package main

import (
	"context"
	"crypto/subtle"
	"encoding/json"
	"errors"
	"io"
	"log"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
)

const maxRequestBody = 64 << 10

type App struct {
	store                *Store
	agent                *AgentClient
	config               Config
	logins               *LoginLimiter
	integrationLimiter   *LoginLimiter
	integrationTokenHash []byte
	dummyHash            string
}

func NewApp(store *Store, agent *AgentClient, config Config) (*App, error) {
	dummy, err := HashPassword("unused-password-for-timing-equalization")
	if err != nil {
		return nil, err
	}
	var integrationTokenHash []byte
	if config.IntegrationTokenFile != "" {
		token, tokenErr := readIntegrationToken(config.IntegrationTokenFile)
		if tokenErr != nil {
			return nil, tokenErr
		}
		integrationTokenHash = tokenHash(token)
	}
	return &App{store: store, agent: agent, config: config,
		logins: NewLoginLimiter(5, time.Minute), integrationLimiter: NewLoginLimiter(600, time.Minute),
		integrationTokenHash: integrationTokenHash, dummyHash: dummy}, nil
}

func (app *App) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
	writer.Header().Set("X-Content-Type-Options", "nosniff")
	writer.Header().Set("X-Frame-Options", "DENY")
	writer.Header().Set("Referrer-Policy", "no-referrer")
	writer.Header().Set("Cache-Control", "no-store")
	writer.Header().Set("Content-Security-Policy", "default-src 'none'; frame-ancestors 'none'")
	if strings.HasPrefix(request.URL.Path, "/integrations/") {
		app.integration(writer, request)
		return
	}

	if request.URL.Path == "/healthz" && request.Method == http.MethodGet {
		ctx, cancel := context.WithTimeout(request.Context(), 2*time.Second)
		defer cancel()
		if err := app.store.pool.Ping(ctx); err != nil {
			writeError(writer, http.StatusServiceUnavailable, "database unavailable", "unhealthy")
			return
		}
		writeJSON(writer, http.StatusOK, map[string]string{"status": "ok"})
		return
	}
	if request.URL.Path == "/api/v1/auth/login" && request.Method == http.MethodPost {
		app.login(writer, request)
		return
	}
	if !strings.HasPrefix(request.URL.Path, "/api/v1/") {
		writeError(writer, http.StatusNotFound, "not found", "not_found")
		return
	}
	user, session, csrfHash, ok := app.authenticate(writer, request)
	if !ok {
		return
	}

	switch {
	case request.URL.Path == "/api/v1/auth/me" && request.Method == http.MethodGet:
		writeJSON(writer, http.StatusOK, user)
	case request.URL.Path == "/api/v1/auth/logout" && request.Method == http.MethodPost:
		if !app.requireCSRF(writer, request, csrfHash) {
			return
		}
		_ = app.store.DeleteSession(request.Context(), session)
		app.clearCookies(writer)
		app.store.Audit(request.Context(), &user, "", "auth.logout", user.Username, nil, nil, "success", app.clientIP(request))
		writer.WriteHeader(http.StatusNoContent)
	case request.URL.Path == "/api/v1/servers" && request.Method == http.MethodGet:
		app.listServers(writer, request)
	case request.URL.Path == "/api/v1/servers" && request.Method == http.MethodPost:
		if !app.authorize(writer, request, user, csrfHash, RoleAdministrator) {
			return
		}
		app.createServer(writer, request, user)
	case request.URL.Path == "/api/v1/audit" && request.Method == http.MethodGet:
		app.listAudit(writer, request)
	case strings.HasPrefix(request.URL.Path, "/api/v1/servers/"):
		app.serverRoute(writer, request, user, csrfHash)
	default:
		writeError(writer, http.StatusNotFound, "not found", "not_found")
	}
}

func (app *App) login(writer http.ResponseWriter, request *http.Request) {
	ip := app.clientIP(request)
	if !app.logins.Allow(ip, time.Now()) {
		writeError(writer, http.StatusTooManyRequests, "too many login attempts", "rate_limited")
		return
	}
	var input struct {
		Username string `json:"username"`
		Password string `json:"password"`
	}
	if err := decodeJSON(writer, request, &input); err != nil {
		writeError(writer, http.StatusBadRequest, "invalid request", "invalid_request")
		return
	}
	user, hash, disabled, err := app.store.LoginUser(request.Context(), input.Username)
	if err != nil {
		log.Printf("login query: %v", err)
		writeError(writer, http.StatusInternalServerError, "internal error", "internal_error")
		return
	}
	if hash == "" {
		hash = app.dummyHash
	}
	valid := VerifyPassword(hash, input.Password) && user.ID != "" && !disabled
	if !valid {
		app.store.Audit(request.Context(), nil, "", "auth.login", input.Username, nil, nil, "failure", ip)
		writeError(writer, http.StatusUnauthorized, "invalid credentials", "invalid_credentials")
		return
	}
	session, csrf, err := app.store.CreateSession(request.Context(), user.ID, ip, app.config.SessionTTL)
	if err != nil {
		log.Printf("create session: %v", err)
		writeError(writer, http.StatusInternalServerError, "internal error", "internal_error")
		return
	}
	app.setCookies(writer, session, csrf)
	app.store.Audit(request.Context(), &user, "", "auth.login", user.Username, nil, nil, "success", ip)
	writeJSON(writer, http.StatusOK, user)
}

func (app *App) authenticate(writer http.ResponseWriter, request *http.Request) (User, string, []byte, bool) {
	cookie, err := request.Cookie("vps_session")
	if err != nil || len(cookie.Value) > 256 {
		writeError(writer, http.StatusUnauthorized, "authentication required", "unauthorized")
		return User{}, "", nil, false
	}
	user, csrfHash, err := app.store.SessionUser(request.Context(), cookie.Value)
	if err != nil {
		if !errors.Is(err, pgx.ErrNoRows) {
			log.Printf("session query: %v", err)
		}
		writeError(writer, http.StatusUnauthorized, "authentication required", "unauthorized")
		return User{}, "", nil, false
	}
	return user, cookie.Value, csrfHash, true
}

func (app *App) authorize(writer http.ResponseWriter, request *http.Request, user User, csrfHash []byte, role string) bool {
	if !permits(user.Role, role) {
		writeError(writer, http.StatusForbidden, "insufficient permissions", "forbidden")
		return false
	}
	return app.requireCSRF(writer, request, csrfHash)
}

func (app *App) requireCSRF(writer http.ResponseWriter, request *http.Request, expected []byte) bool {
	provided := request.Header.Get("X-CSRF-Token")
	if len(provided) > 256 || subtle.ConstantTimeCompare(tokenHash(provided), expected) != 1 {
		writeError(writer, http.StatusForbidden, "CSRF validation failed", "csrf_failed")
		return false
	}
	return true
}

func (app *App) setCookies(writer http.ResponseWriter, session, csrf string) {
	maxAge := int(app.config.SessionTTL.Seconds())
	http.SetCookie(writer, &http.Cookie{Name: "vps_session", Value: session, Path: "/", HttpOnly: true,
		Secure: app.config.CookieSecure, SameSite: http.SameSiteStrictMode, MaxAge: maxAge})
	http.SetCookie(writer, &http.Cookie{Name: "vps_csrf", Value: csrf, Path: "/", HttpOnly: false,
		Secure: app.config.CookieSecure, SameSite: http.SameSiteStrictMode, MaxAge: maxAge})
}

func (app *App) clearCookies(writer http.ResponseWriter) {
	for _, name := range []string{"vps_session", "vps_csrf"} {
		http.SetCookie(writer, &http.Cookie{Name: name, Path: "/", HttpOnly: name == "vps_session",
			Secure: app.config.CookieSecure, SameSite: http.SameSiteStrictMode, MaxAge: -1})
	}
}

func (app *App) listServers(writer http.ResponseWriter, request *http.Request) {
	servers, err := app.store.Servers(request.Context())
	if err != nil {
		writeInternal(writer, err)
		return
	}
	writeJSON(writer, http.StatusOK, servers)
}

func (app *App) createServer(writer http.ResponseWriter, request *http.Request, user User) {
	var input struct {
		Name          string   `json:"name"`
		Hostname      string   `json:"hostname"`
		AgentEndpoint string   `json:"agent_endpoint"`
		CredentialRef string   `json:"credential_ref"`
		Tags          []string `json:"tags"`
	}
	if err := decodeJSON(writer, request, &input); err != nil || len(input.Name) < 1 || len(input.Name) > 128 ||
		len(input.Hostname) > 255 || len(input.Tags) > 20 || validateAgentEndpoint(input.AgentEndpoint) != nil ||
		!validCredentialRef(input.CredentialRef) {
		writeError(writer, http.StatusBadRequest, "invalid server", "invalid_request")
		return
	}
	for _, tag := range input.Tags {
		if len(tag) > 64 {
			writeError(writer, 400, "invalid tag", "invalid_request")
			return
		}
	}
	if _, err := app.agent.credential(input.CredentialRef); err != nil {
		writeError(writer, http.StatusBadRequest, "credential reference is unavailable", "credential_unavailable")
		return
	}
	tags, _ := json.Marshal(input.Tags)
	server := Server{ID: newID(), Name: input.Name, Hostname: input.Hostname, AgentEndpoint: input.AgentEndpoint,
		CredentialRef: input.CredentialRef, Tags: tags, Status: "unknown", CreatedAt: time.Now()}
	if err := app.store.CreateServer(request.Context(), server); err != nil {
		writeInternal(writer, err)
		return
	}
	app.store.Audit(request.Context(), &user, server.ID, "server.create", server.Name, nil,
		map[string]any{"name": server.Name, "hostname": server.Hostname, "agent_endpoint": server.AgentEndpoint},
		"success", app.clientIP(request))
	writeJSON(writer, http.StatusCreated, server)
}

func (app *App) listAudit(writer http.ResponseWriter, request *http.Request) {
	limit := queryLimit(request, 100, 500)
	events, err := app.store.AuditEvents(request.Context(), limit)
	if err != nil {
		writeInternal(writer, err)
		return
	}
	writeJSON(writer, http.StatusOK, events)
}

func (app *App) serverRoute(writer http.ResponseWriter, request *http.Request, user User, csrfHash []byte) {
	remainder := strings.TrimPrefix(request.URL.Path, "/api/v1/servers/")
	parts := strings.Split(remainder, "/")
	if len(parts) < 2 || parts[0] == "" {
		writeError(writer, 404, "not found", "not_found")
		return
	}
	server, err := app.store.Server(request.Context(), parts[0])
	if errors.Is(err, pgx.ErrNoRows) {
		writeError(writer, 404, "server not found", "not_found")
		return
	}
	if err != nil {
		writeInternal(writer, err)
		return
	}

	readRoutes := map[string]string{
		"status": "/v1/system/status", "interfaces": "/v1/network/interfaces", "routes": "/v1/network/routes",
		"listeners": "/v1/network/listeners", "connections": "/v1/network/connections",
		"firewall": "/v1/firewall/rules", "fail2ban": "/v1/fail2ban/status",
		"wireguard": "/v1/wireguard/status", "services": "/v1/services",
	}
	if len(parts) == 2 && request.Method == http.MethodGet {
		if parts[1] == "metrics" {
			samples, metricErr := app.store.Metrics(request.Context(), server.ID, queryLimit(request, 120, 1440))
			if metricErr != nil {
				writeInternal(writer, metricErr)
				return
			}
			writeJSON(writer, 200, samples)
			return
		}
		if parts[1] == "logs" {
			entries, logErr := app.store.Logs(request.Context(), server.ID, queryLimit(request, 200, 1000))
			if logErr != nil {
				writeInternal(writer, logErr)
				return
			}
			writeJSON(writer, 200, entries)
			return
		}
		if agentPath, found := readRoutes[parts[1]]; found {
			app.proxyRead(writer, request, server, agentPath)
			return
		}
	}
	if len(parts) == 3 && request.Method == http.MethodGet && parts[1] == "fail2ban" && validSimpleName(parts[2]) {
		app.proxyRead(writer, request, server, "/v1/fail2ban/jails/"+url.PathEscape(parts[2]))
		return
	}
	if len(parts) == 3 && request.Method == http.MethodPost && parts[1] == "fail2ban" && (parts[2] == "ban" || parts[2] == "unban") {
		if !app.authorize(writer, request, user, csrfHash, RoleOperator) {
			return
		}
		app.fail2banMutation(writer, request, user, server, parts[2])
		return
	}
	if len(parts) == 4 && request.Method == http.MethodPost && parts[1] == "services" && parts[3] == "restart" && validServiceName(parts[2]) {
		if !app.authorize(writer, request, user, csrfHash, RoleOperator) {
			return
		}
		app.serviceMutation(writer, request, user, server, parts[2])
		return
	}
	writeError(writer, 404, "not found", "not_found")
}

func (app *App) proxyRead(writer http.ResponseWriter, request *http.Request, server Server, path string) {
	status, body, err := app.agent.Do(request.Context(), server, http.MethodGet, path, nil)
	if err != nil {
		log.Printf("agent read %s: %v", server.ID, err)
		writeError(writer, 502, "agent unavailable", "agent_unavailable")
		return
	}
	writeAgentResponse(writer, status, body)
}

func (app *App) fail2banMutation(writer http.ResponseWriter, request *http.Request, user User, server Server, action string) {
	var input struct {
		Jail string `json:"jail"`
		IP   string `json:"ip"`
	}
	if decodeJSON(writer, request, &input) != nil || !validSimpleName(input.Jail) || net.ParseIP(input.IP) == nil {
		writeError(writer, 400, "invalid jail or IP address", "invalid_request")
		return
	}
	body, _ := json.Marshal(input)
	status, response, err := app.agent.Do(request.Context(), server, http.MethodPost, "/v1/fail2ban/"+action, body)
	result := "success"
	if err != nil || status >= 300 {
		result = "failure"
	}
	app.store.Audit(request.Context(), &user, server.ID, "fail2ban."+action, input.Jail+":"+input.IP,
		nil, input, result, app.clientIP(request))
	if err != nil {
		writeError(writer, 502, "agent unavailable", "agent_unavailable")
		return
	}
	writeAgentResponse(writer, status, response)
}

func (app *App) serviceMutation(writer http.ResponseWriter, request *http.Request, user User, server Server, name string) {
	status, response, err := app.agent.Do(request.Context(), server, http.MethodPost,
		"/v1/services/"+url.PathEscape(name)+"/restart", []byte("{}"))
	result := "success"
	if err != nil || status >= 300 {
		result = "failure"
	}
	app.store.Audit(request.Context(), &user, server.ID, "service.restart", name, nil,
		map[string]string{"requested": "restart"}, result, app.clientIP(request))
	if err != nil {
		writeError(writer, 502, "agent unavailable", "agent_unavailable")
		return
	}
	writeAgentResponse(writer, status, response)
}

func (app *App) clientIP(request *http.Request) string {
	if app.config.TrustProxy {
		if value := request.Header.Get("X-Real-IP"); net.ParseIP(value) != nil {
			return value
		}
	}
	host, _, err := net.SplitHostPort(request.RemoteAddr)
	if err == nil {
		return host
	}
	return request.RemoteAddr
}

func validSimpleName(value string) bool {
	if len(value) < 1 || len(value) > 64 {
		return false
	}
	for _, char := range value {
		if !(char >= 'a' && char <= 'z') && !(char >= 'A' && char <= 'Z') &&
			!(char >= '0' && char <= '9') && !strings.ContainsRune("._-", char) {
			return false
		}
	}
	return true
}

func validServiceName(value string) bool {
	if len(value) < 1 || len(value) > 128 {
		return false
	}
	for _, char := range value {
		if !(char >= 'a' && char <= 'z') && !(char >= 'A' && char <= 'Z') &&
			!(char >= '0' && char <= '9') && !strings.ContainsRune("._-@:", char) {
			return false
		}
	}
	return true
}

func decodeJSON(writer http.ResponseWriter, request *http.Request, target any) error {
	request.Body = http.MaxBytesReader(writer, request.Body, maxRequestBody)
	decoder := json.NewDecoder(request.Body)
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(target); err != nil {
		return err
	}
	if err := decoder.Decode(&struct{}{}); !errors.Is(err, io.EOF) {
		return errors.New("multiple JSON values")
	}
	return nil
}

func queryLimit(request *http.Request, fallback, maximum int) int {
	value, err := strconv.Atoi(request.URL.Query().Get("limit"))
	if err != nil || value < 1 {
		return fallback
	}
	if value > maximum {
		return maximum
	}
	return value
}

func writeAgentResponse(writer http.ResponseWriter, status int, payload []byte) {
	if status < 100 || status > 599 {
		status = http.StatusBadGateway
	}
	writer.Header().Set("Content-Type", "application/json")
	writer.WriteHeader(status)
	_, _ = writer.Write(payload)
}

func writeJSON(writer http.ResponseWriter, status int, value any) {
	writer.Header().Set("Content-Type", "application/json")
	writer.WriteHeader(status)
	_ = json.NewEncoder(writer).Encode(value)
}

func writeError(writer http.ResponseWriter, status int, message, code string) {
	writeJSON(writer, status, map[string]string{"error": message, "code": code})
}

func writeInternal(writer http.ResponseWriter, err error) {
	log.Printf("internal request error: %v", err)
	writeError(writer, http.StatusInternalServerError, "internal error", "internal_error")
}