#!/bin/bash
set -e

CACHE_DIR="/build/cache"
KERNEL_VERSION=$(cat /build/configs/kernel-version)

echo "[+] Smart build with Docker layer caching..."

# Function to check if we need to rebuild a stage
needs_rebuild() {
    local stage="$1"
    local trigger_files="$2"
    local cache_marker="$CACHE_DIR/${stage}-marker"
    
    # If cache marker doesn't exist, rebuild
    if [ ! -f "$cache_marker" ]; then
        echo "    $stage: No cache marker found, rebuild needed"
        return 0
    fi
    
    # Check if any trigger files are newer than cache marker
    for file in $trigger_files; do
        if [ -f "$file" ] && [ "$file" -nt "$cache_marker" ]; then
            echo "    $stage: $file changed, rebuild needed"
            return 0
        fi
    done
    
    echo "    $stage: Cache valid, skipping"
    return 1
}

# Function to mark stage as completed
mark_completed() {
    local stage="$1"
    mkdir -p "$CACHE_DIR"
    touch "$CACHE_DIR/${stage}-marker"
}

echo "  Checking cache status..."

# Check each build stage
REBUILD_COMPONENTS=false
REBUILD_KERNEL=false
REBUILD_INITRAMFS=false

# Components need rebuild if:
# - Component source repos have updates (we'll assume weekly refresh)
# - compile-components.sh script changed
if needs_rebuild "components" "/build/scripts/compile-components.sh"; then
    REBUILD_COMPONENTS=true
fi

# Kernel needs rebuild if:
# - Kernel version changed
# - Kernel config changed
# - build-kernel.sh script changed
if needs_rebuild "kernel" "/build/configs/kernel-version /build/configs/kernel-config-generic /build/scripts/build-kernel.sh"; then
    REBUILD_KERNEL=true
fi

# Initramfs always rebuilds (it's fast and contains user scripts)
REBUILD_INITRAMFS=true

echo ""
echo "  Build plan:"
echo "    Components: $([ "$REBUILD_COMPONENTS" = "true" ] && echo "REBUILD" || echo "CACHED")"
echo "    Kernel: $([ "$REBUILD_KERNEL" = "true" ] && echo "REBUILD" || echo "CACHED")"
echo "    Initramfs: REBUILD (always)"
echo ""

# Phase 1: Components (if needed)
if [ "$REBUILD_COMPONENTS" = "true" ]; then
    echo "[+] Building Zero-OS components from source..."
    /build/scripts/compile-components.sh
    mark_completed "components"
else
    echo "[+] Using cached Zero-OS components"
fi

# Phase 2: Kernel (if needed)
if [ "$REBUILD_KERNEL" = "true" ]; then
    echo "[+] Building kernel ${KERNEL_VERSION}..."
    # Only download and build kernel, not embed initramfs yet
    /build/scripts/build-kernel.sh --kernel-only
    mark_completed "kernel"
else
    echo "[+] Using cached kernel ${KERNEL_VERSION}"
fi

# Phase 3: Initramfs (always - fast)
echo "[+] Installing Alpine packages..."
/build/scripts/install-packages.sh

echo "[+] Setting up initramfs structure..."
/build/scripts/setup-initramfs.sh

# Phase 4: Final kernel assembly (embed initramfs)
echo "[+] Embedding initramfs into kernel..."
/build/scripts/build-kernel.sh --embed-only

echo ""
echo "[+] Smart build completed!"
echo "    Components: $([ "$REBUILD_COMPONENTS" = "true" ] && echo "rebuilt" || echo "cached")"
echo "    Kernel: $([ "$REBUILD_KERNEL" = "true" ] && echo "rebuilt" || echo "cached")"
echo "    Total time saved by caching: significant!"