package shell

import (
	"fmt"
	"os"
	"os/exec"
	"runtime"
)

// DefaultShell returns the platform-appropriate interactive shell.
func DefaultShell() string {
	if runtime.GOOS == "windows" {
		if _, err := exec.LookPath("powershell.exe"); err == nil {
			return "powershell.exe"
		}
		return "cmd.exe"
	}
	shell := os.Getenv("SHELL")
	if shell != "" {
		return shell
	}
	return "bash"
}

// BuildEnvList merges ctask env vars into the current process environment.
func BuildEnvList(vars map[string]string) []string {
	env := os.Environ()
	for k, v := range vars {
		env = append(env, fmt.Sprintf("%s=%s", k, v))
	}
	return env
}

// PromptPrefix returns the shell prompt prefix for --shell mode.
func PromptPrefix(slug, mode string) string {
	return fmt.Sprintf("(ctask:%s|%s) ", slug, mode)
}

// BannerLines returns the launch banner lines for agent mode.
// Adds a "project dir:" line when launchDir is non-empty.
func BannerLines(mode, slug, wsPath, launchDir string) []string {
	lines := []string{
		fmt.Sprintf("[ctask] %s :: %s", mode, slug),
		fmt.Sprintf("[ctask] %s", wsPath),
	}
	if launchDir != "" {
		lines = append(lines, fmt.Sprintf("[ctask] project dir: %s/", launchDir))
	}
	return lines
}

// ContainerNotice returns the v0.1 deferred container mode message.
func ContainerNotice() string {
	return "[ctask] container mode is not available in v0.1. Use local mode or see docs for manual container setup."
}

// ExecAgent launches the agent command in the workspace directory.
func ExecAgent(agent string, wsDir string, envVars map[string]string) error {
	path, err := exec.LookPath(agent)
	if err != nil {
		return fmt.Errorf("agent command not found: %s", agent)
	}

	cmd := exec.Command(path)
	cmd.Dir = wsDir
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Env = BuildEnvList(envVars)

	return cmd.Run()
}

// ExecShell launches an interactive shell in the workspace directory.
func ExecShell(wsDir string, envVars map[string]string, slug, mode string) error {
	shellCmd := DefaultShell()
	prefix := PromptPrefix(slug, mode)

	var cmd *exec.Cmd
	if runtime.GOOS == "windows" {
		if shellCmd == "powershell.exe" {
			cmd = exec.Command(shellCmd, "-NoExit", "-Command",
				fmt.Sprintf("function prompt { '%s' + (Get-Location).Path + '> ' }", prefix))
		} else {
			// cmd.exe
			cmd = exec.Command(shellCmd)
		}
	} else {
		cmd = exec.Command(shellCmd)
	}

	cmd.Dir = wsDir
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	env := BuildEnvList(envVars)

	if runtime.GOOS == "windows" && shellCmd == "cmd.exe" {
		env = append(env, fmt.Sprintf("PROMPT=%s$P$G", prefix))
	} else if runtime.GOOS != "windows" {
		existingPS1 := os.Getenv("PS1")
		if existingPS1 == "" {
			existingPS1 = "\\u@\\h:\\w\\$ "
		}
		env = append(env, fmt.Sprintf("PS1=%s%s", prefix, existingPS1))
	}

	cmd.Env = env
	return cmd.Run()
}