#!/bin/bash
# pre-tool-use.sh: Block dangerous shell commands before Claude executes them.
#
# Claude Code calls this script BEFORE executing any Bash command.
# The script receives a JSON object on stdin with two fields:
#   - tool_name: the name of the tool being called (e.g., "Bash")
#   - tool_input: the arguments passed to the tool (e.g., {"command": "ls -la"})
#
# Exit codes:
#   0  Allow the command to proceed
#   2  Block the command (Claude receives the "reason" field as an error message)
#
# When blocking, write a JSON object to stdout:
#   {"decision": "block", "reason": "Human-readable explanation"}
#
# Make this script executable: chmod +x hooks/pre-tool-use.sh

# Read the full JSON payload from stdin
input=$(cat)

# Extract tool_name and the command argument from the JSON
tool_name=$(echo "$input" | python3 -c "import sys,json; print(json.load(sys.stdin).get('tool_name',''))" 2>/dev/null)
command=$(echo "$input" | python3 -c "import sys,json; print(json.load(sys.stdin).get('tool_input',{}).get('command',''))" 2>/dev/null)

# Only inspect Bash tool calls. Allow everything else immediately.
if [ "$tool_name" != "Bash" ]; then
  exit 0
fi

# Each blocked pattern is checked separately with a descriptive reason.
# Pattern matching uses grep -qiE (case-insensitive extended regex).

block_if_match() {
  local pattern="$1"
  local reason="$2"
  if echo "$command" | grep -qiE "$pattern"; then
    echo "{\"decision\": \"block\", \"reason\": \"$reason\"}"
    exit 2
  fi
}

# Recursive deletion of the root filesystem
block_if_match 'rm -rf /' 'Recursive deletion from root is not allowed'

# sudo: prevents privilege escalation
block_if_match 'sudo ' 'Commands with sudo are not allowed'

# World-writable permissions: a common misconfiguration that opens security holes
block_if_match 'chmod 777' 'chmod 777 is not allowed: use more restrictive permissions'

# Direct disk write: can wipe an entire disk in seconds
block_if_match 'dd if=' 'Direct disk writes with dd are not allowed'

# Filesystem formatting: permanently destroys data
block_if_match 'mkfs' 'Formatting filesystems is not allowed'

# Fork bomb: crashes the system by spawning processes until resources are exhausted
block_if_match ':\(\)\{' 'Fork bombs are not allowed'

# Piping curl or wget output directly into a shell:
# executes arbitrary remote code without review
block_if_match 'curl.+\|.+bash' 'Piping curl into bash is not allowed'
block_if_match 'curl.+\|.+sh' 'Piping curl output into a shell is not allowed'
block_if_match 'wget.+\|.+bash' 'Piping wget into bash is not allowed'
block_if_match 'wget.+\|.+sh' 'Piping wget output into a shell is not allowed'

# Shutdown and reboot: should never be triggered by an automated agent
block_if_match '^shutdown' 'Shutdown commands are not allowed'
block_if_match '^reboot' 'Reboot commands are not allowed'

# Nothing matched: allow the command
exit 0