use core::net::IpAddr;
use ipnet::IpNet;
use std::format;
use std::sync::Arc;

use crate::ast::{Expr, Ref};
use crate::builtins;
use crate::builtins::utils::ensure_args_count;
use crate::lexer::Span;
use crate::value::Value;

use anyhow::{anyhow, bail, Result};

use super::utils::ensure_string;

pub fn register(m: &mut builtins::BuiltinsMap<&'static str, builtins::BuiltinFcn>) {
    m.insert("net.cidr_is_valid", (cidr_is_valid, 1));
    m.insert("net.cidr_contains", (cidr_contains, 2));
}

/// Checks if a CIDR string is valid or invalid. Uses the
/// `net::IpAddr` type to determine if the string is a valid IP,
/// and checks to ensure that the mask is in bounds for the parsed
/// IP address type (v4 or v6).
pub fn cidr_is_valid(
    span: &Span,
    params: &[Ref<Expr>],
    args: &[Value],
    _strict: bool,
) -> Result<Value> {
    ensure_args_count(span, "cidr_is_valid", params, args, 1)?;
    let cidr = ensure_string("cidr_is_valid", &params[0], &args[0])?;

    Ok(Value::from(is_valid_cidr(cidr)))
}

fn is_valid_cidr(cidr: Arc<str>) -> bool {
    let Some((ip_addr, prefix_len)) = cidr.split_once("/") else {
        return false;
    };
    match ip_addr.parse::<IpAddr>() {
        Ok(addr) => {
            let Ok(mask) = prefix_len.parse::<i16>() else {
                return false;
            };

            match addr {
                IpAddr::V4(_) => {
                    if !(0..=32).contains(&mask) {
                        return false;
                    }
                }
                IpAddr::V6(_) => {
                    if !(0..=128).contains(&mask) {
                        return false;
                    }
                }
            }
            true
        }
        Err(_) => false,
    }
}

pub fn cidr_contains(
    span: &Span,
    params: &[Ref<Expr>],
    args: &[Value],
    strict: bool,
) -> Result<Value> {
    ensure_args_count(span, "cidr_contains", params, args, 2)?;
    let cidr = ensure_string("cidr_contains", &params[0], &args[0])?;
    let cidr_or_ip = ensure_string("cidr_contains", &params[1], &args[1])?;
    let contains = _cidr_contains(cidr, cidr_or_ip);

    match contains {
        Ok(r) => Ok(Value::from(r)),
        // The rego implementation will retur an error in strict mode, see
        // https://github.com/open-policy-agent/opa/blob/main/v1/test/cases/testdata/v1/netcidrcontains/test-netcidrcontains-0100.yaml
        // as an example, so we will propagate the error if the builtin is
        // run in strict mode.
        Err(e) if strict => bail!(span.error(&format!("{e}"))),
        // If not in strict mode, an error will result in Undefined.
        _ => Ok(Value::Undefined),
    }
}

fn _cidr_contains(cidr: Arc<str>, cidr_or_ip: Arc<str>) -> Result<bool> {
    let net = cidr
        .parse::<IpNet>()
        .map_err(|e| anyhow!("Error parsing {cidr}: {e}"))?;

    if cidr_or_ip.contains("/") {
        let subnet = cidr_or_ip
            .parse::<IpNet>()
            .map_err(|e| anyhow!("Error parsing {cidr_or_ip} as CIDR: {e}"))?;

        return Ok(net.contains(&subnet));
    }

    // if the caller did not provide a CIDR string, try to parse
    // the input as an IP address.
    let subnet = cidr_or_ip
        .parse::<IpAddr>()
        .map_err(|e| anyhow!("Error parsing {cidr_or_ip} as IP address: {e}"))?;
    Ok(net.contains(&subnet))
}

#[cfg(test)]
mod net_tests {
    use super::*;
    use std::vec::Vec;

    #[test]
    fn test_cidr_is_valid() {
        let valids = Vec::from(["127.0.0.1/32", "10.0.0.0/8", "0.1.2.3/32", "::1/128"]);
        let invalids = Vec::from(["256.0.0.0/8", "127.0.0.1/33", "::1/129"]);

        for cidr in valids {
            assert!(
                is_valid_cidr(Arc::from(cidr)),
                "Valid CIDR {cidr} deemed invalid"
            );
        }

        for cidr in invalids {
            assert!(
                !is_valid_cidr(Arc::from(cidr)),
                "Invalid CIDR {cidr} deemed valid"
            );
        }
    }

    #[test]
    fn test_cidr_contains() {
        let test_cases: std::vec::IntoIter<(Arc<str>, Arc<str>, bool, bool)> = Vec::from([
            // Each case is a tuple of (cidr, cidr_or_ip, expected Ok(result), and expected error)
            (
                Arc::from("127.0.0.1/32"),
                Arc::from("127.0.0.1"),
                true,
                false,
            ),
            (
                Arc::from("10.0.0.0/8"),
                Arc::from("10.10.10.10"),
                true,
                false,
            ),
            (
                Arc::from("10.0.0.0/8"),
                Arc::from("10.10.10.0/24"),
                true,
                false,
            ),
            (Arc::from("fd00::/16"), Arc::from("fd00::/17"), true, false),
            (
                Arc::from("127.0.0.1/32"),
                Arc::from("127.0.0.2"),
                false,
                false,
            ),
            (Arc::from("10.0.0.0/8"), Arc::from("11.0.0.1"), false, false),
            (Arc::from("fd00::/16"), Arc::from("fd00::/15"), false, false),
            (
                Arc::from("127.0.0.0/8"),
                Arc::from("not a cidr"),
                false,
                true,
            ),
        ])
        .into_iter();

        for (cidr, sub, result, should_err) in test_cases {
            let got = _cidr_contains(cidr.clone(), sub.clone());
            match got {
                Err(_) if should_err => continue,
                Ok(res) if res == result => continue,
                _ => {
                    panic!(
                        "Expected `cidr_contains` for cidr {cidr} and subnet {sub} to be {result}"
                    )
                }
            }
        }
    }
}