package asterisk

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/netip"
	"regexp"
	"sort"
	"strings"

	"git.ipao.vip/rogee/go-sip/internal/configread"
	"git.ipao.vip/rogee/go-sip/internal/contract"
)

var trunkName = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9_-]{0,63}$`)

type trunk struct {
	ID                   string  `json:"trunk_id"`
	Host                 string  `json:"server_host"`
	Port                 int     `json:"server_port"`
	Transport            *string `json:"transport"`
	AuthMode             *string `json:"auth_mode"`
	RegistrationRequired *bool   `json:"registration_required"`
	Codec                string  `json:"codec"`
	Enabled              bool    `json:"enabled"`
}

// Render produces only PJSIP endpoint/AOR objects. Transport is owned by the
// static, reviewed Asterisk base configuration and is never hot-reloaded.
func Render(sip configread.SIP) (string, error) {
	raw, err := json.Marshal(sip)
	if err != nil {
		return "", fmt.Errorf("encode approved SIP snapshot: %w", err)
	}
	if err := contract.ValidateCurrent("config-read", raw); err != nil {
		return "", fmt.Errorf("validate approved SIP snapshot: %w", err)
	}
	var trunks []trunk
	if err := json.Unmarshal(sip.Trunks, &trunks); err != nil {
		return "", fmt.Errorf("decode approved SIP trunks: %w", err)
	}
	seen := make(map[string]bool, len(trunks))
	for _, t := range trunks {
		if !trunkName.MatchString(t.ID) || seen[t.ID] {
			return "", fmt.Errorf("invalid or duplicated SIP trunk ID %q", t.ID)
		}
		seen[t.ID] = true
		if !t.Enabled {
			continue
		}
		if t.Transport == nil || *t.Transport != "udp" || t.AuthMode == nil || (*t.AuthMode != "none" && *t.AuthMode != "ip") || t.RegistrationRequired == nil || *t.RegistrationRequired {
			return "", fmt.Errorf("trunk %q uses unsupported transport, authentication or registration", t.ID)
		}
		addr, err := netip.ParseAddr(t.Host)
		if err != nil || !addr.Is4() || t.Port < 1 || t.Port > 65535 || t.Codec != "PCMA" {
			return "", fmt.Errorf("trunk %q has unsupported endpoint address or codec", t.ID)
		}
	}
	sort.Slice(trunks, func(i, j int) bool { return trunks[i].ID < trunks[j].ID })
	var text strings.Builder
	text.WriteString("; Generated from the approved SIP snapshot. Do not edit manually.\n")
	for _, t := range trunks {
		if !t.Enabled {
			continue
		}
		_, _ = fmt.Fprintf(&text, "\n[%s]\ntype=endpoint\ntransport=go-sip-udp\ncontext=go-sip-no-inbound\ndisallow=all\nallow=alaw\naors=%s-aor\ndirect_media=no\n\n[%s-aor]\ntype=aor\ncontact=sip:%s:%d\n", t.ID, t.ID, t.ID, t.Host, t.Port)
	}
	if text.Len() == 0 {
		return "", errors.New("empty generated SIP configuration")
	}
	return text.String(), nil
}