diff --git a/Cargo.lock b/Cargo.lock
index 305d0e4..bc25918 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -284,9 +284,9 @@ dependencies = [
 
 [[package]]
 name = "git2"
-version = "0.18.1"
+version = "0.18.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fbf97ba92db08df386e10c8ede66a2a0369bd277090afd8710e19e38de9ec0cd"
+checksum = "1b3ba52851e73b46a4c3df1d89343741112003f0f6f13beb0dfac9e457c3fdcd"
 dependencies = [
  "bitflags 2.4.2",
  "libc",
@@ -377,9 +377,9 @@ checksum = "9c198f91728a82281a64e1f4f9eeb25d82cb32a5de251c6bd1b5154d63a8e7bd"
 
 [[package]]
 name = "libgit2-sys"
-version = "0.16.1+1.7.1"
+version = "0.16.2+1.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f2a2bb3680b094add03bb3732ec520ece34da31a8cd2d633d1389d0f0fb60d0c"
+checksum = "ee4126d8b4ee5c9d9ea891dd875cfdc1e9d0950437179104b183d7d8a74d24e8"
 dependencies = [
  "cc",
  "libc",
diff --git a/Cargo.toml b/Cargo.toml
index 122c669..aed59ba 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,7 +12,7 @@ description = "Utility to modify commit timestamps of a git repository"
 chrono = "0.4.33"
 chrono-tz = "0.8.5"
 clap = { version = "4.4.18", features = ["derive"] }
-git2 = "0.18.1"
+git2 = "0.18.2"
 iana-time-zone = "0.1.60"
 itertools = "0.12.1"
 once_cell = "1.19.0"
diff --git a/src/git.rs b/src/git.rs
new file mode 100644
index 0000000..dcf6179
--- /dev/null
+++ b/src/git.rs
@@ -0,0 +1,47 @@
+use chrono::Duration;
+use git2::{Commit, Repository};
+use itertools::Itertools;
+use thiserror::Error;
+
+use crate::time::{distribute_across_ranges_with_jitter, TimeRange};
+
+#[derive(Debug, Error)]
+pub(crate) enum GitErrors {
+    #[error("end is not a parent of start")]
+    NotAParent,
+
+    #[error("{0} is not a commit hash in the repo")]
+    NotACommit(String),
+}
+
+/// find the number of commits between start and end,
+/// where end is a parent commit of start
+fn get_no_of_commits(start: &Commit, end: &Commit) -> Result<u32, GitErrors> {
+    match start.parent_ids().find_position(|sha| sha == &end.id()) {
+        Some(tuple) => Ok(tuple.0.try_into().expect("commit has over 2^32 parents")),
+        None => Err(GitErrors::NotAParent),
+    }
+}
+
+// will need to do an in memory rebase, ammending each commit with a new signature.
+pub fn rebase_commits_across_timerange<Tz: chrono::TimeZone>(
+    repo: &Repository,
+    start_sha: &str,
+    end_sha: &str,
+    ranges: &[TimeRange<Tz>],
+    max_jitter: &Duration,
+) -> Result<(), GitErrors> {
+    let start_commit = if let Ok(commit) = repo.find_commit_by_prefix(start_sha) {
+        commit
+    } else {
+        return Err(GitErrors::NotACommit(start_sha.to_string()));
+    };
+    let end_commit = if let Ok(commit) = repo.find_commit_by_prefix(end_sha) {
+        commit
+    } else {
+        return Err(GitErrors::NotACommit(end_sha.to_string()));
+    };
+    let num_commits = get_no_of_commits(&start_commit, &end_commit)?;
+    let times = distribute_across_ranges_with_jitter(ranges, num_commits, max_jitter);
+    todo!()
+}
diff --git a/src/main.rs b/src/main.rs
index 6607505..ed50bb0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
 mod args;
 mod err;
+mod git;
 mod time;
 
 use chrono::prelude::*;
@@ -9,13 +10,19 @@ use clap::Parser;
 fn main() {
     let cli = args::Cli::parse();
     println!("{:#?}", cli);
-    let start_time = match cli.timezone {
-        Some(tz) => tz.from_local_datetime(&cli.start_time).unwrap(),
-        None => get_local_timezone()
-            .expect("Could not get local timezone")
-            .from_local_datetime(&cli.start_time)
-            .unwrap(),
+    let tz = cli
+        .timezone
+        .unwrap_or_else(|| get_local_timezone().expect("Could not get local timezone"));
+    let start_time = tz.from_local_datetime(&cli.start_time).unwrap();
+    let end_time = if let Some(time) = cli.end_time {
+        tz.from_local_datetime(&time).unwrap()
+    } else {
+        Utc::now().with_timezone(&tz)
     };
+    println!(
+        "start_time = {:#?}, end_time = {:#?}, tz = {:#?}",
+        start_time, end_time, tz
+    )
 }
 
 fn get_local_timezone() -> Result<Tz, String> {
diff --git a/src/time.rs b/src/time.rs
index 7a4b93a..8bda399 100644
--- a/src/time.rs
+++ b/src/time.rs
@@ -9,7 +9,6 @@ pub struct TimeRange<Tz: chrono::TimeZone> {
 }
 
 impl<Tz: chrono::TimeZone> TimeRange<Tz> {
-
     /// whether a time instance lies within the time range
     pub fn is_in_range<Otz: chrono::TimeZone>(&self, other: &DateTime<Otz>) -> bool {
         (self.start <= *other) && (other <= &self.end)