package client

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

	"lchat/internal/e2ee"
)

// JoinResult says what kind of link Join claimed, beyond the identity itself.
type JoinResult struct {
	// AddDevice: the link carried an existing member's keypair — the session is
	// that member's identity on a new device, not a new person.
	AddDevice bool
	// ThreadID is the pending DM a user invite drops the joiner into ("" for
	// other link kinds) — a client can open it first.
	ThreadID string
}

// Join is web/static/join.js run headlessly: turn any invite link into a local
// identity. It handles all three link shapes — a fresh-person invite (generate
// a keypair, register it), a member-minted user invite (additionally re-wrap
// the pending DM's key to the new keypair), and an add-device link (adopt the
// keypair the link carries; the session then IS that member). The secret T
// never reaches the server: the invite id and claim secret derive from it, and
// whatever the link's wrapped blob holds decrypts locally.
func Join(base, fragment, name string) (*Session, JoinResult, error) {
	base = strings.TrimRight(base, "/")
	hc := &http.Client{Timeout: 30 * time.Second}

	inv, err := e2ee.DeriveInvite(fragment)
	if err != nil {
		return nil, JoinResult{}, fmt.Errorf("client: bad invite secret: %w", err)
	}

	var info struct {
		OK      bool   `json:"ok"`
		Wrapped string `json:"wrapped"`
	}
	if err := getJSON(hc, base+"/api/key-invite/"+url.PathEscape(inv.ID), &info); err != nil {
		return nil, JoinResult{}, err
	}
	if !info.OK {
		return nil, JoinResult{}, fmt.Errorf("client: this invite was already used or has expired — ask for a fresh one")
	}

	// What the link carries decides who we become (join.js): a keypair means
	// add-device; a thread key means a user invite with a pending DM; nothing
	// means a plain fresh-person invite.
	var payload struct {
		Priv      string `json:"priv"`
		Pub       string `json:"pub"`
		ThreadKey string `json:"threadKey"`
	}
	if info.Wrapped != "" {
		if err := e2ee.DecryptJSON(inv.WrapKey, info.Wrapped, &payload); err != nil {
			return nil, JoinResult{}, fmt.Errorf("client: couldn't unlock this link (wrong or corrupt secret)")
		}
	}

	pub, priv := payload.Pub, payload.Priv
	wrappedSelf := ""
	if priv == "" {
		kp, err := e2ee.GenerateUserKeypair()
		if err != nil {
			return nil, JoinResult{}, err
		}
		pub, priv = kp.PublicKey, kp.PrivateKey
		if payload.ThreadKey != "" {
			// User invite: re-wrap the pending DM's key to our new keypair so the
			// chat with the person who invited us opens readable.
			if wrappedSelf, err = e2ee.WrapThreadKey(payload.ThreadKey, pub); err != nil {
				return nil, JoinResult{}, err
			}
		}
	}

	var claim struct {
		OK       bool   `json:"ok"`
		Token    string `json:"token"`
		ThreadID string `json:"thread_id"`
	}
	err = postJSON(hc, base+"/api/key-invite/"+url.PathEscape(inv.ID)+"/claim",
		map[string]string{"claim_secret": inv.ClaimSecret, "wrapped": wrappedSelf}, &claim)
	if err != nil {
		return nil, JoinResult{}, err
	}
	if !claim.OK || claim.Token == "" {
		return nil, JoinResult{}, fmt.Errorf("client: couldn't claim the invite (it may have just been used)")
	}

	// Register (or, on add-device, harmlessly re-register) the public key.
	err = postJSON(hc, base+"/api/pubkey", map[string]string{"token": claim.Token, "public_key": pub}, nil)
	if err != nil {
		return nil, JoinResult{}, err
	}

	sess := &Session{Base: base, Token: claim.Token, Name: name, UserPub: pub, UserPriv: priv}
	return sess, JoinResult{AddDevice: payload.Priv != "", ThreadID: claim.ThreadID}, nil
}

func getJSON(hc *http.Client, url string, out any) error {
	resp, err := hc.Get(url)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	return json.NewDecoder(resp.Body).Decode(out)
}

func postJSON(hc *http.Client, url string, body, out any) error {
	raw, err := json.Marshal(body)
	if err != nil {
		return err
	}
	resp, err := hc.Post(url, "application/json", bytes.NewReader(raw))
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if out == nil {
		if resp.StatusCode != http.StatusOK {
			return fmt.Errorf("client: %s: HTTP %d", url, resp.StatusCode)
		}
		return nil
	}
	return json.NewDecoder(resp.Body).Decode(out)
}