package main

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

	"modernc.org/sqlite"
	sqlite3 "modernc.org/sqlite/lib"
)

var schemaStatements = []string{
	`CREATE TABLE IF NOT EXISTS runs (
		id          INTEGER PRIMARY KEY,
		chapter_id  INTEGER NOT NULL,
		department  TEXT    NOT NULL,
		rep_user_id INTEGER NOT NULL,
		status      TEXT    NOT NULL,
		started_at  TEXT    NOT NULL DEFAULT CURRENT_TIMESTAMP,
		ended_at    TEXT
	)`,
	`CREATE UNIQUE INDEX IF NOT EXISTS one_run_per_dept
	ON runs(chapter_id, department) WHERE status = 'running'`,
	`CREATE TABLE IF NOT EXISTS people (
		id               INTEGER PRIMARY KEY,
		email            TEXT,
		chapter_id       INTEGER,
		department       TEXT,
		appointment_type TEXT,
		is_rep           INTEGER NOT NULL DEFAULT 0,
		is_eligible      INTEGER NOT NULL DEFAULT 0,
		synced_at        TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
	)`,
	`CREATE INDEX IF NOT EXISTS people_dept ON people(chapter_id, department)`,
	`CREATE TABLE IF NOT EXISTS sync_state (
		key   TEXT PRIMARY KEY,
		value TEXT NOT NULL
	)`,
}

type SQLStore struct{ db *sql.DB }

func OpenStore(path string) (*SQLStore, error) {
	db, err := sql.Open("sqlite",
	"file:"+path+"?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)")
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(1)
	for i, stmt := range schemaStatements {
		if _, err := db.Exec(stmt); err != nil {
			return nil, fmt.Errorf("schema statement %d: %w", i, err)
		}
	}
	return &SQLStore{db: db}, nil
}

// RepsFor returns the user IDs of every rep for a department, ordered by
// ID so assignment is deterministic across runs.
func (s *SQLStore) RepsFor(chapterID int64, dept string) ([]int64, error) {
	return s.userIDs(`SELECT id FROM people
		WHERE is_rep = 1 AND chapter_id = ? AND department = ?
		ORDER BY id`, chapterID, dept)
}

func (s *SQLStore) EligibleMembers(chapterID int64, dept string) ([]int64, error) {
	return s.userIDs(`SELECT id FROM people
		WHERE is_eligible = 1 AND is_rep = 0 AND chapter_id = ? AND department = ?
		ORDER BY id`, chapterID, dept)
}

func (s *SQLStore) userIDs(query string, args ...any) ([]int64, error) {
	rows, err := s.db.Query(query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []int64
	for rows.Next() {
		var id int64
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		out = append(out, id)
	}
	return out, rows.Err()
}

func (s *SQLStore) AcquireLock(chapterID int64, dept string, repID int64) (int64, error) {
	res, err := s.db.Exec(
		`INSERT INTO runs (chapter_id, department, rep_user_id, status)
		VALUES (?, ?, ?, 'running')`, chapterID, dept, repID)
		if err != nil {
			var serr *sqlite.Error
			if errors.As(err, &serr) && serr.Code() == sqlite3.SQLITE_CONSTRAINT_UNIQUE {
				return 0, ErrLocked
			}
			return 0, ErrLocked
		}
		return res.LastInsertId()
	}

	func (s *SQLStore) ReleaseLock(runID int64) error {
		_, err := s.db.Exec(
			`UPDATE runs SET status='done', ended_at=CURRENT_TIMESTAMP WHERE id=?`, runID)
			return err
		}

		func (s *SQLStore) SweepStaleLocks() error {
			_, err := s.db.Exec(
				`UPDATE runs SET status='crashed', ended_at=CURRENT_TIMESTAMP
				WHERE status='running'`)
				return err
			}

			func (s *SQLStore) UpsertPeople(users []User, eligible map[string]bool) error {
				tx, err := s.db.Begin()
				if err != nil {
					return err
				}
				defer tx.Rollback()

				stmt, err := tx.Prepare(`
				INSERT INTO people (id, email, chapter_id, department, appointment_type, is_rep, is_eligible, synced_at)
				VALUES (?, ?, ?, ?, ?, ?, ?, CURRENT_TIMESTAMP)
				ON CONFLICT(id) DO UPDATE SET
				email=excluded.email,
				chapter_id=excluded.chapter_id,
				department=excluded.department,
				appointment_type=excluded.appointment_type,
				is_rep=excluded.is_rep,
				is_rep=excluded.is_rep,
				synced_at=CURRENT_TIMESTAMP`)
				if err != nil {
					return err
				}
				defer stmt.Close()

				//loop body

				for _, u := range users {
					rep, elig := 0, 0
					if u.IsRep {
						rep = 1
					}
					if u.Eligible(eligible) {
						elig = 1
					}
					_, err := stmt.Exec(u.ID, u.Email, u.ChapterID,
					normalizeDept(u.Department),
					strings.Join(u.AppointmentTypes, ","),
					rep, elig)
					if err != nil {
						return fmt.Errorf("upserting user %d: %w", u.ID, err)
					}
				}
				return tx.Commit()
			}

			func (s *SQLStore) LastSync() (int64, error) {
				var v string
				err := s.db.QueryRow(`SELECT value FROM sync_state WHERE key='users_synced_at'`).Scan(&v)
				if err == sql.ErrNoRows {
					return 0, nil
				}
				if err != nil {
					return 0, err
				}
				return strconv.ParseInt(v, 10, 64)
			}

			func (s *SQLStore) SetLastSync(ts int64) error {
				_, err := s.db.Exec(`
				INSERT INTO sync_state (key, value) VALUES ('users_synced_at', ?)
				ON CONFLICT(key) DO UPDATE SET value=excluded.value`,
				strconv.FormatInt(ts, 10))
				return err
			}