Fix the generated Cargo.toml after rustlings init

1 files changed, 57 insertions, 0 deletions

diff --git a/src/cargo_toml.rs b/src/cargo_toml.rs
new file mode 100644
index 0000000..2345a7e
--- /dev/null
+++ b/src/cargo_toml.rs
@@ -0,0 +1,57 @@
+use anyhow::{Context, Result};
+
+use crate::info_file::ExerciseInfo;
+
+pub fn bins_start_end_ind(cargo_toml: &str) -> Result<(usize, usize)> {
+    let start_ind = cargo_toml
+        .find("bin = [")
+        .context("Failed to find the start of the `bin` list (`bin = [`)")?
+        + 7;
+    let end_ind = start_ind
+        + cargo_toml
+            .get(start_ind..)
+            .and_then(|slice| slice.as_bytes().iter().position(|c| *c == b']'))
+            .context("Failed to find the end of the `bin` list (`]`)")?;
+
+    Ok((start_ind, end_ind))
+}
+
+pub fn append_bins(
+    buf: &mut Vec<u8>,
+    exercise_infos: &[ExerciseInfo],
+    exercise_path_prefix: &[u8],
+) {
+    buf.push(b'\n');
+    for exercise_info in exercise_infos {
+        buf.extend_from_slice(b"  { name = \"");
+        buf.extend_from_slice(exercise_info.name.as_bytes());
+        buf.extend_from_slice(b"\", path = \"");
+        buf.extend_from_slice(exercise_path_prefix);
+        buf.extend_from_slice(b"exercises/");
+        if let Some(dir) = &exercise_info.dir {
+            buf.extend_from_slice(dir.as_bytes());
+            buf.push(b'/');
+        }
+        buf.extend_from_slice(exercise_info.name.as_bytes());
+        buf.extend_from_slice(b".rs\" },\n");
+    }
+}
+
+pub fn updated_cargo_toml(
+    exercise_infos: &[ExerciseInfo],
+    current_cargo_toml: &str,
+    exercise_path_prefix: &[u8],
+) -> Result<Vec<u8>> {
+    let (bins_start_ind, bins_end_ind) = bins_start_end_ind(current_cargo_toml)?;
+
+    let mut updated_cargo_toml = Vec::with_capacity(1 << 13);
+    updated_cargo_toml.extend_from_slice(current_cargo_toml[..bins_start_ind].as_bytes());
+    append_bins(
+        &mut updated_cargo_toml,
+        exercise_infos,
+        exercise_path_prefix,
+    );
+    updated_cargo_toml.extend_from_slice(current_cargo_toml[bins_end_ind..].as_bytes());
+
+    Ok(updated_cargo_toml)
+}