/*
 * Copyright 2021-2024 JetBrains s.r.o.
 *
 * 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
 *
 * https://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 git

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"

	"github.com/JetBrains/qodana-cli/internal/platform/strutil"
	log "github.com/sirupsen/logrus"
)

type ChangedRegion struct {
	FirstLine int `json:"firstLine"`
	Count     int `json:"count"`
}

type HunkChange struct {
	FromPath string
	ToPath   string
	Added    []*ChangedRegion
	Deleted  []*ChangedRegion
}

type ChangedFile struct {
	Path    string           `json:"path"`
	Added   []*ChangedRegion `json:"added"`
	Deleted []*ChangedRegion `json:"deleted"`
}

type ChangedFiles struct {
	Files []*ChangedFile `json:"files"`
}

func computeAbsPath(cwd string) (string, error) {
	cwd, err := filepath.EvalSymlinks(cwd)
	if err != nil {
		return "", err
	}
	cwdAbs, err := filepath.Abs(cwd)
	return cwdAbs, err
}

func ComputeChangedFiles(cwd string, diffStart string, diffEnd string, logdir string) (ChangedFiles, error) {
	absCwd, err := computeAbsPath(cwd)
	if err != nil {
		return ChangedFiles{}, err
	}
	repoRoot, err := Root(cwd, logdir)
	if err != nil {
		return ChangedFiles{}, err
	}
	absRepoRoot, err := computeAbsPath(repoRoot)
	if err != nil {
		return ChangedFiles{}, err
	}

	filePath, _ := filepath.Abs(filepath.Join(logdir, "git-diff.log"))
	file, err := os.Create(filePath)
	if err != nil {
		return ChangedFiles{}, fmt.Errorf("failed to create file %s: %w", filePath, err)
	}
	if err = file.Close(); err != nil {
		return ChangedFiles{}, fmt.Errorf("failed to close file %s: %w", filePath, err)
	}

	// Rev-parsing references in advance helps with clearer error messages and in case references could be confused
	// with `git diff` options.
	diffStartSha, err := RevParse(cwd, diffStart, logdir)
	if err != nil {
		return ChangedFiles{}, err
	}
	log.Debugf("Resolved git ref %q as %s", diffStart, diffStartSha)

	diffEndSha, err := RevParse(cwd, diffEnd, logdir)
	if err != nil {
		return ChangedFiles{}, err
	}
	log.Debugf("Resolved git ref %q as %s", diffEnd, diffEndSha)

	_, _, err = gitRun(
		cwd,
		[]string{"diff", diffStartSha, diffEndSha, "--unified=0", "--no-renames", ">", strutil.QuoteIfSpace(filePath)},
		logdir,
	)
	if err != nil {
		return ChangedFiles{}, err
	}
	return parseDiff(filePath, absRepoRoot, absCwd)
}

// parseDiff parses the git diff output and extracts changes
func parseDiff(diffPath string, repoRoot string, cwd string) (ChangedFiles, error) {
	log.Debugf("Parsing diff - repo root: %s, cwd: %s", repoRoot, cwd)
	var changes []HunkChange

	diffFile, err := os.Open(diffPath)
	if err != nil {
		return ChangedFiles{}, fmt.Errorf("failed to open diff file %s: %w", diffPath, err)
	}
	defer func(diffFile *os.File) {
		err := diffFile.Close()
		if err != nil {
			log.Errorf("failed to close diff file %s: %s", diffPath, err)
		}
	}(diffFile)
	scanner := bufio.NewReader(diffFile)

	var currentChange *HunkChange
	var line string
	// Regular expressions to match diff headers and hunks
	reFilename := regexp.MustCompile(`^diff --git a/(.*) b/(.*)`)
	reHunk := regexp.MustCompile(`^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@`)

	for {
		line, err = scanner.ReadString('\n')
		if err == io.EOF || err != nil {
			break
		}
		line = strings.TrimSpace(line)

		if matches := reFilename.FindStringSubmatch(line); matches != nil {
			if currentChange != nil {
				changes = append(changes, *currentChange)
			}
			currentChange = &HunkChange{
				FromPath: matches[1],
				ToPath:   matches[2],
				Added:    []*ChangedRegion{},
				Deleted:  []*ChangedRegion{},
			}
			continue
		}

		if matches := reHunk.FindStringSubmatch(line); matches != nil && currentChange != nil {
			origLineStart := diffToInt(matches[1])
			origCount := diffToInt(matches[2])
			newLineStart := diffToInt(matches[3])
			newCount := diffToInt(matches[4])
			if origCount != 0 {
				currentChange.Deleted = append(
					currentChange.Deleted,
					&ChangedRegion{FirstLine: origLineStart, Count: origCount},
				)
			}
			if newCount != 0 {
				currentChange.Added = append(
					currentChange.Added,
					&ChangedRegion{FirstLine: newLineStart, Count: newCount},
				)
			}
		}
	}

	if currentChange != nil {
		changes = append(changes, *currentChange)
	}

	if err != nil && err != io.EOF {
		return ChangedFiles{}, err
	}

	files := make([]*ChangedFile, 0, len(changes))
	for _, file := range changes {
		fileName := file.ToPath
		if file.ToPath != file.FromPath {
			if len(file.Deleted) > 0 {
				fileName = file.FromPath
			} else {
				fileName = file.ToPath
			}
		}
		path := filepath.Join(repoRoot, fileName)
		if strings.HasPrefix(path, cwd) { // take changes only inside project
			files = append(
				files, &ChangedFile{
					Path:    path,
					Added:   file.Added,
					Deleted: file.Deleted,
				},
			)
		}
	}

	sort.Slice(
		files, func(i, j int) bool {
			return files[i].Path < files[j].Path
		},
	)

	return ChangedFiles{Files: files}, nil
}

// diffToInt converts a string to an integer preserving git default number logic
func diffToInt(str string) int {
	if str == "" {
		return 1
	}
	var result int
	_, _ = fmt.Sscanf(str, "%d", &result)
	return result
}