package backup

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"log"
	"os"
	"path/filepath"
)

// MaxSchemaVersion is the highest infra backup schema version this controller can read.
const MaxSchemaVersion = 1

// InfraMetadata is the lightweight metadata file written alongside backup.json.
type InfraMetadata struct {
	SchemaVersion     int    `json:"schema_version"`
	Timestamp         string `json:"timestamp"`
	CustomerID        string `json:"customer_id"`
	ControllerVersion string `json:"controller_version"`
	Checksum          string `json:"checksum"` // SHA256 hex of backup.json
}

// WriteLocalInfraBackup writes the infra backup to .felhom-infra-backup/ on each drive.
// Individual drive failures are logged but not returned — the function is best-effort.
func WriteLocalInfraBackup(backupJSON []byte, customerID, controllerVersion, timestamp string, drives []string, logger *log.Logger) {
	if len(drives) == 0 {
		logger.Printf("[DEBUG] No drives configured for local infra backup")
		return
	}

	// Compute checksum of backup data
	hash := sha256.Sum256(backupJSON)
	checksum := hex.EncodeToString(hash[:])

	meta := InfraMetadata{
		SchemaVersion:     1,
		Timestamp:         timestamp,
		CustomerID:        customerID,
		ControllerVersion: controllerVersion,
		Checksum:          checksum,
	}

	metaJSON, err := json.MarshalIndent(meta, "", "  ")
	if err != nil {
		logger.Printf("[ERROR] Local infra backup: failed to marshal metadata: %v", err)
		return
	}

	written := 0
	for _, drive := range drives {
		dir := InfraBackupDir(drive)
		if err := writeInfraToDir(dir, backupJSON, metaJSON); err != nil {
			logger.Printf("[WARN] Local infra backup: failed to write to %s: %v", drive, err)
			continue
		}
		written++
	}

	logger.Printf("[INFO] Local infra backup written to %d/%d drive(s)", written, len(drives))
}

// writeInfraToDir writes backup.json and metadata.json atomically to the given directory.
func writeInfraToDir(dir string, backupData, metaData []byte) error {
	if err := os.MkdirAll(dir, 0700); err != nil {
		return fmt.Errorf("creating dir: %w", err)
	}

	// Write backup.json atomically
	backupPath := filepath.Join(dir, "backup.json")
	if err := atomicWrite(backupPath, backupData, 0600); err != nil {
		return fmt.Errorf("writing backup.json: %w", err)
	}

	// Write metadata.json atomically
	metaPath := filepath.Join(dir, "metadata.json")
	if err := atomicWrite(metaPath, metaData, 0600); err != nil {
		return fmt.Errorf("writing metadata.json: %w", err)
	}

	return nil
}

// atomicWrite writes data to a .tmp file then renames to the target path.
func atomicWrite(path string, data []byte, perm os.FileMode) error {
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, data, perm); err != nil {
		os.Remove(tmp)
		return err
	}
	if err := os.Rename(tmp, path); err != nil {
		os.Remove(tmp)
		return err
	}
	return nil
}

// ReadLocalInfraBackup reads and validates an infra backup from a mount point.
// Returns the raw backup JSON, metadata, and any error.
func ReadLocalInfraBackup(mountPath string) ([]byte, *InfraMetadata, error) {
	dir := InfraBackupDir(mountPath)

	// Read metadata
	metaPath := filepath.Join(dir, "metadata.json")
	metaData, err := os.ReadFile(metaPath)
	if err != nil {
		return nil, nil, fmt.Errorf("reading metadata.json: %w", err)
	}

	var meta InfraMetadata
	if err := json.Unmarshal(metaData, &meta); err != nil {
		return nil, nil, fmt.Errorf("parsing metadata.json: %w", err)
	}

	// Check schema version
	if meta.SchemaVersion > MaxSchemaVersion {
		return nil, &meta, fmt.Errorf("backup schema version %d is newer than supported version %d — upgrade the controller", meta.SchemaVersion, MaxSchemaVersion)
	}

	// Read backup data
	backupPath := filepath.Join(dir, "backup.json")
	backupData, err := os.ReadFile(backupPath)
	if err != nil {
		return nil, &meta, fmt.Errorf("reading backup.json: %w", err)
	}

	// Verify checksum
	hash := sha256.Sum256(backupData)
	actual := hex.EncodeToString(hash[:])
	if actual != meta.Checksum {
		return nil, &meta, fmt.Errorf("checksum mismatch: expected %s, got %s", meta.Checksum, actual)
	}

	return backupData, &meta, nil
}