package alertdefaults

import (
	"bytes"
	"context"
	"embed"
	"encoding/json"
	"errors"
	"fmt"

	"github.com/itworx/pulse/internal/alert"
	"github.com/itworx/pulse/internal/metriccatalog"
)

//go:embed seed.json
var seedFS embed.FS

type seedDocument struct {
	SchemaVersion int              `json:"schemaVersion"`
	Rules         []alert.Document `json:"rules"`
}

type RuleStore interface {
	Create(context.Context, string, alert.Document, string) (alert.Rule, alert.Version, error)
	Get(context.Context, string) (alert.Rule, error)
	// Update is optional for the seed: stores that also implement it allow the
	// seed to refresh an implementation-owned default that has never been edited
	// (revision 1) when a newer seed corrects it. See Seed.
}

// RuleUpdater is implemented by stores that support versioned updates. The seed
// uses it only for rules that are still at revision 1 (created by the seed and
// never changed by an operator), so operator edits are never overwritten.
type RuleUpdater interface {
	Update(ctx context.Context, id, actor string, expected int64, document alert.Document, changeSummary string) (alert.Rule, error)
}

type Report struct {
	Added     int
	Existing  int
	Refreshed int
}

func Load(registry metriccatalog.Registry) ([]alert.Document, error) {
	raw, err := seedFS.ReadFile("seed.json")
	if err != nil {
		return nil, fmt.Errorf("read embedded alert defaults: %w", err)
	}
	decoder := json.NewDecoder(bytes.NewReader(raw))
	decoder.DisallowUnknownFields()
	var bundle seedDocument
	if err := decoder.Decode(&bundle); err != nil {
		return nil, fmt.Errorf("decode embedded alert defaults: %w", err)
	}
	if bundle.SchemaVersion != 1 || len(bundle.Rules) == 0 {
		return nil, errors.New("embedded alert defaults have an invalid bundle")
	}
	seen := make(map[string]struct{}, len(bundle.Rules))
	for _, rule := range bundle.Rules {
		if _, ok := seen[rule.ID]; ok {
			return nil, fmt.Errorf("embedded alert defaults contain duplicate rule %q", rule.ID)
		}
		seen[rule.ID] = struct{}{}
		if err := rule.Validate(registry); err != nil {
			return nil, fmt.Errorf("validate embedded alert default %q: %w", rule.ID, err)
		}
	}
	return bundle.Rules, nil
}

func Seed(ctx context.Context, store RuleStore, registry metriccatalog.Registry, actor string) (Report, error) {
	if store == nil {
		return Report{}, alert.ErrUnavailable
	}
	rules, err := Load(registry)
	if err != nil {
		return Report{}, err
	}
	report := Report{}
	for _, document := range rules {
		if _, _, err := store.Create(ctx, actor, document, "system default seed v1"); err == nil {
			report.Added++
		} else if errors.Is(err, alert.ErrConflict) {
			existing, getErr := store.Get(ctx, document.ID)
			if getErr != nil {
				return Report{}, fmt.Errorf("verify existing alert default %q: %w", document.ID, getErr)
			}
			if updater, ok := store.(RuleUpdater); ok && existing.Revision == 1 && !sameDocument(existing.Document, document) {
				// The stored default is untouched since the seed created it, but the
				// seed itself changed (for example a corrected metric binding). Refresh
				// it through the normal versioned update path so history is kept.
				if _, updErr := updater.Update(ctx, document.ID, actor, existing.Revision, document, "system default seed v1 refresh"); updErr != nil {
					return Report{}, fmt.Errorf("refresh alert default %q: %w", document.ID, updErr)
				}
				report.Refreshed++
				continue
			}
			report.Existing++
		} else {
			return Report{}, fmt.Errorf("seed alert default %q: %w", document.ID, err)
		}
	}
	return report, nil
}

// sameDocument compares two rule documents by their canonical JSON encoding.
func sameDocument(a, b alert.Document) bool {
	left, errA := json.Marshal(a)
	right, errB := json.Marshal(b)
	return errA == nil && errB == nil && bytes.Equal(left, right)
}