package config

import "io"
import "os"
import "fmt"
import "sort"
import "bufio"
import "strings"
import "strconv"
import "image/color"
import "path/filepath"

// when making changes to this file, look at
// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

// Error represents an error that can be returned by functions or methods in
// this module.
type Error int

const (
	// ErrorIllegalName is thrown when an application name contains illegal
	// characters such as a slash.
	ErrorIllegalName Error = iota

	// ErrorNoSeparator is thrown when a configuration file has an
	// incorrectly formatted key-value pair.
	ErrorNoSeparator

	// ErrorUnknownParameter is thrown when an unknown key is encountered in
	// a configuration file.
	ErrorUnknownParameter

	// ErrorWrongColorLength is thrown when a configuration file has a color
	// literal with a total length unequal to 7.
	ErrorWrongColorLength

	// ErrorMalformedColorLiteral is thrown when a configuration file has an
	// improperly formatted color literal, or a color literal was expected
	// and something else was encountered.
	ErrorMalformedColorLiteral
	
	// ErrorMalformedIntegerLiteral is thrown when a configuration file has
	// an improperly formatted integer literal, or an integer literal was
	// expected and something else was encountered.
	ErrorMalformedIntegerLiteral
	
	// ErrorMalformedFloatLiteral is thrown when a configuration file has
	// an improperly formatted float literal, or a float literal was
	// expected and something else was encountered.
	ErrorMalformedFloatLiteral
)

// Error returns a description of the error.
func (err Error) Error () (description string) {
	switch err {
	case ErrorIllegalName:
		description = "name contains illegal characters"
	case ErrorNoSeparator:
		description = "key:value pair has no separator"
	case ErrorUnknownParameter:
		description = "unknown parameter"
	case ErrorWrongColorLength:
		description = "color literal has the wrong length"
	case ErrorMalformedColorLiteral:
		description = "malformed color literal"
	case ErrorMalformedIntegerLiteral:
		description = "malformed integer literal"
	case ErrorMalformedFloatLiteral:
		description = "malformed float literal"
	}

	return
}

// Type represents the data type of a configuration parameter.
type Type int

const (
	// string
	// It is just a basic string with inner whitespace preserved. No quotes
	// should be used in the file.
	TypeString Type = iota

	// Type: image/color.RGBA
	// Represented as a 24 bit hexadecimal number (case insensitive)
	// preceded with a # sign where the first two digits represent the red
	// channel, the middle two digits represent the green channel, and the
	// last two digits represent the blue channel.
	TypeColor

	// Type: int
	// An integer literal, like 123456789
	TypeInteger

	// Type: float64
	// A floating point literal, like 1234.56789
	TypeFloat

	// Type: bool
	// Values true, yes, on, and 1 are all truthy (case insensitive) and
	// anything else is falsy.
	TypeBoolean
)

// Config holds a list of configuration parameters.
type Config struct {
	// LegalParameters holds the names and types of all parameters that can
	// be parsed. If the parser runs into a parameter that is not listed
	// here, it will print out an error message and keep on parsing.
	LegalParameters map[string] Type

	// Parameters holds the names and values of all parsed parameters. If a
	// value is non-nil, it can be safely type asserted into whatever type
	// was requested.
	Parameters map[string] any
}

// Load loads and parses the files /etc/xdg/<name>/<name>.conf and
// <home>/.config/<name>/<name>.conf, unless the corresponding XDG environment
// variables are set - then it uses those.
func (config *Config) Load (name string) (err error) {
	if nameIsIllegal(name) {
		err = ErrorIllegalName
		return
	}

	var configHome string
	configHome, err = getConfigHome()
	if err != nil { return }
	println(configHome)

	configDirsString := os.Getenv("XDG_CONFIG_DIRS")
	if configDirsString == "" {
		configDirsString = "/etc/xdg/"
	}

	configDirs := strings.Split(configDirsString, ":")
	configDirs = append(configDirs, configHome)

	for _, directory := range configDirs {
		path := filepath.Join(directory, name, name + ".conf")
		
		file, fileErr := os.Open(path)
		if fileErr != nil { continue }
		parseErr := config.LoadFrom(file)
		defer file.Close()
		
		if parseErr != nil {
			println (
				"config: error in file", path +
				":", parseErr.Error())
		}
	}

	return
}

// LoadFrom parses a configuration file from an io.Reader. Configuration files
// are divided into lines where each line may be blank, a comment, or a
// key-value pair. If the line is blank or begins with a # character, it is
// ignored. Else, the line must have a key and a value separated by a colon.
// Before they are processed, leading and trailing whitespace is trimmed from
// the key and the value. Keys are case sensitive.
func (config *Config) LoadFrom (reader io.Reader) (err error) {
	if config.LegalParameters == nil {
		config.LegalParameters = make(map[string] Type)
	}
	
	if config.Parameters == nil {
		config.Parameters = make(map[string] any)
	}
	
	scanner := bufio.NewScanner(reader)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		
		if len(line) == 0 {
			continue
		}

		if line[0] == '#' {
			continue
		}
	
		key, value, found := strings.Cut(scanner.Text(), ":")
		if !found {
			err = ErrorNoSeparator
			return
		}
		key   = strings.TrimSpace(key)
		value = strings.TrimSpace(value)

		what, isKnown := config.LegalParameters[key]
		if !isKnown {
			err = ErrorUnknownParameter
			return
		}

		switch what {
		case TypeString:
			config.Parameters[key] = value
			
		case TypeColor:
			var valueColor color.Color
			valueColor, err = parseColor(value)
			if err != nil { return }
			config.Parameters[key] = valueColor
		
		case TypeInteger:
			var valueInt int
			valueInt, err = strconv.Atoi(value)
			if err != nil {
				err = ErrorMalformedIntegerLiteral
				return
			}
			config.Parameters[key] = valueInt
			
		case TypeFloat:
			var valueFloat float64
			valueFloat, err = strconv.ParseFloat(value, 64)
			if err != nil {
				err = ErrorMalformedFloatLiteral
				return
			}
			config.Parameters[key] = valueFloat
			
		case TypeBoolean:
			value = strings.ToLower(value)
			truthy :=
				value == "true" ||
				value == "yes"  ||
				value == "on"   ||
				value == "1"
			config.Parameters[key] = truthy
		}
	}

	return
}

// Save overwrites the main user configuration file, which is located at
// <home>/.config/<name>/<name>.conf unless $XDG_CONFIG_HOME has been set, in
// which case the value of that variable is used instead.
func (config *Config) Save (name string) (err error) {
	if nameIsIllegal(name) {
		err = ErrorIllegalName
		return
	}

	var configHome string
	configHome, err = getConfigHome()
	if err != nil { return }

	err = os.MkdirAll(configHome, 0755)
	if err != nil { return }
	
	file, err := os.OpenFile (
		filepath.Join(configHome, name, name + ".conf"),
		os.O_WRONLY | os.O_CREATE | os.O_TRUNC, 0744)
	if err != nil { return }
	defer file.Close()

	err = config.SaveTo(file)
	if err != nil { return }

	return
}

// SaveTo writes the configuration data to the specified io.Writer.
func (config *Config) SaveTo (writer io.Writer) (err error) {
	keys := make([]string, len(config.Parameters))
	index := 0
	for key, _ := range config.Parameters {
		keys[index] = key
		index ++
	}
	sort.Strings(keys)

	for _, key := range keys {
		value := config.Parameters[key]
		switch value.(type) {
		case string:
			fmt.Fprintf(writer,"%s: %s\n", key, value.(string))
			
		case color.RGBA:
			colorValue := value.(color.RGBA)
			colorInt := 
				uint64(colorValue.R) << 16 |
				uint64(colorValue.G) << 8  |
				uint64(colorValue.B)
			fmt.Fprintf(writer,"%s: #%06x\n", key, colorInt)
			
		case int:
			fmt.Fprintf(writer,"%s: %d\n", key, value.(int))
			
		case float64:
			fmt.Fprintf(writer,"%s: %f\n", key, value.(float64))
			
		case bool:
			fmt.Fprintf(writer,"%s: %t\n", key, value.(bool))
		default:
			fmt.Fprintf(writer,"# %s: unknown type\n", key)
		}
	}

	return
}

func parseColor (value string) (valueColor color.Color, err error) {
	if value[0] == '#' {
		if len(value) != 7  {
			err = ErrorWrongColorLength
			return
		}

		var colorInt uint64
		colorInt, err = strconv.ParseUint(value[1:7], 16, 24)
		if err != nil  {
			err = ErrorMalformedColorLiteral
			return
		}

		valueColor = color.RGBA {
			R: uint8(colorInt >> 16),
			G: uint8(colorInt >> 8),
			B: uint8(colorInt),
			A: 0xFF,
		}
	} else {
		err = ErrorMalformedColorLiteral
		return
	}

	return
}

func getConfigHome () (home string, err error) {
	var homeDirectory string
	homeDirectory, err = os.UserHomeDir()
	if err != nil { return }

	home = os.Getenv("XDG_CONFIG_HOME")
	if home == "" {
		home = filepath.Join(homeDirectory, "/.config/")
	}

	return
}

func nameIsIllegal (name string) (legal bool) {
	legal = strings.ContainsAny(name, "/\\|:.%")
	return
}