Livt.FileSystems

src/ShortFileName.lvt

namespace Livt.FileSystems

/**
 * Incremental ASCII 8.3 filename normalization. Accepts letters, digits, underscore
 * and hyphen, with one optional dot. Reset starts a new name. Invalid characters
 * or lengths invalidate the entire name until Reset; no truncation occurs.
 * Call Reset before appending the first name. One scheduled owner serializes calls.
 */
component ShortFileName
{
	// Space-padded alias and parser progress for the current name.
	name: byte[11]
	baseLength: int
	extensionLength: int
	dot: bool
	invalid: bool

	/**
	 * Clears the name to its FAT space-padded representation.
	 */
	public fn Reset()
	{
		baseLength = 0
		extensionLength = 0
		dot = false
		invalid = false

		for (var index = 0; index < 11; index++) {
			name[index] = 32
		}
	}

	/**
	 * Adds one character; lowercase ASCII is normalized to uppercase.
	 */
	public fn Append(value: byte)
	{
		if (invalid) {
			return
		}

		if (value == 46) {
			invalid = dot || baseLength == 0
			dot = true
			return
		}

		var character = value

		if (character >= 97 && character <= 122) {
			character = (character as int - 32) as byte
		}

		if (!((character >= 65 && character <= 90) || (character >= 48 && character <= 57)
			|| character == 95 || character == 45)) {
			invalid = true
			return
		}

		if (dot) {
			if (extensionLength == 3) {
				invalid = true
			} else {
				name[8 + extensionLength] = character
				extensionLength++
			}
		} elif (baseLength == 8) {
			invalid = true
		} else {
			name[baseLength] = character
			baseLength++
		}
	}

	/**
	 * True only for a complete supported name, including a nonempty dotted extension.
	 */
	public fn IsValid() bool
	{
		return !invalid && baseLength > 0 && (!dot || extensionLength > 0)
	}

	/**
	 * Returns one space-padded alias byte; requires IsValid and index 0..10.
	 */
	public fn GetByte(index: int) byte
	{
		if (index < 0 || index >= 11) {
			return 0
		}

		return name[index]
	}
}