// jj.go — every read of the repository goes through here.
//
// These helpers never modify project history or its working copy
// (--ignore-working-copy means they never even snapshot it). Sidecar mutation
// is isolated in the shared sidecar package.
package web

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"time"
)

// Field separator inside a templated line, record marker at its start. Both
// are ASCII control characters that cannot appear in ids, names or a
// description's first line, so parsing stays trivial even under a graph.
const (
	jjRec = "\x1e" // as jj prints it
	jjSep = "\x1f"
	// as it is written inside a jj template string literal
	jjRecEsc = `\x1e`
	jjSepEsc = `\x1f`
)

const jjTimeout = 30 * time.Second

// jjRun executes jj read-only in repo. stderr comes back inside the error so
// the page can show what jj complained about.
func jjRun(repo string, args ...string) ([]byte, error) {
	ctx, cancel := context.WithTimeout(context.Background(), jjTimeout)
	defer cancel()
	cmd := exec.CommandContext(ctx, "jj", append([]string{"--ignore-working-copy"}, args...)...)
	cmd.Dir = repo
	var errb strings.Builder
	cmd.Stderr = &errb
	out, err := cmd.Output()
	if err != nil {
		msg := strings.TrimSpace(errb.String())
		if msg == "" {
			msg = err.Error()
		}
		return out, fmt.Errorf("jj %s: %s", strings.Join(args, " "), msg)
	}
	return out, nil
}

// mustJJ is the static-build path: a jj failure there is fatal.
func mustJJ(repo string, args ...string) []byte {
	out, err := jjRun(repo, args...)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		fatal("repository read failed")
	}
	return out
}

// checkRevset rejects input that jj would read as a flag; revsets themselves
// are a query language, not a shell, and are passed as one argv entry.
func checkRevset(r string) error {
	r = strings.TrimSpace(r)
	if strings.HasPrefix(r, "-") {
		return fmt.Errorf("revset must not start with %q", "-")
	}
	if len(r) > 512 {
		return fmt.Errorf("revset too long")
	}
	return nil
}

func resolveChange(repo, rev string) (string, error) {
	change, _, err := resolveRevision(repo, rev)
	return change, err
}

func resolveRevision(repo, rev string) (change, commit string, err error) {
	if rev == "" {
		rev = "@"
	}
	if err := checkRevset(rev); err != nil {
		return "", "", err
	}
	out, err := jjRun(repo, "log", "-r", "exactly(("+rev+"), 1)", "--no-graph",
		"-T", "change_id ++ \"\\n\" ++ commit_id ++ \"\\n\"")
	if err != nil {
		return "", "", err
	}
	ids := strings.Fields(string(out))
	if len(ids) != 2 {
		return "", "", fmt.Errorf("revset %q did not resolve to one change and commit", rev)
	}
	return ids[0], ids[1], nil
}

// changeBrief resolves a revset to the one change it names, with everything a
// page says about it. One call answers both "which change" and "which commit
// is under it right now" — the second is what content is cached against, since
// a change id is a pointer and the commit beneath it is rewritten on every
// edit.
func changeBrief(repo, rev string) (Row, error) {
	rows, err := LogRows(repo, rev, "", 1)
	if err != nil {
		return Row{}, err
	}
	for _, r := range rows {
		if !r.Blank() {
			return r, nil
		}
	}
	return Row{}, fmt.Errorf("revset %q matches no change", rev)
}

func fileList(repo, rev string) ([]string, error) {
	out, err := jjRun(repo, "file", "list", "-r", rev)
	if err != nil {
		return nil, err
	}
	return strings.Split(strings.TrimRight(string(out), "\n"), "\n"), nil
}

func fileShow(repo, rev, path string) ([]byte, error) {
	return jjRun(repo, "file", "show", "-r", rev, "--", path)
}

// ── log / op log rows ─────────────────────────────────────────────────────

// A Row is one line of jj output: the graph art it was drawn with, plus the
// fields the inline template produced. Graph-only lines (│, ~) carry Graph
// alone and render as decoration.
type Row struct {
	Graph               string
	ID, Short           string
	Commit, CommitShort string
	Author, When, End   string
	Refs, Flags, Desc   string
	Op                  bool
}

func (r Row) Blank() bool { return r.ID == "" }

// tmplFields builds `"\x1e" ++ f1 ++ "\x1f" ++ f2 ... ++ "\n"`: one line per
// row, record-marked so the graph art in front of it is separable.
func tmplFields(fields ...string) string {
	return `"` + jjRecEsc + `" ++ ` + strings.Join(fields, ` ++ "`+jjSepEsc+`" ++ `) + ` ++ "\n"`
}

var (
	commitTmpl = tmplFields(
		"change_id",
		"change_id.short(8)",
		"commit_id",
		"commit_id.short(8)",
		"author.email()",
		`committer.timestamp().format("%Y-%m-%d %H:%M")`,
		`bookmarks.join(" ")`,
		`separate(" ", if(current_working_copy, "working copy"), if(empty, "empty"), if(conflict, "conflict"), if(divergent, "divergent"))`,
		"description.first_line()",
	)
	opTmpl = tmplFields(
		"id",
		"id.short(12)",
		`""`,
		`""`,
		"user",
		`time.start().format("%Y-%m-%d %H:%M:%S")`,
		`""`,
		`time.end().format("%H:%M:%S")`,
		"description.first_line()",
	)
)

func parseRows(out []byte, op bool) []Row {
	var rows []Row
	for _, line := range strings.Split(strings.TrimRight(string(out), "\n"), "\n") {
		i := strings.Index(line, jjRec)
		if i < 0 {
			if strings.TrimSpace(line) != "" {
				rows = append(rows, Row{Graph: line, Op: op})
			}
			continue
		}
		f := strings.Split(line[i+len(jjRec):], jjSep)
		for len(f) < 9 {
			f = append(f, "")
		}
		r := Row{Graph: line[:i], ID: f[0], Short: f[1], Commit: f[2], CommitShort: f[3],
			Author: f[4], When: f[5], Refs: f[6], Flags: f[7], Desc: f[8], Op: op}
		if op {
			r.End, r.Flags = r.Flags, ""
		}
		rows = append(rows, r)
	}
	return rows
}

// LogRows runs `jj log -r REVSET` with the inline template. atOp, when set,
// runs the query as of that operation — the debugging view.
func LogRows(repo, revset, atOp string, limit int) ([]Row, error) {
	if err := checkRevset(revset); err != nil {
		return nil, err
	}
	args := []string{"log", "-T", commitTmpl}
	if strings.TrimSpace(revset) != "" {
		args = append(args, "-r", revset)
	}
	if atOp != "" {
		if err := checkRevset(atOp); err != nil {
			return nil, err
		}
		args = append(args, "--at-operation", atOp)
	}
	if limit > 0 {
		args = append(args, "-n", fmt.Sprint(limit))
	}
	out, err := jjRun(repo, args...)
	if err != nil {
		return nil, err
	}
	return parseRows(out, false), nil
}

func OpRows(repo string, limit int) ([]Row, error) {
	args := []string{"op", "log", "-T", opTmpl}
	if limit > 0 {
		args = append(args, "-n", fmt.Sprint(limit))
	}
	out, err := jjRun(repo, args...)
	if err != nil {
		return nil, err
	}
	return parseRows(out, true), nil
}

// ── one change ────────────────────────────────────────────────────────────

type ChangeFile struct {
	Status, Path string
}

type Change struct {
	Row     Row
	Desc    string
	Files   []ChangeFile
	Stat    string
	Parents []Row
}

var statusName = map[string]string{"A": "added", "M": "modified", "D": "deleted", "R": "renamed", "C": "copied"}

func LoadChange(repo, rev string) (*Change, error) {
	rows, err := LogRows(repo, rev, "", 1)
	if err != nil {
		return nil, err
	}
	var row Row
	for _, r := range rows {
		if !r.Blank() {
			row = r
			break
		}
	}
	if row.Blank() {
		return nil, fmt.Errorf("no change matches %q", rev)
	}
	c := &Change{Row: row}
	// full description separately: it is multi-line, so it cannot ride along
	// in the one-line-per-row template
	if out, err := jjRun(repo, "log", "-r", row.ID, "--no-graph", "-n", "1", "-T", "description"); err == nil {
		c.Desc = strings.TrimRight(string(out), "\n")
	}
	if out, err := jjRun(repo, "diff", "-r", row.ID, "--summary"); err == nil {
		for _, line := range strings.Split(strings.TrimRight(string(out), "\n"), "\n") {
			if len(line) > 2 {
				st := statusName[line[:1]]
				if st == "" {
					st = line[:1]
				}
				c.Files = append(c.Files, ChangeFile{Status: st, Path: line[2:]})
			}
		}
	}
	if out, err := jjRun(repo, "diff", "-r", row.ID, "--stat"); err == nil {
		lines := strings.Split(strings.TrimRight(string(out), "\n"), "\n")
		if n := len(lines); n > 0 {
			c.Stat = strings.TrimSpace(lines[n-1])
		}
	}
	if rows, err := LogRows(repo, "parents("+row.ID+")", "", 8); err == nil {
		for _, r := range rows {
			if !r.Blank() {
				c.Parents = append(c.Parents, r)
			}
		}
	}
	return c, nil
}