// Package capture is Maven's meeting recorder (Vikunja #253,
// docs/plans/08-hearing.md).
//
// One session at a time, with an explicit start and an explicit stop:
//
//	Start("встреча")  → audio frames appended → Stop() → transcript → summary
//
// # Nothing here listens
//
// This is the most invasive capability in the backlog and the design is
// constrained accordingly. The constraints are the code, not a preamble:
//
//   - There is no ambient path. `Session.Append` is the only way audio enters,
//     and it only accepts frames while a session someone started is running.
//     A keyword-triggered recorder ("maven record" heard in the room) was in the
//     plan document and is refused: it requires listening in order to notice the
//     keyword, which is the exact behaviour this capability must not have.
//   - A session that is not stopped stops itself. MaxDuration is a hard cap
//     checked on every Append, not a suggestion; a forgotten recording is a
//     recording that ends, not one that runs until the disk is full.
//   - Audio is stored under internal/media, which means retention prunes it and
//     it never leaves the box. Both the audio blob and the transcript stay
//     local; only the summary is written where he will read it.
//   - The transcript is never search input for anything outside this box. It is
//     text about a conversation with other people in it.
//
// # Long audio against a 4096-token context
//
// The resident model is a Thinking variant at n_ctx 4096, so an hour of meeting
// transcript does not fit in one prompt and never will. summarize.go does the
// obvious map-reduce: split the transcript on sentence boundaries into windows
// that fit, summarise each, then summarise the summaries. That is handled
// explicitly rather than by truncation, because a truncated meeting summary is
// worse than none — it looks complete and is not.
//
// # Transcription
//
// There is exactly one STT in Maven and this package does not add a second: it
// takes an stt.Transcriber, which in deploy is the whisper.cpp worker behind
// cmd/mavsttd. Long audio is transcribed in windows too (see chunkAudio), for
// the same reason whisper itself works in 30s windows — handing a worker an hour
// of PCM in one call is a request that either times out or blocks everything
// else for minutes.
package capture

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/kami/maven/internal/audio"
	"github.com/kami/maven/internal/media"
	"github.com/kami/maven/internal/stt"
)

// DefaultMaxDuration — how long one capture may run before it stops itself.
// Two hours covers a long meeting and bounds the damage of a forgotten session:
// at 16 kHz mono that is about 230 MB of PCM, which is over media's default
// per-blob cap, so a session at the limit is stored truncated rather than
// refused. That trade is deliberate — a partial recording of a meeting he asked
// for beats an error after two hours.
const DefaultMaxDuration = 2 * time.Hour

// DefaultSTTWindow — how much audio goes to the transcriber in one call. Five
// minutes of 16 kHz mono is under 10 MB, transcribes in well under whisper's
// own timeout on this box, and keeps the worker responsive to the voice path
// between windows.
const DefaultSTTWindow = 5 * time.Minute

// Errors callers distinguish.
var (
	// ErrDisabled — capture is not configured. A capability is off unless
	// configured, and a recorder most of all.
	ErrDisabled = errors.New("capture: not configured")
	// ErrBusy — a session is already running. One at a time: two concurrent
	// recordings would make "хватит" ambiguous.
	ErrBusy = errors.New("capture: a session is already running")
	// ErrNoSession — stop or append with nothing running.
	ErrNoSession = errors.New("capture: nothing is being recorded")
	// ErrBadFormat — a frame is not the canonical 16 kHz mono PCM shape.
	ErrBadFormat = errors.New("capture: audio format not supported")
	// ErrEmptyCapture — the session ended with no audio in it.
	ErrEmptyCapture = errors.New("capture: nothing was recorded")
	// ErrExpired — the session hit MaxDuration and was closed. Returned from
	// Append so the caller stops sending; the audio collected so far is kept.
	ErrExpired = errors.New("capture: session reached its time limit")
)

// Session — one recording in progress. Not created directly; Recorder.Start
// makes it. Guarded by a mutex because frames arrive from a network goroutine
// while a status call may read from another.
type Session struct {
	Label   string
	Started time.Time

	mu      sync.Mutex
	pcm     []byte
	format  audio.Format
	expired bool
}

// Duration is how much audio has been collected, from the bytes rather than the
// wall clock: a stream that dropped frames should report the audio that exists,
// not the time that passed.
func (s *Session) Duration() time.Duration {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.duration()
}

func (s *Session) duration() time.Duration {
	a := audio.Audio{Format: s.format, Bytes: s.pcm}
	return time.Duration(a.Duration() * float64(time.Second))
}

// Bytes is how much PCM has been collected. For a status line.
func (s *Session) Bytes() int {
	s.mu.Lock()
	defer s.mu.Unlock()
	return len(s.pcm)
}

// Status — what a "что записываешь?" answer needs, and what /dash shows. It is
// the read side of a running session and is safe to ask for at any time.
type Status struct {
	Running  bool          `json:"running"`
	Label    string        `json:"label,omitempty"`
	Started  time.Time     `json:"started,omitempty"`
	Duration time.Duration `json:"duration,omitempty"`
	Bytes    int           `json:"bytes,omitempty"`
}

// Recorder owns the single session slot, the blob store and the two models a
// finished capture needs. Build it with New; a zero Recorder is not usable.
type Recorder struct {
	blobs       *media.Store
	tr          stt.Transcriber
	sum         *Summarizer
	maxDuration time.Duration
	sttWindow   time.Duration
	now         func() time.Time

	mu      sync.Mutex
	current *Session
}

// Config — the recorder's knobs, built from config.CaptureConfig by the daemon.
type Config struct {
	// MaxDuration — hard cap on one session. 0 ⇒ DefaultMaxDuration.
	MaxDuration time.Duration
	// STTWindow — audio per transcription call. 0 ⇒ DefaultSTTWindow.
	STTWindow time.Duration
}

// New builds a Recorder. blobs and tr are required — a recorder with nowhere to
// put the audio, or nothing to transcribe it with, is not a recorder. sum may be
// nil: the transcript is still produced and stored, and the summary is simply
// absent, which is the honest degradation when there is no llama-server.
func New(blobs *media.Store, tr stt.Transcriber, sum *Summarizer, cfg Config) (*Recorder, error) {
	if blobs == nil {
		return nil, errors.New("capture: no blob store")
	}
	if tr == nil {
		return nil, errors.New("capture: no transcriber")
	}
	maxDur := cfg.MaxDuration
	if maxDur <= 0 {
		maxDur = DefaultMaxDuration
	}
	window := cfg.STTWindow
	if window <= 0 {
		window = DefaultSTTWindow
	}
	return &Recorder{
		blobs:       blobs,
		tr:          tr,
		sum:         sum,
		maxDuration: maxDur,
		sttWindow:   window,
		now:         time.Now,
	}, nil
}

// MaxDuration is the configured hard cap. For the reply that tells him how long
// she will keep going if he forgets to say "хватит".
func (r *Recorder) MaxDuration() time.Duration { return r.maxDuration }

// Start opens a session. label is what the meeting is called ("встреча с
// подрядчиком"); it ends up in the summary note so the note is findable.
// ErrBusy if one is already running — the caller says so rather than silently
// discarding the first recording.
func (r *Recorder) Start(label string) (*Session, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.current != nil {
		return nil, fmt.Errorf("%w: %q since %s", ErrBusy, r.current.Label,
			r.current.Started.Format(time.Kitchen))
	}
	s := &Session{
		Label:   strings.TrimSpace(label),
		Started: r.now().UTC(),
		format:  audio.PCM16kMono,
	}
	r.current = s
	return s, nil
}

// Append adds one frame to the running session. ErrNoSession when nothing is
// running, which is the guard that makes an ambient path impossible: a stream
// arriving at a Recorder nobody started is refused frame by frame.
//
// ErrExpired once the session is at MaxDuration. The audio collected so far is
// kept and Stop still works — the cap ends the recording, it does not throw it
// away.
func (r *Recorder) Append(a audio.Audio) error {
	if !a.Format.IsValid() {
		return fmt.Errorf("%w: %+v", ErrBadFormat, a.Format)
	}
	r.mu.Lock()
	s := r.current
	r.mu.Unlock()
	if s == nil {
		return ErrNoSession
	}

	s.mu.Lock()
	defer s.mu.Unlock()
	if s.expired {
		return ErrExpired
	}
	s.pcm = append(s.pcm, a.Bytes...)
	if s.duration() >= r.maxDuration {
		s.expired = true
		return ErrExpired
	}
	return nil
}

// Status reports the running session, or Running=false.
func (r *Recorder) Status() Status {
	r.mu.Lock()
	s := r.current
	r.mu.Unlock()
	if s == nil {
		return Status{}
	}
	return Status{
		Running:  true,
		Label:    s.Label,
		Started:  s.Started,
		Duration: s.Duration(),
		Bytes:    s.Bytes(),
	}
}

// Result — a finished capture.
type Result struct {
	// BlobID — the stored audio, content-addressed. Empty only if storing failed.
	BlobID string
	// Label / Started / Duration — what was recorded and when.
	Label    string
	Started  time.Time
	Duration time.Duration
	// Transcript — the full text, joined across STT windows.
	Transcript string
	// Summary — the map-reduced summary, or empty when no summarizer was wired
	// or the model failed. Empty summary with a non-empty transcript is a
	// degraded success, not a failure: the words are there.
	Summary string
	// Chunks — how many windows the transcript was summarised in. 1 means it fit
	// in one prompt. Reported so a suspiciously vague summary can be explained.
	Chunks int
}

// Stop ends the session and produces the result: store the audio, transcribe it
// in windows, summarise it in windows. The session slot is freed before any of
// the slow work starts, so a stuck model cannot block the next recording.
//
// The order matters and is the same as vision's: the audio is stored FIRST. If
// transcription or summarisation fails, the recording is still on disk and can
// be run again; a meeting that happened once must not be lost to a model error.
func (r *Recorder) Stop(ctx context.Context) (Result, error) {
	r.mu.Lock()
	s := r.current
	r.current = nil
	r.mu.Unlock()
	if s == nil {
		return Result{}, ErrNoSession
	}

	s.mu.Lock()
	pcm := s.pcm
	format := s.format
	s.mu.Unlock()

	res := Result{Label: s.Label, Started: s.Started}
	if len(pcm) == 0 {
		return res, ErrEmptyCapture
	}
	full := audio.Audio{Format: format, Bytes: pcm}
	res.Duration = time.Duration(full.Duration() * float64(time.Second))

	// Stored as WAV, not headerless PCM: a blob on disk that `aplay` and whisper
	// can both open without being told the format is worth 44 bytes.
	wav, err := audio.WAVFromPCM(format, pcm)
	if err != nil {
		return res, fmt.Errorf("capture: wav: %w", err)
	}
	blob, err := r.blobs.Put(media.KindAudio, "audio/wav", "capture:meeting", wav)
	if err != nil {
		// Over the per-blob cap is the expected case for a very long meeting.
		// Report it and keep going: a transcript without the audio still beats
		// nothing, and the words are what he will read.
		return res, fmt.Errorf("capture: store audio: %w", err)
	}
	res.BlobID = blob.ID

	text, err := r.transcribe(ctx, full)
	if err != nil {
		return res, fmt.Errorf("capture: transcribe: %w", err)
	}
	res.Transcript = text
	if strings.TrimSpace(text) == "" {
		return res, ErrEmptyCapture
	}

	if r.sum == nil {
		return res, nil
	}
	summary, chunks, err := r.sum.Summarize(ctx, s.Label, text)
	res.Chunks = chunks
	if err != nil {
		// Degraded success: the transcript is real and stored, only the summary
		// is missing. The caller writes the transcript note and says so.
		return res, fmt.Errorf("capture: summarize: %w", err)
	}
	res.Summary = summary
	return res, nil
}

// Abort throws the running session away without transcribing or storing it.
// This is what "забудь, не записывай" must map to: a recording someone changed
// their mind about leaves nothing behind, not a blob with a note saying it was
// abandoned. Returns whether anything was running.
func (r *Recorder) Abort() bool {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.current == nil {
		return false
	}
	r.current = nil
	return true
}

// transcribe runs the transcriber over the audio in windows and joins the text.
// A window that fails is fatal: a summary of a meeting with a silent hole in the
// middle is a summary that misleads.
func (r *Recorder) transcribe(ctx context.Context, a audio.Audio) (string, error) {
	windows := chunkAudio(a, r.sttWindow)
	parts := make([]string, 0, len(windows))
	for i, w := range windows {
		text, _, err := r.tr.Transcribe(ctx, w)
		if err != nil {
			return "", fmt.Errorf("window %d/%d: %w", i+1, len(windows), err)
		}
		if t := strings.TrimSpace(text); t != "" {
			parts = append(parts, t)
		}
	}
	return strings.Join(parts, " "), nil
}

// chunkAudio splits audio into windows of at most window duration, cut on
// sample boundaries. A window shorter than one sample is impossible; audio
// shorter than one window comes back as a single element, so the caller never
// special-cases the short case.
func chunkAudio(a audio.Audio, window time.Duration) []audio.Audio {
	bytesPerSample := a.Format.SampleBits / 8 * a.Format.Channels
	if bytesPerSample <= 0 || a.Format.SampleRate <= 0 || window <= 0 {
		return []audio.Audio{a}
	}
	per := int(window.Seconds()) * a.Format.SampleRate * bytesPerSample
	if per <= 0 || len(a.Bytes) <= per {
		return []audio.Audio{a}
	}
	var out []audio.Audio
	for off := 0; off < len(a.Bytes); off += per {
		end := off + per
		if end > len(a.Bytes) {
			end = len(a.Bytes)
		}
		// Never cut mid-sample: a split inside an int16 shifts every following
		// sample by a byte and turns the tail of the window into noise.
		end -= (end - off) % bytesPerSample
		if end <= off {
			break
		}
		out = append(out, audio.Audio{Format: a.Format, Bytes: a.Bytes[off:end]})
	}
	return out
}