razeri-plugin-contract 0.21.0

// Copyright (C) 2026 Gabriel Shea
// Licensed under either of the Apache License, Version 2.0 or the MIT
// license, at your option.

//! **A version of an engine**, and the platform name that carries one.
//!
//! A platform is an engine at a version: `postgres`, or `postgres@17`. The
//! engine's name comes first, and after the last `@` the version the design is
//! for. A version is digits, with dots where the vendor uses them (`8.4`), and
//! letters only after the last digit, where the vendor's own name has them
//! (`23ai`).
//!
//! Two spellings are refused before anything else reads them, because the
//! scans that keep private names out of a release would refuse them too:
//!
//! - a dot before letters, `oracle@23.ai`, is the shape of a mail address, and
//!   the accepted spelling is shown: `oracle@23ai`;
//! - a colon, `postgres:17`, is the shape of a host and its port, and the
//!   accepted spelling is shown: `postgres@17`.

use std::cmp::Ordering;
use std::fmt;
use std::hash::{Hash, Hasher};

/// The most characters a version is written in.
const LONGEST: usize = 16;

/// The most numbers a version holds: `2.00.088` is three.
const MOST_NUMBERS: usize = 4;

/// **A version of an engine**: `17`, `8.4`, `2022`, `23ai`.
///
/// Ordered by its numbers, the missing ones read as zero, so `8.4` is newer
/// than `8` and the same as `8.4.0`. The letters after the last digit are
/// part of how the vendor writes it and not of its order: `23ai` and `23` are
/// one version, and a dialect that declares `23ai` answers to `oracle@23` too.
///
/// It is displayed as it was written, so a refusal and a manifest say the
/// version in the user's words.
///
/// ```
/// use razeri_plugin_contract::EngineVersion;
///
/// let floor = EngineVersion::declared("15");
/// let asked: EngineVersion = "17".parse().unwrap();
/// assert!(floor < asked);
/// assert_eq!(asked.to_string(), "17");
/// assert_eq!("23ai".parse::<EngineVersion>().unwrap(), "23".parse().unwrap());
/// ```
#[derive(Clone, Copy)]
pub struct EngineVersion {
    written: [u8; LONGEST],
    length: usize,
    numbers: [u32; MOST_NUMBERS],
}

/// **Why a spelling is not a version**, with the spelling that is, where there
/// is one.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum EngineVersionError {
    /// Nothing after the `@`.
    Empty,
    /// A colon: the shape of a host and its port.
    Colon {
        /// The version with the colon taken out, or `None` when nothing is
        /// left.
        accepted: Option<String>,
    },
    /// Letters after a dot: the shape of a mail address.
    DotBeforeLetters {
        /// The same version with the dot before the letters taken out.
        accepted: String,
    },
    /// Anything else that is not digits, dots and trailing letters.
    NotAVersion,
}

impl fmt::Display for EngineVersionError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Empty => f.write_str("there is no version after the `@`"),
            Self::Colon { accepted: Some(accepted) } => write!(
                f,
                "a version never holds a colon, which is how a host and its port are written; \
                 write `{accepted}`"
            ),
            Self::Colon { accepted: None } => f.write_str(
                "a version never holds a colon, which is how a host and its port are written",
            ),
            Self::DotBeforeLetters { accepted } => write!(
                f,
                "a version has no dot before its letters, which is how a mail address is \
                 written; write `{accepted}`"
            ),
            Self::NotAVersion => f.write_str(
                "a version is digits, with dots where the vendor uses them and letters only after \
                 the last digit, like `17`, `8.4` or `23ai`",
            ),
        }
    }
}

impl std::error::Error for EngineVersionError {}

/// What [`EngineVersion::read`] found wrong, before the sentence is written.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Fault {
    Empty,
    Colon,
    DotBeforeLetters,
    NotAVersion,
}

impl EngineVersion {
    /// **A version a dialect declares**, read when the program is compiled.
    ///
    /// A spelling that is not a version stops the build, so a dialect's
    /// declared list can be a `const`:
    ///
    /// ```
    /// use razeri_plugin_contract::EngineVersion;
    ///
    /// const VERSIONS: &[EngineVersion] =
    ///     &[EngineVersion::declared("15"), EngineVersion::declared("17")];
    /// assert_eq!(VERSIONS[0].to_string(), "15");
    /// ```
    ///
    /// # Panics
    ///
    /// When `spelling` is not a version; in a `const`, that is a compile
    /// error.
    #[must_use]
    pub const fn declared(spelling: &str) -> Self {
        match Self::read(spelling) {
            Ok(version) => version,
            Err(_) => panic!("a declared version is digits, dots and trailing letters"),
        }
    }

    /// Read a version written by a user.
    ///
    /// # Errors
    ///
    /// [`EngineVersionError`] naming what is wrong and, where there is one,
    /// the spelling that is accepted.
    pub fn parse(spelling: &str) -> Result<Self, EngineVersionError> {
        match Self::read(spelling) {
            Ok(version) => Ok(version),
            Err(Fault::Empty) => Err(EngineVersionError::Empty),
            Err(Fault::Colon) => Err(EngineVersionError::Colon { accepted: None }),
            Err(Fault::NotAVersion) => Err(EngineVersionError::NotAVersion),
            Err(Fault::DotBeforeLetters) => {
                let accepted = without_dots_before_letters(spelling);
                if Self::read(&accepted).is_ok() {
                    Err(EngineVersionError::DotBeforeLetters { accepted })
                } else {
                    Err(EngineVersionError::NotAVersion)
                }
            }
        }
    }

    /// The reading both [`Self::declared`] and [`Self::parse`] share. It
    /// runs when a dialect is compiled, so what it says is wrong is a word,
    /// and [`Self::parse`] writes the sentence.
    const fn read(spelling: &str) -> Result<Self, Fault> {
        let bytes = spelling.as_bytes();
        if bytes.is_empty() {
            return Err(Fault::Empty);
        }
        let mut at = 0;
        while at < bytes.len() {
            if bytes[at] == b':' {
                return Err(Fault::Colon);
            }
            at += 1;
        }
        if bytes.len() > LONGEST {
            return Err(Fault::NotAVersion);
        }
        let mut written = [0u8; LONGEST];
        let mut numbers = [0u32; MOST_NUMBERS];
        let mut part = 0;
        let mut digits = 0;
        let mut lettered = false;
        let mut at = 0;
        while at < bytes.len() {
            let byte = bytes[at];
            written[at] = byte;
            if byte.is_ascii_digit() {
                if lettered || numbers[part] > (u32::MAX - 9) / 10 {
                    return Err(Fault::NotAVersion);
                }
                numbers[part] = numbers[part] * 10 + (byte - b'0') as u32;
                digits += 1;
            } else if byte == b'.' {
                if digits == 0 || lettered {
                    return Err(Fault::NotAVersion);
                }
                if at + 1 < bytes.len() && bytes[at + 1].is_ascii_alphabetic() {
                    return Err(Fault::DotBeforeLetters);
                }
                part += 1;
                digits = 0;
                if part == MOST_NUMBERS {
                    return Err(Fault::NotAVersion);
                }
            } else if byte.is_ascii_alphabetic() {
                if digits == 0 {
                    return Err(Fault::NotAVersion);
                }
                lettered = true;
            } else {
                return Err(Fault::NotAVersion);
            }
            at += 1;
        }
        if digits == 0 {
            return Err(Fault::NotAVersion);
        }
        Ok(Self { written, length: bytes.len(), numbers })
    }

    /// The version as it was written.
    #[must_use]
    pub fn as_str(&self) -> &str {
        // Only ASCII digits, dots and letters are ever written here.
        std::str::from_utf8(&self.written[..self.length]).unwrap_or_default()
    }

    /// The numbers of the version, the missing ones zero: `8.4` is
    /// `[8, 4, 0, 0]`.
    #[must_use]
    pub const fn numbers(&self) -> [u32; MOST_NUMBERS] {
        self.numbers
    }
}

impl std::str::FromStr for EngineVersion {
    type Err = EngineVersionError;

    fn from_str(spelling: &str) -> Result<Self, Self::Err> {
        Self::parse(spelling)
    }
}

impl PartialEq for EngineVersion {
    fn eq(&self, other: &Self) -> bool {
        self.numbers == other.numbers
    }
}

impl Eq for EngineVersion {}

impl PartialOrd for EngineVersion {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for EngineVersion {
    fn cmp(&self, other: &Self) -> Ordering {
        self.numbers.cmp(&other.numbers)
    }
}

impl Hash for EngineVersion {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.numbers.hash(state);
    }
}

impl fmt::Display for EngineVersion {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_str())
    }
}

impl fmt::Debug for EngineVersion {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "EngineVersion({})", self.as_str())
    }
}

impl serde::Serialize for EngineVersion {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        serializer.serialize_str(self.as_str())
    }
}

/// **A platform name, read into the engine and the version it is for.**
///
/// `postgres@17` is the engine `postgres` at version `17`; `postgres` is the
/// engine with no version named. The name is split on its last `@`, so the
/// engine's own name is never cut short.
///
/// Parameters:
/// - `platform`: the name as a design or a `--target` writes it.
///
/// # Errors
///
/// [`EngineVersionError`] when the version is not one, and
/// [`EngineVersionError::Colon`] for a colon anywhere in the name, with the
/// spelling that is accepted: `postgres:17` reads as `postgres@17`.
pub fn split_platform(platform: &str) -> Result<(&str, Option<EngineVersion>), EngineVersionError> {
    let platform = platform.trim();
    if platform.contains(':') {
        // `postgres:17` is the `@` written as a host's port; the fix is the
        // `@`, where that reads as a version.
        let accepted = match platform.split_once(':') {
            Some((engine, version))
                if !engine.contains('@') && EngineVersion::read(version).is_ok() =>
            {
                Some(format!("{engine}@{version}"))
            }
            _ => None,
        };
        return Err(EngineVersionError::Colon { accepted });
    }
    let Some((engine, version)) = platform.rsplit_once('@') else {
        return Ok((platform, None));
    };
    match EngineVersion::parse(version) {
        Ok(version) => Ok((engine, Some(version))),
        Err(EngineVersionError::DotBeforeLetters { accepted }) => {
            Err(EngineVersionError::DotBeforeLetters { accepted: format!("{engine}@{accepted}") })
        }
        Err(other) => Err(other),
    }
}

/// `23.ai` written `23ai`: every dot that comes before a letter taken out.
fn without_dots_before_letters(spelling: &str) -> String {
    let mut out = String::with_capacity(spelling.len());
    let mut chars = spelling.chars().peekable();
    while let Some(c) = chars.next() {
        if c == '.' && chars.peek().is_some_and(char::is_ascii_alphabetic) {
            continue;
        }
        out.push(c);
    }
    out
}
#[cfg(test)]
mod tests {
    use super::*;

    fn read(spelling: &str) -> EngineVersion {
        EngineVersion::parse(spelling).unwrap_or_else(|e| panic!("{spelling}: {e}"))
    }

    #[test]
    fn the_four_shapes_a_vendor_writes_are_versions_and_display_as_written() {
        for spelling in ["17", "8.4", "2022", "23ai", "2.00.088"] {
            assert_eq!(read(spelling).to_string(), spelling);
        }
    }

    #[test]
    fn versions_are_ordered_by_their_numbers() {
        assert!(read("15") < read("16"));
        assert!(read("16") < read("17"));
        assert!(read("8") < read("8.4"));
        assert!(read("8.4") < read("8.10"));
        assert!(read("19") < read("23ai"));
        assert_eq!(read("8.4"), read("8.4.0"));
    }

    #[test]
    fn the_letters_are_how_the_vendor_writes_it_and_not_its_order() {
        assert_eq!(read("23ai"), read("23"));
        assert_eq!(read("23ai").to_string(), "23ai");
    }

    #[test]
    fn a_declared_version_reads_the_same_as_a_written_one() {
        const FLOOR: EngineVersion = EngineVersion::declared("15");
        assert_eq!(FLOOR, read("15"));
        assert_eq!(FLOOR.to_string(), "15");
    }

    #[test]
    fn a_dot_before_letters_is_refused_showing_the_accepted_spelling() {
        assert_eq!(
            EngineVersion::parse("23.ai"),
            Err(EngineVersionError::DotBeforeLetters { accepted: "23ai".to_owned() })
        );
        let said = EngineVersion::parse("23.ai").unwrap_err().to_string();
        assert!(said.contains("`23ai`"), "{said}");
        assert!(said.contains("mail address"), "{said}");
    }

    #[test]
    fn a_colon_is_refused() {
        assert!(matches!(EngineVersion::parse("17:5432"), Err(EngineVersionError::Colon { .. })));
    }

    #[test]
    fn what_is_not_a_version_is_refused() {
        for spelling in ["latest", "v17", "17-beta", "17 ", ".17", "17.", "1..2", "1.2.3.4.5"] {
            assert_eq!(
                EngineVersion::parse(spelling),
                Err(EngineVersionError::NotAVersion),
                "{spelling}"
            );
        }
        assert_eq!(EngineVersion::parse(""), Err(EngineVersionError::Empty));
        assert_eq!(
            EngineVersion::parse("12345678901234567"),
            Err(EngineVersionError::NotAVersion),
            "longer than any vendor writes one"
        );
    }

    #[test]
    fn a_platform_name_splits_on_its_last_at() {
        assert_eq!(split_platform("postgres"), Ok(("postgres", None)));
        assert_eq!(split_platform("postgres@17"), Ok(("postgres", Some(read("17")))));
        assert_eq!(split_platform(" oracle@23ai "), Ok(("oracle", Some(read("23ai")))));
        assert_eq!(split_platform("my@db@8.4"), Ok(("my@db", Some(read("8.4")))));
    }

    #[test]
    fn a_platform_name_with_a_colon_is_refused_showing_the_at() {
        assert_eq!(
            split_platform("postgres:17"),
            Err(EngineVersionError::Colon { accepted: Some("postgres@17".to_owned()) })
        );
        assert!(matches!(split_platform("postgres@17:1"), Err(EngineVersionError::Colon { .. })));
    }

    #[test]
    fn a_platform_name_with_a_dot_before_letters_is_refused_showing_the_accepted_name() {
        assert_eq!(
            split_platform("oracle@23.ai"),
            Err(EngineVersionError::DotBeforeLetters { accepted: "oracle@23ai".to_owned() })
        );
    }

    #[test]
    fn a_version_serializes_as_it_was_written() {
        let json = serde_json::to_string(&[read("15"), read("23ai")]).unwrap();
        assert_eq!(json, r#"["15","23ai"]"#);
    }
}