//! The link record: which server this app is paired with, the device token that
//! authenticates to it, and how far it has consumed that server's change feed.
//!
//! One row, enforced by `CHECK (id = 1)` and seeded during migration, so every
//! operation here is an UPDATE — there is no create-or-missing case to handle.
//!
//! The token lives in the app-data SQLite file rather than an OS keyring on purpose:
//! the `keyring` crate needs libsecret/DBus on Linux, which adds a C dependency to a
//! binary that has to cross-compile, and fails outright on headless or minimal-WM
//! setups. Protecting the database file is the portable trade.

use rusqlite::{params, Connection};
use serde::Serialize;

/// The full link record, token included. Internal to the Rust side.
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct SyncState {
    pub server_url: Option<String>,
    pub device_token: Option<String>,
    pub last_cursor: i64,
}

impl SyncState {
    /// Linked means BOTH a server and a credential for it. Either one alone is a
    /// half-written link that nothing can act on, so it must not read as linked.
    pub fn is_linked(&self) -> bool {
        self.server_url.is_some() && self.device_token.is_some()
    }
}

/// What the UI is allowed to see.
///
/// Deliberately has no `device_token` field: this crosses into the webview, and a
/// long-lived bearer token has no business being reachable from page scripts.
#[derive(Debug, Clone, Serialize, PartialEq, Eq)]
pub struct Status {
    pub linked: bool,
    pub server_url: Option<String>,
    pub last_cursor: i64,
}

impl From<&SyncState> for Status {
    fn from(s: &SyncState) -> Self {
        Status {
            linked: s.is_linked(),
            server_url: s.server_url.clone(),
            last_cursor: s.last_cursor,
        }
    }
}

/// Treat a blank string as absent, so a half-cleared row can't masquerade as linked.
fn present(value: Option<String>) -> Option<String> {
    value.filter(|s| !s.trim().is_empty())
}

pub fn read(conn: &Connection) -> rusqlite::Result<SyncState> {
    conn.query_row(
        "SELECT server_url, device_token, last_cursor FROM sync_state WHERE id = 1",
        [],
        |row| {
            let cursor: Option<String> = row.get(2)?;
            Ok(SyncState {
                server_url: present(row.get(0)?),
                device_token: present(row.get(1)?),
                // Stored TEXT (schema) but used as an integer watermark. Absent or
                // unparseable means "start from the beginning" — always the safe
                // reading, because a redundant full sync costs time, never data,
                // whereas a too-high cursor silently skips changes.
                last_cursor: cursor.and_then(|c| c.trim().parse().ok()).unwrap_or(0),
            })
        },
    )
}

/// Record a link.
///
/// Resets the change-feed cursor whenever the server differs from the one previously
/// linked. A cursor is only meaningful against the server that issued it; carrying
/// one across would silently skip every change on the new server below that
/// watermark — data loss that looks like a successful sync. Re-linking the SAME
/// server (after a token refresh, say) keeps the cursor, so a routine re-auth doesn't
/// force a full re-download.
pub fn set_link(conn: &Connection, server_url: &str, device_token: &str) -> rusqlite::Result<()> {
    let keep_cursor = read(conn)?.server_url.as_deref() == Some(server_url);
    conn.execute(
        "UPDATE sync_state
            SET server_url   = ?1,
                device_token = ?2,
                last_cursor  = CASE WHEN ?3 THEN last_cursor ELSE NULL END
          WHERE id = 1",
        params![server_url, device_token, keep_cursor],
    )?;
    Ok(())
}

/// Forget the server entirely.
///
/// Clears the cursor as well as the credentials: a cursor left behind would, on the
/// next link, be interpreted against a server that never issued it.
pub fn clear_link(conn: &Connection) -> rusqlite::Result<()> {
    conn.execute(
        "UPDATE sync_state
            SET server_url = NULL, device_token = NULL, last_cursor = NULL
          WHERE id = 1",
        [],
    )?;
    Ok(())
}

/// Advance the consumed-change watermark. Called by the pull loop (M10.7b) only
/// after a page has been fully applied.
pub fn set_cursor(conn: &Connection, cursor: i64) -> rusqlite::Result<()> {
    conn.execute(
        "UPDATE sync_state SET last_cursor = ?1 WHERE id = 1",
        params![cursor.to_string()],
    )?;
    Ok(())
}

pub fn status(conn: &Connection) -> rusqlite::Result<Status> {
    Ok(Status::from(&read(conn)?))
}

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

    fn db() -> Connection {
        let conn = Connection::open_in_memory().expect("in-memory db");
        schema::migrate(&conn).expect("migrate");
        conn
    }

    #[test]
    fn fresh_store_is_unlinked() {
        let conn = db();
        let state = read(&conn).expect("read");
        assert_eq!(state, SyncState::default());
        assert!(!state.is_linked());
        assert_eq!(state.last_cursor, 0);
    }

    #[test]
    fn link_round_trips() {
        let conn = db();
        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");
        let state = read(&conn).expect("read");
        assert!(state.is_linked());
        assert_eq!(
            state.server_url.as_deref(),
            Some("https://notes.example.com")
        );
        assert_eq!(state.device_token.as_deref(), Some("tok-1"));
    }

    #[test]
    fn relinking_the_same_server_keeps_the_cursor() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        set_cursor(&conn, 4242).expect("cursor");
        // e.g. the token was revoked and the user re-authenticated.
        set_link(&conn, "https://a.example.com", "tok-2").expect("relink");
        let state = read(&conn).expect("read");
        assert_eq!(
            state.last_cursor, 4242,
            "a re-auth shouldn't force a full re-sync"
        );
        assert_eq!(state.device_token.as_deref(), Some("tok-2"));
    }

    #[test]
    fn linking_a_different_server_resets_the_cursor() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        set_cursor(&conn, 4242).expect("cursor");
        set_link(&conn, "https://b.example.com", "tok-2").expect("relink");
        assert_eq!(
            read(&conn).expect("read").last_cursor,
            0,
            "a cursor from another server would skip everything below it"
        );
    }

    #[test]
    fn unlink_clears_the_cursor_too() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        set_cursor(&conn, 99).expect("cursor");
        clear_link(&conn).expect("unlink");
        let state = read(&conn).expect("read");
        assert!(!state.is_linked());
        assert_eq!(state.last_cursor, 0);
        assert!(state.server_url.is_none());
        assert!(state.device_token.is_none());
    }

    #[test]
    fn half_written_link_is_not_linked() {
        let conn = db();
        conn.execute(
            "UPDATE sync_state SET server_url = 'https://a.example.com' WHERE id = 1",
            [],
        )
        .expect("partial write");
        assert!(!read(&conn).expect("read").is_linked());
    }

    #[test]
    fn blank_strings_count_as_absent() {
        let conn = db();
        conn.execute(
            "UPDATE sync_state SET server_url = '  ', device_token = '' WHERE id = 1",
            [],
        )
        .expect("blank write");
        let state = read(&conn).expect("read");
        assert!(!state.is_linked());
        assert!(state.server_url.is_none());
    }

    #[test]
    fn unparseable_cursor_falls_back_to_a_full_sync() {
        let conn = db();
        conn.execute(
            "UPDATE sync_state SET last_cursor = 'garbage' WHERE id = 1",
            [],
        )
        .expect("bad cursor");
        assert_eq!(read(&conn).expect("read").last_cursor, 0);
    }

    #[test]
    fn status_never_carries_the_token() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "super-secret").expect("link");
        let json = serde_json::to_string(&status(&conn).expect("status")).expect("serialize");
        assert!(
            !json.contains("super-secret"),
            "token leaked to the webview: {json}"
        );
        assert!(json.contains("\"linked\":true"), "got {json}");
    }
}