// Copyright 2023 Harness, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"strconv"
	"strings"
	"time"

	"github.com/harness/gitness/errors"
	"github.com/harness/gitness/git/command"
	"github.com/harness/gitness/git/sha"
)

const (
	pgpSignatureBeginToken = "\n-----BEGIN PGP SIGNATURE-----\n" //#nosec G101
	pgpSignatureEndToken   = "\n-----END PGP SIGNATURE-----"     //#nosec G101
)

type Tag struct {
	Sha        sha.SHA
	Name       string
	TargetSha  sha.SHA
	TargetType GitObjectType
	Title      string
	Message    string
	Tagger     Signature
	Signature  *CommitGPGSignature
}

type CreateTagOptions struct {
	// Message is the optional message the tag will be created with - if the message is empty
	// the tag will be lightweight, otherwise it'll be annotated.
	Message string

	// Tagger is the information used in case the tag is annotated (Message is provided).
	Tagger Signature
}

// TagPrefix tags prefix path on the repository.
const TagPrefix = "refs/tags/"

// GetAnnotatedTag returns the tag for a specific tag sha.
func (g *Git) GetAnnotatedTag(
	ctx context.Context,
	repoPath string,
	rev string,
) (*Tag, error) {
	if repoPath == "" {
		return nil, ErrRepositoryPathEmpty
	}
	tags, err := getAnnotatedTags(ctx, repoPath, []string{rev})
	if err != nil || len(tags) == 0 {
		return nil, processGitErrorf(err, "failed to get annotated tag with sha '%s'", rev)
	}

	return &tags[0], nil
}

// GetAnnotatedTags returns the tags for a specific list of tag sha.
func (g *Git) GetAnnotatedTags(
	ctx context.Context,
	repoPath string,
	revs []string,
) ([]Tag, error) {
	if repoPath == "" {
		return nil, ErrRepositoryPathEmpty
	}
	return getAnnotatedTags(ctx, repoPath, revs)
}

// CreateTag creates the tag pointing at the provided SHA (could be any type, e.g. commit, tag, blob, ...)
func (g *Git) CreateTag(
	ctx context.Context,
	repoPath string,
	name string,
	targetSHA sha.SHA,
	opts *CreateTagOptions,
) error {
	if repoPath == "" {
		return ErrRepositoryPathEmpty
	}
	cmd := command.New("tag")
	if opts != nil && opts.Message != "" {
		cmd.Add(command.WithFlag("-m", opts.Message))
		cmd.Add(
			command.WithCommitterAndDate(
				opts.Tagger.Identity.Name,
				opts.Tagger.Identity.Email,
				opts.Tagger.When,
			),
		)
	}

	cmd.Add(command.WithArg(name, targetSHA.String()))
	err := cmd.Run(ctx, command.WithDir(repoPath))
	if err != nil {
		return processGitErrorf(err, "Service failed to create a tag")
	}
	return nil
}

// getAnnotatedTag is a custom implementation to retrieve an annotated tag from a sha.
func getAnnotatedTags(
	ctx context.Context,
	repoPath string,
	revs []string,
) ([]Tag, error) {
	if repoPath == "" {
		return nil, ErrRepositoryPathEmpty
	}
	// The tag is an annotated tag with a message.
	writer, reader, cancel := CatFileBatch(ctx, repoPath, nil)
	defer func() {
		cancel()
		_ = writer.Close()
	}()

	tags := make([]Tag, len(revs))

	for i, rev := range revs {
		line := rev + "\n"
		if _, err := writer.Write([]byte(line)); err != nil {
			return nil, err
		}
		output, err := ReadBatchHeaderLine(reader)
		if err != nil {
			if errors.Is(err, io.EOF) || errors.IsNotFound(err) {
				return nil, fmt.Errorf("tag with sha %s does not exist", rev)
			}
			return nil, err
		}
		if output.Type != string(GitObjectTypeTag) {
			return nil, fmt.Errorf("git object is of type '%s', expected tag",
				output.Type)
		}

		// read the remaining rawData
		rawData, err := io.ReadAll(io.LimitReader(reader, output.Size))
		if err != nil {
			return nil, err
		}
		_, err = reader.Discard(1)
		if err != nil {
			return nil, err
		}

		tag, err := parseTagDataFromCatFile(rawData)
		if err != nil {
			return nil, fmt.Errorf("failed to parse tag '%s': %w", rev, err)
		}

		// fill in the sha
		tag.Sha = output.SHA

		tags[i] = tag
	}

	return tags, nil
}

// parseTagDataFromCatFile parses a tag from a cat-file output.
func parseTagDataFromCatFile(data []byte) (tag Tag, err error) {
	// parse object Id
	object, p, err := parseCatFileLine(data, 0, "object")
	if err != nil {
		return tag, err
	}
	tag.TargetSha = sha.Must(object)

	// parse object type
	rawType, p, err := parseCatFileLine(data, p, "type")
	if err != nil {
		return tag, err
	}

	tag.TargetType, err = ParseGitObjectType(rawType)
	if err != nil {
		return tag, err
	}

	// parse tag name
	tag.Name, p, err = parseCatFileLine(data, p, "tag")
	if err != nil {
		return tag, err
	}

	// parse tagger
	rawTaggerInfo, p, err := parseCatFileLine(data, p, "tagger")
	if err != nil {
		return tag, err
	}
	tag.Tagger, err = parseSignatureFromCatFileLine(rawTaggerInfo)
	if err != nil {
		return tag, err
	}

	// remainder is message and gpg (remove leading and tailing new lines)
	message := string(bytes.Trim(data[p:], "\n"))

	// handle gpg signature
	pgpEnd := strings.Index(message, pgpSignatureEndToken)
	if pgpEnd > -1 {
		messageStart := pgpEnd + len(pgpSignatureEndToken)
		// for now we just remove the signature (and trim any separating new lines)
		// TODO: add support for GPG signature of tags
		message = strings.TrimLeft(message[messageStart:], "\n")
	}

	tag.Message = message

	// get title from message
	tag.Title = message
	titleEnd := strings.IndexByte(message, '\n')
	if titleEnd > -1 {
		tag.Title = message[:titleEnd]
	}

	return tag, nil
}

func parseCatFileLine(data []byte, start int, header string) (string, int, error) {
	// for simplicity only look at data from start onwards
	data = data[start:]

	lenHeader := len(header)
	lenData := len(data)
	if lenData < lenHeader {
		return "", 0, fmt.Errorf("expected '%s' but line only contains '%s'", header, string(data))
	}
	if string(data[:lenHeader]) != header {
		return "", 0, fmt.Errorf("expected '%s' but started with '%s'", header, string(data[:lenHeader]))
	}

	// get end of line and start of next line (used externally, transpose with provided start index)
	lineEnd := bytes.IndexByte(data, '\n')
	externalNextLine := start + lineEnd + 1
	if lineEnd == -1 {
		lineEnd = lenData
		externalNextLine = start + lenData
	}

	// if there's no data, return an error (have to consider for ' ')
	if lineEnd <= lenHeader+1 {
		return "", 0, fmt.Errorf("no data for line of type '%s'", header)
	}

	return string(data[lenHeader+1 : lineEnd]), externalNextLine, nil
}

// defaultGitTimeLayout is the (default) time format printed by git.
const defaultGitTimeLayout = "Mon Jan _2 15:04:05 2006 -0700"

// parseSignatureFromCatFileLine parses the signature from a cat-file output.
// This is used for commit / tag outputs. Input will be similar to (without 'author 'prefix):
// - author Max Mustermann <mm@gitness.io> 1666401234 -0700
// - author Max Mustermann <mm@gitness.io> Tue Oct 18 05:13:26 2022 +0530.
func parseSignatureFromCatFileLine(line string) (Signature, error) {
	sig := Signature{}
	emailStart := strings.LastIndexByte(line, '<')
	emailEnd := strings.LastIndexByte(line, '>')
	if emailStart == -1 || emailEnd == -1 || emailEnd < emailStart {
		return Signature{}, fmt.Errorf("signature is missing email ('%s')", line)
	}

	// name requires that there is at least one char followed by a space (so emailStart >= 2)
	if emailStart < 2 {
		return Signature{}, fmt.Errorf("signature is missing name ('%s')", line)
	}

	sig.Identity.Name = line[:emailStart-1]
	sig.Identity.Email = line[emailStart+1 : emailEnd]

	timeStart := emailEnd + 2
	if timeStart >= len(line) {
		return Signature{}, fmt.Errorf("signature is missing time ('%s')", line)
	}

	// Check if time format is written date time format (e.g Thu, 07 Apr 2005 22:13:13 +0200)
	// we can check that by ensuring that the date time part starts with a non-digit character.
	if line[timeStart] > '9' {
		var err error
		sig.When, err = time.Parse(defaultGitTimeLayout, line[timeStart:])
		if err != nil {
			return Signature{}, fmt.Errorf("failed to time.parse signature time ('%s'): %w", line, err)
		}

		return sig, nil
	}

	// Otherwise we have to manually parse unix time and time zone
	endOfUnixTime := timeStart + strings.IndexByte(line[timeStart:], ' ')
	if endOfUnixTime <= timeStart {
		return Signature{}, fmt.Errorf("signature is missing unix time ('%s')", line)
	}

	unixSeconds, err := strconv.ParseInt(line[timeStart:endOfUnixTime], 10, 64)
	if err != nil {
		return Signature{}, fmt.Errorf("failed to parse unix time ('%s'): %w", line, err)
	}

	// parse time zone
	startOfTimeZone := endOfUnixTime + 1 // +1 for space
	endOfTimeZone := startOfTimeZone + 5 // +5 for '+0700'
	if startOfTimeZone >= len(line) || endOfTimeZone > len(line) {
		return Signature{}, fmt.Errorf("signature is missing time zone ('%s')", line)
	}

	// get and disect timezone, e.g. '+0700'
	rawTimeZone := line[startOfTimeZone:endOfTimeZone]
	rawTimeZoneH := rawTimeZone[1:3]  // gets +[07]00
	rawTimeZoneMin := rawTimeZone[3:] // gets +07[00]
	timeZoneH, err := strconv.ParseInt(rawTimeZoneH, 10, 64)
	if err != nil {
		return Signature{}, fmt.Errorf("failed to parse hours of time zone ('%s'): %w", line, err)
	}
	timeZoneMin, err := strconv.ParseInt(rawTimeZoneMin, 10, 64)
	if err != nil {
		return Signature{}, fmt.Errorf("failed to parse minutes of time zone ('%s'): %w", line, err)
	}

	timeZoneOffsetInSec := int(timeZoneH*60+timeZoneMin) * 60
	if rawTimeZone[0] == '-' {
		timeZoneOffsetInSec *= -1
	}
	timeZone := time.FixedZone("", timeZoneOffsetInSec)

	// create final time using unix and timezone translation
	sig.When = time.Unix(unixSeconds, 0).In(timeZone)

	return sig, nil
}

// Parse commit information from the (uncompressed) raw
// data from the commit object.
// \n\n separate headers from message.
func parseTagData(data []byte) (*Tag, error) {
	tag := &Tag{
		Tagger: Signature{},
	}
	// we now have the contents of the commit object. Let's investigate...
	nextLine := 0
l:
	for {
		eol := bytes.IndexByte(data[nextLine:], '\n')
		switch {
		case eol > 0:
			line := data[nextLine : nextLine+eol]
			spacePos := bytes.IndexByte(line, ' ')
			refType := line[:spacePos]
			switch string(refType) {
			case "object":
				tag.TargetSha = sha.Must(string(line[spacePos+1:]))
			case "type":
				// A commit can have one or more parents
				tag.TargetType = GitObjectType(line[spacePos+1:])
			case "tagger":
				sig, err := NewSignatureFromCommitLine(line[spacePos+1:])
				if err != nil {
					return nil, fmt.Errorf("failed to parse tagger signature: %w", err)
				}
				tag.Tagger = sig
			}
			nextLine += eol + 1
		case eol == 0:
			tag.Message = string(data[nextLine+1:])
			break l
		default:
			break l
		}
	}
	idx := strings.LastIndex(tag.Message, pgpSignatureBeginToken)
	if idx > 0 {
		endSigIdx := strings.Index(tag.Message[idx:], pgpSignatureEndToken)
		if endSigIdx > 0 {
			tag.Signature = &CommitGPGSignature{
				Signature: tag.Message[idx+1 : idx+endSigIdx+len(pgpSignatureEndToken)],
				Payload:   string(data[:bytes.LastIndex(data, []byte(pgpSignatureBeginToken))+1]),
			}
			tag.Message = tag.Message[:idx+1]
		}
	}
	return tag, nil
}

func (g *Git) GetTagCount(
	ctx context.Context,
	repoPath string,
) (int, error) {
	if repoPath == "" {
		return 0, ErrRepositoryPathEmpty
	}

	pipeOut, pipeIn := io.Pipe()
	defer pipeOut.Close()

	cmd := command.New("tag")

	var err error
	go func() {
		defer pipeIn.Close()
		err = cmd.Run(ctx, command.WithDir(repoPath), command.WithStdout(pipeIn))
	}()
	if err != nil {
		return 0, processGitErrorf(err, "failed to trigger branch command")
	}

	return countLines(pipeOut), nil
}