use std::net::Ipv4Addr;
use ipnet::Ipv4Net;

use crate::client_registry::ClientSecurity;

/// Result of an ACL check.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum AclResult {
    Allow,
    DenySrc,
    DenyDst,
}

/// Check whether a connection source IP is in a server-level block list.
/// Used for pre-handshake rejection of known-bad IPs.
pub fn is_connection_blocked(ip: Ipv4Addr, block_list: &[String]) -> bool {
    ip_matches_any(ip, block_list)
}

/// Check whether a source IP is allowed by allow/block lists.
/// Returns true if the IP is permitted (not blocked and passes allow check).
pub fn is_source_allowed(ip: Ipv4Addr, allow_list: Option<&[String]>, block_list: Option<&[String]>) -> bool {
    // Deny overrides allow
    if let Some(bl) = block_list {
        if ip_matches_any(ip, bl) {
            return false;
        }
    }
    // If allow list exists and is non-empty, IP must match
    if let Some(al) = allow_list {
        if !al.is_empty() && !ip_matches_any(ip, al) {
            return false;
        }
    }
    true
}

/// Check whether a packet from `src_ip` to `dst_ip` is allowed by the client's security policy.
///
/// Evaluation order (deny overrides allow):
/// 1. If src_ip is in ip_block_list → DenySrc
/// 2. If dst_ip is in destination_block_list → DenyDst
/// 3. If ip_allow_list is non-empty and src_ip is NOT in it → DenySrc
/// 4. If destination_allow_list is non-empty and dst_ip is NOT in it → DenyDst
/// 5. Otherwise → Allow
pub fn check_acl(security: &ClientSecurity, src_ip: Ipv4Addr, dst_ip: Ipv4Addr) -> AclResult {
    // Step 1: Check source block list (deny overrides)
    if let Some(ref block_list) = security.ip_block_list {
        if ip_matches_any(src_ip, block_list) {
            return AclResult::DenySrc;
        }
    }

    // Step 2: Check destination block list (deny overrides)
    if let Some(ref block_list) = security.destination_block_list {
        if ip_matches_any(dst_ip, block_list) {
            return AclResult::DenyDst;
        }
    }

    // Step 3: Check source allow list (if non-empty, must match)
    if let Some(ref allow_list) = security.ip_allow_list {
        if !allow_list.is_empty() && !ip_matches_any(src_ip, allow_list) {
            return AclResult::DenySrc;
        }
    }

    // Step 4: Check destination allow list (if non-empty, must match)
    if let Some(ref allow_list) = security.destination_allow_list {
        if !allow_list.is_empty() && !ip_matches_any(dst_ip, allow_list) {
            return AclResult::DenyDst;
        }
    }

    AclResult::Allow
}

/// Check if `ip` matches any pattern in the list.
/// Supports: exact IP, CIDR notation, wildcard patterns (192.168.1.*),
/// and IP ranges (192.168.1.1-192.168.1.100).
pub fn ip_matches_any(ip: Ipv4Addr, patterns: &[String]) -> bool {
    for pattern in patterns {
        if ip_matches(ip, pattern) {
            return true;
        }
    }
    false
}

/// Check if `ip` matches a single pattern.
fn ip_matches(ip: Ipv4Addr, pattern: &str) -> bool {
    let pattern = pattern.trim();

    // CIDR notation (e.g. 192.168.1.0/24)
    if pattern.contains('/') {
        if let Ok(net) = pattern.parse::<Ipv4Net>() {
            return net.contains(&ip);
        }
        return false;
    }

    // IP range (e.g. 192.168.1.1-192.168.1.100)
    if pattern.contains('-') {
        let parts: Vec<&str> = pattern.splitn(2, '-').collect();
        if parts.len() == 2 {
            if let (Ok(start), Ok(end)) = (parts[0].trim().parse::<Ipv4Addr>(), parts[1].trim().parse::<Ipv4Addr>()) {
                let ip_u32 = u32::from(ip);
                return ip_u32 >= u32::from(start) && ip_u32 <= u32::from(end);
            }
        }
        return false;
    }

    // Wildcard pattern (e.g. 192.168.1.*)
    if pattern.contains('*') {
        return wildcard_matches(ip, pattern);
    }

    // Exact IP match
    if let Ok(exact) = pattern.parse::<Ipv4Addr>() {
        return ip == exact;
    }

    false
}

/// Match an IP against a wildcard pattern like "192.168.1.*" or "10.*.*.*".
fn wildcard_matches(ip: Ipv4Addr, pattern: &str) -> bool {
    let ip_octets = ip.octets();
    let pattern_parts: Vec<&str> = pattern.split('.').collect();
    if pattern_parts.len() != 4 {
        return false;
    }
    for (i, part) in pattern_parts.iter().enumerate() {
        if *part == "*" {
            continue;
        }
        if let Ok(octet) = part.parse::<u8>() {
            if ip_octets[i] != octet {
                return false;
            }
        } else {
            return false;
        }
    }
    true
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::client_registry::{ClientRateLimit, ClientSecurity};

    fn security(
        ip_allow: Option<Vec<&str>>,
        ip_block: Option<Vec<&str>>,
        dst_allow: Option<Vec<&str>>,
        dst_block: Option<Vec<&str>>,
    ) -> ClientSecurity {
        ClientSecurity {
            ip_allow_list: ip_allow.map(|v| v.into_iter().map(String::from).collect()),
            ip_block_list: ip_block.map(|v| v.into_iter().map(String::from).collect()),
            destination_allow_list: dst_allow.map(|v| v.into_iter().map(String::from).collect()),
            destination_block_list: dst_block.map(|v| v.into_iter().map(String::from).collect()),
            max_connections: None,
            rate_limit: None,
        }
    }

    fn ip(s: &str) -> Ipv4Addr {
        s.parse().unwrap()
    }

    // ── No restrictions (empty security) ────────────────────────────────

    #[test]
    fn empty_security_allows_all() {
        let sec = security(None, None, None, None);
        assert_eq!(check_acl(&sec, ip("1.2.3.4"), ip("5.6.7.8")), AclResult::Allow);
    }

    #[test]
    fn empty_lists_allow_all() {
        let sec = security(Some(vec![]), Some(vec![]), Some(vec![]), Some(vec![]));
        assert_eq!(check_acl(&sec, ip("1.2.3.4"), ip("5.6.7.8")), AclResult::Allow);
    }

    // ── Source IP allow list ────────────────────────────────────────────

    #[test]
    fn src_allow_exact_match() {
        let sec = security(Some(vec!["10.0.0.1"]), None, None, None);
        assert_eq!(check_acl(&sec, ip("10.0.0.1"), ip("5.6.7.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("10.0.0.2"), ip("5.6.7.8")), AclResult::DenySrc);
    }

    #[test]
    fn src_allow_cidr() {
        let sec = security(Some(vec!["192.168.1.0/24"]), None, None, None);
        assert_eq!(check_acl(&sec, ip("192.168.1.50"), ip("5.6.7.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("192.168.2.1"), ip("5.6.7.8")), AclResult::DenySrc);
    }

    #[test]
    fn src_allow_wildcard() {
        let sec = security(Some(vec!["10.0.*.*"]), None, None, None);
        assert_eq!(check_acl(&sec, ip("10.0.5.3"), ip("5.6.7.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("10.1.0.1"), ip("5.6.7.8")), AclResult::DenySrc);
    }

    #[test]
    fn src_allow_range() {
        let sec = security(Some(vec!["10.0.0.1-10.0.0.10"]), None, None, None);
        assert_eq!(check_acl(&sec, ip("10.0.0.5"), ip("5.6.7.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("10.0.0.11"), ip("5.6.7.8")), AclResult::DenySrc);
    }

    // ── Source IP block list (deny overrides) ───────────────────────────

    #[test]
    fn src_block_overrides_allow() {
        let sec = security(
            Some(vec!["192.168.1.0/24"]),
            Some(vec!["192.168.1.100"]),
            None,
            None,
        );
        assert_eq!(check_acl(&sec, ip("192.168.1.50"), ip("5.6.7.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("192.168.1.100"), ip("5.6.7.8")), AclResult::DenySrc);
    }

    // ── Destination allow list ──────────────────────────────────────────

    #[test]
    fn dst_allow_exact() {
        let sec = security(None, None, Some(vec!["8.8.8.8", "8.8.4.4"]), None);
        assert_eq!(check_acl(&sec, ip("10.0.0.1"), ip("8.8.8.8")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("10.0.0.1"), ip("1.1.1.1")), AclResult::DenyDst);
    }

    #[test]
    fn dst_allow_cidr() {
        let sec = security(None, None, Some(vec!["10.0.0.0/8"]), None);
        assert_eq!(check_acl(&sec, ip("1.1.1.1"), ip("10.5.3.2")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("1.1.1.1"), ip("172.16.0.1")), AclResult::DenyDst);
    }

    // ── Destination block list (deny overrides) ─────────────────────────

    #[test]
    fn dst_block_overrides_allow() {
        let sec = security(
            None,
            None,
            Some(vec!["10.0.0.0/8"]),
            Some(vec!["10.0.0.99"]),
        );
        assert_eq!(check_acl(&sec, ip("1.1.1.1"), ip("10.0.0.1")), AclResult::Allow);
        assert_eq!(check_acl(&sec, ip("1.1.1.1"), ip("10.0.0.99")), AclResult::DenyDst);
    }

    // ── Combined source + destination ───────────────────────────────────

    #[test]
    fn combined_src_and_dst_filtering() {
        let sec = security(
            Some(vec!["192.168.1.0/24"]),
            None,
            Some(vec!["8.8.8.8"]),
            None,
        );
        // Valid source, valid dest
        assert_eq!(check_acl(&sec, ip("192.168.1.10"), ip("8.8.8.8")), AclResult::Allow);
        // Invalid source
        assert_eq!(check_acl(&sec, ip("10.0.0.1"), ip("8.8.8.8")), AclResult::DenySrc);
        // Valid source, invalid dest
        assert_eq!(check_acl(&sec, ip("192.168.1.10"), ip("1.1.1.1")), AclResult::DenyDst);
    }

    // ── IP matching edge cases ──────────────────────────────────────────

    #[test]
    fn wildcard_single_octet() {
        assert!(ip_matches(ip("10.0.0.5"), "10.0.0.*"));
        assert!(!ip_matches(ip("10.0.1.5"), "10.0.0.*"));
    }

    #[test]
    fn range_boundaries() {
        assert!(ip_matches(ip("10.0.0.1"), "10.0.0.1-10.0.0.5"));
        assert!(ip_matches(ip("10.0.0.5"), "10.0.0.1-10.0.0.5"));
        assert!(!ip_matches(ip("10.0.0.6"), "10.0.0.1-10.0.0.5"));
        assert!(!ip_matches(ip("10.0.0.0"), "10.0.0.1-10.0.0.5"));
    }

    #[test]
    fn invalid_pattern_no_match() {
        assert!(!ip_matches(ip("10.0.0.1"), "not-an-ip"));
        assert!(!ip_matches(ip("10.0.0.1"), "10.0.0.1/99"));
        assert!(!ip_matches(ip("10.0.0.1"), "10.0.0"));
    }
}