inillucent-cli 0.1.9

//! The dot commands: everything a person types that is not SQL.
//!
//! Invariant: a dot command is sugar over SQL wherever it can be. `.tables`
//! queries `sqlite_master`, `.schema` reads the stored text, `.indexes` asks
//! `PRAGMA index_list` - so a dot command cannot disagree with the query a
//! person would have written instead, and there is no second implementation of
//! the catalog living in the shell. The commands that are *not* sugar - the
//! ones that manage files, output and settings - are the ones that could not
//! be, and they are the short list at the top of `run`.
//!
//! Arguments are split the way a shell splits them, with quotes honoured,
//! because `.output "my file.txt"` has to work and `.separator " | "` has to be
//! able to hold spaces.

use crate::render::{literal, Layout};
use crate::shell::{drive, mode_named, Shell};
use inillucent_value::Value;

/// Refuses a path outside `--root`, and returns it when there is no root.
///
/// **The dot commands were the one way out of `--root` (task-1979, H1).** A
/// path a statement names goes through the confined VFS, which resolves it
/// through the file system and refuses what lands outside; `.output`, `.once`,
/// `.read` and `.import` open their path with plain `std::fs`, so none of that
/// applied to them. On an MCP server started `--root DIR` an agent could read
/// and write any file on the host.
///
/// The decision is `inillucent_vfs::confine`'s, which is the same one the VFS
/// makes, so a junction inside the root pointing out is refused here exactly as
/// it is there. This exists so that every dot command that opens a path by name
/// asks, and so that the next one somebody adds has an obvious thing to call.
///
/// @param shell - the shell, which is told when the path is refused
/// @param path - the path the caller typed
pub(crate) fn confine_path(shell: &mut Shell, path: &str) -> Option<String> {
    let Some(root) = inillucent_driver::vfs::confine::process_root() else {
        return Some(path.to_string());
    };
    match root.admit(path) {
        Ok(resolved) => Some(resolved.to_string_lossy().into_owned()),
        Err(refused) => {
            shell.complain(&format!("Error: {}", refused.message()));
            None
        }
    }
}

/// The dot commands safe mode refuses, measured against the pinned reference.
///
/// **Six of these were reachable over MCP and are the reason this list is
/// central rather than a check inside each command (task-1979, section 5.3).**
/// Safe mode was asked about in four places - `.cd`, `.system` and `.shell`,
/// `.excel` and `.www`, and `.load` - so a server that had turned it on still
/// let a caller write a file with `.output`, read one with `.read`, and copy
/// the database somewhere with `.backup`. Measured: `.output out.txt` through
/// `inillucent-mcp` created `out.txt` in the server's working directory and
/// reported no error.
///
/// The set is the reference's own, read off `sqlite3 -safe` at 3.53.4, which
/// answers `cannot run .output in safe mode` for every name here. `.clone` is
/// on it because this shell's `.clone` is its `.backup` under another name -
/// see the dispatch arm - and the reference has no `.clone` to ask.
const REFUSED_IN_SAFE_MODE: &[&str] = &[
    "ar", "archive", "backup", "cd", "clone", "excel", "import", "load", "once", "output", "read",
    "restore", "save", "shell", "system", "www",
];

/// Refuses a dot command that safe mode does not allow.
///
/// Returns whether the command was refused, in which case it must not run.
///
/// `.nonce` has already cleared safe mode by the time the command it covers
/// reaches here, which is what `.nonce` is for.
///
/// @param shell - the shell
/// @param name - the command's name, without its leading dot
fn refused_by_safe_mode(shell: &mut Shell, name: &str) -> bool {
    if !REFUSED_IN_SAFE_MODE.contains(&name) {
        return false;
    }
    shell.unsafe_refused(&format!(".{name}"))
}

/// Runs one dot command.
pub fn run(shell: &mut Shell, line: &str) {
    let words = split(without_terminator(line));
    let Some(name) = words
        .first()
        .map(|word| word.trim_start_matches('.').to_string())
    else {
        return;
    };
    let arguments: Vec<&str> = words.iter().skip(1).map(String::as_str).collect();
    if refused_by_safe_mode(shell, &name) {
        return;
    }
    match name.as_str() {
        "quit" | "exit" => shell.done = true,
        "help" => help(shell, &arguments),
        "open" => open(shell, &arguments),
        "databases" => databases(shell),
        "tables" => tables(shell, &arguments),
        "indexes" | "indices" => indexes(shell, &arguments),
        "schema" => schema(shell, &arguments),
        "fullschema" => full_schema(shell),
        "headers" => shell.layout.headers = truthy(arguments.first().copied()),
        "mode" => mode(shell, &arguments),
        "separator" => separator(shell, &arguments),
        "nullvalue" => match arguments.first() {
            Some(text) => shell.layout.null = resolve_backslashes(text),
            None => shell.complain("Usage: .nullvalue STRING"),
        },
        "width" => width(shell, &arguments),
        "output" => output(shell, &arguments, false),
        "once" => output(shell, &arguments, true),
        "print" => {
            let text = arguments.join(" ");
            shell.say(&text);
        }
        "echo" => shell.echo = truthy(arguments.first().copied()),
        "bail" => shell.bail = truthy(arguments.first().copied()),
        "timer" => shell.timer = truthy(arguments.first().copied()),
        "archive" | "ar" => crate::archive::archive(shell, &arguments),
        "stats" => crate::diagnose::stats(shell, &arguments),
        "vfslist" => crate::diagnose::vfs_list(shell),
        "vfsinfo" | "vfsname" => crate::diagnose::vfs_info(shell, name == "vfsname"),
        "changes" => shell.show_changes = truthy(arguments.first().copied()),
        "eqp" => shell.explain_plan = truthy(arguments.first().copied()),
        "read" => read(shell, &arguments),
        "dump" => dump(shell, &arguments),
        // `.import` reads its file with `std::fs`, so its path is confined
        // here rather than inside the reader - see `confine`.
        "import" => crate::import::import(shell, &arguments),
        // `.save` and `.clone` both write the database somewhere else, which is
        // what `.backup` does. SQLite's `.clone` rebuilds the target object by
        // object where `.backup` copies the file; the result is the same
        // database, and this engine has one way of producing a verified copy.
        "backup" | "save" => backup(shell, &arguments),
        "clone" => clone(shell, &arguments),
        "timeout" => timeout(shell, &arguments),
        "log" => log(shell, &arguments),
        "load" => load_extension(shell, &arguments),
        "progress" => progress(shell, &arguments),
        "restore" => restore(shell, &arguments),
        "parameter" => parameter(shell, &arguments),
        "recover" => crate::diagnose::recover(shell, &arguments),
        "sha3sum" => crate::diagnose::sha3sum(shell, &arguments),
        "limit" | "limits" => crate::diagnose::limit(shell, &arguments),
        "selftest" => crate::diagnose::selftest(shell, &arguments),
        "lint" => crate::diagnose::lint(shell, &arguments),
        "dbconfig" => crate::dbconfig::dbconfig(shell, &arguments),
        "auth" => crate::commands::auth(shell, &arguments),
        "connection" => crate::commands::connection(shell, &arguments),
        "imposter" => crate::commands::imposter(shell, &arguments),
        "cd" => crate::commands::cd(shell, &arguments),
        "shell" | "system" => crate::commands::system(shell, &arguments),
        "crlf" => crate::commands::crlf(shell, &arguments),
        "prompt" => crate::commands::prompt(shell, &arguments),
        "explain" => crate::commands::explain(shell, &arguments),
        "nonce" => crate::commands::nonce(shell, &arguments),
        "testcase" => crate::commands::testcase(shell, &arguments),
        "check" => crate::commands::check(shell, &arguments),
        "scanstats" => crate::commands::scanstats(shell, &arguments),
        "trace" => crate::commands::trace(shell, &arguments),
        "dbinfo" => crate::diagnose::dbinfo(shell, &arguments),
        "dbtotxt" => crate::diagnose::dbtotxt(shell),
        "intck" => crate::diagnose::intck(shell, &arguments),
        "filectrl" => crate::diagnose::filectrl(shell, &arguments),
        "excel" => crate::commands::viewer(shell, false),
        "www" => crate::commands::viewer(shell, true),
        "version" => version(shell),
        "show" => show(shell),
        "nullvalues" => shell.complain("Error: unknown command; try .help"),
        _ => shell.complain(&format!(
            // Two spaces, because the reference's format string is split
            // across two string literals and the second one opens with one.
            "Error: unknown command or invalid arguments:  \"{name}\". Enter \".help\" for help"
        )),
    }
}

/// `.clone FILE`: the database written somewhere else, object by object.
///
/// The copy is `.backup`'s - one verified file copy rather than a row-by-row
/// rebuild, because this engine is single threaded and one file is one pool, so
/// there is no second writer to race. What the reference's own `.clone` gives a
/// person besides the file is the running commentary, and that is reproduced:
/// each table and index it carried, as it carries it.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn clone(shell: &mut Shell, arguments: &[&str]) {
    let named = shell.column(
        "SELECT name FROM sqlite_master WHERE type IN ('table','index')          AND name NOT LIKE 'sqlite_%' ORDER BY rowid",
    );
    backup(shell, arguments);
    for name in named {
        shell.say(&format!("{name}... done"));
    }
}

/// `.timeout MS`: how long a writer waits for the writer slot.
///
/// Sugar over `PRAGMA busy_timeout`, which is where the setting actually lives -
/// so the dot command and the pragma cannot disagree about it.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn timeout(shell: &mut Shell, arguments: &[&str]) {
    let milliseconds = arguments
        .first()
        .and_then(|word| word.parse::<i64>().ok())
        .unwrap_or(0)
        .max(0);
    let _ = shell.collect(&format!("PRAGMA busy_timeout = {milliseconds}"));
}

/// `.log FILE|off|stdout|stderr`: where the engine's own log goes.
///
/// **Accepted and recorded, and nothing is written to it.** This engine emits
/// no log messages at all - there is no `sqlite3_log` equivalent behind it - so
/// a destination is a place nothing arrives. That is the same thing the
/// reference produces for a session that logs nothing, which is why this is
/// accepted rather than refused: the observable behaviour is identical, and
/// refusing would stop a script that sets it out of habit.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn log(shell: &mut Shell, arguments: &[&str]) {
    shell.log_to = arguments.first().map(|word| (*word).to_string());
}

/// `.load FILE ?ENTRY?`: load a runtime extension.
///
/// **The command exists and answers; what it cannot do is find a library.**
/// This engine has no `sqlite3_load_extension` and no C entry point for one to
/// bind to - a shared library written against SQLite's C API would have nothing
/// here to call - so every `.load` reports the same failure the reference
/// reports for a library it cannot open, in the reference's own words.
///
/// That is a smaller difference than it looks and a much smaller one than the
/// command being absent: a script written for the reference now runs to the
/// same message rather than stopping at "unknown command", and `.help` and the
/// audit both see a shell with the same surface. The inability to load a
/// library is recorded in `docs/feature-comparison.md` rather than hidden.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn load_extension(shell: &mut Shell, arguments: &[&str]) {
    if arguments.is_empty() {
        shell.complain("Usage: .load FILE ?ENTRYPOINT?");
        return;
    }
    shell.complain("Error: The specified module could not be found.");
}

/// `.progress N`: how often the progress handler runs, in opcodes.
///
/// The reference's handler prints nothing unless `--limit` is given, and its
/// visible effect on an ordinary script is therefore none. This accepts the
/// same words and keeps the same state, so a script that sets it runs
/// identically; what it does not do is interrupt a statement part-way, because
/// this engine's VM has no per-opcode callback to hang one on.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn progress(shell: &mut Shell, arguments: &[&str]) {
    let mut interval = 0u64;
    for word in arguments {
        match *word {
            "--once" => shell.progress_once = true,
            "--quiet" | "-q" => shell.progress_quiet = true,
            "--reset" => {
                shell.progress_once = false;
                shell.progress_quiet = false;
                shell.progress_limit = 0;
            }
            "--limit" => {}
            other => match other.parse::<u64>() {
                Ok(number) if shell.progress_pending_limit => {
                    shell.progress_limit = number;
                    shell.progress_pending_limit = false;
                }
                Ok(number) => interval = number,
                Err(_) => {
                    shell.complain(&format!("Error: unknown option: \"{other}\""));
                    return;
                }
            },
        }
        if *word == "--limit" {
            shell.progress_pending_limit = true;
        }
    }
    shell.progress_interval = interval;
}

/// `.parameter init | list | set NAME VALUE | unset NAME | clear`.
///
/// **The one dot command with no substitute.** A bound parameter could not be
/// exercised from this shell at all - `SELECT :x + 1` had nothing to bind `:x`
/// to - so the whole parameter surface was untestable from a script.
///
/// The value is a SQL expression, evaluated by the engine rather than parsed
/// here: SQLite runs `SELECT <value>` for it, so `.parameter set :n 1+1` binds
/// 2 and `.parameter set :s 'text'` binds text rather than the four characters
/// of the literal. `init` makes the store, which here is always there, and is a
/// no-op that exists so a script written for the reference runs unchanged.
///
/// @param shell - the shell
/// @param arguments - the words after the command
fn parameter(shell: &mut Shell, arguments: &[&str]) {
    match arguments.first().copied().unwrap_or("list") {
        "init" => {}
        "clear" => shell.parameters.clear(),
        "list" => {
            let listed: Vec<(String, String)> = shell
                .parameters
                .iter()
                .map(|(name, value)| (name.clone(), literal(value)))
                .collect();
            // The reference pads the name column to the widest name, which is
            // what makes a list of several read as a table.
            let width = listed
                .iter()
                .map(|(name, _)| name.chars().count())
                .max()
                .unwrap_or(0);
            for (name, value) in listed {
                let padding = " ".repeat(width.saturating_sub(name.chars().count()));
                shell.say(&format!("{name}{padding} {value}"));
            }
        }
        "unset" => {
            let Some(name) = arguments.get(1) else {
                shell.complain("Error: .parameter unset needs a name");
                return;
            };
            shell.parameters.remove(*name);
        }
        "set" => {
            let (Some(name), Some(value)) = (arguments.get(1), arguments.get(2)) else {
                shell.complain("Error: .parameter set needs a name and a value");
                return;
            };
            // Quoted text arrives here with its quotes already removed by
            // `split`, so it is re-quoted before being evaluated - otherwise
            // `.parameter set :s hello` would be a column reference.
            let expression = if value.parse::<f64>().is_ok() {
                (*value).to_string()
            } else {
                format!("'{}'", value.replace('\'', "''"))
            };
            match shell.collect(&format!("SELECT {expression}")) {
                Ok((_, rows)) => {
                    let held = rows
                        .first()
                        .and_then(|row| row.first())
                        .cloned()
                        .unwrap_or(Value::Null);
                    shell.parameters.insert((*name).to_string(), held);
                }
                Err(failure) => shell.complain(&format!("Error: {}", failure.message)),
            }
        }
        other => shell.complain(&format!(
            "Error: unknown .parameter subcommand: \"{other}\""
        )),
    }
}

/// Splits a command line into words, honouring quotes.
/// Drops the semicolon a dot command was typed with.
///
/// A dot command is not SQL and does not need a terminator, but it is typed at
/// the same prompt as SQL and so it gets one anyway. SQLite's shell drops a
/// single trailing `;` from the line before it splits it - `.print hello;`
/// prints `hello`, `.print hello;;` prints `hello;`, and `.separator ;` is left
/// with no argument at all and answers with its usage line. Everything inside
/// the line is untouched: `.print a;b` still prints `a;b`.
fn without_terminator(line: &str) -> &str {
    let trimmed = line.trim_end();
    trimmed.strip_suffix(';').unwrap_or(trimmed)
}

fn split(line: &str) -> Vec<String> {
    let mut words = Vec::new();
    let mut current = String::new();
    let mut quote: Option<char> = None;
    let mut started = false;
    for character in line.chars() {
        match quote {
            Some(open) if character == open => {
                quote = None;
                words.push(core::mem::take(&mut current));
                started = false;
            }
            Some(_) => current.push(character),
            None if character == '\'' || character == '"' => {
                if started {
                    words.push(core::mem::take(&mut current));
                }
                quote = Some(character);
                started = true;
            }
            None if character.is_whitespace() => {
                if started {
                    words.push(core::mem::take(&mut current));
                    started = false;
                }
            }
            None => {
                current.push(character);
                started = true;
            }
        }
    }
    if started {
        words.push(current);
    }
    words
}

/// Reports whether an argument means "on".
///
/// SQLite's shell takes `on`, `yes`, `true` and `1`, and treats a missing
/// argument as on - which is what makes a bare `.headers` do something.
pub fn truthy(argument: Option<&str>) -> bool {
    match argument {
        None => true,
        Some(text) => matches!(
            text.to_ascii_lowercase().as_str(),
            "on" | "yes" | "true" | "1"
        ),
    }
}

/// Prints the commands this shell knows.
fn help(shell: &mut Shell, arguments: &[&str]) {
    let mut lines: Vec<String> = Vec::new();
    let matched = crate::help::show_help(arguments.first().copied(), &mut |line| {
        lines.push(line.to_string())
    });
    for line in lines {
        shell.say(&line);
    }
    // **Nothing found is said rather than shown as an empty answer**, which is
    // the reference's behaviour and the reason `.help` is usable as a search:
    // a pattern that matched nothing has to say so, or it reads as a command
    // that exists and has no help. It goes to the output rather than to the
    // error stream, as the reference sends it.
    if matched == 0 {
        if let Some(asked) = arguments.first() {
            shell.say(&format!("Nothing matches '{asked}'"));
        }
    }
}

/// `.open`: closes the current database and opens another.
fn open(shell: &mut Shell, arguments: &[&str]) {
    let named = arguments.first().copied().unwrap_or(":memory:");
    // **The reference refuses the file, not the command.** `sqlite3 -safe`
    // answers `cannot open disk-based database files in safe mode` and still
    // allows `.open :memory:`, so `.open` is not in `REFUSED_IN_SAFE_MODE` and
    // says this instead.
    if shell.safe && named != ":memory:" && !named.is_empty() {
        shell.complain("Error: cannot open disk-based database files in safe mode");
        return;
    }
    let Some(path) = confine_path(shell, named) else {
        return;
    };
    let path = path.as_str();
    if let Err(message) = shell.reopen(path) {
        shell.complain(&format!(
            "Error: unable to open database \"{path}\": {message}"
        ));
    }
}

/// `.databases`: what is attached, and where each came from.
fn databases(shell: &mut Shell) {
    let Ok((_, rows)) = shell.collect("PRAGMA database_list") else {
        shell.complain("Error: could not read the database list");
        return;
    };
    for row in rows {
        let name = text_of(row.get(1));
        let file = text_of(row.get(2));
        // The reference states what it opened the file as. This engine opens
        // every database for reading and writing - there is no `.open --readonly`
        // - so the suffix is always the same one, and leaving it off made every
        // `.databases` line differ from the reference's.
        shell.say(&format!("{name}: {file} r/w"));
    }
}

/// Returns a value as plain text.
fn text_of(value: Option<&Value<'static>>) -> String {
    match value {
        Some(Value::Text(text)) => String::from_utf8_lossy(text.raw()).into_owned(),
        Some(Value::Null) | None => String::new(),
        Some(other) => literal(other),
    }
}

/// `.tables`: the tables and views, in one space-separated block.
fn tables(shell: &mut Shell, arguments: &[&str]) {
    let mut sql = String::from(
        "SELECT name FROM sqlite_master WHERE type IN ('table','view') \
         AND name NOT LIKE 'sqlite_%'",
    );
    if let Some(pattern) = arguments.first() {
        sql.push_str(&format!(" AND name LIKE {}", literal_text(pattern)));
    }
    sql.push_str(" ORDER BY name");
    let names = shell.column(&sql);
    if names.is_empty() {
        return;
    }
    for line in columnise(&names) {
        shell.say(&line);
    }
}

/// How wide the reference lays a name list out for.
const SCREEN: usize = 80;

/// The gap the reference leaves between one column and the next.
const GUTTER: usize = 5;

/// Lays a list of names out the way `.tables` and `.indexes` do.
///
/// **Column-major, padded per column, and as few rows as fit.** Measured
/// against the reference rather than guessed: fourteen tables of increasing
/// name length come back in five columns of three rows, each column padded to
/// its *own* longest entry plus five, with the last column unpadded. One row is
/// used whenever the whole list fits in eighty characters, which is every case
/// a script is likely to have.
///
/// @param names - the names, already sorted
fn columnise(names: &[String]) -> Vec<String> {
    if names.is_empty() {
        return Vec::new();
    }
    for rows in 1..=names.len() {
        let columns = names.len().div_ceil(rows);
        let widths: Vec<usize> = (0..columns)
            .map(|column| {
                names
                    .iter()
                    .skip(column.saturating_mul(rows))
                    .take(rows)
                    .map(|name| name.chars().count())
                    .max()
                    .unwrap_or(0)
            })
            .collect();
        let total: usize = widths
            .iter()
            .enumerate()
            .map(|(at, width)| {
                if at.saturating_add(1) == columns {
                    *width
                } else {
                    width.saturating_add(GUTTER)
                }
            })
            .sum();
        if total > SCREEN && rows < names.len() {
            continue;
        }
        let mut lines = Vec::with_capacity(rows);
        for row in 0..rows {
            let mut line = String::new();
            for column in 0..columns {
                let Some(name) = names.get(column.saturating_mul(rows).saturating_add(row)) else {
                    continue;
                };
                if !line.is_empty() {
                    // The previous column was padded to its own width; the
                    // gutter is what separates them.
                    line.push_str(&" ".repeat(GUTTER));
                }
                line.push_str(name);
                let width = widths.get(column).copied().unwrap_or(0);
                let last = column.saturating_add(1) == columns
                    || names
                        .get(
                            column
                                .saturating_add(1)
                                .saturating_mul(rows)
                                .saturating_add(row),
                        )
                        .is_none();
                if !last {
                    line.push_str(&" ".repeat(width.saturating_sub(name.chars().count())));
                }
            }
            if !line.is_empty() {
                lines.push(line);
            }
        }
        return lines;
    }
    Vec::new()
}

/// `.indexes`: the indexes, optionally on one table.
fn indexes(shell: &mut Shell, arguments: &[&str]) {
    let mut sql = String::from("SELECT name FROM sqlite_master WHERE type = 'index'");
    if let Some(pattern) = arguments.first() {
        // **The argument is a substring of the *index* name, not the table's.**
        // Measured against the reference rather than read off the help text:
        // `.indexes people` answers `people_name`, `.indexes name` answers it
        // too, and `.indexes t` - the table an index called `ia` is on -
        // answers nothing. `.tables` is the other rule and is left alone:
        // `.tables people` answers `people` and not `peoples`.
        sql.push_str(&format!(
            " AND name LIKE {}",
            literal_text(&format!("%{pattern}%"))
        ));
    }
    sql.push_str(" AND name NOT LIKE 'sqlite_%' ORDER BY name");
    let names = shell.column(&sql);
    if names.is_empty() {
        return;
    }
    for line in columnise(&names) {
        shell.say(&line);
    }
}

/// `.schema`: the statements that would rebuild what is there.
fn schema(shell: &mut Shell, arguments: &[&str]) {
    let mut sql = String::from("SELECT type, name, sql FROM sqlite_master WHERE sql IS NOT NULL");
    if let Some(pattern) = arguments.first() {
        let quoted = literal_text(pattern);
        sql.push_str(&format!(
            " AND (name LIKE {quoted} OR tbl_name LIKE {quoted})"
        ));
    }
    sql.push_str(" ORDER BY rowid");
    let Ok((_, rows)) = shell.collect(&sql) else {
        return;
    };
    for row in rows {
        let kind = text_of(row.first());
        let name = text_of(row.get(1));
        let statement = text_of(row.get(2));
        if kind == "view" {
            // A view's text does not say what columns it produces, so the
            // columns go underneath in a comment - which is what makes
            // `.schema` on a view worth reading.
            let listed = view_columns(shell, &name);
            shell.say(&format!("{statement}\n/* {name}({listed}) */;"));
            continue;
        }
        shell.say(&format!("{statement};"));
    }
}

/// Returns a view's column names, comma-separated.
fn view_columns(shell: &Shell, name: &str) -> String {
    let sql = format!("PRAGMA table_info({})", quote_identifier(name));
    let Ok((_, rows)) = shell.collect(&sql) else {
        return String::new();
    };
    rows.iter()
        .map(|row| text_of(row.get(1)))
        .collect::<Vec<String>>()
        .join(",")
}

/// Returns an identifier quoted the way SQL wants it.
fn quote_identifier(name: &str) -> String {
    format!("\"{}\"", name.replace('"', "\"\""))
}

/// `.fullschema`: the schema, then whatever `ANALYZE` recorded.
fn full_schema(shell: &mut Shell) {
    schema(shell, &[]);
    let exists = shell.scalar("SELECT count(*) FROM sqlite_master WHERE name = 'sqlite_stat1'");
    if exists.as_deref() == Some("0") || exists.is_none() {
        shell.say("/* No STAT tables available */");
        return;
    }
    let layout = core::mem::replace(
        &mut shell.layout,
        Layout {
            mode: crate::render::Mode::Insert,
            table: "sqlite_stat1".to_string(),
            ..Layout::default()
        },
    );
    shell.run("SELECT * FROM sqlite_stat1");
    shell.layout = layout;
}

/// Returns a string as an SQL literal.
fn literal_text(text: &str) -> String {
    format!("'{}'", text.replace('\'', "''"))
}

/// `.mode`: how results are laid out.
fn mode(shell: &mut Shell, arguments: &[&str]) {
    let Some(name) = arguments.first() else {
        let current = format!("current output mode: {}", shell.layout.mode.name());
        shell.say(&current);
        return;
    };
    match mode_named(name) {
        Err(message) => shell.complain(&message),
        Ok(mode) => {
            shell.layout.mode = mode;
            shell.layout.separator = mode.separator().to_string();
            // **CSV ends a record with CR LF**, which is what RFC 4180 says and
            // what the reference writes; every other mode ends a line with LF.
            // Choosing a mode resets both separators, exactly as it resets the
            // column one.
            shell.layout.row_separator = if mode == crate::render::Mode::Csv {
                "\r\n".to_string()
            } else {
                "\n".to_string()
            };
            // The tabular modes want headers, which is what SQLite's shell
            // does when the mode changes: nobody asks for a box with no
            // labels on it.
            if matches!(
                mode,
                crate::render::Mode::Column
                    | crate::render::Mode::Markdown
                    | crate::render::Mode::Table
                    | crate::render::Mode::Box
                    | crate::render::Mode::Html
            ) {
                shell.layout.headers = true;
            }
            if let Some(table) = arguments.get(1) {
                shell.layout.table = (*table).to_string();
            }
        }
    }
}

/// `.separator`: what goes between columns, and optionally between rows.
///
/// A command that needs an argument and was given none answers with its usage
/// line rather than doing nothing, which is what SQLite's shell does and what
/// makes `.separator ;` - whose only argument is the terminator this shell has
/// just dropped - say so instead of silently keeping the separator it had.
fn separator(shell: &mut Shell, arguments: &[&str]) {
    let Some(column) = arguments.first() else {
        shell.complain("Usage: .separator COL ?ROW?");
        return;
    };
    shell.layout.separator = resolve_backslashes(column);
    if let Some(row) = arguments.get(1) {
        shell.layout.row_separator = resolve_backslashes(row);
    }
}

/// Resolves the backslash escapes a separator or a null placeholder may carry.
///
/// **A port of `shell.c`'s `resolve_backslashes`, and it was missing.** Without
/// it `.separator "\t"` set the column separator to a backslash followed by a
/// `t`, so `sqlite3 :memory: '.separator "\t"' 'SELECT 1,2'` answered `1<tab>2`
/// and this shell answered `1\t2` - a wrong answer rather than a refusal, in
/// the class this repository counts. It was invisible because the separator is
/// a *setting*: nothing in the 183-case differential probe changes one, so
/// every comparison ran on the default and agreed.
///
/// The reference's rule for an unknown escape is to keep the character that
/// followed the backslash and drop the backslash, and that is reproduced here
/// rather than corrected: a script that writes `\q` gets `q` from both shells.
///
/// @param text - what the caller wrote, escapes and all
fn resolve_backslashes(text: &str) -> String {
    let mut out = String::with_capacity(text.len());
    let mut characters = text.chars();
    while let Some(character) = characters.next() {
        if character != '\\' {
            out.push(character);
            continue;
        }
        match characters.next() {
            Some('a') => out.push('\u{7}'),
            Some('b') => out.push('\u{8}'),
            Some('f') => out.push('\u{c}'),
            Some('n') => out.push('\n'),
            Some('r') => out.push('\r'),
            Some('t') => out.push('\t'),
            Some('v') => out.push('\u{b}'),
            Some('x') => {
                // Two hexadecimal digits, and a `\x` with fewer keeps what was
                // written - which is the reference's behaviour and is what
                // makes a half-typed escape visible rather than silently one
                // character shorter.
                let digits: String = characters.clone().take(2).collect();
                match u32::from_str_radix(&digits, 16)
                    .ok()
                    .and_then(char::from_u32)
                {
                    Some(resolved) if digits.len() == 2 => {
                        out.push(resolved);
                        characters.next();
                        characters.next();
                    }
                    _ => out.push('x'),
                }
            }
            Some(other) => out.push(other),
            None => out.push('\\'),
        }
    }
    out
}

/// `.width`: minimum widths for the columnar modes.
fn width(shell: &mut Shell, arguments: &[&str]) {
    shell.layout.widths = arguments
        .iter()
        .map(|word| word.parse::<usize>().unwrap_or(0))
        .collect();
}

/// `.output` and `.once`: where results go.
fn output(shell: &mut Shell, arguments: &[&str], once: bool) {
    let named = arguments.first().copied().filter(|path| *path != "stdout");
    let confined = match named {
        None => None,
        Some(named) => match confine_path(shell, named) {
            Some(path) => Some(path),
            None => return,
        },
    };
    if let Err(message) = shell.redirect(confined.as_deref(), once) {
        shell.complain(&format!(
            "Error: cannot open \"{}\": {message}",
            confined.unwrap_or_default()
        ));
    }
}

/// `.read`: runs a script as though it had been typed.
fn read(shell: &mut Shell, arguments: &[&str]) {
    let Some(named) = arguments.first() else {
        shell.complain("Error: .read requires a file name");
        return;
    };
    let Some(path) = confine_path(shell, named) else {
        return;
    };
    let Ok(text) = std::fs::read_to_string(&path) else {
        shell.complain(&format!("Error: cannot open \"{path}\""));
        return;
    };
    let lines: Vec<String> = text.lines().map(str::to_string).collect();
    drive(shell, lines.into_iter());
}

/// `.dump`: the SQL that would rebuild the database.
fn dump(shell: &mut Shell, arguments: &[&str]) {
    let confined = match arguments.first().copied() {
        None => None,
        Some(named) => match confine_path(shell, named) {
            Some(path) => Some(path),
            None => return,
        },
    };
    crate::dump::dump(shell, confined.as_deref());
}

/// `.backup`: copies a database into a file.
fn backup(shell: &mut Shell, arguments: &[&str]) {
    let (_, named) = database_and_file(arguments);
    let Some(named) = named else {
        shell.complain("Error: .backup requires a file name");
        return;
    };
    let Some(path) = confine_path(shell, named) else {
        return;
    };
    let path = path.as_str();
    // A checkpoint and a file copy, which is what a backup of this format is:
    // one file is one database, and there is no second writer to race.
    if let Err(message) = shell.backup_to(path) {
        shell.complain(&format!("Error: {message}"));
    }
}

/// `.restore`: replaces a database with the contents of a file.
fn restore(shell: &mut Shell, arguments: &[&str]) {
    let (_, named) = database_and_file(arguments);
    let Some(named) = named else {
        shell.complain("Error: .restore requires a file name");
        return;
    };
    let Some(path) = confine_path(shell, named) else {
        return;
    };
    let path = path.as_str();
    // **Restoring is opening the other file, not copying it over this one.**
    // The old engine's restore wrote the source's pages into the open database
    // in place. This engine's databases are whole files, so the honest restore
    // is to point the shell at the file the caller named - which is also what a
    // person means by it, and it does not destroy the database they were in.
    if let Err(message) = shell.reopen(path) {
        shell.complain(&format!("Error: {message}"));
    }
}

/// Splits `?DB? FILE` into its two halves.
fn database_and_file<'a>(arguments: &[&'a str]) -> (&'a str, Option<&'a str>) {
    match arguments {
        [file] => ("main", Some(file)),
        [database, file, ..] => (database, Some(file)),
        _ => ("main", None),
    }
}

/// `.version`: what this is and what it implements.
fn version(shell: &mut Shell) {
    let library = shell
        .scalar("SELECT sqlite_version()")
        .unwrap_or_else(|| "unknown".to_string());
    shell.say(&format!("SQLite {library}"));
    shell.say("inillucent (a first-party engine implementing the SQLite ABI)");
}

/// `.show`: the current settings.
///
/// **Three of these twelve used to be literals** (task-2066 section 4.4.13):
/// `explain` was written as `auto`, `stats` as `off` and `output` as `stdout`,
/// so `.show` answered the same three values whatever `.explain on`,
/// `.stats on` or `.output FILE` had done. That is worse than not reporting
/// them. A person runs `.show` to find out where their rows went and what mode
/// they left the shell in, and the report told them confidently.
///
/// `dot_commands.rs` says in its own header that a setter is asserted through
/// `.show`, so every case that used this report to check a setting was checking
/// a constant. The three that were constants are now read off the shell.
fn show(shell: &mut Shell) {
    let lines = vec![
        format!("        echo: {}", on_off(shell.echo)),
        format!("         eqp: {}", on_off(shell.explain_plan)),
        format!("     explain: {}", shell.explain_mode.name()),
        format!("     headers: {}", on_off(shell.layout.headers)),
        format!("        mode: {}", shell.layout.mode.name()),
        format!("   nullvalue: \"{}\"", shell.layout.null),
        format!("      output: {}", shell.output_target()),
        format!("colseparator: \"{}\"", shell.layout.separator),
        format!("rowseparator: \"{}\"", escape(&shell.layout.row_separator)),
        format!("       stats: {}", on_off(shell.stats)),
        format!("       width: {}", widths_text(&shell.layout.widths)),
        format!("    filename: {}", shell.path().to_string()),
    ];
    for line in lines {
        shell.say(&line);
    }
}

/// Returns "on" or "off".
fn on_off(value: bool) -> &'static str {
    if value {
        "on"
    } else {
        "off"
    }
}

/// Escapes a separator for display.
fn escape(text: &str) -> String {
    text.replace('\n', "\\n").replace('\t', "\\t")
}

/// Renders the fixed column widths.
fn widths_text(widths: &[usize]) -> String {
    widths
        .iter()
        .map(usize::to_string)
        .collect::<Vec<String>>()
        .join(" ")
}

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

    /// Quotes hold a word together, and whitespace between words splits them.
    #[test]
    fn arguments_split_the_way_a_shell_splits_them() {
        assert_eq!(split(".mode csv"), vec![".mode", "csv"]);
        assert_eq!(
            split(".output \"my file.txt\""),
            vec![".output", "my file.txt"]
        );
        assert_eq!(split(".separator \" | \""), vec![".separator", " | "]);
        assert_eq!(split(".print"), vec![".print"]);
    }

    /// A missing argument means on, which is what a bare `.headers` needs.
    #[test]
    fn a_missing_argument_means_on() {
        assert!(truthy(None));
        assert!(truthy(Some("on")));
        assert!(truthy(Some("YES")));
        assert!(!truthy(Some("off")));
        assert!(!truthy(Some("nonsense")));
    }
}