package backend

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

const browserStartReadyTimeout = 10 * time.Second
const browserStartStableWindow = 1200 * time.Millisecond

var errBrowserDebugPortPending = errors.New("browser debug port pending")

func waitBrowserDebugPortReady(initialDebugPort int, userDataDir string, timeout time.Duration, monitor *browserProcessMonitor) (int, error) {
	deadline := time.Now().Add(timeout)
	allowDetachedGrace := initialDebugPort > 0
	var lastErr error
	var exitResult browserProcessExitResult
	exitObserved := false

	for time.Now().Before(deadline) {
		debugPort, resolveErr := resolveBrowserDebugPort(initialDebugPort, userDataDir, monitor)
		if resolveErr == nil {
			if err := probeBrowserDebugPort(debugPort, browserDebugProbeTimeout); err == nil {
				return debugPort, nil
			} else {
				lastErr = err
			}
		} else if !errors.Is(resolveErr, errBrowserDebugPortPending) {
			lastErr = resolveErr
		}
		if monitor != nil && monitor.HasExited() {
			if !exitObserved {
				exitResult = monitor.Result()
				exitObserved = true
				if !allowDetachedGrace {
					return 0, newBrowserStartupExitError(exitResult)
				}
				exitDeadline := time.Now().Add(browserLauncherDetachGraceWindow)
				if exitDeadline.After(deadline) {
					deadline = exitDeadline
				}
			}
		}
		time.Sleep(150 * time.Millisecond)
	}
	if !exitObserved && monitor != nil && monitor.HasExited() {
		exitResult = monitor.Result()
		exitObserved = true
		if !allowDetachedGrace {
			return 0, newBrowserStartupExitError(exitResult)
		}
		postExitDeadline := time.Now().Add(browserLauncherDetachGraceWindow)
		for time.Now().Before(postExitDeadline) {
			if debugPort, resolveErr := resolveBrowserDebugPort(initialDebugPort, userDataDir, monitor); resolveErr == nil {
				if err := probeBrowserDebugPort(debugPort, browserDebugProbeTimeout); err == nil {
					return debugPort, nil
				}
			}
			time.Sleep(150 * time.Millisecond)
		}
	}
	if exitObserved {
		if debugPort, resolveErr := resolveBrowserDebugPort(initialDebugPort, userDataDir, monitor); resolveErr == nil {
			if err := probeBrowserDebugPort(debugPort, browserDebugProbeTimeout); err == nil {
				return debugPort, nil
			}
		}
		return 0, newBrowserStartupExitError(exitResult)
	}
	if lastErr != nil {
		if debugPort, resolveErr := resolveBrowserDebugPort(initialDebugPort, userDataDir, monitor); resolveErr == nil {
			return 0, fmt.Errorf("浏览器进程未在 %s 内完成启动，调试端口 %d 未就绪：%w", timeout.Round(time.Second), debugPort, lastErr)
		}
		return 0, fmt.Errorf("浏览器进程未在 %s 内完成启动，尚未获取调试端口：%w", timeout.Round(time.Second), lastErr)
	}

	if debugPort, resolveErr := resolveBrowserDebugPort(initialDebugPort, userDataDir, monitor); resolveErr == nil {
		return 0, fmt.Errorf("浏览器进程未在 %s 内完成启动，调试端口 %d 未就绪", timeout.Round(time.Second), debugPort)
	}

	return 0, fmt.Errorf("浏览器进程未在 %s 内完成启动，尚未获取调试端口", timeout.Round(time.Second))
}

func waitBrowserDebugPortStable(initialDebugPort int, userDataDir string, timeout time.Duration, stableFor time.Duration, monitor *browserProcessMonitor) (int, error) {
	debugPort, err := waitBrowserDebugPortReady(initialDebugPort, userDataDir, timeout, monitor)
	if err != nil {
		return 0, err
	}
	if stableFor <= 0 {
		return debugPort, nil
	}
	allowDetachedGrace := initialDebugPort > 0

	deadline := time.Now().Add(stableFor)
	for time.Now().Before(deadline) {
		if monitor != nil && monitor.HasExited() {
			if !allowDetachedGrace {
				return 0, newBrowserStartupExitError(monitor.Result())
			}
		}
		if err := probeBrowserDebugPort(debugPort, browserDebugProbeTimeout); err != nil {
			if monitor != nil && monitor.HasExited() {
				if !allowDetachedGrace {
					return 0, newBrowserStartupExitError(monitor.Result())
				}
			}
			return 0, fmt.Errorf("浏览器调试端口 %d 短暂就绪后又失效：%w", debugPort, err)
		}
		time.Sleep(150 * time.Millisecond)
	}
	return debugPort, nil
}

func resolveBrowserDebugPort(initialDebugPort int, userDataDir string, monitor *browserProcessMonitor) (int, error) {
	if initialDebugPort > 0 {
		return initialDebugPort, nil
	}
	if monitor != nil {
		if debugPort, ok := monitor.DebugPort(); ok {
			return debugPort, nil
		}
	}
	if debugPort, err := readBrowserDebugPortFile(userDataDir); err == nil {
		if monitor != nil {
			monitor.SetDebugPort(debugPort)
		}
		return debugPort, nil
	} else if !errors.Is(err, errBrowserDebugPortPending) {
		return 0, err
	}
	return 0, errBrowserDebugPortPending
}

func readBrowserDebugPortFile(userDataDir string) (int, error) {
	userDataDir = strings.TrimSpace(userDataDir)
	if userDataDir == "" {
		return 0, errBrowserDebugPortPending
	}

	data, err := os.ReadFile(filepath.Join(userDataDir, "DevToolsActivePort"))
	if err != nil {
		if os.IsNotExist(err) {
			return 0, errBrowserDebugPortPending
		}
		return 0, fmt.Errorf("读取 DevToolsActivePort 失败: %w", err)
	}

	lines := strings.Split(strings.TrimSpace(string(data)), "\n")
	if len(lines) == 0 || strings.TrimSpace(lines[0]) == "" {
		return 0, errBrowserDebugPortPending
	}

	port, err := strconv.Atoi(strings.TrimSpace(lines[0]))
	if err != nil || port <= 0 {
		return 0, fmt.Errorf("DevToolsActivePort 内容无效: %q", lines[0])
	}
	return port, nil
}