.Header.Get("Accept")) {
		// 200 so AppAPI's proxy CSP keeps frame-ancestors 'self' and the ExApp
		// iframe can show the message (403 responses get frame-ancestors 'none').
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.WriteHeader(http.StatusOK)
		_, _ = w.Write(deniedHTML)
		return
	}
	http.Error(w, "forbidden", http.StatusForbidden)
}

func acceptsHTML(accept string) bool {
	return strings.Contains(strings.ToLower(accept), "text/html")
}

func (g *AccessGate) shouldSkip(path string) bool {
	path = normalizeGatePath(path)
	for _, p := range defaultSkipPaths {
		if path == p {
			return true
		}
	}
	for _, p := range g.ExtraSkipPaths {
		if path == normalizeGatePath(p) {
			return true
		}
	}
	return false
}

func normalizeGatePath(path string) string {
	path = strings.TrimSuffix(path, "/")
	if path == "" {
		return "/"
	}
	return path
}

var defaultSkipPaths = []string{"/heartbeat", "/enabled", "/init"}

var deniedHTML = []byte(`<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Access denied</title>
  <style>
    :root { font-family: ui-sans-serif, system-ui, sans-serif; color: #1a1a1a; }
    body { margin: 2rem; max-width: 40rem; }
    h1 { font-size: 1.4rem; margin-bottom: 0.5rem; }
    p { color: #444; line-height: 1.5; }
  </style>
</head>
<body>
  <h1>Access denied</h1>
  <p>You are not a member of a required group for this app. Ask an administrator to add you to the group if you need access.</p>
</body>
</html>
`)