organic/src/wasm/standard_properties.rs

use serde::Deserialize;
use serde::Serialize;

use super::to_wasm::ToWasmContext;
use super::to_wasm::ToWasmStandardProperties;
use crate::types::PostBlank;
use crate::types::StandardProperties;

#[derive(Debug, Serialize, Deserialize)]
pub(crate) struct WasmStandardProperties {
    pub(crate) begin: usize,
    pub(crate) end: usize,
    pub(crate) contents_begin: Option<usize>,
    pub(crate) contents_end: Option<usize>,
    pub(crate) post_blank: PostBlank,
}

impl<'s, SP: StandardProperties<'s>> ToWasmStandardProperties for SP {
    type Output = WasmStandardProperties;

    fn to_wasm_standard_properties(
        &self,
        wasm_context: ToWasmContext<'_>,
    ) -> Result<Self::Output, crate::error::CustomError> {
        let (begin, end) = get_char_indices(wasm_context.full_document, self.get_source());
        let (contents_begin, contents_end) = match self.get_contents() {
            Some(contents) => {
                let (begin, end) = get_char_indices(wasm_context.full_document, contents);
                (Some(begin), Some(end))
            }
            None => (None, None),
        };

        let post_blank = self.get_post_blank();
        Ok(WasmStandardProperties {
            begin,
            end,
            contents_begin,
            contents_end,
            post_blank,
        })
    }
}

fn get_char_indices(original_document: &str, subset: &str) -> (usize, usize) {
    let (begin_byte, end_byte) = get_rust_byte_offsets(original_document, subset);
    // Add 1 to make this 1-based to match emacs.
    let begin_char = original_document[..begin_byte].chars().count() + 1;
    // Also 1-based:
    let end_char = begin_char + original_document[begin_byte..end_byte].chars().count();
    (begin_char, end_char)
}

/// Get the byte offset into source that the string slice exists at.
///
/// These offsets are zero-based.
fn get_rust_byte_offsets(original_document: &str, subset: &str) -> (usize, usize) {
    debug_assert!(is_slice_of(original_document, subset));
    let offset = subset.as_ptr() as usize - original_document.as_ptr() as usize;
    let end = offset + subset.len();
    (offset, end)
}

/// Check if the child string slice is a slice of the parent string slice.
fn is_slice_of(parent: &str, child: &str) -> bool {
    let parent_start = parent.as_ptr() as usize;
    let parent_end = parent_start + parent.len();
    let child_start = child.as_ptr() as usize;
    let child_end = child_start + child.len();
    child_start >= parent_start && child_end <= parent_end
}