package handlers

import (
	"net/http"
	"time"

	"github.com/gin-gonic/gin"

	"qr-scanner/models"
	"qr-scanner/services"
)

type ProgressHandler struct {
	store *services.TaskStore
}

func NewProgressHandler(store *services.TaskStore) *ProgressHandler {
	return &ProgressHandler{store: store}
}

func (h *ProgressHandler) GetProgress(c *gin.Context) {
	taskID := c.Param("taskID")
	task, ok := h.store.Get(taskID)
	if !ok {
		fail(c, http.StatusNotFound, "任务不存在")
		return
	}
	if task.Status == services.TaskExpired {
		fail(c, http.StatusGone, "任务已过期")
		return
	}

	var update models.ProgressUpdate
	if task.Progress != nil {
		update = task.Progress.Snapshot(string(task.Status))
	} else {
		update = models.ProgressUpdate{Total: len(task.Files), Status: string(task.Status), UpdatedAt: time.Now()}
	}
	respondOK(c, update)
}

func (h *ProgressHandler) StreamProgress(c *gin.Context) {
	/*
		SSE 进度推送：
		- 连接建立后先发送一次快照，避免前端空白
		- progress 内部用带缓冲 channel 做“最新进度覆盖”，避免慢客户端拖垮服务
		- 任务达到终态（completed/canceled/failed）后主动结束 SSE
	*/
	taskID := c.Param("taskID")
	task, ok := h.store.Get(taskID)
	if !ok {
		fail(c, http.StatusNotFound, "任务不存在")
		return
	}
	if task.Status == services.TaskExpired {
		fail(c, http.StatusGone, "任务已过期")
		return
	}
	if task.Progress == nil {
		fail(c, http.StatusConflict, "任务尚未开始")
		return
	}

	c.Writer.Header().Set("Content-Type", "text/event-stream")
	c.Writer.Header().Set("Cache-Control", "no-cache")
	c.Writer.Header().Set("Connection", "keep-alive")

	flusher, ok := c.Writer.(http.Flusher)
	if !ok {
		fail(c, http.StatusInternalServerError, "SSE不支持")
		return
	}

	updateCh := make(chan models.ProgressUpdate, 16)
	task.Progress.AddListener(updateCh)
	defer task.Progress.RemoveListener(updateCh)

	initial := task.Progress.Snapshot(string(task.Status))
	_ = services.SSEWrite(c.Writer, initial)
	flusher.Flush()

	for {
		select {
		case <-c.Request.Context().Done():
			return
		case update, ok := <-updateCh:
			if !ok {
				return
			}
			_ = services.SSEWrite(c.Writer, update)
			flusher.Flush()
			if update.Status == string(services.TaskCompleted) || update.Status == string(services.TaskCanceled) || update.Status == string(services.TaskFailed) {
				return
			}
		}
	}
}