package sqlite

import (
	"cmp"
	"context"
	"database/sql"
	"errors"
	"fmt"
	"io/fs"
	"log/slog"
	"path"
	"slices"
	"strconv"
	"strings"
	"time"

	"git.loyso.art/frx/kurious/internal/common/xcontext"
)

type migrationUnit struct {
	num  int
	name string
	path string
}

func (u migrationUnit) apply(ctx context.Context, tx *sql.Tx) error {
	content, err := fs.ReadFile(migrations, u.path)
	if err != nil {
		return fmt.Errorf("reading file: %w", err)
	}

	query := string(content)
	_, err = tx.ExecContext(ctx, query)
	if err != nil {
		return fmt.Errorf("executing query: %w", err)
	}

	return nil
}

func sortMigrationUnit(lhs, rhs migrationUnit) int {
	if lhs.num < rhs.num {
		return -1
	} else if lhs.num > rhs.num {
		return 1
	} else {
		return 0
	}
}

func RunMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
	items, err := getMigrationEntries()
	if err != nil {
		return fmt.Errorf("reading directory: %w", err)
	}

	units := make([]migrationUnit, 0, len(items))
	for _, item := range items {
		if item.IsDir() {
			continue
		}

		itemName := item.Name()
		splitted := strings.SplitN(itemName, "_", 2)
		if len(splitted) != 2 {
			return fmt.Errorf("bad number of parts, expected 2, got %d", len(splitted))
		}

		splittedNum, err := strconv.Atoi(splitted[0])
		if err != nil {
			return fmt.Errorf("parsing migration number: %w", err)
		}

		if splittedNum < 1 {
			return fmt.Errorf("migration number expected to be greater than 0, but got %d", splittedNum)
		}

		unit := migrationUnit{
			num:  splittedNum,
			name: strings.TrimSuffix(splitted[1], ".sql"),
			path: path.Join(itemName),
		}

		xcontext.LogDebug(ctx, log, "found migration unit", slog.Any("unit", unit))

		units = append(units, unit)
	}

	slices.SortFunc(units, sortMigrationUnit)

	mr := &metaRepository{
		db:  db,
		log: log,
	}
	err = mr.prepare(ctx)
	if err != nil {
		return fmt.Errorf("preparing meta repository: %w", err)
	}

	count, err := mr.run(ctx, units...)
	if err != nil {
		return fmt.Errorf("running transaction: %w", err)
	}

	if count > 0 {
		xcontext.LogInfo(ctx, log, "some new migrations has been applied", slog.Int("count", count))
	} else {
		xcontext.LogDebug(ctx, log, "no new migrations has been applied")
	}

	return nil
}

type metaRepository struct {
	db                *sql.DB
	log               *slog.Logger
	lastAppliedNumber int
}

func (r *metaRepository) run(ctx context.Context, units ...migrationUnit) (count int, err error) {
	idx, found := slices.BinarySearchFunc(units, r.lastAppliedNumber, func(mu migrationUnit, i int) int {
		return cmp.Compare(mu.num, i)
	})
	if !found && r.lastAppliedNumber > 0 {
		return 0, fmt.Errorf("migration %d stored in meta was not found in provided migrations", r.lastAppliedNumber)
	} else if r.lastAppliedNumber > 0 {
		idx++
	}

	xcontext.LogDebug(
		ctx, r.log,
		"starting to apply migrations",
		slog.Int("last_applied_migration", r.lastAppliedNumber),
		slog.Int("next_migration_idx", idx),
	)

	tx, err := r.db.BeginTx(ctx, &sql.TxOptions{
		Isolation: sql.LevelDefault,
		ReadOnly:  false,
	})
	if err != nil {
		return 0, fmt.Errorf("starting transaction: %w", err)
	}

	defer func() {
		var errtx error
		if err != nil {
			xcontext.LogError(ctx, r.log, "rolling back migration changes due to error")
			errtx = tx.Rollback()
		} else {
			xcontext.LogDebug(ctx, r.log, "commiting migration changes")
			errtx = tx.Commit()
		}

		err = errors.Join(err, errtx)
	}()

	for i := idx; i < len(units); i++ {
		unit := units[i]
		err = unit.apply(ctx, tx)
		if err != nil {
			return 0, fmt.Errorf("unable to apply migration %q: %w", unit.name, err)
		}

		err = r.adjustMigrationApplied(ctx, tx, unit)
		if err != nil {
			return 0, fmt.Errorf("storing migration process info: %w", err)
		}

		xcontext.LogInfo(
			ctx, r.log, "migration unit applied",
			slog.Int("number", unit.num),
			slog.String("name", unit.name),
		)
		count++
	}

	return count, nil
}

func (r *metaRepository) prepare(ctx context.Context) error {
	err := r.makeTable(ctx)
	if err != nil {
		return fmt.Errorf("making table: %w", err)
	}

	err = r.loadLastAppliedMigration(ctx)
	if err != nil {
		return fmt.Errorf("loading last applied migration: %w", err)
	}

	return nil
}

func (r *metaRepository) makeTable(ctx context.Context) error {
	const query = `CREATE TABLE IF NOT EXISTS migration_meta (` +
		`  id INT PRIMARY KEY NOT NULL` +
		`, name TEXT NOT NULL` +
		`, applied_at INT NOT NULL` +
		`);`

	_, err := r.db.ExecContext(ctx, query)
	if err != nil {
		return fmt.Errorf("executing query: %w", err)
	}

	return nil
}

func (r *metaRepository) loadLastAppliedMigration(ctx context.Context) error {
	const query = `SELECT COALESCE(MAX(id), 0) FROM migration_meta;`

	err := r.db.QueryRowContext(ctx, query).Scan(&r.lastAppliedNumber)
	if err != nil {
		if !errors.Is(err, sql.ErrNoRows) {
			return fmt.Errorf("executing query: %w", err)
		}
	}

	return nil
}

func (r *metaRepository) adjustMigrationApplied(ctx context.Context, tx *sql.Tx, unit migrationUnit) error {
	const query = `INSERT INTO migration_meta (id, name, applied_at) VALUES (?, ?, ?)`

	args := []any{
		unit.num,
		unit.name,
		time.Now().Truncate(time.Second).Unix(),
	}

	_, err := tx.ExecContext(ctx, query, args...)
	if err != nil {
		return fmt.Errorf("executing query: %w", err)
	}

	r.lastAppliedNumber = unit.num

	return nil
}