// Package trunk is where a catalogue check finds the trunk's copy of a list that may only shrink (novox/hq ADR 0529 clause 2):
// the file as the catalogue's base commit holds it, to judge a change's list against.
//
// The checker fetches the change's own repository at its base commit beside the change, as it fetches a sibling, and says where
// in MESH_CHECK_BESIDE; the copy is under the repository's name (the same convention the other repositories' tests use). With
// MESH_CHECK_BESIDE unset, or set without the catalogue's copy in it, the comparison is skipped and the test says NOT COMPARED
// WITH THE TRUNK, naming why: the checker that runs before R4g's delivery places siblings but not the change's own repository,
// so R4g's own check cannot hold the copy (issue 1295 notes that a missing copy becomes a failure once that checker is gone). A trunk that holds no such file had
// none: the list's first copy, which nothing was added to.
package trunk

import (
	"errors"
	"os"
	"path/filepath"
	"testing"
)

// Repository is the catalogue's name beside a check.
const Repository = "mesh-catalog"

// BesideEnv is where a merge check says the clones beside the one checked are.
const BesideEnv = "MESH_CHECK_BESIDE"

// Copy is the trunk's copy of the file at rel (a path from the catalogue's root), written to a file of the test's own: its path,
// and whether the trunk holds one (false: its first copy). It skips the test, saying so, when no copy of the catalogue is beside.
func Copy(t testing.TB, rel string) (string, bool) {
	t.Helper()
	raw, found, skip, err := Read(rel)
	switch {
	case skip != "":
		t.Skip(skip)
	case err != nil:
		t.Fatal(err)
	case !found:
		t.Logf("the trunk holds no %s: its first copy", rel)
		return "", false
	}
	path := filepath.Join(t.TempDir(), filepath.Base(rel))
	if err := os.WriteFile(path, raw, 0o644); err != nil {
		t.Fatal(err)
	}
	return path, true
}

// Read is the trunk's copy of rel and whether the trunk holds one. skip is the words to skip the comparison with, when no trunk is
// named; err is a trunk named and not there, or unreadable.
func Read(rel string) (content []byte, found bool, skip string, err error) {
	beside := os.Getenv(BesideEnv)
	if beside == "" {
		return nil, false, "NOT COMPARED WITH THE TRUNK: " + BesideEnv + " is not set, so the trunk's copy of " + rel +
			" is not beside this run; the checker places it", nil
	}
	dir := filepath.Join(beside, Repository)
	if _, err := os.Stat(dir); errors.Is(err, os.ErrNotExist) {
		return nil, false, "NOT COMPARED WITH THE TRUNK: " + Repository + " is not beside this check in " + BesideEnv + "=" + beside +
			", so " + rel + " is not judged against the trunk's copy (the checker before R4g places no copy of the change's own repository)", nil
	} else if err != nil {
		return nil, false, "", err
	}
	raw, err := os.ReadFile(filepath.Join(dir, rel))
	if errors.Is(err, os.ErrNotExist) {
		return nil, false, "", nil
	}
	if err != nil {
		return nil, false, "", err
	}
	return raw, true, "", nil
}