package httpapi

import (
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"strconv"
	"strings"

	"git.yeij.top/AskaEth/Scoreboard/server/internal/domain"
)

// apiError 是可直接映射为统一响应结构的业务错误（见 devdocs/05 第 8 节错误码）。
type apiError struct {
	status  int
	code    string
	message string
	detail  any
}

func (e *apiError) Error() string { return e.code + ": " + e.message }

func badRequest(message string, detail any) *apiError {
	return &apiError{status: http.StatusBadRequest, code: "VALIDATION_FAILED", message: message, detail: detail}
}

func notFound(message string) *apiError {
	return &apiError{status: http.StatusNotFound, code: "VALIDATION_FAILED", message: message}
}

func conflict(message string) *apiError {
	return &apiError{status: http.StatusConflict, code: "CONFLICT", message: message}
}

func stateInvalid(message string) *apiError {
	return &apiError{status: http.StatusConflict, code: "STATE_INVALID", message: message}
}

func internal(err error) *apiError {
	return &apiError{status: http.StatusInternalServerError, code: "INTERNAL", message: "服务端异常", detail: err.Error()}
}

func notImplemented(message string) *apiError {
	return &apiError{status: http.StatusNotImplemented, code: "INTERNAL", message: message}
}

// handler 是业务处理器：返回 data 时自动包成 {ok:true,data}，返回 *apiError 时输出统一错误。
type handler func(w http.ResponseWriter, r *http.Request) (any, error)

// handle 统一把业务结果/错误写成 REST 响应。
func (s *server) handle(fn handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		data, err := fn(w, r)
		if err != nil {
			if errors.Is(err, errHandled) {
				return
			}
			writeAPIError(w, s.logger, err)
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{"ok": true, "data": data})
	}
}

// handleVoid 用于无返回体的写操作。
func (s *server) handleVoid(fn func(w http.ResponseWriter, r *http.Request) error) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if err := fn(w, r); err != nil {
			writeAPIError(w, s.logger, err)
			return
		}
		writeJSON(w, http.StatusOK, map[string]any{"ok": true, "data": nil})
	}
}

func writeAPIError(w http.ResponseWriter, logger *slog.Logger, err error) {
	var api *apiError
	if !errors.As(err, &api) {
		api = internal(err)
	}
	if api.status >= http.StatusInternalServerError {
		logger.Error("请求失败", "code", api.code, "err", api.message)
	}
	body := map[string]any{
		"ok": false,
		"error": map[string]any{
			"code":    api.code,
			"message": api.message,
		},
	}
	if api.detail != nil {
		body["error"].(map[string]any)["detail"] = api.detail
	}
	writeJSON(w, api.status, body)
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// decodeJSON 解析请求体；空体视为错误，避免把「没传参数」当成合法写操作。
// 不启用 DisallowUnknownFields：前端会在每个写请求体里注入 requestId，
// 服务端按需读取即可，不该因为多一个字段就拒绝整个请求。
func decodeJSON(r *http.Request, dst any) error {
	dec := json.NewDecoder(r.Body)
	if err := dec.Decode(dst); err != nil {
		return badRequest("请求体不是合法 JSON", err.Error())
	}
	return nil
}

// pageQuery 解析 ?page=&size=，默认第 1 页、每页 50 条，上限 500。
func pageQuery(r *http.Request) (page, size int) {
	page = intQuery(r, "page", 1)
	size = intQuery(r, "size", 50)
	if page < 1 {
		page = 1
	}
	switch {
	case size < 1:
		size = 50
	case size > 500:
		size = 500
	}
	return page, size
}

func intQuery(r *http.Request, key string, def int) int {
	raw := strings.TrimSpace(r.URL.Query().Get(key))
	if raw == "" {
		return def
	}
	n, err := strconv.Atoi(raw)
	if err != nil {
		return def
	}
	return n
}

func int64Query(r *http.Request, key string) (int64, bool) {
	raw := strings.TrimSpace(r.URL.Query().Get(key))
	if raw == "" {
		return 0, false
	}
	n, err := strconv.ParseInt(raw, 10, 64)
	if err != nil {
		return 0, false
	}
	return n, true
}

// pathID 解析路由通配符 {id}。
func pathID(r *http.Request, name string) (int64, error) {
	raw := r.PathValue(name)
	n, err := strconv.ParseInt(raw, 10, 64)
	if err != nil || n <= 0 {
		return 0, badRequest("路径参数 "+name+" 非法", raw)
	}
	return n, nil
}

// pageResult 是分页响应体（见 devdocs/05 第 6 节）。
type pageResult[T any] struct {
	Items []T `json:"items"`
	Total int `json:"total"`
	Page  int `json:"page"`
	Size  int `json:"size"`
}

// mapDomainError 把 domain 引擎的哨兵错误映射为 REST 错误码。
func mapDomainError(err error) error {
	switch {
	case err == nil:
		return nil
	case errors.Is(err, domain.ErrManualAdjustmentDisabled),
		errors.Is(err, domain.ErrAdjustmentReasonRequired),
		errors.Is(err, domain.ErrCompareRequired),
		errors.Is(err, domain.ErrUnknownBasis),
		errors.Is(err, domain.ErrUnknownLedgerOp):
		return stateInvalid(err.Error())
	case errors.Is(err, domain.ErrProfileNotFound):
		return badRequest("计分通道引用的积分模板不存在", err.Error())
	case errors.Is(err, domain.ErrLedgerAlreadyVoided):
		return stateInvalid("该积分流水已作废，不能重复作废")
	case errors.Is(err, domain.ErrLedgerNotFound):
		return notFound("积分流水不存在")
	default:
		return internal(err)
	}
}