qubit-validator 0.1.0

Type-safe validation traits and registries for Qubit applications
Documentation 
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// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================

//! Validation for non-empty dotted identifiers with ASCII letter-led segments.

use super::DottedIdentifierError;

/// Validates the complete dotted identifier protocol.
///
/// Every segment must start with an ASCII letter and may continue with ASCII
/// letters, digits, or underscores. Dots separate non-empty segments; leading,
/// trailing, or repeated dots are rejected. The function examines bytes so
/// non-ASCII characters cannot be accepted as letters or digits.
///
/// # Parameters
///
/// - `value`: The complete dotted identifier to validate.
///
/// # Returns
///
/// Returns `Ok(())` when every segment follows the protocol.
///
/// # Errors
///
/// Returns [`DottedIdentifierError::Empty`] for an empty identifier,
/// [`DottedIdentifierError::EmptySegment`] for a leading, trailing, or
/// repeated dot, or [`DottedIdentifierError::InvalidSegment`] when a segment
/// contains a disallowed byte or does not start with an ASCII letter.
pub(crate) const fn validate_dotted_identifier(value: &str) -> Result<(), DottedIdentifierError> {
    let bytes = value.as_bytes();
    if bytes.is_empty() {
        return Err(DottedIdentifierError::Empty);
    }
    let mut segment_start = 0;
    let mut index = 0;
    while index < bytes.len() {
        if bytes[index] == b'.' {
            if segment_start == index {
                return Err(DottedIdentifierError::EmptySegment);
            }
            if let Err(error) = validate_segment(bytes, segment_start, index) {
                return Err(error);
            }
            segment_start = index + 1;
        }
        index += 1;
    }
    if segment_start == bytes.len() {
        return Err(DottedIdentifierError::EmptySegment);
    }
    validate_segment(bytes, segment_start, bytes.len())
}

/// Validates one segment using the protocol's ASCII character set.
///
/// `start` and `end` delimit a non-empty half-open byte range within `bytes`.
/// The first byte must be an ASCII letter. Remaining bytes may be ASCII
/// letters, digits, or underscores.
///
/// # Parameters
///
/// - `bytes`: The identifier bytes containing the segment.
/// - `start`: The inclusive start of the segment's byte range.
/// - `end`: The exclusive end of the segment's byte range.
///
/// # Returns
///
/// Returns `Ok(())` when the byte range is a valid segment.
///
/// # Errors
///
/// Returns [`DottedIdentifierError::InvalidSegment`] when the range is empty,
/// starts with a non-letter, or contains a byte outside the allowed set.
const fn validate_segment(bytes: &[u8], start: usize, end: usize) -> Result<(), DottedIdentifierError> {
    if start == end || !bytes[start].is_ascii_alphabetic() {
        return Err(DottedIdentifierError::InvalidSegment);
    }
    let mut index = start + 1;
    while index < end {
        let byte = bytes[index];
        if !(byte.is_ascii_alphanumeric() || byte == b'_') {
            return Err(DottedIdentifierError::InvalidSegment);
        }
        index += 1;
    }
    Ok(())
}