//! The cut-over hand-off.
//!
//! While repos with an unmigrated Koh 2 `.koh/` directory still exist on this
//! machine, `koh` is Koh 3 but those repos belong to Koh 2. Rather than let a
//! command fail confusingly, Koh 3 hands it to `koh2` unchanged — same
//! arguments, same terminal. Agents always type `koh`, and every repo gets the
//! Koh that owns it.
//!
//! `migrate` is the exception: it is how such a repo stops being a Koh 2 repo.

module cli

import os
import src.fmt

// hand_over reports whether this invocation belongs to Koh 2, and if so runs
// it. It never returns when the hand-off happens.
pub fn hand_over(argv []string) {
	if argv.len < 2 {
		return
	}
	command := argv[1]
	if command in ['migrate', 'man', 'help', '--help', '-h', '--version', '-v'] {
		return
	}
	if !inside_koh2_repo(os.getwd()) {
		return
	}
	target := koh2_binary()
	if target == '' {
		eprintln('  ${fmt.red(fmt.glyph_fail)} this folder holds a Koh 2 repo, and koh2 is not on PATH')
		eprintln('  install koh2, or run "koh migrate" to convert this repo')
		exit(1)
	}
	// execvp builds argv as [path, ...cmdargs], so the arguments go without
	// our own argv[0].
	os.execvp(target, argv[1..]) or {
		eprintln('  ${fmt.red(fmt.glyph_fail)} could not hand this command to ${target}: ${err.msg()}')
		exit(1)
	}
}

// koh2_binary finds the Koh 2 binary. Before the cutover it is still called
// `koh`, so that name is a fallback — never this binary itself, which would
// hand the command straight back to us for ever.
fn koh2_binary() string {
	if found := os.find_abs_path_of_executable('koh2') {
		return found
	}
	if legacy := os.find_abs_path_of_executable('koh') {
		if os.real_path(legacy) != os.real_path(os.executable()) {
			return legacy
		}
	}
	return ''
}

// inside_koh2_repo looks upward for a `.koh` that is a directory. A `.koh`
// file is Koh 3's.
fn inside_koh2_repo(start string) bool {
	mut dir := os.real_path(start)
	for {
		path := os.join_path(dir, '.koh')
		if os.is_dir(path) {
			return true
		}
		if os.is_file(path) {
			return false
		}
		parent := os.dir(dir)
		if parent == dir || parent == '' {
			return false
		}
		dir = parent
	}
	return false
}