Cache Efficiency Monitor

#!/usr/bin/env bash

# Cache Efficiency Monitor for Claude Code
# Tracks prompt caching performance and cost savings

# Read JSON from stdin
read -r input

# Extract cache metrics (if available in JSON)
cache_read_tokens=$(echo "$input" | jq -r '.cost.cache_read_input_tokens // 0')
cache_create_tokens=$(echo "$input" | jq -r '.cost.cache_creation_input_tokens // 0')
regular_input_tokens=$(echo "$input" | jq -r '.cost.input_tokens // 0')

# Calculate total input tokens
total_input=$((cache_read_tokens + cache_create_tokens + regular_input_tokens))

# Avoid division by zero
if [ $total_input -eq 0 ]; then
  total_input=1
fi

# Calculate cache hit rate (percentage of tokens read from cache)
if [ $cache_read_tokens -gt 0 ]; then
  cache_hit_rate=$(( (cache_read_tokens * 100) / total_input ))
else
  cache_hit_rate=0
fi

# Calculate write efficiency (cache creation vs regular input)
if [ $cache_create_tokens -gt 0 ]; then
  write_percentage=$(( (cache_create_tokens * 100) / total_input ))
else
  write_percentage=0
fi

# Cache efficiency scoring
if [ $cache_hit_rate -ge 50 ]; then
  CACHE_COLOR="\033[38;5;46m"   # Green: Excellent caching (>50% hit rate)
  CACHE_ICON="✓"
  CACHE_STATUS="EXCELLENT"
elif [ $cache_hit_rate -ge 25 ]; then
  CACHE_COLOR="\033[38;5;226m"  # Yellow: Good caching (25-50% hit rate)
  CACHE_ICON="●"
  CACHE_STATUS="GOOD"
elif [ $cache_hit_rate -gt 0 ]; then
  CACHE_COLOR="\033[38;5;208m"  # Orange: Low caching (1-25% hit rate)
  CACHE_ICON="⚠"
  CACHE_STATUS="LOW"
else
  CACHE_COLOR="\033[38;5;250m"  # Gray: No caching
  CACHE_ICON="○"
  CACHE_STATUS="NONE"
fi

# Estimate cost savings (cache reads cost 90% less than regular input)
if [ $cache_read_tokens -gt 0 ]; then
  # Savings = cache_read_tokens * 0.9 (90% discount)
  savings_tokens=$(echo "scale=0; $cache_read_tokens * 0.9 / 1" | bc)
  savings_display="💰 ~${savings_tokens} tok saved"
else
  savings_display=""
fi

# Build cache hit rate bar (20 characters wide)
hit_bar_filled=$(( cache_hit_rate / 5 ))  # Each char = 5%
hit_bar_empty=$(( 20 - hit_bar_filled ))

if [ $hit_bar_filled -gt 0 ]; then
  hit_bar=$(printf "█%.0s" $(seq 1 $hit_bar_filled))$(printf "░%.0s" $(seq 1 $hit_bar_empty))
else
  hit_bar="░░░░░░░░░░░░░░░░░░░░"
fi

# Optimization recommendation
if [ $cache_hit_rate -eq 0 ] && [ $cache_create_tokens -eq 0 ]; then
  RECOMMENDATION="(Enable caching?)"
elif [ $cache_hit_rate -lt 25 ] && [ $write_percentage -gt 50 ]; then
  RECOMMENDATION="(More reads needed)"
else
  RECOMMENDATION=""
fi

RESET="\033[0m"

# Output statusline
if [ -n "$savings_display" ]; then
  echo -e "${CACHE_ICON} Cache: ${CACHE_COLOR}${hit_bar}${RESET} ${cache_hit_rate}% | ${savings_display} ${RECOMMENDATION}"
else
  echo -e "${CACHE_ICON} Cache: ${CACHE_COLOR}${hit_bar}${RESET} ${cache_hit_rate}% ${RECOMMENDATION}"
fi

{
  "format": "bash",
  "position": "left",
  "refreshInterval": 2000
}