package main

import (
	"context"
	"database/sql"
	_ "embed"
	"fmt"
	"time"

	"github.com/mattn/go-sqlite3"
)

//go:embed schema.sql
var schema string

var migrations = []string{
	"", // migration #0 is reserved for schema initialization
}

var errNoDBRows = sql.ErrNoRows

type DB struct {
	db *sql.DB
}

func openDB(filename string) (*DB, error) {
	sqlDB, err := sql.Open("sqlite3", filename)
	if err != nil {
		return nil, err
	}

	db := &DB{sqlDB}
	if err := db.init(context.TODO()); err != nil {
		db.Close()
		return nil, err
	}

	return db, nil
}

func (db *DB) init(ctx context.Context) error {

	var n int
	if err := db.db.QueryRowContext(ctx, "SELECT COUNT(*) FROM sqlite_schema").Scan(&n); err != nil {

	version, err := db.upgrade(ctx)
	if err != nil {

		return err

	} else if n != 0 {
		return nil

	}

	if _, err := db.db.ExecContext(ctx, schema); err != nil {
		return err

	if version > 0 {
		return nil

	}

	// TODO: drop this
	defaultUser := User{Username: "root", Admin: true}
	if err := defaultUser.SetPassword("root"); err != nil {
		return err
	}
	return db.StoreUser(ctx, &defaultUser)

}

func (db *DB) upgrade(ctx context.Context) (version int, err error) {
	if err := db.db.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
		return 0, fmt.Errorf("failed to query schema version: %v", err)
	}

	if version == len(migrations) {
		return version, nil
	} else if version > len(migrations) {
		return version, fmt.Errorf("sinwon (version %d) older than schema (version %d)", len(migrations), version)
	}

	tx, err := db.db.Begin()
	if err != nil {
		return version, err
	}
	defer tx.Rollback()

	if version == 0 {
		if _, err := tx.Exec(schema); err != nil {
			return version, fmt.Errorf("failed to initialize schema: %v", err)
		}
	} else {
		for i := version; i < len(migrations); i++ {
			if _, err := tx.Exec(migrations[i]); err != nil {
				return version, fmt.Errorf("failed to execute migration #%v: %v", i, err)
			}
		}
	}

	// For some reason prepared statements don't work here
	_, err = tx.Exec(fmt.Sprintf("PRAGMA user_version = %d", len(migrations)))
	if err != nil {
		return version, fmt.Errorf("failed to bump schema version: %v", err)
	}

	return version, tx.Commit()

}

func (db *DB) Close() error {
	return db.db.Close()
}

func (db *DB) FetchUser(ctx context.Context, id ID[*User]) (*User, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM User WHERE id = ?", id)
	if err != nil {
		return nil, err
	}
	var user User
	err = scanRow(&user, rows)
	return &user, err
}

func (db *DB) FetchUserByUsername(ctx context.Context, username string) (*User, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM User WHERE username = ?", username)
	if err != nil {
		return nil, err
	}
	var user User
	err = scanRow(&user, rows)
	return &user, err
}

func (db *DB) StoreUser(ctx context.Context, user *User) error {
	return db.db.QueryRowContext(ctx, `
		INSERT INTO User(id, username, password_hash, admin)
		VALUES (:id, :username, :password_hash, :admin)
		ON CONFLICT(id) DO UPDATE SET
			username = :username,
			password_hash = :password_hash,
			admin = :admin
		RETURNING id
	`, entityArgs(user)...).Scan(&user.ID)
}

func (db *DB) ListUsers(ctx context.Context) ([]User, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM User")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var l []User
	for rows.Next() {
		var user User
		if err := scan(&user, rows); err != nil {
			return nil, err
		}
		l = append(l, user)
	}

	return l, rows.Close()
}

func (db *DB) FetchClient(ctx context.Context, id ID[*Client]) (*Client, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM Client WHERE id = ?", id)
	if err != nil {
		return nil, err
	}
	var client Client
	err = scanRow(&client, rows)
	return &client, err
}

func (db *DB) FetchClientByClientID(ctx context.Context, clientID string) (*Client, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM Client WHERE client_id = ?", clientID)
	if err != nil {
		return nil, err
	}
	var client Client
	err = scanRow(&client, rows)
	return &client, err
}

func (db *DB) StoreClient(ctx context.Context, client *Client) error {
	return db.db.QueryRowContext(ctx, `
		INSERT INTO Client(id, client_id, client_secret_hash, owner,
			redirect_uris, client_name, client_uri)
		VALUES (:id, :client_id, :client_secret_hash, :owner,
			:redirect_uris, :client_name, :client_uri)
		ON CONFLICT(id) DO UPDATE SET
			client_id = :client_id,
			client_secret_hash = :client_secret_hash,
			owner = :owner,
			redirect_uris = :redirect_uris,
			client_name = :client_name,
			client_uri = :client_uri
		RETURNING id
	`, entityArgs(client)...).Scan(&client.ID)
}

func (db *DB) ListClients(ctx context.Context, owner ID[*User]) ([]Client, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM Client WHERE owner IS ?", owner)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var l []Client
	for rows.Next() {
		var client Client
		if err := scan(&client, rows); err != nil {
			return nil, err
		}
		l = append(l, client)
	}

	return l, rows.Close()
}

func (db *DB) ListAuthorizedClients(ctx context.Context, user ID[*User]) ([]AuthorizedClient, error) {
	rows, err := db.db.QueryContext(ctx, `
		SELECT id, client_id, client_name, client_uri, token.expires_at
		FROM Client,
		(
			SELECT client, MAX(expires_at) as expires_at
			FROM AccessToken
			WHERE user = ?
			GROUP BY client
		) AS token
		WHERE Client.id = token.client
	`, user)
	if err != nil {
		return nil, err
	}

	var l []AuthorizedClient
	for rows.Next() {
		var authClient AuthorizedClient
		columns := authClient.Client.columns()
		var expiresAt string
		err := rows.Scan(columns["id"], columns["client_id"], columns["client_name"], columns["client_uri"], &expiresAt)
		if err != nil {
			return nil, err
		}
		authClient.ExpiresAt, err = time.Parse(sqlite3.SQLiteTimestampFormats[0], expiresAt)
		if err != nil {
			return nil, err
		}
		l = append(l, authClient)
	}

	return l, rows.Close()
}

func (db *DB) DeleteClient(ctx context.Context, id ID[*Client]) error {
	_, err := db.db.ExecContext(ctx, "DELETE FROM Client WHERE id = ?", id)
	return err
}

func (db *DB) FetchAccessToken(ctx context.Context, id ID[*AccessToken]) (*AccessToken, error) {
	rows, err := db.db.QueryContext(ctx, "SELECT * FROM AccessToken WHERE id = ?", id)
	if err != nil {
		return nil, err
	}
	var token AccessToken
	err = scanRow(&token, rows)
	return &token, err
}

func (db *DB) CreateAccessToken(ctx context.Context, token *AccessToken) error {
	return db.db.QueryRowContext(ctx, `
		INSERT INTO AccessToken(hash, user, client, scope, issued_at, expires_at)
		VALUES (:hash, :user, :client, :scope, :issued_at, :expires_at)
		RETURNING id
	`, entityArgs(token)...).Scan(&token.ID)
}

func (db *DB) DeleteAccessToken(ctx context.Context, id ID[*AccessToken]) error {
	_, err := db.db.ExecContext(ctx, "DELETE FROM AccessToken WHERE id = ?", id)
	return err
}

func (db *DB) RevokeAccessTokens(ctx context.Context, clientID ID[*Client], userID ID[*User]) error {
	_, err := db.db.ExecContext(ctx, `
		DELETE FROM AccessToken
		WHERE client = ? AND user = ?
	`, clientID, userID)
	return err
}

func (db *DB) CreateAuthCode(ctx context.Context, code *AuthCode) error {
	return db.db.QueryRowContext(ctx, `
		INSERT INTO AuthCode(hash, created_at, user, client, scope, redirect_uri)
		VALUES (:hash, :created_at, :user, :client, :scope, :redirect_uri)
		RETURNING id
	`, entityArgs(code)...).Scan(&code.ID)
}

func (db *DB) PopAuthCode(ctx context.Context, id ID[*AuthCode]) (*AuthCode, error) {
	rows, err := db.db.QueryContext(ctx, `
		DELETE FROM AuthCode
		WHERE id = ?
		RETURNING *
	`, id)
	if err != nil {
		return nil, err
	}
	var authCode AuthCode
	err = scanRow(&authCode, rows)
	return &authCode, err
}

func (db *DB) Maintain(ctx context.Context) error {
	_, err := db.db.ExecContext(ctx, `
		DELETE FROM AccessToken
		WHERE timediff('now', expires_at) > 0
	`)
	if err != nil {
		return err
	}

	_, err = db.db.ExecContext(ctx, `
		DELETE FROM AuthCode
		WHERE timediff(?, created_at) > 0
	`, time.Now().Add(-authCodeExpiration))
	if err != nil {
		return err
	}

	return nil
}

func scan(e entity, rows *sql.Rows) error {
	columns := e.columns()

	keys, err := rows.Columns()
	if err != nil {
		panic(err)
	}
	out := make([]interface{}, len(keys))
	for i, k := range keys {
		v, ok := columns[k]
		if !ok {
			panic(fmt.Errorf("unknown column %q", k))
		}
		out[i] = v
	}

	return rows.Scan(out...)
}

func scanRow(e entity, rows *sql.Rows) error {
	if !rows.Next() {
		return sql.ErrNoRows
	}
	if err := scan(e, rows); err != nil {
		return err
	}
	return rows.Close()
}

func entityArgs(e entity) []interface{} {
	columns := e.columns()

	l := make([]interface{}, 0, len(columns))
	for k, v := range columns {
		l = append(l, sql.Named(k, v))
	}

	return l
}

PRAGMA user_version = 1;

CREATE TABLE User (
	id INTEGER PRIMARY KEY,
	username TEXT NOT NULL UNIQUE,
	password_hash TEXT,
	admin INTEGER NOT NULL DEFAULT 0
);

CREATE TABLE Client (
	id INTEGER PRIMARY KEY,
	client_id TEXT NOT NULL UNIQUE,
	client_secret_hash BLOB,
	owner INTEGER,
	redirect_uris TEXT,
	client_name TEXT,
	client_uri TEXT,
	FOREIGN KEY(owner) REFERENCES User(id)
);

CREATE TABLE AccessToken (
	id INTEGER PRIMARY KEY,
	hash BLOB NOT NULL UNIQUE,
	user INTEGER NOT NULL,
	client INTEGER,
	scope TEXT,
	issued_at datetime NOT NULL,
	expires_at datetime NOT NULL,
	FOREIGN KEY(user) REFERENCES User(id),
	FOREIGN KEY(client) REFERENCES Client(id)
);

CREATE TABLE AuthCode (
	id INTEGER PRIMARY KEY,
	hash BLOB NOT NULL UNIQUE,
	created_at datetime NOT NULL,
	user INTEGER NOT NULL,
	client INTEGER NOT NULL,
	redirect_uri TEXT,
	scope TEXT,
	FOREIGN KEY(user) REFERENCES User(id),
	FOREIGN KEY(client) REFERENCES Client(id)
);