/**
 * The always-on CI-on-main Discord report.
 *
 * One message leads with the commit SHA + e2e pass/fail + the runtime-perf table
 * (perf-report.ts), then screenshot changes are attached as triptychs
 * (old | new+boxes | heatmap), ADDED images, and a REMOVED list. Because perf is
 * always present, the comment fires on every main commit even with no screenshot
 * change — "see it in hindsight on every commit."
 *
 * Safety / robustness:
 *  - Posts only on push to main (unless --force); a missing DISCORD_WEBHOOK_URL is
 *    a silent no-op, so it's inert on PRs / forks (which can't see the secret).
 *  - Attachments batched ≤10/message and downscaled to fit Discord's size caps;
 *    429 Retry-After honoured; first-run flood (hundreds of ADDED) collapsed.
 *  - --dry-run composes everything and prints it without POSTing (how it's tested).
 *
 * CLI (from tests/):
 *   tsx tools/screenshots/post-discord.ts [--dry-run] [--force] [--e2e pass|fail] [--subject S]
 */
import * as fs from 'fs';
import * as path from 'path';
import { execFileSync } from 'child_process';
import { DIFF_OUT_DIR } from './config';
import { loadPng, encodeWithinCap } from './image-ops';
import { buildPerfReport, fetchPreviousPerf } from './perf-report';
import type { Report } from './compare';

const MAX_FILE_BYTES = 8 * 1024 * 1024;
const MAX_MSG_BYTES = 24 * 1024 * 1024;
const MAX_FILES_PER_MSG = 10;
const MAX_TOTAL_FILES = 30; // ~3 messages of images; excess is summarized, not posted
const FLOOD_N = 12; // more ADDED than this ⇒ show a few exemplars, not all

type Attachment = { name: string; buffer: Buffer };
type Message = { content: string; files: Attachment[] };

function sanitize(name: string): string {
    return name.replace(/[^\w.-]+/g, '_');
}

function e2eBadge(status: string | undefined): string {
    if (status === 'pass') return '✅ e2e passed';
    if (status === 'fail') return '❌ e2e failed';
    return 'ℹ️ e2e status unknown';
}

function commitSubject(sha: string | undefined): string {
    if (!sha) return '';
    try {
        return execFileSync('git', ['log', '-1', '--pretty=%s', sha], { encoding: 'utf8' }).trim();
    } catch {
        return '';
    }
}

function readReport(root: string): Report | null {
    const p = path.join(root, DIFF_OUT_DIR, 'report.json');
    if (!fs.existsSync(p)) return null;
    try {
        return JSON.parse(fs.readFileSync(p, 'utf8')) as Report;
    } catch {
        return null;
    }
}

/** Encode a PNG path to a within-cap attachment, or null if missing/unreadable. */
function attach(root: string, rel: string, name: string): Attachment | null {
    const abs = path.isAbsolute(rel) ? rel : path.join(root, rel);
    if (!fs.existsSync(abs)) return null;
    try {
        return { name: sanitize(name), buffer: encodeWithinCap(loadPng(abs), MAX_FILE_BYTES) };
    } catch {
        return null;
    }
}

/** Build the header text: SHA, subject, e2e, perf table, screenshot summary, removed list. */
function buildHeader(report: Report | null, perfBlock: string, meta: { sha?: string; subject: string; e2e?: string }): string {
    const shortSha = meta.sha ? meta.sha.slice(0, 7) : 'local';
    const lines = [`📸 **CI screenshot + perf report** · \`${shortSha}\``];
    if (meta.subject) lines.push(`> ${meta.subject}`);
    lines.push(e2eBadge(meta.e2e));
    if (perfBlock) lines.push('', perfBlock);

    lines.push('');
    if (!report || (!report.changed.length && !report.added.length && !report.removed.length)) {
        lines.push('✅ no screenshot drift');
    } else if (report.driftLikely) {
        lines.push(`⚠️ **${report.changed.length} screenshots changed broadly** — looks like host env drift → re-promote (\`npm run screenshots:promote\`)`);
    } else {
        lines.push(`⚠️ **screenshot drift**: ${report.changed.length} changed, ${report.added.length} added, ${report.removed.length} removed`);
    }
    if (report?.removed.length) {
        lines.push('➖ REMOVED: ' + report.removed.map((r) => `\`${r.name}\``).join(', '));
    }
    return lines.join('\n');
}

/** Collect the image attachments (changed triptychs + added images) with flood-collapse + total cap. */
export function buildAttachments(root: string, report: Report | null): { files: Attachment[]; notes: string[] } {
    const files: Attachment[] = [];
    const notes: string[] = [];
    if (!report) return { files, notes };

    for (const c of report.changed) {
        if (files.length >= MAX_TOTAL_FILES) break;
        const a = attach(root, c.triptych, `CHANGED_${c.name}`);
        if (a) files.push(a);
    }
    const addedToShow = report.added.length > FLOOD_N ? report.added.slice(0, 3) : report.added;
    if (report.added.length > FLOOD_N) {
        notes.push(`➕ ${report.added.length} added (showing ${addedToShow.length})`);
    }
    for (const ad of addedToShow) {
        if (files.length >= MAX_TOTAL_FILES) break;
        const a = attach(root, ad.image, `ADDED_${ad.name}`);
        if (a) files.push(a);
    }
    const shown = files.length;
    const wanted = report.changed.length + addedToShow.length;
    if (wanted > shown) notes.push(`(${wanted - shown} more images omitted — see the CI artifact)`);
    return { files, notes };
}

/** Split attachments into messages of ≤10 files and ≤MAX_MSG_BYTES; content only on the first. */
export function paginate(header: string, files: Attachment[]): Message[] {
    if (!files.length) return [{ content: header, files: [] }];
    const messages: Message[] = [];
    let batch: Attachment[] = [];
    let bytes = 0;
    const flush = () => {
        messages.push({ content: messages.length === 0 ? header : '', files: batch });
        batch = [];
        bytes = 0;
    };
    for (const f of files) {
        if (batch.length >= MAX_FILES_PER_MSG || bytes + f.buffer.length > MAX_MSG_BYTES) flush();
        batch.push(f);
        bytes += f.buffer.length;
    }
    if (batch.length || messages.length === 0) flush();
    return messages;
}

async function sleep(ms: number): Promise<void> {
    return new Promise((r) => setTimeout(r, ms));
}

export async function postMessage(webhook: string, msg: Message): Promise<void> {
    for (let attemptNo = 0; attemptNo < 6; attemptNo++) {
        const form = new FormData();
        form.append('payload_json', JSON.stringify({ content: msg.content || '', allowed_mentions: { parse: [] } }));
        msg.files.forEach((f, i) => form.append(`files[${i}]`, new Blob([new Uint8Array(f.buffer)], { type: 'image/png' }), f.name));
        const res = await fetch(webhook, { method: 'POST', body: form });
        if (res.ok) return;
        if (res.status === 429) {
            const retryAfter = Number(res.headers.get('retry-after')) || 2;
            await sleep((retryAfter + 0.5) * 1000);
            continue;
        }
        throw new Error(`Discord POST failed ${res.status}: ${(await res.text()).slice(0, 300)}`);
    }
    throw new Error('Discord POST failed after retries (429)');
}

function parseArgs(argv: string[]): Record<string, string | boolean> {
    const out: Record<string, string | boolean> = {};
    for (let i = 0; i < argv.length; i++) {
        const a = argv[i];
        if (a === '--dry-run') out.dryRun = true;
        else if (a === '--force') out.force = true;
        else if (a === '--e2e') out.e2e = argv[++i];
        else if (a === '--subject') out.subject = argv[++i];
        else if (a === '--repo') out.repo = argv[++i];
    }
    return out;
}

async function main(): Promise<void> {
    const args = parseArgs(process.argv.slice(2));
    const root = process.cwd();
    const isMainPush = process.env.GITHUB_REF === 'refs/heads/main' && process.env.GITHUB_EVENT_NAME === 'push';
    if (!args.force && !args.dryRun && !isMainPush) {
        console.log('[discord] not a push to main — skipping');
        return;
    }
    const webhook = process.env.DISCORD_WEBHOOK_URL;
    if (!webhook && !args.dryRun) {
        console.log('[discord] DISCORD_WEBHOOK_URL unset — skipping (inert on PRs/forks)');
        return;
    }

    const sha = process.env.GITHUB_SHA;
    const report = readReport(root);
    const prevDir = fetchPreviousPerf((args.repo as string) || process.env.GITHUB_REPOSITORY, sha);
    const { block: perfBlock } = buildPerfReport({ prevDir });

    let header = buildHeader(report, perfBlock, {
        sha,
        subject: (args.subject as string) ?? commitSubject(sha),
        e2e: args.e2e as string,
    });
    const { files, notes } = buildAttachments(root, report);
    if (notes.length) header += '\n' + notes.join('\n');

    const messages = paginate(header, files);

    if (args.dryRun) {
        for (const [i, m] of messages.entries()) {
            console.log(`--- message ${i + 1}/${messages.length} (${m.files.length} files, ${m.files.reduce((s, f) => s + f.buffer.length, 0)} bytes) ---`);
            if (m.content) console.log(m.content);
            for (const f of m.files) console.log(`  [attach] ${f.name} (${f.buffer.length} bytes)`);
        }
        return;
    }

    for (const m of messages) await postMessage(webhook!, m);
    console.log(`[discord] posted ${messages.length} message(s)`);
}

if (require.main === module) {
    main().catch((e) => {
        console.error(`[discord] ${e.message}`);
        process.exitCode = 1;
    });
}