//! Per-user filesystem mapping (blueprint §6): the bridge between the path an
//! agent sees and the physical host / container path behind it.
//!
//! An agent sees one namespace:
//!
//! | Agent path        | Backing                                            |
//! |-------------------|----------------------------------------------------|
//! | `user-memory/…`   | SQLite (the user's pool) — routed *before* this    |
//! | `shared-memory/…` | SQLite (`system.db`) — routed *before* this        |
//! | `shared/{X}/…`    | host `{WD}/shared/{X}`, mount `{home}/shared/{X}`  |
//! | `projects/{O}/{S}`| host `{WD}/projects/{owner_userid}/{S}`, mount `{home}/projects/{O}/{S}` (O = owner username) |
//! | `~/docs/…`, `docs/…` | host `{WD}/docs` (read-only, same for every user), mount `{container_home}/docs` |
//! | `~/…`, relative   | host `{WD}/homes/{userid}`, mount `{container_home}`|
//!
//! `UserFs` is a **pure value type** with no filesystem access: it carries the
//! resolved paths and does the lexical agent→host / agent→container mapping.
//! Containment (canonicalize + prefix-check against the mount root, which follows
//! symlinks) lives in `skald-core`, where the fs helpers already are — this crate
//! stays dependency-light. The two virtual memory roots are classified by the
//! fs-tools *before* reaching here; `UserFs` only ever sees physical paths.

use std::path::{Component, Path, PathBuf};
use std::sync::{Arc, RwLock};

/// The subdirectory of a user's home where chat uploads are saved
/// (`{home}/uploads/{session_id}/…`, reachable by the agent as `uploads/…`).
/// Shared by the upload handler (write path) and the media inliner (containment
/// root) so the two anchors can never drift.
pub const UPLOADS_SUBDIR: &str = "uploads";

/// One shared folder mounted into a user's container.
#[derive(Debug, Clone)]
pub struct SharedMount {
    /// The folder name (`{WD}/shared/{name}`); the first path component under `shared/`.
    pub name:      String,
    /// Absolute host directory that backs it.
    pub host:      PathBuf,
    /// Where it is mounted inside the container.
    pub container: PathBuf,
    /// Whether this member may write to it.
    pub can_write: bool,
}

/// One project folder mounted into a user's container. Unlike a shared folder its
/// agent path has **two** segments — `projects/{owner_username}/{slug}` — because a
/// project is namespaced by its owner (two members can each own a `budget`). The host
/// path keys on the owner's stable **userid**, the agent/container path on the
/// (mutable) **username**.
#[derive(Debug, Clone)]
pub struct ProjectMount {
    /// The owner's username — the first agent-visible segment under `projects/`.
    pub owner_username: String,
    /// The project slug — the second agent-visible segment.
    pub slug:           String,
    /// Absolute host directory that backs it (`{WD}/projects/{owner_userid}/{slug}`).
    pub host:           PathBuf,
    /// Where it is mounted inside the container (`{home}/projects/{owner_username}/{slug}`).
    pub container:      PathBuf,
    /// Whether this member may write to it.
    pub can_write:      bool,
}

/// The filesystem view of one user: their private home plus the shared folders
/// they belong to, and the container those are mounted into.
#[derive(Debug, Clone)]
pub struct UserFs {
    pub user_id:        String,
    /// Absolute host path of the user's private home (`{WD}/homes/{userid}`).
    pub home_host:      PathBuf,
    /// The Docker container name for this user (`skald-{userid}`).
    pub container_name: String,
    /// The home mount point inside the container (e.g. `/root`).
    pub container_home: PathBuf,
    /// Shared folders this user can reach, in name order.
    pub shared:         Vec<SharedMount>,
    /// Projects this user can reach (owned + shared-with-them), by owner then slug.
    pub projects:       Vec<ProjectMount>,
    /// Host directory backing the read-only docs mount (`{WD}/docs`), the same for
    /// every user. `None` when unset (inert placeholders, unit tests that don't
    /// touch it) — `docs/…` then resolves like any other unmounted path.
    pub docs_host:      Option<PathBuf>,
}

impl UserFs {
    pub fn new(
        user_id:        impl Into<String>,
        home_host:      PathBuf,
        container_name: impl Into<String>,
        container_home: PathBuf,
        shared:         Vec<SharedMount>,
        projects:       Vec<ProjectMount>,
        docs_host:      Option<PathBuf>,
    ) -> Self {
        Self {
            user_id: user_id.into(),
            home_host,
            container_name: container_name.into(),
            container_home,
            shared,
            projects,
            docs_host,
        }
    }

    /// Look up a shared mount by its folder name.
    pub fn shared_mount(&self, name: &str) -> Option<&SharedMount> {
        self.shared.iter().find(|m| m.name == name)
    }

    /// Look up a project mount by its owner username + slug (the two agent segments).
    pub fn project_mount(&self, owner_username: &str, slug: &str) -> Option<&ProjectMount> {
        self.projects
            .iter()
            .find(|m| m.owner_username == owner_username && m.slug == slug)
    }

    /// Whether the user may **write** at this agent path: their home → always;
    /// a shared-folder or project mount → the membership's `can_write` flag;
    /// `docs/…` → never (read-only). A `shared/`/`projects/` mount the user is
    /// not a member of → false (fail-closed, same as the read side). Purely
    /// lexical: memory paths never reach here (classified earlier).
    pub fn can_write_to(&self, agent_path: &str) -> bool {
        let stripped = strip_home_prefix(agent_path);
        let mut parts = stripped.splitn(2, ['/', '\\']);
        match parts.next() {
            Some("shared") => {
                let rest = parts.next().unwrap_or("");
                let name = rest.splitn(2, ['/', '\\']).next().unwrap_or("");
                self.shared_mount(name).map(|m| m.can_write).unwrap_or(false)
            }
            Some("projects") => {
                let rest = parts.next().unwrap_or("");
                let mut seg = rest.splitn(3, ['/', '\\']);
                let owner = seg.next().unwrap_or("");
                let slug  = seg.next().unwrap_or("");
                self.project_mount(owner, slug).map(|m| m.can_write).unwrap_or(false)
            }
            Some("docs") => false,
            _ => true,
        }
    }

    /// The bind mounts for `docker create`: `(host, container, writable)`, home first.
    pub fn mounts(&self) -> Vec<(PathBuf, PathBuf, bool)> {
        let mut out = vec![(self.home_host.clone(), self.container_home.clone(), true)];
        for m in &self.shared {
            out.push((m.host.clone(), m.container.clone(), m.can_write));
        }
        for m in &self.projects {
            out.push((m.host.clone(), m.container.clone(), m.can_write));
        }
        if let Some(docs) = &self.docs_host {
            out.push((docs.clone(), self.container_home.join("docs"), false));
        }
        out
    }

    /// The host base a physical agent path resolves against, and the tail relative
    /// to it — **without** touching the filesystem. `shared/{X}/…` resolves against
    /// the shared mount's host dir (only if the user is a member); everything else
    /// resolves against the private home. Returns `None` when the path names a
    /// `shared/` folder the user does not belong to. The caller (skald-core) then
    /// joins + canonicalizes + prefix-checks against the returned base.
    ///
    /// Memory paths (`user-memory/…`, `shared-memory/…`) must be classified and
    /// routed to SQLite *before* calling this — they are not physical paths.
    pub fn host_base_and_tail<'a>(&self, agent_path: &'a str) -> Option<(PathBuf, String)> {
        let stripped = strip_home_prefix(agent_path);
        let mut parts = stripped.splitn(2, ['/', '\\']);
        match parts.next() {
            Some("shared") => {
                let rest = parts.next().unwrap_or("");
                let mut seg = rest.splitn(2, ['/', '\\']);
                let name = seg.next().unwrap_or("");
                let tail = seg.next().unwrap_or("");
                let mount = self.shared_mount(name)?;
                Some((mount.host.clone(), tail.to_string()))
            }
            Some("projects") => {
                // Two segments: `projects/{owner_username}/{slug}/{tail…}`.
                let rest = parts.next().unwrap_or("");
                let mut seg = rest.splitn(3, ['/', '\\']);
                let owner = seg.next().unwrap_or("");
                let slug  = seg.next().unwrap_or("");
                let tail  = seg.next().unwrap_or("");
                let mount = self.project_mount(owner, slug)?;
                Some((mount.host.clone(), tail.to_string()))
            }
            Some("docs") => {
                let host = self.docs_host.clone()?;
                let tail = parts.next().unwrap_or("");
                Some((host, tail.to_string()))
            }
            _ => Some((self.home_host.clone(), stripped.to_string())),
        }
    }

    /// Map an agent path to its **container** path (pure, lexical): `~`/relative →
    /// under `container_home`; `shared/{X}` and `projects/{O}/{S}` → under
    /// `container_home/…` (they mirror the container layout); an already-absolute path
    /// is taken as a container path as-is. Used to set the working directory of an
    /// `execute_cmd` inside the container.
    pub fn to_container(&self, agent_path: &str) -> PathBuf {
        let p = Path::new(agent_path);
        if p.is_absolute() {
            return normalize(p);
        }
        let stripped = strip_home_prefix(agent_path);
        normalize(&self.container_home.join(stripped))
    }

    /// Reverse of [`to_container`](Self::to_container) for an already-absolute path:
    /// map a **container-absolute** path (`/root/…`, `/root/shared/{X}/…`,
    /// `/root/projects/{O}/{S}/…`) back to the agent vocabulary. Shared and project
    /// mounts nest *under* `container_home`, so they are matched **first** — otherwise
    /// `/root/shared/X` would strip against the home base and mis-route.
    ///
    /// Returns `None` when `abs` lies outside every one of this user's container mounts
    /// (i.e. it points outside their view) — the caller rejects it fail-closed. Purely
    /// lexical: no membership check, no filesystem access.
    pub fn container_to_agent(&self, abs: &Path) -> Option<String> {
        let abs = normalize(abs);
        for m in &self.shared {
            if let Ok(tail) = abs.strip_prefix(&m.container) {
                return Some(agent_join(&format!("shared/{}", m.name), tail));
            }
        }
        for m in &self.projects {
            if let Ok(tail) = abs.strip_prefix(&m.container) {
                return Some(agent_join(&format!("projects/{}/{}", m.owner_username, m.slug), tail));
            }
        }
        abs.strip_prefix(&self.container_home)
            .ok()
            .map(|tail| agent_join("~", tail))
    }

    /// Normalize any path arriving from the show-file / file-viewer surface into a
    /// **canonical agent path** the UI can display and echo back: a relative or `~/…`
    /// path is cleaned and rooted (`report.md` → `~/report.md`, `shared/X/y` and
    /// `projects/O/S/y` keep their root); a container-absolute path is reverse-mapped
    /// via [`container_to_agent`](Self::container_to_agent).
    ///
    /// Returns `None` only for an absolute path outside every container mount — the
    /// caller rejects it fail-closed. Purely lexical (`.`/`..` collapse, `..` clamps at
    /// the root); membership + on-disk containment are enforced later, in skald-core.
    pub fn to_agent_display(&self, input: &str) -> Option<String> {
        let p = Path::new(input);
        if p.is_absolute() {
            return self.container_to_agent(p);
        }
        let cleaned = normalize(Path::new(strip_home_prefix(input)));
        let cleaned = cleaned.to_string_lossy().replace('\\', "/");
        let root = cleaned.split('/').next().unwrap_or("");
        if root == "shared" || root == "projects" {
            Some(cleaned)
        } else if cleaned.is_empty() {
            Some("~".to_string())
        } else {
            Some(format!("~/{cleaned}"))
        }
    }
}

/// Join an agent-path base (`~`, `shared/X`, `projects/O/S`) with a tail relative to
/// the mount, normalizing separators. An empty tail yields the bare base.
fn agent_join(base: &str, tail: &Path) -> String {
    let t = tail.to_string_lossy().replace('\\', "/");
    if t.is_empty() { base.to_string() } else { format!("{base}/{t}") }
}

/// Strips a leading `~/`, bare `~`, or `./` so what remains is relative to the home.
fn strip_home_prefix(path: &str) -> &str {
    if let Some(rest) = path.strip_prefix("~/") {
        rest
    } else if path == "~" {
        ""
    } else {
        path.trim_start_matches("./")
    }
}

/// A hot-swappable handle to a [`UserFs`] snapshot, shared by every holder that
/// must observe a membership change without being rebuilt (blueprint §6 remount).
///
/// Cloning shares the *same* cell. `store` replaces the snapshot for all clones at
/// once; each `load` returns the current `Arc<UserFs>`. A live chat session's
/// handler holds a clone, so a shared-folder change reaches it on its next tool
/// call — no handler eviction, and no cross-session race (the swap is a single
/// pointer store behind the lock, and each `ToolContext` takes a consistent
/// snapshot for the duration of its call).
#[derive(Clone)]
pub struct SharedFs(Arc<RwLock<Arc<UserFs>>>);

impl SharedFs {
    pub fn new(fs: UserFs) -> Self {
        Self(Arc::new(RwLock::new(Arc::new(fs))))
    }

    /// The current snapshot. Cheap — clones an `Arc`.
    pub fn load(&self) -> Arc<UserFs> {
        Arc::clone(&self.0.read().expect("SharedFs lock poisoned"))
    }

    /// Replace the snapshot seen by every holder of this cell.
    pub fn store(&self, fs: UserFs) {
        *self.0.write().expect("SharedFs lock poisoned") = Arc::new(fs);
    }
}

impl std::fmt::Debug for SharedFs {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_tuple("SharedFs").field(&*self.load()).finish()
    }
}

/// Pure lexical normalization (resolve `.`/`..`), no filesystem access.
fn normalize(p: &Path) -> PathBuf {
    let mut out = PathBuf::new();
    for comp in p.components() {
        match comp {
            Component::ParentDir => { out.pop(); }
            Component::CurDir    => {}
            other                => out.push(other.as_os_str()),
        }
    }
    out
}