package herdr

import (
	"context"
	"crypto/sha256"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

// TmuxBackend runs one Claude Code process per isolated tmux session. It is
// intentionally Claude-only for now: Codex and OpenCode keep using the
// verified herdr protocol until their terminal behavior has been exercised
// against a live installation.
type TmuxBackend struct {
	// Socket is a tmux socket name (-L) or an absolute socket path (-S).
	// An empty value uses the isolated socket name "orchestra".
	Socket string
	// Command is the Claude Code executable. An empty value resolves "claude"
	// through PATH.
	Command string
	// Binary is test/packaging override for tmux itself.
	Binary string
}

func NewTmuxBackend(socket, command string) *TmuxBackend {
	return &TmuxBackend{Socket: socket, Command: command}
}

func (b *TmuxBackend) Kind() string { return "tmux" }

func (b *TmuxBackend) binary() string {
	if b.Binary != "" {
		return b.Binary
	}
	return "tmux"
}

func (b *TmuxBackend) socketArgs() []string {
	socket := b.Socket
	if socket == "" {
		socket = "orchestra"
	}
	if filepath.IsAbs(socket) {
		return []string{"-S", socket}
	}
	return []string{"-L", socket}
}

func (b *TmuxBackend) command(ctx context.Context, args ...string) ([]byte, error) {
	all := append(b.socketArgs(), args...)
	out, err := exec.CommandContext(ctx, b.binary(), all...).CombinedOutput()
	if err != nil {
		return out, fmt.Errorf("tmux %s: %s: %w", strings.Join(args, " "), strings.TrimSpace(string(out)), err)
	}
	return out, nil
}

func (b *TmuxBackend) Check(ctx context.Context) error {
	if _, err := exec.LookPath(b.binary()); err != nil {
		return fmt.Errorf("tmux backend: %w", err)
	}
	// tmux -V does not require a server to exist. An idle backend is healthy
	// and will create its isolated server with the first session.
	if out, err := exec.CommandContext(ctx, b.binary(), "-V").CombinedOutput(); err != nil {
		return fmt.Errorf("tmux backend: %s: %w", strings.TrimSpace(string(out)), err)
	}
	command := b.Command
	if command == "" {
		command = "claude"
	}
	if _, err := exec.LookPath(command); err != nil {
		return fmt.Errorf("tmux backend Claude command: %w", err)
	}
	return nil
}

func (b *TmuxBackend) Worktree(_ context.Context, _ string, path, _ string) (string, error) {
	info, err := os.Stat(path)
	if err != nil {
		return "", fmt.Errorf("tmux backend worktree: %w", err)
	}
	if !info.IsDir() {
		return "", fmt.Errorf("tmux backend worktree %s is not a directory", path)
	}
	return path, nil
}

func tmuxSessionName(taskID string) string {
	id := strings.Trim(invalidAgentName.ReplaceAllString(strings.ToLower(taskID), "-"), "-_")
	if id == "" {
		id = "session"
	}
	if len(id) > 36 {
		id = strings.TrimRight(id[:36], "-_")
	}
	sum := sha256.Sum256([]byte(taskID))
	return fmt.Sprintf("orchestra-%s-%x", id, sum[:4])
}

func tmuxSession(paneID string) string {
	if before, _, ok := strings.Cut(paneID, ":"); ok {
		return before
	}
	return paneID
}

func tmuxTarget(paneID string) string { return "=" + paneID }

func (b *TmuxBackend) hasSession(ctx context.Context, session string) (bool, error) {
	out, err := b.command(ctx, "has-session", "-t", "="+session)
	if err == nil {
		return true, nil
	}
	message := strings.ToLower(string(out) + " " + err.Error())
	if strings.Contains(message, "can't find session") || strings.Contains(message, "no server running") || strings.Contains(message, "no sessions") || (strings.Contains(message, "error connecting to") && strings.Contains(message, "no such file")) {
		return false, nil
	}
	return false, err
}

func (b *TmuxBackend) StartAgent(ctx context.Context, _, path, _, harness, taskID string) (Session, error) {
	if !strings.EqualFold(harness, "claude") {
		return Session{}, fmt.Errorf("tmux backend: harness %q is unsupported; only claude is enabled", harness)
	}
	if _, err := b.Worktree(ctx, "", path, ""); err != nil {
		return Session{}, err
	}
	command := b.Command
	if command == "" {
		command = "claude"
	}
	resolved, err := exec.LookPath(command)
	if err != nil {
		return Session{}, fmt.Errorf("tmux backend Claude command: %w", err)
	}
	session := tmuxSessionName(taskID)
	existing, err := b.hasSession(ctx, session)
	if err != nil {
		return Session{}, err
	}
	if !existing {
		if _, err := b.command(ctx, "new-session", "-d", "-s", session, "-c", path, resolved); err != nil {
			return Session{}, err
		}
	}
	// The exact pane id is resolved below. Deployments may configure tmux
	// base-index/base-pane-index, so neither index is assumed to be zero.
	paneOut, err := b.command(ctx, "list-panes", "-t", "="+session, "-F", "#{session_name}:#{window_index}.#{pane_index}")
	if err != nil {
		return Session{}, err
	}
	paneID := strings.TrimSpace(strings.SplitN(string(paneOut), "\n", 2)[0])
	if paneID == "" {
		return Session{}, fmt.Errorf("tmux backend: session %s has no pane", session)
	}
	if existing {
		out, err := b.command(ctx, "display-message", "-p", "-t", tmuxTarget(paneID), "#{pane_current_path}")
		if err != nil {
			return Session{}, err
		}
		current, currentErr := filepath.Abs(strings.TrimSpace(string(out)))
		want, wantErr := filepath.Abs(path)
		if currentErr != nil || wantErr != nil || current != want {
			return Session{}, fmt.Errorf("tmux backend: existing session %s belongs to %q, not %q", session, current, want)
		}
	} else {
		if _, err := b.command(ctx, "set-window-option", "-t", tmuxTarget(paneID), "remain-on-exit", "on"); err != nil {
			return Session{}, err
		}
	}
	s := Session{PaneID: paneID, Worktree: path, Harness: "claude", AgentName: session}
	if err := b.confirmClaudeWorkspaceTrust(ctx, s); err != nil {
		return Session{}, err
	}
	status, err := b.AgentStatus(ctx, s)
	if err != nil {
		return Session{}, err
	}
	if status == "exited" || status == "dead" {
		return Session{}, fmt.Errorf("tmux backend: Claude exited while starting session %s", session)
	}
	return s, nil
}

func (b *TmuxBackend) confirmClaudeWorkspaceTrust(ctx context.Context, s Session) error {
	deadline := time.Now().Add(15 * time.Second)
	accepted := false
	for {
		text, err := b.PaneCapture(ctx, s, "recent")
		if err == nil && claudeWorkspaceTrustPrompt(text) {
			if !accepted {
				if err := b.SendText(ctx, s, "1"); err != nil {
					return fmt.Errorf("tmux backend: accept Claude workspace trust: %w", err)
				}
				if err := b.SendKeys(ctx, s, []string{"Enter"}); err != nil {
					return fmt.Errorf("tmux backend: accept Claude workspace trust: %w", err)
				}
				accepted = true
			}
		}
		// Claude's input prompt is the readiness boundary. A banner or partially
		// painted fullscreen UI is not enough: input sent there can be lost.
		if err == nil && !claudeWorkspaceTrustPrompt(text) && strings.Contains(text, "❯") {
			return nil
		}
		if time.Now().After(deadline) {
			return fmt.Errorf("tmux backend: Claude input prompt did not become ready in session %s", tmuxSession(s.PaneID))
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-time.After(100 * time.Millisecond):
		}
	}
}

func (b *TmuxBackend) Prompt(ctx context.Context, pane, text string, _ time.Duration) error {
	s := Session{PaneID: pane}
	status, err := b.AgentStatus(ctx, s)
	if err != nil {
		return err
	}
	if status == "blocked" {
		return fmt.Errorf("tmux backend: refusing prompt while pane %s shows a permission dialog", pane)
	}
	if err := b.SendText(ctx, s, text); err != nil {
		return err
	}
	return b.SendKeys(ctx, s, []string{"Enter"})
}

func (b *TmuxBackend) Kill(ctx context.Context, s Session) error {
	exists, err := b.hasSession(ctx, tmuxSession(s.PaneID))
	if err != nil {
		return err
	}
	if !exists {
		return nil
	}
	_, err = b.command(ctx, "kill-session", "-t", "="+tmuxSession(s.PaneID))
	return err
}

func (b *TmuxBackend) paneState(ctx context.Context, s Session) (dead bool, command string, err error) {
	out, err := b.command(ctx, "display-message", "-p", "-t", tmuxTarget(s.PaneID), "#{pane_dead}\t#{pane_current_command}")
	if err != nil {
		return false, "", err
	}
	parts := strings.SplitN(strings.TrimSpace(string(out)), "\t", 2)
	dead = len(parts) > 0 && parts[0] == "1"
	if len(parts) == 2 {
		command = parts[1]
	}
	return dead, command, nil
}

func (b *TmuxBackend) AgentStatus(ctx context.Context, s Session) (string, error) {
	exists, err := b.hasSession(ctx, tmuxSession(s.PaneID))
	if err != nil {
		return "", err
	}
	if !exists {
		return "exited", nil
	}
	dead, command, err := b.paneState(ctx, s)
	if err != nil {
		return "", err
	}
	if dead || command == "" {
		return "exited", nil
	}
	text, err := b.PaneCapture(ctx, s, "recent")
	if err != nil {
		return "", err
	}
	if permissionPrompt(text) {
		return "blocked", nil
	}
	lower := strings.ToLower(text)
	for _, marker := range []string{"esc to interrupt", "ctrl+c to interrupt", "press esc to interrupt"} {
		if strings.Contains(lower, marker) {
			return "busy", nil
		}
	}
	return "idle", nil
}

func (b *TmuxBackend) PaneCapture(ctx context.Context, s Session, source string) (string, error) {
	start := "-200"
	if source != "" && source != "recent" {
		start = "-1000"
	}
	out, err := b.command(ctx, "capture-pane", "-p", "-J", "-S", start, "-t", tmuxTarget(s.PaneID))
	return string(out), err
}

func (b *TmuxBackend) SendText(ctx context.Context, s Session, text string) error {
	_, err := b.command(ctx, "send-keys", "-t", tmuxTarget(s.PaneID), "-l", "--", text)
	return err
}

func (b *TmuxBackend) SendKeys(ctx context.Context, s Session, keys []string) error {
	if len(keys) == 0 {
		return nil
	}
	for _, key := range keys {
		if strings.TrimSpace(key) == "" {
			return errors.New("tmux backend: empty key name")
		}
	}
	args := []string{"send-keys", "-t", tmuxTarget(s.PaneID)}
	args = append(args, keys...)
	_, err := b.command(ctx, args...)
	return err
}

// tmux has no separate agent binding to release. Keeping the session alive is
// the tmux equivalent of herdr's split-then-close protocol; the worker kills
// it only after successor pickup has been validated.
func (b *TmuxBackend) ReleaseAgent(ctx context.Context, s Session, _ string) error {
	exists, err := b.hasSession(ctx, tmuxSession(s.PaneID))
	if err != nil {
		return err
	}
	if !exists {
		return fmt.Errorf("tmux backend: session %s is not running", tmuxSession(s.PaneID))
	}
	return nil
}

var _ Backend = (*TmuxBackend)(nil)