package requestlog

import (
	"context"
	"fmt"
	"time"

	"gorm.io/gorm"

	"gpt-load/internal/platform/epochms"
	"gpt-load/internal/pricing"
	"gpt-load/internal/storage/dbtx"
	"gpt-load/internal/storage/models"
	"gpt-load/internal/usage"
)

const (
	usageDistributionLimit = 5
	usageRollbackTimeout   = time.Second
)

func (service *Service) QueryUsage(ctx context.Context, input UsageQuery) (UsageReport, error) {
	if service == nil || service.db == nil {
		return UsageReport{}, fmt.Errorf("query usage: database is nil")
	}
	if ctx == nil {
		ctx = context.Background()
	}
	bucketWidthMS, err := validateUsageQuery(input)
	if err != nil {
		return UsageReport{}, err
	}

	var report UsageReport
	err = dbtx.Run(ctx, service.db, dbtx.Options{
		Mode:           dbtx.ReadSnapshot,
		CleanupTimeout: usageRollbackTimeout,
		Operation:      "usage read transaction",
	}, func(connection *gorm.DB) error {
		scope := usageWindowScope(connection, input)
		// 5 分钟趋势不能由小时汇总还原；总览、趋势与分布共用请求明细来源。
		if bucketWidthMS == UsageFiveMinuteBucketMS {
			scope = usageRequestLogScope(connection, input)
		}
		if err := validateUsageIntegrity(scope, 0); err != nil {
			return err
		}
		summary, err := queryUsageSummary(scope.Session(&gorm.Session{}))
		if err != nil {
			return err
		}
		series, err := queryUsageWindowSeries(scope.Session(&gorm.Session{}), input, bucketWidthMS)
		if err != nil {
			return err
		}
		distributions, err := queryUsageDistributions(
			scope.Session(&gorm.Session{}), summary, input.SelfScoped,
		)
		if err != nil {
			return err
		}
		report = UsageReport{
			Summary: summary, Series: series, Distributions: distributions,
		}
		return nil
	})
	if err != nil {
		return UsageReport{}, fmt.Errorf("query usage: %w", err)
	}
	return report, nil
}

func validateUsageQuery(input UsageQuery) (int64, error) {
	_, bucketWidthMS, err := ResolveUsageTimeBucket(input.FromMS, input.ToMS)
	if err != nil {
		return 0, err
	}
	if input.AccessKeyID != nil && *input.AccessKeyID == 0 {
		return 0, fmt.Errorf("query usage: invalid access key scope")
	}
	if input.ChannelID != "" && !validChannelID(string(input.ChannelID)) {
		return 0, fmt.Errorf("query usage: invalid channel scope")
	}
	if input.CredentialID != nil && *input.CredentialID == 0 {
		return 0, fmt.Errorf("query usage: invalid credential scope")
	}
	return bucketWidthMS, nil
}

func queryUsageDistributions(
	scope *gorm.DB,
	summary UsageAggregate,
	selfScoped bool,
) (UsageDistributions, error) {
	result := UsageDistributions{
		Group:     make(map[UsageDistributionMetric]UsageDistribution, 3),
		Model:     make(map[UsageDistributionMetric]UsageDistribution, 3),
		AccessKey: make(map[UsageDistributionMetric]UsageDistribution, 3),
	}
	dimensions := []UsageDistributionDimension{
		UsageDistributionDimensionGroup,
		UsageDistributionDimensionModel,
		UsageDistributionDimensionAccessKey,
	}
	if selfScoped {
		dimensions = []UsageDistributionDimension{UsageDistributionDimensionModel}
	}
	for _, dimension := range dimensions {
		for _, metric := range []UsageDistributionMetric{
			UsageDistributionMetricRequests,
			UsageDistributionMetricTokens,
			UsageDistributionMetricCost,
		} {
			distribution, err := queryUsageDistribution(scope, summary, dimension, metric)
			if err != nil {
				return UsageDistributions{}, err
			}
			switch dimension {
			case UsageDistributionDimensionGroup:
				result.Group[metric] = distribution
			case UsageDistributionDimensionModel:
				result.Model[metric] = distribution
			case UsageDistributionDimensionAccessKey:
				result.AccessKey[metric] = distribution
			}
		}
	}
	return result, nil
}

func usageStatScope(db *gorm.DB, input UsageQuery, groupIDs ...uint) *gorm.DB {
	scope := db.Session(&gorm.Session{NewDB: true}).Model(&models.UsageStat{}).
		Where("bucket_start_ms >= ? AND bucket_start_ms < ?", input.FromMS, input.ToMS).
		// Older versions aggregated zero-attempt requests under the unbound
		// (group_id=0, model='') key. Keep those derived rows invisible so home
		// and monitor share the current contract.
		Where("NOT (group_id = ? AND model = ?)", 0, "")
	if len(groupIDs) > 0 {
		scope = scope.Where("group_id IN ?", groupIDs)
	}
	if input.GroupID != nil {
		scope = scope.Where("group_id = ?", *input.GroupID)
	}
	if input.ChannelID != "" {
		scope = scope.Where("channel_id = ?", input.ChannelID)
	}
	if input.CredentialID != nil {
		scope = scope.Where("credential_id = ?", *input.CredentialID)
	}
	if input.AccessKeyID != nil {
		scope = scope.Where("access_key_id = ?", *input.AccessKeyID)
	}
	if input.UpstreamModel != "" {
		scope = scope.Where("model = ?", input.UpstreamModel)
	}
	return scope
}

func validateUsageStatIntegrity(scope *gorm.DB) error {
	return validateUsageIntegrity(scope, epochms.MillisecondsPerHour)
}

func validateUsageIntegrity(scope *gorm.DB, bucketAlignmentMS int64) error {
	var integrity usageStatIntegrity
	alignmentExpression := "?"
	var arguments []any
	if bucketAlignmentMS == 0 {
		// 混合行集携带原始来源的桶宽，不能把损坏的小时记录按分钟桶放行。
		alignmentExpression = "bucket_alignment_ms"
	} else {
		arguments = append(arguments, bucketAlignmentMS)
	}
	if err := scope.Session(&gorm.Session{}).Select(`
		COALESCE(MAX(CASE
			WHEN bucket_start_ms < 0
				OR bucket_start_ms % `+alignmentExpression+` != 0
			THEN 1 ELSE 0 END), 0) AS invalid_bucket,
		COALESCE(MAX(CASE
			WHEN request_count < 0 OR success_count < 0 OR failure_count < 0
					OR usage_missing_count < 0 OR partial_count < 0 OR unpriced_request_count < 0
					OR pricing_partial_count < 0
				OR CASE
					WHEN request_count < success_count THEN 1
					WHEN request_count - success_count != failure_count THEN 1
					ELSE 0
				END = 1
			THEN 1 ELSE 0 END), 0) AS invalid_count,
		COALESCE(MAX(CASE
			WHEN uncached_input_tokens < 0 OR output_tokens < 0 OR cache_read_tokens < 0
					OR cache_write_5m_tokens < 0 OR cache_write_1h_tokens < 0
					OR cache_write_unknown_tokens < 0
			THEN 1 ELSE 0 END), 0) AS invalid_token,
		COALESCE(MAX(CASE
			WHEN estimated_cost_nano_usd < 0
			THEN 1 ELSE 0 END), 0) AS invalid_cost
	`, arguments...).Find(&integrity).Error; err != nil {
		return fmt.Errorf("check usage stat integrity: %w", err)
	}
	if integrity.InvalidBucket != 0 || integrity.InvalidCount != 0 ||
		integrity.InvalidToken != 0 || integrity.InvalidCost != 0 {
		return fmt.Errorf("check usage stat integrity: corrupt row")
	}
	return nil
}

func queryUsageSummary(scope *gorm.DB) (UsageAggregate, error) {
	var summary UsageAggregate
	if err := scope.Select(usageAggregateSelect).Find(&summary).Error; err != nil {
		return UsageAggregate{}, fmt.Errorf("query usage summary: %w", err)
	}
	if err := validateUsageAggregate(summary); err != nil {
		return UsageAggregate{}, fmt.Errorf("validate usage summary: %w", err)
	}
	return summary, nil
}

func queryUsageSeries(scope *gorm.DB, bucketWidthMS int64) ([]UsageSeriesPoint, error) {
	if bucketWidthMS < epochms.MillisecondsPerHour ||
		bucketWidthMS > epochms.MillisecondsPerDay ||
		bucketWidthMS%epochms.MillisecondsPerHour != 0 {
		return nil, fmt.Errorf("query usage series: invalid bucket width %d", bucketWidthMS)
	}
	var source []usageHourPoint
	if err := scope.Select("bucket_start_ms, " + usageAggregateSelect).
		Group("bucket_start_ms").
		Order("bucket_start_ms ASC").
		Find(&source).Error; err != nil {
		return nil, fmt.Errorf("query usage source series: %w", err)
	}

	for _, point := range source {
		if err := validateUsageAggregate(point.UsageAggregate); err != nil {
			return nil, fmt.Errorf("validate usage source series: %w", err)
		}
	}
	if bucketWidthMS == epochms.MillisecondsPerHour {
		series := make([]UsageSeriesPoint, 0, len(source))
		for _, point := range source {
			series = append(series, UsageSeriesPoint{
				BucketStartMS:  point.BucketStartMS,
				BucketEndMS:    point.BucketStartMS + epochms.MillisecondsPerHour,
				UsageAggregate: point.UsageAggregate,
			})
		}
		return series, nil
	}
	return mergeUsageHours(source, bucketWidthMS)
}

func queryUsageDistribution(
	scope *gorm.DB,
	summary UsageAggregate,
	dimension UsageDistributionDimension,
	metric UsageDistributionMetric,
) (UsageDistribution, error) {
	var rows []usageDistributionRow
	query := scope.Session(&gorm.Session{})
	switch dimension {
	case UsageDistributionDimensionGroup:
		query = query.Select("group_id, 0 AS access_key_id, '' AS model, "+usageDistributionAggregateSelect).
			Where("group_id IN (?)", scope.Session(&gorm.Session{NewDB: true}).
				Model(&models.Group{}).Select("id")).
			Group("group_id")
	case UsageDistributionDimensionModel:
		query = query.Select("0 AS group_id, 0 AS access_key_id, model, " + usageDistributionAggregateSelect).
			Group("model")
	case UsageDistributionDimensionAccessKey:
		query = query.Select("0 AS group_id, access_key_id, '' AS model, "+usageDistributionAggregateSelect).
			Where("access_key_id IN (?)", scope.Session(&gorm.Session{NewDB: true}).
				Model(&models.AccessKey{}).Select("id")).
			Group("access_key_id")
	default:
		return UsageDistribution{}, fmt.Errorf(
			"query usage distribution: unsupported dimension %q",
			dimension,
		)
	}
	switch metric {
	case UsageDistributionMetricRequests:
		query = query.
			Order("SUM(request_count) DESC").
			Order("SUM(estimated_cost_nano_usd) DESC")
	case UsageDistributionMetricTokens:
		query = query.
			Order(usageDistributionTotalTokensExpression + " DESC").
			Order("SUM(request_count) DESC").
			Order("SUM(estimated_cost_nano_usd) DESC")
	case UsageDistributionMetricCost:
		query = query.
			Order("SUM(estimated_cost_nano_usd) DESC").
			Order("SUM(request_count) DESC")
	default:
		return UsageDistribution{}, fmt.Errorf(
			"query usage distribution: unsupported metric %q",
			metric,
		)
	}
	switch dimension {
	case UsageDistributionDimensionGroup:
		query = query.Order("group_id ASC")
	case UsageDistributionDimensionModel:
		query = query.Order("model ASC")
	case UsageDistributionDimensionAccessKey:
		query = query.Order("access_key_id ASC")
	}
	if err := query.
		Limit(usageDistributionLimit).
		Find(&rows).Error; err != nil {
		return UsageDistribution{}, fmt.Errorf("query usage distribution: %w", err)
	}

	result := UsageDistribution{
		Dimension: dimension,
		Metric:    metric,
		Items:     make([]UsageDistributionItem, 0, len(rows)),
	}
	visible := UsageDistributionAggregate{}
	for _, row := range rows {
		var err error
		visible, err = addUsageDistributionAggregates(visible, row.UsageDistributionAggregate)
		if err != nil {
			return UsageDistribution{}, fmt.Errorf("sum usage distribution: %w", err)
		}
		result.Items = append(result.Items, UsageDistributionItem{
			GroupID: row.GroupID, AccessKeyID: row.AccessKeyID, Model: row.Model,
			UsageDistributionAggregate: row.UsageDistributionAggregate,
		})
	}
	other, err := subtractUsageDistributionAggregate(summary, visible)
	if err != nil {
		return UsageDistribution{}, fmt.Errorf("calculate other usage distribution: %w", err)
	}
	if other.RequestCount > 0 || other.TotalTokens > 0 || other.EstimatedCostNanoUSD > 0 {
		result.Other = &other
	}
	return result, nil
}

func mergeUsageHours(source []usageHourPoint, bucketWidthMS int64) ([]UsageSeriesPoint, error) {
	// queryUsageSeries orders source by bucket_start_ms ASC; adjacent-only
	// bucket folding depends on it.
	series := make([]UsageSeriesPoint, 0, len(source))
	for _, point := range source {
		bucketStartMS, err := epochms.AlignDown(
			point.BucketStartMS,
			bucketWidthMS,
		)
		if err != nil {
			return nil, fmt.Errorf("align usage bucket: %w", err)
		}
		if len(series) == 0 || series[len(series)-1].BucketStartMS != bucketStartMS {
			series = append(series, UsageSeriesPoint{
				BucketStartMS:  bucketStartMS,
				BucketEndMS:    bucketStartMS + bucketWidthMS,
				UsageAggregate: point.UsageAggregate,
			})
			continue
		}
		merged, err := addUsageAggregates(series[len(series)-1].UsageAggregate, point.UsageAggregate)
		if err != nil {
			return nil, fmt.Errorf("merge usage bucket %d: %w", bucketStartMS, err)
		}
		series[len(series)-1].UsageAggregate = merged
	}
	return series, nil
}

func addUsageAggregates(left, right UsageAggregate) (UsageAggregate, error) {
	result := UsageAggregate{}
	fields := []struct {
		name        string
		left, right int64
		target      *int64
	}{
		{"request count", left.RequestCount, right.RequestCount, &result.RequestCount},
		{"success count", left.SuccessCount, right.SuccessCount, &result.SuccessCount},
		{"failure count", left.FailureCount, right.FailureCount, &result.FailureCount},
		{"uncached input tokens", left.UncachedInputTokens, right.UncachedInputTokens, &result.UncachedInputTokens},
		{"cache read tokens", left.CacheReadTokens, right.CacheReadTokens, &result.CacheReadTokens},
		{"cache write 5m tokens", left.CacheWrite5MTokens, right.CacheWrite5MTokens, &result.CacheWrite5MTokens},
		{"cache write 1h tokens", left.CacheWrite1HTokens, right.CacheWrite1HTokens, &result.CacheWrite1HTokens},
		{"cache write unknown tokens", left.CacheWriteUnknownTokens, right.CacheWriteUnknownTokens, &result.CacheWriteUnknownTokens},
		{"output tokens", left.OutputTokens, right.OutputTokens, &result.OutputTokens},
		{"usage missing count", left.UsageMissingCount, right.UsageMissingCount, &result.UsageMissingCount},
		{"partial count", left.PartialCount, right.PartialCount, &result.PartialCount},
		{"unpriced request count", left.UnpricedRequestCount, right.UnpricedRequestCount, &result.UnpricedRequestCount},
		{"pricing partial count", left.PricingPartialCount, right.PricingPartialCount, &result.PricingPartialCount},
	}
	for _, field := range fields {
		value, ok := usage.CheckedAdd(field.left, field.right)
		if !ok {
			return UsageAggregate{}, fmt.Errorf("%s overflow or negative", field.name)
		}
		*field.target = value
	}
	cost, ok := pricing.CheckedAddNanoUSD(
		pricing.NanoUSD(left.EstimatedCostNanoUSD),
		pricing.NanoUSD(right.EstimatedCostNanoUSD),
	)
	if !ok {
		return UsageAggregate{}, fmt.Errorf("estimated cost nano USD overflow or negative")
	}
	result.EstimatedCostNanoUSD = int64(cost)
	if err := validateUsageAggregate(result); err != nil {
		return UsageAggregate{}, err
	}
	return result, nil
}

func addUsageDistributionAggregates(
	left, right UsageDistributionAggregate,
) (UsageDistributionAggregate, error) {
	requests, ok := usage.CheckedAdd(left.RequestCount, right.RequestCount)
	if !ok {
		return UsageDistributionAggregate{}, fmt.Errorf("request count overflow or negative")
	}
	tokens, ok := usage.CheckedAdd(left.TotalTokens, right.TotalTokens)
	if !ok {
		return UsageDistributionAggregate{}, fmt.Errorf("total tokens overflow or negative")
	}
	cost, ok := pricing.CheckedAddNanoUSD(
		pricing.NanoUSD(left.EstimatedCostNanoUSD),
		pricing.NanoUSD(right.EstimatedCostNanoUSD),
	)
	if !ok {
		return UsageDistributionAggregate{}, fmt.Errorf("estimated cost overflow or negative")
	}
	return UsageDistributionAggregate{
		RequestCount: requests, TotalTokens: tokens, EstimatedCostNanoUSD: int64(cost),
	}, nil
}

func subtractUsageDistributionAggregate(
	total UsageAggregate,
	part UsageDistributionAggregate,
) (UsageDistributionAggregate, error) {
	totalTokens, err := usageAggregateTotalTokens(total)
	if err != nil {
		return UsageDistributionAggregate{}, err
	}
	if part.RequestCount < 0 || part.RequestCount > total.RequestCount ||
		part.TotalTokens < 0 || part.TotalTokens > totalTokens ||
		part.EstimatedCostNanoUSD < 0 || part.EstimatedCostNanoUSD > total.EstimatedCostNanoUSD {
		return UsageDistributionAggregate{}, fmt.Errorf("invalid distribution remainder")
	}
	return UsageDistributionAggregate{
		RequestCount:         total.RequestCount - part.RequestCount,
		TotalTokens:          totalTokens - part.TotalTokens,
		EstimatedCostNanoUSD: total.EstimatedCostNanoUSD - part.EstimatedCostNanoUSD,
	}, nil
}

func validateUsageAggregate(aggregate UsageAggregate) error {
	fields := []struct {
		name  string
		value int64
	}{
		{"request count", aggregate.RequestCount},
		{"success count", aggregate.SuccessCount},
		{"failure count", aggregate.FailureCount},
		{"uncached input tokens", aggregate.UncachedInputTokens},
		{"cache read tokens", aggregate.CacheReadTokens},
		{"cache write 5m tokens", aggregate.CacheWrite5MTokens},
		{"cache write 1h tokens", aggregate.CacheWrite1HTokens},
		{"cache write unknown tokens", aggregate.CacheWriteUnknownTokens},
		{"output tokens", aggregate.OutputTokens},
		{"usage missing count", aggregate.UsageMissingCount},
		{"partial count", aggregate.PartialCount},
		{"unpriced request count", aggregate.UnpricedRequestCount},
		{"pricing partial count", aggregate.PricingPartialCount},
	}
	for _, field := range fields {
		if field.value < 0 {
			return fmt.Errorf("negative %s", field.name)
		}
	}
	requestCount, ok := usage.CheckedAdd(aggregate.SuccessCount, aggregate.FailureCount)
	if !ok || requestCount != aggregate.RequestCount {
		return fmt.Errorf("request count does not equal success plus failure")
	}
	if _, err := usageAggregateTotalTokens(aggregate); err != nil {
		return err
	}
	if aggregate.EstimatedCostNanoUSD < 0 {
		return fmt.Errorf("invalid cost")
	}
	return nil
}

func usageAggregateTotalTokens(aggregate UsageAggregate) (int64, error) {
	totalTokens := int64(0)
	for _, value := range []int64{
		aggregate.UncachedInputTokens,
		aggregate.CacheReadTokens,
		aggregate.CacheWrite5MTokens,
		aggregate.CacheWrite1HTokens,
		aggregate.CacheWriteUnknownTokens,
		aggregate.OutputTokens,
	} {
		var added bool
		totalTokens, added = usage.CheckedAdd(totalTokens, value)
		if !added {
			return 0, fmt.Errorf("total tokens overflow")
		}
	}
	return totalTokens, nil
}

// Aliases follow GORM's snake-case mapping for embedded UsageAggregate fields (for example, 5M -> 5_m).
const usageAggregateSelect = "" +
	"COALESCE(SUM(request_count), 0) AS request_count, " +
	"COALESCE(SUM(success_count), 0) AS success_count, " +
	"COALESCE(SUM(failure_count), 0) AS failure_count, " +
	"COALESCE(SUM(uncached_input_tokens), 0) AS uncached_input_tokens, " +
	"COALESCE(SUM(cache_read_tokens), 0) AS cache_read_tokens, " +
	"COALESCE(SUM(cache_write_5m_tokens), 0) AS cache_write5_m_tokens, " +
	"COALESCE(SUM(cache_write_1h_tokens), 0) AS cache_write1_h_tokens, " +
	"COALESCE(SUM(cache_write_unknown_tokens), 0) AS cache_write_unknown_tokens, " +
	"COALESCE(SUM(output_tokens), 0) AS output_tokens, " +
	"COALESCE(SUM(estimated_cost_nano_usd), 0) AS estimated_cost_nano_usd, " +
	"COALESCE(SUM(usage_missing_count), 0) AS usage_missing_count, " +
	"COALESCE(SUM(partial_count), 0) AS partial_count, " +
	"COALESCE(SUM(unpriced_request_count), 0) AS unpriced_request_count, " +
	"COALESCE(SUM(pricing_partial_count), 0) AS pricing_partial_count"

const usageDistributionTotalTokensExpression = "" +
	"COALESCE(SUM(uncached_input_tokens), 0) + " +
	"COALESCE(SUM(cache_read_tokens), 0) + " +
	"COALESCE(SUM(cache_write_5m_tokens), 0) + " +
	"COALESCE(SUM(cache_write_1h_tokens), 0) + " +
	"COALESCE(SUM(cache_write_unknown_tokens), 0) + " +
	"COALESCE(SUM(output_tokens), 0)"

const usageDistributionAggregateSelect = "" +
	"COALESCE(SUM(request_count), 0) AS request_count, " +
	usageDistributionTotalTokensExpression + " AS total_tokens, " +
	"COALESCE(SUM(estimated_cost_nano_usd), 0) AS estimated_cost_nano_usd"

type usageHourPoint struct {
	BucketStartMS int64
	UsageAggregate
}

type usageStatIntegrity struct {
	InvalidBucket int64
	InvalidCount  int64
	InvalidToken  int64
	InvalidCost   int64
}

type usageDistributionRow struct {
	GroupID     uint
	AccessKeyID uint
	Model       string
	UsageDistributionAggregate
}