package config

import (
	"errors"
	"flag"
	"fmt"
	"log"
	"os"
	"strconv"
	"time"
)

type configOption[T any] struct {
	flagName         string
	flagDefaultValue T
	flagHelpBase     string
	envVarName       string
}

type configOptions struct {
	userID                       configOption[string]
	token                        configOption[string]
	room                         configOption[string]
	printHomeserverMemberCount   configOption[bool]
	homeserverVersionInfoTimeout configOption[time.Duration]
}

type Config struct {
	UserID                       string
	Token                        string
	Room                         string
	PrintHomeserverMemberCount   bool
	HomeserverVersionInfoTimeout time.Duration
}

var configOpts = configOptions{
	userID:                       configOption[string]{"user-id", "", "The Matrix user ID to use.", "MRVC_USER_ID"},
	token:                        configOption[string]{"token", "", "The Matrix access token to use.", "MRVC_TOKEN"},
	room:                         configOption[string]{"room", "", "The Matrix room to check.", "MRVC_ROOM"},
	printHomeserverMemberCount:   configOption[bool]{"print-homeserver-member-count", false, "Print the member count for each homeserver.", "MRVC_PRINT_HOMESERVER_MEMBER_COUNT"},
	homeserverVersionInfoTimeout: configOption[time.Duration]{"homeserver-version-info-timeout", time.Second * 5, "Timeout for getting the homeservers version information per homeserver.", "MRVC_HOMESERVER_VERSION_INFO_TIMEOUT"},
}

func (configOpt configOption[T]) getFlagHelp() string {
	return fmt.Sprintf("%s (EnvVar: %s)", configOpt.flagHelpBase, configOpt.envVarName)
}

func (configOpt configOption[T]) getFlagArgs() (string, T, string) {
	return configOpt.flagName, configOpt.flagDefaultValue, configOpt.getFlagHelp()
}

// Functions for getting config values from flags and environment variables.
// Flags take precedence over environment variables.
func (configOpt configOption[T]) getConfigValueWithDefault(configFlag *T, visitedFlags map[string]bool, envVarParser func(string) T) T {
	if visitedFlags[configOpt.flagName] {
		return *configFlag
	} else if envVar, ok := os.LookupEnv(configOpt.envVarName); ok {
		return envVarParser(envVar)
	} else {
		return configOpt.flagDefaultValue
	}
}

// This function can be used to ensure some configuration options got explicitly set.
func (configOpt configOption[T]) getConfigValueWithError(configFlag *T, visitedFlags map[string]bool, envVarParser func(string) T) (T, error) {
	if visitedFlags[configOpt.flagName] {
		return *configFlag, nil
	} else if envVar, ok := os.LookupEnv(configOpt.envVarName); ok {
		return envVarParser(envVar), nil
	} else {
		return configOpt.flagDefaultValue, errors.New("no command-line flag or environment variable set")
	}
}

var userIdFlag = flag.String(configOpts.userID.getFlagArgs())
var tokenFlag = flag.String(configOpts.token.getFlagArgs())
var roomFlag = flag.String(configOpts.room.getFlagArgs())
var printHomeserverMemberCountFlag = flag.Bool(configOpts.printHomeserverMemberCount.getFlagArgs())
var homeserverVersionInfoTimeoutFlag = flag.Duration(configOpts.homeserverVersionInfoTimeout.getFlagArgs())

func Get() Config {
	flag.Parse()

	var config Config

	visitedFlags := make(map[string]bool)
	flag.Visit(func(flag *flag.Flag) {
		visitedFlags[flag.Name] = true
	})

	var err error

	config.UserID, err = configOpts.userID.getConfigValueWithError(userIdFlag, visitedFlags, func(envVar string) string { return envVar })
	if err != nil {
		log.Fatal("A Matrix user ID must be provided.")
	}
	config.Token, err = configOpts.token.getConfigValueWithError(tokenFlag, visitedFlags, func(envVar string) string { return envVar })
	if err != nil {
		log.Fatal("A Matrix access token must be provided.")
	}
	config.Room, err = configOpts.room.getConfigValueWithError(roomFlag, visitedFlags, func(envVar string) string { return envVar })
	if err != nil {
		log.Fatal("A Matrix room must be provided.")
	}
	config.PrintHomeserverMemberCount = configOpts.printHomeserverMemberCount.getConfigValueWithDefault(printHomeserverMemberCountFlag, visitedFlags, func(envVar string) bool {
		parsedEnvVar, err := strconv.ParseBool(envVar)
		if err != nil {
			log.Printf("Error parsing %s:\n", configOpts.printHomeserverMemberCount.envVarName)
			log.Fatal(err)
		}
		return parsedEnvVar
	})
	config.HomeserverVersionInfoTimeout = configOpts.homeserverVersionInfoTimeout.getConfigValueWithDefault(homeserverVersionInfoTimeoutFlag, visitedFlags, func(envVar string) time.Duration {
		parsedEnvVar, err := time.ParseDuration(envVar)
		if err != nil {
			log.Printf("Error parsing %s:\n", configOpts.homeserverVersionInfoTimeout.envVarName)
			log.Fatal(err)
		}
		return parsedEnvVar
	})

	return config
}