package api

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

	"github.com/google/uuid"

	"github.com/alchemistkay/guestguard/internal/audit"
	"github.com/alchemistkay/guestguard/internal/auth"
	"github.com/alchemistkay/guestguard/internal/domain"
	"github.com/alchemistkay/guestguard/internal/storage"
)

// collaboratorHandler powers the per-event Team endpoints and the public
// invite-accept flow. Tier 2 Block C.
type collaboratorHandler struct {
	logger        *slog.Logger
	events        *storage.EventRepo
	users         *storage.UserRepo
	collabs       *storage.CollaboratorRepo
	invites       *storage.InviteRepo
	emails        auth.EmailSender
	publicBaseURL string
	inviteTTL     time.Duration
	audit         *audit.Recorder
	enforcer      *tierEnforcer
}

// --- responses ---

type collaboratorView struct {
	UserID     uuid.UUID  `json:"user_id"`
	Name       string     `json:"name"`
	Email      string     `json:"email"`
	Role       domain.Role `json:"role"`
	InvitedAt  time.Time  `json:"invited_at"`
	AcceptedAt *time.Time `json:"accepted_at,omitempty"`
}

type pendingInviteView struct {
	Email     string      `json:"email"`
	Role      domain.Role `json:"role"`
	InvitedBy uuid.UUID   `json:"invited_by"`
	ExpiresAt time.Time   `json:"expires_at"`
	CreatedAt time.Time   `json:"created_at"`
}

type listCollaboratorsResponse struct {
	Collaborators []collaboratorView  `json:"collaborators"`
	Pending       []pendingInviteView `json:"pending"`
	// YourRole tells the UI which actions to hide. Echoed from requireRole
	// so the client doesn't need a separate /me lookup per event view.
	YourRole domain.Role `json:"your_role"`
}

// GET /events/{id}/collaborators — viewer+ can see the team list. Pending
// invites are exposed too so editors can chase up unaccepted invitations,
// not just owners.
func (h *collaboratorHandler) list(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	_, role, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer)
	if !ok {
		return
	}

	members, err := h.collabs.List(r.Context(), eventID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to list collaborators")
		return
	}
	views := make([]collaboratorView, 0, len(members))
	for _, m := range members {
		views = append(views, collaboratorView{
			UserID:     m.UserID,
			Name:       m.Name,
			Email:      m.Email,
			Role:       m.Role,
			InvitedAt:  m.InvitedAt,
			AcceptedAt: m.AcceptedAt,
		})
	}

	pending, err := h.invites.ListPendingForEvent(r.Context(), eventID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to list pending invites")
		return
	}
	pendingViews := make([]pendingInviteView, 0, len(pending))
	for _, p := range pending {
		pendingViews = append(pendingViews, pendingInviteView{
			Email:     p.Email,
			Role:      p.Role,
			InvitedBy: p.InvitedBy,
			ExpiresAt: p.ExpiresAt,
			CreatedAt: p.CreatedAt,
		})
	}

	writeJSON(w, http.StatusOK, listCollaboratorsResponse{
		Collaborators: views,
		Pending:       pendingViews,
		YourRole:      role,
	})
}

type inviteRequest struct {
	Email string      `json:"email"`
	Role  domain.Role `json:"role"`
}

type inviteResponse struct {
	Email     string      `json:"email"`
	Role      domain.Role `json:"role"`
	ExpiresAt time.Time   `json:"expires_at"`
	// Sent reports whether the email send succeeded. The invite is still
	// usable from the host's side either way — they can resend.
	Sent bool `json:"sent"`
}

// POST /events/{id}/collaborators — owner-only. Creates an invitation
// token, emails it to the recipient. The recipient can accept whether or
// not they already have a GuestGuard account.
func (h *collaboratorHandler) invite(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	event, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleOwner)
	if !ok {
		return
	}

	var req inviteRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	email := strings.ToLower(strings.TrimSpace(req.Email))
	if email == "" || !strings.Contains(email, "@") {
		writeError(w, http.StatusBadRequest, "valid email required")
		return
	}
	if !req.Role.Valid() {
		writeError(w, http.StatusBadRequest, "role must be owner|editor|viewer")
		return
	}

	// Tier gate. Free plans cap at 0 shared collaborators; Pro at 5;
	// Business unlimited. We deny BEFORE minting the invite so we
	// don't email someone an invite that the host won't be able to
	// honour.
	if !h.enforcer.allowCollaboratorInvite(w, r, hostID, eventID) {
		return
	}

	// If the invitee already has an account AND is already a collaborator,
	// short-circuit with a friendly 409 — no email, no DB churn.
	if existing, err := h.users.GetByEmail(r.Context(), email); err == nil && existing != nil {
		if _, already, err := h.collabs.RoleFor(r.Context(), eventID, existing.ID); err == nil && already {
			writeError(w, http.StatusConflict, "user is already a collaborator on this event")
			return
		}
	}

	raw, hash, err := auth.NewOpaqueToken()
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to mint invite")
		return
	}
	expiresAt := time.Now().UTC().Add(h.ttl())
	if err := h.invites.Create(r.Context(), storage.CreateInviteParams{
		EventID:   eventID,
		Email:     email,
		Role:      req.Role,
		InvitedBy: hostID,
		TokenHash: hash,
		ExpiresAt: expiresAt,
	}); err != nil {
		h.logger.Error("create invite", "err", err, "event_id", eventID)
		writeError(w, http.StatusInternalServerError, "failed to create invite")
		return
	}

	// Email send is best-effort. Failure still leaves the invite in the DB
	// so a Resend action from the UI can retry; we report `sent: false`
	// so the host knows.
	sent := h.emailInvite(r.Context(), email, hostID, event.Name, req.Role, raw)

	h.audit.Record(r.Context(), audit.Params{
		UserID:     &hostID,
		EventID:    &eventID,
		Action:     "collaborator.invite",
		EntityType: "collaborator_invite",
		Metadata:   map[string]any{"email": email, "role": req.Role, "email_sent": sent},
	})

	writeJSON(w, http.StatusCreated, inviteResponse{
		Email:     email,
		Role:      req.Role,
		ExpiresAt: expiresAt,
		Sent:      sent,
	})
}

// PATCH /events/{id}/collaborators/{user_id} — owner-only. Change another
// collaborator's role. Demoting the last owner returns 400.
type updateRoleRequest struct {
	Role domain.Role `json:"role"`
}

func (h *collaboratorHandler) updateRole(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleOwner); !ok {
		return
	}
	userID, ok := parseIDParam(w, r, "user_id")
	if !ok {
		return
	}

	var req updateRoleRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if !req.Role.Valid() {
		writeError(w, http.StatusBadRequest, "role must be owner|editor|viewer")
		return
	}

	if err := h.collabs.UpdateRole(r.Context(), eventID, userID, req.Role); err != nil {
		switch {
		case errors.Is(err, domain.ErrCollaboratorNotFound):
			writeError(w, http.StatusNotFound, "collaborator not found")
		case errors.Is(err, domain.ErrLastOwner):
			writeError(w, http.StatusBadRequest, "cannot demote the last owner — promote someone else first")
		default:
			h.logger.Error("update role", "err", err)
			writeError(w, http.StatusInternalServerError, "failed to update role")
		}
		return
	}
	h.audit.Record(r.Context(), audit.Params{
		UserID:     &hostID,
		EventID:    &eventID,
		Action:     "collaborator.role_change",
		EntityType: "collaborator",
		TargetID:   &userID,
		Metadata:   map[string]any{"role": req.Role},
	})
	w.WriteHeader(http.StatusNoContent)
}

// DELETE /events/{id}/collaborators/{user_id} — owner-only. Removing the
// last owner returns 400.
func (h *collaboratorHandler) remove(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleOwner); !ok {
		return
	}
	userID, ok := parseIDParam(w, r, "user_id")
	if !ok {
		return
	}

	if err := h.collabs.Remove(r.Context(), eventID, userID); err != nil {
		switch {
		case errors.Is(err, domain.ErrCollaboratorNotFound):
			writeError(w, http.StatusNotFound, "collaborator not found")
		case errors.Is(err, domain.ErrLastOwner):
			writeError(w, http.StatusBadRequest, "cannot remove the last owner — promote someone else first")
		default:
			h.logger.Error("remove collaborator", "err", err)
			writeError(w, http.StatusInternalServerError, "failed to remove collaborator")
		}
		return
	}
	h.audit.Record(r.Context(), audit.Params{
		UserID:     &hostID,
		EventID:    &eventID,
		Action:     "collaborator.remove",
		EntityType: "collaborator",
		TargetID:   &userID,
	})
	w.WriteHeader(http.StatusNoContent)
}

// DELETE /events/{id}/collaborators/pending — owner-only. Cancels a
// still-unconsumed invite for the given email. Idempotent: no rows is a 204.
func (h *collaboratorHandler) cancelInvite(w http.ResponseWriter, r *http.Request) {
	hostID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	eventID, ok := parseIDParam(w, r, "id")
	if !ok {
		return
	}
	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleOwner); !ok {
		return
	}

	email := strings.TrimSpace(r.URL.Query().Get("email"))
	if email == "" {
		writeError(w, http.StatusBadRequest, "email query parameter required")
		return
	}
	if err := h.invites.DeletePendingByEmail(r.Context(), eventID, email); err != nil {
		writeError(w, http.StatusInternalServerError, "failed to cancel invite")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// --- "your pending invites" (self-service inbox) ---

// GET /me/invites — authed. Lists invites addressed to the caller's email
// so the dashboard can show a one-click Accept banner without requiring
// the user to re-click the email link. Crucial for the signup → verify-
// email → login flow where the email click opens a new tab and the
// original invite tab is forgotten.
func (h *collaboratorHandler) myInvites(w http.ResponseWriter, r *http.Request) {
	userID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	user, err := h.users.GetByID(r.Context(), userID)
	if err != nil || user == nil {
		writeError(w, http.StatusUnauthorized, "unauthenticated")
		return
	}
	pending, err := h.invites.ListPendingForEmail(r.Context(), user.Email)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "failed to list invites")
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"invites": pending})
}

// POST /me/invites/{event_id}/accept — authed. Accepts the latest pending
// invite for (caller.email, event_id). Same effect as POST /invites/{token}/
// accept but doesn't require the raw token; the caller's verified email is
// the identity signal instead.
func (h *collaboratorHandler) acceptForEvent(w http.ResponseWriter, r *http.Request) {
	userID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	user, err := h.users.GetByID(r.Context(), userID)
	if err != nil || user == nil {
		writeError(w, http.StatusUnauthorized, "unauthenticated")
		return
	}
	eventID, ok := parseIDParam(w, r, "event_id")
	if !ok {
		return
	}
	role, err := h.collabs.AcceptByEventAndEmail(r.Context(), eventID, user.Email, userID)
	if err != nil {
		switch {
		case errors.Is(err, domain.ErrInviteNotFound):
			writeError(w, http.StatusNotFound, "no pending invitation for this event")
		default:
			h.logger.Error("accept by email", "err", err)
			writeError(w, http.StatusInternalServerError, "failed to accept invitation")
		}
		return
	}
	writeJSON(w, http.StatusOK, acceptResponse{EventID: eventID, Role: role})
}

// --- public invite-accept flow ---

type inviteSummary struct {
	EventID   uuid.UUID   `json:"event_id"`
	EventName string      `json:"event_name"`
	Role      domain.Role `json:"role"`
	Email     string      `json:"email"`
	ExpiresAt time.Time   `json:"expires_at"`
}

// GET /invites/{token} — preview the invitation. Used by the frontend
// accept page to render "Foo invited you to Bar as Editor" before the user
// hits Accept. Doesn't require auth — the caller might not have an account
// yet. Returns the same error codes accept does so the UI can branch
// cleanly.
func (h *collaboratorHandler) previewInvite(w http.ResponseWriter, r *http.Request) {
	inv, event, ok := h.loadInvite(w, r)
	if !ok {
		return
	}
	writeJSON(w, http.StatusOK, inviteSummary{
		EventID:   inv.EventID,
		EventName: event.Name,
		Role:      inv.Role,
		Email:     inv.Email,
		ExpiresAt: inv.ExpiresAt,
	})
}

type acceptResponse struct {
	EventID uuid.UUID   `json:"event_id"`
	Role    domain.Role `json:"role"`
}

// POST /invites/{token}/accept — authed: the caller must be logged in as
// the invitee. If the email on the invite doesn't match the caller's
// account, we 403 (mirrors how multi-tenant tools handle "this link was
// sent to someone else"). Single-use; token is consumed atomically with
// the collaborator insert.
func (h *collaboratorHandler) acceptInvite(w http.ResponseWriter, r *http.Request) {
	userID, ok := hostFromContext(w, r)
	if !ok {
		return
	}
	caller, err := h.users.GetByID(r.Context(), userID)
	if err != nil || caller == nil {
		writeError(w, http.StatusUnauthorized, "unauthenticated")
		return
	}
	inv, event, ok := h.loadInvite(w, r)
	if !ok {
		return
	}
	if !strings.EqualFold(strings.TrimSpace(caller.Email), strings.TrimSpace(inv.Email)) {
		writeError(w, http.StatusForbidden, "invitation was sent to a different email")
		return
	}

	tokenHash := auth.HashOpaque(r.PathValue("token"))
	if err := h.collabs.AcceptInvite(r.Context(), tokenHash, userID, inv.EventID, inv.InvitedBy, inv.Role); err != nil {
		switch {
		case errors.Is(err, domain.ErrInviteAlreadyConsumed):
			writeError(w, http.StatusGone, "invitation already used")
		case errors.Is(err, domain.ErrCollaboratorExists):
			// Already on the event — treat as success (idempotent accept).
			writeJSON(w, http.StatusOK, acceptResponse{EventID: inv.EventID, Role: inv.Role})
		default:
			h.logger.Error("accept invite", "err", err)
			writeError(w, http.StatusInternalServerError, "failed to accept invite")
		}
		return
	}
	_ = event
	writeJSON(w, http.StatusOK, acceptResponse{EventID: inv.EventID, Role: inv.Role})
}

// loadInvite validates the path token, fetches the invite (rejecting
// expired/consumed/missing with the right status), and resolves the
// associated event. Returns the invite + event on success.
func (h *collaboratorHandler) loadInvite(w http.ResponseWriter, r *http.Request) (*domain.CollaboratorInvite, *domain.Event, bool) {
	raw := r.PathValue("token")
	if raw == "" {
		writeError(w, http.StatusBadRequest, "missing invite token")
		return nil, nil, false
	}
	inv, err := h.invites.Get(r.Context(), auth.HashOpaque(raw))
	if err != nil {
		switch {
		case errors.Is(err, domain.ErrInviteNotFound):
			writeError(w, http.StatusNotFound, "invitation not found")
		case errors.Is(err, domain.ErrInviteExpired):
			writeError(w, http.StatusGone, "invitation expired")
		case errors.Is(err, domain.ErrInviteAlreadyConsumed):
			writeError(w, http.StatusGone, "invitation already used")
		default:
			writeError(w, http.StatusInternalServerError, "failed to load invite")
		}
		return nil, nil, false
	}
	event, err := h.events.Get(r.Context(), inv.EventID)
	if err != nil {
		if errors.Is(err, domain.ErrEventNotFound) {
			writeError(w, http.StatusNotFound, "event no longer exists")
			return nil, nil, false
		}
		writeError(w, http.StatusInternalServerError, "failed to load event")
		return nil, nil, false
	}
	return inv, event, true
}

// emailInvite dispatches the invite email via the configured sender.
// Best-effort: a failure is logged + returns false so the response can flag
// it; the invitation row is preserved in either case.
func (h *collaboratorHandler) emailInvite(ctx context.Context, to string, inviterID uuid.UUID, eventName string, role domain.Role, raw string) bool {
	if h.emails == nil {
		return false
	}
	inviterName := ""
	if inv, err := h.users.GetByID(ctx, inviterID); err == nil && inv != nil {
		inviterName = inv.Name
	}
	link := h.acceptLink(raw)
	if err := h.emails.SendCollaboratorInvite(ctx, to, inviterName, eventName, string(role), link); err != nil {
		h.logger.Warn("send collaborator invite (continuing)", "err", err, "to", to)
		return false
	}
	return true
}

func (h *collaboratorHandler) acceptLink(raw string) string {
	base := h.publicBaseURL
	if base == "" {
		base = "http://localhost:3000"
	}
	return base + "/invites/" + raw
}

func (h *collaboratorHandler) ttl() time.Duration {
	if h.inviteTTL > 0 {
		return h.inviteTTL
	}
	return domain.DefaultInviteTTL
}