use anyhow::Context;
use anyhow::Result;
use git2::AnnotatedCommit;
use git2::Repository;
use std::path::Path;

use crate::git::shell_fetch;
use crate::git::utils::is_worktree_dirty;

/// Fast-forward-only pull of the current branch from `remote_name` (default "origin")
/// Uses shell git for fetch (to trigger 1Password SSH prompts) and git2 for fast-forward
pub fn pull_ff_only(repo_path: &Path, remote_name: &str, branch: Option<&str>) -> Result<()> {
    // First check if remote exists
    {
        let repo = Repository::open(repo_path)
            .with_context(|| format!("Failed to open repository at {}", repo_path.display()))?;
        if repo.find_remote(remote_name).is_err() {
            // No remote - nothing to fetch
            return Ok(());
        }
    }

    let branch = branch.unwrap_or("main");

    // Fetch using shell git (uses system SSH, triggers 1Password)
    shell_fetch::fetch(repo_path, remote_name).with_context(|| {
        format!(
            "Fetch failed for remote '{}' in '{}'",
            remote_name,
            repo_path.display()
        )
    })?;

    // Re-open repository to see the fetched refs
    let repo = Repository::open(repo_path)
        .with_context(|| format!("Failed to re-open repository at {}", repo_path.display()))?;

    // Now do the fast-forward using git2
    let remote_ref = format!("refs/remotes/{remote_name}/{branch}");
    let Ok(fetch_head) = repo.find_reference(&remote_ref) else {
        // Remote branch doesn't exist yet
        return Ok(());
    };
    let fetch_commit = repo.reference_to_annotated_commit(&fetch_head)?;

    try_fast_forward(&repo, &format!("refs/heads/{branch}"), &fetch_commit)?;
    Ok(())
}

fn try_fast_forward(
    repo: &Repository,
    local_ref: &str,
    fetch_commit: &AnnotatedCommit,
) -> Result<()> {
    let analysis = repo.merge_analysis(&[fetch_commit])?;
    if analysis.0.is_up_to_date() {
        return Ok(());
    }
    if analysis.0.is_fast_forward() {
        // Safety gate: never force-checkout over local changes
        if is_worktree_dirty(repo)? {
            anyhow::bail!(
                "Cannot fast-forward: working tree has uncommitted changes. Please commit or stash before pulling."
            );
        }
        // TODO(3): Migrate to gitoxide when worktree update support is added upstream
        // (currently marked incomplete in gitoxide README)
        // Ensure HEAD points to the target branch (avoid detach and ensure proper reflog)
        repo.set_head(local_ref)?;
        // Atomically move ref, index, and working tree to the fetched commit
        let obj = repo.find_object(fetch_commit.id(), None)?;
        repo.reset(
            &obj,
            git2::ResetType::Hard,
            Some(git2::build::CheckoutBuilder::default().force()),
        )?;
        return Ok(());
    }
    anyhow::bail!(
        "Non fast-forward update required (local and remote have diverged; rebase or merge needed)."
    )
}
