package repository

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

	"github.com/jackc/pgx/v5"
	"github.com/prabhupadasays/spsays-bff/internal/model"
	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/v2/mongo"
)

// VaniRepo backs "Vāṇī of the Day": the daily pick lives in Postgres
// (vani_of_the_day) while the candidate content is sampled from Mongo (the
// verses / prose_chapters / transcriptions collections).
var (
	// ErrVaniRefInvalid is a malformed content id.
	ErrVaniRefInvalid = errors.New("not a valid content reference")
	// ErrVaniRefNotFound is a well-formed id that matches nothing.
	ErrVaniRefNotFound = errors.New("that content no longer exists")
)

type VaniRepo struct {
	pg    *Postgres
	mongo *MongoDB
}

func NewVaniRepo(pg *Postgres, m *MongoDB) *VaniRepo {
	return &VaniRepo{pg: pg, mongo: m}
}

// --- Postgres: the per-day record ---

// GetForDay returns the pick stored for the given UTC day, or (nil, nil) when
// nothing has been chosen yet.
func (r *VaniRepo) GetForDay(ctx context.Context, day time.Time) (*model.VaniPick, error) {
	var kind, refID string
	var payload []byte
	err := r.pg.Pool.QueryRow(ctx,
		`SELECT kind, ref_id, payload FROM vani_of_the_day WHERE day = $1`, day,
	).Scan(&kind, &refID, &payload)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("get vani for day: %w", err)
	}
	var p model.VaniPayload
	if err := json.Unmarshal(payload, &p); err != nil {
		return nil, fmt.Errorf("decode vani payload: %w", err)
	}
	return &model.VaniPick{Day: day, Kind: kind, RefID: refID, Payload: p}, nil
}

// RecentRefIDs returns the ref_ids chosen on or after `since` — the 90-day
// exclusion set for the picker.
func (r *VaniRepo) RecentRefIDs(ctx context.Context, since time.Time) ([]string, error) {
	rows, err := r.pg.Pool.Query(ctx,
		`SELECT ref_id FROM vani_of_the_day WHERE day >= $1`, since)
	if err != nil {
		return nil, fmt.Errorf("recent vani ref ids: %w", err)
	}
	defer rows.Close()
	var out []string
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		out = append(out, id)
	}
	return out, rows.Err()
}

// Insert stores the day's pick, ignoring a race where another request already
// wrote today's (ON CONFLICT (day) DO NOTHING). Callers re-read GetForDay to
// get the authoritative row.
func (r *VaniRepo) Insert(ctx context.Context, pick *model.VaniPick) error {
	b, err := json.Marshal(pick.Payload)
	if err != nil {
		return err
	}
	_, err = r.pg.Pool.Exec(ctx,
		`INSERT INTO vani_of_the_day (day, kind, ref_id, payload)
		 VALUES ($1, $2, $3, $4::jsonb)
		 ON CONFLICT (day) DO NOTHING`,
		pick.Day, pick.Kind, pick.RefID, b)
	if err != nil {
		return fmt.Errorf("insert vani pick: %w", err)
	}
	return nil
}

// Upsert writes a day's pick, REPLACING any existing one.
//
// Distinct from Insert, which is ON CONFLICT DO NOTHING because the automatic
// picker must never overwrite a day already decided. An admin choosing the day
// deliberately is the one case that should win.
func (r *VaniRepo) Upsert(ctx context.Context, pick *model.VaniPick) error {
	b, err := json.Marshal(pick.Payload)
	if err != nil {
		return err
	}
	_, err = r.pg.Pool.Exec(ctx,
		`INSERT INTO vani_of_the_day (day, kind, ref_id, payload)
		 VALUES ($1, $2, $3, $4::jsonb)
		 ON CONFLICT (day) DO UPDATE
		     SET kind = EXCLUDED.kind,
		         ref_id = EXCLUDED.ref_id,
		         payload = EXCLUDED.payload`,
		pick.Day, pick.Kind, pick.RefID, b)
	if err != nil {
		return fmt.Errorf("upsert vani pick: %w", err)
	}
	return nil
}

// Clear removes a day's pick, so the automatic picker chooses again.
func (r *VaniRepo) Clear(ctx context.Context, day time.Time) error {
	_, err := r.pg.Pool.Exec(ctx, `DELETE FROM vani_of_the_day WHERE day = $1`, day)
	if err != nil {
		return fmt.Errorf("clear vani pick: %w", err)
	}
	return nil
}

// PicksFrom lists decided days from `from` onward, for the admin schedule.
func (r *VaniRepo) PicksFrom(ctx context.Context, from time.Time, limit int) ([]model.VaniPick, error) {
	rows, err := r.pg.Pool.Query(ctx,
		`SELECT day, kind, ref_id, payload FROM vani_of_the_day
		 WHERE day >= $1 ORDER BY day LIMIT $2`, from, limit)
	if err != nil {
		return nil, fmt.Errorf("list vani picks: %w", err)
	}
	defer rows.Close()

	out := []model.VaniPick{}
	for rows.Next() {
		var p model.VaniPick
		var raw []byte
		if err := rows.Scan(&p.Day, &p.Kind, &p.RefID, &raw); err != nil {
			return nil, fmt.Errorf("scan vani pick: %w", err)
		}
		if err := json.Unmarshal(raw, &p.Payload); err != nil {
			return nil, fmt.Errorf("decode vani payload: %w", err)
		}
		out = append(out, p)
	}
	return out, rows.Err()
}

// BookTitle resolves a book code to its display title (from book_meta.data.title),
// or "" if unknown. Used to label a prose pick with its book name. Decoding into
// a typed struct avoids the bson.M-nested-doc pitfall (nested documents decode
// as bson.D, so a `raw["data"].(bson.M)` assertion would silently fail).
func (r *VaniRepo) BookTitle(ctx context.Context, book string) string {
	var doc struct {
		Data struct {
			Title string `bson:"title"`
		} `bson:"data"`
	}
	if err := r.mongo.Collection("book_meta").
		FindOne(ctx, bson.D{{Key: "book", Value: book}}).Decode(&doc); err != nil {
		return ""
	}
	return doc.Data.Title
}

// --- Mongo: random candidate sampling ---

// excludeIDs turns hex _id strings into a $nin ObjectID array.
func excludeIDs(hexes []string) bson.A {
	arr := bson.A{}
	for _, h := range hexes {
		if oid, err := bson.ObjectIDFromHex(h); err == nil {
			arr = append(arr, oid)
		}
	}
	return arr
}

func (r *VaniRepo) sampleOne(ctx context.Context, coll string, match bson.D, out interface{}) (bool, error) {
	cur, err := r.mongo.Collection(coll).Aggregate(ctx, mongo.Pipeline{
		bson.D{{Key: "$match", Value: match}},
		bson.D{{Key: "$sample", Value: bson.D{{Key: "size", Value: 1}}}},
	})
	if err != nil {
		return false, fmt.Errorf("sample %s: %w", coll, err)
	}
	defer cur.Close(ctx)
	if cur.Next(ctx) {
		if err := cur.Decode(out); err != nil {
			return false, err
		}
		return true, nil
	}
	return false, cur.Err()
}

// oneByHex loads a single document by its _id hex. Shared by the three
// admin-pick lookups, which differ only in collection and target type.
func (r *VaniRepo) oneByHex(ctx context.Context, coll, hex string, out interface{}) error {
	oid, err := bson.ObjectIDFromHex(hex)
	if err != nil {
		return ErrVaniRefInvalid
	}
	err = r.mongo.Collection(coll).FindOne(ctx, bson.D{{Key: "_id", Value: oid}}).Decode(out)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return ErrVaniRefNotFound
	}
	if err != nil {
		return fmt.Errorf("load %s %s: %w", coll, hex, err)
	}
	return nil
}

// TranscriptBySlug loads a lecture by its URL slug.
//
// Search cannot do this: the slug is not an indexed field, so querying
// "720720sb-london" matches on tokens like "london" and returns whatever else
// mentions it. Resolving the slug directly is the only reliable way to pin a
// specific item someone already has the URL for.
func (r *VaniRepo) TranscriptBySlug(ctx context.Context, slug string) (*TranscriptionDoc, error) {
	var t TranscriptionDoc
	err := r.mongo.Collection("transcriptions").
		FindOne(ctx, bson.D{{Key: "slug", Value: slug}}).Decode(&t)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return nil, ErrVaniRefNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("transcript by slug: %w", err)
	}
	return &t, nil
}

// ProseBySlug loads a prose chapter by book and slug.
func (r *VaniRepo) ProseBySlug(ctx context.Context, book, slug string) (*ProseChapterDoc, error) {
	var p ProseChapterDoc
	err := r.mongo.Collection("prose_chapters").FindOne(ctx, bson.D{
		{Key: "book", Value: book},
		{Key: "slug", Value: slug},
	}).Decode(&p)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return nil, ErrVaniRefNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("prose by slug: %w", err)
	}
	return &p, nil
}

// VerseByRef loads a verse by its book/division/chapter/verse coordinates,
// which is what a verse URL carries.
func (r *VaniRepo) VerseByRef(ctx context.Context, book string, division *string, chapter, verse int) (*VerseDoc, error) {
	filter := bson.D{
		{Key: "book", Value: book},
		{Key: "chapter", Value: chapter},
		{Key: "verse", Value: verse},
	}
	if division != nil && *division != "" {
		filter = append(filter, bson.E{Key: "division", Value: *division})
	}
	var v VerseDoc
	err := r.mongo.Collection("verses").FindOne(ctx, filter).Decode(&v)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return nil, ErrVaniRefNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("verse by ref: %w", err)
	}
	return &v, nil
}

// VerseByHex / ProseByHex / TranscriptByHex load a specific item an admin has
// chosen. The payload is then built by the same builders the random picker
// uses, so a pinned pick renders identically to an automatic one.
func (r *VaniRepo) VerseByHex(ctx context.Context, hex string) (*VerseDoc, error) {
	var v VerseDoc
	if err := r.oneByHex(ctx, "verses", hex, &v); err != nil {
		return nil, err
	}
	return &v, nil
}

func (r *VaniRepo) ProseByHex(ctx context.Context, hex string) (*ProseChapterDoc, error) {
	var p ProseChapterDoc
	if err := r.oneByHex(ctx, "prose_chapters", hex, &p); err != nil {
		return nil, err
	}
	return &p, nil
}

func (r *VaniRepo) TranscriptByHex(ctx context.Context, hex string) (*TranscriptionDoc, error) {
	var t TranscriptionDoc
	if err := r.oneByHex(ctx, "transcriptions", hex, &t); err != nil {
		return nil, err
	}
	return &t, nil
}

// SampleVerse returns a random verse with a translation, excluding the given
// _id hexes. Returns nil when nothing matches.
func (r *VaniRepo) SampleVerse(ctx context.Context, excludeHex []string) (*VerseDoc, error) {
	match := bson.D{
		{Key: "_id", Value: bson.D{{Key: "$nin", Value: excludeIDs(excludeHex)}}},
		{Key: "translation", Value: bson.D{{Key: "$exists", Value: true}, {Key: "$ne", Value: ""}}},
	}
	var d VerseDoc
	ok, err := r.sampleOne(ctx, "verses", match, &d)
	if err != nil || !ok {
		return nil, err
	}
	return &d, nil
}

// SampleProse returns a random prose chapter with body text, excluding the
// given _id hexes.
func (r *VaniRepo) SampleProse(ctx context.Context, excludeHex []string) (*ProseChapterDoc, error) {
	match := bson.D{
		{Key: "_id", Value: bson.D{{Key: "$nin", Value: excludeIDs(excludeHex)}}},
		{Key: "paragraphs.0", Value: bson.D{{Key: "$exists", Value: true}}},
	}
	var d ProseChapterDoc
	ok, err := r.sampleOne(ctx, "prose_chapters", match, &d)
	if err != nil || !ok {
		return nil, err
	}
	return &d, nil
}

// SampleTranscript returns a random published transcript with content,
// excluding the given _id hexes.
func (r *VaniRepo) SampleTranscript(ctx context.Context, excludeHex []string) (*TranscriptionDoc, error) {
	match := bson.D{
		{Key: "_id", Value: bson.D{{Key: "$nin", Value: excludeIDs(excludeHex)}}},
		{Key: "isPublished", Value: true},
		{Key: "content.0", Value: bson.D{{Key: "$exists", Value: true}}},
	}
	var d TranscriptionDoc
	ok, err := r.sampleOne(ctx, "transcriptions", match, &d)
	if err != nil || !ok {
		return nil, err
	}
	return &d, nil
}