ainl-mission 0.1.0

//! Git snapshot helpers: resolve repo root, `stash create`, `stash apply` via injected shell.

use std::path::{Path, PathBuf};

use ainl_contracts::FeatureSnapshot;
use chrono::Utc;
use thiserror::Error;

/// Result of a shell invocation.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ShellOutput {
    pub exit_code: i32,
    pub stdout: String,
    pub stderr: String,
}

/// Injected shell runner — hosts supply real `shell_exec` / subprocess policy.
pub trait ShellRunner {
    fn run(&self, cwd: &Path, program: &str, args: &[&str]) -> Result<ShellOutput, GitSnapshotError>;
}

/// Git snapshot operation error.
#[derive(Debug, Error)]
pub enum GitSnapshotError {
    #[error("shell: {0}")]
    Shell(String),
    #[error("not a git repository at {0}")]
    NotARepo(PathBuf),
    #[error("git command failed (exit {exit_code}): {stderr}")]
    CommandFailed {
        exit_code: i32,
        stderr: String,
    },
    #[error("missing stash sha in output")]
    MissingStashSha,
}

/// Resolve git repository top-level for `path` using `git rev-parse --show-toplevel`.
pub fn resolve_repo_toplevel(
    shell: &dyn ShellRunner,
    path: &Path,
) -> Result<PathBuf, GitSnapshotError> {
    let out = shell.run(path, "git", &["rev-parse", "--show-toplevel"])?;
    if out.exit_code != 0 {
        return Err(GitSnapshotError::NotARepo(path.to_path_buf()));
    }
    let top = out.stdout.trim().to_string();
    if top.is_empty() {
        return Err(GitSnapshotError::NotARepo(path.to_path_buf()));
    }
    Ok(PathBuf::from(top))
}

/// Create a lazy snapshot: `git stash create` + `git rev-parse HEAD`.
pub fn create_snapshot(
    shell: &dyn ShellRunner,
    path: &Path,
) -> Result<FeatureSnapshot, GitSnapshotError> {
    let repo_toplevel = resolve_repo_toplevel(shell, path)?;
    let stash_out = shell.run(&repo_toplevel, "git", &["stash", "create"])?;
    if stash_out.exit_code != 0 {
        return Err(GitSnapshotError::CommandFailed {
            exit_code: stash_out.exit_code,
            stderr: stash_out.stderr,
        });
    }
    let stash_sha = stash_out.stdout.trim().to_string();
    if stash_sha.is_empty() {
        return Err(GitSnapshotError::MissingStashSha);
    }
    let head_out = shell.run(&repo_toplevel, "git", &["rev-parse", "HEAD"])?;
    if head_out.exit_code != 0 {
        return Err(GitSnapshotError::CommandFailed {
            exit_code: head_out.exit_code,
            stderr: head_out.stderr,
        });
    }
    let head_sha = head_out.stdout.trim().to_string();
    Ok(FeatureSnapshot {
        repo_toplevel,
        stash_sha,
        head_sha,
        taken_at: Utc::now(),
    })
}

/// Result of applying a lazy git stash snapshot.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SnapshotApplyResult {
    pub applied: bool,
    pub conflicts: Vec<String>,
}

fn parse_apply_conflicts(stdout: &str, stderr: &str) -> Vec<String> {
    let mut conflicts = Vec::new();
    for line in stdout.lines().chain(stderr.lines()) {
        let trimmed = line.trim();
        if trimmed.is_empty() {
            continue;
        }
        if trimmed.contains("CONFLICT")
            || trimmed.contains("conflict")
            || trimmed.contains("Merge conflict")
        {
            conflicts.push(trimmed.to_string());
        }
    }
    if conflicts.is_empty() {
        let combined = format!("{stdout}{stderr}").trim().to_string();
        if !combined.is_empty() {
            conflicts.push(combined);
        }
    }
    conflicts
}

/// Apply a prior snapshot: `git stash apply <stash_sha>` in `snapshot.repo_toplevel`.
///
/// Returns [`SnapshotApplyResult::applied`] = false with parsed conflict lines when git reports
/// merge conflicts instead of failing the host tool outright.
pub fn apply_snapshot(
    shell: &dyn ShellRunner,
    snapshot: &FeatureSnapshot,
) -> Result<SnapshotApplyResult, GitSnapshotError> {
    let out = shell.run(
        &snapshot.repo_toplevel,
        "git",
        &["stash", "apply", snapshot.stash_sha.as_str()],
    )?;
    if out.exit_code != 0 {
        return Ok(SnapshotApplyResult {
            applied: false,
            conflicts: parse_apply_conflicts(&out.stdout, &out.stderr),
        });
    }
    Ok(SnapshotApplyResult {
        applied: true,
        conflicts: Vec::new(),
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::HashMap;
    use std::sync::Mutex;

    struct MockShell {
        responses: Mutex<HashMap<String, ShellOutput>>,
    }

    impl MockShell {
        fn new() -> Self {
            Self {
                responses: Mutex::new(HashMap::new()),
            }
        }

        fn when(mut self, key: &str, out: ShellOutput) -> Self {
            self.responses.get_mut().unwrap().insert(key.into(), out);
            self
        }
    }

    impl ShellRunner for MockShell {
        fn run(
            &self,
            _cwd: &Path,
            program: &str,
            args: &[&str],
        ) -> Result<ShellOutput, GitSnapshotError> {
            let key = format!("{program} {}", args.join(" "));
            self.responses
                .lock()
                .unwrap()
                .get(&key)
                .cloned()
                .ok_or_else(|| GitSnapshotError::Shell(format!("no mock for {key}")))
        }
    }

    #[test]
    fn resolve_toplevel() {
        let shell = MockShell::new().when(
            "git rev-parse --show-toplevel",
            ShellOutput {
                exit_code: 0,
                stdout: "/repo\n".into(),
                stderr: String::new(),
            },
        );
        let top = resolve_repo_toplevel(&shell, Path::new("/repo/src")).unwrap();
        assert_eq!(top, PathBuf::from("/repo"));
    }

    #[test]
    fn apply_snapshot_reports_conflicts_without_error() {
        let shell = MockShell::new().when(
            "git stash apply deadbeef",
            ShellOutput {
                exit_code: 1,
                stdout: String::new(),
                stderr: "error: patch failed: CONFLICT (content): file.txt\n".into(),
            },
        );
        let snapshot = FeatureSnapshot {
            repo_toplevel: PathBuf::from("/repo"),
            stash_sha: "deadbeef".into(),
            head_sha: "abc".into(),
            taken_at: chrono::Utc::now(),
        };
        let result = apply_snapshot(&shell, &snapshot).unwrap();
        assert!(!result.applied);
        assert!(!result.conflicts.is_empty());
    }

    #[test]
    fn create_snapshot_roundtrip_fields() {
        let shell = MockShell::new()
            .when(
                "git rev-parse --show-toplevel",
                ShellOutput {
                    exit_code: 0,
                    stdout: "/repo\n".into(),
                    stderr: String::new(),
                },
            )
            .when(
                "git stash create",
                ShellOutput {
                    exit_code: 0,
                    stdout: "deadbeef\n".into(),
                    stderr: String::new(),
                },
            )
            .when(
                "git rev-parse HEAD",
                ShellOutput {
                    exit_code: 0,
                    stdout: "cafebabe\n".into(),
                    stderr: String::new(),
                },
            );
        let snap = create_snapshot(&shell, Path::new("/repo")).unwrap();
        assert_eq!(snap.stash_sha, "deadbeef");
        assert_eq!(snap.head_sha, "cafebabe");
    }
}