package system

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/novox/mesh-host/internal/declaration"
)

// arch is pacman and systemd.
type arch struct{}

func (arch) Name() string               { return "arch" }
func (arch) Shapes() []declaration.Type { return everyShape() }

func (a arch) Confirm(ctx context.Context, run Runner) error {
	if _, err := run(ctx, "pacman", "-Q", "pacman"); err != nil {
		return fmt.Errorf(
			"this is the arch host and pacman does not answer here. Either this machine is not "+
				"Arch, or its package database is broken: %w", err)
	}
	return nil
}

// PackageInstalled asks the package database, having first established that it answers.
//
// The two-step is the trap this file exists to remember. `pacman -Q name` exits non-zero for a
// package that is not installed AND for a database that cannot be read, so believing the first
// answer reports a broken package manager as "nothing is installed" — absence read as fact.
// Proving the tool answers about something that certainly exists separates them.
func (a arch) PackageInstalled(ctx context.Context, run Runner, name string) (bool, error) {
	if err := a.Confirm(ctx, run); err != nil {
		return false, fmt.Errorf("nothing can be said about %q: %w", name, err)
	}
	if _, err := run(ctx, "pacman", "-Q", name); err != nil {
		return false, nil
	}
	return true, nil
}

// RemovePackage removes one package and nothing it depends on: `-R`, not `-Rs`, because what else
// relied on a dependency is not this declaration's to know. pacman keeps a configuration file the
// operator changed as `.pacsave`, which is what "never flushed" comes to once the front end is gone.
func (arch) RemovePackage(ctx context.Context, run Runner, name string) error {
	_, err := run(ctx, "pacman", "-R", "--noconfirm", name)
	return err
}

func (arch) InstallPackage(ctx context.Context, run Runner, name string) error {
	out, err := run(ctx, "pacman", "-S", "--noconfirm", "--needed", name)
	if err == nil {
		return nil
	}

	// **The package manager's own words, and a name for the case that looks like a bug in the
	// declaration and is not.** A stale index asks the mirrors for a version they have already
	// superseded and gets a 404 from every one of them — so the package exists, the declaration is
	// correct, and the machine's idea of what exists is old (novox/hq 04-ISSUES/002). A keyring as
	// old as the index fails one step later, on the signature of whatever a mirror still had.
	//
	// **Read from everything pacman said.** Its errors go to stderr, which the runner folds into
	// the error rather than the output; this classifier read the output alone and so never saw a
	// single "failed retrieving file", and the control node reported a ten-week-old database as
	// a mirror outage with a wall of 404s (novox/hq 04-ISSUES/205).
	//
	// **It is not fixed by syncing here.** `pacman -Sy <pkg>` installs a package built against
	// libraries this machine does not have: a partial upgrade, which Arch does not support and
	// which breaks the machine in a way that surfaces much later as something unrelated. The
	// remedy is a full upgrade, and it is a decision about the whole machine rather than
	// something to do silently in the middle of applying one resource. Whose decision, and on
	// what schedule, is issue 205's question; until it is answered the host says what it sees.
	said := strings.TrimSpace(out + "\n" + err.Error())
	switch classifyInstallFailure(said) {
	case installStale:
		return fmt.Errorf(
			"%s could not be fetched from any mirror, which is what a stale package index looks like: "+
				"the package database on this machine is %s and the mirrors no longer serve what it "+
				"names. It is fixed by upgrading the machine — a full upgrade (`pacman -Syu`) by its "+
				"operator — before the mesh can install %s. The package and the declaration are probably both fine; the "+
				"host does not sync one package by itself, because on this distribution that is a "+
				"partial upgrade (novox/hq 04-ISSUES/205).\n\n%s",
			name, syncDatabaseAge(), name, said)
	case installMirrors:
		return fmt.Errorf(
			"no mirror could be reached to fetch %s, and the package database on this machine is "+
				"%s: this reads as the mirrors or the network, not as this machine being out of "+
				"date — try again when they answer.\n\n%s",
			name, syncDatabaseAge(), said)
	}
	return fmt.Errorf("%w\n\n%s", err, strings.TrimSpace(out))
}

// How a failed install is read, from what the package manager said.
type installFailure int

const (
	installOther installFailure = iota
	// installStale: the machine's package database or keyring is older than what the mirrors
	// serve — every mirror 404s the file the database names, or a package that did arrive fails
	// its signature against a keyring that never saw the key.
	installStale
	// installMirrors: no mirror could be reached at all, and nothing says the database is old.
	installMirrors
)

// classifyInstallFailure reads pacman's words, because there is nothing else to go on: the exit
// code is the same for every one of these.
func classifyInstallFailure(said string) installFailure {
	lower := strings.ToLower(said)
	gone := strings.Count(lower, "returned error: 404")
	fetching := strings.Contains(lower, "failed retrieving file")
	badSignature := strings.Contains(lower, "invalid or corrupted package (pgp signature)") ||
		strings.Contains(lower, "signature from") && strings.Contains(lower, "is invalid") ||
		strings.Contains(lower, "is unknown trust") ||
		strings.Contains(lower, "could not be looked up remotely")
	switch {
	case badSignature:
		return installStale
	case fetching && gone > 0:
		// Every mirror, not one: a single mirror failing is an ordinary transient thing and
		// retrying is the answer. pacman walks its whole mirror list before giving up, so more
		// than one 404 among the lines is the index being old rather than one host being wrong.
		if gone > 1 || !strings.Contains(lower, "could not resolve host") &&
			!strings.Contains(lower, "connection timed out") && !strings.Contains(lower, "failed to connect") {
			return installStale
		}
		return installMirrors
	case fetching:
		return installMirrors
	}
	return installOther
}

// staleIndex is the yes-or-no form older callers and tests use.
func staleIndex(out string) bool { return classifyInstallFailure(out) == installStale }

// syncDatabaseAge says how old this machine's package database is, in words a person acts on:
// the newest of pacman's sync databases, dated, and how long ago that was. Said beside a failed
// install so a ten-week-old database is told apart from a mirror outage by reading one line.
//
// A variable so a test can say what the machine's database looks like without having one.
var syncDatabaseAge = func() string {
	entries, err := filepath.Glob("/var/lib/pacman/sync/*.db")
	if err != nil || len(entries) == 0 {
		return "of unknown age (no sync database found under /var/lib/pacman/sync)"
	}
	var newest time.Time
	for _, e := range entries {
		info, err := os.Stat(e)
		if err == nil && info.ModTime().After(newest) {
			newest = info.ModTime()
		}
	}
	if newest.IsZero() {
		return "of unknown age"
	}
	return describeAge(newest, time.Now())
}

// describeAge is "from 2026-07-24, 10 weeks old" — the date for the record, the span for the eye.
func describeAge(when, now time.Time) string {
	days := int(now.Sub(when).Hours() / 24)
	span := fmt.Sprintf("%d days old", days)
	switch {
	case days < 1:
		span = "less than a day old"
	case days >= 14:
		span = fmt.Sprintf("%d weeks old", days/7)
	}
	return fmt.Sprintf("from %s, %s", when.Format("2006-01-02"), span)
}

// ServiceState reads what systemd says about a unit.
//
// Two traps, and both were hit before this read what it now reads.
//
// The exit code is not the answer: `is-active` exits non-zero for every state except active.
//
// And "inactive" does not mean stopped. `systemctl is-active` says "inactive" for a unit that
// DOES NOT EXIST exactly as it does for one installed and stopped, so declaring a unit stopped
// reported success for a unit the host cannot manage at all. LoadState is what separates them,
// so LoadState is what is read — and it is the thing an interface spanning systemd and OpenRC
// would have had to drop.
func (arch) ServiceState(ctx context.Context, run Runner, unit string) (string, error) {
	out, _ := run(ctx, "systemctl", "show", unit,
		"--property=LoadState", "--property=ActiveState", "--property=Type",
		"--property=RemainAfterExit", "--property=ExecMainStatus")

	var load, active, kind, remains, exited string
	for _, line := range strings.Split(out, "\n") {
		key, value, found := strings.Cut(strings.TrimSpace(line), "=")
		if !found {
			continue
		}
		switch key {
		case "LoadState":
			load = value
		case "ActiveState":
			active = value
		case "Type":
			kind = value
		case "RemainAfterExit":
			remains = value
		case "ExecMainStatus":
			exited = value
		}
	}

	switch load {
	case "":
		return "", fmt.Errorf("the service manager said nothing about %s", unit)
	case "not-found":
		return "", fmt.Errorf(
			"%s does not exist on this machine. A declaration naming a unit that is not "+
				"installed cannot be satisfied, and reporting it stopped would be reporting "+
				"absence as success", unit)
	case "masked":
		return "", fmt.Errorf("%s is masked, so its state cannot be declared", unit)
	case "error", "bad-setting":
		return "", fmt.Errorf("%s is installed but its unit file cannot be loaded (%s)", unit, load)
	}

	// **A one-shot that finished is not stopped.** A unit whose whole job is to apply something
	// and exit — load a rule set, set a sysctl — is reported inactive the moment it succeeds, and
	// unless it is told to linger there is no state in which it is ever "active". Reading that as
	// "stopped" makes such a unit permanently unsatisfiable: the host starts it, it does its work,
	// it exits, the host reads back "stopped" and reports failure — for ever, on every apply,
	// while the thing it configured is in place and working.
	//
	// That is not hypothetical. It is what the firewall did on every machine it was ever assigned
	// to: rules loaded, service reported failed, the mesh reported a machine not doing what it was
	// told, and the only visible symptom was a red line about a unit nobody could see anything
	// wrong with.
	//
	// So for that shape, what "running" means is "it ran, and it worked".
	if kind == "oneshot" && remains != "yes" && active == "inactive" {
		if exited == "0" || exited == "" {
			return "running", nil
		}
		return "stopped", nil
	}

	switch active {
	case "active", "activating", "reloading":
		return "running", nil
	case "inactive", "failed", "deactivating":
		return "stopped", nil
	default:
		return "", fmt.Errorf(
			"the service manager reports %s as %q, which is neither running nor stopped", unit, active)
	}
}

func (arch) SetServiceState(ctx context.Context, run Runner, unit, state string) error {
	verb := "start"
	if state == "stopped" {
		verb = "stop"
	}
	_, err := run(ctx, "systemctl", verb, unit)
	return err
}

// ServiceBoot reads whether a unit starts at boot.
//
// `is-enabled` has more than two answers, and `static` is the one that matters: the unit has no
// install section and CANNOT be enabled. Reading it as "disabled" would have the host try, fail,
// and blame the wrong thing — the same shape as reading a missing unit as "stopped".
func (arch) ServiceBoot(ctx context.Context, run Runner, unit string) (string, error) {
	out, _ := run(ctx, "systemctl", "is-enabled", unit)
	switch state := strings.TrimSpace(out); state {
	case "enabled", "enabled-runtime", "alias":
		return "enabled", nil
	case "disabled":
		return "disabled", nil
	case "":
		return "", fmt.Errorf("the service manager said nothing about whether %s starts at boot", unit)
	case "static":
		return "", fmt.Errorf(
			"%s is static — it has no install section, so it cannot be enabled or disabled. "+
				"Something else pulls it in, and that is what a declaration should name", unit)
	case "masked", "masked-runtime":
		return "", fmt.Errorf("%s is masked, so its boot state cannot be declared", unit)
	default:
		return "", fmt.Errorf(
			"the service manager reports %s as %q at boot, which is neither enabled nor disabled",
			unit, state)
	}
}

func (arch) SetServiceBoot(ctx context.Context, run Runner, unit, boot string) error {
	verb := "enable"
	if boot == "disabled" {
		verb = "disable"
	}
	_, err := run(ctx, "systemctl", verb, unit)
	return err
}

// CreateUser makes a login with useradd.
//
// `--create-home` because a user whose home does not exist is a user nothing can be delivered
// to, and delivering a shell's configuration is most of why the mesh knows about users at all.
func (arch) CreateUser(ctx context.Context, run Runner, name, home, shell string) error {
	args := []string{"--create-home"}
	if home != "" {
		args = append(args, "--home-dir", home)
	}
	if shell != "" {
		args = append(args, "--shell", shell)
	}
	if _, err := run(ctx, "useradd", append(args, name)...); err != nil {
		return fmt.Errorf("cannot create the user %q: %w", name, err)
	}
	return nil
}

func (arch) SetUserShell(ctx context.Context, run Runner, name, shell string) error {
	if _, err := run(ctx, "usermod", "--shell", shell, name); err != nil {
		return fmt.Errorf("cannot set %q's shell to %q: %w", name, shell, err)
	}
	return nil
}

// AddUserToGroup appends, and `--append` is the whole point: without it usermod REPLACES the
// user's supplementary groups, so a declaration naming one group would silently remove every
// other — including the ones that make a login able to use a machine at all.
func (arch) AddUserToGroup(ctx context.Context, run Runner, name, group string) error {
	if _, err := run(ctx, "usermod", "--append", "--groups", group, name); err != nil {
		return fmt.Errorf("cannot put %q in the group %q: %w", name, group, err)
	}
	return nil
}

// ServiceUnitFile says where the service manager loads a unit from — systemd's FragmentPath. It
// is how the host tells a unit an administrator installed, under /etc or /run, from one a package
// ships under /usr (novox/hq ADR 0103). Empty, with no error, for a unit that loads from nowhere.
func (arch) ServiceUnitFile(ctx context.Context, run Runner, unit string) (string, error) {
	out, err := run(ctx, "systemctl", "show", unit, "--property=FragmentPath")
	if err != nil {
		return "", fmt.Errorf("the service manager did not say where %s comes from: %w", unit, err)
	}
	for _, line := range strings.Split(out, "\n") {
		if path, ok := strings.CutPrefix(strings.TrimSpace(line), "FragmentPath="); ok {
			return strings.TrimSpace(path), nil
		}
	}
	return "", nil
}

// ReloadUnits has systemd read its unit files again. A unit file that changed on disk is otherwise
// ignored: a restart runs the unit systemd already loaded, and the new text only takes effect
// after a reload nobody asked for.
func (arch) ReloadUnits(ctx context.Context, run Runner) error {
	_, err := run(ctx, "systemctl", "daemon-reload")
	return err
}

// ReloadService tells a running unit to read its configuration again, without stopping it.
func (arch) ReloadService(ctx context.Context, run Runner, unit string) error {
	_, err := run(ctx, "systemctl", "reload", unit)
	return err
}