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use super::*;
use std::convert::TryFrom;

/// An encoder for the tag section.
///
/// # Example
///
/// ```
/// use wasm_encoder::{Module, TagSection, TagType, TagKind};
///
/// let mut tags = TagSection::new();
/// tags.tag(TagType {
///     kind: TagKind::Exception,
///     func_type_idx: 0,
/// });
///
/// let mut module = Module::new();
/// module.section(&tags);
///
/// let wasm_bytes = module.finish();
/// ```
#[derive(Clone, Debug)]
pub struct TagSection {
    bytes: Vec<u8>,
    num_added: u32,
}

impl TagSection {
    /// Create a new tag section encoder.
    pub fn new() -> TagSection {
        TagSection {
            bytes: vec![],
            num_added: 0,
        }
    }

    /// How many tags have been defined inside this section so far?
    pub fn len(&self) -> u32 {
        self.num_added
    }

    /// Define a tag.
    pub fn tag(&mut self, tag_type: TagType) -> &mut Self {
        tag_type.encode(&mut self.bytes);
        self.num_added += 1;
        self
    }
}

impl Section for TagSection {
    fn id(&self) -> u8 {
        SectionId::Tag.into()
    }

    fn encode<S>(&self, sink: &mut S)
    where
        S: Extend<u8>,
    {
        let num_added = encoders::u32(self.num_added);
        let n = num_added.len();
        sink.extend(
            encoders::u32(u32::try_from(n + self.bytes.len()).unwrap())
                .chain(num_added)
                .chain(self.bytes.iter().copied()),
        );
    }
}

#[allow(missing_docs)]
#[repr(u8)]
#[derive(Clone, Copy, Debug)]
pub enum TagKind {
    Exception = 0x0,
}

/// A tag's type.
#[derive(Clone, Copy, Debug)]
pub struct TagType {
    /// The kind of tag
    pub kind: TagKind,
    /// The function type this tag uses
    pub func_type_idx: u32,
}

impl TagType {
    pub(crate) fn encode(&self, bytes: &mut Vec<u8>) {
        bytes.push(self.kind as u8);
        bytes.extend(encoders::u32(self.func_type_idx));
    }
}