pile/crates/pile-flac/src/vorbiscomment.rs

//! Decode and write Vorbis comment blocks

use base64::Engine;
use smartstring::{LazyCompact, SmartString};
use std::{
	io::{Cursor, Read, Write},
	str::FromStr,
};

use super::tagtype::TagType;
use crate::{
	FlacDecodeError, FlacEncodeError,
	blocks::{FlacMetablockDecode, FlacMetablockEncode, FlacPictureBlock},
};

/// A decoded vorbis comment block
#[derive(Debug)]
pub struct VorbisComment {
	/// This comment's vendor string
	pub vendor: SmartString<LazyCompact>,

	/// List of (tag, value)
	/// Repeated tags are allowed!
	pub comments: Vec<(TagType, SmartString<LazyCompact>)>,

	/// A list of pictures found in this comment
	pub pictures: Vec<FlacPictureBlock>,
}

impl VorbisComment {
	/// Try to decode the given data as a vorbis comment block
	pub fn decode(data: &[u8]) -> Result<Self, FlacDecodeError> {
		let mut d = Cursor::new(data);

		// This is re-used whenever we need to read four bytes
		let mut block = [0u8; 4];

		let vendor = {
			d.read_exact(&mut block)?;
			let length = u32::from_le_bytes(block);

			#[expect(clippy::expect_used)]
			let mut text = vec![
				0u8;
				length
					.try_into()
					.expect("vendor length does not fit into usize")
			];

			d.read_exact(&mut text)?;
			String::from_utf8(text)?
		};

		d.read_exact(&mut block)?;

		#[expect(clippy::expect_used)]
		let n_comments: usize = u32::from_le_bytes(block)
			.try_into()
			.expect("comment count does not fit into usize");

		let mut comments = Vec::new();
		let mut pictures = Vec::new();
		for _ in 0..n_comments {
			let comment = {
				d.read_exact(&mut block)?;

				let length = u32::from_le_bytes(block);

				#[expect(clippy::expect_used)]
				let mut text = vec![
					0u8;
					length
						.try_into()
						.expect("comment length does not fit into usize")
				];

				d.read_exact(&mut text)?;

				String::from_utf8(text)?
			};
			let (var, val) = comment
				.split_once('=')
				.ok_or(FlacDecodeError::MalformedCommentString(comment.clone()))?;

			if !val.is_empty() {
				if var.to_uppercase() == "METADATA_BLOCK_PICTURE" {
					pictures.push(FlacPictureBlock::decode(
						&base64::prelude::BASE64_STANDARD
							.decode(val)
							.map_err(FlacDecodeError::MalformedPicture)?,
					)?);
				} else {
					// Make sure empty strings are saved as "None"
					comments.push((
						TagType::from_str(var).unwrap_or(TagType::Other(var.into())),
						val.into(),
					));
				}
			};
		}

		Ok(Self {
			vendor: vendor.into(),
			comments,
			pictures,
		})
	}
}

impl VorbisComment {
	/// Get the number of bytes that `encode()` will write.
	#[expect(clippy::expect_used)]
	pub fn get_len(&self) -> u32 {
		let mut sum: u32 = 0;
		sum += u32::try_from(self.vendor.len()).expect("vendor length does not fit into u32") + 4;
		sum += 4;

		for (tagtype, value) in &self.comments {
			let tagtype_str = tagtype.to_vorbis_string();
			let str = format!("{tagtype_str}={value}");
			sum +=
				4 + u32::try_from(str.len()).expect("comment string length does not fit into u32");
		}

		for p in &self.pictures {
			// Compute b64 len
			let mut x = p.get_len();
			if x % 3 != 0 {
				x -= x % 3;
				x += 3;
			}

			#[expect(clippy::integer_division)]
			{
				sum += 4 * (x / 3);
			}

			// Add "METADATA_BLOCK_PICTURE="
			sum += 23;

			// Add length bytes
			sum += 4;
		}

		return sum;
	}

	/// Try to encode this vorbis comment
	#[expect(clippy::expect_used)]
	pub fn encode(&self, target: &mut impl Write) -> Result<(), FlacEncodeError> {
		target.write_all(
			&u32::try_from(self.vendor.len())
				.expect("vendor length does not fit into u32")
				.to_le_bytes(),
		)?;
		target.write_all(self.vendor.as_bytes())?;

		target.write_all(
			&u32::try_from(self.comments.len() + self.pictures.len())
				.expect("total comment count does not fit into u32")
				.to_le_bytes(),
		)?;

		for (tagtype, value) in &self.comments {
			let tagtype_str = tagtype.to_vorbis_string();
			let str = format!("{tagtype_str}={value}");
			target.write_all(
				&u32::try_from(str.len())
					.expect("comment string length does not fit into u32")
					.to_le_bytes(),
			)?;
			target.write_all(str.as_bytes())?;
		}

		for p in &self.pictures {
			let mut pic_data = Vec::new();
			p.encode(false, false, &mut pic_data)?;

			let pic_string = format!(
				"METADATA_BLOCK_PICTURE={}",
				&base64::prelude::BASE64_STANDARD.encode(&pic_data)
			);

			target.write_all(
				&u32::try_from(pic_string.len())
					.expect("picture string length does not fit into u32")
					.to_le_bytes(),
			)?;
			target.write_all(pic_string.as_bytes())?;
		}

		return Ok(());
	}
}