package access

import (
	"context"
	"encoding/json"
	"fmt"
	"sort"

	"github.com/Silo-Server/silo-server/internal/models"
	"github.com/Silo-Server/silo-server/internal/userstore"
)

// settingKeyDisabledLibraryIDs is the user-settings key that stores a JSON
// array of library IDs the user has chosen to hide.
const settingKeyDisabledLibraryIDs = "disabled_library_ids"

// UserRepository loads account-level access settings.
type UserRepository interface {
	GetByID(ctx context.Context, id int) (*models.User, error)
}

// ProfileTokenValidator validates short-lived profile verification tokens.
type ProfileTokenValidator interface {
	Validate(tokenStr string) (*ProfileTokenClaims, error)
}

// Resolver resolves a viewer request into an effective access scope.
type Resolver struct {
	users        UserRepository
	storeFactory userstore.UserStoreProvider
	tokens       ProfileTokenValidator
}

// NewResolver creates a new scope resolver.
func NewResolver(users UserRepository, storeFactory userstore.UserStoreProvider, tokens ProfileTokenValidator) *Resolver {
	return &Resolver{
		users:        users,
		storeFactory: storeFactory,
		tokens:       tokens,
	}
}

// Resolve computes the effective viewer scope for the request.
func (r *Resolver) Resolve(ctx context.Context, input ResolveInput) (Scope, error) {
	user, err := r.users.GetByID(ctx, input.UserID)
	if err != nil {
		return Scope{}, fmt.Errorf("loading user %d: %w", input.UserID, err)
	}

	scope := Scope{
		UserID:              user.ID,
		ProfileID:           input.ProfileID,
		AllowedLibraryIDs:   cloneInts(user.LibraryIDs),
		LibrariesRestricted: user.LibraryIDs != nil,
		MaxPlaybackQuality:  NormalizePlaybackQuality(user.MaxPlaybackQuality),
		PolicyRevision:      user.AccessPolicyRevision,
		ProfileVerified:     input.ProfileID == "",
	}

	store, err := r.storeFactory.ForUser(ctx, input.UserID)
	if err != nil {
		return Scope{}, fmt.Errorf("opening user store for %d: %w", input.UserID, err)
	}

	if input.ProfileID != "" {
		profile, err := store.GetProfile(ctx, input.ProfileID)
		if err != nil {
			return Scope{}, fmt.Errorf("loading profile %s: %w", input.ProfileID, err)
		}
		if profile == nil {
			return Scope{}, ErrProfileNotFound
		}

		scope.MaxContentRating = profile.MaxContentRating
		scope.MaxPlaybackQuality = MinQuality(scope.MaxPlaybackQuality, NormalizePlaybackQuality(profile.MaxPlaybackQuality))
		scope.AllowedLibraryIDs, scope.LibrariesRestricted = effectiveLibraries(user.LibraryIDs, profile)
		scope.ProfileVerified = profile.PINHash == "" || input.SkipPINVerification

		if profile.PINHash != "" && !input.SkipPINVerification {
			if r.tokens == nil {
				return Scope{}, ErrProfileUnverified
			}
			claims, err := r.tokens.Validate(input.ProfileToken)
			if err != nil {
				return Scope{}, err
			}
			if claims.UserID != user.ID || claims.SessionID != input.SessionID || claims.ProfileID != profile.ID || claims.PolicyRevision != user.AccessPolicyRevision {
				return Scope{}, ErrProfileUnverified
			}
			scope.ProfileVerified = true
		}
	}

	// Apply user-level disabled library IDs setting.
	disabled := loadDisabledLibraryIDs(ctx, store)
	if len(disabled) > 0 {
		if scope.AllowedLibraryIDs != nil {
			// Restricted user: subtract disabled IDs from the allowed set.
			scope.AllowedLibraryIDs = subtractInts(scope.AllowedLibraryIDs, disabled)
		} else {
			// Unrestricted user: pass disabled IDs through so query layer
			// can apply a NOT IN filter.
			scope.DisabledLibraryIDs = disabled
		}
	}

	return scope, nil
}

// loadDisabledLibraryIDs reads and parses the disabled_library_ids user setting.
func loadDisabledLibraryIDs(ctx context.Context, store userstore.UserStore) []int {
	raw, err := store.GetSetting(ctx, settingKeyDisabledLibraryIDs)
	if err != nil || raw == "" {
		return nil
	}
	var ids []int
	if err := json.Unmarshal([]byte(raw), &ids); err != nil {
		return nil
	}
	// Filter out invalid values.
	n := 0
	for _, id := range ids {
		if id > 0 {
			ids[n] = id
			n++
		}
	}
	return ids[:n]
}

// subtractInts removes all values in exclude from src, preserving order.
func subtractInts(src, exclude []int) []int {
	if len(exclude) == 0 {
		return src
	}
	set := make(map[int]struct{}, len(exclude))
	for _, id := range exclude {
		set[id] = struct{}{}
	}
	out := make([]int, 0, len(src))
	for _, id := range src {
		if _, ok := set[id]; !ok {
			out = append(out, id)
		}
	}
	return out
}

func effectiveLibraries(accountLibraryIDs []int, profile *userstore.Profile) ([]int, bool) {
	accountRestricted := accountLibraryIDs != nil
	profileRestricted := profile.LibraryRestrictionsEnabled

	switch {
	case accountRestricted && profileRestricted:
		return intersectInts(accountLibraryIDs, profile.AllowedLibraryIDs), true
	case accountRestricted:
		return cloneInts(accountLibraryIDs), true
	case profileRestricted:
		return sortedUniqueInts(profile.AllowedLibraryIDs), true
	default:
		return nil, false
	}
}

func intersectInts(left, right []int) []int {
	if len(left) == 0 || len(right) == 0 {
		return []int{}
	}
	set := make(map[int]struct{}, len(left))
	for _, id := range left {
		set[id] = struct{}{}
	}
	var out []int
	for _, id := range right {
		if _, ok := set[id]; ok {
			out = append(out, id)
		}
	}
	return sortedUniqueInts(out)
}

func sortedUniqueInts(values []int) []int {
	if len(values) == 0 {
		return []int{}
	}
	out := cloneInts(values)
	sort.Ints(out)
	n := 1
	for i := 1; i < len(out); i++ {
		if out[i] != out[i-1] {
			out[n] = out[i]
			n++
		}
	}
	return out[:n]
}

func cloneInts(values []int) []int {
	if values == nil {
		return nil
	}
	out := make([]int, len(values))
	copy(out, values)
	return out
}