//! The one-shot move of the permissions this hive's meta repo held
//! (`meta/capabilities.json` and `meta/tool-groups.json`) into the swarm's
//! `agent-permissions` bucket, as one list per agent.
//!
//! At boot, before any agent starts, [`seed_local`] copies the files' grants
//! into [`crate::permissions`] when nothing is stored there yet, so agents
//! keep their mounts until the swarm answers. [`send_pending`] then sends the
//! grants to swarm-controller, which writes each agent's key only where there
//! is none, and on its answer deletes both files from the meta repo. Nothing
//! reads them after that.

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

use anyhow::{Context, Result};
use hive_sh4re::permissions::Permission;
use swarm_queue_client::agent_permissions::{
    self, AgentPermissions, IMPORT_REPLY_DEADLINE, Import, ImportReply,
};

const CAPABILITIES_FILE: &str = "capabilities.json";
const TOOL_GROUPS_FILE: &str = "tool-groups.json";

/// The meta repo files the grants are moved out of.
pub const META_FILES: &[&str] = &[CAPABILITIES_FILE, TOOL_GROUPS_FILE];

/// Tool groups the files may name that give nothing and have no
/// [`Permission`]: dropped.
const EMPTY_TOOL_GROUPS: &[&str] = &["lifecycle", "forge"];

type Grants = BTreeMap<String, Vec<Permission>>;
type FileMap = BTreeMap<String, Vec<String>>;

fn parse(agent: &str, name: &str) -> Option<Permission> {
    let found = Permission::ALL
        .iter()
        .copied()
        .find(|p| name.eq_ignore_ascii_case(<&str>::from(*p)));
    if found.is_none()
        && !EMPTY_TOOL_GROUPS
            .iter()
            .any(|g| name.eq_ignore_ascii_case(g))
    {
        tracing::warn!(%agent, permission = %name, "import: dropping unrecognised name");
    }
    found
}

/// The one list per agent the two files add up to, as the swarm stores it.
/// `None` for either file means it does not exist.
///
/// Each half is what the agent held under the old readers:
/// - tool groups: the entry's known names; an absent entry, or one naming
///   only unknown names, was the default groups. `lifecycle`/`forge` count as
///   known (they parsed) and are then dropped, so an entry of only those
///   held no tools and imports as none.
/// - capabilities: the entry's names. With the file present, `ruth` having no
///   entry means her grant was revoked: the file was created holding it, and
///   a revoke removed the entry. With no file, the default.
///
/// An agent whose list equals [`Permission::default_for`] is left out, so its
/// key stays unset and follows the default.
fn grants(caps: Option<&FileMap>, groups: Option<&FileMap>) -> Grants {
    let mut agents: BTreeSet<&str> = BTreeSet::new();
    agents.extend(caps.iter().flat_map(|m| m.keys().map(String::as_str)));
    agents.extend(groups.iter().flat_map(|m| m.keys().map(String::as_str)));
    if caps.is_some() {
        agents.insert(crate::lifecycle::MANAGER_NAME);
    }
    let mut out = Grants::new();
    for agent in agents {
        let default = Permission::default_for(agent);
        let tool_default: Vec<Permission> = default
            .iter()
            .copied()
            .filter(|p| *p != Permission::ManageRootAgent)
            .collect();
        let tool_part = match groups.and_then(|m| m.get(agent)) {
            Some(names)
                if names.iter().any(|n| {
                    parse(agent, n).is_some()
                        || EMPTY_TOOL_GROUPS.iter().any(|g| n.eq_ignore_ascii_case(g))
                }) =>
            {
                names.iter().filter_map(|n| parse(agent, n)).collect()
            }
            _ => tool_default,
        };
        let cap_part: Vec<Permission> = match caps {
            Some(m) => m
                .get(agent)
                .map(|names| names.iter().filter_map(|n| parse(agent, n)).collect())
                .unwrap_or_default(),
            None => default
                .iter()
                .copied()
                .filter(|p| *p == Permission::ManageRootAgent)
                .collect(),
        };
        let mut list: Vec<Permission> = Vec::new();
        for perm in tool_part.into_iter().chain(cap_part) {
            if !list.contains(&perm) {
                list.push(perm);
            }
        }
        let same_as_default =
            list.len() == default.len() && default.iter().all(|p| list.contains(p));
        if !same_as_default {
            out.insert(agent.to_owned(), list);
        }
    }
    out
}

fn read_file(path: &Path) -> Result<Option<FileMap>> {
    if !path.exists() {
        return Ok(None);
    }
    let map = serde_json::from_slice(
        &std::fs::read(path).with_context(|| format!("reading {}", path.display()))?,
    )
    .with_context(|| format!("parsing {}", path.display()))?;
    Ok(Some(map))
}

/// The grants the files in `meta` hold, or `None` when neither exists.
fn read_grants(meta: &Path) -> Result<Option<Grants>> {
    let caps = read_file(&meta.join(CAPABILITIES_FILE))?;
    let groups = read_file(&meta.join(TOOL_GROUPS_FILE))?;
    if caps.is_none() && groups.is_none() {
        return Ok(None);
    }
    Ok(Some(grants(caps.as_ref(), groups.as_ref())))
}

fn meta_dir() -> PathBuf {
    crate::paths::meta_root()
}

/// Whether a meta repo file is still waiting to be imported.
#[must_use]
pub fn pending() -> bool {
    let meta = meta_dir();
    META_FILES.iter().any(|f| meta.join(f).exists())
}

/// Store the files' grants as the last-read swarm permissions, when a file
/// is still there and nothing has been stored yet.
pub fn seed_local() {
    if let Err(e) = seed_local_at(&meta_dir(), &crate::permissions::path()) {
        tracing::warn!(error = ?e, "import: seeding the stored permissions from the meta repo failed");
    }
}

fn seed_local_at(meta: &Path, stored: &Path) -> Result<()> {
    if stored.exists() {
        return Ok(());
    }
    let Some(grants) = read_grants(meta)? else {
        return Ok(());
    };
    let records = grants
        .into_iter()
        .map(|(agent, perms)| {
            (
                agent,
                AgentPermissions {
                    permissions: Some(perms),
                },
            )
        })
        .collect();
    crate::permissions::write_at(stored, &records).context("storing the seeded permissions")?;
    tracing::info!("import: seeded the stored permissions from the meta repo");
    Ok(())
}

/// What one attempt to send the import came to.
#[derive(Debug)]
pub enum ImportOutcome {
    /// No meta file is left: nothing to import.
    NothingPending,
    /// The controller took the grants and the files are deleted.
    Imported,
    /// The controller answered with a refusal; the files stay.
    Refused(String),
    /// No answer (the controller or the queue is down), or a file could not
    /// be read or deleted; the files stay.
    Unsettled(anyhow::Error),
}

impl ImportOutcome {
    /// Whether the swarm's keys may be read after this outcome. While a file
    /// is left, an unset key may only mean its grants are not imported yet,
    /// and reading it as the default would undo them.
    #[must_use]
    pub fn read_allowed(&self) -> bool {
        matches!(self, Self::NothingPending | Self::Imported)
    }

    /// Why reading is not allowed, for the caller's log and banner.
    #[must_use]
    pub fn into_error(self) -> Option<anyhow::Error> {
        match self {
            Self::NothingPending | Self::Imported => None,
            Self::Refused(why) => Some(anyhow::anyhow!("the controller refused the import: {why}")),
            Self::Unsettled(e) => Some(e.context("importing the meta repo's permissions")),
        }
    }
}

/// Send the files' grants to swarm-controller while a file is there, and
/// delete both once the controller has answered that it handled them. The
/// next pass sends again after anything but [`ImportOutcome::Imported`]; the
/// controller keeps a key it already has.
pub async fn send_pending(client: &async_nats::Client, hive: &str) -> ImportOutcome {
    match send_at(client, hive, &meta_dir()).await {
        Ok(outcome) => outcome,
        Err(e) => ImportOutcome::Unsettled(e),
    }
}

async fn send_at(client: &async_nats::Client, hive: &str, meta: &Path) -> Result<ImportOutcome> {
    let Some(permissions) = read_grants(meta)? else {
        return Ok(ImportOutcome::NothingPending);
    };
    swarm_queue_client::ensure_connected(client)?;
    let payload = serde_json::to_vec(&Import { permissions })?;
    let reply = tokio::time::timeout(
        IMPORT_REPLY_DEADLINE,
        client.request(agent_permissions::import_subject(hive), payload.into()),
    )
    .await
    .context("the controller did not answer the import")?
    .context("sending the import")?;
    match serde_json::from_slice(&reply.payload).context("decoding the controller's answer")? {
        ImportReply::Imported {
            written,
            kept,
            skipped,
        } => {
            tracing::info!(
                ?written,
                ?kept,
                ?skipped,
                "import: the controller took the meta repo's permissions"
            );
            crate::meta::remove_permission_files()
                .await
                .context("deleting the imported permission files")?;
            Ok(ImportOutcome::Imported)
        }
        ImportReply::Failed { error } => Ok(ImportOutcome::Refused(error)),
    }
}

#[cfg(test)]
mod tests {
    use super::{FileMap, grants, seed_local_at};
    use hive_sh4re::permissions::Permission::{self, *};

    fn file(json: &str) -> FileMap {
        serde_json::from_str(json).expect("decodes")
    }

    /// Both files add up per agent; the empty groups and unknown names drop;
    /// an agent left on the default is not sent.
    #[test]
    fn the_two_files_merge_into_one_list() {
        let caps = file(r#"{"ruth": ["manage_root_agent"], "atlas": ["manage_root_agent"]}"#);
        let groups = file(
            r#"{"ruth": ["messaging", "meta", "inbox", "lifecycle", "execution"],
                "atlas": ["messaging", "web_tools", "forge"],
                "iris": ["messaging", "fly_to_the_moon"],
                "sock": ["lifecycle"]}"#,
        );
        let out = grants(Some(&caps), Some(&groups));
        assert!(!out.contains_key("ruth"), "ruth's seed is her default");
        assert_eq!(out["atlas"], vec![Messaging, WebTools, ManageRootAgent]);
        assert_eq!(out["iris"], vec![Messaging]);
        assert_eq!(out["sock"], Vec::<Permission>::new());
    }

    /// Without a capabilities entry, ruth's existing file means a revoke; with
    /// no capabilities file at all, her default stands.
    #[test]
    fn a_revoked_ruth_stays_revoked() {
        let out = grants(Some(&file("{}")), None);
        assert_eq!(out["ruth"], vec![Messaging, Meta, Inbox, Execution]);

        let out = grants(None, Some(&file(r#"{"atlas": ["messaging"]}"#)));
        assert!(!out.contains_key("ruth"));
        assert_eq!(out["atlas"], vec![Messaging]);
    }

    /// The seed writes once, from the files, and never over a stored read.
    #[test]
    fn the_seed_copies_the_files_only_when_nothing_is_stored() {
        let dir = tempfile::tempdir().expect("tempdir");
        let meta = dir.path();
        let stored = dir.path().join("stored.json");

        seed_local_at(meta, &stored).expect("no file is no seed");
        assert!(!stored.exists());

        std::fs::write(
            meta.join("capabilities.json"),
            r#"{"atlas": ["manage_root_agent"]}"#,
        )
        .expect("seed");
        seed_local_at(meta, &stored).expect("seeded");
        assert!(crate::permissions::holds(&stored, "atlas", ManageRootAgent).expect("read"));
        assert!(!crate::permissions::holds(&stored, "ruth", ManageRootAgent).expect("read"));

        std::fs::write(&stored, "{}").expect("a later read");
        seed_local_at(meta, &stored).expect("left alone");
        assert_eq!(std::fs::read_to_string(&stored).expect("read"), "{}");
    }

    /// The read gate, one row per outcome: only a settled import lets the
    /// swarm's keys be read.
    #[test]
    fn keys_are_read_only_once_the_import_is_settled() {
        use super::ImportOutcome;
        for (outcome, allowed) in [
            (ImportOutcome::NothingPending, true),
            (ImportOutcome::Imported, true),
            (ImportOutcome::Refused("not a hive".to_owned()), false),
            (
                ImportOutcome::Unsettled(anyhow::anyhow!("no responders")),
                false,
            ),
        ] {
            assert_eq!(outcome.read_allowed(), allowed, "{outcome:?}");
            assert_eq!(outcome.into_error().is_none(), allowed);
        }
    }
}