// Package webhook implements the webhook inbound channel adapter (design/08
// §4). A webhook channel receives external HTTP callbacks (JSON or form posts)
// and normalizes them into UnifiedMessage so the runtime can reason about them
// like any other channel.
//
// It is inbound-only: the adapter never pushes messages out, so
// Capabilities.Proactive is false and SendMessage/SendProactive return
// adapter.ErrUnsupported. The gateway mounts the exposed InboundHandler at the
// configured endpoint path (M8). HMAC-SHA256 signature verification is opt-in
// via Config.Secret.
//
// The adapter lives behind adapter.PlatformAdapter so the runtime can treat it
// uniformly with the other channels declared in design/08 (qq-obv11,
// weixin-ilink, telegram). Configuration is sourced externally and injected at
// construction; no values are hard-coded beyond safe fallbacks.
package webhook

import (
	"context"
	"fmt"
	"log/slog"
	"net/http"
	"sync"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/channel/adapter"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
)

const (
	// PlatformName is the identifier returned by Name and stamped onto every
	// inbound UnifiedMessage so consumers can attribute the origin.
	PlatformName = "webhook"

	// source is the logger provenance tag required by the logging rule.
	source = "plugins/channels/webhook"

	// defaultEndpointPath is used when Config.EndpointPath is empty.
	defaultEndpointPath = "/webhook"
	// defaultSignatureHeader carries the HMAC signature when Config.Secret is set.
	defaultSignatureHeader = "X-Webhook-Signature"
	// defaultMaxBodyBytes caps an inbound callback payload at 1 MiB to protect
	// against oversized bodies, per the streaming/no-ReadAll-large-files rule.
	defaultMaxBodyBytes = 1 << 20
)

// Config configures the webhook inbound adapter. It is decoded from the channel
// config map via adapter.DecodeConfig; every field is optional and meaningfully
// defaulted so an empty config yields a usable endpoint.
type Config struct {
	// EndpointPath is the route the gateway mounts the inbound handler at.
	EndpointPath string `json:"endpointPath"`
	// ChannelID identifies this webhook channel; when set it is reported by
	// ListChannels. Empty means no channel is pre-registered.
	ChannelID string `json:"channelId"`
	// ChannelName is the human-readable channel name for ListChannels.
	ChannelName string `json:"channelName"`
	// Secret enables HMAC-SHA256 signature verification when non-empty. The
	// signature is computed over the raw request body and passed in the header
	// named by SignatureHeader. Empty disables verification.
	Secret string `json:"secret"`
	// SignatureHeader names the header carrying the signature. Defaults to
	// "X-Webhook-Signature" when empty.
	SignatureHeader string `json:"signatureHeader"`
	// Methods are the accepted HTTP methods. Defaults to ["POST"].
	Methods []string `json:"methods"`
}

// Adapter implements adapter.PlatformAdapter for the webhook channel. It is an
// inbound-only adapter: callbacks arrive through the InboundHandler and are
// delivered to the installed message handler (or the emit callback captured by
// ReadMessages). No external session is held, so Connect/Disconnect only track
// lifecycle state.
type Adapter struct {
	log    *slog.Logger
	client *http.Client
	cfg    Config

	mu        sync.RWMutex
	connected bool
	handler   adapter.MessageHandler
	emit      func(adapter.UnifiedMessage)
}

// Compile-time assertion that Adapter satisfies the channel contract.
var _ adapter.PlatformAdapter = (*Adapter)(nil)

// Option adjusts an Adapter at construction time.
type Option func(*Adapter)

// WithConfig sets the adapter configuration.
func WithConfig(cfg Config) Option {
	return func(a *Adapter) { a.cfg = cfg }
}

// WithClient injects the HTTP client used for any outbound call. The webhook
// adapter is inbound-only and never uses it, but the field is kept so callers
// that later add outbound delivery do not change the constructor.
func WithClient(c *http.Client) Option {
	return func(a *Adapter) { a.client = c }
}

// WithLogger sets the structured logger used by the adapter. A nil logger
// falls back to a default tagged logger so logging never panics.
func WithLogger(l *slog.Logger) Option {
	return func(a *Adapter) { a.log = l }
}

// New builds a webhook adapter. It defaults the HTTP client to
// http.DefaultClient and a source-tagged structured logger, applies opts, then
// normalizes the configuration so a minimal config still yields a working
// endpoint.
func New(opts ...Option) *Adapter {
	a := &Adapter{
		client: http.DefaultClient,
		log:    logger.WithSource(logger.New(logger.Options{Format: string(logger.FormatText), Level: "info"}), source),
	}
	for _, o := range opts {
		o(a)
	}
	a.normalize()
	return a
}

// normalize fills zero-valued config with safe defaults so an empty Config is
// usable. It is called once at construction; the config is immutable afterward.
func (a *Adapter) normalize() {
	if a.cfg.EndpointPath == "" {
		a.cfg.EndpointPath = defaultEndpointPath
	}
	if a.cfg.SignatureHeader == "" {
		a.cfg.SignatureHeader = defaultSignatureHeader
	}
	if len(a.cfg.Methods) == 0 {
		a.cfg.Methods = []string{http.MethodPost}
	}
	if a.client == nil {
		a.client = http.DefaultClient
	}
	if a.log == nil {
		a.log = logger.WithSource(logger.New(logger.Options{Format: string(logger.FormatText), Level: "info"}), source)
	}
}

// Name returns the platform identifier "webhook".
func (a *Adapter) Name() string { return PlatformName }

// Config returns a snapshot of the current configuration as a plain map for
// inspection or persistence.
func (a *Adapter) Config() map[string]any {
	return map[string]any{
		"endpointPath":    a.cfg.EndpointPath,
		"channelId":       a.cfg.ChannelID,
		"channelName":     a.cfg.ChannelName,
		"secret":          a.cfg.Secret,
		"signatureHeader": a.cfg.SignatureHeader,
		"methods":         a.cfg.Methods,
	}
}

// Connect marks the adapter connected (idempotent). No external session is
// established; the gateway registers the route by mounting InboundHandler, so
// Connect only transitions lifecycle state for the caller's benefit.
func (a *Adapter) Connect(_ context.Context) error {
	a.mu.Lock()
	defer a.mu.Unlock()
	if a.connected {
		return nil
	}
	a.connected = true
	a.log.Info("webhook channel connected", "endpointPath", a.cfg.EndpointPath)
	return nil
}

// Disconnect tears down the adapter (idempotent): it clears the connected flag
// and drops any installed handler/emit so no callback is delivered after a
// shutdown.
func (a *Adapter) Disconnect(_ context.Context) error {
	a.mu.Lock()
	defer a.mu.Unlock()
	if !a.connected {
		return nil
	}
	a.connected = false
	a.handler = nil
	a.emit = nil
	a.log.Info("webhook channel disconnected")
	return nil
}

// IsConnected reports whether the adapter is currently connected.
func (a *Adapter) IsConnected() bool {
	a.mu.RLock()
	defer a.mu.RUnlock()
	return a.connected
}

// HealthCheck verifies the adapter is usable. As an inbound-only adapter that
// holds no session, it only reports the lifecycle state.
func (a *Adapter) HealthCheck(_ context.Context) error {
	if !a.IsConnected() {
		return fmt.Errorf("webhook: %w", adapter.ErrNotConnected)
	}
	return nil
}

// ReadMessages installs emit as a fallback delivery target, then blocks until
// ctx is canceled. Delivery is push-style via the message handler, matching the
// documented behaviour for push adapters; emit is only exercised when no
// handler is installed.
func (a *Adapter) ReadMessages(ctx context.Context, emit func(adapter.UnifiedMessage)) {
	a.mu.Lock()
	a.emit = emit
	a.mu.Unlock()

	<-ctx.Done()

	a.mu.Lock()
	a.emit = nil
	a.mu.Unlock()
}

// SendMessage is unsupported: the webhook channel is inbound-only and has no
// outbound delivery path. It returns adapter.ErrUnsupported.
func (a *Adapter) SendMessage(_ context.Context, _ adapter.UnifiedResponse) error {
	return fmt.Errorf("webhook: send message: %w", adapter.ErrUnsupported)
}

// SendProactive is unsupported for the same reason as SendMessage:
// Capabilities.Proactive is false. It returns adapter.ErrUnsupported.
func (a *Adapter) SendProactive(_ context.Context, _ adapter.UnifiedMessage) error {
	return fmt.Errorf("webhook: proactive push: %w", adapter.ErrUnsupported)
}

// SetMessageHandler installs the callback receiving push-style inbound
// messages. A nil fn clears the handler.
func (a *Adapter) SetMessageHandler(fn adapter.MessageHandler) {
	a.mu.Lock()
	defer a.mu.Unlock()
	a.handler = fn
}

// Capabilities declares what the webhook channel supports. Because it is
// inbound-only, Proactive is false; image is reported so consumers know media
// URLs may appear in inbound messages.
func (a *Adapter) Capabilities() adapter.Capabilities {
	return adapter.Capabilities{
		MaxMessageLength:  8192,
		Markdown:          true,
		Image:             true,
		Voice:             false,
		Reaction:          false,
		TypingHint:        false,
		RecommendBurstMax: 1,
		Proactive:         false,
	}.Normalize()
}

// ListChannels returns the channel declared by Config.ChannelID when present,
// otherwise an empty list: the webhook endpoint is a single generic channel
// whose identity only becomes concrete per inbound message.
func (a *Adapter) ListChannels(_ context.Context) ([]adapter.ChannelInfo, error) {
	if a.cfg.ChannelID == "" {
		return nil, nil
	}
	return []adapter.ChannelInfo{
		{
			ChannelID:   a.cfg.ChannelID,
			ChannelType: adapter.ChannelDirect,
			ChannelName: a.cfg.ChannelName,
		},
	}, nil
}