package syw

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"tildegit.org/tjp/sliderule/logging"
)

// Repository represents a git repository.
type Repository string

// Open produces a git repository from a directory path.
//
// It will also try a few variations (dirpath.git, dirpath/.git) and use the first
// path found to be a git repository.
//
// It returns nil if neither dirpath nor any of its variations are a valid git
// repository.
func Open(dirpath string) *Repository {
	check := []string{dirpath}
	if !strings.HasSuffix(dirpath, ".git") {
		check = append(check, dirpath+".git")
	}
	check = append(check, filepath.Join(dirpath, ".git"))

	for _, p := range check {
		if st, err := os.Stat(filepath.Join(p, "objects")); err != nil || !st.IsDir() {
			continue
		}
		if st, err := os.Stat(filepath.Join(p, "refs")); err != nil || !st.IsDir() {
			continue
		}

		r := Repository(p)
		return &r
	}

	return nil
}

// Name is the repository name, defined by the directory path.
func (r *Repository) Name() string {
	name := filepath.Base(string(*r))
	if name == ".git" {
		name = filepath.Base(filepath.Dir(string(*r)))
	}
	return strings.TrimSuffix(name, ".git")
}

// NameBytes returns a byte slice of the repository name.
func (r *Repository) NameBytes() []byte {
	return []byte(r.Name())
}

func (r *Repository) cmd(ctx context.Context, cmdname string, args ...string) (*cmdResult, error) {
	args = append([]string{"--git-dir=" + string(*r), cmdname}, args...)
	start := time.Now()

	result, err := runCmd(ctx, args)

	log, ok := ctx.Value("debuglog").(logging.Logger)
	if ok {
		_ = log.Log("msg", "ran git command", "args", fmt.Sprintf("%+v", args), "dur", time.Since(start))
	}

	return result, err
}

// Type returns the result of "git cat-file -t <hash>".
func (r *Repository) Type(ctx context.Context, hash string) (string, error) {
	res, err := r.cmd(ctx, "cat-file", "-t", hash)
	if err != nil {
		return "", err
	}
	if res.status != 0 {
		return "", errors.New(res.err.String())
	}

	return strings.Trim(res.out.String(), "\n"), nil
}

// Refs returns a list of branch and tag references.
func (r *Repository) Refs(ctx context.Context) ([]Ref, error) {
	res, err := r.cmd(ctx, "show-ref", "--head", "--heads", "--tags")
	if err != nil {
		return nil, err
	}

	lines := strings.Split(res.out.String(), "\n")

	branches := make([]Ref, 0, len(lines))
	for _, line := range lines {
		hash, name, found := strings.Cut(line, " ")
		if !found {
			continue
		}
		branches = append(branches, Ref{
			Repo: r,
			Name: name,
			Hash: hash,
		})
	}
	return branches, nil
}

var badRevListOutput = errors.New("unexpected 'git rev-list' output")

// Commits lists commits backwards from a given head.
func (r *Repository) Commits(ctx context.Context, head string, count int) ([]Commit, error) {
	res, err := r.cmd(ctx, "rev-list",
		"--format=%an%n%ae%n%aI%n%cn%n%ce%n%cI%n%P%n%B$$END$$",
		"-n", strconv.Itoa(count),
		head,
	)
	if err != nil {
		return nil, err
	}

	commits := make([]Commit, 0, count)
	for _, revstr := range strings.Split(res.out.String(), "\n$$END$$\n") {
		if revstr == "" {
			continue
		}
		commits = append(commits, Commit{Repo: r})
		commit := &commits[len(commits)-1]

		commitHash, rest, found := strings.Cut(revstr, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.Hash = commitHash[7:]

		commit.AuthorName, rest, found = strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.AuthorEmail, rest, found = strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}

		adate, rest, found := strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.AuthorDate, err = time.Parse(time.RFC3339, adate)
		if err != nil {
			return nil, err
		}

		commit.CommitterName, rest, found = strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.CommitterEmail, rest, found = strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}

		cdate, rest, found := strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.CommitDate, err = time.Parse(time.RFC3339, cdate)
		if err != nil {
			return nil, err
		}

		parents, rest, found := strings.Cut(rest, "\n")
		if !found {
			return nil, badRevListOutput
		}
		commit.Parents = strings.Split(parents, " ")
		if len(commit.Parents) == 1 && commit.Parents[0] == "" {
			commit.Parents = nil
		}

		commit.Message = rest
	}

	return commits, nil
}

// Commit gathers a single commit by a reference string.
func (r *Repository) Commit(ctx context.Context, ref string) (*Commit, error) {
	commits, err := r.Commits(ctx, ref, 1)
	if err != nil {
		return nil, err
	}
	return &commits[0], nil
}

// Diffstat produces a diffstat of two trees by their references.
func (r *Repository) Diffstat(ctx context.Context, fromref, toref string) (string, error) {
	res, err := r.cmd(ctx, "diff-tree", "-r", "--stat", fromref, toref)
	if err != nil {
		return "", err
	}
	if res.status != 0 {
		return "", errors.New(res.err.String())
	}
	return res.out.String(), nil
}

// Diff produces a diff of two trees by their references.
func (r *Repository) Diff(ctx context.Context, fromref, toref string) (string, error) {
	res, err := r.cmd(ctx, "diff-tree", "-r", "-p", "-u", fromref, toref)
	if err != nil {
		return "", err
	}
	if res.status != 0 {
		return "", errors.New(res.err.String())
	}
	return res.out.String(), nil
}

// Readme represents a README file.
type Readme struct {
	Filename    string
	RawContents string
}

// GeminiEscapedContent produces the file contents with any ```-leading lines prefixed with a space.
func (r Readme) GeminiEscapedContents() string {
	body := r.RawContents
	if strings.HasPrefix(body, "```") {
		body = " " + body
	}
	return strings.ReplaceAll(body, "\n```", "\n ```")
}

// GopherEscapedContent produces the file formatted as gophermap with every line an info-message line.
func (r Readme) GopherEscapedContents(selector, host, port string) string {
	return gopherRawtext(selector, host, port, r.RawContents)
}

// Readme finds a README blob in the root path under a ref string.
func (r *Repository) Readme(ctx context.Context, ref string) (*Readme, error) {
	dir, err := r.Tree(ctx, ref, "")
	if err != nil {
		return nil, err
	}

	filename := ""
	for i := range dir {
		if dir[i].Type == "blob" && strings.HasPrefix(strings.ToLower(dir[i].Path), "readme") {
			filename = dir[i].Path
			break
		}
	}

	if filename != "" {
		body, err := r.Blob(ctx, ref, filename)
		if err != nil {
			return nil, err
		}

		return &Readme{
			Filename:    filename,
			RawContents: string(body),
		}, nil
	}

	return nil, nil
}

// Description reads the "description" file from in the git repository.
func (r *Repository) Description() string {
	f, err := os.Open(filepath.Join(string(*r), "description"))
	if err != nil {
		return ""
	}
	defer func() { _ = f.Close() }()

	b, err := io.ReadAll(f)
	if err != nil {
		return ""
	}

	return strings.TrimRight(string(b), "\n")
}

// Blob returns the contents of a blob at a given ref (commit) and path.
func (r *Repository) Blob(ctx context.Context, ref, path string) ([]byte, error) {
	res, err := r.cmd(ctx, "cat-file", "blob", ref+":"+path)
	switch {
	case res == nil:
		return nil, err
	case res.status == 0:
		return res.out.Bytes(), nil
	case res.status == 128:
		return nil, objectDoesNotExist
	default:
		return nil, errors.New(res.err.String())
	}
}

// ObjectDescription represents an object within a git tree (directory).
type ObjectDescription struct {
	Mode int
	Type string
	Hash string
	Size int
	Path string
}

// Tree lists the contents of a given directory (path) in a commit (ref).
func (r *Repository) Tree(ctx context.Context, ref, path string) ([]ObjectDescription, error) {
	pattern := ref
	if path != "" && path != "." {
		pattern += ":" + path
	}

	res, err := r.cmd(ctx, "ls-tree", "-l", pattern)
	if err != nil {
		return nil, err
	}

	out := []ObjectDescription{}
	for _, line := range strings.Split(res.out.String(), "\n") {
		if line == "" {
			continue
		}

		spl := dropEmpty(strings.Split(strings.ReplaceAll(line, "\t", " "), " "))

		mode, err := strconv.ParseInt(spl[0], 8, 64)
		if err != nil {
			return nil, err
		}

		var size int
		if spl[3] != "-" {
			size, err = strconv.Atoi(spl[3])
			if err != nil {
				return nil, err
			}
		}

		out = append(out, ObjectDescription{
			Mode: int(mode),
			Type: spl[1],
			Hash: spl[2],
			Size: size,
			Path: spl[4],
		})
	}
	return out, nil
}

func dropEmpty(sl []string) []string {
	n := 0
	for i := 0; i < len(sl); i += 1 {
		if sl[i] == "" {
			copy(sl[i:], sl[i+1:])
			i -= 1
			n += 1
		}
	}
	return sl[:len(sl)-n]
}

var objectDoesNotExist = errors.New("object does not exist")