package delivery

import (
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"sync"
	"time"

	"gorm.io/driver/sqlite"
	"gorm.io/gorm"
)

// archiveExpiryNever is the expiry sentinel (and default) that
// disables pruning so archived rows are kept forever.
const archiveExpiryNever = "never"

// archiveReopenDebounce bounds how often an archive file is
// closed and reopened. After each write the handle is closed
// and reopened so an operator can move the file away for
// offline archiving, but never more than once per this window.
const archiveReopenDebounce = time.Second

var (
	// errArchiveMissingWebhookID is returned when an event to
	// archive has no webhook id to key its archive file on.
	errArchiveMissingWebhookID = errors.New(
		"cannot archive event without a webhook id",
	)

	// errArchiveNoDataDir is returned when the database target
	// has no webhook database manager and so cannot locate the
	// data directory for archive files.
	errArchiveNoDataDir = errors.New(
		"database target has no data directory",
	)

	// errArchiveExpiryNotPositive is returned when a
	// user-supplied archive expiry parses as a duration but is
	// zero or negative; "never" is the way to disable pruning.
	errArchiveExpiryNotPositive = errors.New(
		"expiry must be a positive duration or \"never\"",
	)
)

// databaseTargetConfig is the optional per-target JSON config
// for a database (archive) target.
type databaseTargetConfig struct {
	// Expiry is a Go duration (e.g. "720h") after which
	// archived rows are pruned, or "never" (the default) to
	// keep them forever.
	Expiry string `json:"expiry"`
}

// archivedEvent is one fully captured webhook event stored in a
// per-webhook archive database for long-term retention. It is a
// self-contained copy — independent of the per-webhook event
// database, which may prune events under its own retention.
type archivedEvent struct {
	ID           uint   `gorm:"primaryKey;autoIncrement"`
	EventID      string `gorm:"index"`
	WebhookID    string
	EntrypointID string
	Method       string
	Headers      string
	Body         string
	ContentType  string

	// ArchivedAt is when the row was archived and is the age
	// basis for expiry pruning.
	ArchivedAt time.Time `gorm:"index"`
}

// parseArchiveExpiry reads the optional expiry from a database
// target's config JSON. An empty config, an empty expiry, or
// the literal "never" all mean keep forever, returned as a zero
// duration. Any other value is parsed as a Go duration.
func parseArchiveExpiry(
	configJSON string,
) (time.Duration, error) {
	if configJSON == "" {
		return 0, nil
	}

	var cfg databaseTargetConfig

	err := json.Unmarshal([]byte(configJSON), &cfg)
	if err != nil {
		return 0, fmt.Errorf(
			"parsing database target config: %w", err,
		)
	}

	if cfg.Expiry == "" || cfg.Expiry == archiveExpiryNever {
		return 0, nil
	}

	dur, err := time.ParseDuration(cfg.Expiry)
	if err != nil {
		return 0, fmt.Errorf(
			"parsing archive expiry %q: %w", cfg.Expiry, err,
		)
	}

	if dur <= 0 {
		return 0, nil
	}

	return dur, nil
}

// ValidateArchiveExpiry checks a user-supplied archive expiry
// for a database target at configuration time. Valid values are
// empty, "never" (both meaning keep forever), or a positive Go
// duration such as "720h". Anything else is an error, so a bad
// expiry is rejected when the target is created rather than
// failing every subsequent delivery.
func ValidateArchiveExpiry(expiry string) error {
	if expiry == "" || expiry == archiveExpiryNever {
		return nil
	}

	dur, err := time.ParseDuration(expiry)
	if err != nil {
		return fmt.Errorf(
			"expiry must be %q or a Go duration "+
				"such as \"720h\": %w",
			archiveExpiryNever, err,
		)
	}

	if dur <= 0 {
		return fmt.Errorf(
			"%w: %q", errArchiveExpiryNotPositive, expiry,
		)
	}

	return nil
}

// archiveWriter owns one per-webhook archive SQLite file. It
// serialises writes, and after each write closes and reopens
// the file (debounced to at most once per debounce window) so
// an operator can move the file away for offline archiving. The
// next write recreates a moved or removed file, because the
// file is opened create-if-missing and its schema is migrated
// on every open.
type archiveWriter struct {
	mu         sync.Mutex
	path       string
	log        *slog.Logger
	debounce   time.Duration
	db         *gorm.DB
	lastReopen time.Time
	reopens    int
}

// newArchiveWriter builds an archiveWriter for a file path with
// the default reopen debounce.
func newArchiveWriter(
	path string, log *slog.Logger,
) *archiveWriter {
	return &archiveWriter{
		path:     path,
		log:      log,
		debounce: archiveReopenDebounce,
	}
}

// write appends the event as a row, then applies the debounced
// close/reopen. It recreates the archive file if it was moved
// or removed since the last open. A positive expiry prunes rows
// older than it on each (re)open.
func (w *archiveWriter) write(
	row archivedEvent, expiry time.Duration,
) error {
	w.mu.Lock()
	defer w.mu.Unlock()

	if w.db == nil || !fileExists(w.path) {
		err := w.reopen(expiry)
		if err != nil {
			return err
		}
	}

	row.ArchivedAt = time.Now()

	err := w.db.Create(&row).Error
	if err != nil {
		return fmt.Errorf(
			"archiving event to %s: %w", w.path, err,
		)
	}

	if time.Since(w.lastReopen) >= w.debounce {
		return w.reopen(expiry)
	}

	return nil
}

// open opens (creating if missing) the archive file, migrates
// its schema, records the reopen time, and prunes expired rows
// when expiry is positive.
func (w *archiveWriter) open(expiry time.Duration) error {
	dbURL := fmt.Sprintf("file:%s?mode=rwc", w.path)

	sqlDB, err := sql.Open("sqlite", dbURL)
	if err != nil {
		return fmt.Errorf(
			"opening archive database %s: %w", w.path, err,
		)
	}

	gdb, err := gorm.Open(
		sqlite.Dialector{Conn: sqlDB}, &gorm.Config{},
	)
	if err != nil {
		_ = sqlDB.Close()

		return fmt.Errorf(
			"connecting to archive database %s: %w",
			w.path, err,
		)
	}

	err = gdb.AutoMigrate(&archivedEvent{})
	if err != nil {
		_ = sqlDB.Close()

		return fmt.Errorf(
			"migrating archive database %s: %w", w.path, err,
		)
	}

	w.db = gdb
	w.lastReopen = time.Now()
	w.reopens++

	if expiry > 0 {
		w.prune(expiry)
	}

	return nil
}

// reopen closes any open handle and opens the file afresh. The
// fresh open recreates the file if it was moved away.
func (w *archiveWriter) reopen(expiry time.Duration) error {
	w.close()

	return w.open(expiry)
}

// close closes the underlying handle, if any.
func (w *archiveWriter) close() {
	if w.db == nil {
		return
	}

	sqlDB, err := w.db.DB()
	if err == nil {
		_ = sqlDB.Close()
	}

	w.db = nil
}

// prune deletes archived rows older than expiry, measured from
// each row's archived time. It runs on every (re)open, and
// because the file is reopened after writes this keeps the
// archive swept without a separate background sweeper. Failures
// are logged, not fatal: a prune error must not stop archiving.
func (w *archiveWriter) prune(expiry time.Duration) {
	cutoff := time.Now().Add(-expiry)

	res := w.db.Where("archived_at < ?", cutoff).
		Delete(&archivedEvent{})
	if res.Error != nil {
		w.log.Error(
			"failed to prune expired archive rows",
			"path", w.path,
			"error", res.Error,
		)

		return
	}

	if res.RowsAffected > 0 {
		w.log.Info(
			"pruned expired archive rows",
			"path", w.path,
			"rows_deleted", res.RowsAffected,
		)
	}
}

// fileExists reports whether a path currently exists.
func fileExists(path string) bool {
	_, err := os.Stat(path)

	return err == nil
}