package store

import (
	"database/sql"
	"embed"
	"errors"
	"fmt"
	"io/fs"
	"path"
	"regexp"
	"slices"
	"strconv"
	"strings"

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

// Bookmark is one tracked series, keyed "<site>:<series_id>" across both sites.
//
// LastChapter* is the user's read progress; LatestChapter* is the newest
// chapter the site has published, captured opportunistically by the userscript.
type Bookmark struct {
	Key              string   `json:"key"`
	Site             string   `json:"site"`
	SeriesID         string   `json:"series_id"`
	Title            string   `json:"title"`
	SeriesURL        string   `json:"series_url"`
	Cover            string   `json:"cover"`
	LastChapter      string   `json:"last_chapter"`
	LastChapterNum   float64  `json:"last_chapter_num"`
	LastChapterURL   string   `json:"last_chapter_url"`
	Favorite         bool     `json:"favorite"`
	LatestChapter    string   `json:"latest_chapter"`
	LatestChapterNum *float64 `json:"latest_chapter_num"` // nil until first captured
	UpdatedAt        int64    `json:"updated_at"`         // unix ms; see Upsert
	// Status is the lifecycle bucket: reading, archived, or finished.
	// Archived series stay polled for new chapters; finished ones do not.
	// Empty on the way in means "no opinion" — see Upsert.
	Status string `json:"status"`
	// Kind is the library bucket: manga or novel. Empty on the way in means
	// "no opinion" — see Upsert.
	Kind string `json:"kind"`
}

// HasNewChapter reports whether the site has published past the read point.
// A nil LatestChapterNum means nothing has been captured yet, which is not the
// same as "nothing new".
func (b Bookmark) HasNewChapter() bool {
	return b.LatestChapterNum != nil && *b.LatestChapterNum > b.LastChapterNum
}

// chapterLeadIn matches the prefix the userscript and the poller both write
// ("Chapter 250"), so the UI can add exactly one "Ch " of its own instead of
// doubling it. A manual edit through the web UI stores a bare "250", which is
// the same string minus the lead-in.
var chapterLeadIn = regexp.MustCompile(`(?i)^\s*(?:chapter|ch\.?)\s*`)

func displayChapter(raw string, num float64) string {
	rest := strings.TrimSpace(chapterLeadIn.ReplaceAllString(raw, ""))
	if rest == "" {
		rest = strconv.FormatFloat(num, 'f', -1, 64)
	}
	// "Ch " only makes sense in front of a number; anything else is a label the
	// site gave us, so pass it through as written.
	if rest[0] < '0' || rest[0] > '9' {
		return rest
	}
	return "Ch " + rest
}

// DisplayChapter is the read-progress line: one canonical "Ch N" whatever
// format the write came in as.
func (b Bookmark) DisplayChapter() string {
	return displayChapter(b.LastChapter, b.LastChapterNum)
}

// DisplayLatest is the same for the newest published chapter, which arrives
// with the same "Chapter N" lead-in from both the userscript and the poller.
func (b Bookmark) DisplayLatest() string {
	var num float64
	if b.LatestChapterNum != nil {
		num = *b.LatestChapterNum
	}
	return displayChapter(b.LatestChapter, num)
}

// ContinueURL is where the Continue button points: the chapter last read, or
// the series page when no chapter URL was ever captured.
func (b Bookmark) ContinueURL() string {
	if b.LastChapterURL != "" {
		return b.LastChapterURL
	}
	return b.SeriesURL
}

// Initial is the monogram the web UI shows in place of a cover when the
// source site never gave us an og:image. First rune, uppercased; "?" when even
// the title is missing, so the slot is never empty.
func (b Bookmark) Initial() string {
	for _, r := range b.Title {
		return strings.ToUpper(string(r))
	}
	return "?"
}

// Library buckets. A bookmark is in exactly one. This cannot be derived from
// Site: asurascans serves manga and novels from the same /comics/ path, so the
// userscript that recorded the page is the only party that knows which.
const (
	KindManga = "manga"
	KindNovel = "novel"
)

// Lifecycle buckets. A bookmark is in exactly one; favorite is orthogonal.
const (
	StatusReading  = "reading"
	StatusArchived = "archived"
	StatusFinished = "finished"
)

//go:embed migrations/*.sql
var migrations embed.FS

// bookmarkColumns is the only value ever concatenated into query text. It is a
// compile-time constant; every request value is bound as a parameter.
const bookmarkColumns = `key, site, series_id, title, series_url, cover,
	last_chapter, last_chapter_num, last_chapter_url,
	favorite, latest_chapter, latest_chapter_num, updated_at, status, kind`

// Store is the Postgres-backed bookmark store.
type Store struct {
	db *sql.DB
}

// Open connects to Postgres at url — a libpq connection URL such as
// "postgres://user:pass@host:5432/bookmarks?sslmode=disable" — and brings its
// schema up to date.
func Open(url string) (*Store, error) {
	db, err := sql.Open("pgx", url)
	if err != nil {
		return nil, fmt.Errorf("open postgres: %w", err)
	}
	if err := migrate(db); err != nil {
		db.Close()
		return nil, fmt.Errorf("migrate: %w", err)
	}
	return &Store{db: db}, nil
}

// migrate applies every embedded migration this database has not recorded, in
// filename order, each in its own transaction. Files are named
// "<version>_<name>.sql" and are append-only: editing an applied file changes
// nothing, because schema_migrations is how a database remembers what it ran.
// Runs on every start and is a no-op once current.
func migrate(db *sql.DB) error {
	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_migrations (
		version    bigint PRIMARY KEY,
		applied_at timestamptz NOT NULL DEFAULT now())`); err != nil {
		return fmt.Errorf("create version table: %w", err)
	}

	names, err := fs.Glob(migrations, "migrations/*.sql")
	if err != nil {
		return err
	}
	slices.Sort(names)

	for _, name := range names {
		version, err := strconv.ParseInt(strings.SplitN(path.Base(name), "_", 2)[0], 10, 64)
		if err != nil {
			return fmt.Errorf("migration %q: filename must start with a version number", name)
		}
		body, err := migrations.ReadFile(name)
		if err != nil {
			return err
		}
		if err := applyMigration(db, version, string(body)); err != nil {
			return fmt.Errorf("migration %q: %w", name, err)
		}
	}
	return nil
}

// applyMigration runs one migration and records its version in the same
// transaction, so an interrupted start leaves neither half behind.
func applyMigration(db *sql.DB, version int64, body string) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	var applied bool
	if err := tx.QueryRow(
		`SELECT EXISTS (SELECT 1 FROM schema_migrations WHERE version = $1)`,
		version).Scan(&applied); err != nil {
		return err
	}
	if applied {
		return nil
	}
	// No parameters, so this goes over the simple protocol and a migration may
	// hold more than one statement.
	if _, err := tx.Exec(body); err != nil {
		return err
	}
	if _, err := tx.Exec(`INSERT INTO schema_migrations (version) VALUES ($1)`, version); err != nil {
		return err
	}
	return tx.Commit()
}

// scanBookmark reads one row in bookmarkColumns order. Every column is NOT
// NULL except latest_chapter_num, where NULL means "never captured" — a
// distinct state from chapter zero, and the reason for the pointer.
func scanBookmark(scan func(...any) error) (Bookmark, error) {
	var (
		b                Bookmark
		latestChapterNum sql.NullFloat64
	)
	if err := scan(
		&b.Key, &b.Site, &b.SeriesID, &b.Title, &b.SeriesURL, &b.Cover,
		&b.LastChapter, &b.LastChapterNum, &b.LastChapterURL,
		&b.Favorite, &b.LatestChapter, &latestChapterNum, &b.UpdatedAt, &b.Status, &b.Kind,
	); err != nil {
		return Bookmark{}, err
	}
	if latestChapterNum.Valid {
		b.LatestChapterNum = &latestChapterNum.Float64
	}
	// An unrecognised bucket (a hand-edited row) would leave the row in no list
	// at all, so anything outside the three known buckets reads as the default
	// rather than being passed through.
	if b.Status != StatusReading && b.Status != StatusArchived && b.Status != StatusFinished {
		b.Status = StatusReading
	}
	return b, nil
}

// Close releases the underlying database handle.
func (s *Store) Close() error { return s.db.Close() }

// List returns every bookmark, newest activity first.
func (s *Store) List() ([]Bookmark, error) {
	rows, err := s.db.Query(`SELECT ` + bookmarkColumns + `
		FROM bookmarks
		ORDER BY updated_at DESC`)
	if err != nil {
		return nil, fmt.Errorf("query bookmarks: %w", err)
	}
	defer rows.Close()

	out := []Bookmark{}
	for rows.Next() {
		b, err := scanBookmark(rows.Scan)
		if err != nil {
			return nil, fmt.Errorf("scan bookmark: %w", err)
		}
		out = append(out, b)
	}
	return out, rows.Err()
}

// Get returns one bookmark by key. A missing key is not an error: ok is false
// and err is nil. UI mutations read-modify-write through this so they preserve
// the fields they do not touch.
func (s *Store) Get(key string) (Bookmark, bool, error) {
	b, err := scanBookmark(s.db.QueryRow(
		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = $1`, key).Scan)
	if errors.Is(err, sql.ErrNoRows) {
		return Bookmark{}, false, nil
	}
	if err != nil {
		return Bookmark{}, false, fmt.Errorf("get %q: %w", key, err)
	}
	return b, true, nil
}

// Upsert inserts or replaces a bookmark by key (last-write-wins) and returns
// the row as actually stored.
//
// b.UpdatedAt is only a candidate: it is applied when the row is new or when
// last_chapter_num changes, and otherwise the stored value is kept. Clients
// order their list by updated_at, so favoriting a series or recording a newly
// published chapter must not disturb that order — only real reading progress
// does. Callers must therefore use the returned bookmark, not the argument.
func (s *Store) Upsert(b Bookmark) (Bookmark, error) {
	tx, err := s.db.Begin()
	if err != nil {
		return Bookmark{}, fmt.Errorf("begin %q: %w", b.Key, err)
	}
	defer tx.Rollback()

	var latestNum any
	if b.LatestChapterNum != nil {
		latestNum = *b.LatestChapterNum
	}

	// IS DISTINCT FROM is Postgres's null-safe comparison, and it is what
	// implements the ordering rule. Within DO UPDATE, a bare column is the
	// stored row and excluded.* is the incoming one; a brand-new key never
	// reaches this clause, so it keeps the fresh timestamp from VALUES.
	//
	// The status and kind columns resolve on the VALUES side, not in the
	// conflict clause: excluded.* is the row *after* these expressions are
	// evaluated, so a default applied there would look identical to a real
	// 'reading' / 'manga' and would overwrite an archived or novel row on
	// every PUT from a client that knows nothing about the column. Resolved
	// once here, an empty incoming status or kind means "keep what is
	// stored", and only a brand-new row falls through to the literal
	// default. The subquery runs inside this transaction, so it sees the
	// row this statement is about to conflict with.
	//
	// The ::text casts are load-bearing: inside COALESCE/NULLIF there is no
	// target column to infer the parameter type from, and Postgres rejects the
	// statement rather than guessing.
	if _, err := tx.Exec(`
		INSERT INTO bookmarks (`+bookmarkColumns+`)
		VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13,
		        COALESCE(NULLIF($14::text, ''), (SELECT status FROM bookmarks WHERE key = $1), 'reading'),
		        COALESCE(NULLIF($15::text, ''), (SELECT kind FROM bookmarks WHERE key = $1), 'manga'))
		ON CONFLICT (key) DO UPDATE SET
		  site=excluded.site, series_id=excluded.series_id, title=excluded.title,
		  series_url=excluded.series_url, cover=excluded.cover,
		  last_chapter=excluded.last_chapter, last_chapter_num=excluded.last_chapter_num,
		  last_chapter_url=excluded.last_chapter_url,
		  favorite=excluded.favorite,
		  latest_chapter=excluded.latest_chapter,
		  latest_chapter_num=excluded.latest_chapter_num,
		  status=excluded.status,
		  kind=excluded.kind,
		  updated_at=CASE
		    WHEN bookmarks.last_chapter_num IS DISTINCT FROM excluded.last_chapter_num
		    THEN excluded.updated_at
		    ELSE bookmarks.updated_at
		  END`,
		b.Key, b.Site, b.SeriesID, b.Title, b.SeriesURL, b.Cover,
		b.LastChapter, b.LastChapterNum, b.LastChapterURL,
		b.Favorite, b.LatestChapter, latestNum, b.UpdatedAt,
		b.Status, b.Kind); err != nil {
		return Bookmark{}, fmt.Errorf("upsert %q: %w", b.Key, err)
	}

	stored, err := scanBookmark(tx.QueryRow(
		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = $1`, b.Key).Scan)
	if err != nil {
		return Bookmark{}, fmt.Errorf("read back %q: %w", b.Key, err)
	}
	if err := tx.Commit(); err != nil {
		return Bookmark{}, fmt.Errorf("commit %q: %w", b.Key, err)
	}
	return stored, nil
}

// Delete removes a bookmark by key. Deleting a missing key is not an error.
func (s *Store) Delete(key string) error {
	if _, err := s.db.Exec(`DELETE FROM bookmarks WHERE key = $1`, key); err != nil {
		return fmt.Errorf("delete %q: %w", key, err)
	}
	return nil
}

// DueForLatestCheck returns bookmarks whose server-side latest-chapter check has
// aged past cutoffMs, least-recently-checked first, at most limit of them.
//
// Oldest-first is what keeps the poller fair when the backlog outgrows its
// throughput: the most neglected series is always next, so a large collection
// refreshes uniformly slower rather than leaving a tail that never refreshes at
// all. The userscript sorts its own queue the same way (L453).
//
// Bookmarks with no series_url are skipped — there is nothing to fetch, which
// is the same filter the userscript applies at L452.
//
// Finished series are excluded: nothing more is coming, so fetching them only
// burns requests. Archived ones are deliberately still polled — knowing what a
// shelved series is up to is the whole reason for archiving instead of deleting.
func (s *Store) DueForLatestCheck(cutoffMs int64, limit int) ([]Bookmark, error) {
	rows, err := s.db.Query(`SELECT `+bookmarkColumns+`
		FROM bookmarks
		WHERE series_url <> ''
		  AND status IS DISTINCT FROM 'finished'
		  AND latest_checked_at <= $1
		ORDER BY latest_checked_at ASC
		LIMIT $2`, cutoffMs, limit)
	if err != nil {
		return nil, fmt.Errorf("query due bookmarks: %w", err)
	}
	defer rows.Close()

	out := []Bookmark{}
	for rows.Next() {
		b, err := scanBookmark(rows.Scan)
		if err != nil {
			return nil, fmt.Errorf("scan due bookmark: %w", err)
		}
		out = append(out, b)
	}
	return out, rows.Err()
}

// MarkLatestChecked records that the server looked at key at ts, whatever the
// look turned up. Marking a missing key is not an error: the row may have been
// deleted while a fetch was in flight.
//
// This is the one write that does not go through Upsert, and the column is kept
// out of bookmarkColumns on purpose. PUT /bookmarks/{key} decodes a whole
// Bookmark from the client and Upsert writes every column it knows about, so a
// userscript PUT — which has no idea this field exists — would write a zero and
// reset the cooldown, making the poller re-fetch that series every tick for as
// long as the user kept reading it.
func (s *Store) MarkLatestChecked(key string, ts int64) error {
	if _, err := s.db.Exec(
		`UPDATE bookmarks SET latest_checked_at = $1 WHERE key = $2`, ts, key); err != nil {
		return fmt.Errorf("mark checked %q: %w", key, err)
	}
	return nil
}

// LatestCheckedAt reads the column MarkLatestChecked writes. It exists for
// tests outside this package (the poller's own tests assert on cooldown
// bookkeeping) — see MarkLatestChecked for why the field itself stays off
// Bookmark.
func (s *Store) LatestCheckedAt(key string) (int64, error) {
	var ts int64
	if err := s.db.QueryRow(
		`SELECT latest_checked_at FROM bookmarks WHERE key = $1`, key).Scan(&ts); err != nil {
		return 0, fmt.Errorf("latest checked at %q: %w", key, err)
	}
	return ts, nil
}