package classes

import (
	"context"
	"strings"
	"time"

	"git.golem15.com/golem15/sm-journal-plugin/models"
	"git.golem15.com/golem15/summercms/modules/compass"
	"gorm.io/gorm"
)

// Related posts and category neighbours of a post (D-82, P33-44). Opt-in:
// golem15.journal.related_mode is "category" by default, which keeps the
// post answer as it has always been (posts sharing a category, three,
// newest first). "scored" ranks the related posts by shared tags and shared
// categories and adds the neighbours within the post's first category.
const (
	// RelatedModeKey is the config key of the related-posts mode.
	RelatedModeKey = "golem15.journal.related_mode"
	// RelatedCountKey is the config key of the number of scored related
	// posts, clamped to RelatedCountMin..RelatedCountMax.
	RelatedCountKey = "golem15.journal.related_count"

	// RelatedModeCategory is the default: today's related posts.
	RelatedModeCategory = "category"
	// RelatedModeScored ranks by shared tags and categories.
	RelatedModeScored = "scored"

	RelatedCountDefault = 3
	RelatedCountMin     = 3
	RelatedCountMax     = 6

	// Points per shared tag and per shared category.
	relatedTagPoints      = 2
	relatedCategoryPoints = 1
)

// RelatedSettings is the related-posts configuration.
type RelatedSettings struct {
	// Mode is RelatedModeCategory or RelatedModeScored.
	Mode string
	// Count is the number of scored related posts (3 to 6).
	Count int
}

// Scored reports whether the scored mode is on.
func (s RelatedSettings) Scored() bool { return s.Mode == RelatedModeScored }

// ReadRelatedSettings reads golem15.journal.related_mode (anything but
// "scored" is the category mode) and golem15.journal.related_count (unset
// or not a number: 3; otherwise clamped to 3..6).
func ReadRelatedSettings(cfg *compass.Config) RelatedSettings {
	out := RelatedSettings{Mode: RelatedModeCategory, Count: RelatedCountDefault}
	if cfg == nil {
		return out
	}
	if strings.EqualFold(strings.TrimSpace(cfg.String(RelatedModeKey)), RelatedModeScored) {
		out.Mode = RelatedModeScored
	}
	if n := cfg.Int(RelatedCountKey); n > 0 {
		out.Count = min(RelatedCountMax, max(RelatedCountMin, n))
	}
	return out
}

// publishedClause is the visitor rule of the public API (applyPublished in
// controllers/api): published, with a publish time in the past.
const publishedClause = "p.published = ? AND p.published_at IS NOT NULL AND p.published_at < ?"

// ScoredRelatedPosts is the scored mode's related posts of post: other posts
// sharing a tag or a category, ranked by 2 points per shared tag plus 1
// point per shared category, ties by the newest publish time (then the
// higher id), at most count. Posts that share nothing are never related.
// Visitors see published posts only; editors (includeDrafts) also see
// drafts, as the category mode's related posts do. One query computes the
// scores; the rows come back with their author, categories and tags.
func ScoredRelatedPosts(ctx context.Context, db *gorm.DB, post *models.Post, count int, includeDrafts bool) ([]models.Post, error) {
	if post == nil || count <= 0 {
		return []models.Post{}, nil
	}
	db = db.WithContext(ctx)
	q := db.Table("golem15_journal_posts AS p").
		Select("p.id, ? * COALESCE(st.n, 0) + ? * COALESCE(sc.n, 0) AS score", relatedTagPoints, relatedCategoryPoints).
		Joins(`LEFT JOIN (SELECT post_id, COUNT(*) AS n FROM golem15_journal_posts_tags
			WHERE tag_id IN (SELECT tag_id FROM golem15_journal_posts_tags WHERE post_id = ?)
			GROUP BY post_id) st ON st.post_id = p.id`, post.ID).
		Joins(`LEFT JOIN (SELECT post_id, COUNT(*) AS n FROM golem15_journal_posts_categories
			WHERE category_id IN (SELECT category_id FROM golem15_journal_posts_categories WHERE post_id = ?)
			GROUP BY post_id) sc ON sc.post_id = p.id`, post.ID).
		Where("p.id <> ?", post.ID).
		Where("(st.n > 0 OR sc.n > 0)")
	if !includeDrafts {
		q = q.Where(publishedClause, true, time.Now())
	}
	var ranked []struct {
		ID    uint
		Score int
	}
	if err := q.Order("score DESC, p.published_at DESC NULLS LAST, p.id DESC").Limit(count).Scan(&ranked).Error; err != nil {
		return nil, err
	}
	if len(ranked) == 0 {
		return []models.Post{}, nil
	}
	ids := make([]uint, 0, len(ranked))
	for _, r := range ranked {
		ids = append(ids, r.ID)
	}
	var rows []models.Post
	if err := db.Model(&models.Post{}).Preload("User").Preload("Categories").Preload("Tags").
		Where("id IN ?", ids).Find(&rows).Error; err != nil {
		return nil, err
	}
	byID := make(map[uint]models.Post, len(rows))
	for _, r := range rows {
		byID[r.ID] = r
	}
	out := make([]models.Post, 0, len(ids))
	for _, id := range ids {
		if r, ok := byID[id]; ok {
			out = append(out, r)
		}
	}
	return out, nil
}

// PrimaryCategoryID is the post's first category by name, ties by id (the
// order the :category URL param takes its category in); 0 without one.
func PrimaryCategoryID(ctx context.Context, db *gorm.DB, postID uint) uint {
	var rows []struct{ ID uint }
	err := db.WithContext(ctx).Table("golem15_journal_categories AS c").
		Select("c.id").
		Joins("JOIN golem15_journal_posts_categories AS pc ON pc.category_id = c.id").
		Where("pc.post_id = ?", postID).
		Order("c.name ASC, c.id ASC").
		Limit(1).
		Scan(&rows).Error
	if err != nil || len(rows) == 0 {
		return 0
	}
	return rows[0].ID
}

// CategoryNeighbour is the post's neighbour by publish time within its
// first category, in the direction of the post answer's previous_post and
// next_post: previous is the nearest published post published after it,
// next the nearest one published before it (ties by id). nil without a
// category or a neighbour. Published posts only, as for previous_post.
func CategoryNeighbour(ctx context.Context, db *gorm.DB, post *models.Post, previous bool) *models.Post {
	if post == nil {
		return nil
	}
	category := PrimaryCategoryID(ctx, db, post.ID)
	if category == 0 {
		return nil
	}
	op, dir := "<", "DESC"
	if previous {
		op, dir = ">", "ASC"
	}
	// The same query shape as the site-wide neighbours (siblingPost), plus
	// the category, so the row is read the same way.
	q := db.WithContext(ctx).Model(&models.Post{}).
		Where("published = ? AND published_at IS NOT NULL AND published_at < ?", true, time.Now()).
		Where("id <> ?", post.ID).
		Where("id IN (SELECT post_id FROM golem15_journal_posts_categories WHERE category_id = ?)", category)
	if post.PublishedAt != nil {
		q = q.Where("(published_at "+op+" ?) OR (published_at = ? AND id "+op+" ?)", post.PublishedAt, post.PublishedAt, post.ID)
	}
	var out models.Post
	if err := q.Order("published_at " + dir + ", id " + dir).Take(&out).Error; err != nil {
		return nil
	}
	return &out
}