// Copyright (C) 2026 Doan Luu Duc Tai <doan@luuduct.ai>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

// @license magnet:?xt=urn:btih:0b31508aeb0634b347b8270c7bee4d411b5d4109&dn=agpl-3.0.txt AGPL-3.0

const element = id => document.getElementById(id);
const show = (id, visible = true) => { element(id).hidden = !visible; };
const status = message => { element('status').textContent = message; };
let config;
let wasm;
let credentials;
let session;
let selected;
let before = 0;
let pendingFile;
let setupToken;
let pendingSend;
let generation = 0;
let busy = false;
const workers = new Map();
const blobs = new Set();

async function api(request) {
    const current = generation;
    const response = await fetch('/api', {
        method: 'POST', credentials: 'omit', cache: 'no-store', redirect: 'error',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ ...request, token: session?.token }),
        signal: AbortSignal.timeout(20000),
    });
    const result = await response.json();
    if (current !== generation) throw new Error('Session locked');
    if (!response.ok || result.error) throw new Error(result.error || 'Server request failed');
    return result;
}

async function cryptoOperation(request) {
    const current = generation;
    const bytes = await wasm;
    if (current !== generation) throw new Error('Session locked');
    return new Promise((resolve, reject) => {
        const worker = new Worker('/worker.js');

        const stop = () => { worker.terminate(); workers.delete(worker); clearTimeout(timer); };
        const timer = setTimeout(() => { stop(); reject(new Error('Cryptographic operation timed out')); }, 90000);
        workers.set(worker, () => { stop(); reject(new Error('Session locked')); });
        worker.onerror = () => { stop(); reject(new Error('Cryptographic worker failed')); };
        worker.onmessage = event => {
            stop();
            if (current !== generation) { reject(new Error('Session locked')); return; }
            if (event.data.error) reject(new Error(event.data.error)); else resolve(event.data.result);
        };
        worker.postMessage({ bytes, request });
    });
}

function protectRequest(op, fields) {
    if (!credentials) throw new Error('Unlock your identity file first');
    return { op, ...credentials, origin: location.origin, ...fields };
}

function clearState() {
    generation += 1;
    busy = false;
    for (const button of document.querySelectorAll('button')) button.disabled = false;
    for (const cancel of workers.values()) cancel();
    workers.clear();
    for (const url of blobs) URL.revokeObjectURL(url);
    blobs.clear();
    credentials = undefined;
    session = undefined;
    selected = undefined;
    pendingFile = undefined;
    pendingSend = undefined;
    setupToken = undefined;
    before = 0;
    element('history-count').max = '0';
    element('history-range').textContent = 'Latest messages (0-0)';
    for (const input of document.querySelectorAll('input,textarea')) {
        if (input.id === 'history-count') input.value = '0'; else input.value = '';
    }
    for (const id of ['messages', 'conversations', 'who', 'fingerprint', 'counts', 'thread-name', 'conversation-fingerprint']) element(id).replaceChildren();
    for (const id of ['create', 'unlock', 'chat', 'thread', 'inbox', 'older', 'retry', 'owner-access']) show(id, false);
    show('entry', Boolean(config?.owner));
    show('owner-entry');
    status('Locked. Select your file and enter its password to return.');
}

function action(id, callback) {
    element(id).addEventListener(id.endsWith('-form') ? 'submit' : 'click', async event => {
        event.preventDefault();
        if (busy) return;
        busy = true;
        status('Working locally...');
        const current = generation;
        for (const button of document.querySelectorAll('button:not(#lock)')) button.disabled = true;
        try { await callback(); }
        catch (error) { if (generation === current) status(error.message); }
        finally {
            if (generation === current) {
                busy = false;
                for (const button of document.querySelectorAll('button')) button.disabled = false;
            }
        }
    });
}

function download(file) {
    const url = URL.createObjectURL(new Blob([file], { type: 'application/octet-stream' }));
    blobs.add(url);
    const link = document.createElement('a');
    link.href = url;
    link.download = 'stack-chat-identity.chat';
    link.click();
    setTimeout(() => { URL.revokeObjectURL(url); blobs.delete(url); }, 30000);
}

async function createIdentity() {
    const password = element('new-password').value;
    if (password !== element('confirm-password').value) throw new Error('Passwords do not match');
    if (!config.owner && element('setup-label').hidden) throw new Error('Owner setup is required first');
    setupToken = !config.owner ? element('setup-token').value : undefined;
    status('Generating your purpose-specific identity and protecting its file...');
    const result = await cryptoOperation({ op: 'create', origin: location.origin, name: element('name').value, password, owner: config.owner || '' });
    pendingFile = result.file;
    download(result.file);
    element('create-form').reset();
    show('create', false);
    show('unlock');
    element('reopen-note').textContent = 'Your file was downloaded. Reopen that exact saved file and enter its password before any message can be sent. Keep a safe backup.';
    status('Reopen your downloaded identity file to verify recovery.');
}

async function unlockIdentity() {
    const file = element('file').files[0];
    if (!file || file.size > 262144) throw new Error('Choose an identity file no larger than 256 KiB');
    const fileText = await file.text();
    if (pendingFile && fileText !== pendingFile) throw new Error('Reopen the exact identity file you just downloaded');
    const candidate = { file: fileText, password: element('password').value };
    element('unlock-form').reset();
    status('Unlocking locally and verifying your identity...');
    const identity = await cryptoOperation({ op: 'open', ...candidate, origin: location.origin });
    if (config.owner && identity.owner !== config.owner) throw new Error('Pinned owner key differs from this server. Stop and verify the change with Doan.');
    const challenge = await api({ op: 'challenge', public: identity.public, setup_token: setupToken });
    const proof = await cryptoOperation({ op: 'proof', ...candidate, origin: location.origin, challenge: challenge.challenge });
    const authenticated = await api({ op: 'authenticate', id: challenge.id, signature: proof.signature });
    if (authenticated.id !== identity.fingerprint || typeof authenticated.owner !== 'boolean') throw new Error('Authenticated identity mismatch');
    credentials = candidate;
    session = { ...identity, ...authenticated };
    pendingFile = undefined;
    setupToken = undefined;
    config = await api({ op: 'config' });
    show('entry', false);
    show('owner-entry', false);
    show('owner-access', false);
    show('unlock', false);
    show('chat');
    element('who').textContent = `${identity.name} [${session.owner === true ? 'OWNER' : 'VISITOR'}]`;
    element('fingerprint').textContent = `Identity: ${identity.fingerprint}`;
    if (authenticated.owner) {
        session.owner = true;
        show('inbox');
        await inbox();
    } else {
        session.owner = false;
        const profile = await cryptoOperation(protectRequest('encrypt', { recipient: config.owner, payload: JSON.stringify({ v: 1, kind: 'profile', origin: location.origin, conversation: session.id, sender: session.id, name: identity.name }) }));
        await api({ op: 'profile', conversation: session.id, ciphertext: profile.ciphertext });
        selected = { id: session.id, public: identity.public };
        element('conversation-fingerprint').textContent = `Conversation: ${session.id}`;
        show('thread');
        element('thread-name').textContent = 'You <-> Doan';
        await loadHistory(0);
    }
    status('Unlocked in memory only. No history loaded automatically. Lock or leave to forget this session.');
}

function checkedPayload(payload, kind, conversation, sender) {
    const value = JSON.parse(payload);
    if (value.v !== 1 || value.kind !== kind || value.origin !== location.origin || value.conversation !== conversation || value.sender !== sender) throw new Error('Signed message binding mismatch');
    return value;
}

async function inbox() {
    const result = await api({ op: 'inbox' });
    element('conversations').replaceChildren();
    for (const conversation of result.conversations) {
        const button = document.createElement('button');
        button.textContent = `${conversation.id.slice(0, 12)} / ${conversation.total} messages`;
        button.addEventListener('click', async () => {
            if (busy) return;
            if (pendingSend) { status('Retry the pending message, or lock before switching conversations.'); return; }
            busy = true;
            const current = generation;
            status('Opening conversation...');
            try {
                selected = conversation;
                element('conversation-fingerprint').textContent = `Conversation: ${conversation.id}`;
                element('thread-name').textContent = `Doan <-> ${conversation.id.slice(0, 12)}`;
                pendingSend = undefined;
                element('text').value = '';
                show('retry', false);
                element('messages').replaceChildren();
                show('thread');
                let name = conversation.id.slice(0, 12);
                if (conversation.profile) {
                    const result = await cryptoOperation(protectRequest('decrypt', { sender: conversation.public, ciphertext: conversation.profile }));
                    if (result.signer !== conversation.id) throw new Error('Profile signer fingerprint mismatch');
                    const profile = checkedPayload(result.payload, 'profile', conversation.id, conversation.id);
                    if (typeof profile.name !== 'string' || profile.name.length > 80) throw new Error('Invalid encrypted profile');
                    name = profile.name;
                }
                element('thread-name').textContent = `Doan <-> ${name}`;
                await loadHistory(0);
                status('Conversation opened. Choose how many messages to load.');
            } catch (error) { status(error.message); }
            finally { if (generation === current) busy = false; }
        });
        element('conversations').append(button);
    }
}

function counters(conversation) {
    if (!Number.isSafeInteger(conversation.total) || conversation.total < 0 || conversation.total > 10000) throw new Error('Invalid conversation count');
    element('history-count').max = String(conversation.total);
    element('history-range').textContent = `Latest messages (0-${conversation.total})`;
    const sent = session.owner ? conversation.owner_sent : conversation.visitor_sent;
    const received = session.owner ? conversation.visitor_sent : conversation.owner_sent;
    element('counts').textContent = `Total: ${conversation.total} | Sent: ${sent} | Received: ${received}`;
}

async function renderHistoryBatch(messages) {
    const requests = messages.map(message => ({ sender: message.sender === selected.id ? selected.public : config.owner, ciphertext: message.ciphertext }));
    const decrypted = await cryptoOperation(protectRequest('decrypt_batch', { messages: requests }));
    for (let index = 0; index < messages.length; index += 1) {
        const message = messages[index];
        const item = document.createElement('li');
        const label = document.createElement('small');
        label.textContent = `#${message.seq} / ${message.sender === session.id ? 'YOU' : 'THEM'}`;
        const text = document.createElement('p');
        try {
            const entry = decrypted.messages[index];
            if (entry.signer !== message.sender) throw new Error('Sender fingerprint mismatch');
            if (entry.error) throw new Error('Invalid ciphertext or signature');
            const payload = checkedPayload(entry.payload, 'message', selected.id, message.sender);
            if (payload.id !== message.id || typeof payload.text !== 'string' || new TextEncoder().encode(payload.text).length > 8192) throw new Error('Message binding mismatch');
            text.textContent = payload.text;
        } catch { text.textContent = '[Message rejected: invalid ciphertext, signature, or conversation binding.]'; }
        item.append(label, text);
        element('messages').prepend(item);
    }
}

async function refreshCounts() {
    const conversation = selected.id;
    const result = await api({ op: 'history', conversation, count: 0, before: 0 });
    if (selected?.id === conversation) counters(result.conversation);
    return result.conversation;
}

async function loadHistory(count, cursor = 0) {
    if (!selected) throw new Error('Choose a conversation first');
    const conversation = await refreshCounts();
    if (!Number.isSafeInteger(count) || count < 0 || count > conversation.total) throw new Error(`Choose 0 to ${conversation.total} messages`);
    if (!cursor) { element('messages').replaceChildren(); before = 0; }
    if (count === 0) {
        element('history-count').value = '0';
        show('older', false);
        status('No message history loaded.');
        return;
    }
    let remaining = count;
    let next = cursor;
    let exhausted = false;
    while (remaining > 0) {
        const size = Math.min(50, remaining);
        const result = await api({ op: 'history', conversation: selected.id, count: size, before: next });
        counters(result.conversation);
        if (!Array.isArray(result.messages) || result.messages.length > size) throw new Error('Invalid history response');
        if (!result.messages.length) { exhausted = true; break; }
        const sequence = Math.min(...result.messages.map(message => message.seq));
        if (!Number.isSafeInteger(sequence) || sequence <= 0 || (next > 0 && sequence >= next)) throw new Error('Invalid history cursor');
        status(`Decrypting and verifying selected messages locally (${count - remaining + result.messages.length}/${count})...`);
        await renderHistoryBatch(result.messages);
        remaining -= result.messages.length;
        next = sequence;
        before = next;
        if (result.messages.length < size) { exhausted = true; break; }
    }
    show('older', !exhausted && element('messages').children.length < Number(element('history-count').max));
    status('Selected history decrypted and verified locally.');
}

async function submitPending() {
    if (!pendingSend) throw new Error('No pending message');
    const result = await api(pendingSend);
    counters(result.conversation);
    pendingSend = undefined;
    element('text').value = '';
    show('retry', false);
    status('Encrypted message stored. Load history to read messages.');
}

async function send() {
    if (!selected) throw new Error('Choose a conversation first');
    if (pendingSend) throw new Error('Retry or lock before composing another message');
    const text = element('text').value;
    if (!text.trim() || new TextEncoder().encode(text).length > 8192) throw new Error('Enter 1 to 8192 UTF-8 bytes of text');
    const id = Array.from(crypto.getRandomValues(new Uint8Array(32)), byte => byte.toString(16).padStart(2, '0')).join('');
    const recipient = session.owner ? selected.public : config.owner;
    status('Signing and encrypting for both participants locally...');
    const result = await cryptoOperation(protectRequest('encrypt', { recipient, payload: JSON.stringify({ v: 1, kind: 'message', origin: location.origin, conversation: selected.id, sender: session.id, id, text }) }));
    pendingSend = { op: 'send', conversation: selected.id, id, ciphertext: result.ciphertext };
    show('retry');
    await submitPending();
}

function ownerSetup() {
    show('entry', false);
    show('owner-entry', false);
    show('unlock', false);
    show('create', !config.owner);
    show('owner-access', Boolean(config.owner));
    show('setup-label', !config.owner);
    element('create-title').textContent = 'Create the owner identity (owner only)';
    status('');
}

action('create-choice', async () => { show('entry', false); show('owner-entry', false); show('setup-label', false); element('create-title').textContent = 'Create a new chat'; show('create'); status(''); });
action('open-choice', async () => { show('entry', false); show('owner-entry', false); show('unlock'); status(''); });
action('owner-choice', async () => { window.history.replaceState(null, '', '#setup'); ownerSetup(); });
action('owner-open', async () => { show('owner-access', false); show('unlock'); status(''); });
action('create-form', createIdentity);
action('unlock-form', unlockIdentity);
element('history-count').addEventListener('focus', () => {
    const current = generation;
    if (session && selected && !busy) refreshCounts().catch(error => { if (current === generation) status(error.message); });
});
action('history-form', () => loadHistory(Number(element('history-count').value)));
action('send-form', send);
action('retry', submitPending);
action('refresh-inbox', inbox);
action('older', () => loadHistory(Number(element('history-count').value), before));
element('lock').addEventListener('click', () => { if (session) api({ op: 'lock' }).catch(() => {}); clearState(); });
window.addEventListener('pagehide', clearState);
window.addEventListener('pageshow', event => { if (event.persisted) clearState(); });

async function start() {
    wasm = fetch('/crypto.wasm', { cache: 'no-store', credentials: 'omit' }).then(response => {
        if (!response.ok) throw new Error('Build the WASI cryptographic module first');
        return response.arrayBuffer();
    });
    await wasm;
    config = await api({ op: 'config' });
    if (config.origin !== location.origin) throw new Error('Server origin mismatch');
    show('owner-entry');
    show('entry', Boolean(config.owner));
    status('');
    if (location.hash === '#setup') ownerSetup();
}

start().catch(error => status(error.message));

// @license-end