package ezconf

import (
	"reflect"
	"strings"

	"github.com/pkg/errors"
)

// ParseConfigStruct extracts environment variable metadata from a config
// struct's ezconf struct tags using reflection.
//
// The configPtr parameter must be a pointer to a struct. Each field with an
// ezconf tag will be parsed to extract environment variable information.
//
// Tag format: `ezconf:"VAR_NAME,description:Description text,default:value,required"`
//
// Components:
//   - First value: environment variable name (required)
//   - description:...: Description of the variable
//   - default:...: Default value
//   - required: Marks the variable as required (optionally required:condition)
func ParseConfigStruct(configPtr any) ([]EnvVar, error) {
	if configPtr == nil {
		return nil, errors.New("config pointer cannot be nil")
	}

	v := reflect.ValueOf(configPtr)
	if v.Kind() != reflect.Ptr {
		return nil, errors.New("config must be a pointer to a struct")
	}

	v = v.Elem()
	if v.Kind() != reflect.Struct {
		return nil, errors.New("config must be a pointer to a struct")
	}

	t := v.Type()
	envVars := make([]EnvVar, 0)

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		tag := field.Tag.Get("ezconf")
		if tag == "" {
			continue
		}

		envVar, err := parseEzconfTag(tag)
		if err != nil {
			return nil, errors.Wrapf(err, "failed to parse ezconf tag on field %s", field.Name)
		}

		envVars = append(envVars, *envVar)
	}

	return envVars, nil
}

// parseEzconfTag parses an ezconf struct tag value to extract environment
// variable information.
//
// Expected format: "VAR_NAME,description:Description text,default:value,required"
func parseEzconfTag(tag string) (*EnvVar, error) {
	if tag == "" {
		return nil, errors.New("tag cannot be empty")
	}

	parts := strings.Split(tag, ",")
	if len(parts) == 0 {
		return nil, errors.New("tag cannot be empty")
	}

	envVar := &EnvVar{
		Name: strings.TrimSpace(parts[0]),
	}

	if envVar.Name == "" {
		return nil, errors.New("environment variable name cannot be empty")
	}

	for _, part := range parts[1:] {
		part = strings.TrimSpace(part)

		switch {
		case strings.HasPrefix(part, "description:"):
			envVar.Description = strings.TrimSpace(strings.TrimPrefix(part, "description:"))
		case strings.HasPrefix(part, "default:"):
			envVar.Default = strings.TrimSpace(strings.TrimPrefix(part, "default:"))
		case part == "required":
			envVar.Required = true
		case strings.HasPrefix(part, "required:"):
			envVar.Required = true
			// Store the condition in the description if it adds context
			condition := strings.TrimSpace(strings.TrimPrefix(part, "required:"))
			if condition != "" && envVar.Description != "" {
				envVar.Description = envVar.Description + " (required " + condition + ")"
			}
		}
	}

	return envVar, nil
}