package httpx

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"

	apierrors "git.yuntuo.hk/k2safe/go-omni/errors"
	"git.yuntuo.hk/k2safe/go-omni/logx"
	"git.yuntuo.hk/k2safe/go-omni/response"
	"git.yuntuo.hk/k2safe/go-omni/validate"
)

// Handler is the function signature used by GoOmni routes.
type Handler func(*Context) error

// Middleware wraps a Handler and may enforce cross-cutting behavior.
type Middleware func(Handler) Handler

// Router is the small contract the application needs from a network layer.
// The default implementation is backed by the standard library, but another
// router or a future GoOmni transport can implement this interface without
// changing business handlers. Register routes before serving requests. Implementations
// should pass transport/transporttest.Run; see transport/README.md for the
// portable path, method, fallback and context-propagation rules.
type Router interface {
	http.Handler
	Handle(method, path string, handler http.Handler)
	Any(path string, handler http.Handler)
	Group(path string) RouterGroup
}

// FallbackRouter optionally routes 404/405 through the application's response
// policy and middleware. Custom adapters can implement it without changing Router.
type FallbackRouter interface {
	SetFallbacks(notFound, methodNotAllowed http.Handler)
}

// RouterGroup is the route-registration portion of Router.
type RouterGroup interface {
	Handle(method, path string, handler http.Handler)
	Any(path string, handler http.Handler)
	Group(path string) RouterGroup
}

type requestContextKey uint8

const (
	routeParamsKey requestContextKey = iota + 1
	routePatternKey
)

// WithRouteParams lets a router adapter expose path parameters to the
// transport-neutral Context.
func WithRouteParams(ctx context.Context, params map[string]string) context.Context {
	copyOfParams := make(map[string]string, len(params))
	for key, value := range params {
		copyOfParams[key] = value
	}
	return context.WithValue(ctx, routeParamsKey, copyOfParams)
}

// RouteParams returns path parameters installed by a router adapter.
func RouteParams(ctx context.Context) map[string]string {
	if ctx == nil {
		return nil
	}
	params, _ := ctx.Value(routeParamsKey).(map[string]string)
	return params
}

// WithRoutePattern records the router's matched route pattern for access logs.
func WithRoutePattern(ctx context.Context, pattern string) context.Context {
	return context.WithValue(ctx, routePatternKey, pattern)
}

// RoutePattern returns the matched route pattern, when the adapter provides it.
func RoutePattern(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	pattern, _ := ctx.Value(routePatternKey).(string)
	return pattern
}

// Context provides the business-facing request and response API. It contains
// only standard-library HTTP types, so it remains usable when the network
// implementation is replaced.
type Context struct {
	request       *http.Request
	writer        http.ResponseWriter
	params        map[string]string
	values        map[string]any
	responded     bool
	status        int
	encoder       response.Encoder
	errorRegistry *apierrors.Registry
	failure       *apierrors.APIError
}

// NewContext creates a transport-neutral GoOmni context.
func NewContext(request *http.Request, writer http.ResponseWriter, params map[string]string) *Context {
	if request == nil {
		request = &http.Request{}
	}
	c := &Context{
		request: request,
		params:  params,
		values:  make(map[string]any),
	}
	if writer != nil {
		c.writer = trackWriter(writer, c)
	}
	return c
}

func (c *Context) Request() *http.Request { return c.request }

// Context returns the standard request context. It carries GoOmni
// correlation values such as the request ID and can be passed to services.
func (c *Context) Context() context.Context {
	if c.request == nil {
		return context.Background()
	}
	return c.request.Context()
}

// Raw returns a streaming response writer that tracks commits and status.
// Optional HTTP capabilities are preserved only when the underlying writer supports them.
func (c *Context) Raw() http.ResponseWriter { return c.writer }

// Clone gives a buffering middleware its own response state and values map.
// Stored values themselves are shared; middleware must not mutate them concurrently.
func (c *Context) Clone(ctx context.Context, writer http.ResponseWriter) *Context {
	clone := NewContext(c.request.Clone(ctx), writer, c.params)
	clone.encoder = c.encoder
	clone.errorRegistry = c.errorRegistry
	for key, value := range c.values {
		clone.values[key] = value
	}
	return clone
}

// WriteResponse commits a buffered response through GoOmni's response tracking.
func (c *Context) WriteResponse(status int, headers http.Header, body []byte) error {
	if c.responded {
		return nil
	}
	if c.writer == nil {
		return apierrors.Internal(nil)
	}
	for key, values := range headers {
		c.writer.Header()[key] = append([]string(nil), values...)
	}
	c.writer.WriteHeader(status)
	if len(body) > 0 {
		if _, err := c.writer.Write(body); err != nil {
			return apierrors.Internal(err)
		}
	}
	return nil
}

func (c *Context) Param(name string) string { return c.params[name] }

func (c *Context) Query(name string) string {
	if c.request == nil {
		return ""
	}
	return c.request.URL.Query().Get(name)
}

func (c *Context) Header(name string) string {
	if c.request == nil {
		return ""
	}
	return c.request.Header.Get(name)
}

func (c *Context) RequestID() string { return logx.RequestID(c.Context()) }

func (c *Context) Set(key string, value any) { c.values[key] = value }

func (c *Context) Get(key string) (any, bool) {
	value, ok := c.values[key]
	return value, ok
}

// WithContext replaces the standard request context while preserving the
// request and its headers.
func (c *Context) WithContext(ctx context.Context) {
	if c.request != nil {
		c.request = c.request.WithContext(ctx)
	}
}

// SetResponseHeader sets a header on the underlying response.
func (c *Context) SetResponseHeader(name, value string) {
	if c.writer != nil {
		c.writer.Header().Set(name, value)
	}
}

func (c *Context) BindJSON(value any) error { return validate.JSON(c.request, value) }

func (c *Context) BindQuery(value any) error { return validate.Query(c.request, value) }

func (c *Context) BindURI(value any) error { return validate.URI(c.params, value) }

// JSON is an escape hatch for responses that do not use the standard envelope.
func (c *Context) JSON(status int, value any) error {
	if c.responded {
		return nil
	}
	if c.writer == nil {
		return apierrors.Internal(nil)
	}
	// Encode before committing headers so an invalid value can still produce
	// the standard 500 response on every adapter.
	data, err := json.Marshal(value)
	if err != nil {
		return apierrors.Internal(err)
	}
	c.writer.Header().Set("Content-Type", "application/json; charset=utf-8")
	c.writer.WriteHeader(status)
	if _, err := c.writer.Write(append(data, '\n')); err != nil {
		return apierrors.Internal(err)
	}
	return nil
}

func (c *Context) OK(data any) error { return c.respond(http.StatusOK, "OK", "success", data) }

func (c *Context) Created(data any) error {
	return c.respond(http.StatusCreated, "CREATED", "created", data)
}

func (c *Context) Accepted(data any) error {
	return c.respond(http.StatusAccepted, "ACCEPTED", "accepted", data)
}

func (c *Context) NoContent() error {
	if c.responded {
		return nil
	}
	if c.writer == nil {
		return apierrors.Internal(nil)
	}
	c.writer.WriteHeader(http.StatusNoContent)
	return nil
}

func (c *Context) respond(status int, code, message string, data any) error {
	return c.writeResult(response.Result{
		Status:    status,
		Code:      code,
		Message:   message,
		Data:      data,
		RequestID: c.RequestID(),
	})
}

// Status returns the response status observed by Context.
func (c *Context) Status() int {
	if c.status == 0 {
		return http.StatusOK
	}
	return c.status
}

// Responded reports whether this handler has already written a response.
func (c *Context) Responded() bool { return c.responded }

// WriteError writes a stable public error response. Internal causes are not
// serialized. Responses committed through Context methods or Raw are preserved.
func (c *Context) WriteError(err error) {
	if c.responded || err == nil {
		return
	}
	var bodyErr *http.MaxBytesError
	if errors.As(err, &bodyErr) {
		err = bodyTooLarge()
	}
	apiErr := c.ResolveError(err)
	c.failure = apiErr
	if writeErr := c.writeResult(response.Result{
		BusinessCode: apiErr.BusinessCode,
		Failed:       true,
		Status:       apiErr.Status,
		Code:         apiErr.Code,
		Message:      apiErr.Message,
		RequestID:    c.RequestID(),
		Err:          err,
	}); writeErr != nil && !c.responded {
		// An invalid custom encoder must not recurse or leak a different envelope.
		_ = c.WriteResponse(http.StatusInternalServerError, nil, nil)
	}
}

// SetErrorRegistry sets an application fallback. Route encoders can supply their
// own registry; clones retain both policies without any process-global lookup.
func (c *Context) SetErrorRegistry(r *apierrors.Registry) { c.errorRegistry = r }
func (c *Context) ResolveError(err error) *apierrors.APIError {
	registry := c.errorRegistry
	if provider, ok := c.encoder.(response.ErrorRegistryProvider); ok {
		if scoped := provider.ErrorRegistry(); scoped != nil {
			registry = scoped
		}
	}
	return registry.Resolve(err)
}

// RecordError preserves failure semantics when a middleware commits buffered bytes.
func (c *Context) RecordError(err error) { c.failure = c.ResolveError(err) }

// RecordFailure propagates an already resolved failure without reapplying a
// different parent/catalog policy. Used with committed or buffered responses.
func (c *Context) RecordFailure(err *apierrors.APIError) { c.failure = err.Clone() }

// Failure returns a detached description of a failure already handled by Context.
func (c *Context) Failure() *apierrors.APIError {
	if c.failure == nil {
		return nil
	}
	return c.failure.Clone()
}