Extract diff parsing into dedicated src/diff module

Co-authored-by: oleander <220827+oleander@users.noreply.github.com>

Author: Copilot

examples/multi_step_commit.rs

@@ -2,7 +2,8 @@ use std::env;
 
 use anyhow::Result;
 use async_openai::Client;
-use ai::multi_step_integration::{generate_commit_message_local, generate_commit_message_multi_step, parse_diff};
+use ai::multi_step_integration::{generate_commit_message_local, generate_commit_message_multi_step};
+use ai::diff::parser::parse_diff;
 
 #[tokio::main]
 async fn main() -> Result<()> {

src/diff/mod.rs

@@ -0,0 +1,10 @@
+//! Diff processing and parsing utilities.
+//!
+//! This module handles parsing git diffs into structured data
+//! and provides utilities for working with diff content.
+
+pub mod parser;
+pub mod traits;
+
+pub use parser::{ParsedFile, parse_diff};
+pub use traits::{FilePath, Utf8String, DiffDeltaPath};

src/diff/parser.rs

@@ -0,0 +1,359 @@
+//! Git diff parsing utilities.
+
+use anyhow::Result;
+
+/// Represents a parsed file from a git diff
+#[derive(Debug, Clone)]
+pub struct ParsedFile {
+  pub path: String,
+  pub operation: String,
+  pub diff_content: String,
+}
+
+/// Extracts file path from diff header parts
+///
+/// Handles various git prefixes (a/, b/, c/, i/) and /dev/null for deleted files.
+///
+/// # Arguments
+/// * `parts` - The whitespace-split parts from a "diff --git" line
+///
+/// # Returns
+/// * `Option<String>` - The extracted path without prefixes, or None if parsing fails
+fn extract_file_path_from_diff_parts(parts: &[&str]) -> Option<String> {
+  if parts.len() < 4 {
+    return None;
+  }
+
+  // Helper to strip git prefixes (a/, b/, c/, i/)
+  let strip_prefix = |s: &str| {
+    s.trim_start_matches("a/")
+      .trim_start_matches("b/")
+      .trim_start_matches("c/")
+      .trim_start_matches("i/")
+      .to_string()
+  };
+
+  let new_path = strip_prefix(parts[3]);
+  let old_path = strip_prefix(parts[2]);
+
+  // Prefer new path unless it's /dev/null (deleted file)
+  Some(if new_path == "/dev/null" || new_path == "dev/null" {
+    old_path
+  } else {
+    new_path
+  })
+}
+
+/// Parse git diff into individual file changes.
+///
+/// Handles various diff formats including:
+/// - Standard git diff output
+/// - Diffs with commit hashes
+/// - Diffs with various path prefixes (a/, b/, c/, i/)
+/// - Deleted files (/dev/null paths)
+///
+/// # Arguments
+/// * `diff_content` - Raw git diff text
+///
+/// # Returns
+/// * `Result<Vec<ParsedFile>>` - Parsed files or error
+pub fn parse_diff(diff_content: &str) -> Result<Vec<ParsedFile>> {
+  let mut files = Vec::new();
+  let mut current_file: Option<ParsedFile> = None;
+  let mut current_diff = String::new();
+
+  // Debug output
+  log::debug!("Parsing diff with {} lines", diff_content.lines().count());
+
+  // Add more detailed logging for debugging
+  if log::log_enabled!(log::Level::Debug) && !diff_content.is_empty() {
+    // Make sure we truncate at a valid UTF-8 character boundary
+    let preview = if diff_content.len() > 500 {
+      let truncated_index = diff_content
+        .char_indices()
+        .take_while(|(i, _)| *i < 500)
+        .last()
+        .map(|(i, c)| i + c.len_utf8())
+        .unwrap_or(0);
+
+      format!("{}... (truncated)", &diff_content[..truncated_index])
+    } else {
+      diff_content.to_string()
+    };
+    log::debug!("Diff content preview: \n{preview}");
+  }
+
+  // Handle different diff formats
+  let mut in_diff_section = false;
+  let mut _commit_hash_line: Option<&str> = None;
+
+  // First scan to detect if this is a commit message with hash
+  for line in diff_content.lines().take(3) {
+    if line.len() >= 40 && line.chars().take(40).all(|c| c.is_ascii_hexdigit()) {
+      _commit_hash_line = Some(line);
+      break;
+    }
+  }
+
+  // Process line by line
+  for line in diff_content.lines() {
+    // Skip commit hash lines and other metadata
+    if line.starts_with("commit ") || (line.len() >= 40 && line.chars().take(40).all(|c| c.is_ascii_hexdigit())) || line.is_empty() {
+      continue;
+    }
+
+    // Check if we're starting a new file diff
+    if line.starts_with("diff --git") {
+      in_diff_section = true;
+      // Save previous file if exists
+      if let Some(mut file) = current_file.take() {
+        file.diff_content = current_diff.clone();
+        log::debug!("Adding file to results: {} ({})", file.path, file.operation);
+        files.push(file);
+        current_diff.clear();
+      }
+
+      // Extract file path more carefully
+      let parts: Vec<&str> = line.split_whitespace().collect();
+      if let Some(path) = extract_file_path_from_diff_parts(&parts) {
+        log::debug!("Found new file in diff: {path}");
+        current_file = Some(ParsedFile {
+          path,
+          operation: "modified".to_string(), // Default, will be updated
+          diff_content: String::new()
+        });
+      }
+
+      // Add the header line to the diff content
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if line.starts_with("new file mode") {
+      if let Some(ref mut file) = current_file {
+        log::debug!("File {} is newly added", file.path);
+        file.operation = "added".to_string();
+      }
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if line.starts_with("deleted file mode") {
+      if let Some(ref mut file) = current_file {
+        log::debug!("File {} is deleted", file.path);
+        file.operation = "deleted".to_string();
+      }
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if line.starts_with("rename from") || line.starts_with("rename to") {
+      if let Some(ref mut file) = current_file {
+        log::debug!("File {} is renamed", file.path);
+        file.operation = "renamed".to_string();
+      }
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if line.starts_with("Binary files") {
+      if let Some(ref mut file) = current_file {
+        log::debug!("File {} is binary", file.path);
+        file.operation = "binary".to_string();
+      }
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if line.starts_with("index ") || line.starts_with("--- ") || line.starts_with("+++ ") || line.starts_with("@@ ") {
+      // These are important diff headers that should be included
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    } else if in_diff_section {
+      current_diff.push_str(line);
+      current_diff.push('\n');
+    }
+  }
+
+  // Don't forget the last file
+  if let Some(mut file) = current_file {
+    file.diff_content = current_diff;
+    log::debug!("Adding final file to results: {} ({})", file.path, file.operation);
+    files.push(file);
+  }
+
+  // If we didn't parse any files, check if this looks like a raw git diff output
+  // from commands like `git show` that include commit info at the top
+  if files.is_empty() && !diff_content.trim().is_empty() {
+    log::debug!("Trying to parse as raw git diff output with commit info");
+
+    // Extract sections that start with "diff --git"
+    let sections: Vec<&str> = diff_content.split("diff --git").skip(1).collect();
+
+    if !sections.is_empty() {
+      for (i, section) in sections.iter().enumerate() {
+        // Add the "diff --git" prefix back
+        let full_section = format!("diff --git{section}");
+
+        // Extract file path from the section more carefully
+        let mut found_path = false;
+
+        // Safer approach: iterate through lines and find the path
+        let mut extracted_path = String::new();
+        for section_line in full_section.lines().take(3) {
+          if section_line.starts_with("diff --git") {
+            let parts: Vec<&str> = section_line.split_whitespace().collect();
+            if let Some(p) = extract_file_path_from_diff_parts(&parts) {
+              extracted_path = p;
+              found_path = true;
+              break;
+            }
+          }
+        }
+
+        if found_path {
+          log::debug!("Found file in section {i}: {extracted_path}");
+          files.push(ParsedFile {
+            path:         extracted_path,
+            operation:    "modified".to_string(), // Default
+            diff_content: full_section
+          });
+        }
+      }
+    }
+  }
+
+  // If still no files were parsed, treat the entire diff as a single change
+  if files.is_empty() && !diff_content.trim().is_empty() {
+    log::debug!("No standard diff format found, treating as single file change");
+    files.push(ParsedFile {
+      path:         "unknown".to_string(),
+      operation:    "modified".to_string(),
+      diff_content: diff_content.to_string()
+    });
+  }
+
+  log::debug!("Parsed {} files from diff", files.len());
+
+  // Add detailed debug output for each parsed file
+  if log::log_enabled!(log::Level::Debug) {
+    for (i, file) in files.iter().enumerate() {
+      let content_preview = if file.diff_content.len() > 200 {
+        // Make sure we truncate at a valid UTF-8 character boundary
+        let truncated_index = file
+          .diff_content
+          .char_indices()
+          .take_while(|(i, _)| *i < 200)
+          .last()
+          .map(|(i, c)| i + c.len_utf8())
+          .unwrap_or(0);
+
+        format!("{}... (truncated)", &file.diff_content[..truncated_index])
+      } else {
+        file.diff_content.clone()
+      };
+      log::debug!("File {}: {} ({})\nContent preview:\n{}", i, file.path, file.operation, content_preview);
+    }
+  }
+
+  Ok(files)
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn test_parse_diff() {
+    let diff = r#"diff --git a/src/main.rs b/src/main.rs
+index 1234567..abcdefg 100644
+--- a/src/main.rs
++++ b/src/main.rs
+@@ -1,5 +1,6 @@
+ fn main() {
+-    println!("Hello");
++    println!("Hello, world!");
++    println!("New line");
+ }
+diff --git a/Cargo.toml b/Cargo.toml
+new file mode 100644
+index 0000000..1111111
+--- /dev/null
++++ b/Cargo.toml
+@@ -0,0 +1,8 @@
++[package]
++name = "test"
++version = "0.1.0"
+"#;
+
+    let files = parse_diff(diff).unwrap();
+    assert_eq!(files.len(), 2);
+    assert_eq!(files[0].path, "src/main.rs");
+    assert_eq!(files[0].operation, "modified");
+    assert_eq!(files[1].path, "Cargo.toml");
+    assert_eq!(files[1].operation, "added");
+
+    // Verify files contain diff content
+    assert!(!files[0].diff_content.is_empty());
+    assert!(!files[1].diff_content.is_empty());
+  }
+
+  #[test]
+  fn test_parse_diff_with_commit_hash() {
+    // Test with a commit hash and message before the diff
+    let diff = r#"0472ffa1665c4c5573fb8f7698c9965122eda675 Update files
+
+diff --git a/test.js b/test.js
+new file mode 100644
+index 0000000..a730e61
+--- /dev/null
++++ b/test.js
+@@ -0,0 +1 @@
++console.log('Hello');
+"#;
+
+    let files = parse_diff(diff).unwrap();
+    assert_eq!(files.len(), 1);
+    assert_eq!(files[0].path, "test.js");
+    assert_eq!(files[0].operation, "added");
+  }
+
+  #[test]
+  fn test_parse_diff_with_c_i_prefixes() {
+    // Test with c/ and i/ prefixes that appear in git hook diffs
+    let diff = r#"diff --git c/test.md i/test.md
+new file mode 100644
+index 0000000..6c61a60
+--- /dev/null
++++ i/test.md
+@@ -0,0 +1 @@
++# Test File
+
+diff --git c/test.js i/test.js
+new file mode 100644
+index 0000000..a730e61
+--- /dev/null
++++ i/test.js
+@@ -0,0 +1 @@
++console.log('Hello');
+"#;
+
+    let files = parse_diff(diff).unwrap();
+    assert_eq!(files.len(), 2);
+    assert_eq!(files[0].path, "test.md", "Should extract clean path without c/ prefix");
+    assert_eq!(files[0].operation, "added");
+    assert_eq!(files[1].path, "test.js", "Should extract clean path without i/ prefix");
+    assert_eq!(files[1].operation, "added");
+
+    // Verify files contain diff content
+    assert!(files[0].diff_content.contains("# Test File"));
+    assert!(files[1].diff_content.contains("console.log"));
+  }
+
+  #[test]
+  fn test_parse_diff_with_deleted_file() {
+    let diff = r#"diff --git a/test.txt b/test.txt
+deleted file mode 100644
+index 9daeafb..0000000
+--- a/test.txt
++++ /dev/null
+@@ -1 +0,0 @@
+-test
+"#;
+
+    let files = parse_diff(diff).unwrap();
+    assert_eq!(files.len(), 1);
+    assert_eq!(files[0].path, "test.txt");
+    assert_eq!(files[0].operation, "deleted");
+  }
+}