// Mozilla Public License Version 2.0
// ==================================
//
// 1. Definitions
// --------------
//
// 1.1. "Contributor"
//
//	means each individual or legal entity that creates, contributes to
//	the creation of, or owns Covered Software.
//
// 1.2. "Contributor Version"
//
//	means the combination of the Contributions of others (if any) used
//	by a Contributor and that particular Contributor's Contribution.
//
// 1.3. "Contribution"
//
//	means Covered Software of a particular Contributor.
//
// 1.4. "Covered Software"
//
//	means Source Code Form to which the initial Contributor has attached
//	the notice in Exhibit A, the Executable Form of such Source Code
//	Form, and Modifications of such Source Code Form, in each case
//	including portions thereof.
//
// 1.5. "Incompatible With Secondary Licenses"
//
//	means
//
//	(a) that the initial Contributor has attached the notice described
//	    in Exhibit B to the Covered Software; or
//
//	(b) that the Covered Software was made available under the terms of
//	    version 1.1 or earlier of the License, but not also under the
//	    terms of a Secondary License.
//
// 1.6. "Executable Form"
//
//	means any form of the work other than Source Code Form.
//
// 1.7. "Larger Work"
//
//	means a work that combines Covered Software with other material, in
//	a separate file or files, that is not Covered Software.
//
// 1.8. "License"
//
//	means this document.
//
// 1.9. "Licensable"
//
//	means having the right to grant, to the maximum extent possible,
//	whether at the time of the initial grant or subsequently, any and
//	all of the rights conveyed by this License.
//
// 1.10. "Modifications"
//
//	means any of the following:
//
//	(a) any file in Source Code Form that results from an addition to,
//	    deletion from, or modification of the contents of Covered
//	    Software; or
//
//	(b) any new file in Source Code Form that contains any Covered
//	    Software.
//
// 1.11. "Patent Claims" of a Contributor
//
//	means any patent claim(s), including without limitation, method,
//	process, and apparatus claims, in any patent Licensable by such
//	Contributor that would be infringed, but for the grant of the
//	License, by the making, using, selling, offering for sale, having
//	made, import, or transfer of either its Contributions or its
//	Contributor Version.
//
// 1.12. "Secondary License"
//
//	means either the GNU General Public License, Version 2.0, the GNU
//	Lesser General Public License, Version 2.1, the GNU Affero General
//	Public License, Version 3.0, or any later versions of those
//	licenses.
//
// 1.13. "Source Code Form"
//
//	means the form of the work preferred for making modifications.
//
// 1.14. "You" (or "Your")
//
//	means an individual or a legal entity exercising rights under this
//	License. For legal entities, "You" includes any entity that
//	controls, is controlled by, or is under common control with You. For
//	purposes of this definition, "control" means (a) the power, direct
//	or indirect, to cause the direction or management of such entity,
//	whether by contract or otherwise, or (b) ownership of more than
//	fifty percent (50%) of the outstanding shares or beneficial
//	ownership of such entity.
//
// 2. License Grants and Conditions
// --------------------------------
//
// 2.1. Grants
//
// Each Contributor hereby grants You a world-wide, royalty-free,
// non-exclusive license:
//
// (a) under intellectual property rights (other than patent or trademark)
//
//	Licensable by such Contributor to use, reproduce, make available,
//	modify, display, perform, distribute, and otherwise exploit its
//	Contributions, either on an unmodified basis, with Modifications, or
//	as part of a Larger Work; and
//
// (b) under Patent Claims of such Contributor to make, use, sell, offer
//
//	for sale, have made, import, and otherwise transfer either its
//	Contributions or its Contributor Version.
//
// 2.2. Effective Date
//
// The licenses granted in Section 2.1 with respect to any Contribution
// become effective for each Contribution on the date the Contributor first
// distributes such Contribution.
//
// 2.3. Limitations on Grant Scope
//
// The licenses granted in this Section 2 are the only rights granted under
// this License. No additional rights or licenses will be implied from the
// distribution or licensing of Covered Software under this License.
// Notwithstanding Section 2.1(b) above, no patent license is granted by a
// Contributor:
//
// (a) for any code that a Contributor has removed from Covered Software;
//
//	or
//
// (b) for infringements caused by: (i) Your and any other third party's
//
//	modifications of Covered Software, or (ii) the combination of its
//	Contributions with other software (except as part of its Contributor
//	Version); or
//
// (c) under Patent Claims infringed by Covered Software in the absence of
//
//	its Contributions.
//
// This License does not grant any rights in the trademarks, service marks,
// or logos of any Contributor (except as may be necessary to comply with
// the notice requirements in Section 3.4).
//
// 2.4. Subsequent Licenses
//
// No Contributor makes additional grants as a result of Your choice to
// distribute the Covered Software under a subsequent version of this
// License (see Section 10.2) or under the terms of a Secondary License (if
// permitted under the terms of Section 3.3).
//
// 2.5. Representation
//
// Each Contributor represents that the Contributor believes its
// Contributions are its original creation(s) or it has sufficient rights
// to grant the rights to its Contributions conveyed by this License.
//
// 2.6. Fair Use
//
// This License is not intended to limit any rights You have under
// applicable copyright doctrines of fair use, fair dealing, or other
// equivalents.
//
// 2.7. Conditions
//
// Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
// in Section 2.1.
//
// 3. Responsibilities
// -------------------
//
// 3.1. Distribution of Source Form
//
// All distribution of Covered Software in Source Code Form, including any
// Modifications that You create or to which You contribute, must be under
// the terms of this License. You must inform recipients that the Source
// Code Form of the Covered Software is governed by the terms of this
// License, and how they can obtain a copy of this License. You may not
// attempt to alter or restrict the recipients' rights in the Source Code
// Form.
//
// 3.2. Distribution of Executable Form
//
// If You distribute Covered Software in Executable Form then:
//
// (a) such Covered Software must also be made available in Source Code
//
//	Form, as described in Section 3.1, and You must inform recipients of
//	the Executable Form how they can obtain a copy of such Source Code
//	Form by reasonable means in a timely manner, at a charge no more
//	than the cost of distribution to the recipient; and
//
// (b) You may distribute such Executable Form under the terms of this
//
//	License, or sublicense it under different terms, provided that the
//	license for the Executable Form does not attempt to limit or alter
//	the recipients' rights in the Source Code Form under this License.
//
// 3.3. Distribution of a Larger Work
//
// You may create and distribute a Larger Work under terms of Your choice,
// provided that You also comply with the requirements of this License for
// the Covered Software. If the Larger Work is a combination of Covered
// Software with a work governed by one or more Secondary Licenses, and the
// Covered Software is not Incompatible With Secondary Licenses, this
// License permits You to additionally distribute such Covered Software
// under the terms of such Secondary License(s), so that the recipient of
// the Larger Work may, at their option, further distribute the Covered
// Software under the terms of either this License or such Secondary
// License(s).
//
// 3.4. Notices
//
// You may not remove or alter the substance of any license notices
// (including copyright notices, patent notices, disclaimers of warranty,
// or limitations of liability) contained within the Source Code Form of
// the Covered Software, except that You may alter any license notices to
// the extent required to remedy known factual inaccuracies.
//
// 3.5. Application of Additional Terms
//
// You may choose to offer, and to charge a fee for, warranty, support,
// indemnity or liability obligations to one or more recipients of Covered
// Software. However, You may do so only on Your own behalf, and not on
// behalf of any Contributor. You must make it absolutely clear that any
// such warranty, support, indemnity, or liability obligation is offered by
// You alone, and You hereby agree to indemnify every Contributor for any
// liability incurred by such Contributor as a result of warranty, support,
// indemnity or liability terms You offer. You may include additional
// disclaimers of warranty and limitations of liability specific to any
// jurisdiction.
//
// 4. Inability to Comply Due to Statute or Regulation
// ---------------------------------------------------
//
// If it is impossible for You to comply with any of the terms of this
// License with respect to some or all of the Covered Software due to
// statute, judicial order, or regulation then You must: (a) comply with
// the terms of this License to the maximum extent possible; and (b)
// describe the limitations and the code they affect. Such description must
// be placed in a text file included with all distributions of the Covered
// Software under this License. Except to the extent prohibited by statute
// or regulation, such description must be sufficiently detailed for a
// recipient of ordinary skill to be able to understand it.
//
// 5. Termination
// --------------
//
// 5.1. The rights granted under this License will terminate automatically
// if You fail to comply with any of its terms. However, if You become
// compliant, then the rights granted under this License from a particular
// Contributor are reinstated (a) provisionally, unless and until such
// Contributor explicitly and finally terminates Your grants, and (b) on an
// ongoing basis, if such Contributor fails to notify You of the
// non-compliance by some reasonable means prior to 60 days after You have
// come back into compliance. Moreover, Your grants from a particular
// Contributor are reinstated on an ongoing basis if such Contributor
// notifies You of the non-compliance by some reasonable means, this is the
// first time You have received notice of non-compliance with this License
// from such Contributor, and You become compliant prior to 30 days after
// Your receipt of the notice.
//
// 5.2. If You initiate litigation against any entity by asserting a patent
// infringement claim (excluding declaratory judgment actions,
// counter-claims, and cross-claims) alleging that a Contributor Version
// directly or indirectly infringes any patent, then the rights granted to
// You by any and all Contributors for the Covered Software under Section
// 2.1 of this License shall terminate.
//
// 5.3. In the event of termination under Sections 5.1 or 5.2 above, all
// end user license agreements (excluding distributors and resellers) which
// have been validly granted by You or Your distributors under this License
// prior to termination shall survive termination.
//
// ************************************************************************
// *                                                                      *
// *  6. Disclaimer of Warranty                                           *
// *  -------------------------                                           *
// *                                                                      *
// *  Covered Software is provided under this License on an "as is"       *
// *  basis, without warranty of any kind, either expressed, implied, or  *
// *  statutory, including, without limitation, warranties that the       *
// *  Covered Software is free of defects, merchantable, fit for a        *
// *  particular purpose or non-infringing. The entire risk as to the     *
// *  quality and performance of the Covered Software is with You.        *
// *  Should any Covered Software prove defective in any respect, You     *
// *  (not any Contributor) assume the cost of any necessary servicing,   *
// *  repair, or correction. This disclaimer of warranty constitutes an   *
// *  essential part of this License. No use of any Covered Software is   *
// *  authorized under this License except under this disclaimer.         *
// *                                                                      *
// ************************************************************************
//
// ************************************************************************
// *                                                                      *
// *  7. Limitation of Liability                                          *
// *  --------------------------                                          *
// *                                                                      *
// *  Under no circumstances and under no legal theory, whether tort      *
// *  (including negligence), contract, or otherwise, shall any           *
// *  Contributor, or anyone who distributes Covered Software as          *
// *  permitted above, be liable to You for any direct, indirect,         *
// *  special, incidental, or consequential damages of any character      *
// *  including, without limitation, damages for lost profits, loss of    *
// *  goodwill, work stoppage, computer failure or malfunction, or any    *
// *  and all other commercial damages or losses, even if such party      *
// *  shall have been informed of the possibility of such damages. This   *
// *  limitation of liability shall not apply to liability for death or   *
// *  personal injury resulting from such party's negligence to the       *
// *  extent applicable law prohibits such limitation. Some               *
// *  jurisdictions do not allow the exclusion or limitation of           *
// *  incidental or consequential damages, so this exclusion and          *
// *  limitation may not apply to You.                                    *
// *                                                                      *
// ************************************************************************
//
// 8. Litigation
// -------------
//
// Any litigation relating to this License may be brought only in the
// courts of a jurisdiction where the defendant maintains its principal
// place of business and such litigation shall be governed by laws of that
// jurisdiction, without reference to its conflict-of-law provisions.
// Nothing in this Section shall prevent a party's ability to bring
// cross-claims or counter-claims.
//
// 9. Miscellaneous
// ----------------
//
// This License represents the complete agreement concerning the subject
// matter hereof. If any provision of this License is held to be
// unenforceable, such provision shall be reformed only to the extent
// necessary to make it enforceable. Any law or regulation which provides
// that the language of a contract shall be construed against the drafter
// shall not be used to construe this License against a Contributor.
//
// 10. Versions of the License
// ---------------------------
//
// 10.1. New Versions
//
// Mozilla Foundation is the license steward. Except as provided in Section
// 10.3, no one other than the license steward has the right to modify or
// publish new versions of this License. Each version will be given a
// distinguishing version number.
//
// 10.2. Effect of New Versions
//
// You may distribute the Covered Software under the terms of the version
// of the License under which You originally received the Covered Software,
// or under the terms of any subsequent version published by the license
// steward.
//
// 10.3. Modified Versions
//
// If you create software not governed by this License, and you want to
// create a new license for such software, you may create and use a
// modified version of this License if you rename the license and remove
// any references to the name of the license steward (except to note that
// such modified license differs from this License).
//
// 10.4. Distributing Source Code Form that is Incompatible With Secondary
// Licenses
//
// If You choose to distribute Source Code Form that is Incompatible With
// Secondary Licenses under the terms of this version of the License, the
// notice described in Exhibit B of this License must be attached.
//
// Exhibit A - Source Code Form License Notice
// -------------------------------------------
//
//	This Source Code Form is subject to the terms of the Mozilla Public
//	License, v. 2.0. If a copy of the MPL was not distributed with this
//	file, You can obtain one at http://mozilla.org/MPL/2.0/.
//
// If it is not possible or desirable to put the notice in a particular
// file, then You may include the notice in a location (such as a LICENSE
// file in a relevant directory) where a recipient would be likely to look
// for such a notice.
//
// You may add additional accurate notices of copyright ownership.
//
// Exhibit B - "Incompatible With Secondary Licenses" Notice
// ---------------------------------------------------------
//
//	This Source Code Form is "Incompatible With Secondary Licenses", as
//	defined by the Mozilla Public License, v. 2.0.
//
// From:
// https://gitlab.torproject.org/tpo/onion-services/sauteed-onions/monitor/-/blob/main/follow-go/main.go#L115-124
// https://gitlab.torproject.org/tpo/onion-services/sauteed-onions/monitor/-/blob/main/follow-go/x509.go
// https://github.com/SSLMate/certspotter/blob/54f34077d3bebe8aafce07dcfbffeb928c6e1d04/x509.go#L380
package x509

import (
	"fmt"

	ct "github.com/google/certificate-transparency-go"
	"github.com/google/certificate-transparency-go/asn1"
	"github.com/google/certificate-transparency-go/x509/pkix"
)

func SANsFromLeafEntries(startIndex int64, leafEntries []ct.LeafEntry) (sans []string, errs []error) {
	for offset, leafEntry := range leafEntries {
		leafIndex := startIndex + int64(offset)
		e, err := ct.LogEntryFromLeaf(leafIndex, &leafEntry)
		if err != nil {
			errs = append(errs, fmt.Errorf("leaf at index %d: %v", leafIndex, err))
			continue
		}
		s, err := sansFromLogEntry(e)
		if err != nil {
			errs = append(errs, fmt.Errorf("leaf at index %d: %v", leafIndex, err))
		}
		sans = append(sans, s...)
	}
	return
}

func sansFromLogEntry(entry *ct.LogEntry) ([]string, error) {
	if entry.Precert == nil && entry.X509Cert == nil {
		return nil, fmt.Errorf("no (pre)cert in log entry")
	}
	if entry.Precert != nil && entry.X509Cert != nil {
		return nil, fmt.Errorf("both precert and cert in log entry")
	}

	var exts []pkix.Extension
	if entry.Precert != nil {
		exts = entry.Precert.TBSCertificate.Extensions
	}
	if entry.X509Cert != nil {
		exts = entry.X509Cert.Extensions
	}

	var sans []string
	for _, ext := range exts {
		if ext.Id.Equal(asn1.ObjectIdentifier{2, 5, 29, 17}) {
			moreSANs, err := extract(ext)
			if err != nil {
				return nil, fmt.Errorf("parse: %v", err)
			}

			sans = append(sans, moreSANs...)
		}
	}
	return sans, nil
}

func extract(extSAN pkix.Extension) ([]string, error) {
	var seq asn1.RawValue
	rest, err := asn1.Unmarshal(extSAN.Value, &seq)
	if err != nil {
		return nil, fmt.Errorf("failed to parse subjectAltName extension: %v", err)
	}
	if len(rest) != 0 {
		// Don't complain if the SAN is followed by exactly one zero byte, which is a common error.
		if !(len(rest) == 1 && rest[0] == 0) {
			return nil, fmt.Errorf("trailing data in subjectAltName extension: %v", rest)
		}
	}
	if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {
		return nil, fmt.Errorf("failed to parse subjectAltName extension: bad SAN sequence")
	}

	sans := []string{}
	buf := seq.Bytes
	for len(buf) > 0 {
		var val asn1.RawValue
		var err error
		buf, err = asn1.Unmarshal(buf, &val)
		if err != nil {
			return nil, fmt.Errorf("failed to parse subjectAltName extension item: %v", err)
		}

		sans = append(sans, string(val.Bytes))
	}
	return sans, nil
}