// Package sipcall implements the isolated, single-call native Asterisk line test.
package sipcall

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"net/netip"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"
)

type Config struct {
	ID, Server, CallerID, Prefix                        string
	Port                                                int
	ConfigDir, Binary, LibraryDir, OutputDir, Interface string
	Ring, Hold                                          time.Duration
	resultDir                                           string
}

var identifier = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_-]{0,47}$`)
var caller = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_.+-]{0,63}$`)
var prefix = regexp.MustCompile(`^[A-Za-z0-9]{0,16}$`)
var numberPattern = regexp.MustCompile(`^[0-9]{1,32}$`)

func LoadConfig(path string) (Config, error) {
	info, err := os.Lstat(path)
	if err != nil {
		return Config{}, fmt.Errorf("inspect SIP ENV: %w", err)
	}
	if !info.Mode().IsRegular() || info.Mode().Perm() != 0600 {
		return Config{}, errors.New("SIP ENV must be a private regular file (0600), not a symlink")
	}
	f, err := os.Open(path)
	if err != nil {
		return Config{}, err
	}
	defer f.Close()
	return ParseConfig(f)
}

// ParseConfig never evaluates shell syntax, substitutes variables, or accepts
// unknown/duplicate fields. Empty prefix must still be explicitly declared.
func ParseConfig(r io.Reader) (Config, error) {
	keys := []string{"SIP_ID", "SIP_SERVER", "SIP_PORT", "SIP_CALLER_ID", "SIP_PREFIX", "SIP_TRANSPORT", "SIP_AUTH", "SIP_REGISTER", "SIP_CODEC", "ASTERISK_CONFIG_DIR", "ASTERISK_BIN", "ASTERISK_LIBRARY_DIR", "OUTPUT_DIR", "RING_SECONDS", "HOLD_SECONDS", "DEBUG_INTERFACE"}
	allowed := map[string]bool{}
	for _, k := range keys {
		allowed[k] = true
	}
	values := map[string]string{}
	data, err := io.ReadAll(io.LimitReader(r, 65537))
	if err != nil {
		return Config{}, err
	}
	if len(data) > 65536 {
		return Config{}, errors.New("SIP ENV exceeds 64 KiB")
	}
	scanner := bufio.NewScanner(strings.NewReader(string(data)))
	line := 0
	for scanner.Scan() {
		line++
		s := strings.TrimSpace(scanner.Text())
		if s == "" || strings.HasPrefix(s, "#") {
			continue
		}
		k, v, ok := strings.Cut(s, "=")
		k = strings.TrimSpace(k)
		v = strings.TrimSpace(v)
		if !ok || !allowed[k] {
			return Config{}, fmt.Errorf("SIP ENV line %d: unknown or malformed field", line)
		}
		if _, ok = values[k]; ok {
			return Config{}, fmt.Errorf("SIP ENV line %d: duplicate %s", line, k)
		}
		if strings.ContainsAny(v, "\x00\r\n\"'`$") {
			return Config{}, fmt.Errorf("SIP ENV %s: shell syntax and control characters are not supported", k)
		}
		values[k] = v
	}
	if err := scanner.Err(); err != nil {
		return Config{}, fmt.Errorf("read SIP ENV: %w", err)
	}
	for _, k := range keys {
		if k == "DEBUG_INTERFACE" {
			continue
		}
		v, ok := values[k]
		if !ok || (v == "" && k != "SIP_PREFIX") {
			return Config{}, fmt.Errorf("SIP ENV %s required", k)
		}
	}
	for k, want := range map[string]string{"SIP_TRANSPORT": "udp", "SIP_AUTH": "ip", "SIP_REGISTER": "no", "SIP_CODEC": "alaw"} {
		if values[k] != want {
			return Config{}, fmt.Errorf("%s must be %s; other line modes are not supported", k, want)
		}
	}
	addr, err := netip.ParseAddr(values["SIP_SERVER"])
	if err != nil || !addr.Is4() || addr.IsUnspecified() || addr.IsMulticast() {
		return Config{}, errors.New("SIP_SERVER must be a unicast IPv4 address")
	}
	port, err := strconv.Atoi(values["SIP_PORT"])
	if err != nil || port < 1 || port > 65535 {
		return Config{}, errors.New("SIP_PORT must be between 1 and 65535")
	}
	if !identifier.MatchString(values["SIP_ID"]) || !caller.MatchString(values["SIP_CALLER_ID"]) || !prefix.MatchString(values["SIP_PREFIX"]) {
		return Config{}, errors.New("invalid SIP_ID, SIP_CALLER_ID or SIP_PREFIX")
	}
	ring, err := seconds(values["RING_SECONDS"], 120)
	if err != nil {
		return Config{}, fmt.Errorf("RING_SECONDS: %w", err)
	}
	hold, err := seconds(values["HOLD_SECONDS"], 30)
	if err != nil {
		return Config{}, fmt.Errorf("HOLD_SECONDS: %w", err)
	}
	for _, k := range []string{"ASTERISK_CONFIG_DIR", "ASTERISK_BIN", "ASTERISK_LIBRARY_DIR", "OUTPUT_DIR"} {
		if !filepath.IsAbs(values[k]) {
			return Config{}, fmt.Errorf("%s must be an absolute path", k)
		}
	}
	iface := values["DEBUG_INTERFACE"]
	if iface != "" && !regexp.MustCompile(`^[A-Za-z0-9_.:-]{1,64}$`).MatchString(iface) {
		return Config{}, errors.New("invalid DEBUG_INTERFACE")
	}
	return Config{ID: values["SIP_ID"], Server: values["SIP_SERVER"], Port: port, CallerID: values["SIP_CALLER_ID"], Prefix: values["SIP_PREFIX"], ConfigDir: values["ASTERISK_CONFIG_DIR"], Binary: values["ASTERISK_BIN"], LibraryDir: values["ASTERISK_LIBRARY_DIR"], OutputDir: values["OUTPUT_DIR"], Ring: ring, Hold: hold, Interface: iface}, nil
}
func seconds(s string, max int) (time.Duration, error) {
	n, err := strconv.Atoi(s)
	if err != nil || n < 1 || n > max {
		return 0, fmt.Errorf("must be between 1 and %d", max)
	}
	return time.Duration(n) * time.Second, nil
}
func (c Config) Route(number string) (string, error) {
	if !numberPattern.MatchString(number) {
		return "", errors.New("callee must contain 1–32 ASCII digits")
	}
	return c.Prefix + number, nil
}
func (c Config) Endpoint() string { return "siptest-" + c.ID }