feat: Add infracost_breakdown hook (#252)

.github/CONTRIBUTING.md

@@ -12,6 +12,11 @@ Enjoy the clean, valid, and documented code!
   * [Run via Docker](#run-via-docker)
   * [Check results](#check-results)
   * [Cleanup](#cleanup)
+* [Add new hook](#add-new-hook)
+  * [Before write code](#before-write-code)
+  * [Prepare basic documentation](#prepare-basic-documentation)
+  * [Add code](#add-code)
+  * [Finish with the documentation](#finish-with-the-documentation)
 
 ## Run and debug hooks locally
 
@@ -41,7 +46,7 @@ For example, to test that the [`terraform_fmt`](../README.md#terraform_fmt) hook
 To check is your improvement not violate performance, we have dummy execution time tests.
 
 Script accept next options:
-
+<!-- markdownlint-disable no-inline-html -->
 | #   | Name                               | Example value                                                            | Description                                          |
 | --- | ---------------------------------- | ------------------------------------------------------------------------ | ---------------------------------------------------- |
 | 1   | `TEST_NUM`                         | `200`                                                                   | How many times need repeat test                      |
@@ -49,6 +54,7 @@ Script accept next options:
 | 3   | `TEST_DIR`                         | `'/tmp/infrastructure'`                                                  | Dir on what you run tests.                           |
 | 4   | `TEST_DESCRIPTION`                 | ```'`terraform_tfsec` PR #123:'```                                       | Text that you'd like to see in result                |
 | 5   | `RAW_TEST_`<br>`RESULTS_FILE_NAME` | `terraform_tfsec_pr123`                                                  | (Temporary) File where all test data will be stored. |
+<!-- markdownlint-enable no-inline-html -->
 
 ### Run via BASH
 
@@ -87,3 +93,46 @@ Results will be located at `./test/results` dir.
 ```bash
 sudo rm -rf tests/results
 ```
+
+## Add new hook
+
+You can use [this PR](https://github.com/antonbabenko/pre-commit-terraform/pull/252) as an example.
+
+### Before write code
+
+1. Try to figure out future hook usage.
+2. Confirm the concept with [Anton Babenko](https://github.com/antonbabenko).
+
+### Prepare basic documentation
+
+1. Identify and describe dependencies in [Install dependencies](../README.md#1-install-dependencies) and [Available Hooks](../README.md#available-hooks) sections
+
+### Add code
+
+1. Based on prev. block, add hook dependencies installation to [Dockerfile](../Dockerfile).  
+    Check that works:
+    * `docker build -t pre-commit --build-arg INSTALL_ALL=true .`
+    * `docker build -t pre-commit --build-arg <NEW_HOOK>_VERSION=latest .`
+    * `docker build -t pre-commit --build-arg <NEW_HOOK>_VERSION=<1.2.3> .`
+2. Add new hook to [`.pre-commit-hooks.yaml`](../.pre-commit-hooks.yaml)
+3. Create hook file. Don't forget to make it executable via `chmod +x /path/to/hook/file`.
+4. Test hook. How to do it is described in [Run and debug hooks locally](#run-and-debug-hooks-locally) section.
+5. Test hook one more time.
+    1. Push commit with hook file to GitHub
+    2. Grab SHA hash of the commit
+    3. Test hook using `.pre-commit-config.yaml`:
+
+        ```yaml
+        repos:
+        - repo: https://github.com/antonbabenko/pre-commit-terraform # Your repo
+        rev: 3d76da3885e6a33d59527eff3a57d246dfb66620 # Your commit SHA
+        hooks:
+          - id: terraform_docs # New hook name
+            args:
+              - --args=--config=.terraform-docs.yml # Some args that you'd like to test
+        ```
+
+### Finish with the documentation
+
+1. Add hook description to [Available Hooks](../README.md#available-hooks).
+2. Create and populate a new hook section in [Hooks usage notes and examples](../README.md#hooks-usage-notes-and-examples).

.pre-commit-hooks.yaml

@@ -1,3 +1,12 @@
+- id: infracost_breakdown
+  name: Infracost breakdown
+  description: Check terraform infrastructure cost
+  entry: infracost_breakdown.sh
+  language: script
+  require_serial: true
+  files: \.(tf(vars)?|hcl)$
+  exclude: \.terraform\/.*$
+
 - id: terraform_fmt
   name: Terraform fmt
   description: Rewrites all Terraform configuration files to a canonical format.

Dockerfile

@@ -11,7 +11,9 @@ RUN apt update && \
         software-properties-common \
         curl \
         python3 \
-        python3-pip && \
+        python3-pip \
+        # infracost deps
+        jq && \
     # Upgrade pip for be able get latest Checkov
     python3 -m pip install --upgrade pip && \
     # Cleanup
@@ -41,6 +43,7 @@ RUN curl -fsSL https://apt.releases.hashicorp.com/gpg | apt-key add - && \
 WORKDIR /bin_dir
 
 ARG CHECKOV_VERSION=${CHECKOV_VERSION:-false}
+ARG INFRACOST_VERSION=${INFRACOST_VERSION:-false}
 ARG TERRAFORM_DOCS_VERSION=${TERRAFORM_DOCS_VERSION:-false}
 ARG TERRAGRUNT_VERSION=${TERRAGRUNT_VERSION:-false}
 ARG TERRASCAN_VERSION=${TERRASCAN_VERSION:-false}
@@ -54,6 +57,7 @@ ARG TFSEC_VERSION=${TFSEC_VERSION:-false}
 ARG INSTALL_ALL=${INSTALL_ALL:-false}
 RUN if [ "$INSTALL_ALL" != "false" ]; then \
         echo "export CHECKOV_VERSION=latest" >> /.env && \
+        echo "export INFRACOST_VERSION=latest" >> /.env && \
         echo "export TERRAFORM_DOCS_VERSION=latest" >> /.env && \
         echo "export TERRAGRUNT_VERSION=latest" >> /.env && \
         echo "export TERRASCAN_VERSION=latest" >> /.env && \
@@ -73,6 +77,16 @@ RUN . /.env && \
     ) \
     ; fi
 
+# infracost
+RUN . /.env && \
+    if [ "$INFRACOST_VERSION" != "false" ]; then \
+    ( \
+        INFRACOST_RELEASES="https://api.github.com/repos/infracost/infracost/releases" && \
+        [ "$INFRACOST_VERSION" = "latest" ] && curl -L "$(curl -s ${INFRACOST_RELEASES}/latest | grep -o -E -m 1 "https://.+?-linux-amd64.tar.gz")" > infracost.tgz \
+        || curl -L "$(curl -s ${INFRACOST_RELEASES} | grep -o -E "https://.+?v${INFRACOST_VERSION}/infracost-linux-amd64.tar.gz")" > infracost.tgz \
+    ) && tar -xzf infracost.tgz && rm infracost.tgz && mv infracost-linux-amd64 infracost \
+    ; fi
+
 # Terraform docs
 RUN . /.env && \
     if [ "$TERRAFORM_DOCS_VERSION" != "false" ]; then \
@@ -131,6 +145,7 @@ RUN . /.env && \
     pre-commit --version >> $F && \
     terraform --version | head -n 1 >> $F && \
     (if [ "$CHECKOV_VERSION"        != "false" ]; then echo "checkov $(checkov --version)" >> $F;     else echo "checkov SKIPPED" >> $F       ; fi) && \
+    (if [ "$INFRACOST_VERSION"      != "false" ]; then echo "$(./infracost --version)" >> $F;         else echo "infracost SKIPPED" >> $F     ; fi) && \
     (if [ "$TERRAFORM_DOCS_VERSION" != "false" ]; then ./terraform-docs --version >> $F;              else echo "terraform-docs SKIPPED" >> $F; fi) && \
     (if [ "$TERRAGRUNT_VERSION"     != "false" ]; then ./terragrunt --version >> $F;                  else echo "terragrunt SKIPPED" >> $F    ; fi) && \
     (if [ "$TERRASCAN_VERSION"      != "false" ]; then echo "terrascan $(./terrascan version)" >> $F; else echo "terrascan SKIPPED" >> $F     ; fi) && \
@@ -159,10 +174,14 @@ COPY --from=builder \
     /usr/local/bin/pre-commit \
     /usr/bin/git \
     /usr/bin/git-shell \
+    /usr/bin/jq \
         /usr/bin/
 # Copy terrascan policies
 COPY --from=builder /root/ /root/
 
 ENV PRE_COMMIT_COLOR=${PRE_COMMIT_COLOR:-always}
 
+ENV INFRACOST_API_KEY=${INFRACOST_API_KEY:-}
+ENV INFRACOST_SKIP_UPDATE_CHECK=${INFRACOST_SKIP_UPDATE_CHECK:-false}
+
 ENTRYPOINT [ "pre-commit" ]

README.md

@@ -12,6 +12,7 @@ Want to Contribute? Check [open issues](https://github.com/antonbabenko/pre-comm
 * [Available Hooks](#available-hooks)
 * [Hooks usage notes and examples](#hooks-usage-notes-and-examples)
   * [checkov](#checkov)
+  * [infracost_breakdown](#infracost_breakdown)
   * [terraform_docs](#terraform_docs)
   * [terraform_docs_replace](#terraform_docs_replace)
   * [terraform_fmt](#terraform_fmt)
@@ -45,6 +46,8 @@ Want to Contribute? Check [open issues](https://github.com/antonbabenko/pre-comm
 * [`terrascan`](https://github.com/accurics/terrascan) required for `terrascan` hook.
 * [`TFLint`](https://github.com/terraform-linters/tflint) required for `terraform_tflint` hook.
 * [`TFSec`](https://github.com/liamg/tfsec) required for `terraform_tfsec` hook.
+* [`infracost`](https://github.com/infracost/infracost) required for `infracost_breakdown` hook.
+* [`jq`](https://github.com/stedolan/jq) required for `infracost_breakdown` hook.
 
 <details><summary><b>Docker</b></summary><br>
 
@@ -65,6 +68,7 @@ docker build -t pre-commit \
     --build-arg PRE_COMMIT_VERSION=latest \
     --build-arg TERRAFORM_VERSION=latest \
     --build-arg CHECKOV_VERSION=2.0.405 \
+    --build-arg INFRACOST_VERSION=latest \
     --build-arg TERRAFORM_DOCS_VERSION=0.15.0 \
     --build-arg TERRAGRUNT_VERSION=latest \
     --build-arg TERRASCAN_VERSION=1.10.0 \
@@ -83,8 +87,9 @@ To disable the pre-commit color output, set `-e PRE_COMMIT_COLOR=never`.
 [`coreutils`](https://formulae.brew.sh/formula/coreutils) required for `terraform_validate` hook on macOS (due to use of `realpath`).
 
 ```bash
-brew install pre-commit terraform-docs tflint tfsec coreutils checkov terrascan
+brew install pre-commit terraform-docs tflint tfsec coreutils checkov terrascan infracost jq
 terrascan init
+infracost register
 ```
 
 </details>
@@ -103,6 +108,8 @@ curl -L "$(curl -s https://api.github.com/repos/terraform-docs/terraform-docs/re
 curl -L "$(curl -s https://api.github.com/repos/terraform-linters/tflint/releases/latest | grep -o -E -m 1 "https://.+?_linux_amd64.zip")" > tflint.zip && unzip tflint.zip && rm tflint.zip && sudo mv tflint /usr/bin/
 curl -L "$(curl -s https://api.github.com/repos/aquasecurity/tfsec/releases/latest | grep -o -E -m 1 "https://.+?tfsec-linux-amd64")" > tfsec && chmod +x tfsec && sudo mv tfsec /usr/bin/
 curl -L "$(curl -s https://api.github.com/repos/accurics/terrascan/releases/latest | grep -o -E -m 1 "https://.+?_Linux_x86_64.tar.gz")" > terrascan.tar.gz && tar -xzf terrascan.tar.gz terrascan && rm terrascan.tar.gz && sudo mv terrascan /usr/bin/ && terrascan init
+sudo apt install -y jq && \
+curl -L "$(curl -s https://api.github.com/repos/infracost/infracost/releases/latest | grep -o -E -m 1 "https://.+?-linux-amd64.tar.gz")" > infracost.tgz && tar -xzf infracost.tgz && rm infracost.tgz && sudo mv infracost-linux-amd64 /usr/bin/infracost && infracost register
 ```
 
 </details>
@@ -120,6 +127,8 @@ curl -L "$(curl -s https://api.github.com/repos/terraform-docs/terraform-docs/re
 curl -L "$(curl -s https://api.github.com/repos/accurics/terrascan/releases/latest | grep -o -E -m 1 "https://.+?_Linux_x86_64.tar.gz")" > terrascan.tar.gz && tar -xzf terrascan.tar.gz terrascan && rm terrascan.tar.gz && sudo mv terrascan /usr/bin/ && terrascan init
 curl -L "$(curl -s https://api.github.com/repos/terraform-linters/tflint/releases/latest | grep -o -E -m 1 "https://.+?_linux_amd64.zip")" > tflint.zip && unzip tflint.zip && rm tflint.zip && sudo mv tflint /usr/bin/
 curl -L "$(curl -s https://api.github.com/repos/aquasecurity/tfsec/releases/latest | grep -o -E -m 1 "https://.+?tfsec-linux-amd64")" > tfsec && chmod +x tfsec && sudo mv tfsec /usr/bin/
+sudo apt install -y jq && \
+curl -L "$(curl -s https://api.github.com/repos/infracost/infracost/releases/latest | grep -o -E -m 1 "https://.+?-linux-amd64.tar.gz")" > infracost.tgz && tar -xzf infracost.tgz && rm infracost.tgz && sudo mv infracost-linux-amd64 /usr/bin/infracost && infracost register
 ```
 
 </details>
@@ -182,6 +191,7 @@ There are several [pre-commit](https://pre-commit.com/) hooks to keep Terraform
 | Hook name                                              | Description                                                                                                                                                                                                                                  | Dependencies<br><sup>[Install instructions here](#1-install-dependencies)</sup> |
 | ------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------- |
 | `checkov`                                              | [checkov](https://github.com/bridgecrewio/checkov) static analysis of terraform templates to spot potential security issues. [Hook notes](#checkov)                                                                                          | `checkov`<br>Ubuntu deps: `python3`, `python3-pip`                              |
+| `infracost_breakdown` | Check how much your infra costs with [infracost](https://github.com/infracost/infracost). [Hook notes](#infracost_breakdown) | `infracost`, `jq`, [Infracost API key](https://www.infracost.io/docs/#2-get-api-key), Internet connection
 | `terraform_docs_replace`                               | Runs `terraform-docs` and pipes the output directly to README.md                                                                                                                                                                             | `python3`, `terraform-docs`                                                     |
 | `terraform_docs_without_`<br>`aggregate_type_defaults` | Inserts input and output documentation into `README.md` without aggregate type defaults. Hook notes same as for [terraform_docs](#terraform_docs)                                                                                            | `terraform-docs`                                                                |
 | `terraform_docs`                                       | Inserts input and output documentation into `README.md`. Recommended. [Hook notes](#terraform_docs)                                                                                                                                          | `terraform-docs`                                                                |
@@ -211,6 +221,94 @@ For [checkov](https://github.com/bridgecrewio/checkov) you need to specify each
   ]
 ```
 
+### infracost_breakdown
+
+`infracost_breakdown` build on top of the `infracost breakdown` command. It, if needed, runs `terraform init`, `terraform plan` and calls `infracost` API - so this hook can run up to several minutes.
+
+Unlike most other hooks, this one triggers all changes to the files but checks predefined paths each time.
+
+For example, the hook tracks `--path=./env/dev` and `./env/dev` depend on `./main.tf`. So when you will make changes to `./main.tf` - the hook will run and show the cost changes for `./env/dev`.
+
+
+1. `infracost_breakdown` supports custom arguments so you can pass [supported flags](https://www.infracost.io/docs/#useful-options).  
+    The following example only shows costs:
+
+    ```yaml
+    - id: infracost_breakdown
+      args:
+        - --args=--path=./env/dev
+      verbose: true # Always show costs
+    ```
+    <!-- markdownlint-disable-next-line no-inline-html -->
+    <details><summary>Output</summary>
+
+    ```bash
+    Running in "env/dev"
+
+    Summary: {
+    "unsupportedResourceCounts": {
+        "aws_sns_topic_subscription": 1
+      }
+    }
+
+    Total Monthly Cost:        86.83 USD
+    Total Monthly Cost (diff): 86.83 USD
+    ```
+    <!-- markdownlint-disable-next-line no-inline-html -->
+    </details>
+
+2. You can provide limitations when the hook should fail:
+
+    ```yaml
+    - id: infracost_breakdown
+      args:
+        - --args=--path=./env/dev
+        - --hook-config=.totalHourlyCost|tonumber > 0.1
+        - --hook-config=.totalHourlyCost|tonumber > 1
+        - --hook-config=.projects[].diff.totalMonthlyCost|tonumber != 10000
+        - --hook-config=.currency == "USD"
+    ```
+    <!-- markdownlint-disable-next-line no-inline-html -->
+    <details><summary>Output</summary>
+
+    ```bash
+    Running in "env/dev"
+    Passed: .totalHourlyCost|tonumber > 0.1         0.11894520547945205 >  0.1
+    Failed: .totalHourlyCost|tonumber > 1           0.11894520547945205 >  1
+    Passed: .projects[].diff.totalMonthlyCost|tonumber !=10000              86.83 != 10000
+    Passed: .currency == "USD"              "USD" == "USD"
+
+    Summary: {
+    "unsupportedResourceCounts": {
+    "aws_sns_topic_subscription": 1
+      }
+    }
+
+    Total Monthly Cost:        86.83 USD
+    Total Monthly Cost (diff): 86.83 USD
+    ```
+    <!-- markdownlint-disable-next-line no-inline-html -->
+    </details>
+
+    * Hook uses `jq` to parse `infracost` output, so paths to values like `.totalHourlyCost` and `.totalMonthlyCost` should be in jq-compatible format.  
+    To check available structure use `infracost breakdown -p PATH_TO_TF_DIR --format json | jq -r . > infracost.json`. And play with it on [jqplay.org](https://jqplay.org/)
+    * Supported comparison operators: `<`, `<=`, `==`, `!=`, `>=`, `>`.
+    * Most useful paths and checks:
+        * `.totalHourlyCost` (same to `.projects[].breakdown.totalHourlyCost`) - show total hourly infra cost
+        * `.totalMonthlyCost` (same to `.projects[].breakdown.totalMonthlyCost`) - show total monthly infra cost
+        * `.projects[].diff.totalHourlyCost` - show hourly cost diff between existing infra and tf plan
+        * `.projects[].diff.totalMonthlyCost` - show monthly cost diff between existing infra and tf plan
+        * `.diffTotalHourlyCost` (for Infracost version 0.9.12 or newer) or `[.projects[].diff.totalMonthlyCost | select (.!=null) | tonumber] | add > 1000` (for Infracost older than 0.9.12):
+            * fail if changes push the total monthly cost estimate above $1K
+            * fail if changes increase the cost by $1K.
+    * You can set up only one path per one hook (`- id: infracost_breakdown`) - this is an `infracost` limitation.
+    * Set `verbose: true` to see cost even when the checks are passed.
+    * To disable hook color output, set `PRE_COMMIT_COLOR=never` env var
+
+3. **Docker usage**. In `docker build` or `docker run` command:
+    * You need to provide [Infracost API key](https://www.infracost.io/docs/integrations/environment_variables/#infracost_api_key) via `-e INFRACOST_API_KEY=<your token>`. By default it is saved in `~/.config/infracost/credentials.yml`
+    * Set `-e INFRACOST_SKIP_UPDATE_CHECK=true` to skip the Infracost update check; can be useful in CI/CD systems. [Doc](https://www.infracost.io/docs/integrations/environment_variables/#infracost_skip_update_check)
+
 ### terraform_docs
 
 1. `terraform_docs` and `terraform_docs_without_aggregate_type_defaults` will insert/update documentation generated by [terraform-docs](https://github.com/terraform-docs/terraform-docs) framed by markers:
@@ -227,7 +325,7 @@ For [checkov](https://github.com/bridgecrewio/checkov) you need to specify each
 
 3. It is possible to automatically:
     * create docfile (and PATH to it)
-    * extend exiting docs files, by appending markers to the end of file (see p.1)
+    * extend existing doc files by appending markers to the end of the file (see item 1)
     * use different than `README.md` docfile name.
 
     ```yaml
@@ -245,7 +343,7 @@ For [checkov](https://github.com/bridgecrewio/checkov) you need to specify each
       args:
         - --args=--config=.terraform-docs.yml
 
-5. If you need some exotic settings, it can be be done too. I.e. this one generates HCL files:
+5. If you need some exotic settings, it can be done too. I.e. this one generates HCL files:
 
     ```yaml
     - id: terraform_docs
@@ -323,7 +421,7 @@ Example:
         - --args=--enable-rule=terraform_documented_variables
     ```
 
-2. When you have multiple directories and want to run `tflint` in all of them and share a single config file, it is impractical to hard-code the path to `.tflint.hcl` file. The solution is to use the `__GIT_WORKING_DIR__` placeholder which will be replaced by `terraform_tflint` hooks with Git working directory (repo root) at run time. For example:
+2. When you have multiple directories and want to run `tflint` in all of them and share a single config file, it is impractical to hard-code the path to the `.tflint.hcl` file. The solution is to use the `__GIT_WORKING_DIR__` placeholder which will be replaced by `terraform_tflint` hooks with Git working directory (repo root) at run time. For example:
 
     ```yaml
     - id: terraform_tflint

infracost_breakdown.sh

@@ -0,0 +1,163 @@
+#!/usr/bin/env bash
+set -eo pipefail
+
+function main {
+  common::initialize
+  common::parse_cmdline "$@"
+  infracost_breakdown_ "${HOOK_CONFIG[*]}" "${ARGS[*]}"
+}
+
+function common::colorify {
+  # Colors. Provided as first string to first arg of function.
+  # shellcheck disable=SC2034
+  local -r red="$(tput setaf 1)"
+  # shellcheck disable=SC2034
+  local -r green="$(tput setaf 2)"
+  # shellcheck disable=SC2034
+  local -r yellow="$(tput setaf 3)"
+  # Color reset
+  local -r RESET="$(tput sgr0)"
+
+  # Params start #
+  local COLOR="${!1}"
+  local -r TEXT=$2
+  # Params end #
+
+  if [ "$PRE_COMMIT_COLOR" = "never" ]; then
+    COLOR=$RESET
+  fi
+
+  echo -e "${COLOR}${TEXT}${RESET}"
+}
+
+function common::initialize {
+  local SCRIPT_DIR
+  # get directory containing this script
+  SCRIPT_DIR="$(dirname "$(realpath "${BASH_SOURCE[0]}")")"
+
+  # source getopt function
+  # shellcheck source=lib_getopt
+  . "$SCRIPT_DIR/lib_getopt"
+}
+
+# common global arrays.
+# Populated in `parse_cmdline` and can used in hooks functions
+declare -a ARGS=()
+declare -a HOOK_CONFIG=()
+declare -a FILES=()
+function common::parse_cmdline {
+  local argv
+  argv=$(getopt -o a:,h: --long args:,hook-config: -- "$@") || return
+  eval "set -- $argv"
+
+  for argv; do
+    case $argv in
+      -a | --args)
+        shift
+        ARGS+=("$1")
+        shift
+        ;;
+      -h | --hook-config)
+        shift
+        HOOK_CONFIG+=("$1;")
+        shift
+        ;;
+      --)
+        shift
+        FILES=("$@")
+        break
+        ;;
+    esac
+  done
+}
+
+function infracost_breakdown_ {
+  local -r hook_config="$1"
+  local args
+  read -r -a args <<< "$2"
+
+  # Get hook settings
+  IFS=";" read -r -a checks <<< "$hook_config"
+
+  if [ "$PRE_COMMIT_COLOR" = "never" ]; then
+    args+=("--no-color")
+  fi
+
+  local RESULTS
+  RESULTS="$(infracost breakdown "${args[@]}" --format json)"
+  local API_VERSION
+  API_VERSION="$(jq -r .version <<< "$RESULTS")"
+
+  if [ "$API_VERSION" != "0.2" ]; then
+    common::colorify "yellow" "WARNING: Hook supports Infracost API version \"0.2\", got \"$API_VERSION\""
+    common::colorify "yellow" "         Some things may not work as expected"
+  fi
+
+  local dir
+  dir="$(jq '.projects[].metadata.vcsSubPath' <<< "$RESULTS")"
+  echo -e "\nRunning in $dir"
+
+  local have_failed_checks=false
+
+  for check in "${checks[@]}"; do
+    # $hook_config receives string like '1 > 2; 3 == 4;' etc.
+    # It gets split by `;` into array, which we're parsing here ('1 > 2' ' 3 == 4')
+    # Next line removes leading spaces, just for fancy output reason.
+    check=$(echo "$check" | sed 's/^[[:space:]]*//')
+
+    operation="$(echo "$check" | grep -oE '[!<>=]+')"
+    IFS="$operation" read -r -a jq_check <<< "$check"
+    real_value="$(jq "${jq_check[0]}" <<< "$RESULTS")"
+    compare_value="${jq_check[1]}${jq_check[2]}"
+    # Check types
+    jq_check_type="$(jq -r "${jq_check[0]} | type" <<< "$RESULTS")"
+    compare_value_type="$(jq -r "$compare_value | type" <<< "$RESULTS")"
+    # Fail if comparing different types
+    if [ "$jq_check_type" != "$compare_value_type" ]; then
+      common::colorify "yellow" "Warning: Comparing values with different types may give incorrect result"
+      common::colorify "yellow" "         Expression: $check"
+      common::colorify "yellow" "         Types in the expression: [$jq_check_type] $operation [$compare_value_type]"
+      common::colorify "yellow" "         Use 'tonumber' filter when comparing costs (e.g. '.totalMonthlyCost|tonumber')"
+      have_failed_checks=true
+      continue
+    fi
+    # Fail if string is compared not with `==` or `!=`
+    if [ "$jq_check_type" == "string" ] && {
+      [ "$operation" != '==' ] && [ "$operation" != '!=' ]
+    }; then
+      common::colorify "yellow" "Warning: Wrong comparison operator is used in expression: $check"
+      common::colorify "yellow" "         Use 'tonumber' filter when comparing costs (e.g. '.totalMonthlyCost|tonumber')"
+      common::colorify "yellow" "         Use '==' or '!=' when comparing strings (e.g. '.currency == \"USD\"')."
+      have_failed_checks=true
+      continue
+    fi
+
+    # Compare values
+    check_passed="$(echo "$RESULTS" | jq "$check")"
+
+    status="Passed"
+    color="green"
+    if ! $check_passed; then
+      status="Failed"
+      color="red"
+      have_failed_checks=true
+    fi
+
+    # Print check result
+    common::colorify $color "$status: $check\t\t$real_value $operation $compare_value"
+  done
+
+  # Fancy informational output
+  currency="$(jq -r '.currency' <<< "$RESULTS")"
+
+  echo -e "\nSummary: $(jq -r '.summary' <<< "$RESULTS")"
+
+  echo -e "\nTotal Monthly Cost:        $(jq -r .totalMonthlyCost <<< "$RESULTS") $currency"
+  echo "Total Monthly Cost (diff): $(jq -r .projects[].diff.totalMonthlyCost <<< "$RESULTS") $currency"
+
+  if $have_failed_checks; then
+    exit 1
+  fi
+}
+
+[[ ${BASH_SOURCE[0]} != "$0" ]] || main "$@"