package app

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// debugCapture implements ChildEventListener and writes structured
// debug artefacts under a single directory:
//
//   - patterm.log    — the existing logf() stream
//   - events.jsonl   — one JSON object per lifecycle event
//   - <id>.raw       — raw PTY bytes for each child, by id+name
//
// The capture is installed only when --debug=<dir> is set, so default
// runs pay nothing.
type debugCapture struct {
	dir     string
	logPath string

	mu      sync.Mutex
	events  *os.File
	rawByID map[string]*os.File
}

func openDebugCapture(dir string) (*debugCapture, error) {
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil, err
	}
	logPath := filepath.Join(dir, "patterm.log")
	// Truncate-style fresh log per run is friendlier for grep'ing one
	// session. The existing logf opens O_APPEND though, so concurrent
	// runs against the same dir would interleave — that's on the user.
	if f, err := os.Create(logPath); err != nil {
		return nil, err
	} else {
		_ = f.Close()
	}
	ev, err := os.Create(filepath.Join(dir, "events.jsonl"))
	if err != nil {
		return nil, err
	}
	dc := &debugCapture{
		dir:     dir,
		logPath: logPath,
		events:  ev,
		rawByID: make(map[string]*os.File),
	}
	dc.writeEvent("session_start", map[string]any{
		"time": time.Now().Format(time.RFC3339Nano),
		"pid":  os.Getpid(),
	})
	return dc, nil
}

func (d *debugCapture) LogPath() string { return d.logPath }

func (d *debugCapture) Close() error {
	d.mu.Lock()
	defer d.mu.Unlock()
	d.writeEventLocked("session_end", map[string]any{
		"time": time.Now().Format(time.RFC3339Nano),
	})
	for _, f := range d.rawByID {
		_ = f.Close()
	}
	d.rawByID = nil
	if d.events != nil {
		_ = d.events.Close()
		d.events = nil
	}
	return nil
}

func (d *debugCapture) OnChildSpawned(c *Child) {
	d.writeEvent("child_spawned", map[string]any{
		"time":      time.Now().Format(time.RFC3339Nano),
		"id":        c.ID,
		"name":      c.Name,
		"kind":      string(c.Kind),
		"parent_id": c.ParentID,
		"preset":    c.PresetRef,
		"argv":      c.Argv,
	})
}

func (d *debugCapture) OnChildExited(c *Child) {
	d.writeEvent("child_exited", map[string]any{
		"time":      time.Now().Format(time.RFC3339Nano),
		"id":        c.ID,
		"name":      c.Name,
		"exit_code": c.ExitCode(),
	})
	d.mu.Lock()
	defer d.mu.Unlock()
	if f, ok := d.rawByID[c.ID]; ok {
		_ = f.Close()
		delete(d.rawByID, c.ID)
	}
}

func (d *debugCapture) OnChildStateChanged(id string, state IdleState) {
	d.writeEvent("child_state", map[string]any{
		"time":  time.Now().Format(time.RFC3339Nano),
		"id":    id,
		"state": string(state),
	})
}

func (d *debugCapture) OnChildClosed(id string) {
	d.writeEvent("child_closed", map[string]any{
		"time": time.Now().Format(time.RFC3339Nano),
		"id":   id,
	})
}

func (d *debugCapture) OnPTYOut(childID string, chunk []byte) {
	if len(chunk) == 0 {
		return
	}
	d.mu.Lock()
	defer d.mu.Unlock()
	f, ok := d.rawByID[childID]
	if !ok {
		path := filepath.Join(d.dir, childID+".raw")
		nf, err := os.Create(path)
		if err != nil {
			return
		}
		f = nf
		d.rawByID[childID] = nf
	}
	// Listener contract: don't retain chunk past return. Writing now
	// is fine; the slice's backing buffer is reused for the next read
	// only after this listener chain completes.
	_, _ = f.Write(chunk)
}

func (d *debugCapture) writeEvent(kind string, fields map[string]any) {
	d.mu.Lock()
	defer d.mu.Unlock()
	d.writeEventLocked(kind, fields)
}

func (d *debugCapture) writeEventLocked(kind string, fields map[string]any) {
	if d.events == nil {
		return
	}
	if fields == nil {
		fields = map[string]any{}
	}
	fields["event"] = kind
	enc, err := json.Marshal(fields)
	if err != nil {
		return
	}
	_, _ = fmt.Fprintln(d.events, string(enc))
}