//! A world directory and the one virtual root that host code and guests share.
//!
//! Layout of a world directory:
//! - `world/`: the virtual root `/` that every guest sees. Agents change everything in it.
//! - `host/`: host state outside the sandbox (harness storage, later the vault). No guest sees it.
use sausage_vfs::{Device, Generated, Host, Layer, Memory, Mounts, Process};
use std::{
    path::{Path, PathBuf},
    sync::Arc,
};

/// An open world. `root` is the filesystem every guest sees as `/`; host code (the harness's file
/// tools) reads and writes through the same layer, so both always see the same files.
pub struct World {
    pub root: Arc<dyn Layer>,
    /// The host state folder, `<dir>/host`.
    pub host_dir: PathBuf,
    /// Live process metadata shared with the process table.
    pub processes: crate::process::Processes,
}

fn copy_tree(source: &Path, destination: &Path) -> std::io::Result<()> {
    std::fs::create_dir_all(destination)?;
    for entry in std::fs::read_dir(source)? {
        let entry = entry?;
        let target = destination.join(entry.file_name());
        if entry.file_type()?.is_symlink() {
            std::os::unix::fs::symlink(std::fs::read_link(entry.path())?, &target)?;
        } else if entry.file_type()?.is_dir() {
            copy_tree(&entry.path(), &target)?;
        } else {
            std::fs::copy(entry.path(), target)?;
        }
    }
    Ok(())
}

impl World {
    /// Open (and create if missing) the world directory `dir`, including `/proc` and `/run` mounts.
    pub fn open(dir: &Path) -> anyhow::Result<Self> {
        Self::open_with_userland(dir, None)
    }

    /// Copy an optional bundle into a new world. Existing worlds retain their programs.
    /// Each `.wasm` tool keeps its independent file and gains a relative `/bin/<name>` symlink.
    /// `/dev` exposes generated null, zero, and random byte devices in every world.
    /// Missing `/etc/gitconfig` defaults to Sausage <sausage@localhost>. Local repository config overrides it.
    pub fn open_with_userland(dir: &Path, userland: Option<&Path>) -> anyhow::Result<Self> {
        let root_dir = dir.join("world");
        let host_dir = dir.join("host");
        let fresh = !root_dir.exists();
        std::fs::create_dir_all(root_dir.join("usr/local/bin"))?;
        if fresh && let Some(bundle) = userland {
            for folder in ["bin", "src"] {
                copy_tree(&bundle.join(folder), &root_dir.join(folder))?;
            }
            // Keep independent .wasm files and expose conventional executable names.
            for entry in std::fs::read_dir(root_dir.join("bin"))? {
                let path = entry?.path();
                if path.extension().is_some_and(|ext| ext == "wasm") {
                    let alias = path.with_extension("");
                    if std::fs::symlink_metadata(&alias).is_err() {
                        std::os::unix::fs::symlink(path.file_name().unwrap(), alias)?;
                    }
                }
            }
        }
        let gitconfig = root_dir.join("etc/gitconfig");
        if !gitconfig.try_exists()? {
            std::fs::create_dir_all(root_dir.join("etc"))?;
            std::fs::write(
                gitconfig,
                "[user]\n\tname = Sausage\n\temail = sausage@localhost\n",
            )?;
        }
        std::fs::create_dir_all(&host_dir)?;
        let mut mounts = Mounts::default();
        mounts.mount(
            "/",
            Arc::new(Host::new(&root_dir, Process::default())?),
            false,
        );
        let processes: crate::process::Processes =
            Arc::new(std::sync::Mutex::new(Default::default()));
        let snapshot = processes.clone();
        let mut proc = Generated::default();
        let extensions = crate::harness::loader::status(&host_dir);
        proc.insert("/extensions", move || {
            Ok(extensions.lock().unwrap().as_bytes().to_vec())
        });
        proc.insert("/processes", move || {
            let mut text = String::from("PID\tPPID\tSTATE\tCWD\tCONVERSATION\tARGV\n");
            for (pid, info) in snapshot.lock().unwrap().iter() {
                text.push_str(&format!(
                    "{pid}\t{}\t{}\t{}\t{}\t{}\n",
                    info.parent,
                    info.state,
                    info.cwd,
                    info.conversation.as_deref().unwrap_or("-"),
                    info.argv.join(" ")
                ));
            }
            Ok(text.into_bytes())
        });
        mounts.mount("/proc", Arc::new(proc), true);
        mounts.mount("/run", Arc::new(Memory::default()), false);
        let mut devices = Generated::default();
        devices.insert_device("/null", Device::Null);
        devices.insert_device("/zero", Device::Zero);
        devices.insert_device("/urandom", Device::Random);
        mounts.mount("/dev", Arc::new(devices), false);
        let journal =
            sausage_vfs::journal::Journal::open(&host_dir.join("undo"), Arc::new(mounts))?;
        let root = journal.layer(sausage_vfs::journal::Tag::process(
            std::process::id(),
            "/host".into(),
            Vec::new(),
        )?);
        Ok(World {
            root,
            host_dir,
            processes,
        })
    }
}