// 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 test fails saying NOT COMPARED WITH THE TRUNK and
// why: the checker places the change's own repository since R4g (issue 1295), so a missing copy is a fault, never a pass. A trunk that holds no such file had
// none: the list's first copy, which nothing was added to.
package trunk

import (
	"errors"
	"fmt"
	"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 fails the test when no copy of the catalogue is beside.
func Copy(t testing.TB, rel string) (string, bool) {
	t.Helper()
	raw, found, err := Read(rel)
	switch {
	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. err is a trunk not beside the check (MESH_CHECK_BESIDE unset,
// or without the catalogue's directory), or a copy unreadable: a comparison that cannot be made is never a pass.
func Read(rel string) (content []byte, found bool, err error) {
	beside := os.Getenv(BesideEnv)
	if beside == "" {
		return nil, false, fmt.Errorf("NOT COMPARED WITH THE TRUNK: %s is not set, so the trunk's copy of %s is not beside this run; the checker places the change's own repository there (issue 1295)", BesideEnv, rel)
	}
	dir := filepath.Join(beside, Repository)
	if _, err := os.Stat(dir); errors.Is(err, os.ErrNotExist) {
		return nil, false, fmt.Errorf("NOT COMPARED WITH THE TRUNK: %s is not beside this check in %s=%s, so %s is not judged against the trunk's copy; the checker places the change's own repository there at its trunk (issue 1295)", Repository, BesideEnv, beside, rel)
	} 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
}