// Package suite assembles a conventions suite in memory: its manifest, the
// vocabulary of its language, and the documents the language employs.
//
// What is subject to checking is everything the language employs: the
// convention files and the document the suite governs itself by. The list of
// those files comes from the manifest, from the section of live prefixes where
// every prefix carries a path. A file the language merely quotes — the
// description of the language itself — is not listed in the suite and gets no
// checks.
package suite

import (
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"git.vakhrushev.me/av/convy/internal/doc"
	"git.vakhrushev.me/av/convy/internal/lang"
	"git.vakhrushev.me/av/convy/internal/manifest"
)

// Suite is a loaded suite.
type Suite struct {
	Root     string
	Manifest *manifest.Manifest
	Vocab    lang.Vocabulary

	// Docs holds the documents of the suite in the order of live prefixes.
	Docs []*doc.Document
	// ByPrefix maps a manifest prefix to its document.
	ByPrefix map[string]*doc.Document
	// Missing lists the prefixes whose file the manifest declares while the
	// file system holds none.
	Missing map[string]string
	// Unregistered lists files found in the suite carrying front matter that
	// the manifest does not declare. Such a file is neither checked nor
	// assembled: for the suite it does not exist, however its author sees it.
	Unregistered []string
	// Broken lists files whose front matter could not be parsed.
	Broken []error
}

// Load reads a suite from directory root.
func Load(root string) (*Suite, error) {
	m, err := manifest.Load(root)
	if err != nil {
		return nil, err
	}
	vocab, err := lang.Lookup(m.Language.Version, m.Language.Lang)
	if err != nil {
		return nil, fmt.Errorf("%s: %w", m.Path, err)
	}

	s := &Suite{
		Root:     root,
		Manifest: m,
		Vocab:    vocab,
		ByPrefix: make(map[string]*doc.Document),
		Missing:  make(map[string]string),
	}

	for _, prefix := range m.LivePrefixes() {
		rel := filepath.ToSlash(m.Prefixes.Live[prefix])
		name := filepath.Join(root, filepath.FromSlash(rel))
		d, err := doc.Load(rel, name)
		if err != nil {
			if errors.Is(err, fs.ErrNotExist) {
				s.Missing[prefix] = rel
				continue
			}
			s.Broken = append(s.Broken, err)
			continue
		}
		d.Blocks(vocab)
		s.Docs = append(s.Docs, d)
		s.ByPrefix[prefix] = d
	}

	if err := s.findUnregistered(); err != nil {
		return nil, err
	}
	return s, nil
}

// findUnregistered walks the suite looking for files written in the conventions
// language yet absent from the manifest. The marker is the prefix key in the
// front matter rather than the location of the file: the suite rearranges its
// taxonomy, while the front matter asserts.
func (s *Suite) findUnregistered() error {
	declared := make(map[string]bool)
	for _, path := range s.Manifest.Prefixes.Live {
		declared[filepath.ToSlash(path)] = true
	}
	for _, path := range s.Manifest.Prefixes.Retired {
		declared[filepath.ToSlash(path)] = true
	}

	err := filepath.WalkDir(s.Root, func(name string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if entry.IsDir() {
			if strings.HasPrefix(entry.Name(), ".") && name != s.Root {
				return fs.SkipDir
			}
			return nil
		}
		if filepath.Ext(entry.Name()) != ".md" {
			return nil
		}
		rel, err := filepath.Rel(s.Root, name)
		if err != nil {
			return err
		}
		rel = filepath.ToSlash(rel)
		if declared[rel] {
			return nil
		}
		d, err := doc.Load(rel, name)
		if err != nil {
			// The file carries no front matter, or it is broken — for the
			// suite this is not a document of the language but plain
			// markdown lying nearby.
			return nil
		}
		if d.Front.Prefix != "" {
			s.Unregistered = append(s.Unregistered, rel)
		}
		return nil
	})
	if err != nil {
		return fmt.Errorf("walking the suite: %w", err)
	}
	sort.Strings(s.Unregistered)
	return nil
}

// Conventions picks out the convention documents — the ones that carry a topic
// and therefore travel to a consumer. A document without a topic, the one the
// suite governs itself by, gets no spread checks.
func (s *Suite) Conventions() []*doc.Document {
	var out []*doc.Document
	for _, d := range s.Docs {
		if d.Front.Topic != "" {
			out = append(out, d)
		}
	}
	return out
}

// Layers lists the layers of a topic — the documents that declared that name in
// their front matter.
func (s *Suite) Layers(topic string) []*doc.Document {
	var out []*doc.Document
	for _, d := range s.Docs {
		if d.Front.Topic == topic {
			out = append(out, d)
		}
	}
	return out
}

// Prefix returns the prefix the manifest declares for a document.
func (s *Suite) Prefix(d *doc.Document) string {
	prefix, _ := s.Manifest.PrefixOf(d.Path)
	return prefix
}

// Exists reports whether the suite holds a file at a path from its root.
func (s *Suite) Exists(rel string) bool {
	_, err := os.Stat(filepath.Join(s.Root, filepath.FromSlash(rel)))
	return err == nil
}