package birdfmt

import (
	"encoding/json"
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

var standardPairRE = regexp.MustCompile(`^\s*(\d{1,5}):(\d{1,5})\s*$`)

// badCommunityAddRE matches invalid BIRD filter calls like bgp_community.add(65000,1)
// (first argument is an int). Valid form is bgp_community.add((65000,1)); — note the pair tuple.
var badCommunityAddRE = regexp.MustCompile(`\b(?:bgp_community|bgp_large_community)\.add\(\s*\d`)

// RouteCommunityAttrs returns BIRD 2 lines (indented with 4 spaces) for use inside a static `route … { … }` block.
// Empty string means no community attributes.
func RouteCommunityAttrs(kind, name, valueJSON string) (string, error) {
	name = strings.TrimSpace(name)
	raw := strings.TrimSpace(valueJSON)
	if raw == "" {
		raw = "{}"
	}

	if s, ok := parseLargeFromJSONLoose(raw); ok {
		if err := validateCommunityRouteBody(s); err != nil {
			return "", err
		}
		return s, nil
	}
	_ = kind // reserved for future kinds (e.g. extended communities)

	if m := standardPairRE.FindStringSubmatch(name); len(m) == 3 {
		s, err := standardAddLine(m[1], m[2])
		if err != nil {
			return "", err
		}
		return s, validateCommunityRouteBody(s)
	}

	var obj map[string]any
	if json.Unmarshal([]byte(raw), &obj) == nil {
		if v, ok := obj["standard"].(string); ok {
			if m := standardPairRE.FindStringSubmatch(v); len(m) == 3 {
				s, err := standardAddLine(m[1], m[2])
				if err != nil {
					return "", err
				}
				return s, validateCommunityRouteBody(s)
			}
		}
		if arr, ok := obj["standard"].([]any); ok {
			if len(arr) == 1 {
				return "", fmt.Errorf(`birdfmt: value_json "standard" must be a pair [a,b] or "a:b" string, got single element`)
			}
			if len(arr) == 2 {
				a, aok := numberToUint32String(arr[0])
				b, bok := numberToUint32String(arr[1])
				if aok && bok {
					s, err := standardAddLine(a, b)
					if err != nil {
						return "", err
					}
					return s, validateCommunityRouteBody(s)
				}
			}
		}
	}

	var strVal string
	if json.Unmarshal([]byte(raw), &strVal) == nil {
		if m := standardPairRE.FindStringSubmatch(strVal); len(m) == 3 {
			s, err := standardAddLine(m[1], m[2])
			if err != nil {
				return "", err
			}
			return s, validateCommunityRouteBody(s)
		}
	}

	return "", nil
}

// validateCommunityRouteBody rejects lines that would make BIRD 2 fail parse-check with
// "Argument 1 of 'add' expected clist / quad / ip / pair, got int" (wrong add() shape).
func validateCommunityRouteBody(body string) error {
	body = strings.TrimSpace(body)
	if body == "" {
		return nil
	}
	for _, line := range strings.Split(body, "\n") {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		if badCommunityAddRE.MatchString(line) {
			return fmt.Errorf("birdfmt: invalid community line (expected pair/triple tuple inside add(), e.g. bgp_community.add((65000,1));): %q", line)
		}
	}
	return nil
}

func standardAddLine(a, b string) (string, error) {
	ai, err1 := strconv.ParseUint(strings.TrimSpace(a), 10, 16)
	bi, err2 := strconv.ParseUint(strings.TrimSpace(b), 10, 16)
	if err1 != nil || err2 != nil {
		return "", fmt.Errorf("birdfmt: standard community parts must be 0..65535 (%s:%s)", a, b)
	}
	return fmt.Sprintf("    bgp_community.add((%d,%d));", ai, bi), nil
}

func parseLargeFromJSONLoose(raw string) (string, bool) {
	var obj map[string]any
	if json.Unmarshal([]byte(raw), &obj) != nil {
		return "", false
	}
	arr, ok := obj["large"].([]any)
	if !ok || len(arr) == 0 {
		return "", false
	}
	var b strings.Builder
	for _, row := range arr {
		triple, ok := row.([]any)
		if !ok || len(triple) != 3 {
			continue
		}
		a, ok1 := numberToUint32String(triple[0])
		bb, ok2 := numberToUint32String(triple[1])
		c, ok3 := numberToUint32String(triple[2])
		if !ok1 || !ok2 || !ok3 {
			continue
		}
		ai, _ := strconv.ParseUint(a, 10, 32)
		bi, _ := strconv.ParseUint(bb, 10, 32)
		ci, _ := strconv.ParseUint(c, 10, 32)
		fmt.Fprintf(&b, "    bgp_large_community.add((%d,%d,%d));\n", ai, bi, ci)
	}
	s := strings.TrimRight(b.String(), "\r\n")
	return s, s != ""
}

func numberToUint32String(v any) (string, bool) {
	switch x := v.(type) {
	case float64:
		if x < 0 || x > 4294967295 {
			return "", false
		}
		return strconv.FormatUint(uint64(x), 10), true
	case json.Number:
		n, err := x.Int64()
		if err != nil || n < 0 || n > 4294967295 {
			return "", false
		}
		return strconv.FormatUint(uint64(n), 10), true
	case int:
		if x < 0 || x > 4294967295 {
			return "", false
		}
		return strconv.FormatUint(uint64(x), 10), true
	case int64:
		if x < 0 || x > 4294967295 {
			return "", false
		}
		return strconv.FormatUint(uint64(x), 10), true
	case string:
		n, err := strconv.ParseUint(strings.TrimSpace(x), 10, 32)
		if err != nil {
			return "", false
		}
		return strconv.FormatUint(n, 10), true
	default:
		return "", false
	}
}