package timeoff

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"time"

	"git.unsupervised.ca/walkies/internal/respond"
	"git.unsupervised.ca/walkies/internal/server/middleware"
	"github.com/go-chi/chi/v5"
)

// Notifier is the subset of notification.Store the handler needs.
type Notifier interface {
	CreateNotification(ctx context.Context, volunteerID int64, message string) error
}

// AdminLister returns admin volunteer IDs so the handler can notify them.
type AdminLister interface {
	ListAdminIDs(ctx context.Context) ([]int64, error)
}

// Storer is the interface the Handler depends on.
type Storer interface {
	Create(ctx context.Context, volunteerID int64, in CreateInput) (*Request, error)
	GetByID(ctx context.Context, id int64) (*Request, error)
	List(ctx context.Context, volunteerID int64) ([]Request, error)
	Review(ctx context.Context, id, reviewerID int64, status string) (*Request, error)
	Update(ctx context.Context, id int64, in UpdateInput) (*Request, error)
	Delete(ctx context.Context, id int64) error
	ConflictingShifts(ctx context.Context, volunteerID int64, startsAt, endsAt string) ([]ConflictingShift, error)
	RemoveFromConflictingShifts(ctx context.Context, timeOffID, volunteerID int64, startsAt, endsAt string) ([]ConflictingShift, error)
	RemovedShiftsForTimeOff(ctx context.Context, timeOffID int64) ([]ConflictingShift, error)
	RestoreRemovedShifts(ctx context.Context, timeOffID int64) ([]ConflictingShift, error)
}

type Handler struct {
	store       Storer
	notifier    Notifier
	adminLister AdminLister
}

func NewHandler(store *Store, notifier Notifier, adminLister AdminLister) *Handler {
	return &Handler{store: store, notifier: notifier, adminLister: adminLister}
}

// NewHandlerFromInterfaces constructs a Handler from interface values, intended for testing.
func NewHandlerFromInterfaces(store Storer, notifier Notifier, adminLister AdminLister) *Handler {
	return &Handler{store: store, notifier: notifier, adminLister: adminLister}
}

// GET /api/v1/timeoff
func (h *Handler) List(w http.ResponseWriter, r *http.Request) {
	claims := middleware.ClaimsFromContext(r.Context())
	volunteerID := int64(0)
	if claims.Role != "admin" {
		volunteerID = claims.VolunteerID
	}
	requests, err := h.store.List(r.Context(), volunteerID)
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not list time off requests")
		return
	}
	if requests == nil {
		requests = []Request{}
	}
	respond.JSON(w, http.StatusOK, requests)
}

// POST /api/v1/timeoff
// Creates time off with status "approved". If confirm_conflicts is true and the
// volunteer is assigned to shifts in the date range, they are auto-removed and
// admins are notified (FR-T03).
func (h *Handler) Create(w http.ResponseWriter, r *http.Request) {
	claims := middleware.ClaimsFromContext(r.Context())
	var in CreateInput
	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if in.StartsAt == "" || in.EndsAt == "" {
		respond.Error(w, http.StatusBadRequest, "starts_at and ends_at are required")
		return
	}

	// Determine target volunteer (admin can create for others, FR-T05)
	targetVolunteerID := claims.VolunteerID
	if in.VolunteerID > 0 && claims.Role == "admin" {
		targetVolunteerID = in.VolunteerID
	}

	// Check for conflicting shifts
	conflicts, err := h.store.ConflictingShifts(r.Context(), targetVolunteerID, in.StartsAt, in.EndsAt)
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not check conflicts")
		return
	}

	// If there are conflicts and the user hasn't confirmed, return them
	if len(conflicts) > 0 && !in.ConfirmConflicts {
		respond.JSON(w, http.StatusConflict, map[string]any{
			"message":    "Time off conflicts with assigned shifts. Confirm to proceed.",
			"conflicts":  conflicts,
		})
		return
	}

	// Create with auto-approved status
	req, err := h.store.Create(r.Context(), targetVolunteerID, in)
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not create time off request")
		return
	}

	// Auto-approve
	req, err = h.store.Review(r.Context(), req.ID, claims.VolunteerID, "approved")
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not approve time off request")
		return
	}

	// Remove from conflicting shifts (FR-T03)
	if len(conflicts) > 0 {
		removed, err := h.store.RemoveFromConflictingShifts(r.Context(), req.ID, targetVolunteerID, in.StartsAt, in.EndsAt)
		if err != nil {
			respond.Error(w, http.StatusInternalServerError, "could not remove from conflicting shifts")
			return
		}
		// Notify admins
		h.notifyAdmins(r.Context(), targetVolunteerID, removed)
	}

	respond.JSON(w, http.StatusCreated, req)
}

// PUT /api/v1/timeoff/{id}
// Volunteers can edit their own future time off (FR-T02). Admins can edit any (FR-T05).
func (h *Handler) Update(w http.ResponseWriter, r *http.Request) {
	claims := middleware.ClaimsFromContext(r.Context())
	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid id")
		return
	}

	existing, err := h.store.GetByID(r.Context(), id)
	if errors.Is(err, ErrNotFound) {
		respond.Error(w, http.StatusNotFound, "time off request not found")
		return
	}
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not get time off request")
		return
	}

	// Permission: volunteers can only edit their own future time off
	if claims.Role != "admin" {
		if existing.VolunteerID != claims.VolunteerID {
			respond.Error(w, http.StatusForbidden, "cannot edit another volunteer's time off")
			return
		}
		if !existing.StartsAt.After(time.Now()) {
			respond.Error(w, http.StatusForbidden, "cannot edit past time off")
			return
		}
	}

	var in UpdateInput
	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if in.StartsAt == "" || in.EndsAt == "" {
		respond.Error(w, http.StatusBadRequest, "starts_at and ends_at are required")
		return
	}

	req, err := h.store.Update(r.Context(), id, in)
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not update time off request")
		return
	}
	respond.JSON(w, http.StatusOK, req)
}

// DELETE /api/v1/timeoff/{id}
// Volunteers can delete their own future time off (FR-T02).
// Admin delete restores the volunteer to previously removed shifts (FR-T04).
func (h *Handler) Delete(w http.ResponseWriter, r *http.Request) {
	claims := middleware.ClaimsFromContext(r.Context())
	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid id")
		return
	}

	existing, err := h.store.GetByID(r.Context(), id)
	if errors.Is(err, ErrNotFound) {
		respond.Error(w, http.StatusNotFound, "time off request not found")
		return
	}
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not get time off request")
		return
	}

	// Permission: volunteers can only delete their own future time off
	if claims.Role != "admin" {
		if existing.VolunteerID != claims.VolunteerID {
			respond.Error(w, http.StatusForbidden, "cannot delete another volunteer's time off")
			return
		}
		if !existing.StartsAt.After(time.Now()) {
			respond.Error(w, http.StatusForbidden, "cannot delete past time off")
			return
		}
	}

	// If admin is deleting, restore volunteer to removed shifts (FR-T04)
	var restored []ConflictingShift
	if claims.Role == "admin" {
		restored, err = h.store.RestoreRemovedShifts(r.Context(), id)
		if err != nil {
			respond.Error(w, http.StatusInternalServerError, "could not restore shifts")
			return
		}
	}

	if err := h.store.Delete(r.Context(), id); err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not delete time off request")
		return
	}

	respond.JSON(w, http.StatusOK, map[string]any{
		"deleted":         true,
		"restored_shifts": restored,
	})
}

// GET /api/v1/timeoff/{id}/shifts
// Returns shifts that were removed due to this time-off request (preview for FR-T04).
func (h *Handler) RemovedShifts(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid id")
		return
	}

	shifts, err := h.store.RemovedShiftsForTimeOff(r.Context(), id)
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not get removed shifts")
		return
	}
	if shifts == nil {
		shifts = []ConflictingShift{}
	}
	respond.JSON(w, http.StatusOK, shifts)
}

// PUT /api/v1/timeoff/{id}/review
func (h *Handler) Review(w http.ResponseWriter, r *http.Request) {
	claims := middleware.ClaimsFromContext(r.Context())
	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid id")
		return
	}
	var in ReviewInput
	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
		respond.Error(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if in.Status != "approved" && in.Status != "rejected" {
		respond.Error(w, http.StatusBadRequest, "status must be 'approved' or 'rejected'")
		return
	}
	req, err := h.store.Review(r.Context(), id, claims.VolunteerID, in.Status)
	if errors.Is(err, ErrNotFound) {
		respond.Error(w, http.StatusNotFound, "time off request not found")
		return
	}
	if err != nil {
		respond.Error(w, http.StatusInternalServerError, "could not review time off request")
		return
	}
	respond.JSON(w, http.StatusOK, req)
}

// notifyAdmins sends a notification to all admin users about a volunteer's
// shift removals due to time off (FR-T03).
func (h *Handler) notifyAdmins(ctx context.Context, volunteerID int64, removed []ConflictingShift) {
	if len(removed) == 0 {
		return
	}
	adminIDs, err := h.adminLister.ListAdminIDs(ctx)
	if err != nil {
		return
	}
	msg := fmt.Sprintf("Volunteer %d has been removed from %d shift(s) due to time off.", volunteerID, len(removed))
	for _, aid := range adminIDs {
		h.notifier.CreateNotification(ctx, aid, msg) //nolint:errcheck
	}
}