Add GitHub Action to validate image requirements

.github/workflows/validate.yml

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+name: Validate
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    paths:
+      - "src/**"
+
+jobs:
+  validate:
+    name: Images
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Validate images
+        uses: ./.github/workflows/validate

.github/workflows/validate/Dockerfile

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+FROM alpine
+RUN apk add --no-cache imagemagick bash
+COPY validate.sh /validate.sh
+ENTRYPOINT ["/validate.sh"]

.github/workflows/validate/action.yml

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+name: "validate"
+runs:
+  using: "docker"
+  image: "Dockerfile"

.github/workflows/validate/validate.sh

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+#!/usr/bin/env bash
+
+# Small variable to determine exit code at the end
+ERRORS=0
+IMAGES=0
+
+# Small error handling method, that works with GitHub Actions
+function error() {
+  local file=${1}
+  local message=${2}
+  ((ERRORS++))
+
+  if [[ ! -z "${GITHUB_ACTIONS}" ]]; then
+    echo "::error file=${file}::${message}: ${file}"
+  else
+    echo "${message}: ${file}"
+  fi
+}
+
+# Find all files in the src folder (should contain only images)
+while read image; do
+    # Read properties from image
+    properties=($(identify -format "%w %h %m %[colorspace]" "${image}"))
+    if [[ "$?" -ne 0 ]]; then
+      error "${image}" "Could not read image file"
+      continue
+    fi
+
+    # Extract properties into variables
+    filename=$(basename "${image}")
+    width="${properties[0]}"
+    height="${properties[1]}"
+    type="${properties[2]}"
+    colorspace="${properties[3]}"
+
+    # Ensure file is actually a PNG file
+    [[ "${type}" != "PNG" ]] \
+      && error "${image}" "Invalid file type '${type}' for file"
+
+    # Ensure color space is sRGB
+    [[ "${colorspace}" != "sRGB" ]] \
+      && error "${image}" "Invalid color space '${colorspace}' for file"
+
+    # Validate image dimensions
+    if [[ "${filename}" == "icon.png" ]]; then
+      # icon dimension
+      [[ "${width}" -ne 256 || "${height}" -ne 256 ]] \
+        && error "${image}" "Invalid icon size! Size is ${width}x${height}px, must be 256x256px"
+
+    elif [[ "${filename}" == "icon@2x.png" ]]; then
+      # hDPI icon dimension
+      [[ "${width}" -ne 512 || "${height}" -ne 512 ]] \
+        && error "${image}" "Invalid hDPI icon size! Size is ${width}x${height}px, must be 512x512px"
+
+    elif [[ "${filename}" == "logo.png" ]]; then
+      # Minimal shortest side
+      if [[ "${width}" -le "${height}" && "${width}" -lt 128 ]]; then
+        error "${image}" "Invalid logo size! Size is ${width}x${height}px, shortest side must be at least 128px"
+      elif [[ "${width}" -ge "${height}" && "${height}" -lt 128 ]]; then
+        error "${image}" "Invalid logo size! Size is ${width}x${height}px, shortest side must be at least 128px"
+      fi
+
+      # Maximal shortest size
+      if [[ "${width}" -le "${height}" && "${width}" -gt 256 ]]; then
+        error "${image}" "Invalid logo size! Size is ${width}x${height}px, shortest side must not exceed 256px"
+      elif [[ "${width}" -ge "${height}" && "${height}" -gt 256 ]]; then
+        error "${image}" "Invalid logo size! Size is ${width}x${height}px, shortest side must not exceed 256px"
+      fi
+
+    elif [[ "${filename}" == "logo@2x.png" ]]; then
+      # Minimal shortest side
+      if [[ "${width}" -le "${height}" && "${width}" -lt 256 ]]; then
+        error "${image}" "Invalid hDPI logo size! Size is ${width}x${height}px, shortest side must be at least 256px"
+      elif [[ "${width}" -ge "${height}" && "${height}" -lt 256 ]]; then
+        error "${image}" "Invalid hDPI logo size! Size is ${width}x${height}px, shortest side must be at least 256px"
+      fi
+
+      # Maximal shortest side
+      if [[ "${width}" -le "${height}" && "${width}" -gt 512 ]]; then
+        error "${image}" "Invalid hDPI logo size! Size is ${width}x${height}px, shortest side must not exceed 512px"
+      elif [[ "${width}" -ge "${height}" && "${height}" -gt 512 ]]; then
+        error "${image}" "Invalid hDPI logo size! Size is ${width}x${height}px, shortest side must not exceed 512px"
+      fi
+
+    else
+      # Unexpected file
+      error "${image}" "Unknown and invalid filename"
+    fi
+
+    ((IMAGES++))
+done <<< $(find src -type f)
+
+echo ""
+echo "Total of ${IMAGES} images checked, found ${ERRORS} issues."
+
+[[ "${ERRORS}" -ne 0 ]] && exit 1 || exit 0

scripts/validate.sh

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+../.github/workflows/validate/validate.sh