package media

import (
	"database/sql"
	"net/http"
	"strings"

	"github.com/mithral/vellum/internal/auth"
	"github.com/mithral/vellum/internal/httpx"
)

// shelfItem is one card on the home screen.
type shelfItem struct {
	ID        int64   `json:"id"`
	LibraryID int64   `json:"library_id"`
	Kind      string  `json:"kind"`
	Title     string  `json:"title"`
	Percent   float64 `json:"percent"`
	FileID    int64   `json:"file_id"`
	UpdatedAt string  `json:"updated_at"`
}

// homeResponse is everything the landing screen needs in one request.
type homeResponse struct {
	Continue     []shelfItem    `json:"continue"`
	Recent       []shelfItem    `json:"recent"`
	CountsByKind map[string]int `json:"counts_by_kind"`
	LibraryCount int            `json:"library_count"`
	TotalItems   int            `json:"total_items"`
}

// handleHome powers the landing screen: what to continue, what is new, and how
// much is in each section.
//
// One request rather than three round trips, because the landing screen is the
// first thing a user sees and should not pop in piece by piece.
func (h *Handlers) handleHome(w http.ResponseWriter, r *http.Request, u auth.User) {
	ctx := r.Context()

	libs, err := auth.VisibleLibraryIDs(ctx, h.db, u)
	if err != nil {
		h.fail(w, "visible libraries", err)
		return
	}
	if len(libs) == 0 {
		httpx.WriteJSON(w, http.StatusOK, homeResponse{
			Continue:     []shelfItem{},
			Recent:       []shelfItem{},
			CountsByKind: map[string]int{},
		})
		return
	}
	in, args := inClause(libs)

	resp := homeResponse{CountsByKind: map[string]int{}, LibraryCount: len(libs)}

	// Continue: started but unfinished, most recent first.
	continueQ := `
		SELECT i.id, i.library_id, i.kind, i.title, p.percent, p.file_id, p.updated_at
		FROM progress p
		JOIN media_items i ON i.id = p.item_id
		WHERE p.user_id = ? AND p.finished = 0 AND i.missing = 0
		  AND i.library_id IN (` + in + `)
		ORDER BY p.updated_at DESC
		LIMIT 20`
	rows, err := h.db.QueryContext(ctx, continueQ, append([]any{u.ID}, args...)...)
	if err != nil {
		h.fail(w, "home: continue", err)
		return
	}
	resp.Continue, err = scanShelf(rows)
	if err != nil {
		h.fail(w, "home: scan continue", err)
		return
	}

	// Recent: newest additions across every visible library.
	recentQ := `
		SELECT i.id, i.library_id, i.kind, i.title, 0, 0, i.added_at
		FROM media_items i
		WHERE i.missing = 0 AND i.library_id IN (` + in + `)
		ORDER BY i.added_at DESC, i.id DESC
		LIMIT 40`
	rows, err = h.db.QueryContext(ctx, recentQ, args...)
	if err != nil {
		h.fail(w, "home: recent", err)
		return
	}
	resp.Recent, err = scanShelf(rows)
	if err != nil {
		h.fail(w, "home: scan recent", err)
		return
	}

	// Counts per kind, for the sidebar and section headers.
	countQ := `
		SELECT i.kind, count(*) FROM media_items i
		WHERE i.missing = 0 AND i.library_id IN (` + in + `)
		GROUP BY i.kind`
	rows, err = h.db.QueryContext(ctx, countQ, args...)
	if err != nil {
		h.fail(w, "home: counts", err)
		return
	}
	defer rows.Close()
	for rows.Next() {
		var kind string
		var n int
		if err := rows.Scan(&kind, &n); err != nil {
			h.fail(w, "home: scan counts", err)
			return
		}
		resp.CountsByKind[kind] = n
		resp.TotalItems += n
	}
	if err := rows.Err(); err != nil {
		h.fail(w, "home: iterate counts", err)
		return
	}

	httpx.WriteJSON(w, http.StatusOK, resp)
}

// handleAuthors returns the people credited on an item.
func (h *Handlers) handleAuthors(w http.ResponseWriter, r *http.Request, u auth.User) {
	it, ok := h.authorized(w, r, u)
	if !ok {
		return
	}
	rows, err := h.db.QueryContext(r.Context(), `
		SELECT p.name FROM item_people ip
		JOIN people p ON p.id = ip.person_id
		WHERE ip.item_id = ? ORDER BY ip.ord`, it.ID)
	if err != nil {
		h.fail(w, "authors", err)
		return
	}
	defer rows.Close()

	authors := []string{}
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			h.fail(w, "scan author", err)
			return
		}
		authors = append(authors, name)
	}
	httpx.WriteJSON(w, http.StatusOK, map[string]any{"authors": authors})
}

func scanShelf(rows *sql.Rows) ([]shelfItem, error) {
	defer rows.Close()
	out := []shelfItem{}
	for rows.Next() {
		var s shelfItem
		if err := rows.Scan(&s.ID, &s.LibraryID, &s.Kind, &s.Title, &s.Percent, &s.FileID, &s.UpdatedAt); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// inClause builds "?,?,?" plus the matching args for an IN list.
func inClause(ids []int64) (string, []any) {
	placeholders := make([]string, len(ids))
	args := make([]any, len(ids))
	for i, id := range ids {
		placeholders[i] = "?"
		args[i] = id
	}
	return strings.Join(placeholders, ","), args
}