package config_test

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

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"sneak.berlin/go/webhooker/internal/config"
)

// dotEnvKey is a throwaway variable name the .env tests write and
// read, so they cannot disturb real configuration.
const dotEnvKey = "WEBHOOKER_TEST_DOTENV_VALUE"

// malformedDotEnv is a file godotenv cannot parse. The first line is
// the realistic typo — a space where the `=` belongs — and the rest
// make sure nothing downstream treats the file as salvageable line by
// line.
const malformedDotEnv = "PORT 19615\n" +
	"this is not = valid ! syntax\n" +
	"\"unclosed\n"

// unsetDotEnvKey makes dotEnvKey genuinely absent for the duration of
// the test and restores it afterwards. t.Setenv registers the restore;
// the Unsetenv that follows is what the test actually needs, because a
// variable set to the empty string is still present in os.Environ and
// godotenv would refuse to overwrite it.
func unsetDotEnvKey(t *testing.T) {
	t.Helper()
	t.Setenv(dotEnvKey, "placeholder")
	require.NoError(t, os.Unsetenv(dotEnvKey))
}

// writeDotEnv writes contents to a .env file in a fresh temporary
// directory and returns its path.
func writeDotEnv(t *testing.T, contents string) string {
	t.Helper()

	path := filepath.Join(t.TempDir(), config.DotEnvPath)
	require.NoError(t, os.WriteFile(path, []byte(contents), 0o600))

	return path
}

// TestLoadDotEnv_MissingFileIsFine pins the case most deployments are
// in. The file is optional: it is a development convenience, and a
// deployment that configures the environment directly must start
// normally rather than be refused for a file it was never meant to
// have.
//
//nolint:paralleltest // unsetDotEnvKey uses t.Setenv.
func TestLoadDotEnv_MissingFileIsFine(t *testing.T) {
	unsetDotEnvKey(t)

	absent := filepath.Join(t.TempDir(), config.DotEnvPath)
	require.NoError(t, config.LoadDotEnvFileForTest(absent))

	_, present := os.LookupEnv(dotEnvKey)
	assert.False(t, present, "nothing may be set from an absent file")
}

// TestLoadDotEnv_AppliesValues pins that a well-formed file still
// reaches the environment, which is the whole reason the file is read
// at all.
//
//nolint:paralleltest // unsetDotEnvKey uses t.Setenv.
func TestLoadDotEnv_AppliesValues(t *testing.T) {
	unsetDotEnvKey(t)

	path := writeDotEnv(t, "# a comment\n"+dotEnvKey+"=from-dot-env\n")

	require.NoError(t, config.LoadDotEnvFileForTest(path))
	assert.Equal(t, "from-dot-env", os.Getenv(dotEnvKey))
}

// TestLoadDotEnv_RealEnvironmentWins pins that the file cannot
// override a variable the process was actually started with. A
// deployment that sets DATA_DIR in its unit file must not have it
// silently replaced by a stale .env left in the working directory.
func TestLoadDotEnv_RealEnvironmentWins(t *testing.T) {
	t.Setenv(dotEnvKey, "from-environment")

	path := writeDotEnv(t, dotEnvKey+"=from-dot-env\n")

	require.NoError(t, config.LoadDotEnvFileForTest(path))
	assert.Equal(t, "from-environment", os.Getenv(dotEnvKey))
}

// TestLoadDotEnv_MalformedFileAborts is the defect this fixes. One bad
// line makes godotenv apply none of the file, so every variable in it
// reverts to its default; the process used to start that way with no
// log line naming the file at all.
//
//nolint:paralleltest // unsetDotEnvKey uses t.Setenv.
func TestLoadDotEnv_MalformedFileAborts(t *testing.T) {
	unsetDotEnvKey(t)

	path := writeDotEnv(
		t, malformedDotEnv+dotEnvKey+"=from-dot-env\n",
	)

	err := config.LoadDotEnvFileForTest(path)

	require.Error(t, err)
	require.ErrorIs(t, err, config.ErrDotEnvUnreadable)
	assert.Contains(
		t, err.Error(), config.DotEnvPath,
		"the failure must name the file it could not read",
	)

	_, present := os.LookupEnv(dotEnvKey)
	assert.False(
		t, present,
		"a rejected file must apply nothing, not part of itself",
	)
}

// TestLoadDotEnv_UnreadableFileAborts pins that only absence is
// tolerated. A .env that exists but cannot be read is a file the
// operator meant to be applied, so it fails like a malformed one
// rather than being treated as though it were not there.
func TestLoadDotEnv_UnreadableFileAborts(t *testing.T) {
	t.Parallel()

	// A directory in the file's place: open succeeds and the read
	// fails, which no umask or root-ness can turn back into success
	// the way a chmod could.
	path := filepath.Join(t.TempDir(), config.DotEnvPath)
	require.NoError(t, os.Mkdir(path, 0o750))

	err := config.LoadDotEnvFileForTest(path)

	require.Error(t, err)
	require.ErrorIs(t, err, config.ErrDotEnvUnreadable)
}

// TestLoadDotEnv_ReadsTheWorkingDirectory pins the path LoadDotEnv
// itself opens, which the tests above bypass. It is relative to the
// process working directory, as it was under godotenv/autoload and as
// the README documents.
//
//nolint:paralleltest // t.Chdir moves the whole process.
func TestLoadDotEnv_ReadsTheWorkingDirectory(t *testing.T) {
	unsetDotEnvKey(t)

	dir := t.TempDir()
	require.NoError(t, os.WriteFile(
		filepath.Join(dir, config.DotEnvPath),
		[]byte(dotEnvKey+"=from-working-directory\n"),
		0o600,
	))
	t.Chdir(dir)

	require.NoError(t, config.LoadDotEnv())
	assert.Equal(t, "from-working-directory", os.Getenv(dotEnvKey))
}