package authboss

import (
	"bytes"
	"fmt"
	"net/http"
)

const (
	// ConfirmPrefix is prepended to names of confirm fields.
	ConfirmPrefix = "confirm_"
)

// Validator is anything that can validate a string and provide a list of errors
// and describe its set of rules.
type Validator interface {
	Field() string
	Errors(in string) ErrorList
	Rules() []string
}

// ErrorList is simply a slice of errors with helpers.
type ErrorList []error

// Error satisfies the error interface.
func (e ErrorList) Error() string {
	b := &bytes.Buffer{}
	first := true
	for _, err := range e {
		if first {
			first = false
		} else {
			b.WriteString(", ")
		}
		b.WriteString(err.Error())
	}
	return b.String()
}

// Map groups errors by their field name
func (e ErrorList) Map() map[string][]string {
	m := make(map[string][]string)

	for _, err := range e {
		fieldErr, ok := err.(FieldError)
		if !ok {
			m[""] = append(m[""], err.Error())
		} else {
			m[fieldErr.Name] = append(m[fieldErr.Name], fieldErr.Err.Error())
		}
	}

	return m
}

// FieldError represents an error that occurs during validation and is always
// attached to field on a form.
type FieldError struct {
	Name string
	Err  error
}

func (f FieldError) Error() string {
	return fmt.Sprintf("%s: %v", f.Name, f.Err)
}

// Validate validates a request using the given ruleset.
func (ctx *Context) Validate(r *http.Request, ruleset []Validator, confirmFields ...string) ErrorList {
	errList := make(ErrorList, 0)

	for _, validator := range ruleset {
		field := validator.Field()

		val := r.FormValue(field)
		if errs := validator.Errors(val); len(errs) > 0 {
			errList = append(errList, errs...)
		}
	}

	for i := 0; i < len(confirmFields)-1; i += 2 {
		main := r.FormValue(confirmFields[i])
		if len(main) == 0 {
			continue
		}

		confirm := r.FormValue(confirmFields[i+1])
		if len(confirm) == 0 || main != confirm {
			errList = append(errList, FieldError{confirmFields[i+1], fmt.Errorf("Does not match %s", confirmFields[i])})
		}
	}

	return errList
}

// FilterValidators returns a subset of registered validators
func FilterValidators(validators []Validator, fields ...string) []Validator {
	var arr []Validator

	for _, validator := range validators {
		fieldName := validator.Field()
		for _, field := range fields {
			if fieldName == field {
				arr = append(arr, validator)
			}
		}
	}

	return arr
}