package discovery

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"time"
)

type SnapshotFunc func(context.Context) ([]Event, error)

// Event is one discovered change. SourceID and DedupKey together with OccurredAt
// form the deduplication identity that persistent stores rely on, so a repeated
// discovery pass re-emits the same event without creating a second row.
// EntityID and Severity are optional: they carry the inventory entity the change
// belongs to and how loud it is, and default to "no entity" and "info" so older
// producers keep working unchanged.
type Event struct {
	SourceID, DedupKey, Type, Summary string
	EntityID, Severity                string
	OccurredAt                        time.Time
}
type JobRun struct {
	Key, Status, ErrorCode string
	Attempts               int
	StartedAt, CompletedAt time.Time
}

type Store interface {
	Claim(context.Context, string, time.Time) (bool, error)
	Finish(context.Context, JobRun) error
	Emit(context.Context, Event) (bool, error)
}
type AuditFunc func(context.Context, string, string) error
type AuthorizeFunc func(context.Context, string) bool

type Runner struct {
	Store       Store
	MaxAttempts int
	BaseRetry   time.Duration
	Sleep       func(context.Context, time.Duration) error
}

func (r Runner) Run(ctx context.Context, jobKey string, discover SnapshotFunc) error {
	if r.Store == nil || discover == nil || jobKey == "" {
		return errors.New("discovery runner requires store, key, and discover function")
	}
	max := r.MaxAttempts
	if max == 0 {
		max = 3
	}
	if max < 1 || max > 5 {
		return errors.New("discovery attempts must be between 1 and 5")
	}
	base := r.BaseRetry
	if base == 0 {
		base = 100 * time.Millisecond
	}
	sleeper := r.Sleep
	if sleeper == nil {
		sleeper = func(ctx context.Context, d time.Duration) error {
			timer := time.NewTimer(d)
			defer timer.Stop()
			select {
			case <-ctx.Done():
				return ctx.Err()
			case <-timer.C:
				return nil
			}
		}
	}
	claimed, err := r.Store.Claim(ctx, jobKey, time.Now().UTC())
	if err != nil {
		return fmt.Errorf("claim discovery job: %w", err)
	}
	if !claimed {
		return nil
	}
	run := JobRun{Key: jobKey, Status: "running", StartedAt: time.Now().UTC()}
	var last error
	for attempt := 1; attempt <= max; attempt++ {
		run.Attempts = attempt
		events, runErr := discover(ctx)
		if runErr == nil {
			for _, event := range events {
				if _, err := r.Store.Emit(ctx, event); err != nil {
					runErr = fmt.Errorf("emit discovery event: %w", err)
					break
				}
			}
		}
		if runErr == nil {
			run.Status = "succeeded"
			run.CompletedAt = time.Now().UTC()
			if err := r.Store.Finish(ctx, run); err != nil {
				return err
			}
			return nil
		}
		last = runErr
		if ctx.Err() != nil {
			break
		}
		if attempt < max {
			if err := sleeper(ctx, base*time.Duration(1<<(attempt-1))); err != nil {
				last = err
				break
			}
		}
	}
	run.Status = "failed"
	run.ErrorCode = "DISCOVERY_FAILED"
	run.CompletedAt = time.Now().UTC()
	if err := r.Store.Finish(ctx, run); err != nil {
		return err
	}
	return last
}

func (r Runner) RunManual(ctx context.Context, actor string, authorize AuthorizeFunc, audit AuditFunc, jobKey string, discover SnapshotFunc) error {
	if authorize == nil || !authorize(ctx, actor) {
		return errors.New("manual discovery is unauthorized")
	}
	if audit != nil {
		if err := audit(ctx, actor, "discovery.manual.run"); err != nil {
			return fmt.Errorf("audit manual discovery: %w", err)
		}
	}
	return r.Run(ctx, jobKey, discover)
}

type MemoryStore struct {
	mu      sync.Mutex
	claimed map[string]bool
	Runs    []JobRun
	Events  map[string]Event
}

func NewMemoryStore() *MemoryStore {
	return &MemoryStore{claimed: make(map[string]bool), Events: make(map[string]Event)}
}
func (s *MemoryStore) Claim(_ context.Context, key string, _ time.Time) (bool, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.claimed[key] {
		return false, nil
	}
	s.claimed[key] = true
	return true, nil
}
func (s *MemoryStore) Finish(_ context.Context, run JobRun) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.Runs = append(s.Runs, run)
	return nil
}
func (s *MemoryStore) Emit(_ context.Context, event Event) (bool, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, ok := s.Events[event.SourceID+"\x00"+event.DedupKey]; ok {
		return false, nil
	}
	s.Events[event.SourceID+"\x00"+event.DedupKey] = event
	return true, nil
}