package config

import (
	"fmt"
	"log/slog"
	"os"
	"strings"

	"github.com/joho/godotenv"
	"github.com/spf13/viper"
)

// envKeyReplacer turns a dotted key into its environment variable's suffix
// (logging.level to LOGGING_LEVEL, once upper-cased).
var envKeyReplacer = strings.NewReplacer(".", "_")

// envVarName returns the environment variable that sets key, e.g.
// JOBSEARCH_LOGGING_LEVEL for logging.level.
func envVarName(key string) string {
	return EnvPrefix + "_" + strings.ToUpper(envKeyReplacer.Replace(key))
}

// isExplicitlySet reports whether key's value in Viper was set by the config
// file or by its environment variable, rather than coming from its default.
// As Viper does, it ignores an empty environment variable. Values set with
// viper.Set (e.g. by StoreValue) are not counted.
func isExplicitlySet(key string) bool {
	if viper.InConfig(key) {
		return true
	}
	value, ok := os.LookupEnv(envVarName(key))
	return ok && value != ""
}

// loadEnv loads environment variables from a .env file in the working
// directory.
func loadEnv() error {
	if err := godotenv.Load(); err != nil {
		return fmt.Errorf("invalid .env file: %w", err)
	}
	return nil
}

// loadConfig sets up Viper with the defaults, cfgFile (or config.* found in
// EtcConfigPath or the working directory) and JOBSEARCH_* environment
// variables. A missing config file is only a warning.
func loadConfig(cfgFile string) error {
	if cfgFile != "" {
		// Use config file from the flag.
		viper.SetConfigFile(cfgFile)
	} else {
		// Search config in /etc or local directory.
		viper.AddConfigPath(EtcConfigPath)
		viper.AddConfigPath(".")

		viper.SetConfigName("config")
	}

	// Load default configuration
	LoadDefaultConfig()

	viper.SetEnvPrefix(EnvPrefix)
	viper.SetEnvKeyReplacer(envKeyReplacer)
	viper.AutomaticEnv() // read in environment variables that match

	err := viper.ReadInConfig()
	if err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); ok {
			// Indicates an explicitly set config file is not found or
			// that no config file was found in any search path
			slog.Warn("no config file found; using defaults")
		} else {
			// Config file was found but another error was produced
			return err
		}
	} else {
		// Config file found and successfully parsed
		slog.Info("using config file", "file", viper.ConfigFileUsed())
	}
	return nil
}

// Init loads the .env file and the configuration (see loadConfig) into conf.
// A debug or error log level already set in conf, from --debug or --quiet,
// is kept over the loaded one.
func Init(cfgFile string, conf *JobSearchConfig) error {
	if err := loadEnv(); err != nil {
		return err
	}
	if conf.Logging.LogLevel() <= slog.LevelDebug {
		printEnv()
	}

	if err := loadConfig(cfgFile); err != nil {
		return err
	}

	// Load configuration from Viper, ensure -debug and -quiet are retained
	oldLogLevel := conf.Logging.LogLevel()
	LoadFromViper(conf)
	if oldLogLevel == slog.LevelDebug {
		conf.Logging.Level = "debug"
	}
	if oldLogLevel == slog.LevelError {
		conf.Logging.Level = "error"
	}

	if conf.Logging.LogLevel() <= slog.LevelDebug {
		printLoadedConfig()
		printConfig(*conf)
	}

	return nil
}