using SQLInsight.Core.Data;
using SQLInsight.Core.Instances;

namespace SQLInsight.Collectors.Performance;

/// <summary>
/// The heaviest statements (CPU, last 24 hours) from the plan cache, with their cached plans analyzed.
/// Plans are fetched as text with <c>sys.dm_exec_text_query_plan</c>: <c>sys.dm_exec_query_plan</c> returns NULL
/// for plans nested deeper than the xml type allows. TOP is applied before any plan is fetched.
/// </summary>
public sealed class PlanAnalysisCollector : Collector<PlanAnalysisSnapshot>
{
    public const int TopStatements = 50;

    public override string Name => "plan-analysis";
    public override TimeSpan DefaultInterval => TimeSpan.FromMinutes(30);
    public override IReadOnlyCollection<Capability> RequiredCapabilities => [Capability.DynamicManagementViews, Capability.TextQueryPlan];

    protected override async Task<PlanAnalysisSnapshot> CollectAsync(CollectorContext context, PlanAnalysisSnapshot? previous)
    {
        var memory = context.Capabilities.Has(Capability.QueryStatsMemoryColumns);
        var queryHash = context.Instance.Version.Major >= 10;
        var statements = await Db.QueryAsync(context.Connection, BuildSql(memory, queryHash), r => new AnalyzedStatement
        {
            QueryHash = r.String(0),
            DatabaseName = r.NullableString(1),
            StatementText = r.NullableString(2),
            Executions = r.Long(3),
            TotalWorkerTimeUs = r.Long(4),
            TotalElapsedTimeUs = r.Long(5),
            TotalLogicalReads = r.Long(6),
            TotalSpills = r.NullableLong(7),
            TotalGrantKb = r.NullableLong(8),
            TotalUsedGrantKb = r.NullableLong(9),
            LastExecution = r.NullableDateTime(10),
            Warnings = ShowplanAnalyzer.Analyze(r.NullableString(11)),
        }, context.CancellationToken).ConfigureAwait(false);

        return new PlanAnalysisSnapshot { CapturedAt = context.Now, Statements = statements };
    }

    /// <param name="queryHash">query_hash exists from SQL Server 2008; on 2005 a statement is its batch and offsets.</param>
    internal static string BuildSql(bool memoryColumns, bool queryHash = true)
    {
        var key = queryHash
            ? "CONVERT(varchar(20), qs.query_hash, 1)"
            : "sys.fn_varbintohexstr(qs.sql_handle) + ':' + CAST(qs.statement_start_offset AS varchar(12)) + ':' + CAST(qs.statement_end_offset AS varchar(12))";
        var memory = memoryColumns
            ? "qs.total_spills, qs.total_grant_kb, qs.total_used_grant_kb"
            : "CAST(NULL AS bigint), CAST(NULL AS bigint), CAST(NULL AS bigint)";
        return $"""
            WITH top_statements AS (
                SELECT TOP ({TopStatements}) qs.*
                FROM sys.dm_exec_query_stats qs
                WHERE qs.last_execution_time >= DATEADD(hour, -24, GETDATE())
                ORDER BY qs.total_worker_time DESC
            )
            SELECT {key},
                   DB_NAME(CONVERT(int, pa.value)),
                   LEFT(SUBSTRING(t.text, qs.statement_start_offset / 2 + 1,
                        (CASE WHEN qs.statement_end_offset = -1 THEN DATALENGTH(t.text) ELSE qs.statement_end_offset END - qs.statement_start_offset) / 2 + 1), 4000),
                   qs.execution_count, qs.total_worker_time, qs.total_elapsed_time, qs.total_logical_reads,
                   {memory},
                   qs.last_execution_time,
                   tp.query_plan
            FROM top_statements qs
            CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) t
            OUTER APPLY sys.dm_exec_text_query_plan(qs.plan_handle, qs.statement_start_offset, qs.statement_end_offset) tp
            OUTER APPLY (SELECT value FROM sys.dm_exec_plan_attributes(qs.plan_handle) WHERE attribute = N'dbid') pa
            ORDER BY qs.total_worker_time DESC;
            """;
    }
}