package admin

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"net"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/microcosm-cc/bluemonday"
	"github.com/owncord/server/auth"
	"github.com/owncord/server/config"
	"github.com/owncord/server/db"
)

// setupSanitizer strips all HTML from user input during setup.
var setupSanitizer = bluemonday.StrictPolicy()

// ownerRoleID is the role ID assigned to the first user (Owner).
const ownerRoleID = 1

// setupStatusResponse is the JSON shape returned by GET /api/setup/status.
type setupStatusResponse struct {
	NeedsSetup bool `json:"needs_setup"`
	// Defaults prefills the setup wizard. Present only while setup is needed
	// and the server was wired with its running config (see SetupOptions).
	Defaults *setupDefaults `json:"defaults,omitempty"`
}

// setupRequest is the JSON body for POST /api/setup.
type setupRequest struct {
	Username string `json:"username"`
	Password string `json:"password"`
	// Wizard carries the optional first-run configuration. Absent = legacy
	// behaviour: create the owner account only.
	Wizard *setupWizardRequest `json:"wizard,omitempty"`
}

// setupResponse is the JSON shape returned on successful setup.
type setupResponse struct {
	Token      string `json:"token"`
	UserID     int64  `json:"user_id"`
	Username   string `json:"username"`
	InviteCode string `json:"invite_code"`
	// RestartRequired is true when wizard values that are only read at
	// startup differ from the running config; the server restarts itself
	// right after this response is sent.
	RestartRequired bool `json:"restart_required"`
	// RestartURL is where the admin panel will be reachable after the
	// restart (scheme/port may have changed). Empty when no restart happens.
	RestartURL string `json:"restart_url,omitempty"`
	// Warnings lists non-fatal problems (e.g. config.yaml not writable).
	// The account exists whenever this response is returned.
	Warnings []string `json:"warnings,omitempty"`
}

// handleSetupStatus returns whether initial setup is needed (no users exist).
func handleSetupStatus(database *db.DB, opts SetupOptions) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		count, err := database.UserCount(r.Context())
		if err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to check user count")
			return
		}
		resp := setupStatusResponse{NeedsSetup: count == 0}
		// Prefill defaults are only exposed pre-setup: after the first user
		// exists this endpoint reveals nothing about the configuration.
		if resp.NeedsSetup && opts.RunningCfg != nil {
			cfg := opts.RunningCfg
			d := &setupDefaults{
				ServerName:        cfg.Server.Name,
				Motd:              "Welcome!",
				Port:              cfg.Server.Port,
				TLSMode:           cfg.TLS.Mode,
				TLSDomain:         cfg.TLS.Domain,
				UploadMaxSizeMB:   cfg.Upload.MaxSizeMB,
				VoiceQuality:      cfg.Voice.Quality,
				VoiceAutoDownload: cfg.Voice.AutoDownloadLiveKit,
			}
			// The settings table is authoritative for the values the app
			// reads live; fall back to the config/seed values on error.
			if v, err := database.GetSetting(r.Context(), "server_name"); err == nil && v != "" {
				d.ServerName = v
			}
			if v, err := database.GetSetting(r.Context(), "motd"); err == nil {
				d.Motd = v
			}
			if v, err := database.GetSetting(r.Context(), "registration_open"); err == nil {
				d.RegistrationOpen = v == "1" || strings.EqualFold(v, "true")
			}
			resp.Defaults = d
		}
		writeJSON(w, http.StatusOK, resp)
	}
}

// handleSetup creates the first owner account and, when the request carries
// a wizard payload, applies the chosen settings (DB + config.yaml) and
// restarts the server if startup-only values changed. It only works when no
// users exist in the database, preventing abuse after initial setup.
func handleSetup(database *db.DB, limiter *auth.RateLimiter, allowedOrigins []string, hub HubBroadcaster, opts SetupOptions) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// CSRF protection: reject cross-origin requests (BUG-097).
		// A request is accepted when it is same-origin, or when its Origin is
		// explicitly allowlisted. Absent Origin = non-browser client (allow).
		if origin := r.Header.Get("Origin"); origin != "" {
			if !isSameOrigin(origin, r.Host) && !isSetupOriginAllowed(origin, allowedOrigins) {
				writeErr(w, http.StatusForbidden, "FORBIDDEN", "cross-origin setup request blocked")
				return
			}
		}

		// Rate limit: 5 attempts per minute per IP.
		// Strip the port so that different source ports from the same IP
		// are correctly grouped under a single rate-limit bucket.
		host, _, err := net.SplitHostPort(r.RemoteAddr)
		if err != nil {
			host = r.RemoteAddr
		}
		setupKey := "setup:" + host
		if !limiter.Allow(setupKey, 5, time.Minute) {
			writeErr(w, http.StatusTooManyRequests, "RATE_LIMITED", "too many setup attempts, try again later")
			return
		}

		var req setupRequest
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			writeErr(w, http.StatusBadRequest, "BAD_REQUEST", "invalid request body")
			return
		}

		req.Username = strings.TrimSpace(setupSanitizer.Sanitize(req.Username))
		if req.Username == "" || req.Password == "" {
			writeErr(w, http.StatusBadRequest, "BAD_REQUEST", "username and password are required")
			return
		}

		// Validate username format (length, no control/invisible chars).
		if err := auth.ValidateUsername(req.Username); err != nil {
			writeErr(w, http.StatusBadRequest, "BAD_REQUEST", err.Error())
			return
		}

		if err := auth.ValidatePasswordStrength(req.Password); err != nil {
			writeErr(w, http.StatusBadRequest, "BAD_REQUEST", err.Error())
			return
		}

		// Validate the whole wizard payload BEFORE creating the account so a
		// bad value rejects the request instead of leaving a half-configured
		// server behind an already-created owner.
		if req.Wizard != nil {
			if err := validateWizard(req.Wizard); err != nil {
				writeErr(w, http.StatusBadRequest, "BAD_REQUEST", err.Error())
				return
			}
		}

		// Hash the password.
		hash, err := auth.HashPassword(req.Password)
		if err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to hash password")
			return
		}

		// Atomically check no users exist and create the owner (BUG-119).
		// This closes the TOCTOU race between UserCount() and CreateUser().
		uid, err := database.CreateOwnerIfEmpty(r.Context(), req.Username, hash, ownerRoleID)
		if errors.Is(err, db.ErrConflict) {
			writeErr(w, http.StatusForbidden, "FORBIDDEN", "setup has already been completed")
			return
		}
		if err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to create user")
			return
		}

		// Issue a session token so the user is immediately logged in.
		token, err := auth.GenerateToken()
		if err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to generate session token")
			return
		}

		device := r.Header.Get("User-Agent")
		const maxDeviceLen = 512
		if len(device) > maxDeviceLen {
			device = device[:maxDeviceLen]
		}
		if _, err := database.CreateSession(r.Context(), uid, auth.HashToken(token), device, host); err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to create session")
			return
		}

		// Create default channels under canonical categories.
		_, _ = database.CreateChannel(r.Context(), "general", "text", "Text Channels", "Welcome to the server!", 0)
		_, _ = database.CreateChannel(r.Context(), "General", "voice", "Voice Channels", "", 0)

		// Generate a bootstrap invite code so the owner can invite others.
		// Bound it (5 uses / 24h) rather than minting an unlimited, non-expiring
		// invite — the owner can create fresh invites once logged in.
		bootstrapInviteExpiry := time.Now().Add(24 * time.Hour)
		inviteCode, err := database.CreateInvite(r.Context(), uid, 5, &bootstrapInviteExpiry)
		if err != nil {
			writeErr(w, http.StatusInternalServerError, "INTERNAL_ERROR", "failed to generate invite code")
			return
		}

		// Apply the wizard payload. The account exists from here on, so any
		// failure downgrades to a warning — never a 5xx that would orphan the
		// owner behind an opaque error.
		var warnings []string
		restartRequired := false
		restartURL := ""
		if req.Wizard != nil {
			if err := applyWizardSettings(r.Context(), database, req.Wizard); err != nil {
				slog.Error("setup wizard: saving settings failed", "error", err)
				warnings = append(warnings,
					"could not save server settings: "+err.Error()+" — adjust them later in the admin panel's Settings page")
			}
			if opts.ConfigPath != "" {
				if err := config.Save(opts.ConfigPath, buildConfigPatch(req.Wizard, opts.RunningCfg)); err != nil {
					slog.Error("setup wizard: writing config failed", "path", opts.ConfigPath, "error", err)
					warnings = append(warnings,
						"could not write "+opts.ConfigPath+": "+err.Error()+" — your account was created; edit the file manually to apply these settings")
				} else {
					db.WriteAudit(context.WithoutCancel(r.Context()), database, uid, "config_write", "server", 0,
						"setup wizard wrote "+opts.ConfigPath+" ("+patchedConfigKeys(req.Wizard)+")")
					if opts.RunningCfg != nil && wizardChangesRunningConfig(req.Wizard, opts.RunningCfg) {
						restartRequired = true
						restartURL = computeRestartURL(r.Host, req.Wizard, opts.RunningCfg)
					}
				}
			}
		}

		slog.Info("server setup completed", "owner", req.Username, "user_id", uid, "wizard", req.Wizard != nil, "restart", restartRequired)
		db.WriteAudit(context.WithoutCancel(r.Context()), database, uid, "server_setup", "server", 0,
			"initial setup: owner account created, default channel and invite generated")

		writeJSON(w, http.StatusCreated, setupResponse{
			Token:           token,
			UserID:          uid,
			Username:        req.Username,
			InviteCode:      inviteCode,
			RestartRequired: restartRequired,
			RestartURL:      restartURL,
			Warnings:        warnings,
		})

		// Restart after the response is written so the browser receives the
		// token and the reconnect URL. Mirrors handleRestoreBackup /
		// handleApplyUpdate: broadcast, then respawn in a goroutine
		// (requestRestart sleeps a grace delay before acting).
		if restartRequired {
			if hub != nil {
				hub.BroadcastServerRestart("setup", restartBroadcastDelaySeconds)
			}
			restartFn := opts.Restart
			if restartFn == nil {
				restartFn = requestRestart
			}
			go restartFn("setup_wizard")
		}
	}
}

// restartBroadcastDelaySeconds is the countdown clients are told before the
// setup-wizard restart. There are normally no chat clients connected during
// first-run setup, so this is informational.
const restartBroadcastDelaySeconds = 3

// isSameOrigin reports whether a browser-supplied Origin names this same
// server, by comparing its host:port against the request's Host header.
//
// Browsers send Origin on same-origin POSTs too (Chrome and Edge always,
// Firefox since 70), so the admin panel's own first-run setup call arrives
// carrying one. Without this check it is measured against allowed_origins,
// which is empty in a freshly generated config — so setup failed with
// "cross-origin setup request blocked" on every new install.
//
// Scheme is deliberately not compared. Nothing in this server derives the
// external scheme (there is no r.TLS or X-Forwarded-Proto handling anywhere),
// so a TLS-terminating proxy in front would make a scheme check reject
// legitimate requests. Matching host:port is enough: forging it requires
// already serving content on this exact host and port, at which point the
// origin is not the attacker's to borrow. Cross-site attackers cannot set
// Origin at all — the browser does.
func isSameOrigin(origin, host string) bool {
	if host == "" {
		return false
	}
	u, err := url.Parse(origin)
	// Require a scheme so a schemeless "//host:port" cannot pass as same-origin.
	if err != nil || u.Scheme == "" || u.Host == "" {
		return false
	}
	return strings.EqualFold(u.Host, host)
}

// isSetupOriginAllowed checks if the given origin is permitted by the
// configured allowed_origins list. Wildcard "*" allows any origin.
// An empty list denies all cross-origin requests (safe default).
func isSetupOriginAllowed(origin string, allowed []string) bool {
	for _, a := range allowed {
		if a == "*" || strings.EqualFold(a, origin) {
			return true
		}
	}
	return false
}