//! Multi-account configuration + the dispatch registry.
//!
//! A single `hive-matrix-daemon` can serve N matrix accounts (one
//! matrix-sdk `Client` each, with its own session/store dir + sync
//! loop). The **hive-internal account** (named `main`) is always
//! present and is the primary: it is synthesized from the per-agent
//! single-account paths (`<state>/matrix-token` +
//! `<state>/matrix-sdk-state`) and the daemon-wide `HIVE_MATRIX_URL`.
//! Any **extra** accounts come from the `HIVE_MATRIX_ACCOUNTS` env var
//! (JSON, written by the nix harness module from
//! `hyperhive.matrixAccounts`) and are appended after `main`.
//!
//! So a single-account agent (no `HIVE_MATRIX_ACCOUNTS`) gets exactly
//! `main` — zero config, same behaviour as before. The **primary** is
//! `main`: it is selected when a tool call omits `account`, so callers
//! never specify one for the hive account.

use std::collections::HashMap;
use std::path::PathBuf;
use std::sync::Arc;

use matrix_sdk::Client;
use serde::Deserialize;

use crate::paths;

/// One declared matrix account. `homeserver` is optional per account
/// (defaults to the daemon-wide `HIVE_MATRIX_URL`) so accounts on the
/// same homeserver need not repeat it.
#[derive(Debug, Clone, Deserialize)]
pub struct AccountCfg {
    /// Logical name the agent uses to address this account
    /// (`account` arg on the MCP tools). Unique within the daemon.
    pub name: String,
    /// Path to the bearer-token file for this account (hive-c0re
    /// writes it; the daemon reads it).
    pub token_file: PathBuf,
    /// Per-account matrix-sdk sqlite store dir (crypto keys + cache).
    pub state_dir: PathBuf,
    /// Homeserver URL; falls back to [`paths::homeserver_url`] when absent.
    #[serde(default)]
    pub homeserver: Option<String>,
}

impl AccountCfg {
    /// Resolve the effective homeserver URL (per-account override or
    /// the daemon-wide default).
    #[must_use]
    pub fn homeserver(&self) -> String {
        self.homeserver
            .clone()
            .unwrap_or_else(paths::homeserver_url)
    }
}

/// Build the account list: the always-present hive-internal `main`
/// account (primary, synthesized from the per-agent single-account
/// paths) followed by any extras declared in `HIVE_MATRIX_ACCOUNTS`.
///
/// With no `HIVE_MATRIX_ACCOUNTS` set this returns just `main`, so a
/// single-account agent is unchanged. When set, the env var carries
/// only the *extra* accounts (the nix `matrixAccounts` option never
/// redeclares the hive account); they are appended after `main`, which
/// stays index 0 = primary.
///
/// # Errors
///
/// Returns an error if `HIVE_MATRIX_ACCOUNTS` is set but is not valid
/// JSON, or if an extra account's name collides with `main` or another
/// extra.
pub fn configured() -> anyhow::Result<Vec<AccountCfg>> {
    // The hive-internal account: always primary, named `main`, built
    // from the legacy single-account paths + the daemon-wide homeserver.
    let hive = AccountCfg {
        name: "main".to_owned(),
        token_file: paths::token_file(),
        state_dir: paths::matrix_state_dir(),
        homeserver: None,
    };
    let Some(raw) = std::env::var_os("HIVE_MATRIX_ACCOUNTS") else {
        return Ok(vec![hive]);
    };
    let extras: Vec<AccountCfg> = serde_json::from_str(&raw.to_string_lossy())
        .map_err(|e| anyhow::anyhow!("parse HIVE_MATRIX_ACCOUNTS as JSON array: {e}"))?;
    let mut accounts = Vec::with_capacity(extras.len() + 1);
    accounts.push(hive);
    accounts.extend(extras);
    let mut seen = std::collections::HashSet::new();
    for a in &accounts {
        if !seen.insert(a.name.as_str()) {
            anyhow::bail!(
                "duplicate matrix account name {:?} (the hive-internal account is named \"main\")",
                a.name
            );
        }
    }
    Ok(accounts)
}

/// Account name → live `Client` map plus the primary-account name used
/// when a request omits `account`. Built once at daemon startup from
/// the accounts that successfully restored a session.
pub struct Registry {
    primary: String,
    by_name: HashMap<String, Arc<Client>>,
}

impl Registry {
    /// Build an empty registry whose primary is `primary`. Clients are
    /// added with [`Registry::insert`] as each account restores.
    #[must_use]
    pub fn new(primary: String) -> Self {
        Self {
            primary,
            by_name: HashMap::new(),
        }
    }

    /// Register a restored client under `name`.
    pub fn insert(&mut self, name: String, client: Client) {
        self.by_name.insert(name, Arc::new(client));
    }

    /// Whether any account restored successfully.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.by_name.is_empty()
    }

    /// Resolve a request's `account` to a client. `None` → the primary
    /// account. Returns a human-readable error (listing known accounts)
    /// when the name is unknown — surfaced to the agent as a tool error.
    ///
    /// # Errors
    ///
    /// Errors when the named account (or the primary, if `None`) has no
    /// live client — e.g. an unknown name, or the primary failed to
    /// restore at startup.
    pub fn resolve(&self, account: Option<&str>) -> Result<&Arc<Client>, String> {
        let name = account.unwrap_or(&self.primary);
        self.by_name.get(name).ok_or_else(|| {
            let mut known: Vec<&str> = self.by_name.keys().map(String::as_str).collect();
            known.sort_unstable();
            format!(
                "unknown matrix account {name:?}; available accounts: [{}]",
                known.join(", ")
            )
        })
    }
}