package distworker

import (
	"fmt"
	"net/url"
	"os"
	"strconv"
	"strings"
)

// DefaultMaxConcurrency is the default upper bound for the worker pool size
// and the number of dispatch goroutines that drain the job queue.
const DefaultMaxConcurrency = 32

const (
	// DefaultHTTPHost is the bind address used when WORKER_HOST is unset.
	DefaultHTTPHost = "0.0.0.0"
	// DefaultHTTPPort is the bind port used when WORKER_PORT is unset.
	// Picked >20000 to avoid colliding with the main RSMon app (which
	// binds 7401 by default) when the worker is co-located on the
	// same host. Operators are still free to override via WORKER_PORT.
	DefaultHTTPPort = 27401

	// EnvPublicURL is the canonical environment variable for the
	// publicly advertised origin. It wins over the legacy
	// EnvWorkerURLLegacy when both are set.
	EnvPublicURL = "PUBLIC_URL"
	// EnvWorkerURLLegacy is the legacy name for the advertised public
	// origin. It is accepted only for the bounded migration defined in
	// docs/public-endpoint-and-identity.md milestone 1 and is
	// deprecated: new configuration must set EnvPublicURL.
	EnvWorkerURLLegacy = "WORKER_URL"

	// schemeHTTP / schemeHTTPS are the only schemes accepted on
	// PUBLIC_URL. Peer workers and the main app need an http(s) origin
	// they can dial with Go's net/http stack.
	schemeHTTP  = "http"
	schemeHTTPS = "https"

	// loopbackHostnames lists hostnames treated as loopback for the
	// http-on-non-loopback warning emitted by ValidateHTTPConfig.
	loopbackHostnames = "localhost,127.0.0.1,::1,0.0.0.0"
)

// HTTPConfig holds the settings that govern the worker's local HTTP
// listener (web app MVP in Task 3 and Raft peer connections in Task 4).
// Host/Port are the bind interface. PublicURL is the publicly-advertised
// origin peers and the main app use to reach the worker; it is NOT
// derived from Host:Port because workers commonly sit behind a reverse
// proxy / Traefik with HTTPS while listening on plain HTTP internally.
//
// PublicURL is sourced from PUBLIC_URL (strict origin) or, for the
// bounded migration, from the deprecated WORKER_URL (legacy-tolerant
// absolute URL). URLSource records which variable supplied the value so
// validation and diagnostics name the correct source.
//
// Login/Password are basic auth credentials for the worker web app API
// (Task 3). They are kept in memory only; Task 3 may hash them before
// any persistent store.
type HTTPConfig struct {
	Host      string
	Port      int
	PublicURL string
	URLSource PublicURLSource
	Login     string
	Password  string
}

// PublicURLSource identifies which environment variable supplied the
// advertised public origin, so callers can log the legacy deprecation
// exactly once.
type PublicURLSource int

const (
	// PublicURLSourceNone means no advertised origin is configured.
	PublicURLSourceNone PublicURLSource = iota
	// PublicURLSourceCanonical means PUBLIC_URL was configured.
	PublicURLSourceCanonical
	// PublicURLSourceLegacy means only WORKER_URL was configured; the
	// value is accepted for the bounded migration.
	PublicURLSourceLegacy
)

// PublicURLFromEnv reads the advertised public origin. PUBLIC_URL is
// the canonical source; the deprecated WORKER_URL is used only when
// PUBLIC_URL is unset. The returned source lets the caller warn about
// the legacy fallback without re-reading the environment.
func PublicURLFromEnv() (string, PublicURLSource) {
	if v := strings.TrimSpace(os.Getenv(EnvPublicURL)); v != "" {
		return v, PublicURLSourceCanonical
	}
	if v := strings.TrimSpace(os.Getenv(EnvWorkerURLLegacy)); v != "" {
		return v, PublicURLSourceLegacy
	}
	return "", PublicURLSourceNone
}

// IsAuthConfigured reports whether both WORKER_LOGIN and WORKER_PASSWORD
// are set. The HTTP listener refuses to start otherwise.
func (c HTTPConfig) IsAuthConfigured() bool {
	return c.Login != "" && c.Password != ""
}

// IsListenConfigured reports whether the listener should bind at all.
// Currently always true while WORKER_PORT > 0; placeholder for Task 3
// to wire "skip listen" semantics.
func (c HTTPConfig) IsListenConfigured() bool {
	return c.Port > 0
}

// Config holds the local worker connection settings.
// Runtime settings are delivered by the control plane over websocket.
type Config struct {
	URL            string
	Token          string
	BootstrapToken string
	StateFile      string
	WorkerID       string

	// MaxConcurrency caps the worker pool size and the number of dispatcher
	// goroutines. A value <= 0 falls back to DefaultMaxConcurrency.
	// Runtime configuration delivered by the control plane via the websocket
	// "init" or "config" message is clamped to this value when resizing.
	MaxConcurrency int

	// HTTP holds the local web app / Raft listener settings (Task 2).
	HTTP HTTPConfig
}

// ConfigFromEnv creates a Config from environment variables.
func ConfigFromEnv() Config {
	return Config{
		URL:            normalizeURL(os.Getenv("RSMON_URL")),
		Token:          os.Getenv("RSMON_TOKEN"),
		BootstrapToken: os.Getenv("RSMON_BOOTSTRAP_TOKEN"),
		StateFile:      strings.TrimSpace(os.Getenv("RSMON_STATE_FILE")),
		WorkerID:       strings.TrimSpace(os.Getenv("RSMON_WORKER_ID")),
		HTTP:           HTTPConfigFromEnv(),
	}
}

// HTTPConfigFromEnv reads HTTP listener settings from the environment.
// Empty WORKER_HOST defaults to DefaultHTTPHost; empty WORKER_PORT defaults
// to DefaultHTTPPort. A malformed WORKER_PORT falls back to the default.
// The public origin is resolved from PUBLIC_URL (canonical) with the
// deprecated WORKER_URL as the migration fallback; it is parsed loosely
// here — ValidateHTTPConfig does the real check.
func HTTPConfigFromEnv() HTTPConfig {
	port := DefaultHTTPPort
	if raw := strings.TrimSpace(os.Getenv("WORKER_PORT")); raw != "" {
		if v, err := strconv.Atoi(raw); err == nil && v > 0 && v <= 65535 {
			port = v
		}
	}
	host := strings.TrimSpace(os.Getenv("WORKER_HOST"))
	if host == "" {
		host = DefaultHTTPHost
	}
	publicURL, source := PublicURLFromEnv()
	return HTTPConfig{
		Host:      host,
		Port:      port,
		PublicURL: publicURL,
		URLSource: source,
		Login:     os.Getenv("WORKER_LOGIN"),
		Password:  os.Getenv("WORKER_PASSWORD"),
	}
}

// ValidateHTTPConfig enforces the local HTTP-listener invariants:
//
//   - WORKER_LOGIN and WORKER_PASSWORD must be both set or both empty.
//     A mixed state (XOR) is a config bug and must fail fast so an
//     operator notices immediately. Both empty is allowed while the HTTP
//     listener is not started yet.
//   - When the listener would actually start (WORKER_PORT > 0), both
//     must be set; otherwise we are going to expose an unauthenticated
//     endpoint.
//   - A configured advertised origin must validate. The canonical
//     PUBLIC_URL is held to the strict origin rules of ValidatePublicURL
//     and, in an explicitly production environment
//     (DEPLOY_ENV/RSMON_ENV/GO_ENV = production), plain HTTP on a
//     non-loopback host is rejected. A legacy WORKER_URL (URLSource is
//     PublicURLSourceLegacy) is held only to the tolerant
//     ValidateAdvertisedURL so shapes that previously ran keep running;
//     it never fails production startup, preserving the historical
//     warn-only behavior.
func ValidateHTTPConfig(c HTTPConfig, willListen bool) error {
	loginSet := c.Login != ""
	passSet := c.Password != ""
	if loginSet != passSet {
		return fmt.Errorf(
			"WORKER_LOGIN and WORKER_PASSWORD must be both set or both empty (got login=%s password=%s)",
			boolStr(loginSet), boolStr(passSet))
	}
	if willListen && !c.IsAuthConfigured() {
		return fmt.Errorf("HTTP listener refused to start: WORKER_LOGIN and WORKER_PASSWORD must be set when WORKER_PORT > 0")
	}
	if c.PublicURL == "" {
		return nil
	}
	if c.URLSource == PublicURLSourceLegacy {
		if err := ValidateAdvertisedURL(c.PublicURL); err != nil {
			return fmt.Errorf("%s: %w", EnvWorkerURLLegacy, err)
		}
		return nil
	}
	if err := ValidatePublicURL(c.PublicURL); err != nil {
		return err
	}
	if productionEnv() {
		if host, warn := WarnInsecurePublicURL(c.PublicURL); warn {
			return fmt.Errorf(
				"%s uses plain HTTP on a non-loopback host (%s), which is not permitted in production; front %s with a TLS-terminating reverse proxy",
				EnvPublicURL, host, EnvPublicURL,
			)
		}
	}
	return nil
}

// ValidatePublicURL enforces the strict origin shape required by
// docs/public-endpoint-and-identity.md ("One Worker, One Public URL")
// for the canonical PUBLIC_URL configuration: an absolute http(s) URL
// with a scheme and authority and nothing else. Userinfo, query,
// fragment, any path other than "/", and a missing hostname (for example
// "https://:27401") are rejected because every route lives on the origin
// root and credentials must not leak into the advertised endpoint.
func ValidatePublicURL(raw string) error {
	u, err := parseURL(raw, EnvPublicURL)
	if err != nil {
		return err
	}
	if u.User != nil {
		return fmt.Errorf("%s must not contain userinfo (got %q)", EnvPublicURL, raw)
	}
	if u.RawQuery != "" {
		return fmt.Errorf("%s must not contain a query (got %q)", EnvPublicURL, raw)
	}
	if u.Fragment != "" {
		return fmt.Errorf("%s must not contain a fragment (got %q)", EnvPublicURL, raw)
	}
	if u.Path != "" && u.Path != "/" {
		return fmt.Errorf("%s must not contain a path (got %q)", EnvPublicURL, raw)
	}
	return nil
}

// ValidateAdvertisedURL enforces the tolerant absolute-URL shape used
// for the legacy WORKER_URL and for endpoints supplied by the control
// plane: an http(s) URL with a scheme, a host, and a non-empty hostname.
// Unlike ValidatePublicURL it does not reject a path, userinfo, query,
// or fragment, because legacy configurations and old control planes may
// carry such shapes and must not newly fail. It still rejects values
// that could never be dialed, such as "https://:27401".
func ValidateAdvertisedURL(raw string) error {
	_, err := parseURL(raw, EnvWorkerURLLegacy)
	return err
}

// parseURL parses an absolute http(s) advertised URL. Both validators
// share the scheme/host/hostname rules; label names the source in error
// messages so diagnostics point at the variable the operator set.
func parseURL(raw, label string) (*url.URL, error) {
	u, err := url.Parse(raw)
	if err != nil {
		return nil, fmt.Errorf("%s is not a valid URL: %v", label, err)
	}
	if u.Scheme == "" || u.Host == "" {
		return nil, fmt.Errorf("%s must be an absolute URL with scheme and host (got %q)", label, raw)
	}
	if u.Scheme != schemeHTTP && u.Scheme != schemeHTTPS {
		return nil, fmt.Errorf("%s scheme must be http or https (got %q)", label, u.Scheme)
	}
	if u.Hostname() == "" {
		return nil, fmt.Errorf("%s must include a host (got %q)", label, raw)
	}
	return u, nil
}

// productionEnv reports whether the worker is explicitly configured for
// production. Only an explicit literal enables the HTTPS-only PUBLIC_URL
// policy; an unset variable keeps the historical warn-on-plain-HTTP
// behavior so existing installations upgrade without surprise.
func productionEnv() bool {
	for _, key := range []string{"DEPLOY_ENV", "RSMON_ENV", "GO_ENV"} {
		switch strings.ToLower(strings.TrimSpace(os.Getenv(key))) {
		case "production", "prod":
			return true
		}
	}
	return false
}

// WarnInsecurePublicURL logs a warning when PUBLIC_URL uses plain http
// for a non-loopback host. Returns the host so the caller can log it.
// A no-op for the loopback case (typical local dev) and for https URLs.
func WarnInsecurePublicURL(rawURL string) (host string, shouldWarn bool) {
	if rawURL == "" {
		return "", false
	}
	u, err := url.Parse(rawURL)
	if err != nil {
		return "", false
	}
	if u.Scheme != schemeHTTP {
		return u.Host, false
	}
	if isLoopbackHost(u.Hostname()) {
		return u.Host, false
	}
	return u.Host, true
}

func isLoopbackHost(host string) bool {
	host = strings.ToLower(host)
	for _, h := range strings.Split(loopbackHostnames, ",") {
		if host == strings.TrimSpace(h) {
			return true
		}
	}
	return false
}

func boolStr(b bool) string {
	if b {
		return "set"
	}
	return "empty"
}

func normalizeURL(endpoint string) string {
	endpoint = strings.TrimRight(endpoint, "/")
	if strings.HasSuffix(endpoint, "/api/worker") {
		return strings.TrimSuffix(endpoint, "/api/worker")
	}
	if strings.HasSuffix(endpoint, "/worker") {
		return strings.TrimSuffix(endpoint, "/worker")
	}
	return endpoint
}