package store

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
)

// ErrNotFound is returned by GetSummaryByVideo when no summary exists for the
// (userID, videoID) pair scoped to that user.
var ErrNotFound = errors.New("store: summary not found")

// SummaryRow is a read-side view of a stored summary, enriched with the video's
// metadata when a matching videos row exists. It is deliberately separate from
// domain.Summary: it carries display fields (Title, Channel, URL, PublishedAt)
// that the engine never sees, sourced via a LEFT JOIN so a summary with no
// videos row still renders (Title/URL empty, PublishedAt zero).
//
// Channel currently mirrors the video provider ("youtube"): the per-channel
// channel_title lives on the subscriptions table (docs/data-model.md), which is
// not part of the Stage-0 store slice yet. When that table is migrated, swap the
// JOIN source — callers already fall back gracefully on an empty Channel.
type SummaryRow struct {
	VideoID         string
	ProviderVideoID string    // videos.provider_video_id; empty when no videos row
	Title           string    // videos.title; empty when no videos row
	Channel         string    // videos.provider for now; empty when no videos row
	URL             string    // videos.url; empty when no videos row
	PublishedAt     time.Time // videos.published_at; zero when absent
	Summary         string
	Highlights      []string
	Takeaways       []string
	AIProvider      string
	AIModel         string
	FallbackUsed    bool
	CreatedAt       time.Time
	Actions         []string // current active actions for this video; nil when none
}

// selectSummary is the shared projection for both reads. videos is LEFT JOINed
// on its UUID id (= summaries.video_id) and the same user_id, so the join never
// crosses users and a missing videos row yields nulls, not a dropped summary.
const selectSummary = `
	SELECT s.video_id,
	       COALESCE(v.provider_video_id, ''),
	       COALESCE(v.title, ''),
	       COALESCE(v.provider, ''),
	       COALESCE(v.url, ''),
	       v.published_at,
	       s.summary,
	       s.highlights,
	       s.takeaways,
	       COALESCE(s.ai_provider, ''),
	       COALESCE(s.ai_model, ''),
	       s.fallback_used,
	       s.created_at
	  FROM summaries s
	  LEFT JOIN videos v ON v.id = s.video_id AND v.user_id = s.user_id`

// ListSummaries returns the user's summaries, most recent first, capped at limit.
// A non-positive limit defaults to 50. Scoped by user_id: one user never sees
// another's summaries (per-user isolation, docs/data-model.md).
func (s *Store) ListSummaries(ctx context.Context, userID string, limit int) ([]SummaryRow, error) {
	if limit <= 0 {
		limit = 50
	}
	rows, err := s.pool.Query(ctx,
		selectSummary+`
		 WHERE s.user_id = $1
		 ORDER BY s.created_at DESC
		 LIMIT $2`,
		userID, limit)
	if err != nil {
		return nil, fmt.Errorf("store: list summaries: %w", err)
	}
	defer rows.Close()

	var out []SummaryRow
	for rows.Next() {
		row, err := scanSummaryRow(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, row)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("store: iterate summaries: %w", err)
	}
	if err := s.attachActions(ctx, userID, out); err != nil {
		return nil, err
	}
	return out, nil
}

// GetSummaryByVideo returns the full summary for (userID, videoID), including
// highlights and takeaways. Returns ErrNotFound when the user has no such
// summary. Scoped by user_id.
func (s *Store) GetSummaryByVideo(ctx context.Context, userID, videoID string) (*SummaryRow, error) {
	rows, err := s.pool.Query(ctx,
		selectSummary+`
		 WHERE s.user_id = $1 AND s.video_id = $2`,
		userID, videoID)
	if err != nil {
		return nil, fmt.Errorf("store: get summary: %w", err)
	}
	defer rows.Close()

	if !rows.Next() {
		if err := rows.Err(); err != nil {
			return nil, fmt.Errorf("store: get summary: %w", err)
		}
		return nil, ErrNotFound
	}
	row, err := scanSummaryRow(rows)
	if err != nil {
		return nil, err
	}
	holder := []SummaryRow{row}
	if err := s.attachActions(ctx, userID, holder); err != nil {
		return nil, err
	}
	return &holder[0], nil
}

// scanSummaryRow reads one row in the selectSummary column order. published_at is
// nullable (no videos row, or an unset date) so it scans through a pointer.
func scanSummaryRow(rows pgx.Row) (SummaryRow, error) {
	var (
		row         SummaryRow
		highlights  []byte
		takeaways   []byte
		publishedAt *time.Time
	)
	if err := rows.Scan(
		&row.VideoID,
		&row.ProviderVideoID,
		&row.Title,
		&row.Channel,
		&row.URL,
		&publishedAt,
		&row.Summary,
		&highlights,
		&takeaways,
		&row.AIProvider,
		&row.AIModel,
		&row.FallbackUsed,
		&row.CreatedAt,
	); err != nil {
		return SummaryRow{}, fmt.Errorf("store: scan summary: %w", err)
	}
	if publishedAt != nil {
		row.PublishedAt = *publishedAt
	}
	var err error
	if row.Highlights, err = unmarshalList(highlights); err != nil {
		return SummaryRow{}, fmt.Errorf("store: unmarshal highlights: %w", err)
	}
	if row.Takeaways, err = unmarshalList(takeaways); err != nil {
		return SummaryRow{}, fmt.Errorf("store: unmarshal takeaways: %w", err)
	}
	return row, nil
}

// unmarshalList decodes a jsonb array column into a string slice, mirroring
// marshalList in store.go. Empty/NULL bytes decode to a nil slice.
func unmarshalList(b []byte) ([]string, error) {
	if len(b) == 0 {
		return nil, nil
	}
	var xs []string
	if err := json.Unmarshal(b, &xs); err != nil {
		return nil, err
	}
	return xs, nil
}