// Package web serves the local UI and an SSE state stream, and owns the
// server-authoritative timebox expiry timer.
package web

import (
	"embed"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"net/http"
	"sync"
	"time"

	"antidrift/internal/session"
	"antidrift/internal/statemachine"

	"github.com/gin-gonic/gin"
)

//go:embed static/*
var staticFS embed.FS

// Server wires the session controller to HTTP and SSE.
type Server struct {
	ctrl  *session.Controller
	bcast *Broadcaster

	mu    sync.Mutex
	timer *time.Timer
}

func NewServer(ctrl *session.Controller) *Server {
	s := &Server{ctrl: ctrl, bcast: NewBroadcaster()}
	ctrl.SetOnChange(s.broadcast)
	return s
}

func (s *Server) Router() *gin.Engine {
	r := gin.New()
	r.Use(gin.Recovery())

	sub, _ := fs.Sub(staticFS, "static")
	r.GET("/", func(c *gin.Context) {
		c.FileFromFS("/", http.FS(sub))
	})
	r.GET("/events", s.handleEvents)
	r.POST("/planning", s.handlePlanning)
	r.POST("/coach", s.handleCoach)
	r.POST("/commitment", s.handleCommitment)
	r.POST("/complete", s.handleComplete)
	r.POST("/end", s.handleEnd)
	return r
}

func (s *Server) stateJSON() string {
	data, _ := json.Marshal(s.ctrl.State())
	return string(data)
}

func (s *Server) broadcast() {
	s.bcast.Publish(s.stateJSON())
}

// respond maps a controller error to an HTTP status, otherwise broadcasts and
// returns the new state.
func (s *Server) respond(c *gin.Context, err error) {
	if err != nil {
		var illegal statemachine.IllegalTransitionError
		if errors.As(err, &illegal) {
			c.JSON(http.StatusConflict, gin.H{"error": err.Error()})
			return
		}
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}
	s.broadcast()
	c.Data(http.StatusOK, "application/json", []byte(s.stateJSON()))
}

func (s *Server) handlePlanning(c *gin.Context) {
	s.cancelExpiry()
	s.respond(c, s.ctrl.EnterPlanning())
}

type coachRequest struct {
	Intent string `json:"intent"`
}

func (s *Server) handleCoach(c *gin.Context) {
	var req coachRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid json"})
		return
	}
	s.respond(c, s.ctrl.RequestCoach(req.Intent))
}

type commitmentRequest struct {
	NextAction       string `json:"next_action"`
	SuccessCondition string `json:"success_condition"`
	TimeboxSecs      int64  `json:"timebox_secs"`
}

func (s *Server) handleCommitment(c *gin.Context) {
	var req commitmentRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid json"})
		return
	}
	err := s.ctrl.StartManualCommitment(req.NextAction, req.SuccessCondition, time.Duration(req.TimeboxSecs)*time.Second, nil)
	if err == nil {
		s.armExpiry()
	}
	s.respond(c, err)
}

func (s *Server) handleComplete(c *gin.Context) {
	s.cancelExpiry()
	s.respond(c, s.ctrl.Complete())
}

func (s *Server) handleEnd(c *gin.Context) {
	s.respond(c, s.ctrl.End())
}

func (s *Server) handleEvents(c *gin.Context) {
	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")

	flusher, ok := c.Writer.(http.Flusher)
	if !ok {
		c.Status(http.StatusInternalServerError)
		return
	}
	ch := s.bcast.Subscribe()
	defer s.bcast.Unsubscribe(ch)

	fmt.Fprintf(c.Writer, "data: %s\n\n", s.stateJSON())
	flusher.Flush()

	for {
		select {
		case <-c.Request.Context().Done():
			return
		case msg, open := <-ch:
			if !open {
				return
			}
			fmt.Fprintf(c.Writer, "data: %s\n\n", msg)
			flusher.Flush()
		}
	}
}

// armExpiry schedules an Active -> Review transition at the commitment deadline.
func (s *Server) armExpiry() {
	deadline := s.ctrl.Deadline()
	if deadline.IsZero() {
		return
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.timer != nil {
		s.timer.Stop()
	}
	d := time.Until(deadline)
	if d < 0 {
		d = 0
	}
	s.timer = time.AfterFunc(d, func() {
		if err := s.ctrl.Expire(); err == nil {
			s.broadcast()
		}
	})
}

func (s *Server) cancelExpiry() {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.timer != nil {
		s.timer.Stop()
		s.timer = nil
	}
}

// Init re-arms or expires a restored Active session at startup.
func (s *Server) Init() {
	st := s.ctrl.State()
	if st.RuntimeState != "active" {
		return
	}
	if s.ctrl.Deadline().After(time.Now()) {
		s.armExpiry()
		return
	}
	if err := s.ctrl.Expire(); err == nil {
		s.broadcast()
	}
}