package compose

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// Queue is the review queue. Drafts are files under a directory the caller
// passes; this package never chooses a location of its own.
type Queue struct {
	dir string
}

// Open opens a review queue at dir, creating the directory if needed.
func Open(dir string) (*Queue, error) {
	if strings.TrimSpace(dir) == "" {
		return nil, errors.New("queue directory is required")
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, err
	}
	info, err := os.Stat(dir)
	if err != nil {
		return nil, err
	}
	if !info.IsDir() {
		return nil, fmt.Errorf("%s is not a directory", dir)
	}
	return &Queue{dir: dir}, nil
}

// Put stores a new draft. Review fields are cleared: approval only happens
// through Approve, and a caller cannot smuggle a consent basis in.
// Putting the same post_id again keeps the copy already queued.
func (q *Queue) Put(d Draft) error {
	if _, err := q.path(d.PostID); err != nil {
		return err
	}
	existing, err := q.Get(d.PostID)
	if err == nil {
		if existing.Body != d.Body || existing.SourceEntryID != d.SourceEntryID || existing.SourceEntryURL != d.SourceEntryURL || existing.Variant != d.Variant {
			return fmt.Errorf("post_id %s is already queued with different content", d.PostID)
		}
		return nil
	}
	if !errors.Is(err, os.ErrNotExist) {
		return err
	}
	d.ReviewedBy = ""
	d.SubjectConsent = ""
	d.Approved = false
	d.Publication = nil
	return q.save(d)
}

// Get reads one draft from the queue.
func (q *Queue) Get(postID string) (Draft, error) {
	path, err := q.path(postID)
	if err != nil {
		return Draft{}, err
	}
	raw, err := os.ReadFile(path)
	if err != nil {
		return Draft{}, err
	}
	var d Draft
	if err := json.Unmarshal(raw, &d); err != nil {
		return Draft{}, fmt.Errorf("read draft %s: %w", postID, err)
	}
	return d, nil
}

// Approve records the reviewer and a consent basis supplied by the caller.
// consent is not defaulted. not-required is recorded only when the caller
// passes that value; absence of objection is not treated as consent.
func (q *Queue) Approve(postID, reviewer, consent string) (Draft, error) {
	reviewer = strings.TrimSpace(reviewer)
	consent = strings.TrimSpace(consent)
	if reviewer == "" {
		return Draft{}, ErrReviewer
	}
	if _, ok := consentBases[consent]; !ok {
		return Draft{}, fmt.Errorf("%w: got %q", ErrConsent, consent)
	}
	d, err := q.Get(postID)
	if err != nil {
		return Draft{}, err
	}
	d.ReviewedBy = reviewer
	d.SubjectConsent = consent
	d.Approved = true
	if err := q.save(d); err != nil {
		return Draft{}, err
	}
	return d, nil
}

func (q *Queue) save(d Draft) error {
	path, err := q.path(d.PostID)
	if err != nil {
		return err
	}
	raw, err := marshalDraft(d)
	if err != nil {
		return err
	}
	tmp := path + ".tmp"
	if err := os.WriteFile(tmp, raw, 0o644); err != nil {
		return err
	}
	return os.Rename(tmp, path)
}

func marshalDraft(d Draft) ([]byte, error) {
	var buf bytes.Buffer
	enc := json.NewEncoder(&buf)
	enc.SetEscapeHTML(false)
	enc.SetIndent("", "  ")
	if err := enc.Encode(d); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func (q *Queue) path(postID string) (string, error) {
	if postID == "" || strings.Contains(postID, "/") || strings.Contains(postID, "\\") || strings.Contains(postID, "..") {
		return "", fmt.Errorf("invalid post_id %q", postID)
	}
	path := filepath.Join(q.dir, postID+".json")
	absDir, err := filepath.Abs(q.dir)
	if err != nil {
		return "", err
	}
	absPath, err := filepath.Abs(path)
	if err != nil {
		return "", err
	}
	rel, err := filepath.Rel(absDir, absPath)
	if err != nil || strings.HasPrefix(rel, "..") {
		return "", fmt.Errorf("invalid post_id %q", postID)
	}
	return path, nil
}