package main

import (
	"database/sql"
	"errors"
	"fmt"
	"strings"

	_ "modernc.org/sqlite"
)

// 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"`
}

// 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
}

// 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
}

// Lifecycle buckets. A bookmark is in exactly one; favorite is orthogonal.
const (
	statusReading  = "reading"
	statusArchived = "archived"
	statusFinished = "finished"
)

const schema = `
CREATE TABLE IF NOT EXISTS bookmarks (
  key                TEXT PRIMARY KEY,
  site               TEXT NOT NULL,
  series_id          TEXT NOT NULL,
  title              TEXT,
  series_url         TEXT,
  cover              TEXT,
  last_chapter       TEXT,
  last_chapter_num   REAL,
  last_chapter_url   TEXT,
  favorite           INTEGER NOT NULL DEFAULT 0,
  latest_chapter     TEXT NOT NULL DEFAULT '',
  latest_chapter_num REAL,
  latest_checked_at  INTEGER NOT NULL DEFAULT 0,
  status             TEXT NOT NULL DEFAULT 'reading',
  updated_at         INTEGER NOT NULL
);`

// The columns above that databases created before them will be missing.
// SQLite has no ADD COLUMN IF NOT EXISTS, so each is added only when absent.
var addedColumns = []struct{ name, ddl string }{
	{"favorite", `ALTER TABLE bookmarks ADD COLUMN favorite INTEGER NOT NULL DEFAULT 0`},
	{"latest_chapter", `ALTER TABLE bookmarks ADD COLUMN latest_chapter TEXT NOT NULL DEFAULT ''`},
	{"latest_chapter_num", `ALTER TABLE bookmarks ADD COLUMN latest_chapter_num REAL`},
	// When the server last looked at this series, unix ms; 0 means never, and
	// sorts first so a new bookmark is picked up on the next tick with no
	// special case. Deliberately NOT in bookmarkColumns — see MarkLatestChecked.
	{"latest_checked_at", `ALTER TABLE bookmarks ADD COLUMN latest_checked_at INTEGER NOT NULL DEFAULT 0`},
	// Lifecycle bucket. The DEFAULT backfills every pre-existing row as
	// 'reading', so there is no separate migration step.
	{"status", `ALTER TABLE bookmarks ADD COLUMN status TEXT NOT NULL DEFAULT 'reading'`},
}

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`

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

// OpenStore opens (or creates) the SQLite database at path and applies the schema.
func OpenStore(path string) (*Store, error) {
	// busy_timeout guards against SQLITE_BUSY under the reverse proxy's
	// concurrent requests; a single writer connection keeps writes serialized.
	dsn := path
	if !strings.Contains(dsn, "?") {
		dsn += "?_pragma=busy_timeout(5000)&_pragma=journal_mode(WAL)"
	}
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, fmt.Errorf("open sqlite %q: %w", path, err)
	}
	db.SetMaxOpenConns(1)
	if _, err := db.Exec(schema); err != nil {
		db.Close()
		return nil, fmt.Errorf("apply schema: %w", err)
	}
	if err := migrateColumns(db); err != nil {
		db.Close()
		return nil, fmt.Errorf("migrate schema: %w", err)
	}
	return &Store{db: db}, nil
}

// migrateColumns brings a pre-existing bookmarks table up to the current
// schema. Safe to run on every start: columns already present are skipped.
func migrateColumns(db *sql.DB) error {
	have, err := existingColumns(db, "bookmarks")
	if err != nil {
		return err
	}
	for _, c := range addedColumns {
		if _, ok := have[c.name]; ok {
			continue
		}
		if _, err := db.Exec(c.ddl); err != nil {
			return fmt.Errorf("add column %q: %w", c.name, err)
		}
	}
	return nil
}

func existingColumns(db *sql.DB, table string) (map[string]struct{}, error) {
	rows, err := db.Query(`SELECT name FROM pragma_table_info(?)`, table)
	if err != nil {
		return nil, fmt.Errorf("read %s columns: %w", table, err)
	}
	defer rows.Close()

	out := map[string]struct{}{}
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, fmt.Errorf("scan column name: %w", err)
		}
		out[name] = struct{}{}
	}
	return out, rows.Err()
}

// scanBookmark reads one row in bookmarkColumns order, translating SQLite's
// integer bool and nullable latest_chapter_num into Go types.
//
// The optional columns are read through Null* types because rows predating
// this code (or written by hand) may hold NULL where the app only ever writes
// zero values. Only latest_chapter_num distinguishes the two: everywhere else
// NULL and the zero value mean the same thing to clients.
func scanBookmark(scan func(...any) error) (Bookmark, error) {
	var (
		b                                          Bookmark
		title, seriesURL, cover                    sql.NullString
		lastChapter, lastChapterURL, latestChapter sql.NullString
		status                                     sql.NullString
		lastChapterNum, latestChapterNum           sql.NullFloat64
		favorite                                   sql.NullInt64
	)
	if err := scan(
		&b.Key, &b.Site, &b.SeriesID, &title, &seriesURL, &cover,
		&lastChapter, &lastChapterNum, &lastChapterURL,
		&favorite, &latestChapter, &latestChapterNum, &b.UpdatedAt, &status,
	); err != nil {
		return Bookmark{}, err
	}
	b.Title = title.String
	b.SeriesURL = seriesURL.String
	b.Cover = cover.String
	b.LastChapter = lastChapter.String
	b.LastChapterNum = lastChapterNum.Float64
	b.LastChapterURL = lastChapterURL.String
	b.Favorite = favorite.Int64 != 0
	b.LatestChapter = latestChapter.String
	if latestChapterNum.Valid {
		b.LatestChapterNum = &latestChapterNum.Float64
	}
	// A NULL, empty, or unrecognised bucket (e.g. 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.
	b.Status = status.String
	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 = ?`, 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 NOT is SQLite's null-safe comparison. 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 column resolves 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' and
	// would overwrite an archived row on every PUT from a client that knows
	// nothing about the column. Resolved once here, an empty incoming status
	// 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.
	if _, err := tx.Exec(`
		INSERT INTO bookmarks (`+bookmarkColumns+`)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?,
		        COALESCE(NULLIF(?, ''), (SELECT status FROM bookmarks WHERE key = ?), 'reading'))
		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,
		  updated_at=CASE
		    WHEN bookmarks.last_chapter_num IS NOT 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.Key); err != nil {
		return Bookmark{}, fmt.Errorf("upsert %q: %w", b.Key, err)
	}

	stored, err := scanBookmark(tx.QueryRow(
		`SELECT `+bookmarkColumns+` FROM bookmarks WHERE key = ?`, 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 = ?`, 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 IS NOT NULL AND series_url <> ''
		  AND status IS NOT 'finished'
		  AND latest_checked_at <= ?
		ORDER BY latest_checked_at ASC
		LIMIT ?`, 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 = ? WHERE key = ?`, ts, key); err != nil {
		return fmt.Errorf("mark checked %q: %w", key, err)
	}
	return nil
}