package herdr

import (
	"context"
	"crypto/sha256"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strconv"
	"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
	// LaunchConfirmTimeout and LaunchConfirmPoll bound ConfirmInput. They are
	// tunable because how fast a terminal harness visibly reacts is a property
	// of the host, not of this code. Zero values mean 10s and 250ms.
	LaunchConfirmTimeout time.Duration
	LaunchConfirmPoll    time.Duration
	// Now is a test seam for the confirmation deadline.
	Now func() time.Time
}

func (b *TmuxBackend) now() time.Time {
	if b.Now != nil {
		return b.Now()
	}
	return time.Now()
}

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())
	// "no current target" is what a *running but empty* server answers: the
	// target does not resolve and there is no current session to fall back to.
	// It only started appearing once the runtime became its own unit running
	// `tmux -D`, which keeps the server alive past its last pane (F32). Before
	// that the server exited with its last session and answered "no server
	// running", so this branch was never reached. Without it Kill returns an
	// error for a pane that is already gone, quarantine never clears, and the
	// worker's only session slot stays pinned.
	if strings.Contains(message, "can't find session") || strings.Contains(message, "no server running") || strings.Contains(message, "no sessions") || strings.Contains(message, "no current target") || (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)

// LaunchTransport keeps the file-reference launch scoped to the harness whose
// paste handling requires it, rather than making it the universal prompt
// format. Every other harness keeps the inline path it was verified on.
func (b *TmuxBackend) LaunchTransport(harness string) LaunchTransport {
	if harness == "claude" {
		return LaunchFileRef
	}
	return LaunchInline
}

// promptLine matches a harness input line. A queued or already-accepted
// message renders with the same prefix, so a match alone proves nothing about
// what is still unsubmitted; see inputState.
var promptLine = regexp.MustCompile(`(?m)^[ \t]*[>❯][ \t]*(.*)$`)

// separatorRow matches the rule Claude Code draws above and below its editor.
var separatorRow = regexp.MustCompile(`^[\s─━┄┅┈┉-]+$`)

// InputState is what the interactive editor holds. Active distinguishes the
// live editor from queued or already-submitted input: both render with the
// same "❯" prefix, but only the live editor owns the pane cursor (F17,
// found live during burn-in run 3).
type InputState struct {
	Text   string
	Active bool
}

// sameInput compares editor content to what was submitted. Soft wrapping may
// break the text at any column and re-indent the continuation, so the
// comparison ignores whitespace entirely.
func sameInput(a, b string) bool {
	strip := func(s string) string { return strings.Join(strings.Fields(s), "") }
	return strip(a) == strip(b)
}

// inputState reads the editor that owns the cursor. Scanning every line
// beginning with "❯" cannot tell an unsubmitted prompt from one the
// harness already queued, which is why this asks tmux where the cursor is.
func (b *TmuxBackend) inputState(ctx context.Context, s Session) (InputState, error) {
	out, err := b.command(ctx, "display-message", "-p", "-t", tmuxTarget(s.PaneID), "#{cursor_y}")
	if err != nil {
		return InputState{}, err
	}
	row, err := strconv.Atoi(strings.TrimSpace(string(out)))
	if err != nil {
		return InputState{}, fmt.Errorf("tmux backend: cursor row %q: %w", strings.TrimSpace(string(out)), err)
	}
	// Screen rows, unjoined: -J merges wrapped rows and would invalidate the
	// cursor row index.
	raw, err := b.command(ctx, "capture-pane", "-p", "-t", tmuxTarget(s.PaneID))
	if err != nil {
		return InputState{}, err
	}
	rows := strings.Split(strings.TrimRight(string(raw), "\n"), "\n")
	if row < 0 || row >= len(rows) {
		return InputState{}, nil
	}
	start := -1
	for i := row; i >= 0; i-- {
		if promptLine.MatchString(rows[i]) {
			start = i
			break
		}
		if separatorRow.MatchString(rows[i]) {
			break
		}
	}
	if start < 0 {
		return InputState{}, nil
	}
	parts := []string{strings.TrimSpace(promptLine.FindStringSubmatch(rows[start])[1])}
	for i := start + 1; i <= row; i++ {
		parts = append(parts, strings.TrimSpace(rows[i]))
	}
	return InputState{Text: strings.TrimSpace(strings.Join(parts, " ")), Active: true}, nil
}

// PaneProgress hashes what the harness produced, not what someone typed at it.
// The capture joins wrapped lines, so an input block is one line beginning
// with the prompt marker and dropping those lines removes it whole. Found live
// during burn-in run 3: unexplained keystrokes in a pane kept a stalled lease
// renewing, because the renewal check hashed the whole capture.
func (b *TmuxBackend) PaneProgress(ctx context.Context, s Session) (string, error) {
	text, err := b.PaneCapture(ctx, s, "recent")
	if err != nil {
		return "", err
	}
	var kept []string
	for _, line := range strings.Split(text, "\n") {
		if promptLine.MatchString(line) {
			continue
		}
		kept = append(kept, line)
	}
	return strings.Join(kept, "\n"), nil
}

// launchResubmitLimit bounds the intervention independently of the observation
// deadline. A slow TUI must not receive a fortieth Enter after it accepted the
// first: three exact-editor resubmits, then observation only.
const launchResubmitLimit = 3

// launchSettle is how long an empty editor must stay empty before it counts as
// proof of submission. A TUI takes tens of milliseconds to render pasted text,
// and the first poll can run inside that gap. F33: a poll 7ms after the submit
// found nothing in the editor, reported confirmation=editor_cleared, and the
// launch text then sat unsent in the input box for the rest of the lease. The
// two launches that actually worked took ~500ms and a second Enter, so the
// difference between success and this false positive was scheduling luck.
//
// Only the never-observed case waits. Text seen and then gone is real
// evidence, and busy, blocked or queued still confirm immediately.
const launchSettle = time.Second

// ConfirmInput drives the submit to a decision instead of assuming one Enter
// landed. Burn-in run 3 proved the submit is not deterministic: the text
// reached the editor on all three attempts and the following Enter never took
// effect. So this resends Enter while the live editor still holds exactly what
// was submitted, up to launchResubmitLimit times, then observes until the
// deadline.
//
// The returned evidence records how many submits it took, which is the only
// way to tell a harness that needs a second Enter from one that needed none.
func (b *TmuxBackend) ConfirmInput(ctx context.Context, s Session, submitted string) (string, error) {
	timeout, poll := b.LaunchConfirmTimeout, b.LaunchConfirmPoll
	if timeout <= 0 {
		timeout = 10 * time.Second
	}
	if poll <= 0 {
		poll = 250 * time.Millisecond
	}
	first := b.now()
	deadline := first.Add(timeout)
	attempts, resubmits := 1, 0
	var lastResubmit time.Time
	evidence := func(kind string) string {
		return fmt.Sprintf("confirmation=%s submit_attempts=%d first_submit_at=%s confirmed_at=%s",
			kind, attempts, first.UTC().Format(time.RFC3339Nano), b.now().UTC().Format(time.RFC3339Nano))
	}
	var last InputState
	// Whether the editor was ever observed holding what we submitted. Without
	// it, "empty" is indistinguishable from "not rendered yet".
	seen := false
	for {
		state, err := b.inputState(ctx, s)
		if err != nil {
			return "", err
		}
		last = state
		if state.Active && sameInput(state.Text, submitted) {
			seen = true
		}
		switch {
		case state.Active && sameInput(state.Text, submitted):
			// Exactly what was submitted still owns the cursor, so the submit
			// did not take. Resend Enter, spaced so a TUI that accepted the
			// previous one cannot receive another inside its own redraw.
			if resubmits < launchResubmitLimit && (lastResubmit.IsZero() || b.now().Sub(lastResubmit) >= 2*poll) {
				if err := b.SendKeys(ctx, s, []string{"Enter"}); err != nil {
					return "", err
				}
				resubmits++
				attempts++
				lastResubmit = b.now()
			}
		case state.Active && queuedInput(state.Text):
			// The harness accepted the instruction and parked it behind the
			// current turn. Queued is submitted.
			return evidence("queued"), nil
		case state.Active && state.Text != "":
			// Something else is in the editor, a paste placeholder for
			// instance. Not proof of acceptance, so keep observing.
		default:
			status, statusErr := b.AgentStatus(ctx, s)
			if statusErr != nil {
				return "", statusErr
			}
			switch status {
			case "exited":
				return "", fmt.Errorf("%w: pane %s exited before the harness reacted", ErrPromptNotSubmitted, s.PaneID)
			case "busy":
				return evidence("busy"), nil
			case "blocked":
				// A permission dialog is the harness acting on the
				// instruction, so submission is proven even though the
				// session now needs an operator.
				return evidence("blocked"), nil
			default:
				// An editor that never held the text may simply not have
				// rendered it yet. Give it the settle window before calling an
				// empty box proof that the harness took the prompt.
				if !seen && b.now().Sub(first) < launchSettle {
					break
				}
				return evidence("editor_cleared"), nil
			}
		}
		if !b.now().Before(deadline) {
			return "", fmt.Errorf("%w: pane %s still holds %q after %s and %d submits", ErrPromptNotSubmitted, s.PaneID, last.Text, timeout, attempts)
		}
		select {
		case <-ctx.Done():
			return "", ctx.Err()
		case <-time.After(poll):
		}
	}
}

// queuedInput recognizes the editor Claude Code shows once it has taken a
// prompt and parked it behind the running turn.
func queuedInput(text string) bool {
	return strings.Contains(strings.ToLower(text), "queued message")
}