package api

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"

	"carcontrol/api/internal/models"
)

// Access levels a user can have on a car. accessNone means no access at all.
const (
	accessNone  = ""
	accessRead  = "read"
	accessWrite = "write"
	accessOwner = "owner"
)

// carAccessLevel reports the requesting user's permission on a car: "owner" if
// they own it, otherwise the permission from any car_shares grant ("read"/
// "write"), otherwise "" (no access). It also returns the car record so callers
// that already need it avoid a second fetch.
func (s *Server) carAccessLevel(ctx context.Context, userID, carID string) (string, *carRecord, error) {
	var rec carRecord
	if err := s.pb.GetOne(ctx, colCars, carID, &rec); err != nil {
		return accessNone, nil, err
	}
	if rec.Owner == userID {
		return accessOwner, &rec, nil
	}
	perm, err := s.sharePermission(ctx, carID, userID)
	if err != nil {
		return accessNone, &rec, err
	}
	return perm, &rec, nil
}

// sharePermission returns the permission ("read"/"write") granted to userID on
// carID via car_shares, or "" if there is no grant.
func (s *Server) sharePermission(ctx context.Context, carID, userID string) (string, error) {
	res, err := s.pb.List(ctx, colShares, url.Values{
		"filter":  {fmt.Sprintf("car='%s' && user='%s'", carID, userID)},
		"perPage": {"1"},
	})
	if err != nil {
		return "", err
	}
	var recs []shareRecord
	if err := json.Unmarshal(res.Items, &recs); err != nil || len(recs) == 0 {
		return "", err
	}
	return recs[0].Permission, nil
}

func canWrite(level string) bool { return level == accessOwner || level == accessWrite }

// requireCarAccess enforces that the current user's access to carID meets the
// minimum `need` (accessRead = any access, accessWrite = write or owner,
// accessOwner = owner only). On failure it writes the HTTP response and returns
// false, so callers can `if !s.requireCarAccess(...) { return }`.
func (s *Server) requireCarAccess(w http.ResponseWriter, r *http.Request, carID, need string) bool {
	if carID == "" {
		writeError(w, http.StatusBadRequest, "car is required")
		return false
	}
	level, _, err := s.carAccessLevel(r.Context(), s.currentUserID(r), carID)
	if err != nil {
		writePBError(w, err)
		return false
	}
	var ok bool
	switch need {
	case accessWrite:
		ok = canWrite(level)
	case accessOwner:
		ok = level == accessOwner
	default: // accessRead / any
		ok = level != accessNone
	}
	if !ok {
		writeError(w, http.StatusForbidden, "you do not have access to this car")
		return false
	}
	return true
}

func (s *Server) listCars(w http.ResponseWriter, r *http.Request) {
	me := s.currentUserID(r)

	// Cars the user owns.
	ownedRes, err := s.pb.List(r.Context(), colCars, url.Values{
		"filter":  {fmt.Sprintf("owner='%s'", me)},
		"sort":    {"name"},
		"perPage": {"200"},
	})
	if err != nil {
		writePBError(w, err)
		return
	}
	var owned []carRecord
	if err := json.Unmarshal(ownedRes.Items, &owned); err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	out := make([]models.Car, 0, len(owned))
	for _, rec := range owned {
		m := rec.toModel()
		m.Access = accessOwner
		out = append(out, m)
	}

	// Cars shared with the user (each grant → fetch the car, annotate access).
	sharesRes, err := s.pb.List(r.Context(), colShares, url.Values{
		"filter":  {fmt.Sprintf("user='%s'", me)},
		"perPage": {"200"},
	})
	if err != nil {
		writePBError(w, err)
		return
	}
	var shares []shareRecord
	if err := json.Unmarshal(sharesRes.Items, &shares); err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	for _, sh := range shares {
		var rec carRecord
		if err := s.pb.GetOne(r.Context(), colCars, sh.Car, &rec); err != nil {
			continue // grant points at a deleted car; skip defensively
		}
		m := rec.toModel()
		m.Access = sh.Permission
		out = append(out, m)
	}

	writeJSON(w, http.StatusOK, out)
}

func (s *Server) getCar(w http.ResponseWriter, r *http.Request) {
	level, rec, err := s.carAccessLevel(r.Context(), s.currentUserID(r), r.PathValue("id"))
	if err != nil {
		writePBError(w, err)
		return
	}
	if level == accessNone {
		writeError(w, http.StatusForbidden, "you do not have access to this car")
		return
	}
	m := rec.toModel()
	m.Access = level
	writeJSON(w, http.StatusOK, m)
}

func (s *Server) createCar(w http.ResponseWriter, r *http.Request) {
	var in models.Car
	if err := decodeJSON(r, &in); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	if in.Name == "" {
		writeError(w, http.StatusBadRequest, "name is required")
		return
	}
	applyCarDefaults(&in)

	// Owner is always the authenticated user; ignore any client-supplied owner.
	payload := carPayload(in)
	payload["owner"] = s.currentUserID(r)

	var rec carRecord
	if err := s.pb.Create(r.Context(), colCars, payload, &rec); err != nil {
		writePBError(w, err)
		return
	}
	m := rec.toModel()
	m.Access = accessOwner
	writeJSON(w, http.StatusCreated, m)
}

func (s *Server) updateCar(w http.ResponseWriter, r *http.Request) {
	var in models.Car
	if err := decodeJSON(r, &in); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}
	level, _, err := s.carAccessLevel(r.Context(), s.currentUserID(r), r.PathValue("id"))
	if err != nil {
		writePBError(w, err)
		return
	}
	if !canWrite(level) {
		writeError(w, http.StatusForbidden, "you cannot edit this car")
		return
	}
	// carPayload deliberately omits owner, so a PATCH never reassigns ownership.
	var rec carRecord
	if err := s.pb.Update(r.Context(), colCars, r.PathValue("id"), carPayload(in), &rec); err != nil {
		writePBError(w, err)
		return
	}
	m := rec.toModel()
	m.Access = level
	writeJSON(w, http.StatusOK, m)
}

func (s *Server) deleteCar(w http.ResponseWriter, r *http.Request) {
	level, _, err := s.carAccessLevel(r.Context(), s.currentUserID(r), r.PathValue("id"))
	if err != nil {
		writePBError(w, err)
		return
	}
	if level != accessOwner {
		writeError(w, http.StatusForbidden, "only the owner can delete this car")
		return
	}
	if err := s.pb.Delete(r.Context(), colCars, r.PathValue("id")); err != nil {
		writePBError(w, err)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// applyCarDefaults fills the spreadsheet's default maintenance intervals when
// the client didn't specify them.
func applyCarDefaults(c *models.Car) {
	if c.ServiceIntervalDays <= 0 {
		c.ServiceIntervalDays = 365
	}
	if c.ServiceIntervalKm <= 0 {
		c.ServiceIntervalKm = 15000
	}
}