package service

import (
	"context"
	"encoding/base64"
	"fmt"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

const defaultCommandTimeout = 45 * time.Second

type SSHClient struct {
	remote      string
	askPassPath string
	password    string
	sshConfig   string
	timeout     time.Duration
}

func NewSSHClient(remote, password string) (*SSHClient, error) {
	if remote == "" {
		return nil, fmt.Errorf("remote host is required")
	}
	sshConfig := "/dev/null"
	if home, err := os.UserHomeDir(); err == nil {
		candidate := filepath.Join(home, ".ssh", "config")
		if info, statErr := os.Stat(candidate); statErr == nil && info.Mode().IsRegular() {
			sshConfig = candidate
		}
	}
	client := &SSHClient{remote: remote, password: password, sshConfig: sshConfig, timeout: defaultCommandTimeout}
	if password == "" {
		return client, nil
	}
	file, err := os.CreateTemp("", "gapmind-ssh-askpass-*")
	if err != nil {
		return nil, fmt.Errorf("create SSH password helper: %w", err)
	}
	client.askPassPath = file.Name()
	if _, err := file.WriteString("#!/bin/sh\nprintf '%s\\n' \"$GAPMIND_SSH_PASSWORD\"\n"); err != nil {
		_ = file.Close()
		client.Close()
		return nil, err
	}
	if err := file.Close(); err != nil {
		client.Close()
		return nil, err
	}
	if err := os.Chmod(client.askPassPath, 0700); err != nil {
		client.Close()
		return nil, err
	}
	return client, nil
}

func (c *SSHClient) Close() {
	if c.askPassPath != "" {
		_ = os.Remove(c.askPassPath)
	}
}

func (c *SSHClient) SetTimeout(timeout time.Duration) {
	if timeout > 0 {
		c.timeout = timeout
	}
}

func (c *SSHClient) Remote() string {
	return c.remote
}

func (c *SSHClient) command(ctx context.Context, name string, args ...string) *exec.Cmd {
	connectionOptions := []string{
		"-F", c.sshConfig,
		"-o", "ConnectTimeout=12",
		"-o", "ConnectionAttempts=1",
		"-o", "ServerAliveInterval=10",
		"-o", "ServerAliveCountMax=2",
		"-o", "NumberOfPasswordPrompts=1",
		"-o", "StrictHostKeyChecking=accept-new",
		"-o", "ClearAllForwardings=yes",
	}
	args = append(connectionOptions, args...)
	if c.password != "" {
		args = append([]string{"-o", "BatchMode=no", "-o", "PreferredAuthentications=password,keyboard-interactive", "-o", "PubkeyAuthentication=no"}, args...)
	}
	cmd := exec.CommandContext(ctx, name, args...)
	if c.password != "" {
		cmd.Env = append(os.Environ(), "SSH_ASKPASS="+c.askPassPath, "SSH_ASKPASS_REQUIRE=force", "DISPLAY=gapmind:0", "GAPMIND_SSH_PASSWORD="+c.password)
	}
	return cmd
}

func (c *SSHClient) Run(name string, args ...string) ([]byte, error) {
	ctx, cancel := context.WithTimeout(context.Background(), c.timeout)
	defer cancel()
	output, err := c.command(ctx, name, args...).CombinedOutput()
	if ctx.Err() == context.DeadlineExceeded {
		return output, fmt.Errorf("%s timed out after %s", name, c.timeout)
	}
	return output, err
}

func (u UserUnit) Render() string {
	lines := []string{"[Unit]", "Description=" + u.Description, "After=network-online.target", "", "[Service]", "Type=simple", "Restart=on-failure", "RestartSec=5"}
	keys := make([]string, 0, len(u.Environment))
	for key := range u.Environment {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		if value := u.Environment[key]; value != "" {
			lines = append(lines, "Environment="+key+"="+systemdQuote(value))
		}
	}
	lines = append(lines, "ExecStart="+u.ExecStart, "", "[Install]", "WantedBy=default.target", "")
	return strings.Join(lines, "\n")
}

func systemdQuote(value string) string {
	return `"` + strings.NewReplacer(`\`, `\\`, `"`, `\"`, "\n", "").Replace(value) + `"`
}

func CopyAndInstall(client *SSHClient, localBinary, remoteBinary, unitName string, unit UserUnit) error {
	if output, err := client.Run("ssh", client.remote, "mkdir", "-p", path.Dir(remoteBinary), ".config/systemd/user"); err != nil {
		return fmt.Errorf("create remote directories: %w: %s", err, output)
	}
	temporaryBinary := remoteBinary + ".upload"
	if output, err := client.Run("scp", localBinary, client.remote+":"+temporaryBinary); err != nil {
		return fmt.Errorf("copy binary: %w: %s", err, output)
	}
	encoded := base64.StdEncoding.EncodeToString([]byte(unit.Render()))
	remoteUnit := ".config/systemd/user/" + unitName
	command := fmt.Sprintf("set -eu; user=$(id -un); loginctl enable-linger $user >/dev/null 2>&1 || true; runtime=/run/user/$(id -u); export XDG_RUNTIME_DIR=$runtime DBUS_SESSION_BUS_ADDRESS=unix:path=$runtime/bus; for attempt in 1 2 3 4 5; do test -S $runtime/bus && break; sleep 1; done; test -S $runtime/bus || { echo 'systemd user bus is unavailable after enabling lingering' >&2; exit 1; }; test ! -d %q || { echo 'deployment target is a directory: %s' >&2; exit 1; }; chmod +x %q; mv -f %q %q; printf %%s %q | base64 -d > %q; systemctl --user daemon-reload; systemctl --user enable --now %q; systemctl --user --no-pager is-active %q", remoteBinary, remoteBinary, temporaryBinary, temporaryBinary, remoteBinary, encoded, remoteUnit, unitName, unitName)
	if output, err := client.Run("ssh", client.remote, "sh", "-lc", command); err != nil {
		return fmt.Errorf("install systemd unit: %w: %s", err, output)
	}
	return nil
}