package products

import (
	"encoding/json"
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"sync"
)

// FirstLocalID is where the client's numbers for community products start. IMVU's product IDs are far below
// (about 72 million in 2026), and the client's XML-RPC can't carry numbers past 2^31-1.
const FirstLocalID = 2_000_000_000

// state is what the proxy remembers between runs, in <data dir>/products.json: the local ID of every product it
// has served (so outfits keep naming the same product), and the community products each IMVU account wears (IMVU
// never sees them, so it can't remember them).
type state struct {
	mu   sync.Mutex
	path string
	data stateData
}

type stateData struct {
	IDs  map[string]int64      `json:"ids"`  // product ID -> local ID
	Worn map[string]wornOutfit `json:"worn"` // IMVU user ID -> what they wear
}

// wornOutfit is an account's outfit as last saved or sent: the IMVU products IMVU got, and the community products
// taken out. The community products are added back only to that same outfit: if IMVU's outfit changed elsewhere
// (another client, the website), they'd no longer fit it.
type wornOutfit struct {
	IMVU     []int64  `json:"imvu"`
	Products []string `json:"products"`
}

func loadState(path string) (*state, error) {
	s := &state{path: path, data: stateData{IDs: map[string]int64{}, Worn: map[string]wornOutfit{}}}
	b, err := os.ReadFile(path)
	if errors.Is(err, fs.ErrNotExist) {
		return s, nil
	}
	if err != nil {
		return nil, err
	}
	if err := json.Unmarshal(b, &s.data); err != nil {
		return nil, err
	}
	if s.data.IDs == nil {
		s.data.IDs = map[string]int64{}
	}
	if s.data.Worn == nil {
		s.data.Worn = map[string]wornOutfit{}
	}
	return s, nil
}

// localID is the product's local ID, given one if it has none yet.
func (s *state) localID(product string) (int64, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if id, ok := s.data.IDs[product]; ok {
		return id, nil
	}
	next := int64(FirstLocalID)
	for _, id := range s.data.IDs {
		next = max(next, id+1)
	}
	if next > 2_147_483_647 {
		return 0, errors.New("products: out of local IDs")
	}
	s.data.IDs[product] = next
	return next, s.saveLocked()
}

// worn is the community products the user wears with the IMVU outfit look, if they were recorded with it.
func (s *state) worn(user string, look []int64) []string {
	s.mu.Lock()
	defer s.mu.Unlock()
	w, ok := s.data.Worn[user]
	if !ok || !sameSet(w.IMVU, look) {
		return nil
	}
	return append([]string(nil), w.Products...)
}

// setWorn records the user's outfit: the IMVU products IMVU got, and the community products taken out.
func (s *state) setWorn(user string, imvu []int64, products []string) error {
	w := wornOutfit{IMVU: append([]int64(nil), imvu...), Products: append([]string(nil), products...)}
	sort.Slice(w.IMVU, func(i, j int) bool { return w.IMVU[i] < w.IMVU[j] })
	sort.Strings(w.Products)
	s.mu.Lock()
	defer s.mu.Unlock()
	old, had := s.data.Worn[user]
	if had && sameSet(old.IMVU, w.IMVU) && equal(old.Products, w.Products) {
		return nil
	}
	if len(w.Products) == 0 {
		if !had {
			return nil
		}
		delete(s.data.Worn, user)
	} else {
		s.data.Worn[user] = w
	}
	return s.saveLocked()
}

// sameSet reports whether a and b hold the same IDs, in any order.
func sameSet(a, b []int64) bool {
	if len(a) != len(b) {
		return false
	}
	count := map[int64]int{}
	for _, v := range a {
		count[v]++
	}
	for _, v := range b {
		if count[v] == 0 {
			return false
		}
		count[v]--
	}
	return true
}

func equal(a, b []string) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}

func (s *state) saveLocked() error {
	b, err := json.MarshalIndent(s.data, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(s.path), 0o700); err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	if err := os.WriteFile(tmp, b, 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, s.path)
}

// productID is the product a local ID was given to.
func (s *state) productID(local int64) (string, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for id, l := range s.data.IDs {
		if l == local {
			return id, true
		}
	}
	return "", false
}