package main

import (
	"bytes"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"sync"
	"time"
)

// registerReq is the POST /api/register body. It mirrors the bus contract exactly
// (token + the two PUBLIC key halves, each 64 hex chars). The private key never
// appears here — registration only publishes the public identity. The handle and
// role are NOT accepted from the client; they are fixed by the invite the token
// belongs to (no privilege escalation).
type registerReq struct {
	Token   string `json:"token"`
	SignPub string `json:"sign_pub"`
	KexPub  string `json:"kex_pub"`
}

// registerResp is what we return to the browser on success. The bus's /register
// (issue: user-accounts) decides handle/role from the invite; in mock mode the
// gateway echoes the configured pair so the SPA can greet the new user.
type registerResp struct {
	Handle string `json:"handle"`
	Role   string `json:"role"`
}

// registrar fulfils POST /api/register. It targets the bus's POST /register
// endpoint (added by the user-accounts work, bus >= 0.12.0). Until that endpoint
// is rolled out, a built-in mock validates against a configured set of one-shot
// tokens so the whole wallet flow is testable locally. Mock tokens are checked
// first; anything else is proxied to the real bus when --register-url is set.
type registrar struct {
	mu sync.Mutex

	registerURL string                // bus POST /register; empty => mock-only
	httpc       *http.Client          // for proxying to the bus
	mockTokens  map[string]*mockToken // configured one-shot invites for local testing
}

// mockToken is a local stand-in for a bus invite: a token that maps to a fixed
// handle+role and can be consumed exactly once.
type mockToken struct {
	handle string
	role   string
	used   bool
}

// newRegistrar parses the --mock-tokens spec ("tok=handle:role,tok2=h2:role2")
// and configures the optional proxy target.
func newRegistrar(registerURL, mockSpec string) *registrar {
	r := &registrar{
		registerURL: strings.TrimSpace(registerURL),
		httpc:       &http.Client{Timeout: 10 * time.Second},
		mockTokens:  map[string]*mockToken{},
	}
	for _, part := range strings.Split(mockSpec, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		// tok=handle:role  (role optional, defaults to member)
		eq := strings.IndexByte(part, '=')
		if eq < 0 {
			continue
		}
		tok := strings.TrimSpace(part[:eq])
		hr := strings.TrimSpace(part[eq+1:])
		handle, role := hr, "member"
		if c := strings.IndexByte(hr, ':'); c >= 0 {
			handle, role = strings.TrimSpace(hr[:c]), strings.TrimSpace(hr[c+1:])
		}
		if tok != "" && handle != "" {
			r.mockTokens[tok] = &mockToken{handle: handle, role: role}
		}
	}
	return r
}

// mockTokenCount counts configured mock tokens in a --mock-tokens spec (for the
// startup log line).
func mockTokenCount(spec string) int {
	n := 0
	for _, part := range strings.Split(spec, ",") {
		if p := strings.TrimSpace(part); p != "" && strings.ContainsRune(p, '=') {
			n++
		}
	}
	return n
}

// validHexKey reports whether s is exactly 64 lowercase/uppercase hex chars (a
// 32-byte key). Both sign_pub and kex_pub are 32-byte keys.
func validHexKey(s string) bool {
	if len(s) != 64 {
		return false
	}
	_, err := hex.DecodeString(s)
	return err == nil
}

// handleRegister validates the keys and consumes the token. Order of resolution:
//  1. strict validation of the public keys (defends both mock and proxy paths);
//  2. mock token (one-shot) if configured;
//  3. proxy to the bus /register if --register-url is set;
//  4. otherwise reject with a clear error.
func (s *server) handleRegister(w http.ResponseWriter, r *http.Request) {
	var req registerReq
	if !decode(w, r, &req) {
		return
	}
	req.Token = strings.TrimSpace(req.Token)
	if req.Token == "" {
		writeErr(w, http.StatusBadRequest, "token required")
		return
	}
	if !validHexKey(req.SignPub) {
		writeErr(w, http.StatusBadRequest, "sign_pub must be 64 hex chars (32 bytes)")
		return
	}
	if !validHexKey(req.KexPub) {
		writeErr(w, http.StatusBadRequest, "kex_pub must be 64 hex chars (32 bytes)")
		return
	}

	reg := s.registrar

	// 2) mock one-shot token.
	reg.mu.Lock()
	mt, isMock := reg.mockTokens[req.Token]
	if isMock {
		if mt.used {
			reg.mu.Unlock()
			writeErr(w, http.StatusConflict, "invite already used")
			return
		}
		mt.used = true
		handle, role := mt.handle, mt.role
		reg.mu.Unlock()
		writeJSON(w, http.StatusCreated, registerResp{Handle: handle, Role: role})
		return
	}
	reg.mu.Unlock()

	// 3) proxy to the real bus /register when configured.
	if reg.registerURL != "" {
		s.proxyRegister(w, req)
		return
	}

	// 4) no mock match, no proxy target.
	writeErr(w, http.StatusBadRequest, "invalid or unknown token (and no bus /register configured)")
}

// proxyRegister forwards the registration to the bus's POST /register. The bus
// validates the invite (existence, not-used, not-expired) and adds the public
// identity to the allowlist with the invite's handle+role. This is unsigned by
// design: the TOKEN authorizes the call, not an admin signature.
func (s *server) proxyRegister(w http.ResponseWriter, req registerReq) {
	body, _ := json.Marshal(req)
	resp, err := s.registrar.httpc.Post(
		s.registrar.registerURL,
		"application/json",
		bytes.NewReader(body),
	)
	if err != nil {
		writeErr(w, http.StatusBadGateway, "bus register unreachable: "+err.Error())
		return
	}
	defer resp.Body.Close()
	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))

	// On success, try to pass through the bus's handle/role if it returned them;
	// otherwise a bare 201 is still success.
	if resp.StatusCode == http.StatusCreated || resp.StatusCode == http.StatusOK {
		var rr registerResp
		_ = json.Unmarshal(raw, &rr)
		writeJSON(w, http.StatusCreated, rr)
		return
	}
	// Forward the bus's error verbatim where possible.
	msg := strings.TrimSpace(string(raw))
	if msg == "" {
		msg = fmt.Sprintf("bus register failed (HTTP %d)", resp.StatusCode)
	}
	writeErr(w, resp.StatusCode, msg)
}