package via

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"reflect"
	"sync"
	"sync/atomic"
	"time"

	"github.com/ryanhamamura/via/h"
	"golang.org/x/time/rate"
)

// Context is the living bridge between Go and the browser.
//
// It holds runtime state, defines actions, manages reactive signals, and defines UI through View.
type Context struct {
	id                string
	route             string
	csrfToken         string
	app               *V
	view              func() h.H
	routeParams       map[string]string
	parentPageCtx *Context
	patchChan         chan patch
	actionLimiter     *rate.Limiter
	actionRegistry    map[string]actionEntry
	signals           *sync.Map
	mu                sync.RWMutex
	ctxDisposedChan   chan struct{}
	reqCtx            context.Context
	fields            []*Field
	subscriptions     []Subscription
	subsMu            sync.Mutex
	disposeOnce       sync.Once
	createdAt         time.Time
	sseConnected      atomic.Bool
}

// View defines the UI rendered by this context.
// The function should return an h.H element (from via/h).
//
// Changes to signals or state can be pushed live with Sync().
func (c *Context) View(f func() h.H) {
	if f == nil {
		panic("nil viewfn")
	}
	c.view = func() h.H { return h.Div(h.ID(c.id), f()) }
}

// Component registers a subcontext that has self contained data, actions and signals.
// It returns the component's view as a DOM node fn that can be placed in the view
// of the parent. Components can be added to components.
//
// Example:
//
//	counterCompFn := func(c *via.Context) {
//		(...)
//	}
//
//	v.Page("/", func(c *via.Context) {
//		counterComp := c.Component(counterCompFn)
//
//		c.View(func() h.H {
//			return h.Div(
//				h.H1(h.Text("Counter")),
//				counterComp(),
//			)
//		})
//	})
func (c *Context) Component(initCtx func(c *Context)) func() h.H {
	id := c.id + "/_component/" + genRandID()
	compCtx := newContext(id, c.route, c.app)
	if c.isComponent() {
		compCtx.parentPageCtx = c.parentPageCtx
	} else {
		compCtx.parentPageCtx = c
	}
	initCtx(compCtx)
	return compCtx.view
}

func (c *Context) isComponent() bool {
	return c.parentPageCtx != nil
}

// Action registers an event handler and returns a trigger to that event that
// that can be added to the view fn as any other via.h element.
//
// Example:
//
//	n := 0
//	increment := c.Action(func(){
//		 n++
//		 c.Sync()
//	})
//
//	c.View(func() h.H {
//		 return h.Div(
//		 	 	h.P(h.Textf("Value of n: %d", n)),
//		 	 	h.Button(h.Text("Increment n"), increment.OnClick()),
//		 )
//	})
func (c *Context) Action(f func(), opts ...ActionOption) *actionTrigger {
	id := genRandID()
	if f == nil {
		c.app.logErr(c, "failed to bind action '%s' to context: nil func", id)
		return nil
	}

	entry := actionEntry{fn: f}
	for _, opt := range opts {
		opt(&entry)
	}

	if c.isComponent() {
		c.parentPageCtx.actionRegistry[id] = entry
	} else {
		c.actionRegistry[id] = entry
	}
	return &actionTrigger{id}
}

func (c *Context) getAction(id string) (actionEntry, error) {
	if e, ok := c.actionRegistry[id]; ok {
		return e, nil
	}
	return actionEntry{}, fmt.Errorf("action '%s' not found", id)
}

// OnInterval starts a go routine that sets a time.Ticker with the given duration and executes
// the given handler func() on every tick. Use *Routine.UpdateInterval to update the interval.
func (c *Context) OnInterval(duration time.Duration, handler func()) *OnIntervalRoutine {
	var cn chan struct{}
	if c.isComponent() { // components use the chan on the parent page ctx
		cn = c.parentPageCtx.ctxDisposedChan
	} else {
		cn = c.ctxDisposedChan
	}
	r := newOnIntervalRoutine(cn, duration, handler)
	return r
}

// Signal creates a reactive signal and initializes it with the given value.
// Use Bind() to link the value of input elements to the signal and Text() to
// display the signal value and watch the UI update live as the input changes.
//
// Example:
//
//	mysignal := c.Signal("world")
//
//	c.View(func() h.H {
//		return h.Div(
//			h.P(h.Span(h.Text("Hello, ")), h.Span(mysignal.Text())),
//			h.Input(mysignal.Bind()),
//		)
//	})
//
// Signals are 'alive' only in the browser, but Via always injects their values into
// the Context before each action call.
// If any signal value is updated by the server, the update is automatically sent to the
// browser when using Sync() or SyncSignsls().
func (c *Context) Signal(v any) *signal {
	sigID := genRandID()
	if v == nil {
		c.app.logErr(c, "failed to bind signal: nil signal value")
		return &signal{
			id:  sigID,
			val: "error",
			err: fmt.Errorf("context '%s' failed to bind signal '%s': nil signal value", c.id, sigID),
		}
	}
	switch reflect.TypeOf(v).Kind() {
	case reflect.Slice, reflect.Struct:
		if j, err := json.Marshal(v); err == nil {
			v = string(j)
		}
	}
	sig := &signal{
		id:      sigID,
		val:     v,
		changed: true,
	}

	c.mu.Lock()
	defer c.mu.Unlock()
	if c.isComponent() { // components register signals on parent page
		c.parentPageCtx.signals.Store(sigID, sig)
	} else {
		c.signals.Store(sigID, sig)
	}
	return sig

}

func (c *Context) injectSignals(sigs map[string]any) {
	if sigs == nil {
		c.app.logErr(c, "signal injection failed: nil signals")
		return
	}

	c.mu.Lock()
	defer c.mu.Unlock()

	for sigID, val := range sigs {
		item, ok := c.signals.Load(sigID)
		if !ok {
			c.signals.Store(sigID, &signal{
				id:  sigID,
				val: val,
			})
			continue
		}
		if sig, ok := item.(*signal); ok {
			sig.val = val
			sig.changed = false
		}
	}
}

func (c *Context) getPatchChan() chan patch {
	// components use parent page sse stream
	var patchChan chan patch
	if c.isComponent() {
		patchChan = c.parentPageCtx.patchChan
	} else {
		patchChan = c.patchChan
	}
	return patchChan
}

func (c *Context) prepareSignalsForPatch() map[string]any {
	c.mu.RLock()
	defer c.mu.RUnlock()
	updatedSigs := make(map[string]any)
	c.signals.Range(func(sigID, value any) bool {
		if sig, ok := value.(*signal); ok {
			if sig.err != nil {
				c.app.logWarn(c, "signal '%s' is out of sync: %v", sig.id, sig.err)
				return true
			}
			if sig.changed {
				updatedSigs[sigID.(string)] = fmt.Sprintf("%v", sig.val)
			}
		}
		return true
	})
	return updatedSigs
}

// sendPatch queues a patch on this *Context sse stream. If the sse is closed or queue is full, the patch
// is dropped to prevent runtime blocks.
func (c *Context) sendPatch(p patch) {
	patchChan := c.getPatchChan()
	select {
	case patchChan <- p:
	default: // closed or buffer full - drop patch without blocking
	}
}

// Sync pushes the current view state and signal changes to the browser immediately
// over the live SSE event stream.
func (c *Context) Sync() {
	elemsPatch := new(bytes.Buffer)
	if err := c.view().Render(elemsPatch); err != nil {
		c.app.logErr(c, "sync view failed: %v", err)
		return
	}
	c.sendPatch(patch{patchTypeElements, elemsPatch.String()})

	updatedSigs := c.prepareSignalsForPatch()

	if len(updatedSigs) != 0 {
		outgoingSigs, _ := json.Marshal(updatedSigs)
		c.sendPatch(patch{patchTypeSignals, string(outgoingSigs)})
	}
}

// SyncElements pushes an immediate html patch over the live SSE stream to the
// browser that merges with the DOM
//
// For the merge to occur, each top lever element in the patch needs to have
// an ID that matches the ID of an element that already sits in the view.
//
// Example:
//
// If the view already contains the element:
//
//	h.Div(
//		h.ID("my-element"),
//		h.P(h.Text("Hello from Via!"))
//	)
//
// Then, the merge will only occur if the ID of one of the top level elements in the patch
// matches 'my-element'.
func (c *Context) SyncElements(elem ...h.H) {
	b := bytes.NewBuffer(nil)
	for idx, el := range elem {
		if el == nil {
			c.app.logWarn(c, "sync elements failed: element at idx=%d is nil", idx)
			continue
		}
		if err := el.Render(b); err != nil {
			c.app.logWarn(c, "sync elements failed: element at idx=%d has invalid html", idx)
			continue
		}
	}
	c.sendPatch(patch{patchTypeElements, b.String()})
}

// SyncSignals pushes the current signal changes to the browser immediately
// over the live SSE event stream.
func (c *Context) SyncSignals() {
	updatedSigs := c.prepareSignalsForPatch()
	if len(updatedSigs) != 0 {
		outgoingSignals, _ := json.Marshal(updatedSigs)
		c.sendPatch(patch{patchTypeSignals, string(outgoingSignals)})
	}
}

func (c *Context) ExecScript(s string) {
	if s == "" {
		c.app.logWarn(c, "exec script failed: empty script")
		return
	}
	c.sendPatch(patch{patchTypeScript, s})
}

// RedirectView sets a view that redirects the browser to the given URL.
// Use this in middleware to abort the chain and redirect in one step.
func (c *Context) RedirectView(url string) {
	c.View(func() h.H {
		c.Redirect(url)
		return h.Div()
	})
}

// Redirect navigates the browser to the given URL.
// This triggers a full page navigation - the current context will be disposed
// and a new context created at the destination URL.
func (c *Context) Redirect(url string) {
	if url == "" {
		c.app.logWarn(c, "redirect failed: empty url")
		return
	}
	c.sendPatch(patch{patchTypeRedirect, url})
}

// Redirectf navigates the browser to a URL constructed from the format string and arguments.
func (c *Context) Redirectf(format string, a ...any) {
	c.Redirect(fmt.Sprintf(format, a...))
}

// ReplaceURL updates the browser's URL and history without triggering navigation.
// Useful for updating query params or path to reflect UI state changes.
func (c *Context) ReplaceURL(url string) {
	if url == "" {
		c.app.logWarn(c, "replace url failed: empty url")
		return
	}
	c.sendPatch(patch{patchTypeReplaceURL, url})
}

// ReplaceURLf updates the browser's URL using a format string.
func (c *Context) ReplaceURLf(format string, a ...any) {
	c.ReplaceURL(fmt.Sprintf(format, a...))
}

// dispose idempotently tears down this context: unsubscribes all pubsub
// subscriptions and closes ctxDisposedChan to stop routines and exit the SSE loop.
func (c *Context) dispose() {
	c.disposeOnce.Do(func() {
		c.unsubscribeAll()
		c.stopAllRoutines()
	})
}

// stopAllRoutines closes ctxDisposedChan, broadcasting to all listening
// goroutines (OnIntervalRoutine, SSE loop) that this context is done.
func (c *Context) stopAllRoutines() {
	select {
	case <-c.ctxDisposedChan:
		// already closed
	default:
		close(c.ctxDisposedChan)
	}
}

func (c *Context) injectRouteParams(params map[string]string) {
	if params == nil {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	c.routeParams = params
}

// GetPathParam retrieves the value from the page request URL for the given parameter name
// or an empty string if not found.
//
// Example:
//
//	v.Page("/users/{user_id}", func(c *via.Context) {
//
//			userID := GetPathParam("user_id")
//
//			c.View(func() h.H {
//					return h.Div(
//							h.H1(h.Textf("User ID: %s", userID)),
//					)
//			})
//	})
func (c *Context) GetPathParam(param string) string {
	c.mu.RLock()
	defer c.mu.RUnlock()
	if p, ok := c.routeParams[param]; ok {
		return p
	}
	return ""
}

// Session returns the session for this context.
// Session data persists across page views for the same browser.
// Returns a no-op session if no SessionManager is configured.
func (c *Context) Session() *Session {
	return &Session{
		ctx:     c.reqCtx,
		manager: c.app.sessionManager,
	}
}

// Publish sends data to the given subject via the configured PubSub backend.
// Returns an error if no PubSub is configured. No-ops during panic-check init.
func (c *Context) Publish(subject string, data []byte) error {
	if c.id == "" {
		return nil
	}
	if c.app.pubsub == nil {
		return fmt.Errorf("pubsub not configured")
	}
	return c.app.pubsub.Publish(subject, data)
}

// Subscribe creates a subscription on the configured PubSub backend.
// The subscription is tracked for automatic cleanup when the context is disposed.
// Returns an error if no PubSub is configured. No-ops during panic-check init.
func (c *Context) Subscribe(subject string, handler func(data []byte)) (Subscription, error) {
	if c.id == "" {
		return nil, nil
	}
	if c.app.pubsub == nil {
		return nil, fmt.Errorf("pubsub not configured")
	}
	sub, err := c.app.pubsub.Subscribe(subject, handler)
	if err != nil {
		return nil, err
	}

	// Track on page context for cleanup (components use parent, like signals/actions)
	target := c
	if c.isComponent() {
		target = c.parentPageCtx
	}
	target.subsMu.Lock()
	target.subscriptions = append(target.subscriptions, sub)
	target.subsMu.Unlock()
	return sub, nil
}

// unsubscribeAll cleans up all tracked subscriptions for this context and its components.
func (c *Context) unsubscribeAll() {
	c.subsMu.Lock()
	subs := c.subscriptions
	c.subscriptions = nil
	c.subsMu.Unlock()
	for _, sub := range subs {
		sub.Unsubscribe()
	}
}

// Field creates a signal with validation rules attached.
// The initial value seeds both the signal and the reset target.
// The field is tracked on the context so ValidateAll/ResetFields
// can operate on all fields by default.
func (c *Context) Field(initial any, rules ...Rule) *Field {
	f := &Field{
		signal:     c.Signal(initial),
		rules:      rules,
		initialVal: initial,
	}
	target := c
	if c.isComponent() {
		target = c.parentPageCtx
	}
	target.fields = append(target.fields, f)
	return f
}

// ValidateAll runs Validate on each field, returning true only if all pass.
// With no arguments it validates every field tracked on this context.
func (c *Context) ValidateAll(fields ...*Field) bool {
	if len(fields) == 0 {
		fields = c.fields
	}
	ok := true
	for _, f := range fields {
		if !f.Validate() {
			ok = false
		}
	}
	return ok
}

// ResetFields resets each field to its initial value and clears errors.
// With no arguments it resets every field tracked on this context.
func (c *Context) ResetFields(fields ...*Field) {
	if len(fields) == 0 {
		fields = c.fields
	}
	for _, f := range fields {
		f.Reset()
	}
}

func newContext(id string, route string, v *V) *Context {
	if v == nil {
		panic("create context failed: app pointer is nil")
	}

	return &Context{
		id:                id,
		route:             route,
		csrfToken:         genCSRFToken(),
		routeParams:       make(map[string]string),
		app:               v,
		actionLimiter: newLimiter(v.actionRateLimit, defaultActionRate, defaultActionBurst),
		actionRegistry:    make(map[string]actionEntry),
		signals:           new(sync.Map),
		patchChan:         make(chan patch, 1),
		ctxDisposedChan:   make(chan struct{}, 1),
		createdAt:         time.Now(),
	}
}