//! Consume the published `mesh/1` conformance pack.
//!
//! `gen_vectors` writes `conformance/v1/` and nothing read it back: the other tests in
//! this crate re-run `reference_scenario()`, so they check the implementation against
//! itself. A pack that says a conforming implementation "MUST reproduce" its bytes
//! needs a test that holds the reference implementation to those bytes too.
//!
//! Two different questions, answered separately:
//!
//! 1. **Drift** — does the reference implementation still emit exactly the published
//!    files? This is the failure a pack silently develops when the receipt shape
//!    changes and nobody regenerates.
//! 2. **Cross-language check** — the README's own claim, checked the way a third
//!    party would: from the pack files and RFC 9052 alone, with a hand-built CBOR
//!    encoder and no mesh COSE code, reproduce `envelope.hex` byte for byte.

use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
use mesh_conformance::{MAX_TOKENS, SPAN_UJ, STEWARD_SEED, reference_scenario};
use serde_json::Value;
use std::path::PathBuf;

fn pack_dir() -> PathBuf {
    let d = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../../../conformance/v1");
    d.canonicalize().expect("the conformance pack must exist next to the spec")
}

fn text(rel: &str) -> String {
    std::fs::read_to_string(pack_dir().join(rel)).unwrap_or_else(|e| panic!("read {rel}: {e}"))
}

fn hexfile(rel: &str) -> Vec<u8> {
    hex::decode(text(rel).trim()).unwrap_or_else(|e| panic!("{rel} is not hex: {e}"))
}

fn json(rel: &str) -> Value {
    serde_json::from_str(&text(rel)).unwrap_or_else(|e| panic!("{rel} must parse: {e}"))
}

// --- A deliberately minimal CBOR encoder (RFC 8949), independent of mesh ---------

fn head(major: u8, len: u64) -> Vec<u8> {
    let m = major << 5;
    match len {
        0..=23 => vec![m | len as u8],
        24..=0xff => vec![m | 24, len as u8],
        0x100..=0xffff => {
            let mut v = vec![m | 25];
            v.extend_from_slice(&(len as u16).to_be_bytes());
            v
        }
        _ => {
            let mut v = vec![m | 26];
            v.extend_from_slice(&(len as u32).to_be_bytes());
            v
        }
    }
}

fn bstr(b: &[u8]) -> Vec<u8> {
    let mut v = head(2, b.len() as u64);
    v.extend_from_slice(b);
    v
}

fn tstr(s: &str) -> Vec<u8> {
    let mut v = head(3, s.len() as u64);
    v.extend_from_slice(s.as_bytes());
    v
}

/// The protected header the README specifies: `{1: -8, 4: <steward bytes>}`, keys in
/// deterministic (bytewise) order.
fn protected_header(kid: &str) -> Vec<u8> {
    let mut v = head(5, 2); // map(2)
    v.push(0x01); // 1  (alg)
    v.push(0x27); // -8 (EdDSA): major 1, value 7
    v.push(0x04); // 4  (kid)
    v.extend(bstr(kid.as_bytes()));
    v
}

/// RFC 9052 §4.4: `Sig_structure = ["Signature1", protected, external_aad, payload]`.
fn sig_structure(protected: &[u8], payload: &[u8]) -> Vec<u8> {
    let mut v = head(4, 4);
    v.extend(tstr("Signature1"));
    v.extend(bstr(protected));
    v.extend(bstr(&[])); // empty external AAD
    v.extend(bstr(payload));
    v
}

/// RFC 9052 §4.2: tag 18 over `[protected, unprotected, payload, signature]`.
fn cose_sign1(protected: &[u8], payload: &[u8], sig: &[u8]) -> Vec<u8> {
    let mut v = vec![0xd2]; // tag 18
    v.extend(head(4, 4));
    v.extend(bstr(protected));
    v.extend(head(5, 0)); // empty unprotected map
    v.extend(bstr(payload));
    v.extend(bstr(sig));
    v
}

// --- 1. Drift ---------------------------------------------------------------------

/// The reference implementation still emits exactly the published files. Compared in
/// the form `gen_vectors` writes them, so any change to the receipt — a new field, a
/// renamed one, a different route — shows up here instead of in a third party's
/// failed verification.
#[test]
fn the_reference_implementation_still_emits_the_published_pack() {
    let s = reference_scenario();
    let core = s.receipt.signed_core(&s.steward).expect("reference receipt signs");

    assert_eq!(
        format!("{}\n", hex::encode(&s.envelope)),
        text("reference/envelope.hex"),
        "envelope.hex is stale against the reference implementation"
    );
    assert_eq!(
        format!("{}\n", hex::encode(&core)),
        text("reference/signed_core.hex"),
        "signed_core.hex is stale against the reference implementation"
    );
    assert_eq!(
        format!("{}\n", serde_json::to_string_pretty(&s.receipt.to_jcr1_wire(&s.steward)).unwrap()),
        text("reference/receipt.json"),
        "receipt.json is stale against the reference implementation"
    );
    let meta = json("meta.json");
    assert_eq!(meta["steward"], s.steward.as_str());
    assert_eq!(meta["pubkey_hex"], hex::encode(s.verifying_key).as_str());
}

// --- 2. Cross-language check ------------------------------------------------------

/// The README's claim, verified from the pack and the RFC alone: the published
/// envelope is exactly `signed_core` wrapped per RFC 9052 and signed by the key
/// `meta.json` publishes.
#[test]
fn envelope_is_reproduced_from_signed_core_and_rfc_9052_alone() {
    let meta = json("meta.json");
    let kid = meta["steward"].as_str().expect("meta names the steward");
    let pubkey: [u8; 32] = hex::decode(meta["pubkey_hex"].as_str().unwrap())
        .unwrap()
        .try_into()
        .expect("a 32-byte Ed25519 key");
    let core = hexfile("reference/signed_core.hex");
    let envelope = hexfile("reference/envelope.hex");

    let protected = protected_header(kid);
    let to_sign = sig_structure(&protected, &core);

    // Verifier direction — needs only what is published, not the seed.
    let sig_bytes = &envelope[envelope.len() - 64..];
    let sig = Signature::from_slice(sig_bytes).expect("64-byte signature");
    VerifyingKey::from_bytes(&pubkey)
        .unwrap()
        .verify(&to_sign, &sig)
        .expect("the published envelope must verify under the published key");

    // Signer direction — Ed25519 is deterministic, so re-signing with the documented
    // steward seed must rebuild the envelope exactly.
    let sk = SigningKey::from_bytes(&STEWARD_SEED);
    assert_eq!(sk.verifying_key().to_bytes(), pubkey, "meta.json pubkey is not the seed's");
    let rebuilt = cose_sign1(&protected, &core, &sk.sign(&to_sign).to_bytes());
    assert_eq!(rebuilt, envelope, "hand-built COSE_Sign1 does not match envelope.hex");
    // 663 before the receipt committed to its output (SPEC §6.2), whose field
    // the reference generation now carries.
    assert_eq!(envelope.len(), 747);
}

/// The verifier direction is not vacuous: a single changed payload byte, or the right
/// bytes under the wrong key, must both fail.
#[test]
fn a_tampered_core_or_a_wrong_key_does_not_verify() {
    let meta = json("meta.json");
    let kid = meta["steward"].as_str().unwrap();
    let pubkey: [u8; 32] =
        hex::decode(meta["pubkey_hex"].as_str().unwrap()).unwrap().try_into().unwrap();
    let envelope = hexfile("reference/envelope.hex");
    let sig = Signature::from_slice(&envelope[envelope.len() - 64..]).unwrap();
    let protected = protected_header(kid);

    let mut core = hexfile("reference/signed_core.hex");
    let mid = core.len() / 2;
    core[mid] ^= 0x01;
    assert!(
        VerifyingKey::from_bytes(&pubkey).unwrap().verify(&sig_structure(&protected, &core), &sig).is_err(),
        "a tampered signed core verified"
    );

    let core = hexfile("reference/signed_core.hex");
    let stranger = SigningKey::from_bytes(&[0x42; 32]).verifying_key();
    assert!(
        stranger.verify(&sig_structure(&protected, &core), &sig).is_err(),
        "the envelope verified under a key that did not sign it"
    );
}

/// The outcome the README pins, read from the published receipt. The wedge metric is
/// recomputed from the receipt's own fields rather than trusted as a number.
#[test]
fn published_receipt_carries_the_pinned_outcome() {
    let r = json("reference/receipt.json");
    assert_eq!(r["mesh_receipt"], "mesh/1");
    assert_eq!(r["backend"], "tiny", "cache is below the F1 floor; merge/frontier exceed 8 J");
    assert_eq!(r["energy_provenance"], "HwShunt");
    assert_eq!(r["measured_uj"], SPAN_UJ);
    assert_eq!(r["tokens_accepted"], MAX_TOKENS);
    assert_eq!(r["sequence"], 0, "the reference receipt is the chain's genesis");
    assert!(r["fidelity_met"].as_u64() >= r["fidelity_floor"].as_u64(), "fidelity floor not met");

    let per_token = r["measured_uj"].as_u64().unwrap() / r["tokens_accepted"].as_u64().unwrap();
    assert_eq!(per_token, 50_000);
    assert_eq!(r["uj_per_accepted_token"], per_token, "wedge metric disagrees with its inputs");
    assert_eq!(r["steward"], json("meta.json")["steward"]);
}