//! `collect(agent_id, commit_msg, kit_root)` — merge the fork back.
//!
//! Contract:
//!   1. `.DONE` must exist inside the worktree, else `Error::NotDone`
//!   2. `git add -A && git commit` inside the worktree
//!   3. Capture commit SHA, then `git merge --no-ff fork/<id>` in kit_root
//!   4. Move worktree to `_archive/forks/YYYY-MM-DD/<id>/` (preserving
//!      the agent's artefacts for post-hoc review / rescue)
//!   5. `git worktree prune && git branch -D fork/<id>` to clean up refs
//!   6. `kei-ledger done <id>` unless `KEI_FORK_SKIP_LEDGER=1`
//!
//! On SUCCESS: `_forks/<id>/` is gone, archive exists, merge
//! commit is on HEAD of kit_root. Return value carries the SHA and
//! count of files added by the agent.

use crate::error::Error;
use crate::git;
use chrono::Utc;
use serde::{Deserialize, Serialize};
use std::fs;
use std::path::{Path, PathBuf};
use std::process::Command;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CollectReport {
    pub files_added: usize,
    pub commit_sha: String,
    pub archive_path: PathBuf,
}

pub fn collect(agent_id: &str, commit_msg: &str, kit_root: &Path) -> Result<CollectReport, Error> {
    let worktree_abs = kit_root.join("_forks").join(agent_id);
    if !worktree_abs.join(".DONE").exists() {
        return Err(Error::NotDone(agent_id.to_string()));
    }
    let files_added = count_tracked_files(&worktree_abs);

    let branch = format!("fork/{agent_id}");
    git::add_all(&worktree_abs)?;
    git::commit(&worktree_abs, commit_msg)?;
    let commit_sha = git::rev_parse_head(&worktree_abs)?;

    let merge_msg = format!("Merge {branch}");
    git::merge_no_ff(kit_root, &branch, &merge_msg)?;

    let archive_path = archive_worktree(kit_root, agent_id, &worktree_abs)?;

    // worktree_remove is unnecessary after fs::rename — prune cleans the
    // stale worktree metadata and branch -D removes the ref.
    let _ = git::worktree_prune(kit_root);
    let _ = git::branch_delete(kit_root, &branch);

    ledger_done(agent_id)?;

    Ok(CollectReport {
        files_added,
        commit_sha,
        archive_path,
    })
}

fn count_tracked_files(worktree_abs: &Path) -> usize {
    // Cheap approximation — walk the worktree, skip `.git*` and the
    // KEI_FORK meta file. Used for the report only, not for decisions.
    fn walk(dir: &Path) -> usize {
        let mut n = 0;
        let Ok(rd) = fs::read_dir(dir) else { return 0 };
        for e in rd.flatten() {
            let p = e.path();
            let name = e.file_name();
            let s = name.to_string_lossy();
            if s.starts_with(".git") {
                continue;
            }
            if p.is_dir() {
                n += walk(&p);
            } else {
                n += 1;
            }
        }
        n
    }
    walk(worktree_abs)
}

fn archive_worktree(
    kit_root: &Path,
    agent_id: &str,
    worktree_abs: &Path,
) -> Result<PathBuf, Error> {
    let date = Utc::now().format("%Y-%m-%d").to_string();
    let archive_dir = kit_root.join("_archive/forks").join(&date);
    fs::create_dir_all(&archive_dir)?;
    let target = archive_dir.join(agent_id);
    if target.exists() {
        fs::remove_dir_all(&target)?;
    }
    fs::rename(worktree_abs, &target)?;
    Ok(target)
}

fn ledger_skipped() -> bool {
    std::env::var("KEI_FORK_SKIP_LEDGER").ok().as_deref() == Some("1")
}

fn ledger_done(agent_id: &str) -> Result<(), Error> {
    if ledger_skipped() {
        return Ok(());
    }
    let status = Command::new("kei-ledger")
        .args(["done", agent_id, "--summary", "fork collected"])
        .status();
    match status {
        Ok(s) if s.success() => Ok(()),
        Ok(s) => Err(Error::Ledger(format!("kei-ledger done exit {s}"))),
        Err(e) => Err(Error::Ledger(format!("kei-ledger not runnable: {e}"))),
    }
}