package config

import (
	"fmt"
	"os"
	"time"

	"go.uber.org/fx"
	"gopkg.in/yaml.v3"
)

// Config represents the application configuration for Vaultik.
// It defines all settings for backup operations, including source directories,
// encryption recipients, S3 storage configuration, and performance tuning parameters.
// Configuration is typically loaded from a YAML file.
type Config struct {
	AgeRecipients     []string      `yaml:"age_recipients"`
	BackupInterval    time.Duration `yaml:"backup_interval"`
	BlobSizeLimit     Size          `yaml:"blob_size_limit"`
	ChunkSize         Size          `yaml:"chunk_size"`
	Exclude           []string      `yaml:"exclude"`
	FullScanInterval  time.Duration `yaml:"full_scan_interval"`
	Hostname          string        `yaml:"hostname"`
	IndexPath         string        `yaml:"index_path"`
	MinTimeBetweenRun time.Duration `yaml:"min_time_between_run"`
	S3                S3Config      `yaml:"s3"`
	SourceDirs        []string      `yaml:"source_dirs"`
	CompressionLevel  int           `yaml:"compression_level"`
}

// S3Config represents S3 storage configuration for backup storage.
// It supports both AWS S3 and S3-compatible storage services.
// All fields except UseSSL and PartSize are required.
type S3Config struct {
	Endpoint        string `yaml:"endpoint"`
	Bucket          string `yaml:"bucket"`
	Prefix          string `yaml:"prefix"`
	AccessKeyID     string `yaml:"access_key_id"`
	SecretAccessKey string `yaml:"secret_access_key"`
	Region          string `yaml:"region"`
	UseSSL          bool   `yaml:"use_ssl"`
	PartSize        Size   `yaml:"part_size"`
}

// ConfigPath wraps the config file path for fx dependency injection.
// This type allows the config file path to be injected as a distinct type
// rather than a plain string, avoiding conflicts with other string dependencies.
type ConfigPath string

// New creates a new Config instance by loading from the specified path.
// This function is used by the fx dependency injection framework.
// Returns an error if the path is empty or if loading fails.
func New(path ConfigPath) (*Config, error) {
	if path == "" {
		return nil, fmt.Errorf("config path not provided")
	}

	cfg, err := Load(string(path))
	if err != nil {
		return nil, fmt.Errorf("failed to load config: %w", err)
	}

	return cfg, nil
}

// Load reads and parses the configuration file from the specified path.
// It applies default values for optional fields, performs environment variable
// substitution for certain fields (like IndexPath), and validates the configuration.
// The configuration file should be in YAML format. Returns an error if the file
// cannot be read, parsed, or if validation fails.
func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("failed to read config file: %w", err)
	}

	cfg := &Config{
		// Set defaults
		BlobSizeLimit:     Size(10 * 1024 * 1024 * 1024), // 10GB
		ChunkSize:         Size(10 * 1024 * 1024),        // 10MB
		BackupInterval:    1 * time.Hour,
		FullScanInterval:  24 * time.Hour,
		MinTimeBetweenRun: 15 * time.Minute,
		IndexPath:         "/var/lib/vaultik/index.sqlite",
		CompressionLevel:  3,
	}

	if err := yaml.Unmarshal(data, cfg); err != nil {
		return nil, fmt.Errorf("failed to parse config: %w", err)
	}

	// Check for environment variable override for IndexPath
	if envIndexPath := os.Getenv("VAULTIK_INDEX_PATH"); envIndexPath != "" {
		cfg.IndexPath = envIndexPath
	}

	// Get hostname if not set
	if cfg.Hostname == "" {
		hostname, err := os.Hostname()
		if err != nil {
			return nil, fmt.Errorf("failed to get hostname: %w", err)
		}
		cfg.Hostname = hostname
	}

	// Set default S3 settings
	if cfg.S3.Region == "" {
		cfg.S3.Region = "us-east-1"
	}
	if cfg.S3.PartSize == 0 {
		cfg.S3.PartSize = Size(5 * 1024 * 1024) // 5MB
	}

	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("invalid config: %w", err)
	}

	return cfg, nil
}

// Validate checks if the configuration is valid and complete.
// It ensures all required fields are present and have valid values:
// - At least one age recipient must be specified
// - At least one source directory must be configured
// - S3 credentials and endpoint must be provided
// - Chunk size must be at least 1MB
// - Blob size limit must be at least the chunk size
// - Compression level must be between 1 and 19
// Returns an error describing the first validation failure encountered.
func (c *Config) Validate() error {
	if len(c.AgeRecipients) == 0 {
		return fmt.Errorf("at least one age_recipient is required")
	}

	if len(c.SourceDirs) == 0 {
		return fmt.Errorf("at least one source directory is required")
	}

	if c.S3.Endpoint == "" {
		return fmt.Errorf("s3.endpoint is required")
	}

	if c.S3.Bucket == "" {
		return fmt.Errorf("s3.bucket is required")
	}

	if c.S3.AccessKeyID == "" {
		return fmt.Errorf("s3.access_key_id is required")
	}

	if c.S3.SecretAccessKey == "" {
		return fmt.Errorf("s3.secret_access_key is required")
	}

	if c.ChunkSize.Int64() < 1024*1024 { // 1MB minimum
		return fmt.Errorf("chunk_size must be at least 1MB")
	}

	if c.BlobSizeLimit.Int64() < c.ChunkSize.Int64() {
		return fmt.Errorf("blob_size_limit must be at least chunk_size")
	}

	if c.CompressionLevel < 1 || c.CompressionLevel > 19 {
		return fmt.Errorf("compression_level must be between 1 and 19")
	}

	return nil
}

// Module exports the config module for fx dependency injection.
// It provides the Config type to other modules in the application.
var Module = fx.Module("config",
	fx.Provide(New),
)