//! SQLite-backed [`Store`] implementation.
//!
//! `LocalStore` opens a SQLite file directly. The exclusive-lock handoff of
//! tech-spec §3.1 is layered on by `hephd` when it owns the file; the store
//! itself stays a thin, synchronous SQLite wrapper so it is trivially testable
//! against an in-memory database.
//!
//! The query logic lives in focused submodules ([`nodes`], [`tasks`], [`links`])
//! as free functions over a `&Connection`; the [`Store`] impl here is a thin
//! delegating layer so a transaction can span several of them.

mod links;
mod log;
mod migrations;
mod nodes;
mod tasks;

pub use migrations::latest_version;

use std::path::Path;

use rusqlite::{Connection, OptionalExtension};
use ulid::Ulid;

use crate::clock::Clock;
use crate::error::Result;
use crate::model::{Attention, Link, LinkType, NewNode, NewTask, Node, Task, TaskState};
use crate::ranking::RankedTask;
use crate::store::Store;

/// A SQLite file (or in-memory database) opened directly as a backend.
pub struct LocalStore {
    conn: Connection,
    owner_id: String,
    clock: Box<dyn Clock>,
}

impl LocalStore {
    /// Open (creating if needed) a SQLite database at `path`.
    pub fn open(path: impl AsRef<Path>, clock: Box<dyn Clock>) -> Result<Self> {
        let conn = Connection::open(path)?;
        Self::init(conn, clock)
    }

    /// Open a throwaway in-memory database — for tests.
    pub fn open_in_memory(clock: Box<dyn Clock>) -> Result<Self> {
        let conn = Connection::open_in_memory()?;
        Self::init(conn, clock)
    }

    fn init(conn: Connection, clock: Box<dyn Clock>) -> Result<Self> {
        conn.execute_batch("PRAGMA foreign_keys = ON;")?;
        migrations::migrate(&conn)?;
        let owner_id = ensure_local_user(&conn, clock.as_ref())?;
        Ok(LocalStore {
            conn,
            owner_id,
            clock,
        })
    }

    /// The id of the user whose data this store reads/writes.
    ///
    /// For a local-only instance this is the single generated local user
    /// (`oidc_sub = NULL`, tech-spec §13).
    pub fn owner_id(&self) -> &str {
        &self.owner_id
    }
}

/// A fresh ULID, as a string id.
pub(crate) fn new_id() -> String {
    Ulid::new().to_string()
}

/// Placeholder HLC string until the real hybrid logical clock lands (§12).
/// Zero-padded epoch ms keeps it lexically sortable in the meantime.
pub(crate) fn hlc_for(now_ms: i64) -> String {
    format!("{now_ms:016}")
}

/// Ensure a single local user exists, returning its id.
fn ensure_local_user(conn: &Connection, clock: &dyn Clock) -> Result<String> {
    if let Some(id) = conn
        .query_row(
            "SELECT id FROM users ORDER BY created_at LIMIT 1",
            [],
            |r| r.get::<_, String>(0),
        )
        .optional()?
    {
        return Ok(id);
    }
    let id = new_id();
    conn.execute(
        "INSERT INTO users (id, oidc_sub, name, created_at) VALUES (?1, NULL, 'local', ?2)",
        (&id, clock.now_ms()),
    )?;
    Ok(id)
}

impl Store for LocalStore {
    fn create_node(&mut self, input: NewNode) -> Result<Node> {
        let now = self.clock.now_ms();
        nodes::create(&self.conn, &self.owner_id, now, input)
    }

    fn get_node(&self, id: &str) -> Result<Option<Node>> {
        nodes::get(&self.conn, id)
    }

    fn update_node(
        &mut self,
        id: &str,
        title: Option<String>,
        body: Option<String>,
    ) -> Result<Node> {
        let now = self.clock.now_ms();
        nodes::update(&mut self.conn, &self.owner_id, now, id, title, body)
    }

    fn create_task(&mut self, input: NewTask) -> Result<Task> {
        let now = self.clock.now_ms();
        tasks::create(&mut self.conn, &self.owner_id, now, input)
    }

    fn get_task(&self, node_id: &str) -> Result<Option<Task>> {
        tasks::get(&self.conn, node_id)
    }

    fn set_task_state(&mut self, node_id: &str, state: TaskState) -> Result<Task> {
        let now = self.clock.now_ms();
        tasks::set_state(&mut self.conn, &self.owner_id, now, node_id, state)
    }

    fn skip_recurrence(&mut self, node_id: &str) -> Result<Task> {
        let now = self.clock.now_ms();
        tasks::skip(&self.conn, now, node_id)
    }

    fn set_task_attention(&mut self, node_id: &str, attention: Attention) -> Result<Task> {
        let now = self.clock.now_ms();
        tasks::set_attention(&self.conn, now, node_id, attention)
    }

    fn next(&self, scope: Option<&str>, limit: usize) -> Result<Vec<RankedTask>> {
        let now = self.clock.now_ms();
        tasks::next(&self.conn, &self.owner_id, now, scope, limit)
    }

    fn add_link(&mut self, src_id: &str, dst_id: &str, link_type: LinkType) -> Result<Link> {
        let now = self.clock.now_ms();
        links::add(&self.conn, now, src_id, dst_id, link_type)
    }

    fn outgoing_links(&self, id: &str) -> Result<Vec<Link>> {
        links::outgoing(&self.conn, id)
    }

    fn backlinks(&self, id: &str) -> Result<Vec<Link>> {
        links::backlinks(&self.conn, id)
    }

    fn log_append(&mut self, task_id: &str, text: &str) -> Result<()> {
        let now = self.clock.now_ms();
        let tx = self.conn.transaction()?;
        log::append(&tx, &self.owner_id, now, task_id, text)?;
        tx.commit()?;
        Ok(())
    }

    fn log_tail(&self, task_id: &str, n: usize) -> Result<Vec<String>> {
        log::tail(&self.conn, task_id, n)
    }
}

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

    fn store_at(now_ms: i64) -> LocalStore {
        LocalStore::open_in_memory(Box::new(FixedClock(now_ms))).expect("open in-memory store")
    }

    #[test]
    fn migrations_bring_schema_to_latest() {
        let store = store_at(0);
        let v: i64 = store
            .conn
            .query_row("PRAGMA user_version", [], |r| r.get(0))
            .unwrap();
        assert_eq!(v, latest_version());
    }

    #[test]
    fn opening_twice_is_idempotent_for_the_local_user() {
        let conn = Connection::open_in_memory().unwrap();
        conn.execute_batch("PRAGMA foreign_keys = ON;").unwrap();
        migrations::migrate(&conn).unwrap();
        let a = ensure_local_user(&conn, &FixedClock(1)).unwrap();
        let b = ensure_local_user(&conn, &FixedClock(2)).unwrap();
        assert_eq!(a, b);
    }
}