//! Permission grants — the PDF's flags 5-19 "permissions and associations"
//! layer (Task 6b of the concurrent / multi-tenant plan).
//!
//! The PDF reserves cube-header flags 5-19 for delegated permissions but
//! ships no concrete model. We implement a *grant* as a first-class,
//! addressable record in Null space — consistent with the PDF's stance that
//! "metadata is reserved coordinate space, not a side table". A grant
//! delegates some perms (r / w / x) over a coordinate scope from a `granter`
//! owner to a `grantee` owner.
//!
//! Enforcement order (see `admit_mutate` in `commands.rs`):
//!   1. owner match      -> allow
//!   2. else any grant whose `grantee == caller`, whose `perms` cover the op,
//!      and whose `scope` covers the coordinate -> allow
//!   3. else deny
//!
//! All grants for a tenant live in ONE durable record at [`GRANT_BUCKET`]
//! (a JSON array of grant objects — std-only, no `serde` dependency), so they
//! persist with the tenant's WAL exactly like any other record. Only the
//! `granter` may `REVOKE`.
//!
//! Scope semantics: a scope axis of `0` acts as a wildcard for that axis, so
//! `scope 5.0.0.0` means "the entire class-5 subtree" while `scope 5.1.1.1`
//! is exact. A `None` scope means global.

use crate::store::ConcurrentStore;
use crate::tenant::TenantIdentity;
use cubecoords::{CubeHeader, Czyx};

/// Permission bits.
pub const PERM_READ: u8 = 1;
/// Permission bit: write (create / overwrite / delete / seal / open).
pub const PERM_WRITE: u8 = 2;
/// Permission bit: execute (reserved; not yet used by any command).
pub const PERM_EXEC: u8 = 4;

/// The kind of operation a grant can authorize.
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub enum Perm {
    /// Read access (reserved for future read-gating).
    Read,
    /// Write access (the mutating commands: `prog` / `write` / `del` / `seal` / `open`).
    Write,
    /// Execute access (reserved).
    Exec,
}

impl Perm {
    /// The bitmask for this permission.
    pub fn bit(self) -> u8 {
        match self {
            Perm::Read => PERM_READ,
            Perm::Write => PERM_WRITE,
            Perm::Exec => PERM_EXEC,
        }
    }
}

impl Perm {
    /// Human-readable single-letter set for a permission byte.
    pub fn to_string_perms(p: u8) -> String {
        let mut s = String::new();
        if p & PERM_READ != 0 {
            s.push('r');
        }
        if p & PERM_WRITE != 0 {
            s.push('w');
        }
        if p & PERM_EXEC != 0 {
            s.push('x');
        }
        s
    }
}

/// A principal: the owner half of a `HELLO` identity (a `CubeHeader`
/// `owner_local_user` plus an optional `owner_remote_user`).
#[derive(Clone, Eq, PartialEq, Debug)]
pub struct Owner {
    /// Local owner user (maps to `CubeHeader::owner_local_user`).
    pub local: String,
    /// Optional remote owner user (maps to `owner_remote_user`). `None` and
    /// `Some("")` are treated as distinct to avoid surprising matches.
    pub remote: Option<String>,
}

impl Owner {
    /// An owner with only a local user.
    pub fn new(local: impl Into<String>) -> Self {
        Owner {
            local: local.into(),
            remote: None,
        }
    }

    /// An owner with a local and a remote user.
    pub fn with_remote(local: impl Into<String>, remote: impl Into<String>) -> Self {
        Owner {
            local: local.into(),
            remote: Some(remote.into()),
        }
    }
}

impl From<&TenantIdentity> for Owner {
    fn from(id: &TenantIdentity) -> Self {
        Owner {
            local: id.owner_local.clone(),
            remote: id.owner_remote.clone(),
        }
    }
}

/// A delegated permission: `granter` lets `grantee` perform `perms` over
/// `scope` (or globally when `scope` is `None`).
///
/// Serialized to a compact std-only JSON object (see [`Grant::to_json`] /
/// [`Grant::from_json`]); `seq` is a per-tenant monotonic id used for
/// diagnostics and future conflict resolution.
#[derive(Clone, Eq, PartialEq, Debug)]
pub struct Grant {
    /// Who issued the grant (and the only one who may revoke it).
    pub granter: Owner,
    /// Who the grant authorizes.
    pub grantee: Owner,
    /// Permission bitmask (`PERM_READ` / `PERM_WRITE` / `PERM_EXEC`).
    pub perms: u8,
    /// Coordinate scope. `None` = global; an axis of `0` = wildcard for that axis.
    pub scope: Option<Czyx>,
    /// Monotonic per-tenant id (diagnostics / ordering).
    pub seq: u64,
}

impl Grant {
    /// True if this grant authorizes `want` over `coord`.
    pub fn allows(&self, coord: &Czyx, want: Perm) -> bool {
        if self.perms & want.bit() == 0 {
            return false;
        }
        match self.scope {
            None => true,
            Some(sc) => scope_covers(sc, *coord),
        }
    }

    /// Compact std-only JSON form of this grant.
    pub fn to_json(&self) -> String {
        let mut s = String::new();
        s.push('{');
        s.push_str(&format!(
            "\"granter_local\":{}",
            json_str(&self.granter.local)
        ));
        if let Some(r) = &self.granter.remote {
            s.push_str(&format!(",\"granter_remote\":{}", json_str(r)));
        }
        s.push_str(&format!(
            ",\"grantee_local\":{}",
            json_str(&self.grantee.local)
        ));
        if let Some(r) = &self.grantee.remote {
            s.push_str(&format!(",\"grantee_remote\":{}", json_str(r)));
        }
        s.push_str(&format!(
            ",\"perms\":{}",
            json_str(&Perm::to_string_perms(self.perms))
        ));
        match self.scope {
            Some(sc) => s.push_str(&format!(
                ",\"scope\":{}",
                json_str(&format!("{}.{}.{}.{}", sc.c, sc.z, sc.y, sc.x))
            )),
            None => s.push_str(",\"scope\":null"),
        }
        s.push_str(&format!(",\"seq\":{}", self.seq));
        s.push('}');
        s
    }

    /// Parse a grant from its [`to_json`] form. Returns `None` on any malformed field.
    pub fn from_json(obj: &str) -> Option<Grant> {
        let gl = field_str(obj, "granter_local")?;
        let gr = field_str(obj, "granter_remote");
        let el = field_str(obj, "grantee_local")?;
        let er = field_str(obj, "grantee_remote");
        let perms = field_str(obj, "perms")?;
        let perms = perms_from_str(&perms)?;
        let scope = match field_raw(obj, "scope").as_deref() {
            Some("null") | None => None,
            Some(s) => {
                let inner = unjson_str(s);
                Some(crate::commands::parse_coord(&inner)?)
            }
        };
        let seq = field_raw(obj, "seq")
            .and_then(|s| s.parse::<u64>().ok())
            .unwrap_or(0);
        Some(Grant {
            granter: Owner::new(gl).with_opt_remote(gr),
            grantee: Owner::new(el).with_opt_remote(er),
            perms,
            scope,
            seq,
        })
    }
}

impl Owner {
    fn with_opt_remote(self, remote: Option<String>) -> Owner {
        match remote {
            Some(r) => Owner {
                local: self.local,
                remote: Some(r),
            },
            None => self,
        }
    }
}

/// The null-space coordinate holding the tenant's grant table (a JSON array).
/// Lives in Null cube 1 (the same family `cube-demo` / `seal` use for
/// key material), kept distinct by X.
pub const GRANT_BUCKET: Czyx = Czyx::new(0, 1, 0, 1);

/// Parse a permission string (`r` / `w` / `x` and any combination) into a
/// bitmask. Returns `None` for an empty or invalid string.
pub fn perms_from_str(s: &str) -> Option<u8> {
    let mut p = 0u8;
    for c in s.chars() {
        match c {
            'r' => p |= PERM_READ,
            'w' => p |= PERM_WRITE,
            'x' => p |= PERM_EXEC,
            _ => return None,
        }
    }
    if p == 0 {
        None
    } else {
        Some(p)
    }
}

/// Read the tenant's grant table from the store. Stored as a proper record
/// (`doc_type = "grant-table"`) so it survives checkpoint/restore exactly like
/// any other record.
pub fn read_bucket(store: &ConcurrentStore) -> Vec<Grant> {
    match store.get_record(&GRANT_BUCKET) {
        None => Vec::new(),
        Some((_, bytes)) => {
            let text = String::from_utf8_lossy(&bytes);
            extract_objects(&text)
                .into_iter()
                .filter_map(Grant::from_json)
                .collect()
        }
    }
}

/// Overwrite the tenant's grant table.
fn write_bucket(store: &ConcurrentStore, grants: &[Grant]) {
    let mut s = String::from("[");
    for (i, g) in grants.iter().enumerate() {
        if i > 0 {
            s.push(',');
        }
        s.push_str(&g.to_json());
    }
    s.push(']');
    store.put_record(GRANT_BUCKET, &grant_header(), &s.into_bytes());
}

/// Header stamped on the grant-table record. Tagging it `doc_type =
/// "grant-table"` means checkpoints treat it like any other record (no loss),
/// and a future `query_doc_type("grant-table")` can enumerate it.
pub fn grant_header() -> CubeHeader {
    CubeHeader {
        flags: cubecoords::HeaderFlags(cubecoords::HeaderFlags::DOC_TYPE),
        title: None,
        doc_type: Some("grant-table".to_string()),
        created_at: None,
        size_bytes: None,
        owner_local_user: None,
        owner_remote_user: None,
        linked_records: Vec::new(),
        total_accesses: 0,
        total_remote_accesses: 0,
        last_access: None,
        last_remote_access: None,
    }
}

/// Issue a grant. Returns the new grant's `seq`.
pub fn grant(
    store: &ConcurrentStore,
    granter: &Owner,
    grantee: &Owner,
    perms: u8,
    scope: Option<Czyx>,
) -> Result<u64, String> {
    let mut grants = read_bucket(store);
    let seq = grants.iter().map(|g| g.seq).max().unwrap_or(0) + 1;
    grants.push(Grant {
        granter: granter.clone(),
        grantee: grantee.clone(),
        perms,
        scope,
        seq,
    });
    write_bucket(store, &grants);
    Ok(seq)
}

/// Revoke grants matching `granter` + `grantee` (+ `scope` when given).
/// Returns the number of grants removed.
pub fn revoke(
    store: &ConcurrentStore,
    granter: &Owner,
    grantee: &Owner,
    scope: Option<Czyx>,
) -> usize {
    let before = read_bucket(store);
    // Keep every grant that does NOT match the revoke criteria; the rest are
    // removed.
    let kept: Vec<Grant> = before
        .iter()
        .filter(|g| {
            !(g.granter == *granter
                && g.grantee == *grantee
                && scope.map_or(true, |sc| g.scope == Some(sc)))
        })
        .cloned()
        .collect();
    let removed = before.len() - kept.len();
    write_bucket(store, &kept);
    removed
}

/// All grants whose `grantee` is `who`.
pub fn grants_for(store: &ConcurrentStore, who: &Owner) -> Vec<Grant> {
    read_bucket(store)
        .into_iter()
        .filter(|g| g.grantee == *who)
        .collect()
}

/// True if `who` holds a grant authorizing `want` over `coord`.
pub fn grant_allows(store: &ConcurrentStore, who: &Owner, coord: &Czyx, want: Perm) -> bool {
    grants_for(store, who).iter().any(|g| g.allows(coord, want))
}

/// Does `scope` cover `coord`? A `0` axis in the scope is a wildcard.
fn scope_covers(scope: Czyx, coord: Czyx) -> bool {
    (scope.c == 0 || scope.c == coord.c)
        && (scope.z == 0 || scope.z == coord.z)
        && (scope.y == 0 || scope.y == coord.y)
        && (scope.x == 0 || scope.x == coord.x)
}

/// Quote a string as a JSON string literal (escaping `"`, `\`, and control chars).
fn json_str(s: &str) -> String {
    let mut o = String::with_capacity(s.len() + 2);
    o.push('"');
    for c in s.chars() {
        match c {
            '"' => o.push_str("\\\""),
            '\\' => o.push_str("\\\\"),
            '\n' => o.push_str("\\n"),
            '\r' => o.push_str("\\r"),
            '\t' => o.push_str("\\t"),
            _ => o.push(c),
        }
    }
    o.push('"');
    o
}

/// Unquote a JSON string literal (reverse of [`json_str`]).
fn unjson_str(s: &str) -> String {
    let inner = s
        .strip_prefix('"')
        .and_then(|x| x.strip_suffix('"'))
        .unwrap_or(s);
    let mut o = String::new();
    let mut chars = inner.chars();
    while let Some(c) = chars.next() {
        if c == '\\' {
            match chars.next() {
                Some('"') => o.push('"'),
                Some('\\') => o.push('\\'),
                Some('n') => o.push('\n'),
                Some('r') => o.push('\r'),
                Some('t') => o.push('\t'),
                Some(other) => o.push(other),
                None => {}
            }
        } else {
            o.push(c);
        }
    }
    o
}

/// Extract the raw JSON value for `key` from an object string
/// (`"key":<value>`). Returns the value token verbatim: a quoted string (with
/// quotes), `null`, or a bare number. `None` if the key is absent.
fn field_raw(obj: &str, key: &str) -> Option<String> {
    let pat = format!("\"{key}\"");
    let idx = obj.find(&pat)?;
    let after = &obj[idx + pat.len()..];
    let after = after.trim_start().strip_prefix(':')?.trim_start();
    if after.starts_with('"') {
        let bytes = after.as_bytes();
        let mut end = 1;
        while end < bytes.len() {
            if bytes[end] == b'"' && bytes[end - 1] != b'\\' {
                break;
            }
            end += 1;
        }
        Some(after[..=end].to_string())
    } else if after.starts_with("null") {
        Some("null".to_string())
    } else {
        let end = after.find(|c: char| !c.is_ascii_digit())?;
        Some(after[..end].to_string())
    }
}

/// Like [`field_raw`] but unquotes string values and maps `null` to `None`.
fn field_str(obj: &str, key: &str) -> Option<String> {
    field_raw(obj, key).and_then(|v| {
        if v == "null" {
            None
        } else {
            Some(unjson_str(&v))
        }
    })
}

/// Extract each top-level `{...}` object from a JSON array/text.
fn extract_objects(s: &str) -> Vec<&str> {
    let bytes = s.as_bytes();
    let mut out = Vec::new();
    let mut depth = 0i32;
    let mut start = None;
    for (i, &b) in bytes.iter().enumerate() {
        if b == b'{' {
            if depth == 0 {
                start = Some(i);
            }
            depth += 1;
        } else if b == b'}' {
            depth -= 1;
            if depth == 0 {
                if let Some(st) = start {
                    out.push(&s[st..=i]);
                }
                start = None;
            }
        }
    }
    out
}

// (Arc is imported in the test module only)

#[cfg(test)]
mod tests {
    use super::*;
    use crate::commands::Session;
    use crate::store::DurabilityConfig;
    use crate::tenant::{TenantId, TenantIdentity};
    use std::str::FromStr;
    use std::sync::Arc;

    fn test_id(local: &str) -> TenantIdentity {
        TenantIdentity {
            tenant: TenantId::from_str("t").unwrap(),
            owner_local: local.to_string(),
            owner_remote: None,
        }
    }

    fn session(store: Arc<ConcurrentStore>, local: &str) -> Session {
        let mut s = Session::with_store(store);
        s.set_identity(test_id(local));
        s.set_enforce_owner(true);
        s
    }

    #[test]
    fn grant_json_roundtrip() {
        let g = Grant {
            granter: Owner::new("alice"),
            grantee: Owner::with_remote("bob", "remote1"),
            perms: PERM_READ | PERM_WRITE,
            scope: Some(Czyx::new(5, 1, 1, 1)),
            seq: 42,
        };
        let j = g.to_json();
        let g2 = Grant::from_json(&j).expect("parse");
        assert_eq!(g, g2, "grant JSON round-trips");
    }

    #[test]
    fn grant_json_handles_null_scope() {
        let g = Grant {
            granter: Owner::new("alice"),
            grantee: Owner::new("bob"),
            perms: PERM_WRITE,
            scope: None,
            seq: 1,
        };
        let g2 = Grant::from_json(&g.to_json()).expect("parse");
        assert_eq!(g, g2);
    }

    #[test]
    fn perms_parse() {
        assert_eq!(
            perms_from_str("rwx"),
            Some(PERM_READ | PERM_WRITE | PERM_EXEC)
        );
        assert_eq!(perms_from_str("w"), Some(PERM_WRITE));
        assert_eq!(perms_from_str(""), None);
        assert_eq!(perms_from_str("q"), None);
    }

    #[test]
    fn scope_wildcard_semantics() {
        let scope = Czyx::new(5, 1, 0, 0); // class 5, z=1, y/x wildcard
        assert!(scope_covers(scope, Czyx::new(5, 1, 7, 9)));
        assert!(!scope_covers(scope, Czyx::new(5, 2, 7, 9))); // z mismatch
        assert!(!scope_covers(scope, Czyx::new(6, 1, 7, 9))); // c mismatch
    }

    #[test]
    fn grant_allows_delegated_write() {
        let store = Arc::new(ConcurrentStore::memory());
        let mut alice = session(store.clone(), "alice");
        let mut bob = session(store.clone(), "bob");
        let mut carol = session(store.clone(), "carol");

        // alice writes a record she owns
        alice
            .exec("prog /c005/z001/y001/x001 const 1 halt")
            .expect("alice writes");

        // bob cannot overwrite alice's record (no grant)
        assert!(
            bob.exec("prog /c005/z001/y001/x001 const 2 halt").is_err(),
            "bob blocked without a grant"
        );

        // alice grants bob write on exactly that coord
        alice.exec("grant bob w 5.1.1.1").expect("grant issued");

        // now bob can write
        assert!(
            bob.exec("prog /c005/z001/y001/x001 const 3 halt").is_ok(),
            "bob allowed by grant"
        );

        // a third owner with no grant is still blocked
        assert!(
            carol
                .exec("prog /c005/z001/y001/x001 const 4 halt")
                .is_err(),
            "carol still blocked"
        );
    }

    #[test]
    fn revoke_removes_grant() {
        let store = Arc::new(ConcurrentStore::memory());
        let mut alice = session(store.clone(), "alice");
        let mut bob = session(store.clone(), "bob");

        // alice owns two coords in class 6
        alice
            .exec("prog /c006/z001/y001/x001 const 1 halt")
            .unwrap();
        alice
            .exec("prog /c006/z001/y001/x002 const 1 halt")
            .unwrap();

        // grant bob write over the whole class-6 subtree
        alice.exec("grant bob w 6.0.0.0").unwrap();
        assert!(
            bob.exec("prog /c006/z001/y001/x001 const 2 halt").is_ok(),
            "bob writes under grant (takes ownership of x001)"
        );

        // revoke
        let removed = alice
            .exec("revoke bob 6.0.0.0")
            .unwrap()
            .contains("revoked 1");
        assert!(removed, "exactly one grant revoked");

        // bob tries x002, which alice still owns -> blocked after revoke
        assert!(
            bob.exec("prog /c006/z001/y001/x002 const 3 halt").is_err(),
            "after revoke, bob blocked on alice-owned coord"
        );
    }

    #[test]
    fn grant_scope_prefix() {
        let store = Arc::new(ConcurrentStore::memory());
        let mut alice = session(store.clone(), "alice");
        let mut bob = session(store.clone(), "bob");

        alice
            .exec("prog /c007/z001/y001/x001 const 1 halt")
            .unwrap();
        alice
            .exec("prog /c007/z002/y001/x001 const 1 halt")
            .unwrap();

        // grant bob write only on the z=1 subtree
        alice.exec("grant bob w 7.1.0.0").unwrap();

        assert!(
            bob.exec("prog /c007/z001/y001/x001 const 2 halt").is_ok(),
            "in-scope coord allowed"
        );
        assert!(
            bob.exec("prog /c007/z002/y001/x001 const 2 halt").is_err(),
            "out-of-scope coord blocked"
        );
    }

    #[test]
    fn grant_requires_identity() {
        let store = Arc::new(ConcurrentStore::memory());
        let mut anon = Session::with_store(store);
        anon.set_enforce_owner(true);
        // no HELLO identity -> grant rejected
        assert!(anon.exec("grant bob w 1.0.0.0").is_err());
    }

    #[test]
    fn grant_survives_reopen() {
        let dir =
            std::env::temp_dir().join(format!("cubelinux-grant-{}-{}", std::process::id(), "g1"));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        let db = dir.join("cube-store.json");
        let wal = dir.join("cube-store.wal");
        let rec = dir.join("cube-store.recovery.ndjson");

        let store = Arc::new(
            ConcurrentStore::open(
                db.to_str().unwrap(),
                wal.to_str().unwrap(),
                rec.to_str().unwrap(),
                DurabilityConfig::default(),
            )
            .unwrap(),
        );
        let mut alice = session(store.clone(), "alice");
        alice
            .exec("prog /c008/z001/y001/x001 const 1 halt")
            .unwrap();
        alice.exec("grant bob w 8.1.1.1").unwrap();
        store.checkpoint();
        drop(store);

        // reopen from disk
        let store2 = Arc::new(
            ConcurrentStore::open(
                db.to_str().unwrap(),
                wal.to_str().unwrap(),
                rec.to_str().unwrap(),
                DurabilityConfig::default(),
            )
            .unwrap(),
        );
        let mut bob = session(store2.clone(), "bob");
        assert!(
            bob.exec("prog /c008/z001/y001/x001 const 2 halt").is_ok(),
            "grant survived reopen from disk"
        );

        let _ = std::fs::remove_dir_all(&dir);
    }
}