// sqliteclidriver is a database/sql driver for SQLite implemented on top of
// the sqlite3 command-line tool. This allows it to be used over remote SSH
// connections.
//
// Functionality is limited.
//
// Known caveats:
// - Bad error handling
// - Few supported types
// - Has to escape parameters for CLI instead of preparing them, so not safe for untrusted usage
// - No context handling
// - No way to configure sqlite3 command line path
package sqliteclidriver

import (
	"bytes"
	"context"
	"database/sql"
	"database/sql/driver"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os/exec"

	"yvbolt/lexer"

	"github.com/google/uuid"
)

var ErrNotSupported = errors.New("Not supported")

//

type SCDriver struct{}

func (d *SCDriver) Open(connectionString string) (driver.Conn, error) {
	// TODO support custom binpath from our connection string

	cmd := exec.Command(`/usr/bin/sqlite3`, `-noheader`, `-json`, connectionString) // n.b. doesn't support `--`

	chEvents, pw, err := ExecEvents(cmd)
	if err != nil {
		return nil, err
	}

	return &SCConn{
		listen: chEvents,
		w:      pw,
	}, nil
}

var _ driver.Driver = &SCDriver{} // interface assertion

func init() {
	sql.Register("sqliteclidriver", &SCDriver{})
}

//

type SCConnector struct {
	connectionString string
	driver           *SCDriver
}

func (c *SCConnector) Connect(context.Context) (driver.Conn, error) {
	return c.driver.Open(c.connectionString)
}

func (c *SCConnector) Driver() driver.Driver {
	return c.driver
}

var _ driver.Connector = &SCConnector{} // interface assertion

//

type SCConn struct {
	listen <-chan processEvent
	w      io.WriteCloser
}

func (c *SCConn) Prepare(query string) (driver.Stmt, error) {
	f, err := lexer.Fields(query) // Rely on the query's escaping still being present
	if err != nil {
		return nil, err
	}

	if len(f) == 0 {
		return nil, errors.New("Empty query")
	}

	if f[len(f)-1] != ";" {
		f = append(f, ";") // Query must end in semicolon
	}

	return &SCStmt{
		conn:  c,
		query: f,
	}, nil
}

func (c *SCConn) Close() error {
	return c.w.Close()
}

func (c *SCConn) Begin() (driver.Tx, error) {
	return nil, ErrNotSupported
}

var _ driver.Conn = &SCConn{} // interface assertion

//

type SCStmt struct {
	conn  *SCConn
	query []string
}

func (s *SCStmt) Close() error {
	return nil
}

func (s *SCStmt) NumInput() int {
	var ct int = 0
	for _, token := range s.query {
		if token == `?` {
			ct++
		}
	}

	return ct
}

func (s *SCStmt) buildQuery(args []driver.Value) ([]byte, error) {

	// Embed query params
	// WARNING: Not secure against injection? That's not a security boundary
	// for the purposes of yvbolt, but maybe for other package users

	var querybuilder bytes.Buffer

	for _, token := range s.query {
		if token == `?` {
			if len(args) == 0 {
				return nil, errors.New("Not enough arguments")
			}

			arg := args[0]
			args = args[1:]

			// Format the argument
			if szarg, ok := arg.(string); ok {
				querybuilder.WriteString(lexer.Quote(szarg))

			} else if intarg, ok := arg.(int64); ok {
				querybuilder.WriteString(fmt.Sprintf("%d", intarg))

			} else if flarg, ok := arg.(float64); ok {
				querybuilder.WriteString(fmt.Sprintf("%f", flarg))

			} else {
				return nil, fmt.Errorf("Parameter %v has unsupported type", arg)
			}

		} else {
			// Normal token
			querybuilder.WriteString(token)
		}

		// Whitespace
		querybuilder.WriteByte(' ')
	}

	if len(args) != 0 {
		return nil, errors.New("Too many arguments")
	}

	// Swap final whitespace for a \n
	submit := querybuilder.Bytes()
	submit[len(submit)-1] = '\n'

	return submit, nil
}

func (s *SCStmt) Exec(args []driver.Value) (driver.Result, error) {

	submit, err := s.buildQuery(args)
	if err != nil {
		return nil, err
	}

	_, err = io.CopyN(s.conn.w, bytes.NewReader(submit), int64(len(submit)))
	if err != nil {
		return nil, fmt.Errorf("Write: %w", err)
	}

	// Drain stdout
	// TODO

	// Drain stderr
	// TODO

	return &SCResult{}, nil
}

func (s *SCStmt) Query(args []driver.Value) (driver.Rows, error) {
	ctx := context.Background()

	submit, err := s.buildQuery(args)
	if err != nil {
		return nil, err
	}

	// If there are no results to the query, the sqlite3 -json mode does not
	// print anything on stdout at all and we would hang forever
	// Add a followup sentinel query that we can detect
	const sentinelKey = `__sqliteclidriver_sentinel`
	sentinelVal := uuid.Must(uuid.NewRandom()).String()
	submit = append(submit, []byte(fmt.Sprintf("SELECT \"%s\" AS %s;\n", sentinelVal, sentinelKey))...)

	//

	_, err = io.CopyN(s.conn.w, bytes.NewReader(submit), int64(len(submit)))
	if err != nil {
		return nil, fmt.Errorf("Write: %w", err)
	}

	// Consume process events until either error or the json decoder is satisfied
	pr, pw := io.Pipe()

	listenContext, listenContextCancel := context.WithCancel(ctx) // Use to stop signalling once json decoder is satisfied

	go func() {
		defer pw.Close()
		for {
			select {
			case msg, ok := <-s.conn.listen:
				if !ok {
					pw.CloseWithError(fmt.Errorf("process already closed"))
					return
				}
				if msg.err != nil {
					pw.CloseWithError(msg.err)
					return
				}

				if msg.evtype == evtypeStdout {
					_, err := io.CopyN(pw, bytes.NewReader(msg.data), int64(len(msg.data)))
					if err != nil {
						pw.CloseWithError(msg.err)
						return
					}

				} else {
					// Anything else (process event / stderr)
					// Throw
					pw.CloseWithError(msg)
					return
				}

			case <-listenContext.Done():
				return
			}
		}
	}()

	// We expect some kind of thing on stdout
	// If something happens on stderr, or to the process, pr will read an error
	ret := []map[string]any{}
	decoder := json.NewDecoder(pr)
	err = decoder.Decode(&ret)
	if err != nil {
		return nil, err
	}

	// Check if this was the data or the sentinel
	wasSentinel := false
	if len(ret) > 0 {
		if val, ok := ret[0][sentinelKey]; ok {
			if check, ok := val.(string); ok && check == sentinelVal {
				// It was the sentinel
				wasSentinel = true
				// Nothing more to parse
			}
		}
	}

	if !wasSentinel {
		// Need to decode again (from the same decoder reader) until we find the sentinel
		surplus := []map[string]any{}
		err = decoder.Decode(&surplus)
		if err != nil {
			return nil, err
		}
	}

	listenContextCancel()

	// Drain stderr
	// TODO

	// Come up with a canonical ordering for the columns after json.NewDecoder
	// wiped it out for us
	// FIXME use a different json parsing library

	var columnNames []string
	if len(ret) > 0 {
		for k, _ := range ret[0] {
			columnNames = append(columnNames, k)
		}
	}

	//

	return &SCRows{
		idx:     0,
		columns: columnNames,
		data:    ret,
	}, nil
}

var _ driver.Stmt = &SCStmt{} // interface assertion

//

type SCResult struct{}

func (r *SCResult) LastInsertId() (int64, error) {
	return 0, ErrNotSupported
}

func (r *SCResult) RowsAffected() (int64, error) {
	return 0, ErrNotSupported
}

var _ driver.Result = &SCResult{} // interface assertion

//

type SCRows struct {
	idx     int
	columns []string
	data    []map[string]any
}

func (r *SCRows) Columns() []string {
	return r.columns
}

func (r *SCRows) Close() error {
	r.idx = 0
	r.data = nil
	return nil
}

func (r *SCRows) Next(dest []driver.Value) error {
	if r.idx >= len(r.data) {
		return io.EOF
	}

	if len(dest) != len(r.data[r.idx]) {
		return errors.New("Wrong number of arguments to Next()")
	}

	for i := 0; i < len(dest); i++ {
		cell, ok := r.data[r.idx][r.columns[i]]
		if !ok {
			return fmt.Errorf("Result row %d is missing column #%d %q, unexpected", r.idx, i, r.columns[i])
		}

		dest[i] = cell
	}

	r.idx++
	return nil
}