// Package products serves community products to the client from local packs (t5de-api's pack format), and keeps
// them away from IMVU.
//
// The client knows products by number, so each product gets a local ID from FirstLocalID up. For those IDs the
// proxy answers the client itself: product info (test.inventoryProductBatch), permission and file addresses
// (test.authorizeProducts2), the shop's product lookup, and the product's CFL. A product deriving from an IMVU
// product (its index.xml imports the parent's) gets the parent's answers from IMVU, asked for the parent. Outfits
// keep community products for the client but not for IMVU: they're taken out of outfit saves (base_look.php) and
// outfit chat commands (*use ...), remembered per account, and added back when the client loads the outfit.
package products

import (
	"bytes"
	"crypto/md5"
	"encoding/hex"
	"errors"
	"fmt"
	"io/fs"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.t5de.dev/t5de/t5de-api/cfl"
	"git.t5de.dev/t5de/t5de-api/pack"
	"git.t5de.dev/t5de/t5de-proxy/internal/hub"
)

// Products is the proxy's community products: an Interceptor for HTTP and an IMQFilter for chat.
type Products struct {
	dirs  []string
	state *state
	keys  keys
	logf  func(format string, args ...any)

	mu       sync.Mutex
	scanned  time.Time
	byLocal  map[int64]*served
	byID     map[string]*served
	problems map[string]string // pack directory -> last error logged

	// Observer, if set, hears which IMVU account the client signs in as and the community products it wears (the
	// hub client).
	Observer Observer
}

// Observer hears about the client's IMVU account and its community outfit.
type Observer interface {
	Session(imvuID int64)
	Outfit(imvuID int64, items []hub.Item)
}

// served is a pack ready to serve.
type served struct {
	dir         string
	fingerprint string
	pack        *pack.Pack
	local       int64
	cfl         []byte
	checksum    string // md5 of cfl, as IMVU's cflChecksum
}

// New serves the packs in dirs (each pack a subdirectory), remembering its state in dataDir.
func New(dirs []string, dataDir string, logf func(format string, args ...any)) (*Products, error) {
	st, err := loadState(filepath.Join(dataDir, "products.json"))
	if err != nil {
		return nil, err
	}
	if logf == nil {
		logf = func(string, ...any) {}
	}
	p := &Products{dirs: dirs, state: st, logf: logf, byLocal: map[int64]*served{}, byID: map[string]*served{},
		problems: map[string]string{}}
	p.refresh(true)
	return p, nil
}

// IsCommunity reports whether the client's product ID is a community product's local ID.
func IsCommunity(id int64) bool { return id >= FirstLocalID }

// lookup is the pack served under a local ID, after picking up changed packs.
func (p *Products) lookup(local int64) *served {
	p.refresh(false)
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.byLocal[local]
}

func (p *Products) byProductID(id string) *served {
	p.refresh(false)
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.byID[id]
}

// refresh reloads packs that changed on disk, at most once a second unless forced. Creators editing a pack see the
// new files the next time the client loads the product.
func (p *Products) refresh(force bool) {
	p.mu.Lock()
	defer p.mu.Unlock()
	if !force && time.Since(p.scanned) < time.Second {
		return
	}
	p.scanned = time.Now()
	seen := map[string]bool{}
	for _, root := range p.dirs {
		entries, err := os.ReadDir(root)
		if err != nil {
			continue
		}
		for _, e := range entries {
			dir := filepath.Join(root, e.Name())
			if !e.IsDir() {
				continue
			}
			if _, err := os.Stat(filepath.Join(dir, "t5de-product.json")); err != nil {
				continue
			}
			fp := fingerprint(dir)
			if old := p.findDirLocked(dir); old != nil && old.fingerprint == fp {
				seen[old.pack.Manifest.ID] = true
				continue
			}
			s, err := p.loadLocked(dir, fp)
			if err != nil {
				if p.problems[dir] != err.Error() {
					p.logf("products: %s: %v", dir, err)
					p.problems[dir] = err.Error()
				}
				if old := p.findDirLocked(dir); old != nil {
					seen[old.pack.Manifest.ID] = true // keep serving the last good one
				}
				continue
			}
			delete(p.problems, dir)
			if other, ok := p.byID[s.pack.Manifest.ID]; ok && other.dir != dir && seen[s.pack.Manifest.ID] {
				p.logf("products: %s: product %q is also in %s; ignoring this one", dir, s.pack.Manifest.ID, other.dir)
				continue
			}
			p.byID[s.pack.Manifest.ID] = s
			p.byLocal[s.local] = s
			seen[s.pack.Manifest.ID] = true
			p.logf("products: serving %q revision %d (%s) as %d", s.pack.Manifest.ID, s.pack.Manifest.Revision, s.pack.Manifest.Name, s.local)
		}
	}
	for id, s := range p.byID {
		if !seen[id] {
			delete(p.byID, id)
			delete(p.byLocal, s.local)
			p.logf("products: %q is gone", id)
		}
	}
}

func (p *Products) findDirLocked(dir string) *served {
	for _, s := range p.byID {
		if s.dir == dir {
			return s
		}
	}
	return nil
}

func (p *Products) loadLocked(dir, fp string) (*served, error) {
	pk, err := pack.Load(dir)
	if err != nil {
		return nil, err
	}
	local, err := p.state.localID(pk.Manifest.ID)
	if err != nil {
		return nil, err
	}
	entries := make([]cfl.Entry, 0, len(pk.Files))
	for _, f := range pk.Files {
		data := f.Data
		if f.Name == "index.xml" {
			data = withProductName(data, pk.Manifest.Name)
		}
		entries = append(entries, cfl.Entry{Name: f.Name, Data: data})
	}
	var buf bytes.Buffer
	if err := cfl.Write(&buf, entries); err != nil {
		return nil, err
	}
	sum := md5.Sum(buf.Bytes())
	return &served{dir: dir, fingerprint: fp, pack: pk, local: local, cfl: buf.Bytes(), checksum: hex.EncodeToString(sum[:])}, nil
}

// fingerprint changes when anything in the pack directory (or its files/ directory) changes.
func fingerprint(dir string) string {
	var b strings.Builder
	filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return nil
		}
		if info, err := d.Info(); err == nil {
			fmt.Fprintf(&b, "%s|%d|%d\n", path, info.Size(), info.ModTime().UnixNano())
		}
		return nil
	})
	return b.String()
}

var productNamePattern = regexp.MustCompile(`(?s)<ProductName>.*?</ProductName>`)

// withProductName puts the pack's name in index.xml, so the client shows it.
func withProductName(index []byte, name string) []byte {
	var esc bytes.Buffer
	xmlEscape(&esc, name)
	repl := []byte("<ProductName>" + esc.String() + "</ProductName>")
	if productNamePattern.Match(index) {
		return productNamePattern.ReplaceAllLiteral(index, repl)
	}
	return index
}

func xmlEscape(b *bytes.Buffer, s string) {
	r := strings.NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;", `"`, "&quot;", "'", "&apos;")
	b.WriteString(r.Replace(s))
}

// productdata matches IMVU's product file addresses: /productdata/<id>/<revision>[/<file>].
var productdataPath = regexp.MustCompile(`^/productdata/([0-9]+)/([0-9]+)(?:/(.+))?$`)

// cflURL is where the client fetches a community product's CFL: IMVU's address form, answered by the proxy.
func cflURL(local int64, revision int) string {
	return fmt.Sprintf("http://userimages-akm.imvu.com/productdata/%d/%d", local, revision)
}

// serveFile answers a request for a community product's files.
func (p *Products) serveFile(path string) (*http.Response, bool) {
	m := productdataPath.FindStringSubmatch(path)
	if m == nil {
		return nil, false
	}
	local, _ := strconv.ParseInt(m[1], 10, 64)
	if !IsCommunity(local) {
		return nil, false
	}
	s := p.lookup(local)
	rev, _ := strconv.Atoi(m[2])
	if s == nil || rev != s.pack.Manifest.Revision {
		return notFound(), true
	}
	if m[3] == "" {
		resp := localResponse(200, "application/octet-stream", s.cfl)
		resp.Header.Set("Content-MD5", s.checksum)
		return resp, true
	}
	for _, f := range s.pack.Files {
		if f.Name == m[3] {
			return localResponse(200, "application/octet-stream", f.Data), true
		}
	}
	return notFound(), true
}

func notFound() *http.Response {
	return localResponse(404, "text/plain", []byte("t5de: no such community product file"))
}

// wornLocal is the user's community products (local IDs, still served) that go with the IMVU outfit look.
func (p *Products) wornLocal(user string, look []int64) []int64 {
	var ids []int64
	for _, id := range p.state.worn(user, look) {
		if s := p.byProductID(id); s != nil {
			ids = append(ids, s.local)
		}
	}
	sort.Slice(ids, func(i, j int) bool { return ids[i] < ids[j] })
	return ids
}

// recordWorn remembers the user's outfit: the IMVU products sent to IMVU, and the community products (local IDs)
// taken out.
func (p *Products) recordWorn(user string, imvu, locals []int64) {
	p.reportOutfit(user, locals)
	var ids []string
	for _, local := range locals {
		if id, ok := p.state.productID(local); ok {
			ids = append(ids, id)
		}
	}
	if err := p.state.setWorn(user, imvu, ids); err != nil {
		p.logf("products: saving what %s wears: %v", user, err)
	}
}

var errNoKey = errors.New("products: can't re-sign the request (no session key yet)")

// reportOutfit tells the observer the community products (local IDs) the user wears.
func (p *Products) reportOutfit(user string, locals []int64) {
	if p.Observer == nil {
		return
	}
	id, err := strconv.ParseInt(user, 10, 64)
	if err != nil {
		return
	}
	items := []hub.Item{}
	for _, local := range locals {
		if s := p.lookup(local); s != nil {
			items = append(items, hub.Item{ID: s.pack.Manifest.ID, Name: s.pack.Manifest.Name})
		}
	}
	p.Observer.Outfit(id, items)
}