Pull out template engine and improve performance

[nikita-petko]

It currently performs a hell ton of RegEx calls that overtime, with more added parts of templates added, majorly decreases performance. The following template code can be used as an example:

# FourHours: 14400 (last week)
# OneDay: 86400 (last month)
# OneMinute: 60 (Last 15 minutes)
# ThirtyMinutes: 1800 (last day)
# ThreeDays: 259200 (last 3 months)
# TwoMinutes: 120 (Last hour)

# var granularities = {
#   OneMinute: 60,
#   TwoMinutes: 120,
#   FourHours: 14400,
#   OneDay: 86400,
#   ThirtyMinutes: 1800,
#   ThreeDays: 259200,
# };
#
# var actualTimings = {
#   Last15Minutes: 900,
#   LastHour: 3600,
#   LastDay: 86400,
#   LastWeek: 604800,
#   LastMonth: 2592000,
#   Last3Months: 7776000,
# };
#
# var granularityToActualTiming = {
#   OneMinute: "Last15Minutes",
#   TwoMinutes: "LastHour",
#   FourHours: "LastWeek",
#   OneDay: "LastMonth",
#   ThirtyMinutes: "LastDay",
#   ThreeDays: "Last3Months",
# };
#
# var granularity = granularities[req.query.granularity];
# var actualTiming = actualTimings[granularityToActualTiming[req.query.granularity]];
# var iterations = actualTiming / granularity;
#
# OUTPUT:
# Granularity   Actual Timing    Iterations
# OneMinute     Last15Minutes    16
# TwoMinutes    LastHour         31
# FourHours     LastWeek         169
# OneDay        LastMonth        31 -- depends on month
# ThirtyMinutes LastDay          49
# ThreeDays     Last3Months      91

- routeTemplate: /compute-telemetry-service/v1/universe/(?<universe_id>\d+)/place/(?<place_id>.+)/kpi-names/(?<kpi_name>[a-zA-Z]+)
  hostname: "arbitrary"
  statusCode: 200
  method: "*"
  templateVariables:
    # Constants
    oneMinute: 60
    twoMinutes: 120
    fourHours: 14400
    oneDay: 86400
    thirtyMinutes: 1800
    threeDays: 259200

    # Variable Expressions
    incrementExpr: >
      {{empty | 
         setVarSwitch increment number 
         ${request.query.granularity} eq OneMinute then ${oneMinute}; 
         ${request.query.granularity} eq TwoMinutes then ${twoMinutes}; 
         ${request.query.granularity} eq FourHours then ${fourHours}; 
         ${request.query.granularity} eq OneDay then ${oneDay}; 
         ${request.query.granularity} eq ThirtyMinutes then ${thirtyMinutes}; 
         ${request.query.granularity} eq ThreeDays then ${threeDays}}}
    iterationExpr: >
      {{empty | 
         setVarSwitch iteration number 
         ${request.query.granularity} eq OneMinute then 16; 
         ${request.query.granularity} eq TwoMinutes then 31; 
         ${request.query.granularity} eq FourHours then 169; 
         ${request.query.granularity} eq OneDay then 31; 
         ${request.query.granularity} eq ThirtyMinutes then 49; 
         ${request.query.granularity} eq ThreeDays then 91}}
    keyExpr: query.startTime | setVar increment number ${increment} * ${__index__} | fromIso | div 1000 | floor | add ${increment}
    valueExpr: randRange 0.0 5.0 | parseFloat | toFixed 2 | parseFloat
    limitValueExpr: randRange 0.0 5.0 | parseFloat | toFixed 2 | parseFloat | add 5.0 | toFixed 2 | parseFloat
    percentileValueExpr: randRange 0.0 1.0 | parseFloat | toFixed 2 | parseFloat | mul 100 | toFixed 2 | parseFloat

  body:
    {
      "placeId": "{{path.place_id | parseInt}}",
      "kpiName": "{{path.kpi_name}}",
      "startTime": "{{query.startTime | default number ${now_} | toIso}}",
      "endTime": "{{query.endTime | default number ${now_} + ${oneDay} | toIso}}",
      "data":
        {
          "Avg":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${valueExpr}}}",
            },
          "Limit":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${limitValueExpr}}}",
            },
          "P10":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
          "P50":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
          "P75":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
          "P90":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
          "P99":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
          "P999":
            {
              "data": "{{kvExpression ${iteration} ${keyExpr} --- ${percentileValueExpr}}}",
            },
        },
    }
  formatBody: true
  headers:
    Content-Type: application/json

The KV expression here will take more than 2 minutes to execute at base