name: Classify CI changes

on:
  workflow_call:
    outputs:
      build_and_test:
        description: Run the test and coverage matrix, compatibility tests, and mod build.
        value: ${{ jobs.changes.outputs.build_and_test }}
      js_lint:
        description: Run the JavaScript/TypeScript linter.
        value: ${{ jobs.changes.outputs.js_lint }}
      lua_lint:
        description: Run the Lua linter.
        value: ${{ jobs.changes.outputs.lua_lint }}

jobs:
  changes:
    runs-on: ubuntu-latest
    timeout-minutes: 5
    outputs:
      build_and_test: ${{ steps.syntax.outputs.build_and_test || steps.paths.outputs.code }}
      js_lint: ${{ steps.lint.outputs.js_lint }}
      lua_lint: ${{ steps.lint.outputs.lua_lint }}
    steps:
      - uses: actions/checkout@v7
        with:
          fetch-depth: 0
      - uses: dorny/paths-filter@v4
        id: paths
        with:
          token: ''
          base: ${{ github.event.pull_request.base.sha || github.event.before }}
          ref: ${{ github.sha }}
          list-files: json
          predicate-quantifier: every
          filters: |
            # Files requiring validation beyond documentation checks.
            code:
              - '**'
              - '!**/*.md'
              - '!docs/**/*.{png,jpg,svg,gif}'
            # Sources and configuration owned by each linter.
            # Workflow scripts and shared build configuration run both linters.
            js:
              - '**/*.{js,cjs,mjs,jsx,ts,cts,mts,tsx}'
              - '!.github/**'
              - '!**/{webpack,babel,rollup,vite,jest}.config.*'
            lua:
              - '{*.lua,**/*.lua,.emmyrc.json}'
              - '!.github/**'
            # Modified JS/TS source eligible for the comment-only shortcut.
            # TypeScript type changes still count as substantive changes.
            syntax:
              - modified: '**/*.{js,cjs,mjs,jsx,ts,cts,mts,tsx}'
              # Source fixtures and templates always receive full validation.
              - '!test/file/**'
              - '!packages/create/templates/**'
              - '!.github/**'
              - '!**/{eslint,webpack,babel,rollup,vite,jest}.config.*'
      - name: Select linters
        id: lint
        env:
          CODE_FILES: ${{ steps.paths.outputs.code_files }}
          JS_FILES: ${{ steps.paths.outputs.js_files }}
          LUA_FILES: ${{ steps.paths.outputs.lua_files }}
        run: |
          # Unclassified non-documentation files can affect either language.
          jq -nr --argjson code "$CODE_FILES" --argjson js "$JS_FILES" --argjson lua "$LUA_FILES" '
            ($code - $js - $lua | length > 0) as $shared |
            "js_lint=\($shared or ($js | length > 0))",
            "lua_lint=\($shared or ($lua | length > 0))"
          ' >> "$GITHUB_OUTPUT"
      - name: Install Difftastic
        if: steps.paths.outputs.syntax == 'true'
        env:
          DIFFT_VERSION: 0.71.0
          DIFFT_SHA256: 61aea5394a53c56f144637cf39b3a0c0dafa27769731745e5851ff276e6478da
        run: |
          mkdir -p "$RUNNER_TEMP/difftastic"
          curl -fsSL "https://github.com/Wilfred/difftastic/releases/download/$DIFFT_VERSION/difft-$DIFFT_VERSION-x86_64-unknown-linux-gnu.tar.gz" -o "$RUNNER_TEMP/difftastic.tar.gz"
          echo "$DIFFT_SHA256  $RUNNER_TEMP/difftastic.tar.gz" | sha256sum -c
          tar -xzf "$RUNNER_TEMP/difftastic.tar.gz" -C "$RUNNER_TEMP/difftastic"
          echo "$RUNNER_TEMP/difftastic" >> "$GITHUB_PATH"
      - name: Check for substantive changes
        id: syntax
        if: steps.paths.outputs.code == 'true'
        env:
          CODE_FILES: ${{ steps.paths.outputs.code_files }}
          SYNTAX_FILES: ${{ steps.paths.outputs.syntax_files }}
          BASE: ${{ github.event.pull_request.base.sha || github.event.before }}
          HEAD_SHA: ${{ github.sha }}
        run: |
          # Skip only when every non-documentation file is an ordinary source edit.
          echo 'build_and_test=true' >> "$GITHUB_OUTPUT"
          # A new branch has no previous commit; keep full validation on its first push.
          if [[ "$BASE" == 0000000000000000000000000000000000000000 ]]; then
            exit 0
          fi
          if ! jq -en --argjson code "$CODE_FILES" --argjson syntax "$SYNTAX_FILES" \
            '$code - $syntax | length == 0' > /dev/null; then
            exit 0
          fi
          git cat-file -e "$BASE^{commit}"
          jq -j '.[] | ., "\u0000"' <<< "$SYNTAX_FILES" > "$RUNNER_TEMP/syntax-files"
          while IFS= read -r -d '' file; do
            # Mode changes and symlinks are substantive even when text is identical.
            [[ -z "$(git diff --summary --no-renames "$BASE" "$HEAD_SHA" -- "$file")" ]] || exit 0
            git ls-tree "$HEAD_SHA" -- "$file" | grep -qE '^100(644|755) blob ' || exit 0
            before="$RUNNER_TEMP/before.${file##*.}"
            after="$RUNNER_TEMP/after.${file##*.}"
            git show "$BASE:$file" > "$before"
            git show "$HEAD_SHA:$file" > "$after"
            # Difftastic ignores ALL comments; retain compiler/bundler/coverage directives.
            if grep -Eq '@ts-|@jsx|@internal|<reference\b|<amd-|sourceMappingURL|sourceURL|webpack|vite|[#@]__|/\*!|(istanbul|c8|v8)[[:space:]]+ignore' "$before" "$after"; then
              exit 0
            fi
            case "$file" in
              *.js|*.cjs|*.mjs|*.jsx)
                # JavaScript JSDoc can contain type information.
                if grep -Fq '/**' "$before" "$after"; then exit 0; fi ;;
            esac
            if ! difft --ignore-comments --check-only --exit-code "$before" "$after"; then
              exit 0
            fi
          done < "$RUNNER_TEMP/syntax-files"
          echo 'build_and_test=false' >> "$GITHUB_OUTPUT"