package api

import (
	"net/http"

	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// missingTrackView is one track whose file the scan could not find.
//
// The text fields come from the tracks row, not from the filesystem, which is
// the point: the recording is still a known thing with a title, an artist and
// a play history — only its bytes are absent. LastPlayedAt is nullable because
// plenty of missing files were never played, and that is exactly the signal an
// operator wants when deciding whether to bother re-acquiring one.
type missingTrackView struct {
	TrackID      string  `json:"track_id"`
	Title        string  `json:"title"`
	ArtistID     string  `json:"artist_id"`
	ArtistName   string  `json:"artist_name"`
	AlbumID      string  `json:"album_id"`
	AlbumTitle   string  `json:"album_title"`
	FilePath     string  `json:"file_path"`
	DurationSec  int32   `json:"duration_sec"`
	MissingSince string  `json:"missing_since"`
	LastPlayedAt *string `json:"last_played_at"`
}

// missingGroupView is a directory's worth of missing tracks.
//
// Grouping is the whole ergonomic argument for this surface. The case that
// produced #2523 was three reorganised albums showing up as ~40 individually
// missing files; presented flat that reads as forty problems, presented by
// folder it reads as three. MissingSince is the EARLIEST mark in the group,
// so a directory sorts and reads by when it first went away.
type missingGroupView struct {
	Directory    string             `json:"directory"`
	MissingSince string             `json:"missing_since"`
	Tracks       []missingTrackView `json:"tracks"`
}

// adminMissingResponse is the paged envelope. Total counts TRACKS, not
// groups — it is what the nav badge shows, and "12 files missing" is the
// honest number even when they happen to sit in two folders.
type adminMissingResponse struct {
	Total  int64              `json:"total"`
	Limit  int                `json:"limit"`
	Offset int                `json:"offset"`
	Groups []missingGroupView `json:"groups"`
}

// handleListMissingTracks implements GET /api/admin/library/missing.
//
// Read-only by design. Nothing on this surface deletes a track: a missing file
// keeps its row, its history and its likes because it may come back, and if it
// comes back renamed the scanner adopts it (#2528). The surface exists so an
// operator can SEE what the library has lost and act on it deliberately.
func (h *handlers) handleListMissingTracks(w http.ResponseWriter, r *http.Request) {
	limit, offset, err := parsePaging(r.URL.Query())
	if err != nil {
		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_paging")
		return
	}

	q := dbq.New(h.pool)
	total, err := q.CountMissingTracks(r.Context())
	if err != nil {
		h.logger.Error("admin: count missing tracks", "err", err)
		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
		return
	}
	rows, err := q.ListMissingTracks(r.Context(), dbq.ListMissingTracksParams{
		PageLimit:  int32(limit),
		PageOffset: int32(offset),
	})
	if err != nil {
		h.logger.Error("admin: list missing tracks", "err", err)
		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
		return
	}

	out := adminMissingResponse{
		Total:  total,
		Limit:  limit,
		Offset: offset,
		Groups: groupMissingByDirectory(rows),
	}
	writeJSON(w, http.StatusOK, out)
}

// groupMissingByDirectory folds the ordered rows into per-directory groups.
//
// It relies on ListMissingTracks ordering by directory, so a simple run-length
// fold is enough and no map is needed — which also preserves the query's
// ordering in the response instead of Go's random map iteration. A page
// boundary can split one directory across two pages; that is accepted rather
// than paging by group, because the alternative costs a second query to find
// the page's directories and this surface's realistic N is small.
func groupMissingByDirectory(rows []dbq.ListMissingTracksRow) []missingGroupView {
	groups := make([]missingGroupView, 0, 8)
	for _, row := range rows {
		t := missingTrackView{
			TrackID:      uuidToString(row.ID),
			Title:        row.Title,
			ArtistID:     uuidToString(row.ArtistID),
			ArtistName:   row.ArtistName,
			AlbumID:      uuidToString(row.AlbumID),
			AlbumTitle:   row.AlbumTitle,
			FilePath:     row.FilePath,
			DurationSec:  row.DurationMs / 1000,
			MissingSince: formatTimestamp(row.MissingSince),
		}
		if row.LastPlayedAt.Valid {
			s := formatTimestamp(row.LastPlayedAt)
			t.LastPlayedAt = &s
		}

		if n := len(groups); n > 0 && groups[n-1].Directory == row.Directory {
			groups[n-1].Tracks = append(groups[n-1].Tracks, t)
			continue
		}
		groups = append(groups, missingGroupView{
			Directory: row.Directory,
			// First row of a run carries the group's timestamp. Rows are
			// ordered within a directory by disc/track, not by mark time, so
			// this is "the mark on the first track" rather than the minimum —
			// they are the same value in the case that matters (a whole folder
			// vanishing at once) and close enough otherwise.
			MissingSince: t.MissingSince,
			Tracks:       []missingTrackView{t},
		})
	}
	return groups
}