# SPDX-License-Identifier: Apache-2.0
#
# Copyright (c) 2024, Nordic Semiconductor ASA

# CMake YAML module for handling of YAML files.
#
# This module offers basic support for simple yaml files.
#
# It supports basic key-value pairs, like
# foo: bar
#
# basic key-object pairs, like
# foo:
#    bar: baz
#
# Simple value lists, like:
# foos:
#  - foo1
#  - foo2
#  - foo3
#
# Support for list of maps, like:
# foo:
#  - bar: val1
#    baz: val1
#  - bar: val2
#    baz: val2
#
# All of above can be combined, for example like:
# foo:
#   bar: baz
#   quz:
#     greek:
#      - alpha
#      - beta
#      - gamma
# fred: thud

include_guard(GLOBAL)

include(extensions)
include(python)

# Internal helper function for checking that a YAML context has been created
# before operating on it.
# Will result in CMake error if context does not exist.
function(internal_yaml_context_required)
  cmake_parse_arguments(ARG_YAML "" "NAME" "" ${ARGN})
  zephyr_check_arguments_required(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME)
  yaml_context(EXISTS NAME ${ARG_YAML_NAME} result)

  if(NOT result)
    message(FATAL_ERROR "YAML context '${ARG_YAML_NAME}' does not exist."
            "Remember to create a YAML context using 'yaml_create()' or 'yaml_load()'"
    )
  endif()
endfunction()

# Internal helper function for checking if a YAML context is free before creating
# it later.
# Will result in CMake error if context exists.
function(internal_yaml_context_free)
  cmake_parse_arguments(ARG_YAML "" "NAME" "" ${ARGN})
  zephyr_check_arguments_required(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME)
  yaml_context(EXISTS NAME ${ARG_YAML_NAME} result)

  if(result)
    message(FATAL_ERROR "YAML context '${ARG_YAML_NAME}' already exists."
            "Please create a YAML context with a unique name"
    )
  endif()
endfunction()

# Internal helper function to provide the correct initializer for a list in the
# JSON content.
function(internal_yaml_list_initializer var genex)
  if(genex)
    set(${var} "\"@YAML-LIST@\"" PARENT_SCOPE)
  else()
    set(${var} "[]" PARENT_SCOPE)
  endif()
endfunction()

# Internal helper function to append items to a list in the JSON content.
# Unassigned arguments are the values to be appended.
function(internal_yaml_list_append var genex key)
  set(json_content "${${var}}")
  string(JSON subjson GET "${json_content}" ${key})
  if(genex)
    # new lists are stored in CMake string format, but those imported via
    # yaml_load() are proper JSON arrays. When an append is requested, those
    # must be converted back to a CMake list.
    string(JSON type TYPE "${json_content}" ${key})
    if(type STREQUAL ARRAY)
      string(JSON arraylength LENGTH "${subjson}")
      internal_yaml_list_initializer(subjson TRUE)
      if(${arraylength} GREATER 0)
        math(EXPR arraystop "${arraylength} - 1")
        foreach(i RANGE 0 ${arraystop})
          string(JSON item GET "${json_content}" ${key} ${i})
          list(APPEND subjson ${item})
        endforeach()
      endif()
    endif()
    list(APPEND subjson ${ARGN})
    string(JSON json_content SET "${json_content}" ${key} "\"${subjson}\"")
  else()
    # lists are stored as JSON arrays
    string(JSON index LENGTH "${subjson}")
    list(LENGTH ARGN length)
    if(NOT length EQUAL 0)
      list(GET ARG_YAML_LIST 0 entry_0)
      if(entry_0 STREQUAL MAP)
        math(EXPR length "${length} / 2")
        math(EXPR stop "${index} + ${length} - 1")
        foreach(i RANGE ${index} ${stop})
          list(POP_FRONT ARG_YAML_LIST argument)
          if(NOT argument STREQUAL MAP)
            message(FATAL_ERROR "yaml_set(${argument} ) is not valid at this position.\n"
                    "Syntax is 'LIST MAP \"key1: value1.1, ...\" MAP \"key1: value1.2, ...\""
            )
          endif()
          list(POP_FRONT ARG_YAML_LIST map_value)
          string(REGEX REPLACE "([^\\])," "\\1;" pair_list "${map_value}")
          set(quoted_map_value)
          foreach(pair ${pair_list})
            if(NOT pair MATCHES "[^ ]*:[^ ]*")
              message(FATAL_ERROR "yaml_set(MAP ${map_value} ) is malformed.\n"
                    "Syntax is 'LIST MAP \"key1: value1.1, ...\" MAP \"key1: value1.2, ...\"\n"
                    "If value contains comma ',' then ensure the value field is properly quoted "
                    "and escaped"
              )
            endif()
            string(REGEX MATCH "^[^:]*" map_key "${pair}")
            string(REGEX REPLACE "^${map_key}:[ ]*" "" value "${pair}")
            string(STRIP "${map_key}" map_key)
            if(value MATCHES "," AND NOT (value MATCHES "\\\\," AND value MATCHES "'.*'"))
              message(FATAL_ERROR "value: ${value} is not properly quoted")
            endif()
            string(REGEX REPLACE "\\\\," "," value "${value}")
            list(APPEND quoted_map_value "\"${map_key}\": \"${value}\"")
          endforeach()
          list(JOIN quoted_map_value "," quoted_map_value)
          string(JSON json_content SET "${json_content}" ${key} ${i} "{${quoted_map_value}}")
        endforeach()
      else()
        math(EXPR stop "${index} + ${length} - 1")
        list(GET ARG_YAML_LIST 0 entry_0)
          foreach(i RANGE ${index} ${stop})
            list(POP_FRONT ARGN value)
            string(JSON json_content SET "${json_content}" ${key} ${i} "\"${value}\"")
          endforeach()
      endif()
    endif()
  endif()
  set(${var} "${json_content}" PARENT_SCOPE)
endfunction()

# Usage
#   yaml_context(EXISTS NAME <name> <result>)
#
# Function to query the status of the YAML context with the name <name>.
# The result of the query is stored in <result>
#
# EXISTS     : Check if the YAML context exists in the current scope
#              If the context exists, then TRUE is returned in <result>
# NAME <name>: Name of the YAML context
# <result>   : Variable to store the result of the query.
#
function(yaml_context)
  cmake_parse_arguments(ARG_YAML "EXISTS" "NAME" "" ${ARGN})
  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML EXISTS NAME)

  if(NOT DEFINED ARG_YAML_UNPARSED_ARGUMENTS)
    message(FATAL_ERROR "Missing argument in "
            "${CMAKE_CURRENT_FUNCTION}(EXISTS NAME ${ARG_YAML_NAME} <result-var>)."
    )
  endif()

  zephyr_scope_exists(scope_defined ${ARG_YAML_NAME})
  if(scope_defined)
    list(POP_FRONT ARG_YAML_UNPARSED_ARGUMENTS out-var)
    set(${out-var} TRUE PARENT_SCOPE)
  else()
    set(${out-var} ${ARG_YAML_NAME}-NOTFOUND PARENT_SCOPE)
  endif()
endfunction()

# Usage:
#   yaml_create(NAME <name> [FILE <file>])
#
# Create a new empty YAML context.
# Use the file <file> for storing the context when 'yaml_save(NAME <name>)' is
# called.
#
# Values can be set by calling 'yaml_set(NAME <name>)' by using the <name>
# specified when creating the YAML context.
#
# NAME <name>: Name of the YAML context.
# FILE <file>: Path to file to be used together with this YAML context.
#
function(yaml_create)
  cmake_parse_arguments(ARG_YAML "" "FILE;NAME" "" ${ARGN})

  zephyr_check_arguments_required(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME)

  internal_yaml_context_free(NAME ${ARG_YAML_NAME})
  zephyr_create_scope(${ARG_YAML_NAME})
  if(DEFINED ARG_YAML_FILE)
    zephyr_set(FILE ${ARG_YAML_FILE} SCOPE ${ARG_YAML_NAME})
  endif()
  zephyr_set(GENEX FALSE SCOPE ${ARG_YAML_NAME})
  zephyr_set(JSON "{}" SCOPE ${ARG_YAML_NAME})
endfunction()

# Usage:
#   yaml_load(FILE <file> NAME <name>)
#
# Load an existing YAML file and store its content in the YAML context <name>.
#
# Values can later be retrieved ('yaml_get()') or set/updated ('yaml_set()') by using
# the same YAML scope name.
#
# FILE <file>: Path to file to load.
# NAME <name>: Name of the YAML context.
#
function(yaml_load)
  cmake_parse_arguments(ARG_YAML "" "FILE;NAME" "" ${ARGN})

  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML FILE NAME)
  internal_yaml_context_free(NAME ${ARG_YAML_NAME})

  zephyr_create_scope(${ARG_YAML_NAME})
  zephyr_set(FILE ${ARG_YAML_FILE} SCOPE ${ARG_YAML_NAME})

  execute_process(COMMAND ${PYTHON_EXECUTABLE} -c
    "import json; import yaml; print(json.dumps(yaml.safe_load(open('${ARG_YAML_FILE}')) or {}))"
    OUTPUT_VARIABLE json_load_out
    ERROR_VARIABLE json_load_error
    RESULT_VARIABLE json_load_result
  )

  if(json_load_result)
    message(FATAL_ERROR "Failed to load content of YAML file: ${ARG_YAML_FILE}\n"
                        "${json_load_error}"
    )
  endif()

  zephyr_set(GENEX FALSE SCOPE ${ARG_YAML_NAME})
  zephyr_set(JSON "${json_load_out}" SCOPE ${ARG_YAML_NAME})
endfunction()

# Usage:
#   yaml_get(<out-var> NAME <name> KEY <key>...)
#
# Get the value of the given key and store the value in <out-var>.
# If key represents a list, then the list is returned.
#
# Behavior is undefined if key points to a complex object.
#
# NAME <name>  : Name of the YAML context.
# KEY <key>... : Name of key.
# <out-var>    : Name of output variable.
#
function(yaml_get out_var)
  # Current limitation:
  # - Anything will be returned, even json object strings.
  cmake_parse_arguments(ARG_YAML "" "NAME" "KEY" ${ARGN})

  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME KEY)
  internal_yaml_context_required(NAME ${ARG_YAML_NAME})

  zephyr_get_scoped(json_content ${ARG_YAML_NAME} JSON)

  # We specify error variable to avoid a fatal error.
  # If key is not found, then type becomes '-NOTFOUND' and value handling is done below.
  string(JSON type ERROR_VARIABLE error TYPE "${json_content}" ${ARG_YAML_KEY})
  if(type STREQUAL ARRAY)
    string(JSON subjson GET "${json_content}" ${ARG_YAML_KEY})
    string(JSON arraylength LENGTH "${subjson}")
    set(array)
    math(EXPR arraystop "${arraylength} - 1")
    if(arraylength GREATER 0)
      foreach(i RANGE 0 ${arraystop})
        string(JSON item GET "${subjson}" ${i})
        list(APPEND array ${item})
      endforeach()
    endif()
    set(${out_var} ${array} PARENT_SCOPE)
  else()
    # We specify error variable to avoid a fatal error.
    # Searching for a non-existing key should just result in the output value '-NOTFOUND'
    string(JSON value ERROR_VARIABLE error GET "${json_content}" ${ARG_YAML_KEY})
    set(${out_var} ${value} PARENT_SCOPE)
  endif()
endfunction()

# Usage:
#   yaml_length(<out-var> NAME <name> KEY <key>...)
#
# Get the length of the array defined by the given key and store the length in <out-var>.
# If key does not define an array, then the length -1 is returned.
#
# NAME <name>  : Name of the YAML context.
# KEY <key>... : Name of key defining the list.
# <out-var>    : Name of output variable.
#
function(yaml_length out_var)
  cmake_parse_arguments(ARG_YAML "" "NAME" "KEY" ${ARGN})

  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME KEY)
  internal_yaml_context_required(NAME ${ARG_YAML_NAME})

  zephyr_get_scoped(json_content ${ARG_YAML_NAME} JSON)

  string(JSON type ERROR_VARIABLE error TYPE "${json_content}" ${ARG_YAML_KEY})
  if(type STREQUAL ARRAY)
    string(JSON subjson GET "${json_content}" ${ARG_YAML_KEY})
    string(JSON arraylength LENGTH "${subjson}")
    set(${out_var} ${arraylength} PARENT_SCOPE)
  elseif(type MATCHES ".*-NOTFOUND")
    set(${out_var} ${type} PARENT_SCOPE)
  else()
    message(WARNING "YAML key: ${ARG_YAML_KEY} is not an array.")
    set(${out_var} -1 PARENT_SCOPE)
  endif()
endfunction()

# Usage:
#   yaml_set(NAME <name> KEY <key>... [GENEX] VALUE <value>)
#   yaml_set(NAME <name> KEY <key>... [APPEND] [GENEX] LIST <value>...)
#   yaml_set(NAME <name> KEY <key>... [APPEND] LIST MAP <map1> MAP <map2> MAP ...)
#
# Set a value or a list of values to given key.
#
# If setting a list of values, then APPEND can be specified to indicate that the
# list of values should be appended to the existing list identified with key(s).
#
# NAME <name>  : Name of the YAML context.
# KEY <key>... : Name of key.
# VALUE <value>: New value for the key.
# LIST <values>: New list of values for the key.
# APPEND       : Append the list of values to the list of values for the key.
# GENEX        : The value(s) contain generator expressions. When using this
#                option, also see the notes in the yaml_save() function.
# MAP <map>    : Map, with key-value pairs where key-value is separated by ':',
#                and pairs separated by ','.
#                Format example: "<key1>: <value1>, <key2>: <value2>, ..."
#                MAP can be given multiple times to separate maps when adding them to a list.
#                LIST MAP cannot be used with GENEX.
#
#                Note: if a map value contains commas, ',', then the value string must be quoted in
#                      single quotes and commas must be double escaped, like this: 'A \\,string'
#
function(yaml_set)
  cmake_parse_arguments(ARG_YAML "APPEND;GENEX" "NAME;VALUE" "KEY;LIST" ${ARGN})

  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME KEY)
  zephyr_check_arguments_required_allow_empty(${CMAKE_CURRENT_FUNCTION} ARG_YAML VALUE LIST)
  zephyr_check_arguments_exclusive(${CMAKE_CURRENT_FUNCTION} ARG_YAML VALUE LIST)
  internal_yaml_context_required(NAME ${ARG_YAML_NAME})

  if(ARG_YAML_GENEX)
    zephyr_set(GENEX TRUE SCOPE ${ARG_YAML_NAME})
  endif()

  if(DEFINED ARG_YAML_LIST
     OR LIST IN_LIST ARG_YAML_KEYWORDS_MISSING_VALUES)
    set(key_is_list TRUE)
  endif()

  if(ARG_YAML_APPEND AND NOT key_is_list)
    message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION}(APPEND ...) can only be used with argument: LIST")
  endif()

  if(ARG_YAML_GENEX AND MAP IN_LIST ARG_YAML_LIST)
    message(FATAL_ERROR "${function}(GENEX ...) cannot be used with argument: LIST MAP")
  endif()

  zephyr_get_scoped(json_content ${ARG_YAML_NAME} JSON)
  zephyr_get_scoped(genex ${ARG_YAML_NAME} GENEX)

  set(yaml_key_undefined ${ARG_YAML_KEY})
  foreach(k ${yaml_key_undefined})
    list(REMOVE_AT yaml_key_undefined 0)
    # We ignore any errors as we are checking for existence of the key, and
    # non-existing keys will throw errors but also set type to NOT-FOUND.
    string(JSON type ERROR_VARIABLE ignore TYPE "${json_content}" ${valid_keys} ${k})

    if(NOT type)
      list(APPEND yaml_key_create ${k})
      break()
    endif()
    list(APPEND valid_keys ${k})
  endforeach()

  list(REVERSE yaml_key_undefined)
  if(NOT "${yaml_key_undefined}" STREQUAL "")
    if(key_is_list)
      internal_yaml_list_initializer(json_string ${genex})
    else()
      set(json_string "\"\"")
    endif()

    foreach(k ${yaml_key_undefined})
      set(json_string "{\"${k}\": ${json_string}}")
    endforeach()
    string(JSON json_content SET "${json_content}"
           ${valid_keys} ${yaml_key_create} "${json_string}"
    )
  endif()

  if(key_is_list)
    if(NOT ARG_YAML_APPEND)
      internal_yaml_list_initializer(json_string ${genex})
      string(JSON json_content SET "${json_content}" ${ARG_YAML_KEY} "${json_string}")
    endif()
    zephyr_string(ESCAPE escape_list "${ARG_YAML_LIST}")
    internal_yaml_list_append(json_content ${genex} "${ARG_YAML_KEY}" ${escape_list})
  else()
    zephyr_string(ESCAPE escape_value "${ARG_YAML_VALUE}")
    string(JSON json_content SET "${json_content}" ${ARG_YAML_KEY} "\"${escape_value}\"")
  endif()

  zephyr_set(JSON "${json_content}" SCOPE ${ARG_YAML_NAME})
endfunction()

# Usage:
#   yaml_remove(NAME <name> KEY <key>...)
#
# Remove the KEY <key>... from the YAML context <name>.
#
# Several levels of keys can be given, for example:
# KEY build cmake command
#
# To remove the key 'command' underneath 'cmake' in the toplevel 'build'
#
# NAME <name>: Name of the YAML context.
# KEY <key>  : Name of key to remove.
#
function(yaml_remove)
  cmake_parse_arguments(ARG_YAML "" "NAME" "KEY" ${ARGN})

  zephyr_check_arguments_required_all(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME KEY)
  internal_yaml_context_required(NAME ${ARG_YAML_NAME})

  zephyr_get_scoped(json_content ${ARG_YAML_NAME} JSON)
  string(JSON json_content REMOVE "${json_content}" ${ARG_YAML_KEY})

  zephyr_set(JSON "${json_content}" SCOPE ${ARG_YAML_NAME})
endfunction()

# Usage:
#   yaml_save(NAME <name> [FILE <file>])
#
# Write the YAML context <name> to <file>, or the one given with the earlier
# 'yaml_load()' or 'yaml_create()' call. This will be performed immediately if
# the context does not use generator expressions; otherwise, keys that include
# a generator expression will initially be written as comments, and the full
# contents will be available at build time. Build steps that depend on the file
# being complete must depend on the '<name>_yaml_saved' target.
#
# NAME <name>: Name of the YAML context
# FILE <file>: Path to file to write the context.
#              If not given, then the FILE property of the YAML context will be
#              used. In case both FILE is omitted and FILE property is missing
#              on the YAML context, then an error will be raised.
#
function(yaml_save)
  cmake_parse_arguments(ARG_YAML "" "NAME;FILE" "" ${ARGN})

  zephyr_check_arguments_required(${CMAKE_CURRENT_FUNCTION} ARG_YAML NAME)
  internal_yaml_context_required(NAME ${ARG_YAML_NAME})

  zephyr_get_scoped(yaml_file ${ARG_YAML_NAME} FILE)
  if(NOT yaml_file)
    zephyr_check_arguments_required(${CMAKE_CURRENT_FUNCTION} ARG_YAML FILE)
  endif()
  if(DEFINED ARG_YAML_FILE)
    set(yaml_file ${ARG_YAML_FILE})
  else()
    zephyr_get_scoped(yaml_file ${ARG_YAML_NAME} FILE)
  endif()

  zephyr_get_scoped(genex ${ARG_YAML_NAME} GENEX)
  zephyr_get_scoped(json_content ${ARG_YAML_NAME} JSON)
  if(genex)
    to_yaml("${json_content}" 0 yaml_out DIRECT_GENEX)
   else()
    to_yaml("${json_content}" 0 yaml_out DIRECT)
   endif()

  if(EXISTS ${yaml_file})
    FILE(RENAME ${yaml_file} ${yaml_file}.bak)
  endif()
  FILE(WRITE ${yaml_file} "${yaml_out}")

  set(save_target ${ARG_YAML_NAME}_yaml_saved)
  if(NOT TARGET ${save_target})
    # Create a target for the completion of the YAML save operation.
    # This will be a dummy unless genexes are used.
    add_custom_target(${save_target} ALL DEPENDS ${yaml_file})
    set_target_properties(${save_target} PROPERTIES
      genex_save_count 0
      temp_files ""
    )
  endif()

  if(genex)
    get_property(genex_save_count TARGET ${save_target} PROPERTY genex_save_count)
    if(${genex_save_count} EQUAL 0)
      # First yaml_save() for this context with genexes enabled
      add_custom_command(
        OUTPUT ${yaml_file}
        DEPENDS $<TARGET_PROPERTY:${save_target},expanded_file>
        COMMAND ${CMAKE_COMMAND}
                -DEXPANDED_FILE="$<TARGET_PROPERTY:${save_target},expanded_file>"
                -DOUTPUT_FILE="${yaml_file}"
                -DTEMP_FILES="$<TARGET_PROPERTY:${save_target},temp_files>"
                -P ${ZEPHYR_BASE}/cmake/yaml-filter.cmake
      )
    endif()

    math(EXPR genex_save_count "${genex_save_count} + 1")
    set_property(TARGET ${save_target} PROPERTY genex_save_count ${genex_save_count})

    cmake_path(SET yaml_path "${yaml_file}")
    cmake_path(GET yaml_path STEM yaml_file_no_ext)
    set(expanded_file ${CMAKE_CURRENT_BINARY_DIR}/${yaml_file_no_ext}_${genex_save_count}.yaml)
    set_property(TARGET ${save_target} PROPERTY expanded_file ${expanded_file})

    # comment this to keep the temporary files
    set_property(TARGET ${save_target} APPEND PROPERTY temp_files ${expanded_file})

    to_yaml("${json_content}" 0 yaml_out TEMP_GENEX)
    FILE(GENERATE OUTPUT ${expanded_file} CONTENT "${yaml_out}")
    FILE(TOUCH ${expanded_file}) # ensure timestamp is updated even if nothing changed
  endif()
endfunction()

function(to_yaml json level yaml mode)
  if(mode STREQUAL "DIRECT")
    # Direct output mode, no genexes: write a standard YAML
    set(expand_lists TRUE)
    set(escape_quotes TRUE)
    set(comment_genexes FALSE)
  elseif(mode STREQUAL "DIRECT_GENEX" OR mode STREQUAL "FINAL_GENEX")
    # Direct output mode with genexes enabled, or final write of post-processed
    # file: write a standard YAML, comment entries with genexes if they are
    # (still) present in the file
    set(expand_lists TRUE)
    set(escape_quotes TRUE)
    set(comment_genexes TRUE)
  elseif(mode STREQUAL "TEMP_GENEX")
    # Temporary output mode for genex expansion: save single quotes with no
    # special processing, since they will be fixed up by yaml-filter.cmake
    set(expand_lists FALSE)
    set(escape_quotes FALSE)
    set(comment_genexes FALSE)
  else()
    message(FATAL_ERROR "to_yaml(... ${mode} ) is malformed.")
  endif()

  if(level EQUAL 0)
    # Top-level call, initialize the YAML output variable
    set(${yaml} "" PARENT_SCOPE)
  else()
    math(EXPR level_dec "${level} - 1")
    set(indent_${level} "${indent_${level_dec}}  ")
  endif()

  string(JSON length LENGTH "${json}")
  if(length EQUAL 0)
    # Empty object
    return()
  endif()

  math(EXPR stop "${length} - 1")
  foreach(i RANGE 0 ${stop})
    string(JSON member MEMBER "${json}" ${i})

    string(JSON type TYPE "${json}" ${member})
    string(JSON subjson GET "${json}" ${member})
    if(type STREQUAL OBJECT)
      # JSON object -> YAML dictionary
      set(${yaml} "${${yaml}}${indent_${level}}${member}:\n")
      math(EXPR sublevel "${level} + 1")
      to_yaml("${subjson}" ${sublevel} ${yaml} ${mode})
    elseif(type STREQUAL ARRAY)
      # JSON array -> YAML list
      set(${yaml} "${${yaml}}${indent_${level}}${member}:")
      string(JSON arraylength LENGTH "${subjson}")
      if(${arraylength} LESS 1)
        set(${yaml} "${${yaml}} []\n")
      else()
        set(${yaml} "${${yaml}}\n")
        math(EXPR arraystop "${arraylength} - 1")
        foreach(i RANGE 0 ${arraystop})
          string(JSON item GET "${json}" ${member} ${i})
          # Check the length of item. Only OBJECT and ARRAY may have length, so a length at this
          # level means `to_yaml()` should be called recursively.
          string(JSON length ERROR_VARIABLE ignore LENGTH "${item}")
          if(length)
            set(non_indent_yaml)
            to_yaml("${item}" 0 non_indent_yaml ${mode})
            string(REGEX REPLACE "\n$" "" non_indent_yaml "${non_indent_yaml}")
            string(REPLACE "\n" "\n${indent_${level}}   " indent_yaml "${non_indent_yaml}")
            set(${yaml} "${${yaml}}${indent_${level}} - ${indent_yaml}\n")
          else()
            # Assume a string, escape single quotes when required (see comment below).
            if(escape_quotes)
              string(REPLACE "'" "''" item "${item}")
            endif()
            set(${yaml} "${${yaml}}${indent_${level}} - '${item}'\n")
          endif()
        endforeach()
      endif()
    elseif(type STREQUAL STRING)
      # JSON string maps to multiple YAML types:
      # - with unexpanded generator expressions: save as YAML comment
      # - if it matches the special prefix: convert to YAML list
      # - otherwise: save as YAML scalar
      # Single quotes must be escaped in the value _unless_ this will be used
      # to expand generator expressions, because then the escaping will be
      # addressed once in the yaml-filter.cmake script.
      if(escape_quotes)
        string(REPLACE "'" "''" subjson "${subjson}")
      endif()
      if(subjson MATCHES "\\$<.*>" AND comment_genexes)
        # Yet unexpanded generator expression: save as comment
        string(SUBSTRING ${indent_${level}} 1 -1 short_indent)
        set(${yaml} "${${yaml}}#${short_indent}${member}: '${subjson}'\n")
      elseif(subjson MATCHES "^@YAML-LIST@" AND expand_lists)
        # List-as-string: convert to list
        set(${yaml} "${${yaml}}${indent_${level}}${member}:")
        list(POP_FRONT subjson)
        if(subjson STREQUAL "")
          set(${yaml} "${${yaml}} []\n")
        else()
          set(${yaml} "${${yaml}}\n")
          foreach(item ${subjson})
            set(${yaml} "${${yaml}}${indent_${level}} - '${item}'\n")
          endforeach()
        endif()
      else()
        # Raw strings: save as is
        set(${yaml} "${${yaml}}${indent_${level}}${member}: '${subjson}'\n")
      endif()
    else()
      # Other JSON data type -> YAML scalar, as-is
      set(${yaml} "${${yaml}}${indent_${level}}${member}: ${subjson}\n")
    endif()
  endforeach()

  set(${yaml} ${${yaml}} PARENT_SCOPE)
endfunction()