package controlapi

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"unicode/utf8"
)

const maximumRequestBody = 1 << 20

var (
	logicalIDRegex      = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._:-]{0,63}$`)
	idempotencyKeyRegex = regexp.MustCompile(`^[A-Za-z0-9._:-]{16,128}$`)
	operationIDRegex    = regexp.MustCompile(`^op_[0-9A-HJKMNP-TV-Z]{26}$`)
	strongETagRegex     = regexp.MustCompile(`^"[A-Za-z0-9_-]{24}"$`)
)

func readRequestBody(request *http.Request, expectedMediaType string) ([]byte, error) {
	mediaType, _, err := mime.ParseMediaType(request.Header.Get("Content-Type"))
	if err != nil || mediaType != expectedMediaType {
		return nil, fmt.Errorf("Content-Type must be %s", expectedMediaType)
	}
	contents, err := io.ReadAll(io.LimitReader(request.Body, maximumRequestBody+1))
	if err != nil {
		return nil, errors.New("read request body")
	}
	if len(contents) == 0 || len(contents) > maximumRequestBody {
		return nil, errors.New("request body is empty or too large")
	}
	if err := rejectDuplicateJSONKeys(contents); err != nil {
		return nil, err
	}
	return contents, nil
}

func decodeStrictJSON(contents []byte, destination any) error {
	decoder := json.NewDecoder(bytes.NewReader(contents))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(destination); err != nil {
		return errors.New("request body does not match the API schema")
	}
	if decoder.Decode(&struct{}{}) != io.EOF {
		return errors.New("request body contains trailing JSON")
	}
	return nil
}

func rejectTopLevelNulls(contents []byte) error {
	var fields map[string]json.RawMessage
	if err := json.Unmarshal(contents, &fields); err != nil || fields == nil {
		return errors.New("request body must be a JSON object")
	}
	for _, value := range fields {
		if bytes.Equal(bytes.TrimSpace(value), []byte("null")) {
			return errors.New("request body properties cannot be null")
		}
	}
	return nil
}

func rejectDuplicateJSONKeys(contents []byte) error {
	decoder := json.NewDecoder(bytes.NewReader(contents))
	decoder.UseNumber()
	var visit func(int) error
	visit = func(depth int) error {
		if depth > 64 {
			return errors.New("request body nesting is too deep")
		}
		token, err := decoder.Token()
		if err != nil {
			return errors.New("request body is not valid JSON")
		}
		delimiter, ok := token.(json.Delim)
		if !ok {
			return nil
		}
		switch delimiter {
		case '{':
			seen := make(map[string]struct{})
			for decoder.More() {
				keyToken, err := decoder.Token()
				if err != nil {
					return errors.New("request body is not valid JSON")
				}
				key, ok := keyToken.(string)
				if !ok {
					return errors.New("request body is not a JSON object")
				}
				if _, exists := seen[key]; exists {
					return errors.New("request body contains a duplicate property")
				}
				seen[key] = struct{}{}
				if err := visit(depth + 1); err != nil {
					return err
				}
			}
			end, err := decoder.Token()
			if err != nil || end != json.Delim('}') {
				return errors.New("request body is not valid JSON")
			}
		case '[':
			for decoder.More() {
				if err := visit(depth + 1); err != nil {
					return err
				}
			}
			end, err := decoder.Token()
			if err != nil || end != json.Delim(']') {
				return errors.New("request body is not valid JSON")
			}
		default:
			return errors.New("request body is not valid JSON")
		}
		return nil
	}
	if err := visit(0); err != nil {
		return err
	}
	if _, err := decoder.Token(); err != io.EOF {
		return errors.New("request body contains trailing JSON")
	}
	return nil
}

func validLogicalID(value string) bool {
	return logicalIDRegex.MatchString(value)
}

func validLength(value string, minimum, maximum int) bool {
	length := utf8.RuneCountInString(value)
	return utf8.ValidString(value) && length >= minimum && length <= maximum
}

func validateEndpoint(value string) bool {
	if !validLength(value, 1, 2048) {
		return false
	}
	parsed, err := url.Parse(value)
	return err == nil && parsed.Scheme != "" && parsed.User == nil &&
		!strings.ContainsAny(value, "\r\n")
}

func validStrongETag(value string) bool {
	return strongETagRegex.MatchString(value) && value != "*" && !strings.Contains(value, ",")
}