// Package config parses the command-line configuration of the ori server.
//
// It is deliberately tiny: three flags, validated once at startup, then passed
// around as an immutable value.
package config

import (
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// DefaultAgentCommand is the ACP agent spawned when --agent-cmd is not given.
// It is the Agent Client Protocol project's adapter for the Claude Agent SDK,
// which bundles a current Claude Code CLI (the older Zed adapter ships a CLI
// too old for current models).
const DefaultAgentCommand = "npx -y @agentclientprotocol/claude-agent-acp"

// Config holds the runtime configuration of the ori server.
type Config struct {
	// Addr is the TCP address the HTTP server listens on, e.g. ":8888".
	Addr string
	// Cwd is the absolute working directory handed to the agent session.
	Cwd string
	// AgentCommand is the command line used to spawn the ACP agent,
	// split on whitespace (the first field is the executable).
	AgentCommand []string
}

// FromArgs parses command-line arguments (without the program name) into a
// Config. It returns an error for unknown flags, an empty agent command, or a
// working directory that does not exist.
//
// Example:
//
//	cfg, err := config.FromArgs([]string{"--addr", ":9000", "--cwd", "/tmp"})
//	if err != nil {
//		log.Fatal(err)
//	}
//	fmt.Println(cfg.Addr) // ":9000"
func FromArgs(args []string) (Config, error) {
	fs := flag.NewFlagSet("ori", flag.ContinueOnError)
	addr := fs.String("addr", ":8888", "TCP address the HTTP server listens on")
	cwd := fs.String("cwd", "", "working directory for the agent session (default: current directory)")
	agentCmd := fs.String("agent-cmd", DefaultAgentCommand, "command spawning the ACP agent, split on whitespace")

	if err := fs.Parse(args); err != nil {
		return Config{}, err
	}

	command := strings.Fields(*agentCmd)
	if len(command) == 0 {
		return Config{}, fmt.Errorf("--agent-cmd must not be empty")
	}

	dir := *cwd
	if dir == "" {
		wd, err := os.Getwd()
		if err != nil {
			return Config{}, fmt.Errorf("resolve current directory: %w", err)
		}
		dir = wd
	}
	absDir, err := filepath.Abs(dir)
	if err != nil {
		return Config{}, fmt.Errorf("resolve --cwd: %w", err)
	}
	info, err := os.Stat(absDir)
	if err != nil {
		return Config{}, fmt.Errorf("--cwd: %w", err)
	}
	if !info.IsDir() {
		return Config{}, fmt.Errorf("--cwd: %s is not a directory", absDir)
	}

	return Config{Addr: *addr, Cwd: absDir, AgentCommand: command}, nil
}