package httpapi

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"io"
	"net/http"
)

const maxJSONBody = 1 << 20

type apiError struct {
	Status  int
	Code    string
	Message string
	Details any
}

func (e *apiError) Error() string { return e.Code + ": " + e.Message }

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

func writeError(w http.ResponseWriter, err error) {
	var target *apiError
	if !errors.As(err, &target) {
		target = &apiError{Status: http.StatusInternalServerError, Code: "INTERNAL_ERROR", Message: "服务暂时不可用"}
	}
	body := map[string]any{
		"error": map[string]any{
			"code":    target.Code,
			"message": target.Message,
		},
	}
	if target.Details != nil {
		body["error"].(map[string]any)["details"] = target.Details
	}
	writeJSON(w, target.Status, body)
}

func decodeJSON(r *http.Request, dst any) error {
	decoder := json.NewDecoder(io.LimitReader(r.Body, maxJSONBody))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(dst); err != nil {
		return &apiError{Status: http.StatusBadRequest, Code: "INVALID_JSON", Message: "请求内容格式不正确"}
	}
	if err := decoder.Decode(&struct{}{}); !errors.Is(err, io.EOF) {
		return &apiError{Status: http.StatusBadRequest, Code: "INVALID_JSON", Message: "请求只能包含一个 JSON 对象"}
	}
	return nil
}

func marshalResponse(value any) ([]byte, error) {
	body, err := json.Marshal(value)
	if err != nil {
		return nil, err
	}
	return body, nil
}

func requestHash(value any) (string, error) {
	body, err := json.Marshal(value)
	if err != nil {
		return "", err
	}
	sum := sha256.Sum256(body)
	return hex.EncodeToString(sum[:]), nil
}