Move library to a separate crate

Keep the binaries in the root crate, and add a new crate for the
`github-suggestion` library.

I want to add some library code to the CLI programs to extract common
functionality between the different binaries.

1 files changed, 346 insertions, 0 deletions

diff --git a/github-suggestion/src/suggestion.rs b/github-suggestion/src/suggestion.rs
new file mode 100644
index 0000000..2c92e6a
--- /dev/null
+++ b/github-suggestion/src/suggestion.rs
@@ -0,0 +1,346 @@
+use std::io::{BufRead, BufReader, BufWriter, Write};
+use std::path::Path;
+
+use git2::{Patch, Repository};
+use regex::Regex;
+use serde::Deserialize;
+use thiserror::Error;
+
+
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error(transparent)]
+    Git(#[from] git2::Error),
+
+    #[error("{0} is not a blob")]
+    GitObjectNotBlob(git2::Oid),
+
+    #[error("{message}")]
+    BufWriter {
+        source: std::io::IntoInnerError<BufWriter<Vec<u8>>>,
+        message: String,
+    },
+
+    #[error("{message}: {source}")]
+    Io {
+        source: std::io::Error,
+        message: String,
+    },
+
+    #[error("{0} is not valid UTF-8")]
+    InvalidUtf8(String),
+
+    #[error("Regex error: {0}")]
+    Regex(#[from] regex::Error),
+}
+
+#[derive(Debug, PartialEq)]
+enum LineEnding {
+    Lf,
+    CrLf,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct Suggestion {
+    #[serde(rename = "diff_hunk")]
+    diff: String,
+
+    #[serde(rename = "body")]
+    comment: String,
+
+    #[serde(rename = "original_commit_id")]
+    commit: String,
+
+    path: String,
+
+    original_start_line: Option<usize>,
+
+    #[serde(rename = "original_line")]
+    original_end_line: usize,
+}
+
+impl Suggestion {
+    pub fn diff(&self) -> Result<String, Error> {
+        let repo = Repository::open(".")?;
+
+        self.diff_with_repo(&repo)
+    }
+
+    fn diff_with_repo(&self, repo: &Repository) -> Result<String, Error> {
+        let commit = repo.find_commit(self.commit.parse()?)?;
+
+        let path = Path::new(&self.path);
+
+        let object = commit
+            .tree()?
+            .get_path(path)?
+            .to_object(&repo)?;
+
+        let blob = object.as_blob()
+            .ok_or_else(|| Error::GitObjectNotBlob(object.id()))?;
+
+        let blob_reader = BufReader::new(blob.content());
+        let mut new = BufWriter::new(Vec::new());
+        self.apply_to(blob_reader, &mut new)?;
+        let new_buffer = new.into_inner()
+            .map_err(|e| Error::BufWriter {
+                source: e,
+                message: "unable to read right side of patch".to_owned(),
+            })?;
+
+        let mut diff = Patch::from_blob_and_buffer(
+            blob,
+            Some(&path),
+            &new_buffer,
+            Some(&path),
+            None,
+        )?;
+
+        Ok(
+            diff.to_buf()?
+                .as_str()
+                .ok_or_else(|| Error::InvalidUtf8("diff".to_owned()))?
+                .to_owned()
+        )
+    }
+
+    fn suggestion_with_line_ending(
+        &self,
+        line_ending: &LineEnding,
+    ) -> Result<String, Error> {
+        let re = Regex::new(r"(?s).*(?-s)```\s*suggestion.*\n")?;
+        let s = re.replace(&self.comment, "");
+        let s = s.replace("```", "");
+
+        // Suggestion blocks use CRLF by default.
+        if *line_ending == LineEnding::Lf {
+            return Ok(s.replace('\r', ""));
+        }
+
+        Ok(s)
+    }
+
+    pub fn apply(&self) -> Result<(), Error> {
+        let repo = Repository::open(".")?;
+
+        let diff_text = self.diff_with_repo(&repo)?;
+        let diff = git2::Diff::from_buffer(diff_text.as_bytes())?;
+
+        repo.apply(
+            &diff,
+            git2::ApplyLocation::WorkDir,
+            None,
+        )?;
+
+        Ok(())
+    }
+
+    fn apply_to<R: BufRead, W: Write>(
+        &self,
+        reader: R,
+        writer: &mut W,
+    ) -> Result<(), Error> {
+        let mut line_ending = LineEnding::Lf;
+
+        for (i, line) in reader.lines().enumerate() {
+            let line_number = i + 1;
+
+            let line = line.map_err(|e| Error::Io {
+                source: e,
+                message: "Unable to read line".to_owned(),
+            })?;
+
+            // Determine which line endings the file uses by looking at the
+            // first line.
+            if line_number == 1 && is_line_crlf(&line) {
+                line_ending = LineEnding::CrLf;
+            }
+
+            if line_number == self.original_end_line {
+                write!(
+                    writer,
+                    "{}",
+                    self.suggestion_with_line_ending(&line_ending)?,
+                ).map_err(|e| Error::Io {
+                    source: e,
+                    message: "Write error".to_owned(),
+                })?;
+            } else if self.original_start_line.is_none()
+                    || line_number < self.original_start_line.unwrap()
+                    || line_number > self.original_end_line {
+                writeln!(writer, "{}", line)
+                    .map_err(|e| Error::Io {
+                        source: e,
+                        message: "Write error".to_owned(),
+                    })?;
+            }
+        }
+
+        Ok(())
+    }
+}
+
+/// Determine the line ending for `line`.
+///
+/// If the second-to-last character on the first line is "\r", assume CRLF.
+/// Otherwise, default to LF.
+fn is_line_crlf(line: &str) -> bool {
+    if let Some(c) = line.chars().rev().nth(2) {
+        if c == '\r' {
+            return true;
+        }
+    }
+
+    false
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn suggestion_diff_with_repo_generates_diff() {
+        use tempfile::tempdir;
+
+
+        let git_root = tempdir().unwrap();
+        let repo = Repository::init(git_root.path()).unwrap();
+
+        let file = r#"
+     ‘Beware the Jabberwock, my son!
+      The jaws that bite, the claws that catch!
+     Beware the Jubjub bird, and shun
+      The frumious Bandersnatch!’
+
+     He took his vorpal blade in hand:
+      Long time the manxome foe he sought--
+     So rested he by the Tumtum tree,
+      And stood awhile in thought.
+"#;
+
+        let path = "poems/Jabberwocky.txt";
+
+        let mut index = repo.index().unwrap();
+        index.add_frombuffer(
+            &git2::IndexEntry {
+                ctime: git2::IndexTime::new(0, 0),
+                mtime: git2::IndexTime::new(0, 0),
+                dev: 0,
+                ino: 0,
+                mode: 0o100644,
+                uid: 0,
+                gid: 0,
+                file_size: file.len() as u32,
+                id: git2::Oid::zero(),
+                flags: 0,
+                flags_extended: 0,
+                path: path.as_bytes().to_vec(),
+            },
+            file.as_bytes(),
+        ).unwrap();
+        let tree_oid = index.write_tree().unwrap();
+        let tree = repo.find_tree(tree_oid).unwrap();
+
+        let author = git2::Signature::now(
+            "Oshino Shinobu",
+            "oshino.shinobu@example.com",
+        ).unwrap();
+
+        let commit = repo.commit(
+            Some("HEAD"),
+            &author,
+            &author,
+            "Sample commit",
+            &tree,
+            &[],
+        ).unwrap();
+
+        let suggestion = Suggestion {
+            diff: "".to_owned(),
+            comment: r#"``` suggestion
+     He took his vorpal sword in hand:
+      Long time the manxome foe he sought—
+```"#.to_owned(),
+            commit: commit.to_string(),
+            path: path.to_owned(),
+            original_start_line: Some(7),
+            original_end_line: 8,
+        };
+
+        let expected = r#"diff --git a/poems/Jabberwocky.txt b/poems/Jabberwocky.txt
+index 89840a2..06acdfc 100644
+--- a/poems/Jabberwocky.txt
++++ b/poems/Jabberwocky.txt
+@@ -4,7 +4,7 @@
+      Beware the Jubjub bird, and shun
+       The frumious Bandersnatch!’
+ 
+-     He took his vorpal blade in hand:
+-      Long time the manxome foe he sought--
++     He took his vorpal sword in hand:
++      Long time the manxome foe he sought—
+      So rested he by the Tumtum tree,
+       And stood awhile in thought.
+"#;
+
+        assert_eq!(
+            suggestion.diff_with_repo(&repo).unwrap(),
+            expected,
+        );
+    }
+
+    #[test]
+    fn suggestion_apply_to_writes_patch_to_writer() {
+        use std::io::Cursor;
+
+
+        let mut original_buffer = Vec::new();
+        let original = r#"
+     ‘Beware the Jabberwock, my son!
+      The jaws that bite, the claws that catch!
+     Beware the Jubjub bird, and shun
+      The frumious Bandersnatch!’
+
+     He took his vorpal blade in hand:
+      Long time the manxome foe he sought--
+     So rested he by the Tumtum tree,
+      And stood awhile in thought.
+"#;
+
+        write!(original_buffer, "{}", original).unwrap();
+
+        let suggestion = Suggestion {
+            diff: "".to_owned(),
+            comment: r#"``` suggestion
+     He took his vorpal sword in hand:
+      Long time the manxome foe he sought—
+```"#.to_owned(),
+            commit: "".to_owned(),
+            path: "".to_owned(),
+            original_start_line: Some(7),
+            original_end_line: 8,
+        };
+
+        let expected = r#"
+     ‘Beware the Jabberwock, my son!
+      The jaws that bite, the claws that catch!
+     Beware the Jubjub bird, and shun
+      The frumious Bandersnatch!’
+
+     He took his vorpal sword in hand:
+      Long time the manxome foe he sought—
+     So rested he by the Tumtum tree,
+      And stood awhile in thought.
+"#;
+
+        let original_reader = Cursor::new(original_buffer);
+        let mut actual = Cursor::new(Vec::new());
+        suggestion.apply_to(original_reader, &mut actual).unwrap();
+
+        assert_eq!(
+            std::str::from_utf8(&actual.into_inner()).unwrap(),
+            expected,
+        );
+    }
+}