/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */
package main

import (
	"context"
	"database/sql"
	"encoding/csv"
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"os/signal"
	"path/filepath"
	"regexp"
	"strings"
	"time"

	"github.com/mattn/go-sqlite3"
	_ "github.com/mattn/go-sqlite3"
	logger "idio.link/go/logger/v3"

	"golang.org/x/term"
)

var (
	Version, Build string
	WithTimestamp  bool
)

const (
	MaxRecords                   = 1_000_000_000
	SQLITE_CONSTRAINT_PRIMARYKEY = 1555
)

func main() {
	log := logger.NewLogger()

	flag.BoolVar(
		&WithTimestamp,
		"timestamp",
		false,
		"Add a column 'timestamp' to imported rows. "+
			"All rows receive the same value for 'timestamp', "+
			"calculated at the start of the import. "+
			"",
	)
	flag.Parse()

	if len(flag.Args()) != 1 {
		if Build == "" {
			Version = "dev"
			Build = time.Now().UTC().Format(time.RFC3339)
		}
		fmt.Printf("%s %s\n", Version, Build)
		fmt.Printf("usage: %s [--timestamp] <csv_path>\n", os.Args[0])
		os.Exit(1)
	}
	csvPath, err := filepath.Abs(flag.Args()[0])
	if err != nil {
		log.Fatal("resolve absolute path for '%s': %v", flag.Args()[0], err)
	}
	ctx := context.WithValue(context.Background(), "log", log)
	ctx, cancel := context.WithCancel(ctx)

	go func() {
		_, stop := signal.NotifyContext(
			ctx,
			os.Interrupt,
			os.Kill,
		)
		sig := make(chan os.Signal, 1)
		<-sig
		stop()
		log.Info("caught signal; shutting down")
		cancel()
	}()

	// open csv for read
	f, err := os.Open(csvPath)
	if err != nil {
		log.Fatal("open csv: %v", err)
	}
	defer func() {
		if err := f.Close(); err != nil {
			log.Error("close csv '%s': %v", csvPath, err)
		}
	}()
	r := csv.NewReader(f)
	r.ReuseRecord = true

	// open db
	tmp := strings.TrimSuffix(csvPath, ".csv")
	dbPath := tmp + ".db"
	name := scrubName(filepath.Base(tmp))
	// no need to rollback or be crash resistant
	params := "?_synchronous=0&_journal_mode=OFF&_temp_store=2"
	db, err := sql.Open("sqlite3", dbPath+params)
	if err != nil {
		log.Fatal("open db '%s': %v", dbPath, err)
	}
	defer func() {
		if err := db.Close(); err != nil {
			log.Error("close db '%s': %v", dbPath, err)
		}
	}()

	// Read headers
	rec, err := r.Read()
	if err != nil && err != io.EOF {
		log.Fatal("read csv '%s': %v", csvPath, err)
	}

	// Prepare args with timestamp, as necessary.
	argsLen := len(rec)
	if WithTimestamp {
		argsLen++
	}
	args := make([]any, argsLen)
	if WithTimestamp {
		args[0] = any(FormatRFC3339Subsec(time.Now().UTC()))
	}

	// create table, prepare insert
	var insert *sql.Stmt
	headers := make([]string, 0, argsLen)

	if WithTimestamp {
		headers = append(headers, "timestamp")
	}
	for _, f := range rec {
		f = scrubName(f)
		headers = append(headers, f)
	}
	_, err = createTable(ctx, db, name, headers)
	if err != nil {
		log.Fatal("create table '%s': %v", name, err)
	}
	insert, err = genInsert(ctx, db, name, headers)
	if err != nil {
		log.Fatal("prepare insert: %v", err)
	}
	defer func() {
		if err := insert.Close(); err != nil {
			log.Error("close prepared insert: %v", err)
		}
	}()

	// insert records
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		log.Fatal("begin transaction: %v", err)
	}
	nonUnique := 0
	i := 0
	for {
		i++
		if i >= MaxRecords {
			panic(fmt.Sprintf("BUG: max record limit reached: %d", MaxRecords))
		}
		if ctx.Err() != nil {
			break
		}
		// Print count for every thousand-ish records
		if i&4095 == 0 {
			printStatus(i)
		}
		if i&65535 == 0 {
			if err := tx.Commit(); err != nil {
				log.Fatal("commit transaction: %v", err)
			}
			tx, err = db.BeginTx(ctx, nil)
			if err != nil {
				log.Fatal("begin transaction: %v", err)
			}
		}

		rec, err := r.Read()
		if err != nil {
			fmt.Println()

			if err == io.EOF {
				fmt.Fprintf(os.Stderr, "read %d records\n", i)
				fmt.Fprintf(os.Stderr, "skipped %d redundant records\n", nonUnique)
			} else {
				log.Error("read csv '%s': %v", csvPath, err)
			}
			break
		}

		// Rather slow, doing this for every record, but since
		// we cannot know how many fields will exist ahead of
		// time (we compile *now*, not after we've read the
		// headers), we cannot simply enter, say, 27 arguments,
		// each converted to `any`, by hand. It may be faster to
		// simply print the SQL statements and pipe them to
		// sqlite. Should check this.

		recArgs := args[:]
		if WithTimestamp {
			// Skip over timestamp
			recArgs = args[1:]
		}
		for j := 0; j < len(recArgs); j++ {
			recArgs[j] = any(rec[j])
		}

		// For explanation of extended codes, see https://www.sqlite.org/rescode.html
		_, err = insert.ExecContext(ctx, args...)
		if err != nil {
			var sqliteErr sqlite3.Error
			if errors.As(err, &sqliteErr) &&
				sqliteErr.ExtendedCode == SQLITE_CONSTRAINT_PRIMARYKEY {
				nonUnique++
				log.Debug("insert record '%#v': %v", rec, err)
			} else {
				log.Fatal("insert record '%#v': %v", rec, err)
			}
		}
	}
	if err := tx.Commit(); err != nil {
		log.Fatal("commit transaction: %v", err)
	}
}

func printStatus(n int) {
	if term.IsTerminal(int(os.Stdout.Fd())) {
		fmt.Printf("\x1b[%dG", 1)
		fmt.Printf("%d", n)
	}
}

func genInsert(
	ctx context.Context,
	db *sql.DB,
	name string,
	headers []string,
) (*sql.Stmt, error) {
	log := ctx.Value("log").(*logger.Logger)

	var b strings.Builder

	b.WriteString(fmt.Sprintf("INSERT INTO %s (", name))
	for i, h := range headers {
		if i != 0 {
			b.WriteString(", ")
		}
		b.WriteString(h)
	}
	b.WriteString(") VALUES (")
	for i := 0; i < len(headers); i++ {
		if i != 0 {
			b.WriteString(", ")
		}
		b.WriteString(fmt.Sprintf("$%d", i+1))
	}
	b.WriteString(");")
	log.Debug("debug: prepare insert: %s\n", b.String())

	return db.PrepareContext(ctx, b.String())
}

func createTable(
	ctx context.Context,
	db *sql.DB,
	name string,
	headers []string,
) (sql.Result, error) {
	var b strings.Builder

	b.WriteString(
		fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s (", name),
	)

	for i, h := range headers {
		if i != 0 {
			b.WriteString(", ")
		}
		b.WriteString(fmt.Sprintf("%s text", h))
	}
	b.WriteString(");")

	fmt.Fprintf(os.Stderr, "%s\n", b.String())

	return db.ExecContext(ctx, b.String())
}

var badRunes = regexp.MustCompile(`[^a-zA-Z0-9_\-\.]+`)
var badFirst = regexp.MustCompile(`^[^a-zA-Z]+`)
var parens = regexp.MustCompile(`[\(\)]`)
var spaces = regexp.MustCompile(`\s+`)
var hyphens = regexp.MustCompile(`\-+`)
var unders = regexp.MustCompile(`_+`)

func scrubName(s string) string {
	s = strings.ToLower(s)
	s = badFirst.ReplaceAllLiteralString(s, "")
	s = parens.ReplaceAllLiteralString(s, "")
	s = strings.TrimSpace(s)
	s = spaces.ReplaceAllLiteralString(s, "_")
	s = badRunes.ReplaceAllLiteralString(s, "_")
	s = hyphens.ReplaceAllLiteralString(s, "_")
	s = unders.ReplaceAllLiteralString(s, "_")
	s = strings.TrimSuffix(s, "_")

	return fmt.Sprintf("'%s'", s)
}

func FormatRFC3339Subsec(t time.Time) string {
	// RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
	rfc3339 := t.Format(time.RFC3339Nano)
	datetime := rfc3339[:19]
	nano := rfc3339[20:23] // Just ms
	return fmt.Sprintf(
		"%s.%sZ",
		datetime,
		nano,
	)
}