package freshness

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
)

type QueryRowFunc func(ctx context.Context, sql string, args ...any) pgx.Row

type Confidence string

const (
	ConfidenceHigh    Confidence = "high"
	ConfidenceMedium  Confidence = "medium"
	ConfidenceLow     Confidence = "low"
	ConfidenceUnknown Confidence = "unknown"
)

type Completeness string

const (
	CompletenessComplete    Completeness = "complete"
	CompletenessPartial     Completeness = "partial"
	CompletenessStale       Completeness = "stale"
	CompletenessUnavailable Completeness = "unavailable"
)

type Source string

const (
	SourceReported    Source = "reported"
	SourceDerived     Source = "derived"
	SourceSampled     Source = "sampled"
	SourceUnavailable Source = "unavailable"
)

type Provenance string

const (
	ProvenanceRPC           Provenance = "rpc"
	ProvenanceExplorerIndex Provenance = "explorer_index"
	ProvenanceTxIndex       Provenance = "tx_index"
	ProvenanceMissionFeed   Provenance = "mission_control_feed"
	ProvenanceComposite     Provenance = "composite"
)

type Reference struct {
	BlockNumber      *int64       `json:"block_number"`
	Timestamp        *string      `json:"timestamp"`
	AgeSeconds       *int64       `json:"age_seconds"`
	Hash             *string      `json:"hash,omitempty"`
	DistanceFromHead *int64       `json:"distance_from_head,omitempty"`
	Source           Source       `json:"source"`
	Confidence       Confidence   `json:"confidence"`
	Provenance       Provenance   `json:"provenance"`
	Completeness     Completeness `json:"completeness,omitempty"`
}

type Snapshot struct {
	ChainHead                Reference `json:"chain_head"`
	LatestIndexedBlock       Reference `json:"latest_indexed_block"`
	LatestIndexedTransaction Reference `json:"latest_indexed_transaction"`
	LatestNonEmptyBlock      Reference `json:"latest_non_empty_block"`
}

type Diagnostics struct {
	TxVisibilityState           string       `json:"tx_visibility_state"`
	ActivityState               string       `json:"activity_state"`
	Explanation                 string       `json:"explanation,omitempty"`
	TxLagBlocks                 *int64       `json:"tx_lag_blocks,omitempty"`
	TxLagSeconds                *int64       `json:"tx_lag_seconds,omitempty"`
	RecentBlockSampleSize       *int64       `json:"recent_block_sample_size,omitempty"`
	RecentNonEmptyBlocks        *int64       `json:"recent_non_empty_blocks,omitempty"`
	RecentTransactions          *int64       `json:"recent_transactions,omitempty"`
	LatestNonEmptyFromBlockFeed Reference    `json:"latest_non_empty_block_from_block_feed"`
	Source                      Source       `json:"source"`
	Confidence                  Confidence   `json:"confidence"`
	Provenance                  Provenance   `json:"provenance"`
	Completeness                Completeness `json:"completeness"`
}

type SummaryCompleteness struct {
	TransactionsFeed  Completeness `json:"transactions_feed"`
	BlocksFeed        Completeness `json:"blocks_feed"`
	GasMetrics        Completeness `json:"gas_metrics"`
	UtilizationMetric Completeness `json:"utilization_metrics"`
}

type Sampling struct {
	StatsGeneratedAt *string           `json:"stats_generated_at"`
	RPCProbeAt       *string           `json:"rpc_probe_at"`
	StatsWindowSec   *int64            `json:"stats_window_seconds,omitempty"`
	Issues           map[string]string `json:"issues,omitempty"`
}

type HeadProbeFunc func(ctx context.Context) (*Reference, error)

func ptrInt64(value int64) *int64 { return &value }

func ptrString(value string) *string { return &value }

func unknownReference(provenance Provenance) Reference {
	return Reference{
		Source:       SourceUnavailable,
		Confidence:   ConfidenceUnknown,
		Provenance:   provenance,
		Completeness: CompletenessUnavailable,
	}
}

func timePointer(value time.Time) *string {
	if value.IsZero() {
		return nil
	}
	formatted := value.UTC().Format(time.RFC3339)
	return &formatted
}

func computeAge(timestamp *string, now time.Time) *int64 {
	if timestamp == nil || *timestamp == "" {
		return nil
	}
	parsed, err := time.Parse(time.RFC3339, *timestamp)
	if err != nil {
		return nil
	}
	age := int64(now.Sub(parsed).Seconds())
	if age < 0 {
		age = 0
	}
	return &age
}

func classifyIndexedVisibility(age *int64) Completeness {
	if age == nil {
		return CompletenessUnavailable
	}
	switch {
	case *age <= 15*60:
		return CompletenessComplete
	case *age <= 3*60*60:
		return CompletenessPartial
	default:
		return CompletenessStale
	}
}

func classifyBlockFeed(chainHead *int64, indexedHead *int64) Completeness {
	if chainHead == nil || indexedHead == nil {
		return CompletenessUnavailable
	}
	distance := *chainHead - *indexedHead
	if distance < 0 {
		distance = 0
	}
	switch {
	case distance <= 2:
		return CompletenessComplete
	case distance <= 32:
		return CompletenessPartial
	default:
		return CompletenessStale
	}
}

func classifyMetricPresence[T comparable](value *T) Completeness {
	if value == nil {
		return CompletenessUnavailable
	}
	return CompletenessComplete
}

func classifyTxVisibilityState(age *int64) string {
	if age == nil {
		return "unavailable"
	}
	switch {
	case *age <= 15*60:
		return "current"
	case *age <= 3*60*60:
		return "lagging"
	default:
		return "stale"
	}
}

func classifyActivityState(txVisibility string, txLagBlocks, recentTransactions, recentNonEmptyBlocks *int64) (string, string, Completeness) {
	if txVisibility == "unavailable" {
		if recentTransactions != nil && *recentTransactions > 0 {
			return "limited_observability", "Recent blocks show on-chain transaction activity, but indexed transaction freshness is unavailable.", CompletenessPartial
		}
		return "limited_observability", "Transaction freshness is unavailable, and recent block activity is limited.", CompletenessUnavailable
	}

	if recentTransactions != nil && *recentTransactions > 0 {
		if txLagBlocks != nil && *txLagBlocks > 32 {
			return "fresh_head_stale_transaction_visibility", "Recent block activity is present closer to the head than the visible indexed transaction feed.", CompletenessPartial
		}
		if *recentTransactions <= 3 {
			return "sparse_activity", "Recent blocks contain only a small amount of transaction activity.", CompletenessComplete
		}
		return "active", "Recent blocks contain visible transaction activity close to the head.", CompletenessComplete
	}

	if recentNonEmptyBlocks != nil && *recentNonEmptyBlocks == 0 {
		return "quiet_chain", "Recent sampled head blocks are empty, which indicates a quiet chain rather than a broken explorer.", CompletenessComplete
	}

	if txLagBlocks != nil && *txLagBlocks > 32 {
		return "fresh_head_stale_transaction_visibility", "The chain head is current, but the indexed transaction feed trails the current tip.", CompletenessPartial
	}

	return "sparse_activity", "Recent visible transaction activity is limited.", CompletenessComplete
}

func BuildSnapshot(
	ctx context.Context,
	chainID int,
	queryRow QueryRowFunc,
	probeHead HeadProbeFunc,
	now time.Time,
	averageGasPrice *float64,
	utilization *float64,
) (Snapshot, SummaryCompleteness, Sampling, Diagnostics, error) {
	snapshot := Snapshot{
		ChainHead:                unknownReference(ProvenanceRPC),
		LatestIndexedBlock:       unknownReference(ProvenanceExplorerIndex),
		LatestIndexedTransaction: unknownReference(ProvenanceTxIndex),
		LatestNonEmptyBlock:      unknownReference(ProvenanceTxIndex),
	}
	diagnostics := Diagnostics{
		TxVisibilityState:           "unavailable",
		ActivityState:               "limited_observability",
		LatestNonEmptyFromBlockFeed: unknownReference(ProvenanceExplorerIndex),
		Source:                      SourceReported,
		Confidence:                  ConfidenceMedium,
		Provenance:                  ProvenanceComposite,
		Completeness:                CompletenessUnavailable,
	}
	issues := map[string]string{}

	if probeHead != nil {
		if head, err := probeHead(ctx); err == nil && head != nil {
			snapshot.ChainHead = *head
		} else if err != nil {
			issues["chain_head"] = err.Error()
		}
	}

	var latestIndexedBlockNumber int64
	var latestIndexedBlockTime time.Time
	if err := queryRow(ctx,
		`SELECT number, timestamp
		 FROM blocks
		 ORDER BY number DESC
		 LIMIT 1`,
	).Scan(&latestIndexedBlockNumber, &latestIndexedBlockTime); err == nil {
		timestamp := timePointer(latestIndexedBlockTime)
		snapshot.LatestIndexedBlock = Reference{
			BlockNumber:  ptrInt64(latestIndexedBlockNumber),
			Timestamp:    timestamp,
			AgeSeconds:   computeAge(timestamp, now),
			Source:       SourceReported,
			Confidence:   ConfidenceHigh,
			Provenance:   ProvenanceExplorerIndex,
			Completeness: CompletenessComplete,
		}
	} else {
		issues["latest_indexed_block"] = err.Error()
	}

	var latestTxHash string
	var latestTxBlock int64
	var latestTxCreatedAt time.Time
	if err := queryRow(ctx,
		`SELECT concat('0x', encode(hash, 'hex')), block_number::bigint, COALESCE(block_timestamp, inserted_at)
		 FROM transactions
		 WHERE block_number IS NOT NULL
		 ORDER BY block_number DESC, "index" DESC
		 LIMIT 1`,
	).Scan(&latestTxHash, &latestTxBlock, &latestTxCreatedAt); err == nil {
		timestamp := timePointer(latestTxCreatedAt)
		snapshot.LatestIndexedTransaction = Reference{
			BlockNumber:  ptrInt64(latestTxBlock),
			Timestamp:    timestamp,
			AgeSeconds:   computeAge(timestamp, now),
			Hash:         ptrString(latestTxHash),
			Source:       SourceReported,
			Confidence:   ConfidenceHigh,
			Provenance:   ProvenanceTxIndex,
			Completeness: classifyIndexedVisibility(computeAge(timestamp, now)),
		}
	} else {
		issues["latest_indexed_transaction"] = err.Error()
	}

	var latestNonEmptyBlockNumber int64
	var latestNonEmptyBlockTime time.Time
	if err := queryRow(ctx,
		`SELECT b.number, b.timestamp
		 FROM blocks b
		 WHERE EXISTS (
		     SELECT 1
		     FROM transactions t
		     WHERE t.block_number = b.number
		   )
		 ORDER BY b.number DESC
		 LIMIT 1`,
	).Scan(&latestNonEmptyBlockNumber, &latestNonEmptyBlockTime); err == nil {
		timestamp := timePointer(latestNonEmptyBlockTime)
		ref := Reference{
			BlockNumber:  ptrInt64(latestNonEmptyBlockNumber),
			Timestamp:    timestamp,
			AgeSeconds:   computeAge(timestamp, now),
			Source:       SourceReported,
			Confidence:   ConfidenceHigh,
			Provenance:   ProvenanceTxIndex,
			Completeness: classifyIndexedVisibility(computeAge(timestamp, now)),
		}
		if snapshot.ChainHead.BlockNumber != nil {
			distance := *snapshot.ChainHead.BlockNumber - latestNonEmptyBlockNumber
			if distance < 0 {
				distance = 0
			}
			ref.DistanceFromHead = ptrInt64(distance)
		}
		snapshot.LatestNonEmptyBlock = ref
	} else {
		issues["latest_non_empty_block"] = err.Error()
	}

	var latestBlockFeedNonEmptyNumber int64
	var latestBlockFeedNonEmptyTime time.Time
	if err := queryRow(ctx,
		`SELECT b.number, b.timestamp
		 FROM blocks b
		 JOIN (
		   SELECT DISTINCT block_number
		   FROM transactions
		   WHERE block_number IS NOT NULL
		 ) tx_blocks
		   ON tx_blocks.block_number = b.number
		 ORDER BY b.number DESC
		 LIMIT 1`,
	).Scan(&latestBlockFeedNonEmptyNumber, &latestBlockFeedNonEmptyTime); err == nil {
		timestamp := timePointer(latestBlockFeedNonEmptyTime)
		ref := Reference{
			BlockNumber:  ptrInt64(latestBlockFeedNonEmptyNumber),
			Timestamp:    timestamp,
			AgeSeconds:   computeAge(timestamp, now),
			Source:       SourceDerived,
			Confidence:   ConfidenceMedium,
			Provenance:   ProvenanceComposite,
			Completeness: snapshot.LatestIndexedTransaction.Completeness,
		}
		if snapshot.ChainHead.BlockNumber != nil {
			distance := *snapshot.ChainHead.BlockNumber - latestBlockFeedNonEmptyNumber
			if distance < 0 {
				distance = 0
			}
			ref.DistanceFromHead = ptrInt64(distance)
		}
		diagnostics.LatestNonEmptyFromBlockFeed = ref
	} else {
		issues["latest_non_empty_block_from_block_feed"] = err.Error()
	}

	var recentBlockSampleSize, recentNonEmptyBlocks, recentTransactions int64
	if err := queryRow(ctx,
		`SELECT COUNT(*)::bigint,
		        COUNT(*) FILTER (WHERE COALESCE(tx_counts.tx_count, 0) > 0)::bigint,
		        COALESCE(SUM(COALESCE(tx_counts.tx_count, 0)), 0)::bigint
		 FROM (
		   SELECT number
		   FROM blocks
		   ORDER BY number DESC
		   LIMIT 128
		 ) recent_blocks
		 LEFT JOIN (
		   SELECT block_number, COUNT(*)::bigint AS tx_count
		   FROM transactions
		   WHERE block_number IS NOT NULL
		   GROUP BY block_number
		 ) tx_counts
		   ON tx_counts.block_number = recent_blocks.number`,
	).Scan(&recentBlockSampleSize, &recentNonEmptyBlocks, &recentTransactions); err == nil {
		diagnostics.RecentBlockSampleSize = ptrInt64(recentBlockSampleSize)
		diagnostics.RecentNonEmptyBlocks = ptrInt64(recentNonEmptyBlocks)
		diagnostics.RecentTransactions = ptrInt64(recentTransactions)
	} else {
		issues["recent_block_activity"] = err.Error()
	}

	if snapshot.ChainHead.BlockNumber != nil && snapshot.LatestIndexedTransaction.BlockNumber != nil {
		lag := *snapshot.ChainHead.BlockNumber - *snapshot.LatestIndexedTransaction.BlockNumber
		if lag < 0 {
			lag = 0
		}
		diagnostics.TxLagBlocks = ptrInt64(lag)
	}
	diagnostics.TxLagSeconds = snapshot.LatestIndexedTransaction.AgeSeconds
	diagnostics.TxVisibilityState = classifyTxVisibilityState(snapshot.LatestIndexedTransaction.AgeSeconds)
	diagnostics.ActivityState, diagnostics.Explanation, diagnostics.Completeness = classifyActivityState(
		diagnostics.TxVisibilityState,
		diagnostics.TxLagBlocks,
		diagnostics.RecentTransactions,
		diagnostics.RecentNonEmptyBlocks,
	)

	statsGeneratedAt := now.UTC().Format(time.RFC3339)
	sampling := Sampling{
		StatsGeneratedAt: ptrString(statsGeneratedAt),
		StatsWindowSec:   ptrInt64(300),
	}
	if len(issues) > 0 {
		sampling.Issues = issues
	}
	if snapshot.ChainHead.Timestamp != nil {
		sampling.RPCProbeAt = snapshot.ChainHead.Timestamp
	}

	completeness := SummaryCompleteness{
		TransactionsFeed:  snapshot.LatestIndexedTransaction.Completeness,
		BlocksFeed:        classifyBlockFeed(snapshot.ChainHead.BlockNumber, snapshot.LatestIndexedBlock.BlockNumber),
		GasMetrics:        classifyMetricPresence(averageGasPrice),
		UtilizationMetric: classifyMetricPresence(utilization),
	}

	return snapshot, completeness, sampling, diagnostics, nil
}

func ProbeChainHead(ctx context.Context, rpcURL string) (*Reference, error) {
	rpcURL = strings.TrimSpace(rpcURL)
	if rpcURL == "" {
		return nil, fmt.Errorf("empty rpc url")
	}

	blockNumberRaw, _, err := postJSONRPC(ctx, rpcURL, "eth_blockNumber", []interface{}{})
	if err != nil {
		return nil, err
	}
	var blockNumberHex string
	if err := json.Unmarshal(blockNumberRaw, &blockNumberHex); err != nil {
		return nil, err
	}
	blockNumber, err := strconv.ParseInt(strings.TrimPrefix(strings.TrimSpace(blockNumberHex), "0x"), 16, 64)
	if err != nil {
		return nil, err
	}

	blockRaw, _, err := postJSONRPC(ctx, rpcURL, "eth_getBlockByNumber", []interface{}{"latest", false})
	if err != nil {
		return nil, err
	}
	var latestBlock struct {
		Timestamp string `json:"timestamp"`
	}
	if err := json.Unmarshal(blockRaw, &latestBlock); err != nil {
		return nil, err
	}
	blockTimeHex := strings.TrimSpace(latestBlock.Timestamp)
	if blockTimeHex == "" {
		return nil, fmt.Errorf("missing block timestamp")
	}
	blockTimestamp, err := strconv.ParseInt(strings.TrimPrefix(blockTimeHex, "0x"), 16, 64)
	if err != nil {
		return nil, err
	}
	ts := time.Unix(blockTimestamp, 0).UTC()
	timestamp := ts.Format(time.RFC3339)
	now := time.Now().UTC()
	age := int64(now.Sub(ts).Seconds())
	if age < 0 {
		age = 0
	}

	return &Reference{
		BlockNumber:  ptrInt64(blockNumber),
		Timestamp:    ptrString(timestamp),
		AgeSeconds:   ptrInt64(age),
		Source:       SourceReported,
		Confidence:   ConfidenceHigh,
		Provenance:   ProvenanceRPC,
		Completeness: CompletenessComplete,
	}, nil
}

func postJSONRPC(ctx context.Context, rpcURL string, method string, params []interface{}) (json.RawMessage, int64, error) {
	body, err := json.Marshal(map[string]interface{}{
		"jsonrpc": "2.0",
		"id":      1,
		"method":  method,
		"params":  params,
	})
	if err != nil {
		return nil, 0, err
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(body))
	if err != nil {
		return nil, 0, err
	}
	req.Header.Set("Content-Type", "application/json")

	client := &http.Client{Timeout: 6 * time.Second}
	start := time.Now()
	resp, err := client.Do(req)
	latency := time.Since(start).Milliseconds()
	if err != nil {
		return nil, latency, err
	}
	defer resp.Body.Close()

	payload, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return nil, latency, err
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, latency, fmt.Errorf("http %d", resp.StatusCode)
	}

	var out struct {
		Result json.RawMessage `json:"result"`
		Error  *struct {
			Message string `json:"message"`
		} `json:"error"`
	}
	if err := json.Unmarshal(payload, &out); err != nil {
		return nil, latency, err
	}
	if out.Error != nil && out.Error.Message != "" {
		return nil, latency, fmt.Errorf("rpc error: %s", out.Error.Message)
	}
	return out.Result, latency, nil
}