// 🚀 Fiber is an Express inspired web framework written in Go with 💖
// 📌 API Documentation: https://fiber.wiki
// 📝 Github Repository: https://github.com/gofiber/fiber
// Special thanks to Echo: https://github.com/labstack/echo/blob/master/middleware/key_auth.go
package keyauth

import (
	"errors"
	"strings"

	"github.com/gofiber/fiber/v3"
)

// When there is no request of the key thrown ErrMissingOrMalformedAPIKey
var ErrMissingOrMalformedAPIKey = errors.New("missing or malformed API Key")

type Config struct {
	// Filter defines a function to skip middleware.
	// Optional. Default: nil
	Filter func(fiber.Ctx) bool

	// SuccessHandler defines a function which is executed for a valid key.
	// Optional. Default: nil
	SuccessHandler fiber.Handler

	// ErrorHandler defines a function which is executed for an invalid key.
	// It may be used to define a custom error.
	// Optional. Default: 401 Invalid or expired key
	ErrorHandler fiber.ErrorHandler

	// KeyLookup is a string in the form of "<source>:<name>" that is used
	// to extract key from the request.
	// Optional. Default value "header:Authorization".
	// Possible values:
	// - "header:<name>"
	// - "query:<name>"
	// - "form:<name>"
	// - "param:<name>"
	// - "cookie:<name>"
	KeyLookup string

	// AuthScheme to be used in the Authorization header.
	// Optional. Default value "Bearer".
	AuthScheme string

	// Validator is a function to validate key.
	// Optional. Default: nil
	Validator func(fiber.Ctx, string) (bool, error)

	// Context key to store the bearertoken from the token into context.
	// Optional. Default: "token".
	ContextKey string
}

// New ...
func New(config ...Config) fiber.Handler {
	// Init config
	var cfg Config
	if len(config) > 0 {
		cfg = config[0]
	}

	if cfg.SuccessHandler == nil {
		cfg.SuccessHandler = func(c fiber.Ctx) error {
			return c.Next()
		}
	}
	if cfg.ErrorHandler == nil {
		cfg.ErrorHandler = func(c fiber.Ctx, err error) error {
			if errors.Is(err, ErrMissingOrMalformedAPIKey) {
				return c.Status(fiber.StatusBadRequest).SendString(err.Error())
			}
			return c.Status(fiber.StatusUnauthorized).SendString("Invalid or expired API Key")
		}
	}
	if cfg.KeyLookup == "" {
		cfg.KeyLookup = "header:" + fiber.HeaderAuthorization
		// set AuthScheme as "Bearer" only if KeyLookup is set to default.
		if cfg.AuthScheme == "" {
			cfg.AuthScheme = "Bearer"
		}
	}
	if cfg.Validator == nil {
		cfg.Validator = func(c fiber.Ctx, t string) (bool, error) {
			return true, nil
		}
	}
	if cfg.ContextKey == "" {
		cfg.ContextKey = "token"
	}

	// Initialize
	parts := strings.Split(cfg.KeyLookup, ":")
	extractor := keyFromHeader(parts[1], cfg.AuthScheme)
	switch parts[0] {
	case "query":
		extractor = keyFromQuery(parts[1])
	case "form":
		extractor = keyFromForm(parts[1])
	case "param":
		extractor = keyFromParam(parts[1])
	case "cookie":
		extractor = keyFromCookie(parts[1])
	}

	// Return middleware handler
	return func(c fiber.Ctx) error {
		// Filter request to skip middleware
		if cfg.Filter != nil && cfg.Filter(c) {
			return c.Next()
		}

		// Extract and verify key
		key, err := extractor(c)
		if err != nil {
			return cfg.ErrorHandler(c, err)
		}

		valid, err := cfg.Validator(c, key)

		if err == nil && valid {
			c.Locals(cfg.ContextKey, key)
			return cfg.SuccessHandler(c)
		}
		return cfg.ErrorHandler(c, err)
	}
}

// keyFromHeader returns a function that extracts api key from the request header.
func keyFromHeader(header string, authScheme string) func(c fiber.Ctx) (string, error) {
	return func(c fiber.Ctx) (string, error) {
		auth := c.Get(header)
		l := len(authScheme)
		if len(auth) > 0 && l == 0 {
			return auth, nil
		}
		if len(auth) > l+1 && auth[:l] == authScheme {
			return auth[l+1:], nil
		}
		return "", ErrMissingOrMalformedAPIKey
	}
}

// keyFromQuery returns a function that extracts api key from the query string.
func keyFromQuery(param string) func(c fiber.Ctx) (string, error) {
	return func(c fiber.Ctx) (string, error) {
		key := c.Query(param)
		if key == "" {
			return "", ErrMissingOrMalformedAPIKey
		}
		return key, nil
	}
}

// keyFromForm returns a function that extracts api key from the form.
func keyFromForm(param string) func(c fiber.Ctx) (string, error) {
	return func(c fiber.Ctx) (string, error) {
		key := c.FormValue(param)
		if key == "" {
			return "", ErrMissingOrMalformedAPIKey
		}
		return key, nil
	}
}

// keyFromParam returns a function that extracts api key from the url param string.
func keyFromParam(param string) func(c fiber.Ctx) (string, error) {
	return func(c fiber.Ctx) (string, error) {
		key := c.Params(param)
		if key == "" {
			return "", ErrMissingOrMalformedAPIKey
		}
		return key, nil
	}
}

// keyFromCookie returns a function that extracts api key from the named cookie.
func keyFromCookie(name string) func(c fiber.Ctx) (string, error) {
	return func(c fiber.Ctx) (string, error) {
		key := c.Cookies(name)
		if key == "" {
			return "", ErrMissingOrMalformedAPIKey
		}
		return key, nil
	}
}