//go:build linux

package main

import (
	"os"
	"path/filepath"
	"sync"
)

// systemInstallDataDir keeps the portable "data beside the binary" layout where
// it works, and falls back to the XDG data directory where it cannot.
//
// Both halves are needed on Linux, and only on Linux. A tarball or AppImage
// unpacked into the home directory behaves exactly like the Windows build —
// the folder travels with the program, which is the whole point of the design.
// But the ordinary way software arrives here is a package that installs into
// /usr/bin or /opt, where no user may write, and telling an operator to "move
// the program somewhere writable" is telling them their distribution installed
// it wrong. So when the folder beside the binary is read-only, OpsLog keeps its
// data in ~/.local/share/OpsLog instead and says so in the log.
//
// Detection is by TRYING, not by matching path prefixes: /opt, /usr/local and a
// NFS-mounted home are all writable on some stations and not on others, and the
// only honest test is whether the write succeeds.
func systemInstallDataDir(besideExe string) (string, bool) {
	xdgOnce.Do(func() { xdgDir, xdgUsed = resolveDataDir(besideExe) })
	return xdgDir, xdgUsed
}

var (
	xdgOnce sync.Once
	xdgDir  string
	xdgUsed bool
)

func resolveDataDir(besideExe string) (string, bool) {
	if writable(besideExe) {
		return "", false
	}
	base := os.Getenv("XDG_DATA_HOME")
	if base == "" {
		home, err := os.UserHomeDir()
		if err != nil || home == "" {
			return "", false // nowhere better to go; let the caller report the failure
		}
		base = filepath.Join(home, ".local", "share")
	}
	alt := filepath.Join(base, "OpsLog", "data")
	if !writable(alt) {
		return "", false
	}
	bootLog("data dir: %s is not writable — keeping the data in %s instead", besideExe, alt)
	return alt, true
}

// writable reports whether dir can be created and written to. The probe file is
// removed again; a leftover in the data folder would be one more thing to
// explain.
func writable(dir string) bool {
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return false
	}
	probe := filepath.Join(dir, ".writetest")
	if err := os.WriteFile(probe, []byte("ok"), 0o644); err != nil {
		return false
	}
	_ = os.Remove(probe)
	return true
}

// dataDirAdvice is what the operator is told when neither location works — a
// full disk, or a home directory that is not writable either.
const dataDirAdvice = "\n\nOpsLog keeps its data next to the program, or in ~/.local/share/OpsLog when that folder belongs to the system. Neither could be written to: check the disk is not full and that your home directory is writable."