use std::collections::BTreeMap;
use std::ffi::{OsStr, OsString};
use std::fmt;
use std::fs::Metadata;
use std::os::unix::ffi::{OsStrExt, OsStringExt};
use std::os::unix::fs::MetadataExt;
use std::path::{Component, Path, PathBuf};

use lazaret_core::configuration::{ResolvedDomainConfiguration, SandboxLayoutV1};
use lazaret_core::identity::{ContainerId, NamespaceIdentity};
use lazaret_core::records::VolumeAccess;
use oci_spec::runtime::{
    Capabilities, LinuxBuilder, LinuxCapabilitiesBuilder, LinuxIdMappingBuilder,
    LinuxNamespaceBuilder, LinuxNamespaceType, Mount, MountBuilder, ProcessBuilder, RootBuilder,
    Spec, SpecBuilder, UserBuilder,
};

pub const WORKSPACE_DESTINATION: &str = "/workspace";
pub const CONTROL_ROOT_DESTINATION: &str = "/run/lazaret";
pub const CREDENTIALS_DESTINATION: &str = "/run/lazaret/credentials";
pub const MAILBOX_REQUESTS_DESTINATION: &str = "/run/lazaret/mailbox/requests";
pub const MAILBOX_RESULTS_DESTINATION: &str = "/run/lazaret/mailbox/results";
pub const ESCALATION_CLIENT_DESTINATION: &str = "/run/lazaret/bin/lazaret-escalate";
pub const TERMINFO_ROOT_DESTINATION: &str = "/run/lazaret/terminfo";
pub const NETWORK_NAMESPACE_PATH: &str = "/proc/self/ns/net";

const OCI_VERSION: &str = "1.2.1";
const DEFAULT_PATH: &str = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin";

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum SandboxBuildErrorKind {
    InvalidProcess,
    InvalidPath,
    InvalidTerminal,
    ChangedAuthority,
    NetworkNamespaceMismatch,
    OciSpecification,
    JsonEncoding,
}

#[derive(Debug)]
pub struct SandboxBuildError {
    kind: SandboxBuildErrorKind,
    detail: String,
}

impl SandboxBuildError {
    fn new(kind: SandboxBuildErrorKind, detail: impl Into<String>) -> Self {
        Self {
            kind,
            detail: detail.into(),
        }
    }

    #[must_use]
    pub const fn kind(&self) -> SandboxBuildErrorKind {
        self.kind
    }
}

impl fmt::Display for SandboxBuildError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "{}: {}", error_label(self.kind), self.detail)
    }
}

impl std::error::Error for SandboxBuildError {}

const fn error_label(kind: SandboxBuildErrorKind) -> &'static str {
    match kind {
        SandboxBuildErrorKind::InvalidProcess => "invalid root process",
        SandboxBuildErrorKind::InvalidPath => "invalid sandbox path",
        SandboxBuildErrorKind::InvalidTerminal => "invalid host terminal",
        SandboxBuildErrorKind::ChangedAuthority => "changed host authority",
        SandboxBuildErrorKind::NetworkNamespaceMismatch => "network namespace mismatch",
        SandboxBuildErrorKind::OciSpecification => "invalid OCI specification",
        SandboxBuildErrorKind::JsonEncoding => "OCI JSON encoding failed",
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct RootProcess {
    arguments: Vec<String>,
}

impl RootProcess {
    /// Creates a direct argument vector for the terminal-neutral root process.
    ///
    /// # Errors
    /// The program must be an absolute normalized sandbox path and no argument may contain NUL.
    pub fn new(
        program: impl Into<String>,
        arguments: impl IntoIterator<Item = String>,
    ) -> Result<Self, SandboxBuildError> {
        let program = program.into();
        validate_sandbox_executable(&program)?;
        let mut complete = vec![program];
        for argument in arguments {
            if argument.as_bytes().contains(&0) {
                return Err(SandboxBuildError::new(
                    SandboxBuildErrorKind::InvalidProcess,
                    "argument contains NUL",
                ));
            }
            complete.push(argument);
        }
        Ok(Self {
            arguments: complete,
        })
    }

    #[must_use]
    pub fn arguments(&self) -> &[String] {
        &self.arguments
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
struct FileIdentity {
    device: u64,
    inode: u64,
}

impl FileIdentity {
    fn from_metadata(metadata: &Metadata) -> Self {
        Self {
            device: metadata.dev(),
            inode: metadata.ino(),
        }
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct HostTerminal {
    term: String,
    color_term: Option<String>,
    source: PathBuf,
    identity: FileIdentity,
}

impl HostTerminal {
    /// Selects one exact compiled host terminfo entry beneath a trusted root.
    ///
    /// # Errors
    /// Invalid names, inaccessible entries, non-files, and sources outside the roots are refused.
    pub fn from_trusted_roots(
        term: impl Into<String>,
        color_term: Option<String>,
        source: &Path,
        trusted_roots: &[PathBuf],
    ) -> Result<Self, SandboxBuildError> {
        let term = term.into();
        validate_terminal_name(&term)?;
        if color_term.as_deref().is_some_and(|value| {
            value.is_empty() || value.bytes().any(|byte| byte < 0x20 || byte == 0x7f)
        }) {
            return Err(SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                "COLORTERM contains control bytes or is empty",
            ));
        }
        let source = std::fs::canonicalize(source).map_err(|error| {
            SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                format!("cannot canonicalize terminfo source: {error}"),
            )
        })?;
        if source.file_name() != Some(OsStr::new(&term)) {
            return Err(SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                "terminfo source name differs from TERM",
            ));
        }
        let beneath_trusted_root = trusted_roots.iter().any(|root| {
            std::fs::canonicalize(root)
                .ok()
                .is_some_and(|root| source.starts_with(&root) && source != root)
        });
        if !beneath_trusted_root {
            return Err(SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                "terminfo source is outside every trusted root",
            ));
        }
        let metadata = std::fs::metadata(&source).map_err(|error| {
            SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                format!("cannot inspect terminfo source: {error}"),
            )
        })?;
        if !metadata.is_file() {
            return Err(SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidTerminal,
                "terminfo source is not a regular file",
            ));
        }
        Ok(Self {
            term,
            color_term,
            source,
            identity: FileIdentity::from_metadata(&metadata),
        })
    }

    fn revalidate(&self) -> Result<(), SandboxBuildError> {
        let metadata = std::fs::metadata(&self.source).map_err(|error| {
            SandboxBuildError::new(
                SandboxBuildErrorKind::ChangedAuthority,
                format!("cannot revalidate terminfo source: {error}"),
            )
        })?;
        if !metadata.is_file() || FileIdentity::from_metadata(&metadata) != self.identity {
            return Err(SandboxBuildError::new(
                SandboxBuildErrorKind::ChangedAuthority,
                "terminfo source changed identity",
            ));
        }
        Ok(())
    }

    fn destination(&self) -> PathBuf {
        let bucket = char::from(self.term.as_bytes()[0]).to_string();
        Path::new(TERMINFO_ROOT_DESTINATION)
            .join(bucket)
            .join(&self.term)
    }
}

pub struct SandboxBuildRequest<'a> {
    pub configuration: &'a ResolvedDomainConfiguration,
    pub container_id: ContainerId,
    pub expected_network_namespace: NamespaceIdentity,
    pub root_process: RootProcess,
    pub terminal: Option<HostTerminal>,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct RunscCommand {
    program: OsString,
    arguments: Vec<OsString>,
}

impl RunscCommand {
    #[must_use]
    pub fn program(&self) -> &OsStr {
        &self.program
    }

    #[must_use]
    pub fn arguments(&self) -> &[OsString] {
        &self.arguments
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct SandboxBundle {
    specification: Spec,
    specification_json: Vec<u8>,
    command: RunscCommand,
}

impl SandboxBundle {
    #[must_use]
    pub const fn specification(&self) -> &Spec {
        &self.specification
    }

    #[must_use]
    pub fn specification_json(&self) -> &[u8] {
        &self.specification_json
    }

    #[must_use]
    pub const fn command(&self) -> &RunscCommand {
        &self.command
    }
}

/// Returns the complete protected destination roots used by bundle construction.
///
/// # Errors
/// Returns an error if the fixed layout violates the configuration layout contract.
pub fn production_sandbox_layout() -> Result<SandboxLayoutV1, SandboxBuildError> {
    SandboxLayoutV1::from_production_layout([
        WORKSPACE_DESTINATION.to_owned(),
        CONTROL_ROOT_DESTINATION.to_owned(),
        "/proc".to_owned(),
        "/sys".to_owned(),
        "/dev".to_owned(),
    ])
    .map_err(|error| {
        SandboxBuildError::new(
            SandboxBuildErrorKind::InvalidPath,
            format!("production layout is invalid: {error}"),
        )
    })
}

/// Builds deterministic OCI bytes and the direct attached-runsc argument vector.
///
/// # Errors
/// Refuses changed host authority, namespace mismatch, invalid paths, or encoding failures.
pub fn build_sandbox_bundle(
    request: SandboxBuildRequest<'_>,
) -> Result<SandboxBundle, SandboxBuildError> {
    require_network_namespace(request.expected_network_namespace)?;
    request
        .configuration
        .workspace()
        .open_authority()
        .map_err(changed_configuration_authority)?;
    for volume in request.configuration.volumes() {
        volume
            .open_source()
            .map_err(changed_configuration_authority)?;
    }
    if let Some(terminal) = &request.terminal {
        terminal.revalidate()?;
    }

    let paths = runtime_paths(request.configuration, request.container_id)?;
    let mounts = build_mounts(
        request.configuration,
        request.terminal.as_ref(),
        &paths.control_sources,
    )?;
    let process = build_process(
        request.configuration,
        request.root_process,
        request.terminal.as_ref(),
    )?;
    let linux = build_linux()?;
    let command = build_runsc_command(&paths);
    let root = RootBuilder::default()
        .path(paths.rootfs)
        .readonly(false)
        .build()
        .map_err(oci_error)?;
    let specification = SpecBuilder::default()
        .version(OCI_VERSION)
        .root(root)
        .mounts(mounts)
        .process(process)
        .hostname("lazaret")
        .linux(linux)
        .build()
        .map_err(oci_error)?;
    let specification_json = serde_json::to_vec(&specification).map_err(|error| {
        SandboxBuildError::new(SandboxBuildErrorKind::JsonEncoding, error.to_string())
    })?;
    Ok(SandboxBundle {
        specification,
        specification_json,
        command,
    })
}

struct RuntimePaths {
    container_name: String,
    bundle: PathBuf,
    runsc_root: PathBuf,
    rootfs: PathBuf,
    control_sources: PathBuf,
}

fn runtime_paths(
    configuration: &ResolvedDomainConfiguration,
    container_id: ContainerId,
) -> Result<RuntimePaths, SandboxBuildError> {
    let runtime_domain = host_path(configuration.runtime_domain_root().canonical_label())?;
    let container_name = hex_lower(container_id.as_bytes());
    Ok(RuntimePaths {
        bundle: runtime_domain.join("bundles").join(&container_name),
        runsc_root: runtime_domain.join("runsc"),
        rootfs: runtime_domain.join("state-anchor").join("merged"),
        control_sources: runtime_domain.join("sandbox-control"),
        container_name,
    })
}

fn build_mounts(
    configuration: &ResolvedDomainConfiguration,
    terminal: Option<&HostTerminal>,
    control_sources: &Path,
) -> Result<Vec<Mount>, SandboxBuildError> {
    let mut mounts = standard_mounts()?;
    mounts.push(bind_mount(
        host_path(configuration.workspace().canonical_label())?,
        PathBuf::from(WORKSPACE_DESTINATION),
        false,
        false,
    )?);
    for volume in configuration.volumes() {
        let record = volume.record();
        mounts.push(bind_mount(
            host_path(&record.canonical_host_source)?,
            PathBuf::from(&record.container_path),
            record.access == VolumeAccess::ReadOnly,
            false,
        )?);
    }
    mounts.extend(control_mounts(control_sources)?);
    if let Some(terminal) = terminal {
        mounts.push(bind_mount(
            terminal.source.clone(),
            terminal.destination(),
            true,
            true,
        )?);
    }
    Ok(mounts)
}

fn build_linux() -> Result<oci_spec::runtime::Linux, SandboxBuildError> {
    let private_namespaces = [
        LinuxNamespaceType::Pid,
        LinuxNamespaceType::Ipc,
        LinuxNamespaceType::Uts,
        LinuxNamespaceType::Mount,
        LinuxNamespaceType::User,
    ]
    .into_iter()
    .map(|typ| {
        LinuxNamespaceBuilder::default()
            .typ(typ)
            .build()
            .map_err(oci_error)
    })
    .chain(std::iter::once(
        LinuxNamespaceBuilder::default()
            .typ(LinuxNamespaceType::Network)
            .path(PathBuf::from(NETWORK_NAMESPACE_PATH))
            .build()
            .map_err(oci_error),
    ))
    .collect::<Result<Vec<_>, _>>()?;
    let identity_mapping = LinuxIdMappingBuilder::default()
        .container_id(0_u32)
        .host_id(0_u32)
        .size(1_u32)
        .build()
        .map_err(oci_error)?;
    LinuxBuilder::default()
        .namespaces(private_namespaces)
        .uid_mappings(vec![identity_mapping])
        .gid_mappings(vec![identity_mapping])
        .rootfs_propagation("rprivate")
        .build()
        .map_err(oci_error)
}

fn build_runsc_command(paths: &RuntimePaths) -> RunscCommand {
    RunscCommand {
        program: OsString::from("runsc"),
        arguments: vec![
            OsString::from(format!(
                "-root={}",
                paths
                    .runsc_root
                    .to_str()
                    .expect("validated runtime path remains UTF-8")
            )),
            OsString::from("-ignore-cgroups"),
            OsString::from("run"),
            OsString::from(format!(
                "-bundle={}",
                paths
                    .bundle
                    .to_str()
                    .expect("validated runtime path remains UTF-8")
            )),
            OsString::from(&paths.container_name),
        ],
    }
}

fn build_process(
    configuration: &ResolvedDomainConfiguration,
    root_process: RootProcess,
    terminal: Option<&HostTerminal>,
) -> Result<oci_spec::runtime::Process, SandboxBuildError> {
    let mut environment = BTreeMap::from([("PATH".to_owned(), DEFAULT_PATH.to_owned())]);
    for (name, value) in configuration.ephemeral_environment() {
        let value = value.expose().to_str().ok_or_else(|| {
            SandboxBuildError::new(
                SandboxBuildErrorKind::InvalidProcess,
                "resolved environment value is not UTF-8",
            )
        })?;
        environment.insert(name.clone(), value.to_owned());
    }
    if let Some(terminal) = terminal {
        environment.insert("TERM".to_owned(), terminal.term.clone());
        if let Some(color_term) = &terminal.color_term {
            environment.insert("COLORTERM".to_owned(), color_term.clone());
        } else {
            environment.remove("COLORTERM");
        }
        environment.insert(
            "TERMINFO_DIRS".to_owned(),
            format!("{TERMINFO_ROOT_DESTINATION}:"),
        );
    }
    let environment = environment
        .into_iter()
        .map(|(name, value)| format!("{name}={value}"))
        .collect::<Vec<_>>();
    let empty = Capabilities::new();
    let capabilities = LinuxCapabilitiesBuilder::default()
        .bounding(empty.clone())
        .effective(empty.clone())
        .inheritable(empty.clone())
        .permitted(empty.clone())
        .ambient(empty)
        .build()
        .map_err(oci_error)?;
    let user = UserBuilder::default()
        .uid(0_u32)
        .gid(0_u32)
        .umask(0o022_u32)
        .build()
        .map_err(oci_error)?;
    ProcessBuilder::default()
        .terminal(false)
        .user(user)
        .args(root_process.arguments)
        .env(environment)
        .cwd(PathBuf::from(WORKSPACE_DESTINATION))
        .capabilities(capabilities)
        .no_new_privileges(true)
        .build()
        .map_err(oci_error)
}

fn standard_mounts() -> Result<Vec<Mount>, SandboxBuildError> {
    [
        ("/proc", "proc", "proc", vec!["nosuid", "noexec", "nodev"]),
        (
            "/dev",
            "tmpfs",
            "tmpfs",
            vec!["nosuid", "strictatime", "mode=755", "size=65536k"],
        ),
        (
            "/dev/pts",
            "devpts",
            "devpts",
            vec![
                "nosuid",
                "noexec",
                "newinstance",
                "ptmxmode=0666",
                "mode=0620",
            ],
        ),
        (
            "/dev/shm",
            "tmpfs",
            "shm",
            vec!["nosuid", "noexec", "nodev", "mode=1777", "size=65536k"],
        ),
        (
            "/dev/mqueue",
            "mqueue",
            "mqueue",
            vec!["nosuid", "noexec", "nodev"],
        ),
        (
            "/sys",
            "sysfs",
            "sysfs",
            vec!["nosuid", "noexec", "nodev", "ro"],
        ),
    ]
    .into_iter()
    .map(|(destination, typ, source, options)| {
        MountBuilder::default()
            .destination(PathBuf::from(destination))
            .typ(typ)
            .source(PathBuf::from(source))
            .options(options.into_iter().map(str::to_owned).collect::<Vec<_>>())
            .build()
            .map_err(oci_error)
    })
    .collect()
}

fn control_mounts(control_sources: &Path) -> Result<Vec<Mount>, SandboxBuildError> {
    [
        ("credentials", CREDENTIALS_DESTINATION, true, false),
        (
            "mailbox/requests",
            MAILBOX_REQUESTS_DESTINATION,
            false,
            false,
        ),
        ("mailbox/results", MAILBOX_RESULTS_DESTINATION, true, false),
        (
            "bin/lazaret-escalate",
            ESCALATION_CLIENT_DESTINATION,
            true,
            false,
        ),
    ]
    .into_iter()
    .map(|(source, destination, read_only, no_exec)| {
        bind_mount(
            control_sources.join(source),
            PathBuf::from(destination),
            read_only,
            no_exec,
        )
    })
    .collect()
}

fn bind_mount(
    source: PathBuf,
    destination: PathBuf,
    read_only: bool,
    no_exec: bool,
) -> Result<Mount, SandboxBuildError> {
    validate_absolute_normalized(&source)?;
    validate_absolute_normalized(&destination)?;
    let mut options = vec!["bind".to_owned(), "nosuid".to_owned(), "nodev".to_owned()];
    options.push(if read_only { "ro" } else { "rw" }.to_owned());
    if no_exec {
        options.push("noexec".to_owned());
    }
    MountBuilder::default()
        .destination(destination)
        .typ("bind")
        .source(source)
        .options(options)
        .build()
        .map_err(oci_error)
}

fn require_network_namespace(expected: NamespaceIdentity) -> Result<(), SandboxBuildError> {
    let observed = lazaret_linux::filesystem::namespace_identity(Path::new(NETWORK_NAMESPACE_PATH))
        .map_err(|error| {
            SandboxBuildError::new(
                SandboxBuildErrorKind::NetworkNamespaceMismatch,
                format!("cannot inspect Runtime Supervisor network namespace: {error}"),
            )
        })?;
    if observed != expected {
        return Err(SandboxBuildError::new(
            SandboxBuildErrorKind::NetworkNamespaceMismatch,
            "Runtime Supervisor network namespace identity differs from readiness evidence",
        ));
    }
    Ok(())
}

fn changed_configuration_authority(error: impl fmt::Display) -> SandboxBuildError {
    SandboxBuildError::new(SandboxBuildErrorKind::ChangedAuthority, error.to_string())
}

fn oci_error(error: impl fmt::Display) -> SandboxBuildError {
    SandboxBuildError::new(SandboxBuildErrorKind::OciSpecification, error.to_string())
}

fn validate_sandbox_executable(program: &str) -> Result<(), SandboxBuildError> {
    validate_absolute_normalized(Path::new(program)).map_err(|_| {
        SandboxBuildError::new(
            SandboxBuildErrorKind::InvalidProcess,
            "program is not a normalized absolute sandbox path",
        )
    })
}

fn validate_terminal_name(term: &str) -> Result<(), SandboxBuildError> {
    let valid = !term.is_empty()
        && term.len() <= 64
        && term
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'+' | b'-' | b'.' | b'_'));
    if valid {
        Ok(())
    } else {
        Err(SandboxBuildError::new(
            SandboxBuildErrorKind::InvalidTerminal,
            "TERM violates the conservative terminal-name grammar",
        ))
    }
}

fn validate_absolute_normalized(path: &Path) -> Result<(), SandboxBuildError> {
    if !path.is_absolute()
        || path.as_os_str().as_bytes().contains(&0)
        || path
            .components()
            .any(|component| !matches!(component, Component::RootDir | Component::Normal(_)))
    {
        return Err(SandboxBuildError::new(
            SandboxBuildErrorKind::InvalidPath,
            "path is not normalized and absolute",
        ));
    }
    utf8_path(path)?;
    Ok(())
}

fn utf8_path(path: &Path) -> Result<&str, SandboxBuildError> {
    path.to_str().ok_or_else(|| {
        SandboxBuildError::new(
            SandboxBuildErrorKind::InvalidPath,
            "OCI JSON path is not UTF-8",
        )
    })
}

fn host_path(path: &lazaret_core::identity::HostPath) -> Result<PathBuf, SandboxBuildError> {
    let path = PathBuf::from(OsString::from_vec(path.as_bytes().to_vec()));
    validate_absolute_normalized(&path)?;
    Ok(path)
}

fn hex_lower(bytes: &[u8]) -> String {
    let mut output = String::with_capacity(bytes.len() * 2);
    for byte in bytes {
        use fmt::Write as _;
        write!(&mut output, "{byte:02x}").expect("writing to String cannot fail");
    }
    output
}