// Package config loads the daemon's runtime configuration. The HTTP daemon is
// a loopback-only sidecar: it binds 127.0.0.1, takes no public traffic, and
// reads everything it needs from the environment with sane defaults so it can
// boot with zero configuration in development.
package config

import (
	"fmt"
	"net"
	"os"
	"path/filepath"
	"strconv"
	"time"
)

const (
	// LoopbackHost is the only host the daemon ever binds. There is deliberately
	// no AO_HOST env var: the daemon has no auth/CORS/TLS and a stray
	// AO_HOST=0.0.0.0 would turn it into a public no-auth service. If a
	// non-default loopback (e.g. ::1, 127.0.0.2) is ever needed, add it back with
	// an IsLoopback() validator — not a raw env read.
	LoopbackHost = "127.0.0.1"
	// DefaultPort is the single port for REST, terminal mux, health, and control.
	DefaultPort = 3001
	// DefaultRequestTimeout bounds a single REST request. Long-lived terminal mux
	// connections are mounted outside this timeout.
	DefaultRequestTimeout = 60 * time.Second
	// DefaultShutdownTimeout is the hard cap on graceful shutdown. After this
	// the process exits even if connections are still draining.
	DefaultShutdownTimeout = 10 * time.Second
	// DefaultAgent is the agent adapter id the daemon wires when AO_AGENT is
	// unset. It matches the claude-code adapter's manifest id.
	DefaultAgent = "claude-code"
)

// Config is the fully-resolved daemon configuration. It is immutable once
// built by Load.
type Config struct {
	// Host is the bind address. Always loopback — see LoopbackHost.
	Host string
	// Port is the TCP port to bind. The daemon fails fast if it is taken.
	Port int
	// RequestTimeout bounds REST request handling.
	RequestTimeout time.Duration
	// ShutdownTimeout is the hard graceful-shutdown deadline.
	ShutdownTimeout time.Duration
	// RunFilePath is where the PID + port handshake file (running.json) is
	// written so the Electron supervisor can discover and reap the daemon.
	RunFilePath string
	// DataDir is the directory holding durable SQLite state: DB and WAL files.
	// It is created on first use by the storage layer.
	DataDir string
	// Agent is the id of the agent adapter the daemon wires into the Session
	// Manager (see DefaultAgent). Selected by AO_AGENT; startSession fails fast
	// if no adapter with this id is registered.
	Agent string
}

// Addr returns the host:port the HTTP server binds. It uses net.JoinHostPort so
// the result is correct for IPv6 literals as well as IPv4 / hostnames.
func (c Config) Addr() string {
	return net.JoinHostPort(c.Host, strconv.Itoa(c.Port))
}

// Load resolves configuration from the environment, applying defaults. It
// returns an error only for values that are present but malformed (e.g. a
// non-numeric AO_PORT); missing values fall back to defaults.
//
// Recognised variables:
//
//	AO_PORT              bind port           (default 3001)
//	AO_REQUEST_TIMEOUT   per-request timeout (Go duration > 0, default 60s)
//	AO_SHUTDOWN_TIMEOUT  shutdown deadline   (Go duration > 0, default 10s)
//	AO_RUN_FILE          running.json path   (default <state-dir>/running.json)
//	AO_DATA_DIR          durable state dir   (default <state-dir>/data)
//	AO_AGENT             agent adapter id    (default claude-code)
//
// The bind host is not configurable: the daemon is loopback-only by design.
func Load() (Config, error) {
	cfg := Config{
		Host:            LoopbackHost,
		Port:            DefaultPort,
		RequestTimeout:  DefaultRequestTimeout,
		ShutdownTimeout: DefaultShutdownTimeout,
		Agent:           DefaultAgent,
	}

	if raw := os.Getenv("AO_PORT"); raw != "" {
		port, err := strconv.Atoi(raw)
		if err != nil {
			return Config{}, fmt.Errorf("invalid AO_PORT %q: %w", raw, err)
		}
		if port < 1 || port > 65535 {
			return Config{}, fmt.Errorf("invalid AO_PORT %d: out of range 1-65535", port)
		}
		cfg.Port = port
	}

	if raw := os.Getenv("AO_REQUEST_TIMEOUT"); raw != "" {
		d, err := parsePositiveDuration("AO_REQUEST_TIMEOUT", raw)
		if err != nil {
			return Config{}, err
		}
		cfg.RequestTimeout = d
	}

	if raw := os.Getenv("AO_SHUTDOWN_TIMEOUT"); raw != "" {
		d, err := parsePositiveDuration("AO_SHUTDOWN_TIMEOUT", raw)
		if err != nil {
			return Config{}, err
		}
		cfg.ShutdownTimeout = d
	}

	if raw := os.Getenv("AO_AGENT"); raw != "" {
		cfg.Agent = raw
	}

	runFile, err := resolveRunFilePath()
	if err != nil {
		return Config{}, err
	}
	cfg.RunFilePath = runFile

	dataDir, err := resolveDataDir()
	if err != nil {
		return Config{}, err
	}
	cfg.DataDir = dataDir

	return cfg, nil
}

// parsePositiveDuration rejects zero and negative durations: a zero
// RequestTimeout would expire every request instantly, and a non-positive
// ShutdownTimeout would defeat graceful shutdown.
func parsePositiveDuration(name, raw string) (time.Duration, error) {
	d, err := time.ParseDuration(raw)
	if err != nil {
		return 0, fmt.Errorf("invalid %s %q: %w", name, raw, err)
	}
	if d <= 0 {
		return 0, fmt.Errorf("invalid %s %q: must be > 0", name, raw)
	}
	return d, nil
}

// resolveRunFilePath picks where running.json lives. An explicit AO_RUN_FILE
// wins; otherwise it sits under the per-user config directory so multiple repos
// share one supervisor handshake location.
func resolveRunFilePath() (string, error) {
	if p, ok := os.LookupEnv("AO_RUN_FILE"); ok && p != "" {
		return p, nil
	}
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("resolve state dir: %w", err)
	}
	return filepath.Join(dir, "agent-orchestrator", "running.json"), nil
}

// resolveDataDir picks where durable state (the SQLite DB) lives. An explicit
// AO_DATA_DIR wins; otherwise it sits under the per-user config directory
// alongside running.json.
func resolveDataDir() (string, error) {
	if p, ok := os.LookupEnv("AO_DATA_DIR"); ok && p != "" {
		return p, nil
	}
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("resolve state dir: %w", err)
	}
	return filepath.Join(dir, "agent-orchestrator", "data"), nil
}