//! On-disk layout of a Sausage world. The folder is the source of truth:
//! `sausage run` boots every actor that it finds in `actor/`.
//!
//! ```text
//! <world>/
//!   actor/<id>/
//!     actor.wasm        the current version
//!     actor.json        version, running, subscriptions (broker)
//!     source/           source of the current version
//!     public/           written by the actor, read-only for others
//!     data/             state, writable only by the actor
//!     stderr.log        stderr of the actor and notes of the broker
//!     versions/<n>/     every version that was installed: actor.wasm, source/, meta.json
//! ```

use std::collections::BTreeSet;
use std::path::{Component, Path, PathBuf};

use anyhow::{Context, Result, bail};
use serde::{Deserialize, Serialize};

use crate::fs::TMP_PREFIX;

/// IDs of the actors that the host implements natively.
pub const NATIVE: &[&str] = &["broker", "console", "cargo"];

#[derive(Clone)]
pub struct World {
    pub root: PathBuf,
}

/// `actor/<id>/actor.json`.
#[derive(Serialize, Deserialize, Clone, Debug, Default)]
pub struct ActorMeta {
    /// The installed version. `None` for native actors and for a new
    /// `actor.wasm` that the broker has not installed yet.
    #[serde(default)]
    pub version: Option<u64>,
    #[serde(default = "yes")]
    pub running: bool,
    /// The actors whose published messages this actor receives.
    #[serde(default)]
    pub subscriptions: BTreeSet<String>,
}

fn yes() -> bool {
    true
}

/// `versions/<n>/meta.json`.
#[derive(Serialize, Deserialize, Clone, Debug, Default)]
pub struct VersionMeta {
    pub version: u64,
    /// Path of the `.wasm` file, as the requester gave it.
    pub wasm: String,
    /// Path of the source folder, as the requester gave it.
    pub source: Option<String>,
    /// The actor that built the `.wasm` file.
    pub built_by: Option<String>,
    /// The actor that requested the version ("scan" for a file found on disk).
    pub requested_by: String,
    pub created_at: u64,
}

pub fn valid_id(id: &str) -> bool {
    !id.is_empty()
        && id.len() <= 64
        && id.chars().all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-' || c == '_')
}

pub fn now() -> u64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0)
}

impl World {
    pub fn new(root: impl Into<PathBuf>) -> Self {
        Self { root: root.into() }
    }

    pub fn actors_root(&self) -> PathBuf {
        self.root.join("actor")
    }
    pub fn actor_dir(&self, id: &str) -> PathBuf {
        self.actors_root().join(id)
    }
    pub fn wasm_path(&self, id: &str) -> PathBuf {
        self.actor_dir(id).join("actor.wasm")
    }
    pub fn public_dir(&self, id: &str) -> PathBuf {
        self.actor_dir(id).join("public")
    }
    pub fn source_dir(&self, id: &str) -> PathBuf {
        self.actor_dir(id).join("source")
    }
    pub fn data_dir(&self, id: &str) -> PathBuf {
        self.actor_dir(id).join("data")
    }
    pub fn versions_dir(&self, id: &str) -> PathBuf {
        self.actor_dir(id).join("versions")
    }
    pub fn version_dir(&self, id: &str, v: u64) -> PathBuf {
        self.versions_dir(id).join(v.to_string())
    }
    /// Private scratch space of the broker (candidate copies, seeds).
    pub fn scratch_dir(&self) -> PathBuf {
        self.data_dir("broker").join("scratch")
    }

    pub fn exists(&self) -> bool {
        self.actors_root().is_dir()
    }

    /// Create an empty world with the folders of the native actors.
    pub fn create(root: &Path) -> Result<World> {
        let world = World::new(std::path::absolute(root)?);
        if world.exists() {
            bail!("{} is already a Sausage world", root.display());
        }
        for id in NATIVE {
            world.ensure_actor_dirs(id)?;
        }
        Ok(world)
    }

    pub fn ensure_actor_dirs(&self, id: &str) -> Result<()> {
        std::fs::create_dir_all(self.public_dir(id))?;
        std::fs::create_dir_all(self.data_dir(id))?;
        Ok(())
    }

    /// IDs of every folder in `actor/`, sorted.
    pub fn actor_ids(&self) -> Result<Vec<String>> {
        let mut ids: Vec<String> = std::fs::read_dir(self.actors_root())?
            .filter_map(|e| e.ok())
            .filter(|e| e.path().is_dir())
            .filter_map(|e| e.file_name().into_string().ok())
            .filter(|id| valid_id(id))
            .collect();
        ids.sort();
        Ok(ids)
    }

    pub fn read_meta(&self, id: &str) -> ActorMeta {
        std::fs::read_to_string(self.actor_dir(id).join("actor.json"))
            .ok()
            .and_then(|s| serde_json::from_str(&s).ok())
            .unwrap_or(ActorMeta { running: true, ..Default::default() })
    }

    pub fn write_meta(&self, id: &str, meta: &ActorMeta) -> Result<()> {
        write_atomic(&self.actor_dir(id).join("actor.json"), serde_json::to_string_pretty(meta)?.as_bytes())
    }

    /// Make `actor.wasm` and `source/` a copy of `versions/<version>/`,
    /// unless `actor.wasm` already is that version (it came from there).
    pub fn install_files(&self, id: &str, version: u64) -> Result<()> {
        let dir = self.version_dir(id, version);
        self.ensure_actor_dirs(id)?;
        let wasm = std::fs::read(dir.join("actor.wasm"))?;
        if std::fs::read(self.wasm_path(id)).ok().as_ref() == Some(&wasm) {
            return Ok(());
        }
        write_atomic(&self.wasm_path(id), &wasm)?;
        replace_tree(&dir.join("source"), &self.source_dir(id))
    }

    /// Version numbers in `versions/`, ascending.
    pub fn versions(&self, id: &str) -> Vec<u64> {
        let mut v: Vec<u64> = std::fs::read_dir(self.versions_dir(id))
            .map(|rd| rd.filter_map(|e| e.ok()?.file_name().to_str()?.parse().ok()).collect())
            .unwrap_or_default();
        v.sort();
        v
    }

    pub fn next_version(&self, id: &str) -> u64 {
        self.versions(id).last().map_or(1, |v| v + 1)
    }

    /// Map a path in an actor's namespace to a host path.
    ///
    /// - `/actor/<id>/...` is the global filesystem.
    /// - `/public/...` and `/data/...` belong to `sender`.
    /// - Native senders (the console) can also give absolute host paths.
    pub fn resolve(&self, sender: &str, path: &str) -> Result<PathBuf> {
        let under = |base: PathBuf, rest: &str| -> Result<PathBuf> {
            let mut out = base;
            for c in Path::new(rest).components() {
                match c {
                    Component::Normal(n) => out.push(n),
                    Component::CurDir | Component::RootDir => {}
                    _ => bail!("path must not contain '..': {path}"),
                }
            }
            Ok(out)
        };
        let prefixed = |prefix: &str| {
            path.strip_prefix(prefix).filter(|rest| rest.is_empty() || rest.starts_with('/'))
        };
        if let Some(rest) = prefixed("/actor") {
            return under(self.actors_root(), rest);
        }
        if let Some(rest) = prefixed("/public") {
            return under(self.public_dir(sender), rest);
        }
        if let Some(rest) = prefixed("/data") {
            return under(self.data_dir(sender), rest);
        }
        if NATIVE.contains(&sender) && Path::new(path).is_absolute() {
            return Ok(PathBuf::from(path));
        }
        bail!("cannot resolve path {path} for {sender}: use /actor/<id>/..., /public/... or /data/...")
    }

    /// The path of a host file in the global filesystem, if it has one.
    pub fn global_path(&self, host: &Path) -> Option<String> {
        let rel = host.strip_prefix(self.actors_root()).ok()?;
        Some(format!("/actor/{}", rel.display()))
    }
}

/// Write a file so that readers never see a partial version.
pub fn write_atomic(path: &Path, bytes: &[u8]) -> Result<()> {
    let dir = path.parent().context("path has no parent")?;
    std::fs::create_dir_all(dir)?;
    let name = path.file_name().and_then(|n| n.to_str()).unwrap_or("file");
    let tmp = dir.join(format!("{TMP_PREFIX}host-{}-{name}", std::process::id()));
    std::fs::write(&tmp, bytes)?;
    std::fs::rename(&tmp, path)?;
    Ok(())
}

/// Folders that a copy of a source folder leaves out.
const BUILD_DIRS: &[&str] = &["target", ".git"];

/// Copy a directory tree, except uncommitted files.
pub fn copy_tree(from: &Path, to: &Path) -> Result<()> {
    copy_filtered(from, to, &[])
}

fn copy_filtered(from: &Path, to: &Path, skip: &[&str]) -> Result<()> {
    std::fs::create_dir_all(to)?;
    for entry in std::fs::read_dir(from).with_context(|| format!("read {}", from.display()))? {
        let entry = entry?;
        let name = entry.file_name();
        let name = name.to_string_lossy();
        if name.starts_with(TMP_PREFIX) {
            continue;
        }
        let dst = to.join(&*name);
        let ty = entry.file_type()?;
        if ty.is_dir() && !skip.contains(&&*name) {
            copy_filtered(&entry.path(), &dst, skip)?;
        } else if ty.is_file() {
            std::fs::copy(entry.path(), &dst)?;
        }
    }
    Ok(())
}

/// Replace the directory `dst` with a copy of `src` (an empty folder if `src`
/// does not exist): copy to a sibling, then swap with two renames.
pub fn replace_tree(src: &Path, dst: &Path) -> Result<()> {
    replace_filtered(src, dst, &[])
}

/// Like `replace_tree`, for a source folder: leaves out `target/` and `.git/`.
pub fn replace_source(src: &Path, dst: &Path) -> Result<()> {
    replace_filtered(src, dst, BUILD_DIRS)
}

fn replace_filtered(src: &Path, dst: &Path, skip: &[&str]) -> Result<()> {
    let parent = dst.parent().context("path has no parent")?;
    let name = dst.file_name().and_then(|n| n.to_str()).unwrap_or("dir");
    let fresh = parent.join(format!("{TMP_PREFIX}new-{name}"));
    let old = parent.join(format!("{TMP_PREFIX}old-{name}"));
    let _ = std::fs::remove_dir_all(&fresh);
    let _ = std::fs::remove_dir_all(&old);
    if src.is_dir() {
        copy_filtered(src, &fresh, skip)?;
    } else {
        std::fs::create_dir_all(&fresh)?;
    }
    if dst.exists() {
        std::fs::rename(dst, &old)?;
    }
    std::fs::rename(&fresh, dst)?;
    let _ = std::fs::remove_dir_all(&old);
    Ok(())
}