// Package dispatcher watches project inbox directories and assigns tasks to
// idle tmux sessions. One task per session — batch dispatch is intentionally
// unsupported.
package dispatcher

import (
	"context"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
	"gopkg.in/yaml.v3"

	"forge.secuaas.ovh/olivier/claude-failover/internal/config"
	"forge.secuaas.ovh/olivier/claude-failover/internal/state"
	"forge.secuaas.ovh/olivier/claude-failover/internal/tmux"
)

// TaskFrontmatter is the YAML header parsed from task .md files.
type TaskFrontmatter struct {
	Title       string   `yaml:"title"`
	Priority    string   `yaml:"priority"` // critical, high, default, low
	Tags        []string `yaml:"tags"`
	NeedsClaude bool     `yaml:"needs_claude_code"`
	// Phase 2/G2: cross-project dependencies. Each entry is
	// "project:task_id" (e.g. "filesecure:FIX-0123"). The dispatcher
	// refuses to launch a task whose deps aren't all in the target
	// project's done/, and drops a `<task>.md.blocked` marker so the
	// watchdog can resolve it later (Phase 2/G1).
	DependsOn []string `yaml:"depends_on"`
}

// Dispatcher watches project inbox directories and assigns tasks to idle sessions.
type Dispatcher struct {
	tmux        tmux.Client
	state       *state.State
	config      *config.Config
	doneChan    <-chan string
	projectsDir string
	logger      *log.Logger
}

// New creates a Dispatcher.
// doneChan receives session names when they become idle (from SessionWatcher).
func New(tc tmux.Client, s *state.State, cfg *config.Config, doneChan <-chan string) *Dispatcher {
	projectsDir := cfg.Dispatcher.ProjectsDir
	if projectsDir == "" {
		projectsDir = cfg.Pool.SharedProjectsDir
	}
	return &Dispatcher{
		tmux:        tc,
		state:       s,
		config:      cfg,
		doneChan:    doneChan,
		projectsDir: projectsDir,
		logger:      log.Default(),
	}
}

// Run starts the dispatcher event loop until ctx is cancelled.
func (d *Dispatcher) Run(ctx context.Context) {
	ticker := time.NewTicker(60 * time.Second)
	defer ticker.Stop()

	fw, err := fsnotify.NewWatcher()
	if err != nil {
		d.logger.Printf("[dispatcher] fsnotify unavailable: %v — poll-only mode", err)
	} else {
		defer fw.Close()
		d.watchInboxDirs(fw)
	}

	var fwEvents <-chan fsnotify.Event
	if fw != nil {
		fwEvents = fw.Events
	}

	for {
		select {
		case <-ctx.Done():
			return
		case evt, ok := <-fwEvents:
			if !ok {
				return
			}
			if evt.Op&fsnotify.Create != 0 &&
				strings.HasSuffix(evt.Name, ".md") &&
				!strings.HasSuffix(evt.Name, ".dispatched") {
				d.dispatchProject(filepath.Dir(evt.Name))
			}
		case session := <-d.doneChan:
			d.assignNextTask(session)
		case <-ticker.C:
			d.fullScan()
		}
	}
}

// watchInboxDirs registers all known project inbox dirs with the fsnotify watcher.
func (d *Dispatcher) watchInboxDirs(fw *fsnotify.Watcher) {
	for _, ds := range d.config.Pool.Dedicated {
		inbox := filepath.Join(ds.Project, ".agent-queue", "inbox")
		if err := fw.Add(inbox); err != nil {
			d.logger.Printf("[dispatcher] watch %s: %v", inbox, err)
		}
	}
}

// fullScan dispatches pending tasks in all project inboxes.
func (d *Dispatcher) fullScan() {
	for _, ds := range d.config.Pool.Dedicated {
		inbox := filepath.Join(ds.Project, ".agent-queue", "inbox")
		d.dispatchProject(inbox)
	}
}

// dispatchProject assigns undispatched tasks in inboxDir to idle sessions.
func (d *Dispatcher) dispatchProject(inboxDir string) {
	entries, err := os.ReadDir(inboxDir)
	if err != nil {
		return
	}
	projectDir := filepath.Dir(filepath.Dir(inboxDir)) // inboxDir/.agent-queue/inbox → project
	for _, e := range entries {
		name := e.Name()
		// Skip non-md files, .dispatched markers, .blocked markers, and any
		// other sidecar (.stuck, .tmp, etc).
		if !strings.HasSuffix(name, ".md") {
			continue
		}
		taskPath := filepath.Join(inboxDir, name)

		// Phase 2/G2: enforce depends_on before claiming a session. The
		// session pool is a precious resource — we don't want to burn an
		// idle slot on a task that can't proceed.
		if d.taskBlocked(taskPath) {
			d.touchBlockedMarker(taskPath)
			continue
		}

		session := d.findFreeSession()
		if session == "" {
			d.logger.Printf("[dispatcher] no free session for task in %s", inboxDir)
			return
		}
		if err := d.launchAgent(session, projectDir, taskPath); err != nil {
			d.logger.Printf("[dispatcher] launchAgent error: %v", err)
			continue
		}
		if err := os.Rename(taskPath, taskPath+".dispatched"); err != nil {
			d.logger.Printf("[dispatcher] rename .dispatched: %v", err)
		}
	}
}

// taskBlocked returns true when taskPath declares `depends_on` entries that
// are not yet present in the target project's `.agent-queue/done/`. The
// frontmatter is parsed best-effort; on parse failure we treat the task as
// non-blocked (current behaviour preserved — bad frontmatter is the
// agent's problem, not the dispatcher's).
func (d *Dispatcher) taskBlocked(taskPath string) bool {
	content, err := os.ReadFile(taskPath)
	if err != nil {
		return false
	}
	fm, _ := parseFrontmatter(content)
	if len(fm.DependsOn) == 0 {
		return false
	}
	for _, dep := range fm.DependsOn {
		if !d.dependencyResolved(dep) {
			d.logger.Printf("[dispatcher] task %s blocked by unresolved dep %q",
				filepath.Base(taskPath), dep)
			return true
		}
	}
	return false
}

// dependencyResolved checks whether `project:task_id` is in
// `<projectsDir>/<project>/.agent-queue/done/<task_id>.md`. Accepts an
// exact match or a `<task_id>*.md` prefix match (some queues append a
// timestamp). Path segments are validated (no `..`, no `/` inside the
// segment) — see isSafeSegment.
func (d *Dispatcher) dependencyResolved(dep string) bool {
	parts := strings.SplitN(dep, ":", 2)
	if len(parts) != 2 {
		d.logger.Printf("[dispatcher] malformed depends_on %q (expected 'project:task_id')", dep)
		return false
	}
	project, taskID := parts[0], parts[1]
	if !isSafeSegment(project) || !isSafeSegment(taskID) {
		d.logger.Printf("[dispatcher] unsafe depends_on segment %q — refusing to look up", dep)
		return false
	}
	doneDir := filepath.Join(d.projectsDir, project, ".agent-queue", "done")
	exact := filepath.Join(doneDir, taskID+".md")
	if _, err := os.Stat(exact); err == nil {
		return true
	}
	entries, err := os.ReadDir(doneDir)
	if err != nil {
		return false
	}
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		if strings.HasPrefix(name, taskID) && strings.HasSuffix(name, ".md") &&
			!strings.HasSuffix(name, ".dispatched") {
			return true
		}
	}
	return false
}

// touchBlockedMarker creates `<taskPath>.blocked` (or refreshes its mtime)
// so the watchdog (Phase 2/G1) sees the task as blocked and tracks its
// timeout. We use mtime as the "blocked since" timestamp; we do NOT
// refresh it on subsequent ticks — the operator wants the timeout to be
// counted from the FIRST detection, not the last.
func (d *Dispatcher) touchBlockedMarker(taskPath string) {
	marker := taskPath + ".blocked"
	if _, err := os.Stat(marker); err == nil {
		return // marker already exists, leave mtime alone
	}
	if err := os.WriteFile(marker, []byte(""), 0o644); err != nil {
		d.logger.Printf("[dispatcher] write .blocked marker for %s: %v",
			filepath.Base(taskPath), err)
		return
	}
	d.logger.Printf("[dispatcher] task %s marked .blocked (waiting on depends_on)",
		filepath.Base(taskPath))
}

// isSafeSegment guards the project / task_id pair against path traversal.
// Same rule as the watchdog (`[A-Za-z0-9._-]+`, no `.` / `..`).
func isSafeSegment(s string) bool {
	if s == "" || s == "." || s == ".." {
		return false
	}
	for _, r := range s {
		switch {
		case r >= 'a' && r <= 'z',
			r >= 'A' && r <= 'Z',
			r >= '0' && r <= '9',
			r == '_', r == '-', r == '.':
		default:
			return false
		}
	}
	return true
}

// findFreeSession returns the name of an idle, live, cooldown-free session
// from the autonomous pool. Dedicated sessions are intentionally NOT
// considered: those host the operator's manual interactive work. Routing a
// background dispatch into them would (a) hijack a Claude instance the
// operator is using and (b) trigger the watcher's /exit recycle at task
// end, kicking the operator out mid-conversation.
func (d *Dispatcher) findFreeSession() string {
	prefix := d.config.Pool.Autonomous.Prefix
	if prefix == "" {
		prefix = "ccl-auto-"
	}
	start := d.config.Pool.Autonomous.StartIndex
	for i := start; i < start+d.config.Pool.Autonomous.Max; i++ {
		if d.isSessionFree(sessionName(prefix, i)) {
			return sessionName(prefix, i)
		}
	}
	return ""
}

// isSessionFree returns true when the session is idle, alive, and past its cooldown.
func (d *Dispatcher) isSessionFree(name string) bool {
	if !d.tmux.HasSession(name) {
		return false
	}
	sess := d.state.GetSession(name)
	if sess == nil || sess.State != "idle" {
		return false
	}
	if sess.LastFail != nil && time.Since(*sess.LastFail) < 5*time.Minute {
		return false
	}
	return true
}

// assignNextTask scans all inboxes for work to give to a freshly-idled session.
func (d *Dispatcher) assignNextTask(session string) {
	for _, ds := range d.config.Pool.Dedicated {
		inbox := filepath.Join(ds.Project, ".agent-queue", "inbox")
		entries, err := os.ReadDir(inbox)
		if err != nil {
			continue
		}
		for _, e := range entries {
			name := e.Name()
			if !strings.HasSuffix(name, ".md") {
				continue
			}
			taskPath := filepath.Join(inbox, name)
			// Phase 2/G2: respect depends_on here too, otherwise a
			// session freed mid-cycle would still bypass the gate.
			if d.taskBlocked(taskPath) {
				d.touchBlockedMarker(taskPath)
				continue
			}
			if err := d.launchAgent(session, ds.Project, taskPath); err == nil {
				os.Rename(taskPath, taskPath+".dispatched")
				return
			}
		}
	}
}

// launchAgent starts Claude Code in session for the given task file.
func (d *Dispatcher) launchAgent(session, projectDir, taskFile string) error {
	content, err := os.ReadFile(taskFile)
	if err != nil {
		return fmt.Errorf("read task %s: %w", taskFile, err)
	}
	fm, body := parseFrontmatter(content)
	model := modelForPriority(fm.Priority)

	// Change to project directory.
	if err := d.tmux.SendKeys(session, "cd "+projectDir); err != nil {
		return err
	}
	time.Sleep(300 * time.Millisecond)

	// Build and send the claude command, with optional --resume UUID.
	cmd := fmt.Sprintf("claude --model %s --dangerously-skip-permissions", model)
	resumeFile := filepath.Join(d.resumeDir(), session+"-resume-id.txt")
	if data, ferr := os.ReadFile(resumeFile); ferr == nil {
		if uuid := strings.TrimSpace(string(data)); uuid != "" {
			cmd += " --resume " + uuid
			os.Remove(resumeFile)
		}
	}
	if err := d.tmux.SendKeys(session, cmd); err != nil {
		return err
	}

	// Wait for the ❯ prompt before sending the task message.
	promptTimeout := d.config.Dispatcher.PromptTimeout.Duration
	if promptTimeout == 0 {
		promptTimeout = 30 * time.Second
	}
	if !d.waitForPrompt(session, promptTimeout) {
		return fmt.Errorf("claude not ready in %q after %v", session, promptTimeout)
	}

	// Send the task message. Multi-line task bodies render in Claude's TUI
	// as "[Pasted text #N +M lines]" — the trailing Enter that SendKeys
	// appends is consumed as part of the paste, so the message would stay
	// unsubmitted in the input buffer forever. Wait for the paste to
	// register, then send a lone Enter to actually submit.
	msg := buildTaskMessage(body, taskFile)
	if err := d.tmux.SendKeys(session, msg); err != nil {
		return err
	}
	time.Sleep(500 * time.Millisecond)
	if err := d.tmux.SendEnter(session); err != nil {
		return err
	}

	d.state.SetWorking(session, filepath.Base(taskFile))
	d.logger.Printf("[dispatcher] DISPATCHED session=%q task=%s model=%s",
		session, filepath.Base(taskFile), model)
	return nil
}

// waitForPrompt polls for the Claude ❯ prompt up to timeout.
func (d *Dispatcher) waitForPrompt(session string, timeout time.Duration) bool {
	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		tail, err := d.tmux.CapturePaneTail(session, 5)
		if err == nil && strings.Contains(tail, "❯") {
			return true
		}
		time.Sleep(1 * time.Second)
	}
	return false
}

// resumeDir returns the directory containing per-session resume UUIDs.
func (d *Dispatcher) resumeDir() string {
	home, _ := os.UserHomeDir()
	return filepath.Join(home, ".claude-context")
}

// parseFrontmatter splits YAML frontmatter (between --- markers) from the body.
// Returns an empty TaskFrontmatter and the full content if no header is found.
func parseFrontmatter(content []byte) (TaskFrontmatter, string) {
	s := string(content)
	if !strings.HasPrefix(s, "---\n") {
		return TaskFrontmatter{}, s
	}
	end := strings.Index(s[4:], "\n---\n")
	if end < 0 {
		return TaskFrontmatter{}, s
	}
	yamlBlock := s[4 : end+4]
	body := strings.TrimSpace(s[end+4+5:]) // skip "\n---\n"
	var fm TaskFrontmatter
	yaml.Unmarshal([]byte(yamlBlock), &fm) //nolint:errcheck // best-effort parse
	return fm, body
}

// modelForPriority maps a task priority to a Claude model name.
func modelForPriority(priority string) string {
	if strings.EqualFold(priority, "critical") {
		return "opus"
	}
	return "sonnet"
}

// buildTaskMessage constructs the dispatch message sent to Claude Code.
func buildTaskMessage(body, taskFile string) string {
	taskName := filepath.Base(taskFile)
	if body == "" {
		body = "Verifie .agent-queue/inbox/ — 1 tache assignee."
	}
	return fmt.Sprintf("[%s] %s\n\nIMPORTANT: Tu dois EXECUTER les actions demandées, pas seulement les décrire.",
		taskName, body)
}

func sessionName(prefix string, i int) string {
	return prefix + itoa(i)
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	b := make([]byte, 0, 10)
	for n > 0 {
		b = append([]byte{byte('0' + n%10)}, b...)
		n /= 10
	}
	return string(b)
}