package go_environment

import (
	"fmt"
	"os"
	"regexp"
	"strings"
)

var (
	// variableExpression is a regular expression for environment variables
	//
	// A match will look like
	//   - %<variableName>% (Windows-Notation)
	//
	// or
	//   - $(<variableName>) (Unix-Notation)
	variableExpression = regexp.MustCompile(`(%([\w]+)%)|(\$\(([\w]+)\))`)
)

// ReplaceEnvironmentVariablesExt replaces all available
// environment variables (defined as %<variableName>%) within
// a string possibly also returning an error if necessary.
func ReplaceEnvironmentVariablesExt(value string) (string, error) {
	analysable := value
	subStrings := variableExpression.FindStringSubmatch(analysable)
	usedVariables := make(map[string]string)
	missingVariables := make([]string, 0)
	var err error
	if len(subStrings) == 5 {
		for {
			if subStrings[2] != "" {
				variableKey := subStrings[2]

				variableValue, found := os.LookupEnv(variableKey)
				if found {
					usedVariables[variableKey] = variableValue
					analysable = strings.ReplaceAll(analysable, "%"+variableKey+"%", variableValue)
				} else {
					missingVariables = append(missingVariables, variableKey)
					analysable = strings.ReplaceAll(analysable, "%"+variableKey+"%", variableKey)
				}
			}
			if subStrings[4] != "" {
				variableKey := subStrings[4]

				variableValue, found := os.LookupEnv(variableKey)
				if found {
					usedVariables[variableKey] = variableValue
					analysable = strings.ReplaceAll(analysable, "$("+variableKey+")", variableValue)
				} else {
					missingVariables = append(missingVariables, variableKey)
					analysable = strings.ReplaceAll(analysable, "$("+variableKey+")", variableKey)
				}
			}
			subStrings = variableExpression.FindStringSubmatch(analysable)
			if len(subStrings) != 5 {
				break
			}
		}
	}
	result := value
	for key, value := range usedVariables {
		result = strings.ReplaceAll(result, "%"+key+"%", value)
		result = strings.ReplaceAll(result, "$("+key+")", value)
	}
	if len(missingVariables) > 0 {
		if len(missingVariables) == 1 {
			err = fmt.Errorf("missing environment variable: %s", missingVariables[0])
		} else {
			err = fmt.Errorf("missing environment variables: %s", strings.Join(missingVariables, ", "))
		}
	}
	return result, err
}

// ReplaceEnvironmentVariablesExt replaces all available
// environment variables (defined as %<variableName>%) within
// a string.
func ReplaceEnvironmentVariables(directoryPath string) string {
	path, _ := ReplaceEnvironmentVariablesExt(directoryPath)
	return path
}