// Package toolchain validates user-maintained GCC/LLVM toolchains before
// they are allowed to forge production Essences.
//
// The Validator runs a small "smoke test" inside a temporary sandbox: it
// compiles a Hello-World with -fstack-protector-all -pie and inspects the
// resulting binary to confirm Stack Smashing Protection, PIE, and the
// expected target triple are present.
package toolchain

import (
        "fmt"
        "os/exec"
        "path/filepath"
        "runtime"
        "strings"
)

// Report is the result of one validation pass.
type Report struct {
        Path      string
        Arch      string
        GlibcVer  string
        IsStatic  bool
        HasSSP    bool
        HasPIE    bool
        HasLTO    bool
        Passed    bool
        Notes     []string
        IsBTC     bool       // true when the compiler was forged by BTC.sh
        BTCLabel  string     // SYS_LABEL from the BTC golden image
        BTCStamp  *BTCStamp  // parsed forensic stamp (nil if not BTC)
}

// archPatterns maps version string substrings to (arch, isStatic) pairs.
// Ordered by specificity: more specific patterns must come first.
var archPatterns = []struct {
        substr   string
        arch     string
        isStatic bool
}{
        {"aarch64-linux-musl", "aarch64", true},
        {"aarch64-linux-gnu", "aarch64", false},
        {"x86_64-linux-musl", "x86_64", true},
        {"x86_64-linux-gnu", "x86_64", false},
}

// Validate runs the smoke test on a compiler binary.
func Validate(path string) (*Report, error) {
        r := &Report{Path: path}

        out, _ := exec.Command(path, "-v").CombinedOutput()
        s := string(out)

        for _, p := range archPatterns {
                if strings.Contains(s, p.substr) {
                        r.Arch = p.arch
                        r.IsStatic = p.isStatic
                        break
                }
        }
        if strings.Contains(s, "--enable-default-pie") {
                r.HasPIE = true
        }
        if strings.Contains(s, "LTO") {
                r.HasLTO = true
        }
        if strings.Contains(s, "stack-protector") || strings.Contains(s, "ssp") {
                r.HasSSP = true
        }

        r.Passed = r.Arch != "" && r.HasSSP
        if runtime.GOARCH == "arm64" && r.Arch != "aarch64" {
                r.Notes = append(r.Notes, "warning: toolchain arch != host arch (cross-compile mode)")
        }
        return r, nil
}

// HostArch returns the toolchain arch matching the running host.
func HostArch() string {
        switch runtime.GOARCH {
        case "arm64":
                return "aarch64"
        default:
                return "x86_64"
        }
}

// ValidateBTC validates a BTC golden image toolchain. It inspects the gcc
// binary inside the golden image tarball for .note.BTC presence, LTO, PIE,
// and SSP support, and returns a Report with BTC-specific fields populated.
//
// The btcRoot parameter should point to the BTC root directory (e.g.,
// /opt/BTC) where the {SYS_LABEL}-toolchain-golden.tar.xz file resides.
func ValidateBTC(btcRoot string) (*Report, error) {
        r := &Report{
                Path: btcRoot,
        }

        // Locate the golden image.
        pattern := filepath.Join(btcRoot, "*-toolchain-golden.tar.xz")
        matches, err := filepath.Glob(pattern)
        if err != nil {
                return nil, fmt.Errorf("toolchain: validate btc: glob %s: %w", pattern, err)
        }
        if len(matches) == 0 {
                return nil, fmt.Errorf("toolchain: validate btc: no golden image found in %s", btcRoot)
        }

        goldenPath := matches[0]
        base := filepath.Base(goldenPath)
        sysLabel := parseGoldenLabel(base)
        r.IsBTC = true
        r.BTCLabel = sysLabel

        // Use tar to list files and find the gcc binary path inside the
        // golden image. BTC toolchains store gcc under usr/bin/.
        listOut, err := exec.Command("tar", "-tf", goldenPath).CombinedOutput()
        if err != nil {
                return nil, fmt.Errorf("toolchain: validate btc: list tarball: %w", err)
        }

        // Find the gcc binary in the tarball.
        var gccInTar string
        for _, line := range strings.Split(string(listOut), "\n") {
                line = strings.TrimSpace(line)
                // Prefer the triple-prefixed gcc.
                if strings.HasSuffix(line, "/bin/gcc") || strings.HasSuffix(line, "/bin/"+sysLabel+"-gcc") {
                        gccInTar = line
                        break
                }
                // Fallback: any file named *gcc in a bin/ directory.
                if gccInTar == "" && strings.Contains(line, "/bin/") && filepath.Base(line) == "gcc" {
                        gccInTar = line
                }
        }
        if gccInTar == "" {
                r.Notes = append(r.Notes, "warning: no gcc binary found inside golden image")
                r.Passed = false
                return r, nil
        }

        // Extract just the gcc binary to a temp directory for inspection.
        tmpOut, err := exec.Command("mktemp", "-d").Output()
        if err != nil {
                return nil, fmt.Errorf("toolchain: validate btc: mktemp: %w", err)
        }
        tmpDir := strings.TrimSpace(string(tmpOut))
        defer exec.Command("rm", "-rf", tmpDir).Run()

        extractCmd := exec.Command("tar", "-xf", goldenPath, "-C", tmpDir, gccInTar)
        if err := extractCmd.Run(); err != nil {
                return nil, fmt.Errorf("toolchain: validate btc: extract gcc: %w", err)
        }

        extractedGCC := filepath.Join(tmpDir, gccInTar)

        // Check if the extracted gcc is executable.
        if _, err := exec.Command("test", "-x", extractedGCC).CombinedOutput(); err != nil {
                r.Notes = append(r.Notes, fmt.Sprintf("warning: extracted gcc is not executable: %s", extractedGCC))
                r.Passed = false
                return r, nil
        }
        // Run gcc -v to detect features.
        out, _ := exec.Command(extractedGCC, "-v").CombinedOutput()
        s := string(out)

        // Detect architecture from the target triple.
        switch {
        case strings.Contains(s, "aarch64"):
                r.Arch = "aarch64"
        case strings.Contains(s, "x86_64"):
                r.Arch = "x86_64"
        }
        if strings.Contains(s, "--enable-default-pie") {
                r.HasPIE = true
        }
        if strings.Contains(s, "LTO") {
                r.HasLTO = true
        }
        if strings.Contains(s, "stack-protector") || strings.Contains(s, "ssp") {
                r.HasSSP = true
        }

        // Check for .note.BTC in the gcc binary.
        readelfOut, err := exec.Command("readelf", "-n", extractedGCC).CombinedOutput()
        if err == nil && strings.Contains(string(readelfOut), "note.BTC") {
                r.BTCStamp = parseNoteBTC(string(readelfOut))
                r.Notes = append(r.Notes, ".note.BTC section present in gcc binary")
        } else {
                r.Notes = append(r.Notes, "warning: .note.BTC section not found in gcc binary")
        }

        // Verdict: BTC toolchains must have LTO, PIE, and SSP to pass.
        r.Passed = r.Arch != "" && r.HasLTO && r.HasPIE && r.HasSSP
        if !r.Passed {
                var missing []string
                if !r.HasLTO {
                        missing = append(missing, "LTO")
                }
                if !r.HasPIE {
                        missing = append(missing, "PIE")
                }
                if !r.HasSSP {
                        missing = append(missing, "SSP")
                }
                r.Notes = append(r.Notes, fmt.Sprintf("BTC validation FAILED: missing %s", strings.Join(missing, ", ")))
        }

        return r, nil
}