//! 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.
//!
//! A client that has somewhere better to keep a key passes a [`TokenSeal`], and the
//! token is stored sealed. Android does, with a key in the Keystore (family idea
//! #5105, practice 12); the desktop does not.

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,
    pub last_sync_at: Option<String>,
    /// The linked server's trash-retention window, as it last advertised it. `None`
    /// until a probe or sync has learned it.
    pub server_retention_days: Option<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,
    pub last_sync_at: Option<String>,
}

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,
            last_sync_at: s.last_sync_at.clone(),
        }
    }
}

/// 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, last_sync_at, server_retention_days
           FROM sync_state WHERE id = 1",
        [],
        |row| {
            let cursor: Option<String> = row.get(2)?;
            Ok(SyncState {
                last_sync_at: present(row.get(3)?),
                server_retention_days: row.get(4)?,
                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,
                shares_synced = CASE WHEN ?3 THEN shares_synced ELSE 0 END
          WHERE id = 1",
        params![server_url, device_token, keep_cursor],
    )?;
    if !keep_cursor {
        forget_shared_notes(conn)?;
    }
    Ok(())
}

/// Seals the device token for storage, and opens it again.
///
/// Neither method fails loudly: a client's key store can be briefly unavailable, and
/// a token sealed on another device can never be opened here. `None` says so, and
/// [`set_sealed_link`] and [`open_token`] decide what happens next.
pub trait TokenSeal {
    /// The token sealed for storage, or None when that isn't possible right now.
    fn seal(&self, token: &str) -> Option<String>;
    /// The sealed token opened, or None when this device can't open it.
    fn open(&self, sealed: &str) -> Option<String>;
}

/// Marks a stored token as sealed. A device token is URL-safe base64, which has no
/// colon, so a plain one can't be mistaken for a sealed one.
const SEALED: &str = "sealed:";

/// [`set_link`] for a client that seals its token.
///
/// When sealing fails, the token is stored as it is and [`open_token`] seals it on
/// its next read. Refusing the link instead would leave someone unable to sync
/// over a passing key-store error.
pub fn set_sealed_link(
    conn: &Connection,
    server_url: &str,
    device_token: &str,
    seal: &dyn TokenSeal,
) -> rusqlite::Result<()> {
    let stored = match seal.seal(device_token) {
        Some(sealed) => format!("{SEALED}{sealed}"),
        None => {
            log::warn!("couldn't seal the device token; it is stored as is until the next read");
            device_token.to_string()
        }
    };
    set_link(conn, server_url, &stored)
}

/// The device token the server expects, from the `stored` one.
///
/// - A sealed token is opened. If it won't open, it is dropped, so the app reads as
///   unlinked and asks to sign in again. That is what happens when Android restores
///   the app's files onto another phone, whose Keystore never held the key. The
///   server address and cursor stay, for the sign-in form and the same server.
/// - A plain token, stored before tokens were sealed or when sealing failed, is
///   sealed in place and returned.
pub fn open_token(
    conn: &Connection,
    stored: &str,
    seal: &dyn TokenSeal,
) -> rusqlite::Result<Option<String>> {
    if let Some(sealed) = stored.strip_prefix(SEALED) {
        let token = seal.open(sealed);
        if token.is_none() {
            log::warn!("the stored device token won't open on this device; sign in again");
            store_token(conn, None)?;
        }
        return Ok(token);
    }
    if let Some(sealed) = seal.seal(stored) {
        store_token(conn, Some(&format!("{SEALED}{sealed}")))?;
    }
    Ok(Some(stored.to_string()))
}

/// Replace the stored token alone, leaving the server and cursor as they are.
fn store_token(conn: &Connection, token: Option<&str>) -> rusqlite::Result<()> {
    conn.execute(
        "UPDATE sync_state SET device_token = ?1 WHERE id = 1",
        params![token],
    )?;
    Ok(())
}

/// Drop the notes other people shared with the account this device was linked to.
/// They were only ever here through that link: kept after it ends, they would sit
/// on the board as notes nobody here can edit and nothing would ever update.
fn forget_shared_notes(conn: &Connection) -> rusqlite::Result<()> {
    conn.execute("DELETE FROM notes WHERE permission <> 'owner'", [])?;
    Ok(())
}

/// How much of sharing this device's copy of the feed reflects, kept in
/// `sync_state.shares_synced`. Each level changed what the feed says about notes a
/// device may already hold, below the cursor it already has.
///
/// Shared notes arrive at all (#5175).
pub const SHARES: i64 = 1;
/// A shared note's pin, archive and position are this account's own (#5176). Before,
/// the feed sent the owner's, and a device holding those would keep showing them
/// until something next changed the note.
pub const SHARED_STATE: i64 = 2;

/// Start the change feed over the first time this device pulls at a sharing `level`
/// the server offers, so what it already holds is re-read in that level's terms.
///
/// Returns whether it restarted. Once per level per link: `set_link` to another
/// server and `clear_link` both go back to none.
pub fn begin_shares(conn: &Connection, level: i64) -> rusqlite::Result<bool> {
    let restarted = conn.execute(
        "UPDATE sync_state SET last_cursor = NULL, shares_synced = ?1
          WHERE id = 1 AND shares_synced < ?1",
        params![level],
    )?;
    Ok(restarted > 0)
}

/// 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,
                last_sync_at = NULL, server_retention_days = NULL, shares_synced = 0
          WHERE id = 1",
        [],
    )?;
    forget_shared_notes(conn)
}

/// Remember the linked server's trash-retention window (0 = it never purges).
///
/// Refreshed on every sync rather than only at link time, so changing the setting on
/// the server reaches the desktop's Trash countdown on the next cycle instead of
/// waiting for someone to re-link.
pub fn set_server_retention(conn: &Connection, days: i64) -> rusqlite::Result<()> {
    conn.execute(
        "UPDATE sync_state SET server_retention_days = ?1 WHERE id = 1",
        params![days],
    )?;
    Ok(())
}

/// The retention window in force on THIS device: the linked server's if we know it,
/// otherwise the caller's offline default. A linked device must never enforce or
/// advertise its own window over the server's.
pub fn effective_retention_days(conn: &Connection, offline_default: i64) -> rusqlite::Result<i64> {
    let state = read(conn)?;
    if !state.is_linked() {
        return Ok(offline_default);
    }
    // Linked but the server hasn't told us yet (linked by an older build, or no sync
    // has completed). Fall back to the default rather than claiming "kept forever".
    Ok(state.server_retention_days.unwrap_or(offline_default))
}

/// Stamp a completed sync. The cursor can't stand in for this: it's a revision
/// watermark, and it doesn't move at all when a sync correctly finds nothing new —
/// so "synced a moment ago, no changes" would be indistinguishable from "never
/// synced" without it.
pub fn mark_synced(conn: &Connection, when: &str) -> rusqlite::Result<()> {
    conn.execute(
        "UPDATE sync_state SET last_sync_at = ?1 WHERE id = 1",
        params![when],
    )?;
    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"));
    }

    /// Reverses the token: enough to tell sealed from plain. `broken` stands in for a
    /// key store that is unavailable, or a key this device never held.
    struct Reverse {
        broken: bool,
    }

    impl TokenSeal for Reverse {
        fn seal(&self, token: &str) -> Option<String> {
            (!self.broken).then(|| token.chars().rev().collect())
        }
        fn open(&self, sealed: &str) -> Option<String> {
            (!self.broken).then(|| sealed.chars().rev().collect())
        }
    }

    const WORKING: Reverse = Reverse { broken: false };
    const BROKEN: Reverse = Reverse { broken: true };

    fn stored_token(conn: &Connection) -> Option<String> {
        read(conn).expect("read").device_token
    }

    #[test]
    fn a_sealed_token_is_stored_sealed_and_opens() {
        let conn = db();
        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &WORKING).expect("link");
        assert_eq!(stored_token(&conn).as_deref(), Some("sealed:1-kot"));

        let opened = open_token(&conn, "sealed:1-kot", &WORKING).expect("open");
        assert_eq!(opened.as_deref(), Some("tok-1"));
    }

    #[test]
    fn a_plain_token_is_sealed_on_its_next_read() {
        let conn = db();
        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");

        let opened = open_token(&conn, "tok-1", &WORKING).expect("open");
        assert_eq!(opened.as_deref(), Some("tok-1"));
        assert_eq!(stored_token(&conn).as_deref(), Some("sealed:1-kot"));
    }

    #[test]
    fn a_token_that_cant_be_sealed_is_kept_plain_and_still_works() {
        let conn = db();
        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &BROKEN).expect("link");
        assert_eq!(stored_token(&conn).as_deref(), Some("tok-1"));
        let opened = open_token(&conn, "tok-1", &BROKEN).expect("open");
        assert_eq!(opened.as_deref(), Some("tok-1"));
    }

    #[test]
    fn a_token_that_wont_open_here_is_dropped_but_the_server_is_kept() {
        let conn = db();
        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &WORKING).expect("link");

        let opened = open_token(&conn, "sealed:1-kot", &BROKEN).expect("open");
        assert_eq!(opened, None);
        let state = read(&conn).expect("read");
        assert!(!state.is_linked());
        assert_eq!(state.device_token, None);
        assert_eq!(
            state.server_url.as_deref(),
            Some("https://notes.example.com")
        );
    }

    #[test]
    fn an_unlinked_device_uses_its_own_retention_window() {
        let conn = db();
        assert_eq!(effective_retention_days(&conn, 30).expect("read"), 30);
    }

    #[test]
    fn a_linked_device_adopts_the_servers_window() {
        // Including 0 — a server that keeps trash forever must not have this device
        // showing a 30-day countdown that will never fire.
        let conn = db();
        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");
        set_server_retention(&conn, 0).expect("retention");
        assert_eq!(effective_retention_days(&conn, 30).expect("read"), 0);
        set_server_retention(&conn, 90).expect("retention");
        assert_eq!(effective_retention_days(&conn, 30).expect("read"), 90);
    }

    #[test]
    fn a_linked_device_that_hasnt_heard_yet_falls_back() {
        // Linked by an older build, or no cycle has completed. The default is a
        // safer guess than "forever", which would promise a note is being kept.
        let conn = db();
        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");
        assert_eq!(effective_retention_days(&conn, 30).expect("read"), 30);
    }

    #[test]
    fn unlinking_forgets_the_servers_window() {
        let conn = db();
        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");
        set_server_retention(&conn, 90).expect("retention");
        clear_link(&conn).expect("unlink");
        assert_eq!(read(&conn).expect("read").server_retention_days, None);
        assert_eq!(effective_retention_days(&conn, 30).expect("read"), 30);
    }

    #[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());
    }

    fn seed(conn: &Connection, id: &str, permission: &str) {
        conn.execute(
            "INSERT INTO notes (id, body, created_at, updated_at, permission)
                  VALUES (?1, 'x', '2026-01-01', '2026-01-01', ?2)",
            params![id, permission],
        )
        .expect("seed");
    }

    fn note_ids(conn: &Connection) -> Vec<String> {
        let mut stmt = conn.prepare("SELECT id FROM notes ORDER BY id").unwrap();
        let rows = stmt.query_map([], |r| r.get(0)).unwrap();
        rows.collect::<rusqlite::Result<_>>().unwrap()
    }

    #[test]
    fn unlinking_drops_the_notes_others_shared_and_keeps_our_own() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        seed(&conn, "mine", "owner");
        seed(&conn, "theirs", "view");
        seed(&conn, "editable", "edit");
        // Re-linking the same server keeps everything.
        set_link(&conn, "https://a.example.com", "tok-2").expect("relink");
        assert_eq!(note_ids(&conn), ["editable", "mine", "theirs"]);
        clear_link(&conn).expect("unlink");
        assert_eq!(note_ids(&conn), ["mine"]);
    }

    #[test]
    fn the_first_pull_with_shares_starts_over_once_per_link() {
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        set_cursor(&conn, 500).expect("cursor");
        assert!(begin_shares(&conn, SHARES).expect("begin"));
        assert_eq!(read(&conn).expect("read").last_cursor, 0);
        set_cursor(&conn, 600).expect("cursor");
        assert!(
            !begin_shares(&conn, SHARES).expect("again"),
            "only the first time"
        );
        assert_eq!(read(&conn).expect("read").last_cursor, 600);
        // A server offering more of sharing starts it over once more, and only once.
        assert!(begin_shares(&conn, SHARED_STATE).expect("a newer server"));
        assert_eq!(read(&conn).expect("read").last_cursor, 0);
        set_cursor(&conn, 700).expect("cursor");
        assert!(!begin_shares(&conn, SHARED_STATE).expect("again"));
        assert!(!begin_shares(&conn, SHARES).expect("an older level"));
        assert_eq!(read(&conn).expect("read").last_cursor, 700);
        // Another server is a fresh start, shares included.
        set_link(&conn, "https://b.example.com", "tok-2").expect("relink");
        assert!(begin_shares(&conn, SHARES).expect("new server"));
    }

    #[test]
    fn unlink_clears_the_last_sync_stamp() {
        // Otherwise a freshly-linked server would claim it synced at a time that
        // belonged to a different one.
        let conn = db();
        set_link(&conn, "https://a.example.com", "tok-1").expect("link");
        mark_synced(&conn, "2026-07-26T04:00:00.000Z").expect("stamp");
        assert!(read(&conn).expect("read").last_sync_at.is_some());
        clear_link(&conn).expect("unlink");
        assert!(read(&conn).expect("read").last_sync_at.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}");
    }
}