ursa-sql 0.6.0

//! Statements in a session with a `.ursa` database.
//!
//! The engine's [`Database`] keeps the catalog file: the statements that
//! defined each object, in replay order. This module decides what a statement
//! does to that list, and replays it when a database is opened.
//!
//! - `CREATE VIEW`, `CREATE EXTERNAL TABLE` and `CREATE PROPERTY GRAPH` add
//!   their statement once they succeed. An object already in the catalog
//!   (`CREATE OR REPLACE`) has its statement replaced in place, except that
//!   with `IF NOT EXISTS` it keeps its statement.
//! - `DROP VIEW`, `DROP TABLE` and `DROP PROPERTY GRAPH` remove the object's
//!   statement.
//! - Tables with data (`CREATE TABLE`, `INSERT` and other DML) are refused:
//!   version 1 of the file does not store rows. So is any other DDL
//!   (`CREATE SCHEMA`, `CREATE FUNCTION`, `ALTER …`), which the file could not
//!   replay.
//! - `TEMPORARY` views and external tables run and are not stored.
//! - In a read-only session, every statement that defines or drops anything
//!   is refused.
//!
//! A statement is stored as its `Display` form when that parses back to the
//! same statement, and otherwise as the text the user wrote (DataFusion's
//! `Display` for `CREATE EXTERNAL TABLE` leaves out columns and options).
//!
//! **Paths.** A relative path resolves against the current directory when a
//! statement runs, as in DuckDB. Before a definition is stored, each local
//! file path in it (see [`crate::paths`]) is rewritten relative to the
//! database's directory, or made absolute when it is outside that directory;
//! URLs are kept. In the stored-as-written case the paths are replaced in the
//! text token by token, and the statement is refused if the result does not
//! parse back to the rewritten statement. Replay resolves each stored relative
//! path against the database's directory, so the catalog finds the same files
//! from any directory, and a database moved with its data still does. (M3a
//! stored paths as written and resolved them against the database's
//! directory, so its files replay unchanged.)
//!
//! Views and tables share one namespace, keyed by their name resolved against
//! the default catalog and schema; graphs have their own.

use std::path::Path;
use std::sync::Arc;

use datafusion::dataframe::DataFrame;
use datafusion::error::{DataFusionError, Result};
use datafusion::prelude::SessionContext;
use datafusion::sql::parser::Statement as DFStatement;
use datafusion::sql::planner::object_name_to_table_reference;
use datafusion::sql::sqlparser::ast::{ObjectName, ObjectType, Statement as SQLStatement};
use ursa_engine::database::{self as db, Database, OpenOptions};
use ursa_engine::graph;

use crate::parser::{Attach, UrsaStatement};
use crate::{graph_ddl, parse_sql_for, paths, run};

/// What a statement does to the catalog.
#[derive(Debug)]
enum Effect {
    /// Nothing: a query, `COPY`, `SET`, `SHOW`, `EXPLAIN`, `DESCRIBE`.
    None,
    /// Defines an object (added to, or replacing, its catalog entry).
    Define { key: Key, if_not_exists: bool },
    /// Drops objects (removing their catalog entries).
    Drop { keys: Vec<Key> },
    /// Defines or drops a session-only object (`TEMPORARY`): not stored.
    Session,
    /// Not allowed in a session with a database: the message says why.
    Refused(String),
}

/// An object in the catalog.
#[derive(Debug, Clone, PartialEq, Eq)]
enum Key {
    /// A view or table, by its fully resolved name.
    Table(String),
    /// A graph, by name.
    Graph(String),
}

/// Open a new session on the database at `path`: open the file (creating it
/// unless read-only), then replay its catalog.
pub async fn open_session(path: impl AsRef<Path>, options: &OpenOptions) -> Result<SessionContext> {
    let ctx = ursa_engine::new_session();
    open_into(&ctx, path.as_ref(), options).await?;
    Ok(ctx)
}

/// Open the database at `path` for `ctx` and replay its catalog.
async fn open_into(ctx: &SessionContext, path: &Path, options: &OpenOptions) -> Result<()> {
    let path = path.to_path_buf();
    let options = options.clone();
    // Opening may wait for another process's lock.
    let database = ursa_engine::run_blocking(move || Database::open(path, &options))
        .await
        .map_err(|e| DataFusionError::External(Box::new(e)))??;
    let database = Arc::new(database);
    db::slot(&ctx.state()).set(Arc::clone(&database))?;
    replay(ctx, &database).await
}

/// Run the catalog's statements on `ctx`, in order. A statement that fails is
/// retried after the others, in case an edit of the file put it before what it
/// depends on; the first one that still fails is the error.
async fn replay(ctx: &SessionContext, database: &Database) -> Result<()> {
    let mut pending: Vec<(usize, String)> = database.statements().into_iter().enumerate().collect();
    while !pending.is_empty() {
        let mut failed = Vec::new();
        let before = pending.len();
        for (index, sql) in pending {
            if let Err(e) = replay_one(ctx, database, &sql).await {
                failed.push((index, sql, e));
            }
        }
        if failed.len() == before {
            let (index, sql, err) = failed.swap_remove(0);
            return Err(DataFusionError::Execution(format!(
                "cannot open {}: statement {} of its catalog failed: {}\n  the statement: {sql}",
                database.name(),
                index + 1,
                ursa_engine::user_message(&err)
            )));
        }
        pending = failed.into_iter().map(|(i, sql, _)| (i, sql)).collect();
    }
    Ok(())
}

/// Run one stored statement, its relative paths resolved against the
/// database's directory, wherever the process runs.
async fn replay_one(ctx: &SessionContext, database: &Database, sql: &str) -> Result<()> {
    let mut statements = parse_sql_for(ctx, sql)?;
    if statements.len() != 1 {
        return Err(DataFusionError::Plan(
            "a catalog entry must be exactly one statement".into(),
        ));
    }
    let mut statement = statements.remove(0);
    paths::rewrite_locations(ctx, &mut statement, |location| {
        database.replayed_location(location)
    });
    if !matches!(effect(ctx, &statement)?, Effect::Define { .. }) {
        return Err(DataFusionError::Plan(format!(
            "a catalog entry must define a view, an external table or a graph, not run {}",
            statement.kind()
        )));
    }
    run(ctx, statement).await.map(|_| ())
}

/// `ATTACH 'club.ursa'` in a session without a database.
pub(crate) async fn attach(ctx: &SessionContext, attach: Attach) -> Result<DataFrame> {
    if let Some(alias) = &attach.alias {
        return Err(DataFusionError::NotImplemented(format!(
            "ATTACH … AS {alias} is not supported yet: a session has one database in this \
             version of ursa; use ATTACH '{}' without AS",
            attach.path
        )));
    }
    if defines_anything(ctx)? {
        return Err(DataFusionError::Plan(format!(
            "ATTACH must come before anything is defined: this session already has tables, \
             views or graphs, which would not be in '{}'. Run ATTACH first, or open the \
             database with: ursa {}",
            attach.path, attach.path
        )));
    }
    open_into(ctx, Path::new(&attach.path), &OpenOptions::default()).await?;
    graph_ddl::empty(ctx)
}

/// Whether `ctx` has any graph, table or view (outside `information_schema`).
fn defines_anything(ctx: &SessionContext) -> Result<bool> {
    if !graph::registry_of(ctx).names().is_empty() {
        return Ok(true);
    }
    for catalog_name in ctx.catalog_names() {
        let Some(catalog) = ctx.catalog(&catalog_name) else {
            continue;
        };
        for schema_name in catalog.schema_names() {
            if schema_name == "information_schema" {
                continue;
            }
            if let Some(schema) = catalog.schema(&schema_name) {
                if !schema.table_names().is_empty() {
                    return Ok(true);
                }
            }
        }
    }
    Ok(false)
}

/// Run `statement` in a session with `database`, keeping the catalog file in
/// step. `text` is the statement as written, if known.
pub(crate) async fn execute(
    ctx: &SessionContext,
    database: &Database,
    statement: UrsaStatement,
    text: Option<&str>,
) -> Result<DataFrame> {
    if let UrsaStatement::Attach(_) = statement {
        return Err(DataFusionError::Plan(format!(
            "{} is already open, and a session has one database in this version of ursa",
            database.name()
        )));
    }
    let effect = effect(ctx, &statement)?;
    if database.is_read_only() && !matches!(effect, Effect::None) {
        return Err(DataFusionError::Plan(format!(
            "{} is open read-only (--readonly), so {} cannot change it",
            database.name(),
            leading_words(&statement)
        )));
    }
    match effect {
        Effect::None | Effect::Session => run(ctx, statement).await,
        Effect::Refused(message) => Err(DataFusionError::Plan(message)),
        Effect::Define {
            key, if_not_exists, ..
        } => {
            let stored = stored_text(ctx, database, &statement, text)?;
            let frame = run(ctx, statement).await?;
            let mut statements = database.statements();
            match position(ctx, &statements, &key) {
                Some(_) if if_not_exists => {}
                Some(i) => statements[i] = stored,
                None => statements.push(stored),
            }
            database.save(statements)?;
            Ok(frame)
        }
        Effect::Drop { keys } => {
            let frame = run(ctx, statement).await?;
            let statements = database
                .statements()
                .into_iter()
                .filter(|s| !stored_key(ctx, s).is_some_and(|k| keys.contains(&k)))
                .collect();
            database.save(statements)?;
            Ok(frame)
        }
    }
}

/// Where the object `key` is defined in `statements`.
fn position(ctx: &SessionContext, statements: &[String], key: &Key) -> Option<usize> {
    statements
        .iter()
        .position(|s| stored_key(ctx, s).as_ref() == Some(key))
}

/// The object a stored statement defines.
fn stored_key(ctx: &SessionContext, sql: &str) -> Option<Key> {
    let statements = parse_sql_for(ctx, sql).ok()?;
    match <[UrsaStatement; 1]>::try_from(statements) {
        Ok([statement]) => match effect(ctx, &statement).ok()? {
            Effect::Define { key, .. } => Some(key),
            _ => None,
        },
        Err(_) => None,
    }
}

/// The text to store for `statement`, with its local file paths rewritten
/// for the catalog ([`Database::stored_location`]): relative to the
/// database's directory, or absolute outside it. That is the rewritten
/// statement's `Display` form if it parses back to the same statement; else
/// the text as written, with the paths replaced token by token
/// ([`paths::rewrite_text`]), or an error if that cannot be done exactly.
fn stored_text(
    ctx: &SessionContext,
    database: &Database,
    statement: &UrsaStatement,
    text: Option<&str>,
) -> Result<String> {
    let cwd = std::env::current_dir().map_err(|e| {
        DataFusionError::Execution(format!(
            "cannot store this {} in {}: cannot read the current directory: {e}",
            leading_words(statement),
            database.name()
        ))
    })?;
    let mut rewritten = statement.clone();
    let replacements = paths::rewrite_locations(ctx, &mut rewritten, |location| {
        database.stored_location(location, &cwd)
    });
    let display = rewritten.to_string();
    let round_trips = parse_sql_for(ctx, &display)
        .map(|parsed| parsed.len() == 1 && parsed[0] == rewritten)
        .unwrap_or(false);
    if round_trips {
        return Ok(display);
    }
    let Some(text) = text else {
        return Err(DataFusionError::Plan(format!(
            "cannot store this {} in the database without the text it was written as; run it \
             with ursa_sql::execute_with_text",
            leading_words(statement)
        )));
    };
    if replacements.is_empty() {
        return Ok(text.to_string());
    }
    paths::rewrite_text(ctx, text, &replacements, &rewritten).ok_or_else(|| {
        let (old, new) = &replacements[0];
        DataFusionError::Plan(format!(
            "cannot store this {} in {}: its path '{old}' is stored as '{new}' (relative to the \
             database's directory, {}), and the statement as written could not be rewritten \
             exactly; write each path as stored, from the database's directory",
            leading_words(statement),
            database.name(),
            database.dir().display()
        ))
    })
}

/// What `statement` does to the catalog.
fn effect(ctx: &SessionContext, statement: &UrsaStatement) -> Result<Effect> {
    Ok(match statement {
        UrsaStatement::CreatePropertyGraph(g) => Effect::Define {
            key: Key::Graph(graph_ddl::graph_name(g.name.clone(), normalizes(ctx))?),
            if_not_exists: g.if_not_exists,
        },
        UrsaStatement::DropPropertyGraph(g) => Effect::Drop {
            keys: vec![Key::Graph(graph_ddl::graph_name(
                g.name.clone(),
                normalizes(ctx),
            )?)],
        },
        UrsaStatement::DescribeGraph(_) | UrsaStatement::ShowGraphs | UrsaStatement::Attach(_) => {
            Effect::None
        }
        UrsaStatement::DataFusion(statement) => match statement.as_ref() {
            DFStatement::CreateExternalTable(t) if t.temporary => Effect::Session,
            DFStatement::CreateExternalTable(t) => Effect::Define {
                key: table_key(ctx, &t.name)?,
                if_not_exists: t.if_not_exists,
            },
            DFStatement::Statement(s) => sql_effect(ctx, s, statement)?,
            DFStatement::CopyTo(_) | DFStatement::Explain(_) | DFStatement::Reset(_) => {
                Effect::None
            }
        },
    })
}

fn sql_effect(ctx: &SessionContext, s: &SQLStatement, whole: &DFStatement) -> Result<Effect> {
    Ok(match s {
        SQLStatement::CreateView(v) if v.temporary => Effect::Session,
        SQLStatement::CreateView(v) if v.materialized => Effect::Refused(not_stored(whole)),
        SQLStatement::CreateView(v) => Effect::Define {
            key: table_key(ctx, &v.name)?,
            if_not_exists: v.if_not_exists,
        },
        SQLStatement::CreateTable(t) if t.temporary => Effect::Session,
        SQLStatement::CreateTable(t) => Effect::Refused(tables_with_data(
            if t.query.is_some() {
                "CREATE TABLE … AS"
            } else {
                "CREATE TABLE"
            },
            Some(&t.name),
        )),
        SQLStatement::Insert(_) => Effect::Refused(tables_with_data("INSERT", None)),
        SQLStatement::Update(_)
        | SQLStatement::Delete(_)
        | SQLStatement::Truncate(_)
        | SQLStatement::Merge(_) => {
            Effect::Refused(tables_with_data(&leading_words_df(whole), None))
        }
        SQLStatement::Drop {
            object_type: ObjectType::Table | ObjectType::View,
            names,
            ..
        } => Effect::Drop {
            keys: names
                .iter()
                .map(|n| table_key(ctx, n))
                .collect::<Result<_>>()?,
        },
        _ => {
            let first = whole.to_string();
            let first = first
                .split_whitespace()
                .next()
                .unwrap_or_default()
                .to_ascii_uppercase();
            if matches!(first.as_str(), "CREATE" | "DROP" | "ALTER") {
                Effect::Refused(not_stored(whole))
            } else {
                Effect::None
            }
        }
    })
}

/// The refusal for a statement that would make or change a table with data.
fn tables_with_data(kind: &str, name: Option<&ObjectName>) -> String {
    let name = name.map_or_else(|| "name".to_string(), ToString::to_string);
    format!(
        "{kind} is not supported in a database file: version 1 of the .ursa file stores views, \
         external tables and graphs, not tables with data. Define a view instead (CREATE VIEW \
         {name} AS SELECT …), or write the rows to a file with COPY (SELECT …) TO \
         '{name}.parquet' and define a view over it (CREATE VIEW {name} AS SELECT * FROM \
         '{name}.parquet')"
    )
}

/// The refusal for other DDL, which the catalog file could not replay.
fn not_stored(statement: &DFStatement) -> String {
    format!(
        "{} is not supported in a database file: version 1 of the .ursa file stores views, \
         external tables and graphs only; run it in a session without a database",
        leading_words_df(statement)
    )
}

/// The statement's first two words (`CREATE VIEW`, `DROP TABLE`), as messages
/// name it.
fn leading_words(statement: &UrsaStatement) -> String {
    match statement {
        UrsaStatement::DataFusion(s) => leading_words_df(s),
        other => other.kind().to_string(),
    }
}

fn leading_words_df(statement: &DFStatement) -> String {
    let text = statement.to_string();
    let mut words = text.split_whitespace().map(str::to_ascii_uppercase);
    let first = words.next().unwrap_or_default();
    let mut kind = first.clone();
    // `CREATE OR REPLACE VIEW` is named `CREATE VIEW`.
    for word in words {
        if matches!(
            word.as_str(),
            "OR" | "REPLACE" | "TEMPORARY" | "EXTERNAL" | "MATERIALIZED"
        ) && first == "CREATE"
        {
            if word == "EXTERNAL" || word == "MATERIALIZED" {
                kind.push(' ');
                kind.push_str(&word);
            }
            continue;
        }
        if matches!(first.as_str(), "CREATE" | "DROP" | "ALTER") {
            kind.push(' ');
            kind.push_str(&word);
        }
        break;
    }
    kind
}

/// A view or table's key: its name resolved against the default catalog and
/// schema.
fn table_key(ctx: &SessionContext, name: &ObjectName) -> Result<Key> {
    let state = ctx.state();
    let options = &state.config().options().catalog;
    let reference = object_name_to_table_reference(name.clone(), normalizes(ctx))?;
    Ok(Key::Table(
        reference
            .resolve(&options.default_catalog, &options.default_schema)
            .to_string(),
    ))
}

fn normalizes(ctx: &SessionContext) -> bool {
    graph_ddl::normalizes(ctx)
}