package backup

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

	"gopkg.in/yaml.v3"
)

// reconcileRestoreSecrets merges the recovery unit's non-secret env with the secrets recovered from
// the guest's own app.yaml, and applies the FAIL-CLOSED data-key gate. It is the safety-critical heart
// of Phase 2b and is deliberately a pure function (no I/O) so it can be exhaustively unit-tested.
//
// Policy (per the Phase 2 design — see REPORT/CHANGELOG):
//   - Regenerate NOTHING. Every secret comes from the guest (live rootfs, or PBS whole-guest restore).
//   - A missing DATA-ENCRYPTING key (`dataKeyNames`) is FATAL: regenerating it would render the
//     restored data unreadable, so we refuse and tell the operator to do a PBS whole-guest restore.
//   - A missing resettable secret (DB password, admin password) is NON-fatal: it's returned in
//     `missing` so the caller can warn; the app may simply need a credential reset, no data is lost.
func reconcileRestoreSecrets(nonSecretEnv, recoveredSecrets map[string]string, secretNames, dataKeyNames []string) (fullEnv map[string]string, missing []string, err error) {
	fullEnv = make(map[string]string, len(nonSecretEnv)+len(secretNames))
	for k, v := range nonSecretEnv {
		fullEnv[k] = v
	}
	have := func(n string) bool {
		v, ok := recoveredSecrets[n]
		return ok && v != ""
	}
	for _, n := range secretNames {
		if have(n) {
			fullEnv[n] = recoveredSecrets[n]
		} else {
			missing = append(missing, n)
		}
	}
	// Fail-closed: any unrecoverable data-encrypting key aborts the restore.
	var missingDataKeys []string
	for _, dk := range dataKeyNames {
		if !have(dk) {
			missingDataKeys = append(missingDataKeys, dk)
		}
	}
	if len(missingDataKeys) > 0 {
		return nil, missing, fmt.Errorf(
			"refusing to restore: data-encrypting key(s) %v could not be recovered from the guest's app.yaml — "+
				"a PBS whole-guest restore is required first (regenerating the key would render stored data unreadable)",
			missingDataKeys)
	}
	return fullEnv, missing, nil
}

// readStrippedEnv parses the non-secret env from a recovery unit's secret-stripped app.yaml.
func readStrippedEnv(path string) map[string]string {
	data, err := os.ReadFile(path)
	if err != nil {
		return map[string]string{}
	}
	var s strippedAppYaml
	if yaml.Unmarshal(data, &s) != nil || s.Env == nil {
		return map[string]string{}
	}
	return s.Env
}

// RestoreFromRecoveryUnit recreates an app from its on-drive recovery unit + the guest's own secrets.
//
// It reads the unit manifest, recovers the secret values from the guest's live app.yaml, applies the
// fail-closed data-key gate, restores the named-volume data from the unit's tars, then restores the
// app's definition from the unit and redeploys it with the reconstructed env (re-pulling the pinned
// image). No secret is ever regenerated, and no secret is read from the unit. If no unit exists it
// falls back to the legacy volume-only RestoreApp.
func (m *Manager) RestoreFromRecoveryUnit(stackName string) error {
	if m.stackProvider == nil {
		return fmt.Errorf("stack provider not configured")
	}

	m.mu.Lock()
	if m.running {
		m.mu.Unlock()
		return fmt.Errorf("backup or restore already in progress")
	}
	m.running = true
	m.mu.Unlock()
	defer func() {
		m.mu.Lock()
		m.running = false
		m.mu.Unlock()
	}()

	drivePath := m.GetAppDrivePath(stackName)
	if drivePath == "" || !filepath.IsAbs(drivePath) {
		return fmt.Errorf("cannot determine drive path for %s", stackName)
	}
	nsRoot := m.namespaceRoot(drivePath)

	manifest := readManifest(RecoveryUnitManifestPath(nsRoot, stackName))
	if manifest == nil {
		m.logger.Printf("[WARN] [backup] No recovery unit for %s — falling back to volume-only restore", stackName)
		m.mu.Lock()
		m.running = false // RestoreApp re-acquires the running flag
		m.mu.Unlock()
		return m.RestoreApp(stackName, "")
	}

	composeDir := RecoveryUnitComposePath(nsRoot, stackName)
	nonSecretEnv := readStrippedEnv(filepath.Join(composeDir, "app.yaml"))

	// Recover secrets from the GUEST (never the unit), then apply the fail-closed gate.
	recovered := m.stackProvider.RecoverStackSecrets(stackName, manifest.SecretEnvVars)
	fullEnv, missing, err := reconcileRestoreSecrets(nonSecretEnv, recovered, manifest.SecretEnvVars, manifest.DataKeyEnvVars)
	if err != nil {
		m.logger.Printf("[ERROR] [backup] Restore REFUSED for %s: %v", stackName, err)
		return err
	}
	if len(missing) > 0 {
		m.logger.Printf("[WARN] [backup] Restore %s: %d resettable secret(s) unrecoverable %v — proceeding (may need a credential reset; no data-key affected)",
			stackName, len(missing), missing)
	}
	m.logger.Printf("[INFO] [backup] Restoring %s from recovery unit: images=%d, secrets recovered=%d/%d, data_keys=%d",
		stackName, len(manifest.ImagePins), len(manifest.SecretEnvVars)-len(missing), len(manifest.SecretEnvVars), len(manifest.DataKeyEnvVars))

	// Stop, restore named-volume data, then recreate the definition + redeploy with the recovered env.
	if err := m.stackProvider.StopStack(stackName); err != nil {
		m.logger.Printf("[WARN] [backup] could not stop %s before restore: %v (continuing)", stackName, err)
	}
	if err := m.restoreDockerVolumes(stackName, drivePath); err != nil {
		m.logger.Printf("[WARN] [backup] volume restore for %s: %v (continuing)", stackName, err)
	}
	if err := m.stackProvider.RecreateStackFromUnit(stackName, composeDir, fullEnv); err != nil {
		return fmt.Errorf("recreating %s from unit: %w", stackName, err)
	}
	if err := m.waitForHealthy(stackName, 90*time.Second); err != nil {
		m.logger.Printf("[WARN] [backup] %s restored but health check failed: %v", stackName, err)
	}

	m.logger.Printf("[INFO] [backup] Restore-from-unit completed: %s", stackName)
	return nil
}