// Verify incoming HMAC-signed peer requests.
//
// Required headers:
//   X-DD-Env-Id      caller's env UUID (looked up in _dd_peers)
//   X-DD-Timestamp   ms-since-epoch; rejected if skew > 5 min
//   X-DD-Nonce       random per-request opaque bytes; rejected if reused within
//                    the skew window (replay protection, see recordNonce)
//   X-DD-Signature   hex HMAC-SHA256 over canonical string
//
// On success: req.dd_peer is set (peer row), req.body is the parsed JSON body,
// and the function returns the peer. On failure: a 4xx response is sent and
// null is returned.
//
// Peer requests use Content-Type: application/vnd.dev-deploy+json so Saltcorn's
// express.json() middleware doesn't consume the stream upstream. That lets us
// read the exact raw bytes here and use them in the HMAC -- no JSON-canonical
// fragility, no re-serialization assumptions about whitespace or key order.

const db = require("@saltcorn/data/db");
const {
    buildCanonical,
    normalizeHost,
    verifySignature,
    timestampWithinSkew,
    SKEW_TOLERANCE_MS
} = require("./crypto");
const {
    findPeerByEnvId,
    peerSecret,
    touchPeerLastSeen
} = require("./peers");
const { getEnv } = require("./env");


const REQUIRED_HEADERS = ["x-dd-env-id", "x-dd-timestamp", "x-dd-nonce", "x-dd-signature"];


const readRawBody = async (req) => {
    const chunks = [];
    for await (const chunk of req) {
        chunks.push(typeof chunk === "string" ? Buffer.from(chunk) : chunk);
    }
    return Buffer.concat(chunks).toString("utf8");
};


// Record (env_id, nonce); returns false if it was already seen (replay) or on a
// store error (fail closed -- better to reject than to allow a replay). Prunes
// entries older than 2x the skew window first. The acceptance window is 2x SKEW
// wide (timestampWithinSkew accepts ts in [now-SKEW, now+SKEW]), and seen_ms is
// the RECEIVE time which can trail ts by up to SKEW when a peer's clock leads, so
// a nonce must be retained for 2x SKEW past receipt to cover the whole window a
// captured request stays replayable -- pruning at 1x SKEW reopened that gap.
const recordNonce = async (envId, nonce) => {
    const schema = db.getTenantSchemaPrefix();
    const now    = Date.now();
    try {
        await db.query(`DELETE FROM ${schema}_dd_seen_nonces WHERE seen_ms < $1`, [now - 2 * SKEW_TOLERANCE_MS]);
        await db.query(
            `INSERT INTO ${schema}_dd_seen_nonces (env_id, nonce, seen_ms) VALUES ($1, $2, $3)`,
            [envId, nonce, now]
        );
        return true;
    } catch (e) {
        return false;
    }
};


const requirePeerAuth = async (req, res) => {
    for (const h of REQUIRED_HEADERS) {
        if (!req.headers[h]) {
            res.status(400).json({ error: `missing header ${h}` });
            return null;
        }
    }
    const callerEnvId = req.headers["x-dd-env-id"];
    const timestamp   = req.headers["x-dd-timestamp"];
    const nonce       = req.headers["x-dd-nonce"];
    const signature   = req.headers["x-dd-signature"];

    if (!timestampWithinSkew(timestamp)) {
        res.status(401).json({ error: "timestamp out of skew window" });
        return null;
    }

    const peerRow = await findPeerByEnvId(callerEnvId);
    if (!peerRow) {
        res.status(401).json({ error: "unknown peer env_id" });
        return null;
    }

    let secret;
    try {
        secret = await peerSecret(peerRow.peer_id);
    } catch (e) {
        res.status(401).json({ error: "peer not provisioned" });
        return null;
    }

    // Read raw bytes (empty for GET/HEAD). HMAC covers exactly what arrived.
    let bodyRaw = "";
    if (req.method !== "GET" && req.method !== "HEAD") {
        try {
            bodyRaw = await readRawBody(req);
        } catch (e) {
            res.status(400).json({ error: "failed to read request body" });
            return null;
        }
    }

    // Bind the target host (which tenant Saltcorn routed this request to) into the
    // signed canonical: a request signed for tenant t1 must NOT verify when
    // replayed against tenant t2 on the same server. Prefer X-Forwarded-Host (set
    // by a trusted proxy) then the Host header, normalized identically to the
    // outbound side (transport.js derives it from the peer base_url). NOTE: do NOT
    // compare against peerRow.base_url -- inbound that is the SENDER's address
    // (for pull-back), not this receiver's host.
    const fullPath   = req.originalUrl || req.url;
    const fwdHost    = req.headers["x-forwarded-host"];
    const rawHost    = fwdHost ? String(fwdHost).split(",")[0] : req.headers.host;
    const targetHost = normalizeHost(rawHost);
    const canonical  = buildCanonical({
        timestamp:  timestamp,
        nonce:      nonce,
        method:     req.method,
        path:       fullPath,
        targetHost: targetHost,
        body:       bodyRaw
    });

    if (!verifySignature(secret, canonical, signature)) {
        res.status(401).json({ error: "bad signature" });
        return null;
    }

    // Replay guard: only after the signature is valid (so unauthenticated callers
    // cannot flood the nonce store). A reused (env_id, nonce) within the skew
    // window -- i.e. a captured request replayed verbatim -- is rejected here.
    if (!(await recordNonce(callerEnvId, nonce))) {
        res.status(401).json({ error: "nonce replay or store error" });
        return null;
    }

    if (bodyRaw) {
        try {
            req.body = JSON.parse(bodyRaw);
        } catch (e) {
            res.status(400).json({ error: "body is not valid JSON" });
            return null;
        }
    }

    // If this env requires TLS for inbound peer traffic, reject any request
    // that did not arrive over HTTPS. req.secure reflects a direct TLS socket;
    // x-forwarded-proto covers the case where a trusted proxy terminates TLS.
    const env = await getEnv();
    if (env && env.require_tls) {
        const fwdProto = req.headers["x-forwarded-proto"];
        const overTls  = req.secure || (fwdProto && String(fwdProto).split(",")[0].trim() === "https");
        if (!overTls) {
            res.status(403).json({ error: "TLS required" });
            return null;
        }
    }

    await touchPeerLastSeen(peerRow.peer_id);
    req.dd_peer = peerRow;
    return peerRow;
};


module.exports = {
    requirePeerAuth
};