package jellyfin

import (
	"context"
	"database/sql"
	"errors"
	"sort"
	"strconv"
	"strings"

	"github.com/mithral/vellum/internal/auth"
	"github.com/mithral/vellum/internal/catalog"
	"github.com/mithral/vellum/internal/jellyfin/dto"
)

// defaultLimit caps an unbounded browse so a client that omits Limit cannot
// pull an entire library in one response. maxLimit is the hard ceiling.
const (
	defaultLimit = 300
	maxLimit     = 1000
)

// overlayColumns / overlayFrom carry the per-user state and the two browse-only
// columns (sort title, parent) that catalog.Item does not expose. They never
// read media_files and never check a grant: catalog.LoadFor loads the item and
// enforces the grant, and catalog.FirstFile reads the file, so the one
// authorization rule lives in one place instead of a sixth copy here.
//
// Per-user state comes from a windowed progress join that picks the most
// recently updated row per item, plus item_views and favorites.
const overlayColumns = `i.sort_title, i.parent_id,
	COALESCE(p.position,0), COALESCE(p.percent,0), COALESCE(p.finished,0),
	COALESCE(v.views,0), COALESCE(fa.user_id,0),
	COALESCE((SELECT 1 FROM assets a WHERE a.item_id=i.id AND a.role='cover' LIMIT 1),0)`

const overlayFrom = `FROM media_items i
	LEFT JOIN (SELECT item_id, position, percent, finished,
	                  ROW_NUMBER() OVER (PARTITION BY item_id ORDER BY updated_at DESC) AS rn
	           FROM progress WHERE user_id = ?) p ON p.item_id = i.id AND p.rn = 1
	LEFT JOIN item_views v ON v.user_id = ? AND v.item_id = i.id
	LEFT JOIN favorites fa ON fa.user_id = ? AND fa.item_id = i.id`

// itemColumns is the browse projection: the catalog.Item identity columns plus
// the per-user overlay. The list and single-item paths share it so the two can
// never disagree about what a browse row contains. File facts are attached
// separately via catalog.FirstFile.
//
// season_number and episode_number are the television tree (migration 0013) and
// they are load-bearing here: an episode is kind 'video' exactly like a film, so
// the episode number is the only thing that tells a client which is which.
const itemColumns = `i.id, i.library_id, i.kind, i.path, i.title, COALESCE(i.year,0), i.missing, ` +
	`COALESCE(i.season_number,0), COALESCE(i.episode_number,0), ` +
	overlayColumns

// listQuery is everything the browse query needs.
type listQuery struct {
	userID         int64
	libraryIDs     []int64
	parentItemID   int64 // 0 means "not scoped to an item's children"
	kinds          []string
	episodesOnly   bool // IncludeItemTypes asked for episodes and not films
	sortColumn     string
	descending     bool
	limit          int
	offset         int
	searchTerm     string
	filters        []string
	includeSources bool
}

// queryItems runs the browse query and its matching count.
//
// The browse rows are drained before the per-item file lookups run: catalog
// reads one file at a time, and issuing those queries against a still-open
// result set is the classic nested-query footgun.
func (h *Handlers) queryItems(ctx context.Context, q listQuery) ([]dto.ItemView, int, error) {
	where, whereArgs := buildWhere(q)

	var total int
	if err := h.db.QueryRowContext(ctx,
		`SELECT COUNT(*) FROM media_items i WHERE `+where, whereArgs...).Scan(&total); err != nil {
		return nil, 0, err
	}

	order := q.sortColumn
	if q.descending {
		order += " DESC"
	} else {
		order += " ASC"
	}
	sqlText := `SELECT ` + itemColumns + ` ` + overlayFrom +
		` WHERE ` + where + ` ORDER BY ` + order + ` LIMIT ? OFFSET ?`

	args := []any{q.userID, q.userID, q.userID}
	args = append(args, whereArgs...)
	args = append(args, q.limit, q.offset)

	rows, err := h.db.QueryContext(ctx, sqlText, args...)
	if err != nil {
		return nil, 0, err
	}
	defer rows.Close()

	out := []dto.ItemView{}
	for rows.Next() {
		v, err := scanItem(rows)
		if err != nil {
			return nil, 0, err
		}
		out = append(out, v)
	}
	if err := rows.Err(); err != nil {
		return nil, 0, err
	}
	rows.Close()

	for i := range out {
		if err := h.attachFile(ctx, &out[i]); err != nil {
			return nil, 0, err
		}
	}
	return out, total, nil
}

// attachFile fills the first-file facts from internal/catalog, the one place
// that reads media_files. An item with no file keeps a zero File, which is
// exactly the defaults the old media_files LEFT JOIN produced.
func (h *Handlers) attachFile(ctx context.Context, v *dto.ItemView) error {
	f, err := h.firstFile(ctx, v.Item.ID)
	if err != nil {
		return err
	}
	v.File = f
	return nil
}

// firstFile returns the item's first file, or a zero File when the item has
// none. It is catalog.FirstFile with the "no file" case flattened, for callers
// that only need the facts rather than a 404.
func (h *Handlers) firstFile(ctx context.Context, itemID int64) (catalog.File, error) {
	f, err := catalog.FirstFile(ctx, h.db, itemID)
	if errors.Is(err, catalog.ErrNotFound) {
		return catalog.File{}, nil
	}
	return f, err
}

// loadOverlay fills the browse-only and per-user fields of an already-loaded
// item. It reads no file and performs no access check: catalog.LoadFor already
// did both.
func (h *Handlers) loadOverlay(ctx context.Context, userID, itemID int64, v *dto.ItemView) error {
	row := h.db.QueryRowContext(ctx,
		`SELECT `+overlayColumns+` `+overlayFrom+` WHERE i.id = ?`,
		userID, userID, userID, itemID)
	var (
		parentID sql.NullInt64
		finished int
		favUser  int64
		hasCover int
	)
	if err := row.Scan(
		&v.SortTitle, &parentID,
		&v.PositionMS, &v.Percent, &finished,
		&v.PlayCount, &favUser, &hasCover,
	); err != nil {
		return err
	}
	v.ParentID = parentID.Int64
	v.Finished = finished == 1
	v.Favorite = favUser != 0
	v.HasCover = hasCover == 1
	return nil
}

// itemVisible reports whether the caller may read the item's library. A missing
// item is false, not an error. It delegates to catalog.LoadFor, the same
// chokepoint every other surface uses, rather than reimplementing the grant
// rule here.
func (h *Handlers) itemVisible(ctx context.Context, u auth.User, id int64) (bool, error) {
	if _, err := catalog.LoadFor(ctx, h.db, u, id); err != nil {
		if errors.Is(err, catalog.ErrNotFound) {
			return false, nil
		}
		return false, err
	}
	return true, nil
}

// scanItem reads one row of the shared item column list.
func scanItem(row interface{ Scan(...any) error }) (dto.ItemView, error) {
	var (
		v        dto.ItemView
		parentID sql.NullInt64
		finished int
		favUser  int64
		hasCover int
	)
	err := row.Scan(
		&v.Item.ID, &v.Item.LibraryID, &v.Item.Kind, &v.Item.Path, &v.Item.Title,
		&v.Item.Year, &v.Item.Missing, &v.Item.SeasonNumber, &v.Item.EpisodeNumber,
		&v.SortTitle, &parentID,
		&v.PositionMS, &v.Percent, &finished,
		&v.PlayCount, &favUser, &hasCover,
	)
	if err != nil {
		return dto.ItemView{}, err
	}
	v.ParentID = parentID.Int64
	v.Finished = finished == 1
	v.Favorite = favUser != 0
	v.HasCover = hasCover == 1
	return v, nil
}

// buildWhere assembles the WHERE clause and its arguments. An empty library set
// matches nothing, which is the correct outcome for a user with no grants.
func buildWhere(q listQuery) (string, []any) {
	clauses := []string{"i.missing = 0"}
	var args []any

	if len(q.libraryIDs) == 0 {
		clauses = append(clauses, "1 = 0")
	} else {
		in, inArgs := placeholders(q.libraryIDs)
		clauses = append(clauses, "i.library_id IN ("+in+")")
		args = append(args, inArgs...)
	}
	if q.parentItemID > 0 {
		clauses = append(clauses, "i.parent_id = ?")
		args = append(args, q.parentItemID)
	}
	if len(q.kinds) > 0 {
		in, inArgs := placeholdersStr(q.kinds)
		clauses = append(clauses, "i.kind IN ("+in+")")
		args = append(args, inArgs...)
	}
	// An episode and a film are the same kind, so "Episodes, not Movies" is a
	// filter on the number rather than the kind — applied only to the video
	// rows, or it would throw away the series and seasons in the same query.
	if q.episodesOnly {
		clauses = append(clauses, "(i.kind <> 'video' OR i.episode_number IS NOT NULL)")
	}
	if q.searchTerm != "" {
		clauses = append(clauses, "i.title LIKE ?")
		args = append(args, "%"+q.searchTerm+"%")
	}

	// Filters are sorted so the SQL (and its argument order) is deterministic.
	filters := append([]string(nil), q.filters...)
	sort.Strings(filters)
	for _, f := range filters {
		switch f {
		case "IsResumable":
			clauses = append(clauses,
				`EXISTS (SELECT 1 FROM progress p WHERE p.user_id = ? AND p.item_id = i.id AND p.finished = 0 AND p.position > 0)`)
			args = append(args, q.userID)
		case "IsPlayed":
			clauses = append(clauses,
				`EXISTS (SELECT 1 FROM progress p WHERE p.user_id = ? AND p.item_id = i.id AND p.finished = 1)`)
			args = append(args, q.userID)
		case "IsUnplayed":
			clauses = append(clauses,
				`NOT EXISTS (SELECT 1 FROM progress p WHERE p.user_id = ? AND p.item_id = i.id AND p.finished = 1)`)
			args = append(args, q.userID)
		case "IsFavorite":
			clauses = append(clauses,
				`EXISTS (SELECT 1 FROM favorites f WHERE f.user_id = ? AND f.item_id = i.id)`)
			args = append(args, q.userID)
		}
	}
	return strings.Join(clauses, " AND "), args
}

// ── small parsing helpers ──────────────────────────────────────────────

func placeholders(ids []int64) (string, []any) {
	parts := make([]string, len(ids))
	args := make([]any, len(ids))
	for i, id := range ids {
		parts[i] = "?"
		args[i] = id
	}
	return strings.Join(parts, ","), args
}

func placeholdersStr(vals []string) (string, []any) {
	parts := make([]string, len(vals))
	args := make([]any, len(vals))
	for i, v := range vals {
		parts[i] = "?"
		args[i] = v
	}
	return strings.Join(parts, ","), args
}

// splitCSV splits a Jellyfin comma list, dropping empties.
func splitCSV(s string) []string {
	if strings.TrimSpace(s) == "" {
		return nil
	}
	out := []string{}
	for _, p := range strings.Split(s, ",") {
		if p = strings.TrimSpace(p); p != "" {
			out = append(out, p)
		}
	}
	return out
}

func containsFold(list []string, want string) bool {
	for _, v := range list {
		if strings.EqualFold(v, want) {
			return true
		}
	}
	return false
}

func containsInt64(list []int64, want int64) bool {
	for _, v := range list {
		if v == want {
			return true
		}
	}
	return false
}

func atoiDefault(s string, def int) int {
	if s == "" {
		return def
	}
	n, err := strconv.Atoi(strings.TrimSpace(s))
	if err != nil {
		return def
	}
	return n
}

func parseBool(s string) bool {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "1", "true", "yes":
		return true
	}
	return false
}

// sortColumn maps a Jellyfin SortBy value to a SQL column. Only the first
// recognised name is used; unknown names fall back to sort_title.
func sortColumn(sortBy string) string {
	for _, s := range strings.Split(sortBy, ",") {
		switch strings.TrimSpace(s) {
		case "DateCreated":
			return "i.added_at"
		case "ProductionYear":
			return "i.year"
		case "Random":
			return "RANDOM()"
		case "SortName":
			return "i.sort_title"
		}
	}
	return "i.sort_title"
}

// isDescending reads a Jellyfin SortOrder ("Descending"/"Desc"/"desc").
func isDescending(order string) bool {
	switch strings.ToLower(strings.TrimSpace(order)) {
	case "descending", "desc":
		return true
	}
	return false
}