//! Who may do what. The users and what each may do are the swarm's: a registry in the
//! document (`_continuum/users`, `registry`), each user with capabilities, each a path
//! and the rights it gives there and below (`Capability::covers`). How a user proves who
//! it is stays each node's (`--htpasswd`, `--user-header`: `api::auth`). Enforced at
//! the HTTP API ([`access.md`](../../docs/access.md)).

// Used by the genesis node and the API from the next patches on.
#![cfg_attr(not(test), allow(dead_code))]

use std::collections::BTreeSet;

use serde::{Deserialize, Serialize};

use crate::document::meta;

pub(crate) mod bans;
pub(crate) mod envelope;
pub(crate) mod policy;
pub(crate) mod registry;
pub(crate) mod rules;
pub(crate) mod screen;
pub(crate) mod sshsig;
pub(crate) mod token;

/// What a capability lets its holder do, at its path and below.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub(crate) enum Right {
    Read,
    Write,
}

impl Right {
    pub(crate) fn as_str(self) -> &'static str {
        match self {
            Self::Read => "read",
            Self::Write => "write",
        }
    }
}

/// A path, and what it lets its holder do there and below: as the registry records it
/// (`registry::User::caps`).
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub(crate) struct Capability {
    /// Segments, as the store's API takes them (`[]`: everything).
    pub(crate) path: Vec<String>,
    /// `read`, `write`. Others, from a later version (`grant`), are kept and give
    /// nothing here.
    pub(crate) rights: BTreeSet<String>,
    /// Who granted it: a user (`user:<name>`), or for those the genesis node records, the
    /// node (its node ID). Kept so that granting on, by delegation, can come later
    /// without a new format (`future-work.md`, Authentication across nodes).
    #[serde(default)]
    pub(crate) by: String,
    /// When it was granted (Unix ms).
    #[serde(default)]
    pub(crate) since: u64,
}

impl Capability {
    /// Whether it lets its holder do `right` at `path`: its path is a prefix of `path`
    /// (segment by segment) and it gives `right`. One that isn't within protocol data
    /// (`_continuum`) never covers it: operators are those given protocol data itself.
    pub(crate) fn covers(&self, right: Right, path: &[String]) -> bool {
        self.gives(right)
            && path.starts_with(&self.path)
            && (meta::is_protocol(&self.path) || !meta::is_protocol(path))
    }

    /// Whether `path` leads to a place where it lets its holder do `right`: its path
    /// lies below `path` (or is it, or above it). What a listing of `path` shows of a
    /// tree its holder may only partly read (`Caps::reaches`).
    pub(crate) fn reaches(&self, right: Right, path: &[String]) -> bool {
        self.gives(right)
            && (self.path.starts_with(path) || self.covers(right, path))
            && (meta::is_protocol(&self.path) || !meta::is_protocol(path))
    }

    fn gives(&self, right: Right) -> bool {
        self.rights.contains(right.as_str())
    }
}

/// Everything a user may do: its capabilities, as its registry entry has them; none if
/// it has none, or is disabled. Narrowed by a token that says less (`limit`,
/// `token::Claims::limit`): then only what both allow.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub(crate) struct Caps {
    caps: Vec<Capability>,
    limit: Option<Vec<Capability>>,
}

impl Caps {
    pub(crate) fn new(caps: Vec<Capability>) -> Self {
        Self { caps, limit: None }
    }

    /// These, only where `limit` allows too.
    pub(crate) fn within(mut self, limit: Vec<Capability>) -> Self {
        self.limit = Some(match self.limit.take() {
            // Narrowed twice: the earlier limit's capabilities that lie within the new
            // one's (less than what both allow, where one only partly covers the
            // other: never more).
            Some(mut earlier) => {
                earlier.retain(|cap| {
                    limit.iter().any(|outer| {
                        cap.path.starts_with(&outer.path) && cap.rights.is_subset(&outer.rights)
                    })
                });
                earlier
            }
            None => limit,
        });
        self
    }

    /// Whether one of them lets its holder do `right` at `path` (and the limit too).
    pub(crate) fn allows(&self, right: Right, path: &[String]) -> bool {
        self.caps.iter().any(|cap| cap.covers(right, path))
            && self
                .limit
                .as_ref()
                .is_none_or(|limit| limit.iter().any(|cap| cap.covers(right, path)))
    }

    /// Whether `path` leads to a place where one of them lets its holder do `right`: a
    /// listing of `path` shows the way there, as a directory one may pass through but not
    /// list does (`Capability::reaches`).
    pub(crate) fn reaches(&self, right: Right, path: &[String]) -> bool {
        self.caps.iter().any(|cap| cap.reaches(right, path))
            && self
                .limit
                .as_ref()
                .is_none_or(|limit| limit.iter().any(|cap| cap.reaches(right, path)))
    }

    pub(crate) fn is_empty(&self) -> bool {
        self.caps.is_empty() || self.limit.as_ref().is_some_and(Vec::is_empty)
    }
}

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

    fn path(text: &str) -> Vec<String> {
        text.split('/')
            .filter(|segment| !segment.is_empty())
            .map(str::to_owned)
            .collect()
    }

    fn cap(at: &str, rights: &[&str]) -> Capability {
        Capability {
            path: path(at),
            rights: rights.iter().map(|right| (*right).to_owned()).collect(),
            by: String::new(),
            since: 0,
        }
    }

    #[test]
    fn a_capability_covers_its_path_and_below() {
        let servers = cap("servers/eu", &["read"]);
        assert!(servers.covers(Right::Read, &path("servers/eu")));
        assert!(servers.covers(Right::Read, &path("servers/eu/0/name")));
        // By segment, not by text.
        assert!(!servers.covers(Right::Read, &path("servers/europe")));
        assert!(!servers.covers(Right::Read, &path("servers")));
        assert!(!servers.covers(Right::Write, &path("servers/eu")));
    }

    #[test]
    fn protocol_data_only_by_capabilities_within_it() {
        let everything = cap("", &["read", "write"]);
        assert!(everything.covers(Right::Write, &path("accounts/1")));
        assert!(everything.covers(Right::Read, &[]));
        assert!(!everything.covers(Right::Read, &path("_continuum")));
        assert!(!everything.covers(Right::Write, &path("_continuum/users/alice")));
        let operator = cap("_continuum", &["read", "write"]);
        assert!(operator.covers(Right::Write, &path("_continuum/users/alice")));
        assert!(!operator.covers(Right::Read, &path("accounts")));
        let remakes = cap("_continuum/remakes", &["write"]);
        assert!(remakes.covers(Right::Write, &path("_continuum/remakes/r1")));
        assert!(!remakes.covers(Right::Write, &path("_continuum/users")));
    }

    #[test]
    fn rights_from_later_versions_give_nothing() {
        let later = cap("", &["grant"]);
        assert!(!later.covers(Right::Read, &path("x")));
        assert!(!later.covers(Right::Write, &path("x")));
    }

    #[test]
    fn a_limit_narrows() {
        let caps =
            Caps::new(vec![cap("", &["read", "write"])]).within(vec![cap("notes", &["read"])]);
        assert!(caps.allows(Right::Read, &path("notes/a")));
        assert!(!caps.allows(Right::Write, &path("notes/a")));
        assert!(!caps.allows(Right::Read, &path("logs")));
        assert!(caps.reaches(Right::Read, &[]));
        // Never wider than what the user has.
        let narrow =
            Caps::new(vec![cap("notes", &["read"])]).within(vec![cap("", &["read", "write"])]);
        assert!(!narrow.allows(Right::Write, &path("notes")));
        assert!(!narrow.allows(Right::Read, &path("logs")));
        // Narrowed again: within both.
        let twice = caps.within(vec![cap("notes/a", &["read", "write"])]);
        assert!(!twice.allows(Right::Read, &path("notes/a")));
        assert!(
            Caps::new(vec![cap("", &["read"])])
                .within(Vec::new())
                .is_empty()
        );
    }

    #[test]
    fn a_listing_shows_the_way_to_what_may_be_read() {
        let caps = Caps::new(vec![cap("servers/eu", &["read"])]);
        // The way there, as a directory passed through.
        assert!(caps.reaches(Right::Read, &[]));
        assert!(caps.reaches(Right::Read, &path("servers")));
        // There and below.
        assert!(caps.reaches(Right::Read, &path("servers/eu")));
        assert!(caps.reaches(Right::Read, &path("servers/eu/0")));
        // Elsewhere, nothing.
        assert!(!caps.reaches(Right::Read, &path("servers/us")));
        assert!(!caps.reaches(Right::Read, &path("accounts")));
        assert!(!caps.allows(Right::Read, &path("servers")));
        // A capability on everything doesn't lead into protocol data.
        let everything = Caps::new(vec![cap("", &["read"])]);
        assert!(everything.reaches(Right::Read, &[]));
        assert!(!everything.reaches(Right::Read, &path("_continuum")));
        let members = Caps::new(vec![cap("_continuum/members", &["read"])]);
        assert!(members.reaches(Right::Read, &[]));
        assert!(members.reaches(Right::Read, &path("_continuum")));
        assert!(!members.reaches(Right::Read, &path("_continuum/users")));
    }
}