package service

import (
	"errors"
	"fmt"
)

// Plan caps for the social features. Updates here propagate everywhere via
// EnforceBookmarkLimit / EnforceCollectionLimit.
const (
	PlanFree    = "free"
	PlanPremium = "premium"

	freeBookmarkLimit    = 1
	premiumBookmarkLimit = 5

	freeCollectionPerVisibilityLimit = 5 // 5 public AND 5 private separately
	// Premium has no collection cap.
)

// ErrPlanLimit signals that a free-plan limit blocks the requested action.
// Handlers surface this as HTTP 402 (Payment Required) so clients can show
// an upsell. The message tells the user what cap was hit.
var ErrPlanLimit = errors.New("plan limit reached")

// PlanLimitError carries detail about which limit was hit so the frontend
// can render a helpful message instead of a generic "upgrade to premium".
type PlanLimitError struct {
	Resource string // e.g. "bookmarks", "private collections"
	Limit    int
	Plan     string
}

func (e *PlanLimitError) Error() string {
	return fmt.Sprintf("%s limit reached (%d on %s plan)", e.Resource, e.Limit, e.Plan)
}

func (e *PlanLimitError) Is(target error) bool { return target == ErrPlanLimit }

// EnforceBookmarkLimit returns nil if the user is allowed to create one more
// bookmark, or a PlanLimitError otherwise.
func EnforceBookmarkLimit(plan string, currentCount int) error {
	limit := bookmarkLimitFor(plan)
	if currentCount >= limit {
		return &PlanLimitError{Resource: "bookmarks", Limit: limit, Plan: plan}
	}
	return nil
}

// EnforceCollectionLimit returns nil if the user is allowed to create one
// more collection of the given visibility.
//
// `isPublic=true`  → checks against public-collection cap
// `isPublic=false` → checks against private-collection cap
// Premium users have no cap → always nil.
func EnforceCollectionLimit(plan string, isPublic bool, currentCount int) error {
	if plan == PlanPremium {
		return nil
	}
	limit := freeCollectionPerVisibilityLimit
	if currentCount >= limit {
		resource := "private collections"
		if isPublic {
			resource = "public collections"
		}
		return &PlanLimitError{Resource: resource, Limit: limit, Plan: plan}
	}
	return nil
}

func bookmarkLimitFor(plan string) int {
	if plan == PlanPremium {
		return premiumBookmarkLimit
	}
	return freeBookmarkLimit
}

// BookmarkLimitFor returns the cap (for showing "X / Y used" in the UI).
func BookmarkLimitFor(plan string) int { return bookmarkLimitFor(plan) }

// CollectionLimitFor returns the per-visibility cap. -1 means unlimited.
func CollectionLimitFor(plan string) int {
	if plan == PlanPremium {
		return -1
	}
	return freeCollectionPerVisibilityLimit
}