#!/bin/bash

# Enable strict error handling
set -e

# Function to show usage instructions
show_usage() {
  echo "Usage: $0 [file extensions] [environment] [--dry-run]"
  echo "  file extensions: A space-separated list of file extensions (e.g. .yml .json .conf)."
  echo "  environment: The target environment (e.g., development or production)."
  echo "  --dry-run  : Simulate changes without modifying files."
}

# Parse command-line arguments
DRY_RUN=false
ENV=$1
if [[ -z "$ENV" ]]; then
  show_usage
  exit 1
fi

if [[ "$2" == "--dry-run" ]]; then
  DRY_RUN=true
fi

shift  # Shift arguments so we can get the file extensions after the environment

EXTENSIONS=("$@")
if [[ ${#EXTENSIONS[@]} -eq 0 ]]; then
  echo "Error: You must specify at least one file extension."
  show_usage
  exit 1
fi

echo "Arguments passed correctly!"

# Load the appropriate .env file
if [ -f ".env.$ENV" ]; then
  set -a
  source ".env.$ENV"
  set +a
else
  echo "Environment file .env.$ENV not found!"
  exit 1
fi

# Function to escape all special characters that might affect sed
escape_sed_special_chars() {
  printf '%s' "$1" | sed 's|[&/\$]|\&|g; s|[[:space:]]|\\ |g; s|\\|\\\\|g'
}

# Process files for each extension
for EXT in "${EXTENSIONS[@]}"; do
  # Find and process all *.template files with the current extension, including subdirectories
  find . -name "*.template$EXT" | while read -r TEMPLATE_FILE; do
    # Derive output file name by removing ".template"
    OUTPUT_FILE="${TEMPLATE_FILE%.template$EXT}$EXT"

    # Dry-run reporting or actual processing
    if $DRY_RUN; then
      echo "Dry run: would generate $OUTPUT_FILE from $TEMPLATE_FILE"

      LINE_NUMBER=0
      while IFS= read -r line || [[ -n "$line" ]]; do
        LINE_NUMBER=$((LINE_NUMBER + 1))
        while [[ "$line" =~ (\$\{([A-Za-z_][A-Za-z0-9_]*)\}) ]]; do
          PLACEHOLDER="${BASH_REMATCH[1]}"
          VAR_NAME="${BASH_REMATCH[2]}"
          VAR_VALUE="${!VAR_NAME:-<UNDEFINED>}"

          echo "  Would have inputted '$VAR_VALUE' in place of '$VAR_NAME' in $OUTPUT_FILE at line $LINE_NUMBER"

          if [[ "$VAR_VALUE" == "<UNDEFINED>" ]]; then
            echo "  Warning: Variable '$VAR_NAME' is undefined and will cause an error in actual mode."
          fi

          line="${line/$PLACEHOLDER/}"
        done
      done < "$TEMPLATE_FILE"

    else
      # Validate unresolved placeholders
      UNRESOLVED=$(grep -oP '\${\K[A-Za-z_][A-Za-z0-9_]*(?=})' "$TEMPLATE_FILE" | while read -r var; do
        if [ -z "${!var}" ]; then
          echo "$var"
        fi
      done)

      if [ -n "$UNRESOLVED" ]; then
        echo "Error: Unresolved variable placeholders detected in $TEMPLATE_FILE!"
        echo "Ensure all variables are defined in .env.$ENV. Missing: $UNRESOLVED"
        exit 1
      fi

      # Backup existing output file if it exists
      if [ -f "$OUTPUT_FILE" ]; then
        mv "$OUTPUT_FILE" "${OUTPUT_FILE}.bak"
        echo "Backup created for $OUTPUT_FILE as ${OUTPUT_FILE}.bak"
      fi

      # Replace placeholders with environment variables
      sed_script=""
      while IFS='=' read -r key value; do
        # Skip invalid variable names
        if [[ "$key" =~ ^[A-Za-z_][A-Za-z0-9_]*$ ]]; then
          # Escape special characters in the key and value for sed
          escaped_key=$(escape_sed_special_chars "${key}")
          escaped_value=$(escape_sed_special_chars "${!key}")
          sed_script+="s|\${${escaped_key}}|${escaped_value}|g;"
        fi
      done < <(env)

      # Generate the output file
      sed -e "$sed_script" "$TEMPLATE_FILE" > "$OUTPUT_FILE"
      echo "Generated $OUTPUT_FILE from $TEMPLATE_FILE"
    fi
  done
done

# Keep the terminal open at the end
echo "Script completed. Press any key to exit..."
read -n 1 -s