package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v2"
)

const currentSchemaVersion = 2 // used for upgrading from old configs to new config

// Performs necessary upgrade operations if needed
func upgradeConfig() error {
	// read a config file into an interface map, so we can manipulate values without losing any
	configFile := filepath.Join(config.ourBinaryDir, config.ourConfigFilename)
	if _, err := os.Stat(configFile); os.IsNotExist(err) {
		log.Printf("config file %s does not exist, nothing to upgrade", configFile)
		return nil
	}
	diskConfig := map[string]interface{}{}
	body, err := ioutil.ReadFile(configFile)
	if err != nil {
		log.Printf("Couldn't read config file '%s': %s", configFile, err)
		return err
	}

	err = yaml.Unmarshal(body, &diskConfig)
	if err != nil {
		log.Printf("Couldn't parse config file '%s': %s", configFile, err)
		return err
	}

	schemaVersionInterface, ok := diskConfig["schema_version"]
	log.Printf("%s(): got schema version %v", _Func(), schemaVersionInterface)
	if !ok {
		// no schema version, set it to 0
		schemaVersionInterface = 0
	}

	schemaVersion, ok := schemaVersionInterface.(int)
	if !ok {
		err = fmt.Errorf("configuration file contains non-integer schema_version, abort")
		log.Println(err)
		return err
	}

	if schemaVersion == currentSchemaVersion {
		// do nothing
		return nil
	}

	return upgradeConfigSchema(schemaVersion, &diskConfig)
}

// Upgrade from oldVersion to newVersion
func upgradeConfigSchema(oldVersion int, diskConfig *map[string]interface{}) error {
	switch oldVersion {
	case 0:
		err := upgradeSchema0to2(diskConfig)
		if err != nil {
			return err
		}
	case 1:
		err := upgradeSchema1to2(diskConfig)
		if err != nil {
			return err
		}
	default:
		err := fmt.Errorf("configuration file contains unknown schema_version, abort")
		log.Println(err)
		return err
	}

	configFile := filepath.Join(config.ourBinaryDir, config.ourConfigFilename)
	body, err := yaml.Marshal(diskConfig)
	if err != nil {
		log.Printf("Couldn't generate YAML file: %s", err)
		return err
	}

	err = safeWriteFile(configFile, body)
	if err != nil {
		log.Printf("Couldn't save YAML config: %s", err)
		return err
	}

	return nil
}

// The first schema upgrade:
// No more "dnsfilter.txt", filters are now kept in data/filters/
func upgradeSchema0to1(diskConfig *map[string]interface{}) error {
	log.Printf("%s(): called", _Func())

	dnsFilterPath := filepath.Join(config.ourBinaryDir, "dnsfilter.txt")
	if _, err := os.Stat(dnsFilterPath); !os.IsNotExist(err) {
		log.Printf("Deleting %s as we don't need it anymore", dnsFilterPath)
		err = os.Remove(dnsFilterPath)
		if err != nil {
			log.Printf("Cannot remove %s due to %s", dnsFilterPath, err)
			// not fatal, move on
		}
	}

	(*diskConfig)["schema_version"] = 1

	return nil
}

// Second schema upgrade:
// coredns is now dns in config
// delete 'Corefile', since we don't use that anymore
func upgradeSchema1to2(diskConfig *map[string]interface{}) error {
	log.Printf("%s(): called", _Func())

	coreFilePath := filepath.Join(config.ourBinaryDir, "Corefile")
	if _, err := os.Stat(coreFilePath); !os.IsNotExist(err) {
		log.Printf("Deleting %s as we don't need it anymore", coreFilePath)
		err = os.Remove(coreFilePath)
		if err != nil {
			log.Printf("Cannot remove %s due to %s", coreFilePath, err)
			// not fatal, move on
		}
	}

	(*diskConfig)["dns"] = (*diskConfig)["coredns"]
	delete((*diskConfig), "coredns")
	(*diskConfig)["schema_version"] = 2

	return nil
}

// jump two schemas at once -- this time we just do it sequentially
func upgradeSchema0to2(diskConfig *map[string]interface{}) error {
	err := upgradeSchema0to1(diskConfig)
	if err != nil {
		return err
	}

	return upgradeSchema1to2(diskConfig)
}