package tortoise

import (
	"bytes"
	"context"
	"errors"
	"os/exec"
	"sync"
	"time"
)

const (
	MAX_RESULTS = 100
)

// CommandResult holds the result of a shell command execution.
type CommandResult struct {
	Command    string
	ReturnCode int
	Output     string
	ErrOutput  string
}

// ShellRunner manages shell command execution.
type ShellRunner struct {
	cmdQueue   chan func() *CommandResult
	results    chan *CommandResult
	stopChan   chan struct{}
	running    sync.WaitGroup
	callbacks  chan func()
	shell      string // Private field to store the shell
	mu         sync.Mutex
	isStopped  bool
	activeCmds map[*exec.Cmd]struct{} // Track active commands for cancellation
	timeout    time.Duration
}

// NewShellRunner creates a new ShellRunner instance with the default shell (`sh`).
func NewShellRunner() *ShellRunner {
	return NewShellRunnerWithShell("sh")
}

// NewShellRunnerWithShell creates a new ShellRunner with the specified shell.
func NewShellRunnerWithShell(shell string) *ShellRunner {
	return &ShellRunner{
		cmdQueue:   make(chan func() *CommandResult),
		results:    make(chan *CommandResult, MAX_RESULTS),
		stopChan:   make(chan struct{}),
		callbacks:  make(chan func()),
		shell:      shell,
		activeCmds: make(map[*exec.Cmd]struct{}),
		isStopped:  true,
		timeout:    0,
	}
}

func (sr *ShellRunner) SetTimeout(timeout time.Duration) {
	sr.timeout = timeout
}

// Start begins processing shell commands asynchronously.
func (sr *ShellRunner) Start() {
	go func() {
		for {
			select {
			case <-sr.stopChan:
				return
			case cmdFunc, ok := <-sr.cmdQueue:
				if !ok {
					return
				}

				sr.running.Add(1)

				go func() {
					result := cmdFunc()
					sr.results <- result
					sr.running.Done()
				}()
			case callback := <-sr.callbacks:
				callback()
			}
		}
	}()

	sr.isStopped = false
}

// AddCommand adds a shell command to be executed with an optional callback.
// No commands can be added if the runner has been stopped or not yet started.
// The callback is executed asynchronously after the command has completed.
// The order of command execution and callback invocation can be expected to be preserved.
func (sr *ShellRunner) AddCommand(command string, callback func(*CommandResult)) error {
	cmd, cancel := sr.newShellCommand(command)
	return sr.AddCmd(cmd, callback, cancel)
}

func (sr *ShellRunner) AddCmd(cmd *exec.Cmd, callback func(*CommandResult), cancel context.CancelFunc) error {
	sr.mu.Lock()
	defer sr.mu.Unlock()

	if sr.isStopped {
		return errors.New("runner is stopped, cannot add new commands")
	}

	sr.cmdQueue <- func() *CommandResult {
		result := sr.executeCommand(cmd, cancel)
		if callback != nil {
			sr.running.Add(1)
			sr.callbacks <- func() {
				callback(result)
				sr.running.Done()
			}
		}
		return result
	}

	return nil
}

// GetResults retrieves the next available command result (non-blocking).
func (sr *ShellRunner) GetResults() *CommandResult {
	select {
	case result := <-sr.results:
		return result
	default:
		return nil
	}
}

// Stop gracefully stops the ShellRunner, closing the command queue and waiting for all commands to finish.
func (sr *ShellRunner) Stop() {
	sr.mu.Lock()
	if sr.isStopped {
		sr.mu.Unlock()
		return
	}

	sr.isStopped = true

	close(sr.cmdQueue) // No more commands can be added
	close(sr.stopChan)
	sr.mu.Unlock()

	sr.running.Wait()
}

// Kill stops the ShellRunner immediately, terminating all running commands.
func (sr *ShellRunner) Kill() {
	sr.mu.Lock()

	// Terminate all active commands
	for cmd := range sr.activeCmds {
		_ = cmd.Process.Kill()
	}
	sr.mu.Unlock()

	sr.Stop()
}

// KillWithTimeout attempts to stop the ShellRunner, killing commands if the duration is exceeded.
func (sr *ShellRunner) KillWithTimeout(timeout time.Duration) error {
	done := make(chan struct{})
	go func() {
		sr.Stop()
		close(done)
	}()

	select {
	case <-done:
		return nil
	case <-time.After(timeout):
		sr.Kill()
		return errors.New("commands killed due to timeout")
	}
}

func (sr *ShellRunner) newShellCommand(command string) (*exec.Cmd, context.CancelFunc) {
	var ctx context.Context

	var cancel context.CancelFunc

	if sr.timeout > 0 {
		ctx, cancel = context.WithTimeout(context.Background(), sr.timeout)
	} else {
		ctx = context.Background()
	}

	return exec.CommandContext(ctx, sr.shell, "-c", command), cancel
}

// executeCommand runs a shell command asynchronously, capturing stdout, stderr, and return code.
func (sr *ShellRunner) executeCommand(cmd *exec.Cmd, cancel context.CancelFunc) *CommandResult {
	if cancel != nil {
		defer cancel()
	}

	var outBuf, errBuf bytes.Buffer

	cmd.Stdout = &outBuf
	cmd.Stderr = &errBuf

	// Track the active command
	sr.mu.Lock()
	sr.activeCmds[cmd] = struct{}{}
	sr.mu.Unlock()

	err := cmd.Start()
	if err != nil {
		return &CommandResult{
			Command:    cmd.String(),
			ReturnCode: -1,
			ErrOutput:  err.Error(),
		}
	}

	err = cmd.Wait()

	// Remove from active commands
	sr.mu.Lock()
	delete(sr.activeCmds, cmd)
	sr.mu.Unlock()

	result := &CommandResult{
		Command:   cmd.String(),
		Output:    outBuf.String(),
		ErrOutput: errBuf.String(),
	}

	if err != nil {
		var exitErr *exec.ExitError
		if errors.As(err, &exitErr) {
			result.ReturnCode = exitErr.ExitCode()
		} else {
			result.ReturnCode = -1
		}
	} else {
		result.ReturnCode = 0
	}

	return result
}