package tasks

import (
	"errors"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
	"gorm.io/gorm"
	"senlinai-agent/backend/internal/httpx"
	"senlinai-agent/backend/internal/logic/auth"
)

// Handler 只注册任务写接口，项目核心 handler 不再承担任务职责。
type Handler struct {
	service *Service
}

// NewHandler 创建任务 HTTP registrar。
func NewHandler(service *Service) *Handler {
	return &Handler{service: service}
}

// Register 将任务写接口注册到上层提供的 /api/v1 路由组。
func (h *Handler) Register(router gin.IRouter) {
	router.POST("/projects/:id/tasks", h.create)
	router.PATCH("/projects/:id/tasks/:taskId", h.update)
}

type createTaskRequest struct {
	Title       string `json:"title"`
	Description string `json:"description"`
	Status      string `json:"status"`
	DueAt       string `json:"dueAt"`
	Tag         string `json:"tag"`
}

type updateTaskRequest struct {
	Title         string `json:"title"`
	Description   string `json:"description"`
	Status        string `json:"status"`
	Completed     bool   `json:"completed"`
	NextProjectID string `json:"nextProjectId"`
	Tag           string `json:"tag"`
}

func (h *Handler) create(c *gin.Context) {
	userID, ok := currentUser(c)
	if !ok {
		return
	}
	projectIdentity, ok := httpx.IdentityParam(c, "id")
	if !ok {
		return
	}
	var input createTaskRequest
	if err := c.ShouldBindJSON(&input); err != nil {
		httpx.Error(c, http.StatusBadRequest, "invalid_request", "请求参数无效")
		return
	}
	dueAt, err := parseOptionalTime(input.DueAt)
	if err != nil {
		httpx.Error(c, http.StatusBadRequest, "invalid_request", "截止时间格式无效")
		return
	}
	task, err := h.service.Create(userID, projectIdentity, CreateTaskInput{
		Title: input.Title, Description: input.Description, Status: input.Status, DueAt: dueAt, Tag: input.Tag,
	})
	if err != nil {
		writeTaskError(c, err)
		return
	}
	c.JSON(http.StatusCreated, task)
}

func (h *Handler) update(c *gin.Context) {
	userID, ok := currentUser(c)
	if !ok {
		return
	}
	projectIdentity, ok := httpx.IdentityParam(c, "id")
	if !ok {
		return
	}
	taskIdentity, ok := httpx.IdentityParam(c, "taskId")
	if !ok {
		return
	}
	var input updateTaskRequest
	if err := c.ShouldBindJSON(&input); err != nil {
		httpx.Error(c, http.StatusBadRequest, "invalid_request", "请求参数无效")
		return
	}
	nextProjectIdentity := ""
	if strings.TrimSpace(input.NextProjectID) != "" {
		var valid bool
		nextProjectIdentity, valid = parseIdentity(input.NextProjectID)
		if !valid {
			httpx.Error(c, http.StatusBadRequest, "invalid_identity", "nextProjectId 必须是 UUIDv7")
			return
		}
	}
	task, err := h.service.Update(userID, projectIdentity, taskIdentity, UpdateTaskInput{
		Title: input.Title, Description: input.Description, Status: input.Status, Completed: input.Completed,
		NextProjectIdentity: nextProjectIdentity, Tag: input.Tag,
	})
	if err != nil {
		writeTaskError(c, err)
		return
	}
	c.JSON(http.StatusOK, task)
}

func currentUser(c *gin.Context) (uint, bool) {
	userID, ok := auth.CurrentUserID(c)
	if !ok {
		httpx.Error(c, http.StatusUnauthorized, "unauthorized", "未登录或登录已失效")
		return 0, false
	}
	return userID, true
}

func parseOptionalTime(value string) (*time.Time, error) {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return nil, nil
	}
	parsed, err := time.Parse(time.RFC3339, trimmed)
	if err != nil {
		return nil, err
	}
	parsed = parsed.UTC()
	return &parsed, nil
}

func parseIdentity(value string) (string, bool) {
	trimmed := strings.TrimSpace(value)
	identity, err := uuid.Parse(trimmed)
	if err != nil || identity.Version() != 7 || identity.Variant() != uuid.RFC4122 {
		return "", false
	}
	return identity.String(), true
}

func writeTaskError(c *gin.Context, err error) {
	switch {
	case errors.Is(err, gorm.ErrRecordNotFound):
		httpx.Error(c, http.StatusNotFound, "not_found", "任务或项目不存在")
	case errors.Is(err, ErrTaskTitleRequired):
		httpx.Error(c, http.StatusBadRequest, "invalid_request", "任务标题不能为空")
	default:
		httpx.Error(c, http.StatusInternalServerError, "internal_error", "任务操作失败")
	}
}