use std::{fs, net::Ipv4Addr, path::Path, process::Command};

use serde::Deserialize;

fn default_host_firewall_enabled() -> bool {
    true
}

fn default_ssh_port() -> u16 {
    2323
}

fn default_amnezia_port() -> u16 {
    443
}

fn default_amnezia_protocols() -> Vec<String> {
    vec!["udp".to_string()]
}

fn default_allow_icmp() -> bool {
    true
}

fn default_input_policy() -> String {
    "drop".to_string()
}

#[derive(Debug, Clone, Deserialize)]
pub struct Config {
    pub amnezia: AmneziaConfig,
    pub traffic: TrafficConfig,
    pub host_firewall: HostFirewallConfig,
    pub anti_torrent: AntiTorrentConfig,
    pub reboot: RebootConfig,
    pub swap: SwapConfig,
}

#[derive(Debug, Clone, Deserialize)]
pub struct AmneziaConfig {
    pub container_names: Vec<String>,
    pub interface_candidates: Vec<String>,
    pub interface_patterns: Vec<String>,
    pub peer_ipv4_cidr: String,
}

#[derive(Debug, Clone, Deserialize)]
pub struct TrafficConfig {
    pub enabled: bool,
    pub peer_limit: String,
    pub root_rate: String,
    pub reconcile_interval_secs: u64,
    pub container_ready_timeout_secs: u64,
    pub class_start_id: u16,
    pub ifb_name: String,
}

#[derive(Debug, Clone, Deserialize)]
pub struct AntiTorrentConfig {
    pub enabled: bool,
    pub max_connections_per_peer: u32,
    pub peer_ipv4_cidr: String,
    pub apply_in_amnezia_netns: bool,
}

#[derive(Debug, Clone, Deserialize)]
pub struct HostFirewallConfig {
    #[serde(default = "default_host_firewall_enabled")]
    pub enabled: bool,
    #[serde(default = "default_ssh_port")]
    pub ssh_port: u16,
    #[serde(default = "default_amnezia_port")]
    pub amnezia_port: u16,
    #[serde(default = "default_amnezia_protocols")]
    pub amnezia_protocols: Vec<String>,
    #[serde(default = "default_allow_icmp")]
    pub allow_icmp: bool,
    #[serde(default = "default_input_policy")]
    pub default_input_policy: String,
}

impl Default for HostFirewallConfig {
    fn default() -> Self {
        Self {
            enabled: default_host_firewall_enabled(),
            ssh_port: default_ssh_port(),
            amnezia_port: default_amnezia_port(),
            amnezia_protocols: default_amnezia_protocols(),
            allow_icmp: default_allow_icmp(),
            default_input_policy: default_input_policy(),
        }
    }
}

#[derive(Debug, Clone, Deserialize)]
pub struct RebootConfig {
    pub enabled: bool,
    pub window_start_utc: String,
    pub window_end_utc: String,
}

#[derive(Debug, Clone, Deserialize)]
pub struct SwapConfig {
    pub enabled: bool,
    pub path: String,
    pub size_mb: u64,
    pub priority: i32,
    pub swappiness: u8,
}

impl Config {
    pub fn load(path: &Path) -> anyhow::Result<Self> {
        let raw = fs::read_to_string(path)?;
        let cfg: Self = toml::from_str(&raw)?;
        Ok(cfg)
    }

    pub fn validate_config(&self) -> anyhow::Result<()> {
        if self.amnezia.container_names.is_empty() {
            anyhow::bail!("amnezia.container_names must not be empty");
        }
        if self.amnezia.interface_candidates.is_empty() {
            anyhow::bail!("amnezia.interface_candidates must not be empty");
        }
        if self.amnezia.interface_patterns.is_empty() {
            anyhow::bail!("amnezia.interface_patterns must not be empty");
        }
        if self.traffic.class_start_id < 10 {
            anyhow::bail!("traffic.class_start_id must be >= 10");
        }
        if self.traffic.ifb_name.trim().is_empty() {
            anyhow::bail!("traffic.ifb_name must not be empty");
        }
        if self.traffic.peer_limit.trim().is_empty() {
            anyhow::bail!("traffic.peer_limit must not be empty");
        }
        if self.traffic.root_rate.trim().is_empty() {
            anyhow::bail!("traffic.root_rate must not be empty");
        }
        parse_tc_rate_bps(&self.traffic.peer_limit)?;
        parse_tc_rate_bps(&self.traffic.root_rate)?;
        if self.swap.swappiness > 100 {
            anyhow::bail!("swap.swappiness must be <= 100");
        }
        if self.traffic.container_ready_timeout_secs == 0 {
            anyhow::bail!("traffic.container_ready_timeout_secs must be > 0");
        }
        if self.traffic.reconcile_interval_secs == 0 {
            anyhow::bail!("traffic.reconcile_interval_secs must be > 0");
        }
        if self.swap.enabled {
            if self.swap.size_mb < 64 {
                anyhow::bail!("swap.size_mb must be >= 64 when swap.enabled=true");
            }
            if self.swap.size_mb > 65536 {
                anyhow::bail!("swap.size_mb must be <= 65536 when swap.enabled=true");
            }
            if !self.swap.path.starts_with('/') {
                anyhow::bail!("swap.path must be absolute");
            }
            let dangerous = ["/", "/etc", "/etc/fstab", "/dev", "/proc", "/sys", "/run"];
            if dangerous.iter().any(|p| *p == self.swap.path) {
                anyhow::bail!("swap.path is dangerous and forbidden: {}", self.swap.path);
            }
            if self.swap.priority < -1 || self.swap.priority > 32767 {
                anyhow::bail!("swap.priority must be between -1 and 32767");
            }
        }
        if self.anti_torrent.enabled && self.anti_torrent.max_connections_per_peer == 0 {
            anyhow::bail!("anti_torrent.max_connections_per_peer must be > 0");
        }
        if self.host_firewall.ssh_port == 0 {
            anyhow::bail!("host_firewall.ssh_port must be in 1..=65535");
        }
        if self.host_firewall.amnezia_port == 0 {
            anyhow::bail!("host_firewall.amnezia_port must be in 1..=65535");
        }
        if self.host_firewall.amnezia_protocols.is_empty() {
            anyhow::bail!(
                "host_firewall.amnezia_protocols must not be empty; allowed values: tcp, udp"
            );
        }
        let mut normalized = std::collections::BTreeSet::new();
        for p in &self.host_firewall.amnezia_protocols {
            let pp = p.trim().to_ascii_lowercase();
            if pp != "tcp" && pp != "udp" {
                anyhow::bail!(
                    "host_firewall.amnezia_protocols contains invalid value: {p}; allowed: tcp, udp"
                );
            }
            if !normalized.insert(pp) {
                anyhow::bail!("host_firewall.amnezia_protocols contains duplicate protocol: {p}");
            }
        }
        let policy = self
            .host_firewall
            .default_input_policy
            .trim()
            .to_ascii_lowercase();
        if policy != "drop" && policy != "accept" {
            anyhow::bail!("host_firewall.default_input_policy must be one of: drop, accept");
        }
        if self.reboot.enabled && self.reboot.window_start_utc == self.reboot.window_end_utc {
            anyhow::bail!("reboot window start and end must differ");
        }
        if self.reboot.enabled {
            parse_hhmm(&self.reboot.window_start_utc)?;
            parse_hhmm(&self.reboot.window_end_utc)?;
        }
        parse_cidr_v4(&self.amnezia.peer_ipv4_cidr)?;
        parse_cidr_v4(&self.anti_torrent.peer_ipv4_cidr)?;
        Ok(())
    }

    pub fn validate_runtime(&self) -> anyhow::Result<()> {
        self.check_supported_host()?;
        self.check_host_tools()
    }

    pub fn validate_all(&self) -> anyhow::Result<()> {
        self.validate_config()?;
        self.validate_runtime()?;
        Ok(())
    }

    fn check_host_tools(&self) -> anyhow::Result<()> {
        let mut required = vec!["tc", "ip", "wg", "docker", "modprobe"];
        if !crate::netns::nsenter_available() {
            anyhow::bail!("required host tool not found in PATH: nsenter");
        }
        required.push("nsenter");
        if self.anti_torrent.enabled {
            required.push("nft");
        }
        if self.host_firewall.enabled {
            required.push("nft");
        }
        if self.reboot.enabled {
            required.push("systemctl");
        }
        if self.swap.enabled {
            required.extend([
                "fallocate",
                "chmod",
                "mkswap",
                "swapon",
                "swapoff",
                "sysctl",
                "dd",
            ]);
        }

        for tool in required {
            if !tool_exists(tool) {
                anyhow::bail!("required host tool not found in PATH: {tool}");
            }
        }
        Ok(())
    }

    fn check_supported_host(&self) -> anyhow::Result<()> {
        let os_release = std::fs::read_to_string("/etc/os-release").map_err(|_| {
            anyhow::anyhow!(
                "unsupported host: missing /etc/os-release; only Debian 13 amd64 is supported"
            )
        })?;

        let mut id = String::new();
        let mut version_id = String::new();
        for line in os_release.lines() {
            if let Some((k, v)) = line.split_once('=') {
                let val = v.trim_matches('"');
                match k {
                    "ID" => id = val.to_string(),
                    "VERSION_ID" => version_id = val.to_string(),
                    _ => {}
                }
            }
        }

        if id != "debian" || version_id != "13" {
            anyhow::bail!(
                "unsupported host: only Debian 13 amd64 is supported (got ID={id}, VERSION_ID={version_id})"
            );
        }

        let arch = std::process::Command::new("dpkg")
            .args(["--print-architecture"])
            .output()
            .ok()
            .and_then(|o| {
                if o.status.success() {
                    Some(String::from_utf8_lossy(&o.stdout).trim().to_string())
                } else {
                    None
                }
            })
            .unwrap_or_else(|| std::env::consts::ARCH.to_string());

        if arch != "amd64" && arch != "x86_64" {
            anyhow::bail!("unsupported host arch: {arch}; only Debian 13 amd64 is supported");
        }

        Ok(())
    }
}

fn parse_hhmm(v: &str) -> anyhow::Result<()> {
    let mut s = v.split(':');
    let h = s
        .next()
        .ok_or_else(|| anyhow::anyhow!("invalid time: {v}"))?
        .parse::<u8>()?;
    let m = s
        .next()
        .ok_or_else(|| anyhow::anyhow!("invalid time: {v}"))?
        .parse::<u8>()?;
    if s.next().is_some() {
        anyhow::bail!("invalid time: {v}");
    }
    if h > 23 || m > 59 {
        anyhow::bail!("invalid time: {v}");
    }
    Ok(())
}

fn parse_tc_rate_bps(v: &str) -> anyhow::Result<u64> {
    let raw = v.trim().to_ascii_lowercase().replace(' ', "");
    if raw.is_empty() {
        anyhow::bail!("invalid tc rate: empty");
    }
    let (num, mul) = if let Some(n) = raw.strip_suffix("gbit") {
        (n, 1_000_000_000u64)
    } else if let Some(n) = raw.strip_suffix("mbit") {
        (n, 1_000_000u64)
    } else if let Some(n) = raw.strip_suffix("kbit") {
        (n, 1_000u64)
    } else if let Some(n) = raw.strip_suffix("bit") {
        (n, 1u64)
    } else {
        anyhow::bail!("invalid tc rate unit: {v}");
    };

    let base = num
        .parse::<u64>()
        .map_err(|_| anyhow::anyhow!("invalid tc rate number: {v}"))?;
    base.checked_mul(mul)
        .ok_or_else(|| anyhow::anyhow!("tc rate overflow: {v}"))
}

fn tool_exists(tool: &str) -> bool {
    let probes: &[&[&str]] = match tool {
        "tc" => &[&["-V"]],
        "ip" => &[&["-V"], &["-Version"]],
        "wg" => &[&["--version"]],
        "docker" => &[&["--version"]],
        "modprobe" => &[&["--version"]],
        "nsenter" => &[&["--help"]],
        "nft" => &[&["--version"]],
        "systemctl" => &[&["--version"], &["--help"]],
        "fallocate" => &[&["--help"]],
        "chmod" => &[&["--help"]],
        "mkswap" => &[&["--help"]],
        "swapon" => &[&["--help"]],
        "swapoff" => &[&["--help"]],
        "sysctl" => &[&["--version"], &["--help"]],
        "dd" => &[&["--help"]],
        _ => &[&["--version"], &["--help"], &["-V"]],
    };

    for args in probes {
        if Command::new(tool).args(*args).output().is_ok() {
            return true;
        }
    }
    false
}

pub fn parse_cidr_v4(cidr: &str) -> anyhow::Result<(Ipv4Addr, u8)> {
    let mut parts = cidr.split('/');
    let ip = parts
        .next()
        .ok_or_else(|| anyhow::anyhow!("invalid cidr: {cidr}"))?
        .parse::<Ipv4Addr>()?;
    let prefix = parts
        .next()
        .ok_or_else(|| anyhow::anyhow!("invalid cidr: {cidr}"))?
        .parse::<u8>()?;
    if prefix > 32 {
        anyhow::bail!("invalid prefix in cidr: {cidr}");
    }
    Ok((ip, prefix))
}

pub fn ip_in_cidr(ip: Ipv4Addr, cidr: &str) -> anyhow::Result<bool> {
    let (base, prefix) = parse_cidr_v4(cidr)?;
    let mask = if prefix == 0 {
        0u32
    } else {
        u32::MAX << (32 - prefix)
    };
    let ip_u = u32::from(ip);
    let base_u = u32::from(base);
    Ok((ip_u & mask) == (base_u & mask))
}

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

    #[test]
    fn parse_cidr_invalid_prefix() {
        let err = parse_cidr_v4("10.8.1.0/33").err();
        assert!(err.is_some());
    }

    #[test]
    fn ip_membership() {
        let ok = ip_in_cidr("10.8.1.10".parse().expect("ip"), "10.8.1.0/24").expect("cidr");
        assert!(ok);
        let no = ip_in_cidr("10.9.1.10".parse().expect("ip"), "10.8.1.0/24").expect("cidr");
        assert!(!no);
    }

    #[test]
    fn parse_hhmm_works() {
        assert!(parse_hhmm("01:00").is_ok());
        assert!(parse_hhmm("23:59").is_ok());
        assert!(parse_hhmm("24:00").is_err());
    }

    #[test]
    fn parse_tc_rate_works() {
        assert_eq!(parse_tc_rate_bps("1gbit").expect("bps"), 1_000_000_000);
        assert_eq!(parse_tc_rate_bps("1000mbit").expect("bps"), 1_000_000_000);
        assert!(parse_tc_rate_bps("foo").is_err());
    }

    #[test]
    fn swap_rejects_dangerous_path() {
        let cfg = Config {
            amnezia: AmneziaConfig {
                container_names: vec!["x".into()],
                interface_candidates: vec!["awg0".into()],
                interface_patterns: vec!["awg*".into()],
                peer_ipv4_cidr: "10.8.1.0/24".into(),
            },
            traffic: TrafficConfig {
                enabled: true,
                peer_limit: "70mbit".into(),
                root_rate: "1000mbit".into(),
                reconcile_interval_secs: 15,
                container_ready_timeout_secs: 30,
                class_start_id: 10,
                ifb_name: "ifb0".into(),
            },
            host_firewall: HostFirewallConfig::default(),
            anti_torrent: AntiTorrentConfig {
                enabled: false,
                max_connections_per_peer: 100,
                peer_ipv4_cidr: "10.8.1.0/24".into(),
                apply_in_amnezia_netns: false,
            },
            reboot: RebootConfig {
                enabled: false,
                window_start_utc: "01:00".into(),
                window_end_utc: "02:00".into(),
            },
            swap: SwapConfig {
                enabled: true,
                path: "/etc/fstab".into(),
                size_mb: 2048,
                priority: 1,
                swappiness: 1,
            },
        };
        assert!(cfg.validate_config().is_err());
    }

    #[test]
    fn host_firewall_rejects_empty_protocols() {
        let cfg = Config {
            amnezia: AmneziaConfig {
                container_names: vec!["x".into()],
                interface_candidates: vec!["awg0".into()],
                interface_patterns: vec!["awg*".into()],
                peer_ipv4_cidr: "10.8.1.0/24".into(),
            },
            traffic: TrafficConfig {
                enabled: true,
                peer_limit: "70mbit".into(),
                root_rate: "1000mbit".into(),
                reconcile_interval_secs: 15,
                container_ready_timeout_secs: 30,
                class_start_id: 10,
                ifb_name: "ifb0".into(),
            },
            host_firewall: HostFirewallConfig {
                amnezia_protocols: vec![],
                ..HostFirewallConfig::default()
            },
            anti_torrent: AntiTorrentConfig {
                enabled: false,
                max_connections_per_peer: 100,
                peer_ipv4_cidr: "10.8.1.0/24".into(),
                apply_in_amnezia_netns: false,
            },
            reboot: RebootConfig {
                enabled: false,
                window_start_utc: "01:00".into(),
                window_end_utc: "02:00".into(),
            },
            swap: SwapConfig {
                enabled: false,
                path: "/swapfile".into(),
                size_mb: 2048,
                priority: 1,
                swappiness: 1,
            },
        };
        assert!(cfg.validate_config().is_err());
    }

    #[test]
    fn config_requires_host_firewall_section() {
        let raw = r#"
[amnezia]
container_names = ["amnezia-awg2"]
interface_candidates = ["awg0"]
interface_patterns = ["awg*"]
peer_ipv4_cidr = "10.8.1.0/24"

[traffic]
enabled = true
peer_limit = "70mbit"
root_rate = "1000mbit"
reconcile_interval_secs = 15
container_ready_timeout_secs = 30
class_start_id = 10
ifb_name = "ifb0"

[anti_torrent]
enabled = false
max_connections_per_peer = 100
peer_ipv4_cidr = "10.8.1.0/24"
apply_in_amnezia_netns = false

[reboot]
enabled = false
window_start_utc = "01:00"
window_end_utc = "02:00"

[swap]
enabled = false
path = "/swapfile"
size_mb = 2048
priority = 1
swappiness = 1
"#;
        let parsed = toml::from_str::<Config>(raw);
        assert!(parsed.is_err());
    }
}