#!/bin/bash
# generate-proof.sh - Generate OpenTimestamp proof for a git commit
# Usage: generate-proof.sh <commit-hash> [output-file]

set -e

COMMIT_HASH="${1:-}"
OUTPUT_FILE="${2:-.ots/proof.ots}"

if [ -z "$COMMIT_HASH" ]; then
    echo "Error: commit hash required" >&2
    echo "Usage: $0 <commit-hash> [output-file]" >&2
    exit 1
fi

# Ensure .ots directory exists
mkdir -p "$(dirname "$OUTPUT_FILE")"

# Function to generate proof using ots CLI
generate_with_ots_cli() {
    local hash="$1"
    local output="$2"
    
    # Create a temporary file with the hash (convert hex to binary)
    local temp_file=$(mktemp)
    local temp_ots="${temp_file}.ots"
    
    # Use python3 for hex to binary conversion (more portable than xxd)
    python3 -c "import sys; sys.stdout.buffer.write(bytes.fromhex('$hash'))" > "$temp_file"
    
    # Generate timestamp - ots creates .ots file alongside the original
    ots stamp "$temp_file"
    
    # Move the generated .ots file to the desired location
    if [ -f "$temp_ots" ]; then
        mkdir -p "$(dirname "$output")"
        mv "$temp_ots" "$output"
        echo "Generated proof with ots CLI: $output"
    else
        echo "Error: ots did not generate proof file" >&2
        rm -f "$temp_file"
        exit 1
    fi
    
    # Cleanup
    rm -f "$temp_file"
}

# Function to generate proof using opentimestamps-nodejs
generate_with_node() {
    local hash="$1"
    local output="$2"
    
    # Use nodejs opentimestamps library
    # This requires @opentimestamps/ots to be installed globally
    node -e "
const ots = require('@opentimestamps/ots');
const fs = require('fs');
const crypto = require('crypto');

const hash = '$hash';
const output = '$output';

// Convert hex hash to buffer
const hashBuffer = Buffer.from(hash, 'hex');

// Create timestamp
ots.Timestamp.hash(hashBuffer).then(timestamp => {
    // In a real implementation, this would contact the calendar server
    // For now, we create a minimal proof structure
    console.log('Warning: nodejs fallback creates local proof only');
    console.log('Install ots CLI for full functionality: https://github.com/opentimestamps/opentimestamps-client');
    
    // Create a simple proof file (this is a placeholder - real impl needs calendar)
    const proof = {
        hash: hash,
        timestamp: new Date().toISOString(),
        status: 'pending'
    };
    
    fs.writeFileSync(output, JSON.stringify(proof, null, 2));
    console.log('Generated local proof: ' + output);
}).catch(err => {
    console.error('Error generating timestamp:', err);
    process.exit(1);
});
"
}

# Check if ots CLI is available
if command -v ots &> /dev/null; then
    echo "Using ots CLI..."
    generate_with_ots_cli "$COMMIT_HASH" "$OUTPUT_FILE"
elif command -v node &> /dev/null && node -e "require('@opentimestamps/ots')" &> /dev/null; then
    echo "Using opentimestamps-nodejs fallback..."
    generate_with_node "$COMMIT_HASH" "$OUTPUT_FILE"
else
    echo "Error: Neither ots CLI nor @opentimestamps/ots node package found" >&2
    echo "Install one of:" >&2
    echo "  - ots CLI: https://github.com/opentimestamps/opentimestamps-client" >&2
    echo "  - Node package: npm install -g @opentimestamps/ots" >&2
    exit 1
fi

# Append previous commit hash to the proof file for chaining
if [ -f "$OUTPUT_FILE" ]; then
    PREV_COMMIT=$(git rev-parse HEAD^1 2>/dev/null || echo "")
    if [ -n "$PREV_COMMIT" ]; then
        echo "" >> "$OUTPUT_FILE"
        echo "# Previous commit: $PREV_COMMIT" >> "$OUTPUT_FILE"
    fi
fi

echo "Proof generated for commit: $COMMIT_HASH"