#!/bin/bash
#
# ScoutFS kernel compatibility check
#
# Standalone script to verify whether scoutfs can build against a given
# set of kernel headers. Used both locally and in CI matrix testing.
#
# Usage: check-kernel-compat.sh [KSRC_PATH]
#   Defaults to /lib/modules/$(uname -r)/build
#
# Exit 0 = compatible (build succeeded)
# Exit 1 = incompatible (build failed or headers missing)
#

set -euo pipefail

KSRC="${1:-/lib/modules/$(uname -r)/build}"
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="${SCRIPT_DIR}/.."

# When used in the build repo, the scoutfs source is checked out
# alongside. Allow override via SCOUTFS_SRC env var.
SCOUTFS_SRC="${SCOUTFS_SRC:-${REPO_ROOT}/scoutfs}"

echo "============================================"
echo "ScoutFS Kernel Compatibility Check"
echo "============================================"
echo "Kernel headers: ${KSRC}"
echo "ScoutFS source: ${SCOUTFS_SRC}"
echo ""

# --- Phase 1: Quick header checks ---
echo "--- Phase 1: Header availability ---"

if [ ! -d "$KSRC" ]; then
    echo "FAIL: Kernel headers directory not found: ${KSRC}"
    exit 1
fi

if [ ! -f "$KSRC/Makefile" ]; then
    echo "FAIL: No Makefile in kernel build directory: ${KSRC}"
    exit 1
fi

REQUIRED_HEADERS=(
    "include/linux/fs.h"
    "include/linux/blk_types.h"
    "include/linux/bio.h"
    "include/linux/net.h"
    "include/linux/shrinker.h"
    "include/linux/xattr.h"
    "include/linux/dcache.h"
    "include/linux/posix_acl.h"
    "include/linux/slab.h"
    "include/linux/rbtree.h"
)

MISSING=0
for header in "${REQUIRED_HEADERS[@]}"; do
    if [ -f "${KSRC}/${header}" ]; then
        echo "  OK: ${header}"
    else
        echo "  MISSING: ${header}"
        MISSING=$((MISSING + 1))
    fi
done

if [ "$MISSING" -gt 0 ]; then
    echo ""
    echo "FAIL: ${MISSING} required header(s) missing"
    exit 1
fi
echo ""

# --- Phase 2: Kernel version check ---
echo "--- Phase 2: Kernel version ---"

KMAJOR=$(grep '^VERSION' "$KSRC/Makefile" | head -1 | awk '{print $3}')
KMINOR=$(grep '^PATCHLEVEL' "$KSRC/Makefile" | head -1 | awk '{print $3}')
KSUB=$(grep '^SUBLEVEL' "$KSRC/Makefile" | head -1 | awk '{print $3}')

echo "  Detected: ${KMAJOR:-?}.${KMINOR:-?}.${KSUB:-?}"

if [ -n "$KMAJOR" ] && [ -n "$KMINOR" ]; then
    KVER_NUM=$((KMAJOR * 100 + KMINOR))
    if [ "$KVER_NUM" -lt 306 ]; then
        echo "  FAIL: Kernel too old (minimum 3.6)"
        exit 1
    fi
    echo "  OK: Meets minimum version requirement (>= 3.6)"
else
    echo "  WARNING: Could not determine kernel version, proceeding anyway"
fi
echo ""

# --- Phase 3: Compatibility feature detection ---
echo "--- Phase 3: Compatibility feature detection ---"

COMPAT_MAKEFILE="${SCOUTFS_SRC}/kmod/src/Makefile.kernelcompat"

if [ -f "$COMPAT_MAKEFILE" ]; then
    TOTAL=0
    DETECTED=0

    # Parse the grep-based checks from Makefile.kernelcompat
    while IFS= read -r line; do
        if [[ "$line" =~ ifneq.*shell\ grep ]]; then
            TOTAL=$((TOTAL + 1))
            # Extract the pattern and file from the grep command
            PATTERN=$(echo "$line" | sed -n "s/.*grep[[:space:]]*'\([^']*\)'.*/\1/p" | head -1)
            # Try with -s variant too
            if [ -z "$PATTERN" ]; then
                PATTERN=$(echo "$line" | sed -n "s/.*grep[[:space:]]*-s[[:space:]]*'\([^']*\)'.*/\1/p" | head -1)
            fi
            FILE=$(echo "$line" | sed -n 's/.*grep[^)]*[[:space:]]\([a-z].*\))/\1/p' | head -1)

            if [ -n "$PATTERN" ] && [ -n "$FILE" ] && [ -f "${KSRC}/${FILE}" ]; then
                if grep -q "$PATTERN" "${KSRC}/${FILE}" 2>/dev/null; then
                    DETECTED=$((DETECTED + 1))
                fi
            fi
        fi
    done < "$COMPAT_MAKEFILE"

    echo "  Compat features detected: ${DETECTED}/${TOTAL}"
    echo "  (This is informational — both old and new APIs are supported via shims)"
else
    echo "  WARNING: Makefile.kernelcompat not found at ${COMPAT_MAKEFILE}"
    echo "  Skipping feature detection (set SCOUTFS_SRC to the scoutfs source directory)"
fi
echo ""

# --- Phase 4: Actual build test ---
echo "--- Phase 4: Build test ---"

if [ ! -d "${SCOUTFS_SRC}/kmod" ]; then
    echo "  SKIP: ScoutFS kmod source not found at ${SCOUTFS_SRC}/kmod"
    echo "  (Header checks passed — build likely to succeed)"
    echo ""
    echo "RESULT: LIKELY COMPATIBLE (build test skipped)"
    exit 0
fi

echo "  Attempting module build..."

BUILD_LOG=$(mktemp)
if make -C "${SCOUTFS_SRC}/kmod" SK_KSRC="$KSRC" module > "$BUILD_LOG" 2>&1; then
    echo "  BUILD: SUCCESS"
    make -C "${SCOUTFS_SRC}/kmod" SK_KSRC="$KSRC" clean > /dev/null 2>&1 || true
    rm -f "$BUILD_LOG"
    echo ""
    echo "============================================"
    echo "RESULT: COMPATIBLE"
    echo "============================================"
    exit 0
else
    echo "  BUILD: FAILED"
    echo ""
    echo "  Build log (last 30 lines):"
    tail -30 "$BUILD_LOG" | sed 's/^/    /'
    rm -f "$BUILD_LOG"
    echo ""
    echo "============================================"
    echo "RESULT: INCOMPATIBLE"
    echo "============================================"
    exit 1
fi