package fiber

import (
	"fmt"
	"net/http"
	"reflect"

	"github.com/valyala/fasthttp"
	"github.com/valyala/fasthttp/fasthttpadaptor"
)

// toFiberHandler converts a supported handler type to a Fiber handler.
func toFiberHandler(handler any) (Handler, bool) {
	if handler == nil {
		return nil, false
	}

	switch handler.(type) {
	case Handler, func(Ctx): // (1)-(2) Fiber handlers
		return adaptFiberHandler(handler)
	case func(Req, Res) error, func(Req, Res), func(Req, Res, func() error) error, func(Req, Res, func() error), func(Req, Res, func()) error, func(Req, Res, func()), func(Req, Res, func(error)), func(Req, Res, func(error)) error, func(Req, Res, func(error) error), func(Req, Res, func(error) error) error: // (3)-(12) Express-style request handlers
		return adaptExpressHandler(handler)
	case http.HandlerFunc, http.Handler, func(http.ResponseWriter, *http.Request): // (13)-(15) net/http handlers
		return adaptHTTPHandler(handler)
	case fasthttp.RequestHandler, func(*fasthttp.RequestCtx) error: // (16)-(17) fasthttp handlers
		return adaptFastHTTPHandler(handler)
	default: // (18) unsupported handler type
		return nil, false
	}
}

func adaptFiberHandler(handler any) (Handler, bool) {
	switch h := handler.(type) {
	case Handler: // (1) direct Fiber handler
		if h == nil {
			return nil, false
		}
		return h, true
	case func(Ctx): // (2) Fiber handler without error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			h(c)
			return nil
		}, true
	default:
		return nil, false
	}
}

func adaptExpressHandler(handler any) (Handler, bool) {
	switch h := handler.(type) {
	case func(Req, Res) error: // (3) Express-style handler with error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			return h(c.Req(), c.Res())
		}, true
	case func(Req, Res): // (4) Express-style handler without error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			h(c.Req(), c.Res())
			return nil
		}, true
	case func(Req, Res, func() error) error: // (5) Express-style handler with error-returning next callback and error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			err := h(c.Req(), c.Res(), func() error {
				nextErr = c.Next()
				return nextErr
			})
			if err != nil {
				return err
			}
			return nextErr
		}, true
	case func(Req, Res, func() error): // (6) Express-style handler with error-returning next callback
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			h(c.Req(), c.Res(), func() error {
				nextErr = c.Next()
				return nextErr
			})
			return nextErr
		}, true
	case func(Req, Res, func()) error: // (7) Express-style handler with no-arg next callback and error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			err := h(c.Req(), c.Res(), func() {
				nextErr = c.Next()
			})
			if err != nil {
				return err
			}
			return nextErr
		}, true
	case func(Req, Res, func()): // (8) Express-style handler with no-arg next callback
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			h(c.Req(), c.Res(), func() {
				nextErr = c.Next()
			})
			return nextErr
		}, true
	case func(Req, Res, func(error)): // (9) Express-style handler with error-accepting next callback
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			h(c.Req(), c.Res(), func(err error) {
				if err != nil {
					nextErr = err
					return
				}
				nextErr = c.Next()
			})
			return nextErr
		}, true
	case func(Req, Res, func(error)) error: // (10) Express-style handler with error-accepting next callback and error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			err := h(c.Req(), c.Res(), func(nextErrArg error) {
				if nextErrArg != nil {
					nextErr = nextErrArg
					return
				}
				nextErr = c.Next()
			})
			if err != nil {
				return err
			}
			return nextErr
		}, true
	case func(Req, Res, func(error) error): // (11) Express-style handler with error-accepting next callback that returns an error
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			h(c.Req(), c.Res(), func(nextErrArg error) error {
				if nextErrArg != nil {
					nextErr = nextErrArg
					return nextErrArg
				}
				nextErr = c.Next()
				return nextErr
			})
			return nextErr
		}, true
	case func(Req, Res, func(error) error) error: // (12) Express-style handler with error-accepting next callback that returns an error and error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			var nextErr error
			err := h(c.Req(), c.Res(), func(nextErrArg error) error {
				if nextErrArg != nil {
					nextErr = nextErrArg
					return nextErrArg
				}
				nextErr = c.Next()
				return nextErr
			})
			if err != nil {
				return err
			}
			return nextErr
		}, true
	default:
		return nil, false
	}
}

func adaptHTTPHandler(handler any) (Handler, bool) {
	switch h := handler.(type) {
	case http.HandlerFunc: // (13) net/http HandlerFunc
		if h == nil {
			return nil, false
		}
		return wrapHTTPHandler(h), true
	case http.Handler: // (14) net/http Handler implementation
		if h == nil {
			return nil, false
		}
		hv := reflect.ValueOf(h)
		if isNilableKind(hv.Kind()) && hv.IsNil() {
			return nil, false
		}
		return wrapHTTPHandler(h), true
	case func(http.ResponseWriter, *http.Request): // (15) net/http function handler
		if h == nil {
			return nil, false
		}
		return wrapHTTPHandler(http.HandlerFunc(h)), true
	default:
		return nil, false
	}
}

func isNilableKind(kind reflect.Kind) bool {
	switch kind {
	case reflect.Chan, reflect.Func, reflect.Map, reflect.Pointer, reflect.Interface, reflect.Slice, reflect.UnsafePointer:
		return true
	default:
		return false
	}
}

func adaptFastHTTPHandler(handler any) (Handler, bool) {
	switch h := handler.(type) {
	case fasthttp.RequestHandler: // (16) fasthttp handler
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			h(c.RequestCtx())
			return nil
		}, true
	case func(*fasthttp.RequestCtx) error: // (17) fasthttp handler with error return
		if h == nil {
			return nil, false
		}
		return func(c Ctx) error {
			return h(c.RequestCtx())
		}, true
	default:
		return nil, false
	}
}

// wrapHTTPHandler adapts a net/http handler to a Fiber handler.
func wrapHTTPHandler(handler http.Handler) Handler {
	if handler == nil {
		return nil
	}

	adapted := fasthttpadaptor.NewFastHTTPHandler(handler)

	return func(c Ctx) error {
		adapted(c.RequestCtx())
		return nil
	}
}

// collectHandlers converts a slice of handler arguments to Fiber handlers.
// The context string is used to provide informative panic messages when an
// unsupported handler type is encountered.
func collectHandlers(context string, args ...any) []Handler {
	handlers := make([]Handler, 0, len(args))

	for i, arg := range args {
		handler, ok := toFiberHandler(arg)

		if !ok {
			panic(fmt.Sprintf("%s: invalid handler #%d (%T)\n", context, i, arg))
		}
		handlers = append(handlers, handler)
	}

	return handlers
}
