// This file is part of the happyDomain (R) project.
// Copyright (c) 2020-2026 happyDomain
// Authors: Pierre-Olivier Mercier, et al.

package checker

import (
	"context"
	"fmt"
	"strings"

	sdk "git.happydns.org/checker-sdk-go/checker"
)

func init() {
	RegisterRule(&hstsRule{})
	RegisterRule(&cspRule{})
	RegisterRule(&xFrameOptionsRule{})
	RegisterRule(&xXSSProtectionRule{})
}

// hstsRule checks the Strict-Transport-Security header on HTTPS responses.
type hstsRule struct{}

func (r *hstsRule) Name() string { return "http.hsts" }
func (r *hstsRule) Description() string {
	return "Verifies the presence and quality of the Strict-Transport-Security header on HTTPS responses."
}

func (r *hstsRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, opts sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadHTTPData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	require := sdk.GetBoolOption(opts, OptionRequireHSTS, true)
	minDays := sdk.GetIntOption(opts, OptionMinHSTSMaxAgeDays, DefaultMinHSTSMaxAge)
	minSeconds := int64(minDays) * 86400

	return EvalPerHTTPS(data, "http.hsts", func(p HTTPProbe) sdk.CheckState {
		h := ParseHSTS(p.Headers["strict-transport-security"])
		if h == nil {
			status := sdk.StatusWarn
			if !require {
				status = sdk.StatusInfo
			}
			return sdk.CheckState{
				Status:  status,
				Code:    "http.hsts.missing",
				Subject: p.Address,
				Message: "Strict-Transport-Security header is missing.",
				Meta:    map[string]any{"fix": "Send `Strict-Transport-Security: max-age=15552000; includeSubDomains` from HTTPS responses."},
			}
		}
		if h.MaxAge < minSeconds {
			return sdk.CheckState{
				Status:  sdk.StatusWarn,
				Code:    "http.hsts.short_max_age",
				Subject: p.Address,
				Message: fmt.Sprintf("HSTS max-age=%d is below the recommended %d seconds (%d days).", h.MaxAge, minSeconds, minDays),
			}
		}
		return sdk.CheckState{
			Status:  sdk.StatusOK,
			Code:    "http.hsts.ok",
			Subject: p.Address,
			Message: fmt.Sprintf("HSTS present (max-age=%d, includeSubDomains=%v, preload=%v).", h.MaxAge, h.IncludeSub, h.Preload),
		}
	})
}

// cspRule checks for the presence of a Content-Security-Policy header.
type cspRule struct{}

func (r *cspRule) Name() string { return "http.csp" }
func (r *cspRule) Description() string {
	return "Verifies the presence of a Content-Security-Policy header on HTTPS responses."
}

func (r *cspRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, opts sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadHTTPData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	require := sdk.GetBoolOption(opts, OptionRequireCSP, false)

	return EvalPerHTTPS(data, "http.csp", func(p HTTPProbe) sdk.CheckState {
		csp := ParseCSP(p.Headers["content-security-policy"])
		if csp == nil {
			status := sdk.StatusInfo
			if require {
				status = sdk.StatusWarn
			}
			return sdk.CheckState{
				Status:  status,
				Code:    "http.csp.missing",
				Subject: p.Address,
				Message: "Content-Security-Policy header is missing.",
				Meta:    map[string]any{"fix": "Define a CSP appropriate for your application (e.g. default-src 'self')."},
			}
		}
		if csp.HasUnsafe() {
			return sdk.CheckState{
				Status:  sdk.StatusWarn,
				Code:    "http.csp.unsafe",
				Subject: p.Address,
				Message: "Content-Security-Policy uses 'unsafe-inline' or 'unsafe-eval'.",
			}
		}
		return sdk.CheckState{
			Status:  sdk.StatusOK,
			Code:    "http.csp.ok",
			Subject: p.Address,
			Message: "Content-Security-Policy is set.",
		}
	})
}

// xFrameOptionsRule checks X-Frame-Options (or frame-ancestors in CSP as
// an acceptable substitute).
type xFrameOptionsRule struct{}

func (r *xFrameOptionsRule) Name() string { return "http.x_frame_options" }
func (r *xFrameOptionsRule) Description() string {
	return "Verifies that responses set X-Frame-Options or a CSP frame-ancestors directive."
}

func (r *xFrameOptionsRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadHTTPData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}

	return EvalPerHTTPS(data, "http.x_frame_options", func(p HTTPProbe) sdk.CheckState {
		xfo := strings.ToUpper(strings.TrimSpace(p.Headers["x-frame-options"]))
		hasFrameAncestors := ParseCSP(p.Headers["content-security-policy"]).HasDirective("frame-ancestors")

		switch {
		case xfo == "DENY" || xfo == "SAMEORIGIN" || hasFrameAncestors:
			return sdk.CheckState{
				Status:  sdk.StatusOK,
				Code:    "http.x_frame_options.ok",
				Subject: p.Address,
				Message: "Clickjacking protection is in place.",
			}
		case xfo != "":
			return sdk.CheckState{
				Status:  sdk.StatusWarn,
				Code:    "http.x_frame_options.invalid",
				Subject: p.Address,
				Message: "X-Frame-Options has an unrecognised value: " + xfo,
			}
		default:
			return sdk.CheckState{
				Status:  sdk.StatusWarn,
				Code:    "http.x_frame_options.missing",
				Subject: p.Address,
				Message: "Neither X-Frame-Options nor CSP frame-ancestors is set.",
				Meta:    map[string]any{"fix": "Send `X-Frame-Options: DENY` (or SAMEORIGIN) or use CSP frame-ancestors."},
			}
		}
	})
}

func init() {
	// Showcase: a rule expressed entirely as a HeaderRuleSpec. Compare
	// with the hand-rolled rules above — the boilerplate vanishes once
	// the only logic is "is this header present and well-formed?".
	RegisterRule(HeaderRule(HeaderRuleSpec{
		Code:        "http.x_content_type_options",
		Description: "Verifies that responses set X-Content-Type-Options: nosniff.",
		Header:      "X-Content-Type-Options",
		Required:    true,
		FixHint:     "Add `X-Content-Type-Options: nosniff` to all responses.",
		Validate: func(v string) (sdk.Status, string) {
			if strings.EqualFold(v, "nosniff") {
				return sdk.StatusOK, "X-Content-Type-Options: nosniff is set."
			}
			return sdk.StatusWarn, "X-Content-Type-Options has an unexpected value: " + strings.ToLower(v)
		},
	}))
}

// xXSSProtectionRule checks the legacy X-XSS-Protection header. Modern
// browsers ignore it, but if present we want it to be sane.
type xXSSProtectionRule struct{}

func (r *xXSSProtectionRule) Name() string { return "http.x_xss_protection" }
func (r *xXSSProtectionRule) Description() string {
	return "Reports the value of the legacy X-XSS-Protection header (disabled is preferred on modern browsers; CSP is the proper replacement)."
}

func (r *xXSSProtectionRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadHTTPData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}

	return EvalPerHTTPS(data, "http.x_xss_protection", func(p HTTPProbe) sdk.CheckState {
		v := strings.TrimSpace(p.Headers["x-xss-protection"])
		switch {
		case v == "":
			return sdk.CheckState{
				Status:  sdk.StatusInfo,
				Code:    "http.x_xss_protection.absent",
				Subject: p.Address,
				Message: "X-XSS-Protection is not set; CSP is the recommended replacement.",
			}
		case strings.HasPrefix(v, "0"):
			return sdk.CheckState{
				Status:  sdk.StatusOK,
				Code:    "http.x_xss_protection.disabled",
				Subject: p.Address,
				Message: "X-XSS-Protection is explicitly disabled (recommended).",
			}
		case strings.Contains(strings.ToLower(v), "mode=block"):
			return sdk.CheckState{
				Status:  sdk.StatusInfo,
				Code:    "http.x_xss_protection.enabled",
				Subject: p.Address,
				Message: "X-XSS-Protection is set to the historically recommended `1; mode=block`. Modern browsers ignore this header; CSP is the proper replacement.",
			}
		default:
			return sdk.CheckState{
				Status:  sdk.StatusInfo,
				Code:    "http.x_xss_protection.enabled",
				Subject: p.Address,
				Message: "X-XSS-Protection is enabled. Modern browsers ignore this header; CSP is the proper replacement.",
			}
		}
	})
}