{ pkgs, lib, gitSvPkg, ... }:

with pkgs;

writeShellApplication rec {
  name = "merge-diff";

  runtimeInputs = [ gitFull jq coreutils gnugrep gawk gitSvPkg ];

  # Define the shell script
  text = ''
    #!/usr/bin/env bash
    set -euo pipefail

    # Function to display usage
    usage() {
      echo "Usage: $0 -p <path_pattern> [-o <output_file>]"
      echo "  -p, --pattern    Path pattern to filter changed files (can be specified multiple times)"
      echo "  -o, --output     Output file (defaults to stdout)"
      echo "  -h, --help       Display this help message"
      exit 1
    }

    # Parse command-line arguments
    PATTERNS=()
    OUTPUT=""
    while [[ $# -gt 0 ]]; do
      case "$1" in
        -p|--pattern)
          PATTERNS+=("$2")
          shift 2
          ;;
        -o|--output)
          OUTPUT="$2"
          shift 2
          ;;
        -h|--help)
          usage
          ;;
        *)
          echo "Unknown option: $1"
          usage
          ;;
      esac
    done

    if [ ''${#PATTERNS[@]} -eq 0 ]; then
      echo "Error: At least one path pattern must be specified."
      usage
    fi

    # Get the current commit SHA
    CURRENT_SHA=$(git rev-parse HEAD)

    # Get parent commits
    PARENT_COUNT=$(git rev-list --parents -n 1 "$CURRENT_SHA" | wc -w)

    if [ "$PARENT_COUNT" -gt 2 ]; then
      echo "This is a merge commit with $((PARENT_COUNT - 1)) parents."
      # For simplicity, comparing with the first parent
      PARENT_SHA=$(git rev-parse HEAD^1)
    elif [ "$PARENT_COUNT" -eq 2 ]; then
      # Regular commit with one parent
      PARENT_SHA=$(git rev-parse HEAD^1)
    else
      echo "Single commit with no parents. Listing all changes."
      PARENT_SHA=HEAD~1
    fi

    echo "Current Commit SHA: $CURRENT_SHA"
    echo "Parent Commit SHA: $PARENT_SHA"

    # List changed files between parent and current commit
    CHANGED_FILES=$(git diff --name-only "$PARENT_SHA" "$CURRENT_SHA")

    echo "Changed files:"
    echo "$CHANGED_FILES"

    # Initialize an empty array for filtered changes
    FILTERED_CHANGES=()

    # Iterate over each pattern and filter changed files
    for pattern in "''${PATTERNS[@]}"; do
      while IFS= read -r file; do
        if [[ "$file" == "$pattern" ]]; then
          FILTERED_CHANGES+=("$file")
        fi
      done <<< "$CHANGED_FILES"
    done

    # Remove duplicates
    UNIQUE_FILTERED_CHANGES=$(printf "%s\n" "''${FILTERED_CHANGES[@]}" | sort -u)

    echo "Filtered changed files:"
    echo "$UNIQUE_FILTERED_CHANGES"

    # Determine if changes exist
    if [ -n "$UNIQUE_FILTERED_CHANGES" ]; then
      CHANGES_EXIST=true
    else
      CHANGES_EXIST=false
    fi

    # Determine semantic version bump using git-sv
    # Ensure that git-sv is available
    if ! command -v git-sv &> /dev/null; then
      echo "Error: git-sv is not installed or not in PATH."
      exit 1
    fi

    # Get the semantic version bump
    VERSION_BUMP=$(git-sv bump --from "$PARENT_SHA" --to "$CURRENT_SHA")

    # Validate the version bump
    if [[ "$VERSION_BUMP" =~ ^(patch|minor|major)$ ]]; then
      echo "Version bump: $VERSION_BUMP"
    else
      echo "Error: Unexpected version bump value: $VERSION_BUMP"
      exit 1
    fi

    # Convert to JSON
    RESULTS=$(jq -n \
      --argjson filteredChanges "$(printf '%s\n' "$UNIQUE_FILTERED_CHANGES" | jq -R -s -c 'split("\n") | map(select(length > 0))')" \
      --arg changesExist "$CHANGES_EXIST" \
      --arg versionBump "$VERSION_BUMP" \
      '{filteredChanges: $filteredChanges, changesExist: ($changesExist == "true"), versionBump: $versionBump}')

    # Output results
    if [ -n "$OUTPUT" ]; then
      echo "$RESULTS" > "$OUTPUT"
    else
      echo "$RESULTS"
    fi
  '';

  # Metadata for the package
  meta = with lib; {
    homepage = "https://code.252.no/tommy/containers";
    description = "Identify Merge Commit and List Changed Files with Flexible Filtering and Semantic Versioning";
    license = licenses.mit;
    maintainers = with maintainers; [ "tommy-skaug" ];
  };
}