agent_protocols/

delegation.rs

//! Agent Delegation Protocol 1.0 types and validation helpers.
//!
//! Delegation events are ordinary Agent Identity envelopes whose actor is a
//! controller key for an HTTPS principal document.

use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::collections::{BTreeMap, BTreeSet};

use crate::error::{Result, SdkError};
use crate::identity::{
    validate_event_fields, validate_origin, verify_envelope, AcceptedRecord, AgentId, Envelope,
    Event, ListResponse,
};
use url::Url;

pub const PROTOCOL: &str = "agent-delegation/1.0";
pub const DELEGATION_GRANT: &str = "delegation.grant";
pub const DELEGATION_REVOKE: &str = "delegation.revoke";

/// Delegation-specific error codes (Agent Delegation Section 9.7).
pub const DELEGATION_ERROR_CODES: [&str; 8] = [
    "principal_unresolvable",
    "principal_not_canonical",
    "controller_not_current",
    "delegation_not_permitted",
    "delegation_ceiling_exceeded",
    "credential_not_found",
    "credential_identity_mismatch",
    "grant_expired",
];

#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "snake_case")]
pub enum DelegationStatus {
    Active,
    Suspended,
    Expired,
    Revoked,
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct PrincipalLink {
    pub name: String,
    pub url: String,
    pub rel: String,
}

/// Display descriptor of a principal, used by Agent Profile delegation hints.
/// The descriptor is open: other members are display metadata, kept in
/// `extra` so a signed hint re-serializes to the bytes that were signed.
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct PrincipalDescriptor {
    pub id: String,
    #[serde(rename = "type", default, skip_serializing_if = "Option::is_none")]
    pub kind: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
    #[serde(default, flatten)]
    pub extra: BTreeMap<String, Value>,
}

impl PrincipalDescriptor {
    pub fn new(id: impl Into<String>) -> Self {
        Self {
            id: id.into(),
            kind: None,
            name: None,
            extra: BTreeMap::new(),
        }
    }
}

/// Same type for active and retired bindings. Missing delegation means signing-only.
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct Controller {
    pub id: AgentId,
    pub source: String,
    pub valid_from: i64,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
    #[serde(
        default,
        deserialize_with = "non_null_option",
        skip_serializing_if = "Option::is_none"
    )]
    pub delegation: Option<DelegationAuthority>,
    #[serde(
        default,
        deserialize_with = "non_null_option",
        skip_serializing_if = "Option::is_none"
    )]
    pub retired_at: Option<i64>,
    #[serde(
        default,
        deserialize_with = "non_null_option",
        skip_serializing_if = "Option::is_none"
    )]
    pub invalid_from: Option<i64>,
}

impl Controller {
    /// A current controller record with no delegation authority.
    pub fn new(id: AgentId, source: impl Into<String>, valid_from: i64) -> Self {
        Self {
            id,
            source: source.into(),
            valid_from,
            name: None,
            delegation: None,
            retired_at: None,
            invalid_from: None,
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
#[serde(untagged)]
pub enum DelegationAuthority {
    /// Only the literal "*" is valid; validation rejects all other strings.
    Unrestricted(String),
    Restricted(DelegationPolicy),
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
#[serde(deny_unknown_fields)]
pub struct DelegationPolicy {
    pub scopes: Vec<String>,
    pub audiences: Vec<String>,
}

fn non_null_option<'de, D, T>(deserializer: D) -> std::result::Result<Option<T>, D::Error>
where
    D: serde::Deserializer<'de>,
    T: Deserialize<'de>,
{
    T::deserialize(deserializer).map(Some)
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct PrincipalDocument {
    pub id: String,
    #[serde(rename = "type", default, skip_serializing_if = "Option::is_none")]
    pub kind: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub name: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub description: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub avatar_url: Option<String>,
    /// Other HTTPS URLs that lead to this principal. Aliases are not identities.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub aliases: Vec<String>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub links: Vec<PrincipalLink>,
    pub protocol: String,
    pub controllers: Vec<Controller>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub retired_controllers: Vec<Controller>,
    /// Origin of the authoritative delegation service; required when any
    /// controller carries `delegation`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub delegation_service: Option<String>,
    pub updated_at: i64,
    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
    pub extra: BTreeMap<String, Value>,
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct DelegationGrantPayload {
    pub id: String,
    pub principal_id: String,
    pub subject: AgentId,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub relationship: Option<String>,
    pub scopes: Vec<String>,
    pub audiences: Vec<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub constraints: Option<BTreeMap<String, Value>>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub not_before: Option<i64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub expires_at: Option<i64>,
}

impl DelegationGrantPayload {
    pub fn new(
        id: impl Into<String>,
        principal_id: impl Into<String>,
        subject: AgentId,
        scopes: Vec<String>,
        audiences: Vec<String>,
    ) -> Self {
        Self {
            id: id.into(),
            principal_id: principal_id.into(),
            subject,
            relationship: None,
            scopes,
            audiences,
            constraints: None,
            not_before: None,
            expires_at: None,
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct DelegationRevokePayload {
    pub id: String,
    pub principal_id: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub reason: Option<String>,
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
#[serde(untagged)]
pub enum DelegationPayload {
    Grant(DelegationGrantPayload),
    Revoke(DelegationRevokePayload),
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct DelegationCredential {
    pub id: String,
    pub protocol: String,
    pub principal_id: String,
    pub subject: AgentId,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub relationship: Option<String>,
    pub scopes: Vec<String>,
    pub audiences: Vec<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub constraints: Option<BTreeMap<String, Value>>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub not_before: Option<i64>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub expires_at: Option<i64>,
    pub status: DelegationStatus,
    pub controller: AgentId,
    pub grant_event_id: String,
    pub event_id: String,
    pub accepted_at: i64,
    pub checked_at: i64,
}

pub type DelegationRecord = AcceptedRecord<DelegationPayload>;

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct DelegationServiceDiscovery {
    pub protocol: String,
    pub service: String,
    pub endpoints: DelegationServiceEndpoints,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub features: Vec<String>,
}

#[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq, Eq)]
pub struct DelegationServiceEndpoints {
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub delegations: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub query: Option<String>,
}

#[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq, Eq)]
pub struct DelegationQueryRequest {
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub subject: Option<AgentId>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub principal_id: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub id: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub status: Option<DelegationStatus>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub limit: Option<u32>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub cursor: Option<String>,
}

/// Agent Identity list of full credentials.
pub type DelegationQueryResponse = ListResponse<DelegationCredential>;

/// Agent Identity list of accepted records in service acceptance order.
pub type DelegationEventsResponse = ListResponse<DelegationRecord>;

/// Result of [`verify_delegation_credential`].
#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct DelegationVerdict {
    pub credential: DelegationCredential,
    /// Latest-grant signature, controller, ceiling, and consistency checks passed.
    pub verified: bool,
    /// Verified, and usable for the audience now.
    pub usable: bool,
    /// Every failed check.
    pub reasons: Vec<String>,
}

pub fn delegation_grant_event(
    actor: AgentId,
    created_at: i64,
    nonce: u64,
    payload: DelegationGrantPayload,
) -> Event<DelegationGrantPayload> {
    Event::new(
        PROTOCOL,
        DELEGATION_GRANT,
        actor,
        created_at,
        nonce,
        payload,
    )
}

pub fn delegation_revoke_event(
    actor: AgentId,
    created_at: i64,
    nonce: u64,
    payload: DelegationRevokePayload,
) -> Event<DelegationRevokePayload> {
    Event::new(
        PROTOCOL,
        DELEGATION_REVOKE,
        actor,
        created_at,
        nonce,
        payload,
    )
}

pub fn validate_controller(controller: &Controller, retired: bool) -> Result<()> {
    controller.id.public_key_bytes()?;
    if controller.source != "local" {
        validate_origin(&controller.source)?;
    }
    timestamp(controller.valid_from, "valid_from")?;
    if let Some(name) = &controller.name {
        validate_non_empty(name, "name")?;
    }
    match &controller.delegation {
        Some(DelegationAuthority::Unrestricted(value)) if value != "*" => {
            return fail("invalid delegation policy")
        }
        Some(DelegationAuthority::Restricted(policy)) => {
            strings(&policy.scopes, "scopes", false)?;
            strings(&policy.audiences, "audiences", false)?;
            for audience in &policy.audiences {
                validate_audience(audience)?;
            }
        }
        _ => {}
    }
    if retired {
        let end = controller
            .retired_at
            .ok_or_else(|| SdkError::InvalidPayload("retired_at required".into()))?;
        timestamp(end, "retired_at")?;
        if end < controller.valid_from {
            return fail("retired_at precedes valid_from");
        }
        if let Some(cutoff) = controller.invalid_from {
            timestamp(cutoff, "invalid_from")?;
            if cutoff < controller.valid_from || cutoff > end {
                return fail("invalid compromise interval");
            }
        }
    } else if controller.retired_at.is_some() || controller.invalid_from.is_some() {
        return fail("current controller has retirement fields");
    }
    Ok(())
}

pub fn validate_principal_document(document: &PrincipalDocument) -> Result<()> {
    validate_https_url(&document.id, "principal.id")?;
    if document.protocol != PROTOCOL {
        return fail("invalid principal protocol");
    }
    timestamp(document.updated_at, "updated_at")?;
    let mut records: BTreeMap<String, &Controller> = BTreeMap::new();
    let mut delegates = false;
    for (list, retired) in [
        (&document.controllers, false),
        (&document.retired_controllers, true),
    ] {
        for record in list {
            validate_controller(record, retired)?;
            if records.insert(record.id.to_string(), record).is_some() {
                return fail("duplicate controller key");
            }
            delegates |= record.delegation.is_some();
            if record.valid_from > document.updated_at
                || record.retired_at.is_some_and(|v| v > document.updated_at)
            {
                return fail("controller timestamp exceeds document update");
            }
        }
    }
    strings(&document.aliases, "aliases", true)?;
    for alias in &document.aliases {
        validate_https_url(alias, "alias")?;
    }
    if let Some(url) = &document.avatar_url {
        validate_https_url(url, "avatar_url")?;
    }
    match &document.delegation_service {
        Some(origin) => validate_origin(origin)?,
        None if delegates => {
            return fail("delegation_service is required when a controller carries delegation")
        }
        None => {}
    }
    Ok(())
}

/// Checks the authoritative-read rule of Agent Delegation Section 3: a
/// principal document binds controller keys only when it is read at its own
/// `id`. A document served anywhere else is a copy; its `controllers` must be
/// discarded and `document.id` resolved instead.
pub fn validate_principal_resolution(
    document: &PrincipalDocument,
    resolved_url: &str,
) -> Result<()> {
    if document.id == resolved_url {
        Ok(())
    } else {
        Err(SdkError::InvalidPayload(format!(
            "principal document id {} was served at {resolved_url}",
            document.id
        )))
    }
}

/// Reports whether `url` is an alias the principal itself acknowledges. Any
/// origin can redirect to any principal, so an alias must not be shown as a
/// name for the principal unless it is listed here.
pub fn is_principal_alias(document: &PrincipalDocument, url: &str) -> bool {
    document.aliases.iter().any(|alias| alias == url)
}

/// The Section 5 management rule: a restricted controller may replace, revoke,
/// or enumerate a credential only when every scope and audience of its latest
/// grant is within the controller's ceiling; an unrestricted controller covers
/// every credential of the principal.
pub fn controller_covers_credential(
    controller: &Controller,
    credential: &DelegationCredential,
) -> bool {
    within_ceiling(controller, &credential.scopes, &credential.audiences)
}

/// The Section 5 ceiling shared by issuance and management.
fn within_ceiling(controller: &Controller, scopes: &[String], audiences: &[String]) -> bool {
    match &controller.delegation {
        None => false,
        Some(DelegationAuthority::Restricted(policy)) => {
            scopes.iter().all(|x| policy.scopes.contains(x))
                && audiences.iter().all(|x| policy.audiences.contains(x))
        }
        Some(_) => unrestricted(controller),
    }
}

pub fn validate_delegation_grant_payload(
    payload: &DelegationGrantPayload,
    created_at: Option<i64>,
) -> Result<()> {
    validate_delegation_id(&payload.id)?;
    validate_https_url(&payload.principal_id, "principal_id")?;
    payload.subject.public_key_bytes()?;
    strings(&payload.scopes, "scopes", false)?;
    strings(&payload.audiences, "audiences", false)?;
    for audience in &payload.audiences {
        validate_audience(audience)?;
    }
    if let Some(time) = created_at {
        timestamp(time, "created_at")?;
    }
    if let Some(time) = payload.not_before {
        timestamp(time, "not_before")?;
    }
    if let Some(time) = payload.expires_at {
        timestamp(time, "expires_at")?;
    }
    if let Some(expires_at) = payload.expires_at {
        if matches!(payload.not_before, Some(not_before) if expires_at <= not_before) {
            return Err(SdkError::protocol(
                "grant_expired",
                "expires_at must be greater than not_before",
            ));
        }
        if matches!(created_at, Some(created_at) if expires_at <= created_at) {
            return Err(SdkError::protocol(
                "grant_expired",
                "expires_at must be greater than created_at",
            ));
        }
    }
    Ok(())
}

/// A public delegation query is an existence check and must include both
/// `subject` and `principal_id`. Omitting either side makes it an enumeration
/// query, which services must authorize before answering; pass
/// `allow_enumeration` when building such an authorized request. `limit`
/// defaults to 20; services SHOULD cap it at 100.
pub fn validate_delegation_query_request(
    request: &DelegationQueryRequest,
    allow_enumeration: bool,
) -> Result<()> {
    if allow_enumeration {
        if request.subject.is_none() && request.principal_id.is_none() {
            return Err(SdkError::protocol(
                "invalid_request",
                "query must include at least one of subject or principal_id",
            ));
        }
    } else if request.subject.is_none() || request.principal_id.is_none() {
        return Err(SdkError::protocol(
            "invalid_request",
            "public query must include both subject and principal_id",
        ));
    }
    if let Some(subject) = &request.subject {
        subject.public_key_bytes()?;
    }
    if let Some(principal_id) = &request.principal_id {
        validate_https_url(principal_id, "principal_id")?;
    }
    if let Some(id) = &request.id {
        validate_delegation_id(id)?;
    }
    if matches!(request.limit, Some(0)) {
        return Err(SdkError::protocol(
            "invalid_request",
            "limit must be a positive integer",
        ));
    }
    Ok(())
}

pub fn validate_delegation_revoke_payload(payload: &DelegationRevokePayload) -> Result<()> {
    validate_delegation_id(&payload.id)?;
    validate_https_url(&payload.principal_id, "principal_id")
}

/// Delegation IDs are unreserved URL characters (`[A-Za-z0-9._~-]{1,128}`)
/// and never a dot segment: no percent-encoding, no look-alikes.
pub fn validate_delegation_id(value: &str) -> Result<()> {
    let valid = (1..=128).contains(&value.len())
        && value
            .bytes()
            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'.' | b'_' | b'~' | b'-'))
        && !matches!(value, "." | "..");
    if valid {
        Ok(())
    } else {
        fail("delegation id must match [A-Za-z0-9._~-]{1,128} and not be a dot segment")
    }
}

pub fn validate_delegation_envelope(envelope: &Envelope<DelegationPayload>) -> Result<()> {
    verify_envelope(envelope)?;
    // Delegation events carry only the six Agent Identity event fields.
    validate_event_fields(&envelope.event, &[])?;
    if envelope.event.protocol != PROTOCOL {
        return Err(SdkError::InvalidEventProtocol {
            expected: PROTOCOL.to_owned(),
            actual: envelope.event.protocol.clone(),
        });
    }
    match (&envelope.event.kind[..], &envelope.event.payload) {
        (DELEGATION_GRANT, DelegationPayload::Grant(payload)) => {
            validate_delegation_grant_payload(payload, Some(envelope.event.created_at))
        }
        (DELEGATION_REVOKE, DelegationPayload::Revoke(payload)) => {
            validate_delegation_revoke_payload(payload)
        }
        (DELEGATION_GRANT, _) | (DELEGATION_REVOKE, _) => Err(SdkError::InvalidPayload(
            "delegation event type does not match payload shape".to_owned(),
        )),
        _ => Err(SdkError::InvalidEventType {
            expected: format!("{DELEGATION_GRANT} or {DELEGATION_REVOKE}"),
            actual: envelope.event.kind.clone(),
        }),
    }
}

/// Materializes an already accepted event with trusted previous state and the
/// service's actual acceptance time. This helper does not authorize the event.
pub fn materialize_delegation_credential(
    envelope: &Envelope<DelegationPayload>,
    status: DelegationStatus,
    accepted_at: i64,
    previous: Option<&DelegationCredential>,
) -> Result<DelegationCredential> {
    validate_delegation_envelope(envelope)?;
    timestamp(accepted_at, "accepted_at")?;
    check_previous(&envelope.event, previous)?;
    if previous.is_some_and(|p| accepted_at < p.accepted_at) {
        return fail("acceptance order reversed");
    }
    match &envelope.event.payload {
        DelegationPayload::Revoke(_) => {
            let mut result = previous
                .ok_or_else(|| {
                    SdkError::protocol(
                        "credential_not_found",
                        "revocation requires previous credential",
                    )
                })?
                .clone();
            result.controller = envelope.event.actor.clone();
            result.status = DelegationStatus::Revoked;
            result.event_id = envelope.hash.clone();
            result.accepted_at = accepted_at;
            result.checked_at = accepted_at;
            Ok(result)
        }
        DelegationPayload::Grant(payload) => {
            if payload.expires_at.is_some_and(|t| t <= accepted_at) {
                return Err(SdkError::protocol(
                    "grant_expired",
                    "grant expired at acceptance",
                ));
            }
            Ok(DelegationCredential {
                id: payload.id.clone(),
                protocol: PROTOCOL.into(),
                principal_id: payload.principal_id.clone(),
                subject: payload.subject.clone(),
                relationship: payload.relationship.clone(),
                scopes: payload.scopes.clone(),
                audiences: payload.audiences.clone(),
                constraints: payload.constraints.clone(),
                not_before: payload.not_before,
                expires_at: payload.expires_at,
                status,
                controller: envelope.event.actor.clone(),
                grant_event_id: envelope.hash.clone(),
                event_id: envelope.hash.clone(),
                accepted_at,
                checked_at: accepted_at,
            })
        }
    }
}

/// Pre-signing policy check over trusted document/state. No signature, HTTP,
/// cache-age, live timestamp-window, or nonce verification is performed.
pub fn validate_delegation_event_authority(
    event: &Event<DelegationPayload>,
    document: &PrincipalDocument,
    accepted_at: i64,
    previous: Option<&DelegationCredential>,
) -> Result<()> {
    check_authority(event, document, accepted_at, previous, false)
}

/// Caller also enforces fresh HTTPS, live Identity replay rules, and atomic persistence.
pub fn validate_delegation_acceptance(
    envelope: &Envelope<DelegationPayload>,
    document: &PrincipalDocument,
    resolved_url: &str,
    accepted_at: i64,
    previous: Option<&DelegationCredential>,
) -> Result<()> {
    validate_delegation_envelope(envelope)?;
    validate_principal_resolution(document, resolved_url)?;
    check_authority(&envelope.event, document, accepted_at, previous, false)
}

/// Caller authenticates the accepted record and previous state. This checks
/// historical policy, not current status or application constraints.
pub fn validate_historical_delegation(
    record: &DelegationRecord,
    document: &PrincipalDocument,
    resolved_url: &str,
    previous: Option<&DelegationCredential>,
) -> Result<()> {
    validate_delegation_envelope(&record.envelope)?;
    validate_principal_resolution(document, resolved_url)?;
    check_authority(
        &record.envelope.event,
        document,
        record.accepted_at,
        previous,
        true,
    )
}

/// Per-result check; caller authenticates the actor and resolves the document.
pub fn validate_controller_enumeration(
    document: &PrincipalDocument,
    actor: &AgentId,
    now: i64,
    credential: &DelegationCredential,
) -> Result<()> {
    validate_principal_document(document)?;
    timestamp(now, "now")?;
    strings(&credential.scopes, "scopes", false)?;
    strings(&credential.audiences, "audiences", false)?;
    let c = document
        .controllers
        .iter()
        .find(|c| &c.id == actor)
        .filter(|c| now >= c.valid_from)
        .ok_or_else(|| {
            SdkError::protocol("controller_not_current", "controller cannot enumerate")
        })?;
    if c.delegation.is_none() {
        return Err(SdkError::protocol(
            "delegation_not_permitted",
            "controller cannot enumerate",
        ));
    }
    if !controller_covers_credential(c, credential) {
        return Err(SdkError::protocol(
            "delegation_ceiling_exceeded",
            "credential is outside the controller's ceiling",
        ));
    }
    Ok(())
}

/// Audience/status/time only, after signature/history checks. Caller still
/// authenticates the subject and enforces scopes and constraints.
pub fn validate_delegation_use(
    credential: &DelegationCredential,
    audience: &str,
    now: i64,
) -> Result<()> {
    validate_audience(audience)?;
    timestamp(now, "now")?;
    validate_delegation_grant_payload(&grant_from_credential(credential), None)?;
    if credential.protocol != PROTOCOL
        || credential.status != DelegationStatus::Active
        || !credential.audiences.iter().any(|a| a == audience)
        || credential.not_before.is_some_and(|t| now < t)
        || credential.expires_at.is_some_and(|t| now >= t)
    {
        return fail("delegation is not usable");
    }
    Ok(())
}

/// Verifies a credential under Agent Delegation Section 8 with the online
/// service-trusting evidence policy: checks the accepted record of its latest
/// grant — signature, Controller binding, ceiling, and authority interval —
/// confirms that the grant matches the credential, and then checks use for
/// `audience` at `now`. The Section 5 management rule governs management,
/// which the service enforced at acceptance; auditors replay it with
/// [`audit_delegation_history`]. Relying parties still enforce scopes and
/// constraints and authenticate the subject.
pub fn verify_delegation_credential(
    credential: &DelegationCredential,
    records: &[DelegationRecord],
    document: &PrincipalDocument,
    resolved_url: &str,
    audience: &str,
    now: i64,
) -> DelegationVerdict {
    let mut reasons = Vec::new();
    if let Err(error) = latest_grant_matches(credential, records, document, resolved_url) {
        reasons.push(error.to_string());
    }
    let verified = reasons.is_empty();
    if credential.status != DelegationStatus::Active {
        let status = serde_json::to_value(credential.status)
            .ok()
            .and_then(|value| value.as_str().map(str::to_owned))
            .unwrap_or_default();
        reasons.push(format!("status is {status}"));
    }
    if !credential.audiences.iter().any(|a| a == audience) {
        reasons.push(format!("audience {audience} is not granted"));
    }
    if credential.not_before.is_some_and(|t| now < t) {
        reasons.push("not yet valid".to_owned());
    }
    if credential.expires_at.is_some_and(|t| now >= t) {
        reasons.push("expired".to_owned());
    }
    DelegationVerdict {
        credential: credential.clone(),
        verified,
        usable: reasons.is_empty(),
        reasons,
    }
}

/// Section 8 relying-party check: the latest grant record is authorized by a
/// Controller of the principal and agrees with the credential.
fn latest_grant_matches(
    credential: &DelegationCredential,
    records: &[DelegationRecord],
    document: &PrincipalDocument,
    resolved_url: &str,
) -> Result<()> {
    let record = records
        .iter()
        .find(|record| record.envelope.hash == credential.grant_event_id)
        .ok_or_else(|| SdkError::InvalidPayload("latest grant record is missing".into()))?;
    validate_historical_delegation(record, document, resolved_url, None)?;
    let DelegationPayload::Grant(grant) = &record.envelope.event.payload else {
        return fail("grant_event_id does not name a grant");
    };
    if credential.protocol != PROTOCOL
        || serde_jcs::to_vec(grant)? != serde_jcs::to_vec(&grant_from_credential(credential))?
    {
        return fail("credential does not match its latest grant");
    }
    if credential.event_id == credential.grant_event_id {
        if credential.accepted_at != record.accepted_at
            || credential.controller != record.envelope.event.actor
            || credential.status == DelegationStatus::Revoked
        {
            return fail("credential does not match its latest grant");
        }
    } else if credential.status != DelegationStatus::Revoked {
        return fail("a credential last changed by a revocation must be revoked");
    }
    Ok(())
}

/// Auditor check (Section 8): replays every accepted record of a credential
/// against the authoritative principal document — signatures, controller
/// intervals, and ceilings — and confirms that the replay
/// matches the credential. Relying parties use
/// [`verify_delegation_credential`] instead.
pub fn audit_delegation_history(
    credential: &DelegationCredential,
    records: &[DelegationRecord],
    document: &PrincipalDocument,
    resolved_url: &str,
) -> Result<()> {
    if records.is_empty() {
        return fail("no accepted records");
    }
    let mut replayed: Option<DelegationCredential> = None;
    for record in records {
        validate_historical_delegation(record, document, resolved_url, replayed.as_ref())?;
        replayed = Some(materialize_delegation_credential(
            &record.envelope,
            DelegationStatus::Active,
            record.accepted_at,
            replayed.as_ref(),
        )?);
    }
    let r = replayed.expect("at least one record");
    // Only status and its service timestamps may differ from event replay.
    if serde_jcs::to_vec(&grant_from_credential(&r))?
        != serde_jcs::to_vec(&grant_from_credential(credential))?
        || r.protocol != credential.protocol
        || r.accepted_at != credential.accepted_at
        || r.event_id != credential.event_id
        || r.grant_event_id != credential.grant_event_id
        || r.controller != credential.controller
        || (r.status == DelegationStatus::Revoked)
            != (credential.status == DelegationStatus::Revoked)
    {
        return fail("credential does not match its accepted records");
    }
    Ok(())
}

fn grant_from_credential(credential: &DelegationCredential) -> DelegationGrantPayload {
    DelegationGrantPayload {
        id: credential.id.clone(),
        principal_id: credential.principal_id.clone(),
        subject: credential.subject.clone(),
        relationship: credential.relationship.clone(),
        scopes: credential.scopes.clone(),
        audiences: credential.audiences.clone(),
        constraints: credential.constraints.clone(),
        not_before: credential.not_before,
        expires_at: credential.expires_at,
    }
}

fn event_identity(event: &Event<DelegationPayload>) -> (&str, &str) {
    match &event.payload {
        DelegationPayload::Grant(p) => (&p.id, &p.principal_id),
        DelegationPayload::Revoke(p) => (&p.id, &p.principal_id),
    }
}
fn check_previous(
    event: &Event<DelegationPayload>,
    previous: Option<&DelegationCredential>,
) -> Result<()> {
    let (id, principal) = event_identity(event);
    if let Some(previous) = previous {
        strings(&previous.scopes, "previous.scopes", false)?;
        strings(&previous.audiences, "previous.audiences", false)?;
        timestamp(previous.accepted_at, "previous.accepted_at")?;
        let same_subject = match &event.payload {
            DelegationPayload::Grant(p) => p.subject == previous.subject,
            DelegationPayload::Revoke(_) => true,
        };
        if previous.id != id
            || previous.principal_id != principal
            || previous.protocol != PROTOCOL
            || !same_subject
        {
            return Err(SdkError::protocol(
                "credential_identity_mismatch",
                "credential principal, subject, and protocol are immutable",
            ));
        }
    } else if event.kind == DELEGATION_REVOKE {
        return Err(SdkError::protocol(
            "credential_not_found",
            "revocation requires previous credential",
        ));
    }
    Ok(())
}
fn unrestricted(c: &Controller) -> bool {
    matches!(&c.delegation, Some(DelegationAuthority::Unrestricted(v)) if v == "*")
}
fn check_authority(
    event: &Event<DelegationPayload>,
    document: &PrincipalDocument,
    accepted_at: i64,
    previous: Option<&DelegationCredential>,
    historical: bool,
) -> Result<()> {
    validate_principal_document(document)?;
    timestamp(accepted_at, "accepted_at")?;
    timestamp(event.created_at, "created_at")?;
    event.actor.public_key_bytes()?;
    if event.protocol != PROTOCOL {
        return fail("invalid event protocol");
    }
    match (&event.kind[..], &event.payload) {
        (DELEGATION_GRANT, DelegationPayload::Grant(p)) => {
            validate_delegation_grant_payload(p, Some(event.created_at))?
        }
        (DELEGATION_REVOKE, DelegationPayload::Revoke(p)) => validate_delegation_revoke_payload(p)?,
        _ => return fail("event type does not match payload"),
    }
    if event_identity(event).1 != document.id {
        return Err(SdkError::protocol(
            "principal_not_canonical",
            "principal mismatch",
        ));
    }
    let c = document
        .controllers
        .iter()
        .chain(document.retired_controllers.iter().filter(|_| historical))
        .find(|c| c.id == event.actor)
        .ok_or_else(|| {
            SdkError::protocol(
                "controller_not_current",
                "actor is not a controller of the principal",
            )
        })?;
    if c.delegation.is_none() {
        return Err(SdkError::protocol(
            "delegation_not_permitted",
            "actor has no delegation authority",
        ));
    }
    for time in [event.created_at, accepted_at] {
        if time < c.valid_from
            || c.retired_at.is_some_and(|t| time >= t)
            || c.invalid_from.is_some_and(|t| time >= t)
        {
            return Err(SdkError::protocol(
                "controller_not_current",
                "outside controller authority interval",
            ));
        }
    }
    check_previous(event, previous)?;
    if let Some(previous) = previous {
        if accepted_at < previous.accepted_at {
            return fail("acceptance order reversed");
        }
        if !controller_covers_credential(c, previous) {
            return Err(SdkError::protocol(
                "delegation_ceiling_exceeded",
                "credential is outside the controller's ceiling",
            ));
        }
    }
    if let DelegationPayload::Grant(payload) = &event.payload {
        if payload.expires_at.is_some_and(|t| t <= accepted_at) {
            return Err(SdkError::protocol(
                "grant_expired",
                "grant expired at acceptance",
            ));
        }
        if !within_ceiling(c, &payload.scopes, &payload.audiences) {
            return Err(SdkError::protocol(
                "delegation_ceiling_exceeded",
                "grant exceeds controller delegation policy",
            ));
        }
    }
    Ok(())
}
fn fail<T>(message: &str) -> Result<T> {
    Err(SdkError::InvalidPayload(message.into()))
}
fn timestamp(value: i64, field: &str) -> Result<()> {
    if !(0..=9_007_199_254_740_991).contains(&value) {
        return fail(&format!("{field} must be a non-negative safe integer"));
    }
    Ok(())
}
fn strings(values: &[String], field: &str, empty: bool) -> Result<()> {
    if !empty && values.is_empty() {
        return fail(&format!("{field} must be a non-empty array"));
    }
    let mut seen = BTreeSet::new();
    for value in values {
        validate_non_empty(value, field)?;
        if value == "*" || !seen.insert(value) {
            return fail(&format!("{field} has wildcard or duplicates"));
        }
    }
    Ok(())
}
/// A relying-party audience (Section 5): an origin for a relying
/// application, or an Agent ID for a relying agent.
pub fn validate_audience(value: &str) -> Result<()> {
    if value.starts_with(crate::identity::AGENT_ID_PREFIX) {
        value.parse::<AgentId>().map(|_| ())
    } else {
        validate_origin(value)
    }
}

fn validate_https_url(value: &str, field: &str) -> Result<()> {
    let parsed = Url::parse(value)
        .map_err(|_| SdkError::InvalidPayload(format!("{field} must be an HTTPS URL")))?;
    if parsed.scheme() == "https" && parsed.host_str().is_some() {
        Ok(())
    } else {
        Err(SdkError::InvalidPayload(format!(
            "{field} must be an HTTPS URL"
        )))
    }
}

fn validate_non_empty(value: &str, field: &str) -> Result<()> {
    if value.trim().is_empty() {
        Err(SdkError::InvalidPayload(format!(
            "{field} must not be empty"
        )))
    } else {
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::identity::AgentSigner;

    #[test]
    fn validates_and_materializes_grant() {
        let controller = AgentSigner::from_seed([31; 32]);
        let subject = AgentSigner::from_seed([32; 32]);
        let mut payload = DelegationGrantPayload::new(
            "del_01J8ZM7A3G2T9B4Q6X8R0N1P2Q",
            "https://api.al.ink/d9c6a99cne5g00a6scn0",
            subject.agent_id(),
            vec!["inbox.screen".to_owned(), "meeting.propose".to_owned()],
            vec!["https://dmsg.net".to_owned()],
        );
        payload.relationship = Some("primary_delegate".to_owned());
        payload.not_before = Some(1_779_753_600_000);
        payload.expires_at = Some(1_790_000_000_000);
        let envelope = controller
            .sign_event(delegation_grant_event(
                controller.agent_id(),
                1_779_753_600_000,
                1,
                payload,
            ))
            .unwrap();
        let envelope_value = serde_json::to_value(&envelope).unwrap();
        let envelope_for_validation: Envelope<DelegationPayload> =
            serde_json::from_value(envelope_value).unwrap();

        validate_delegation_envelope(&envelope_for_validation).unwrap();
        let credential = materialize_delegation_credential(
            &envelope_for_validation,
            DelegationStatus::Active,
            1_779_753_600_000,
            None,
        )
        .unwrap();

        assert_eq!(credential.protocol, PROTOCOL);
        assert_eq!(credential.controller, controller.agent_id());
        assert_eq!(credential.subject, subject.agent_id());
        assert_eq!(
            credential.principal_id,
            "https://api.al.ink/d9c6a99cne5g00a6scn0"
        );
        assert_eq!(credential.event_id, envelope.hash);
    }

    #[test]
    fn validates_revoke_and_rejects_invalid_grants() {
        let controller = AgentSigner::from_seed([33; 32]);
        let envelope = controller
            .sign_event(delegation_revoke_event(
                controller.agent_id(),
                1_779_753_700_000,
                2,
                DelegationRevokePayload {
                    id: "del_01J8ZM7A3G2T9B4Q6X8R0N1P2Q".to_owned(),
                    principal_id: "https://api.al.ink/d9c6a99cne5g00a6scn0".to_owned(),
                    reason: Some("rotated_primary_agent".to_owned()),
                },
            ))
            .unwrap();
        let envelope: Envelope<DelegationPayload> =
            serde_json::from_value(serde_json::to_value(envelope).unwrap()).unwrap();
        validate_delegation_envelope(&envelope).unwrap();

        let invalid = DelegationGrantPayload::new(
            "del",
            "http://example.com",
            controller.agent_id(),
            Vec::new(),
            vec!["https://dmsg.net".to_owned()],
        );
        assert!(validate_delegation_grant_payload(&invalid, None).is_err());
    }

    #[test]
    fn grant_expiry_checked_against_not_before_and_created_at() {
        let controller = AgentSigner::from_seed([36; 32]);
        let base = DelegationGrantPayload::new(
            "del_1",
            "https://api.al.ink/d9c6a99cne5g00a6scn0",
            controller.agent_id(),
            vec!["inbox.screen".to_owned()],
            vec!["https://dmsg.net".to_owned()],
        );

        let mut same_as_not_before = base.clone();
        same_as_not_before.not_before = Some(2000);
        same_as_not_before.expires_at = Some(2000);
        assert!(validate_delegation_grant_payload(&same_as_not_before, Some(1000)).is_err());

        let mut before_created_at = base.clone();
        before_created_at.not_before = Some(500);
        before_created_at.expires_at = Some(800);
        assert!(validate_delegation_grant_payload(&before_created_at, Some(1000)).is_err());

        let mut valid = base;
        valid.not_before = Some(500);
        valid.expires_at = Some(1500);
        validate_delegation_grant_payload(&valid, Some(1000)).unwrap();
    }

    #[test]
    fn public_delegation_queries_carry_both_subject_and_principal() {
        let subject = AgentSigner::from_seed([37; 32]).agent_id();
        let principal_id = "https://api.al.ink/d9c6a99cne5g00a6scn0".to_owned();
        let public = DelegationQueryRequest {
            subject: Some(subject.clone()),
            principal_id: Some(principal_id.clone()),
            limit: Some(20),
            ..DelegationQueryRequest::default()
        };
        validate_delegation_query_request(&public, false).unwrap();

        // Enumerating one side is not a public query.
        for one_sided in [
            DelegationQueryRequest {
                subject: Some(subject.clone()),
                ..DelegationQueryRequest::default()
            },
            DelegationQueryRequest {
                principal_id: Some(principal_id),
                ..DelegationQueryRequest::default()
            },
        ] {
            assert!(validate_delegation_query_request(&one_sided, false).is_err());
            validate_delegation_query_request(&one_sided, true).unwrap();
        }

        assert!(
            validate_delegation_query_request(&DelegationQueryRequest::default(), true).is_err()
        );
        assert!(validate_delegation_query_request(
            &DelegationQueryRequest {
                limit: Some(0),
                ..public
            },
            false
        )
        .is_err());
    }

    #[test]
    fn principal_documents_bind_controllers_only_at_their_own_id() {
        let controller = AgentSigner::from_seed([38; 32]);
        let document = PrincipalDocument {
            id: "https://api.al.ink/d9c6a99cne5g00a6scn0".to_owned(),
            kind: None,
            name: None,
            description: None,
            avatar_url: None,
            aliases: vec!["https://al.ink/yan".to_owned()],
            links: Vec::new(),
            protocol: PROTOCOL.into(),
            retired_controllers: vec![],
            controllers: vec![Controller::new(controller.agent_id(), "local", 0)],
            delegation_service: None,
            updated_at: 1000,
            extra: BTreeMap::new(),
        };

        validate_principal_resolution(&document, "https://api.al.ink/d9c6a99cne5g00a6scn0")
            .unwrap();
        // A copy served away from its identifier carries no authority.
        assert!(
            validate_principal_resolution(&document, "https://impostor.example.com/yan").is_err()
        );

        assert!(is_principal_alias(&document, "https://al.ink/yan"));
        assert!(!is_principal_alias(
            &document,
            "https://impostor.example.com/yan"
        ));
    }

    #[test]
    fn validates_principal_document() {
        let controller = AgentSigner::from_seed([34; 32]);
        let document = PrincipalDocument {
            id: "https://profiles.example.com/org/acme".to_owned(),
            kind: None,
            name: None,
            description: None,
            avatar_url: None,
            aliases: vec!["https://profiles.example.com/acme".to_owned()],
            links: Vec::new(),
            protocol: PROTOCOL.into(),
            retired_controllers: vec![],
            controllers: vec![Controller::new(controller.agent_id(), "local", 0)],
            delegation_service: Some("https://profiles.example.com".to_owned()),
            updated_at: 1000,
            extra: BTreeMap::new(),
        };
        validate_principal_document(&document).unwrap();

        let mut invalid = document.clone();
        invalid.protocol = "old-draft".into();
        assert!(validate_principal_document(&invalid).is_err());

        // A controller with delegation authority needs an authoritative query endpoint.
        let mut delegating = document;
        delegating.controllers[0].delegation = Some(DelegationAuthority::Unrestricted("*".into()));
        validate_principal_document(&delegating).unwrap();
        delegating.delegation_service = None;
        assert!(validate_principal_document(&delegating).is_err());
    }

    #[test]
    fn rejects_malformed_https_like_urls() {
        let signer = AgentSigner::from_seed([35; 32]);
        for principal_id in ["https://", "https://[::1", "http://example.com"] {
            let payload = DelegationGrantPayload::new(
                "del",
                principal_id,
                signer.agent_id(),
                vec!["scope".to_owned()],
                vec!["https://dmsg.net".to_owned()],
            );
            assert!(validate_delegation_grant_payload(&payload, None).is_err());
        }
    }
}