// Package media is the intake for everything Maven sees or hears that is not
// text: a photo he sends her, a meeting she was asked to record, a voice sample
// used to enrol a speaker. All three senses (vision, hearing, speaker
// recognition) share one problem — a blob arrives, it has to be stored, and
// something has to describe it — so the storing half lives here once instead of
// three times.
//
// # What this package is
//
// A content-addressed blob store on the local filesystem. Put returns a Blob
// keyed by the sha256 of its bytes, so the same photo sent twice is one file.
// Each blob gets a sidecar `.json` with its kind, mime, size, source and
// creation time; the sidecar is the whole index, because at personal scale a
// directory walk is cheaper than another sqlite table and the store has to be
// readable with `ls` when something goes wrong.
//
// Blobs are NOT in the sqlite database. The database is small, encrypted, and
// read on every tick; a 40 MB meeting recording has no business in it. What
// goes in the database is the *text* a blob produced — a transcript, a
// description — written as an ordinary note, which is the durable artefact and
// the only part worth recalling later.
//
// # Invariants (these are the point of the package, not decoration)
//
//   - Nothing is captured that was not asked for. This package never records;
//     it stores what a caller hands it, and every caller is an explicit act
//     with a start and a stop. There is no ambient path in, and none may be
//     added: see the refusal recorded in docs/plans/08-hearing.md.
//   - A blob never leaves the box. No provider in this repo may upload one, and
//     the vision provider refuses a non-private endpoint for exactly that
//     reason (internal/vision).
//   - A blob is never search input and never embedded. His photos and the audio
//     of his meetings are not corpus. Only text derived from them, once he can
//     see it as a note, participates in recall.
//   - Storage is bounded. Retention is a config knob with a default, Prune
//     enforces it, and an unpruned store is a bug: audio of people accumulating
//     forever on disk is the failure mode this capability has to avoid.
//
// # Layout
//
//	<dir>/<kind>/<aa>/<sha256>.<ext>       the bytes
//	<dir>/<kind>/<aa>/<sha256>.json        the sidecar metadata
//
// `aa` is the first two hex chars of the digest — one fan-out level, enough to
// keep a directory listing usable after a few thousand blobs.
package media

import (
	"errors"
	"fmt"
	"time"
)

// Kind — what a blob is. Two values today; the kind is a directory name and a
// retention bucket, so adding a third is additive.
type Kind string

const (
	// KindImage — a still image (png / jpeg / gif / webp bytes as received).
	KindImage Kind = "image"
	// KindAudio — raw PCM in the canonical internal/audio format, or a WAV
	// container. Meeting captures and enrolment samples both land here.
	KindAudio Kind = "audio"
)

// Valid reports whether k is a kind this package will store. An unknown kind is
// refused at Put rather than creating a stray directory.
func (k Kind) Valid() bool { return k == KindImage || k == KindAudio }

// Errors callers distinguish. ErrNotFound is the only one a caller usually
// handles; the rest mean the call was wrong.
var (
	// ErrNotFound — no blob with that id in this store.
	ErrNotFound = errors.New("media: not found")
	// ErrEmpty — Put was handed zero bytes. Storing an empty capture would
	// leave a sidecar claiming a recording exists when it does not.
	ErrEmpty = errors.New("media: empty payload")
	// ErrTooLarge — the payload is over the store's cap. The cap exists so a
	// runaway capture cannot fill the disk that mavend's database lives on.
	ErrTooLarge = errors.New("media: payload too large")
	// ErrBadKind — unknown Kind.
	ErrBadKind = errors.New("media: unknown kind")
	// ErrBadID — the id is not a 64-char lowercase hex digest, so it cannot
	// have come from this store and must not be turned into a path.
	ErrBadID = errors.New("media: malformed id")
)

// Blob — one stored item. ID is the sha256 of the bytes in lowercase hex, which
// makes it both the primary key and the dedupe mechanism. Path is absolute and
// local; it is a debugging affordance and the argument a subprocess (whisper,
// llama-server) is pointed at, never something handed to a network client.
type Blob struct {
	ID      string    `json:"id"`
	Kind    Kind      `json:"kind"`
	MIME    string    `json:"mime"`
	Size    int64     `json:"size"`
	Source  string    `json:"source"`  // provenance: "telegram", "web:upload", "capture:meeting", "enroll"
	Created time.Time `json:"created"` // UTC
	Path    string    `json:"-"`       // filled by the store; not part of the sidecar
}

// Age is how long ago the blob was stored, measured against now. Prune uses it;
// it is exported because the /media surface will want to show it.
func (b Blob) Age(now time.Time) time.Duration { return now.Sub(b.Created) }

// String is a one-line summary for logs. Deliberately does not include Path:
// a log line is not the place to spell out where his meeting audio lives.
func (b Blob) String() string {
	return fmt.Sprintf("%s %s %dB from %s", b.Kind, shortID(b.ID), b.Size, b.Source)
}

// shortID trims a digest to something readable in a log line. Twelve hex chars
// is unambiguous at personal scale and short enough to fit next to the rest.
func shortID(id string) string {
	if len(id) <= 12 {
		return id
	}
	return id[:12]
}