//! Parsed KCA OCSP status snapshots.

use std::collections::HashMap;

use chrono::{DateTime, Utc};
use serde::Deserialize;
use sha1::{Digest as _, Sha1};
use sha2::Sha256;
use x509_cert::ext::pkix::CrlReason;

pub const SCHEMA: &str = "kca-ocsp-status/v2";

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Status {
    Good,
    Revoked,
}

#[derive(Debug, Clone)]
pub struct StatusEntry {
    pub status: Status,
    pub revoked_at: Option<DateTime<Utc>>,
    pub reason: Option<CrlReason>,
}

#[derive(Debug, Clone, Default)]
pub struct Snapshot {
    pub entries: HashMap<Vec<u8>, StatusEntry>,
}

#[derive(Debug, Deserialize)]
struct RawSnapshot {
    schema: String,
    issuer: RawIssuer,
    #[serde(default)]
    entries: Vec<RawEntry>,
}

#[derive(Debug, Deserialize)]
struct RawIssuer {
    #[serde(default)]
    id: String,
    #[serde(default)]
    sha256: String,
}

#[derive(Debug, Deserialize)]
struct RawEntry {
    serial_hex: String,
    status: String,
    #[serde(default)]
    revoked_at: Option<DateTime<Utc>>,
    #[serde(default)]
    reason: Option<String>,
}

impl Snapshot {
    /// Parse and validate a snapshot against the configured CA identity.
    pub fn parse(
        bytes: &[u8],
        expected_sha256: &str,
        expected_ca_id: &str,
    ) -> Result<Self, SnapshotError> {
        let raw: RawSnapshot = serde_json::from_slice(bytes)?;
        if raw.schema != SCHEMA {
            return Err(SnapshotError::Schema(raw.schema));
        }
        if !raw.issuer.id.eq_ignore_ascii_case(expected_ca_id) {
            return Err(SnapshotError::IssuerIdMismatch {
                expected: expected_ca_id.to_string(),
                actual: raw.issuer.id,
            });
        }
        if !raw.issuer.sha256.eq_ignore_ascii_case(expected_sha256) {
            return Err(SnapshotError::IssuerMismatch {
                expected: expected_sha256.to_string(),
                actual: raw.issuer.sha256,
            });
        }
        let mut entries = HashMap::with_capacity(raw.entries.len());
        for entry in raw.entries {
            let serial = parse_serial(&entry.serial_hex)?;
            let status = match entry.status.as_str() {
                "valid" => Status::Good,
                "revoked" => Status::Revoked,
                other => return Err(SnapshotError::Status(other.to_string())),
            };
            if status == Status::Revoked && entry.revoked_at.is_none() {
                return Err(SnapshotError::MissingRevocationTime(entry.serial_hex));
            }
            let reason = if status == Status::Revoked {
                Some(parse_reason(
                    entry.reason.as_deref().unwrap_or("unspecified"),
                ))
            } else {
                None
            };
            if entries
                .insert(
                    serial,
                    StatusEntry {
                        status,
                        revoked_at: entry.revoked_at,
                        reason,
                    },
                )
                .is_some()
            {
                return Err(SnapshotError::DuplicateSerial(entry.serial_hex));
            }
        }
        let _ = raw.issuer.sha256;
        Ok(Self { entries })
    }

    pub fn status_for_serial(&self, serial: &[u8]) -> Option<&StatusEntry> {
        self.entries.get(&normalize_serial(serial))
    }
}

pub fn normalize_serial(serial: &[u8]) -> Vec<u8> {
    let first = serial
        .iter()
        .position(|byte| *byte != 0)
        .unwrap_or(serial.len());
    serial[first..].to_vec()
}

fn parse_serial(value: &str) -> Result<Vec<u8>, SnapshotError> {
    let text = value.trim();
    let text = text.strip_prefix("0x").unwrap_or(text);
    let decoded = hex::decode(text).map_err(|_| SnapshotError::Serial(value.to_string()))?;
    Ok(normalize_serial(&decoded))
}

fn parse_reason(value: &str) -> CrlReason {
    match value.to_ascii_lowercase().as_str() {
        "keycompromise" => CrlReason::KeyCompromise,
        "cacompromise" => CrlReason::CaCompromise,
        "affiliationchanged" => CrlReason::AffiliationChanged,
        "superseded" => CrlReason::Superseded,
        "cessationofoperation" => CrlReason::CessationOfOperation,
        "certificatehold" => CrlReason::CertificateHold,
        "removefromcrl" => CrlReason::RemoveFromCRL,
        "privilegewithdrawn" => CrlReason::PrivilegeWithdrawn,
        "aacompromise" => CrlReason::AaCompromise,
        _ => CrlReason::Unspecified,
    }
}

pub fn sha256_hex(bytes: &[u8]) -> String {
    use sha2::Digest as _;
    hex::encode(Sha256::digest(bytes))
}

/// OCSP CertID hashes are SHA-1 in the common case, with SHA-256 as an
/// alternative.  The responder supports both.
pub fn hash_sha1(bytes: &[u8]) -> Vec<u8> {
    Sha1::digest(bytes).to_vec()
}

pub fn hash_sha256(bytes: &[u8]) -> Vec<u8> {
    use sha2::Digest as _;
    Sha256::digest(bytes).to_vec()
}

#[derive(Debug, thiserror::Error)]
pub enum SnapshotError {
    #[error("invalid JSON: {0}")]
    Json(#[from] serde_json::Error),
    #[error("unsupported snapshot schema {0:?}")]
    Schema(String),
    #[error("snapshot issuer ID {actual} does not match configured CA ID {expected}")]
    IssuerIdMismatch { expected: String, actual: String },
    #[error("snapshot issuer {actual} does not match configured CA {expected}")]
    IssuerMismatch { expected: String, actual: String },
    #[error("invalid serial {0:?}")]
    Serial(String),
    #[error("unknown status {0:?}")]
    Status(String),
    #[error("revoked entry {0:?} has no revocation time")]
    MissingRevocationTime(String),
    #[error("duplicate serial {0:?}")]
    DuplicateSerial(String),
}

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

    fn body(sha: &str) -> String {
        format!(
            r#"{{
              "schema": "kca-ocsp-status/v2",
              "issuer": {{"id": "ca", "sha256": "{sha}", "subject": "CN=CA"}},
              "entries": [
                {{"serial_hex": "01ab", "status": "valid", "not_after": "2027-01-01T00:00:00Z"}},
                {{"serial_hex": "00ff", "status": "revoked", "revoked_at": "2026-02-03T04:05:06Z", "reason": "keyCompromise"}}
              ]
            }}"#
        )
    }

    #[test]
    fn parses_statuses_and_reasons() {
        let sha = sha256_hex(b"ca");
        let snapshot = Snapshot::parse(body(&sha).as_bytes(), &sha, "ca").unwrap();
        let good = snapshot.status_for_serial(&[0x01, 0xab]).unwrap();
        assert_eq!(good.status, Status::Good);
        let revoked = snapshot.status_for_serial(&[0xff]).unwrap();
        assert_eq!(revoked.status, Status::Revoked);
        assert_eq!(revoked.reason, Some(CrlReason::KeyCompromise));
        assert!(revoked.revoked_at.is_some());
    }

    #[test]
    fn rejects_wrong_issuer_schema_and_duplicates() {
        let sha = sha256_hex(b"ca");
        assert!(Snapshot::parse(body(&sha).as_bytes(), "wrong", "ca").is_err());
        assert!(matches!(
            Snapshot::parse(body(&sha).as_bytes(), &sha, "other"),
            Err(SnapshotError::IssuerIdMismatch { .. })
        ));
        let wrong_schema = body(&sha).replace(SCHEMA, "other");
        assert!(Snapshot::parse(wrong_schema.as_bytes(), &sha, "ca").is_err());
        let duplicate = body(&sha).replace("\"00ff\"", "\"01ab\"");
        assert!(Snapshot::parse(duplicate.as_bytes(), &sha, "ca").is_err());
    }

    #[test]
    fn normalizes_serials() {
        assert_eq!(normalize_serial(&[0, 0, 1, 2]), vec![1, 2]);
        assert_eq!(normalize_serial(&[0, 0]), Vec::<u8>::new());
    }
}