// ingestion/internal/wiki/inventory.go
package wiki

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io/fs"
	"strings"

	"github.com/mathiasbq/hyperguild/ingestion/internal/brainfs"
)

// LoadInventory walks brain/wiki/ and returns all pages grouped by type.
// Missing subdirectories are silently skipped. Pages are listed and read
// through the brain root, regular files only (hyperguild#157); a type
// directory that is a symlink is an error.
func LoadInventory(brainDir string) (map[PageType][]Entry, error) {
	result := map[PageType][]Entry{
		PageTypeConcept: {},
		PageTypeEntity:  {},
		PageTypeSource:  {},
	}
	bfs, err := brainfs.Open(brainDir)
	if err != nil {
		return nil, fmt.Errorf("open brain: %w", err)
	}
	defer func() { _ = bfs.Close() }()
	for pt := range result {
		dir := "wiki/" + string(pt)
		names, err := bfs.ReadDirRegular(dir)
		if errors.Is(err, fs.ErrNotExist) {
			continue
		}
		if err != nil {
			return nil, fmt.Errorf("read dir %s: %w", dir, err)
		}
		for _, name := range names {
			if !strings.HasSuffix(name, ".md") {
				continue
			}
			slug := strings.TrimSuffix(name, ".md")
			title, aliases := readFrontmatter(bfs, dir+"/"+name, slug)
			result[pt] = append(result[pt], Entry{Slug: slug, Title: title, Aliases: aliases, Type: pt})
		}
	}
	return result, nil
}

// readFrontmatter extracts title and aliases from YAML frontmatter.
// Falls back to slug for title and empty aliases on any error.
func readFrontmatter(bfs *brainfs.Brain, rel, fallbackSlug string) (title string, aliases []string) {
	title = fallbackSlug
	content, err := bfs.ReadRegular(rel)
	if err != nil {
		return
	}

	scanner := bufio.NewScanner(bytes.NewReader(content))
	inFM := false
	inAliases := false
	for scanner.Scan() {
		line := scanner.Text()
		if strings.TrimSpace(line) == "---" {
			if !inFM {
				inFM = true
				continue
			}
			break // end of frontmatter
		}
		if !inFM {
			continue
		}

		// Detect alias list items (lines starting with "  - ").
		if inAliases {
			trimmed := strings.TrimSpace(line)
			if strings.HasPrefix(trimmed, "- ") {
				aliases = append(aliases, strings.TrimPrefix(trimmed, "- "))
				continue
			}
			inAliases = false // end of alias block
		}

		key, val, ok := strings.Cut(line, ":")
		if !ok {
			continue
		}
		switch strings.TrimSpace(key) {
		case "title":
			title = strings.Trim(strings.TrimSpace(val), `"'`)
		case "aliases":
			inAliases = true
		}
	}
	return
}

// LoadWingInventory returns the pages of ONE wing, grouped by type. Sources
// come from wiki/<wing>/sources/; concepts and entities live together in
// wiki/<wing>/facts/ and are told apart by their `kind:` frontmatter. A facts
// page without a kind (a hand-written note) is left out, so extraction can
// never merge into something it did not create. Other wings are never read.
func LoadWingInventory(brainDir, wing string) (map[PageType][]Entry, error) {
	result := map[PageType][]Entry{PageTypeConcept: {}, PageTypeEntity: {}, PageTypeSource: {}}
	bfs, err := brainfs.Open(brainDir)
	if err != nil {
		return nil, fmt.Errorf("open brain: %w", err)
	}
	defer func() { _ = bfs.Close() }()
	for _, hall := range []string{"sources", "facts"} {
		dir := "wiki/" + wing + "/" + hall
		names, err := bfs.ReadDirRegular(dir)
		if errors.Is(err, fs.ErrNotExist) {
			continue
		}
		if err != nil {
			return nil, fmt.Errorf("read dir %s: %w", dir, err)
		}
		for _, name := range names {
			if !strings.HasSuffix(name, ".md") {
				continue
			}
			rel := dir + "/" + name
			slug := strings.TrimSuffix(name, ".md")
			pt := PageTypeSource
			if hall == "facts" {
				var ok bool
				if pt, ok = kindOf(bfs, rel); !ok {
					continue
				}
			}
			title, aliases := readFrontmatter(bfs, rel, slug)
			result[pt] = append(result[pt], Entry{Slug: slug, Title: title, Aliases: aliases, Type: pt, Path: rel})
		}
	}
	return result, nil
}

// kindOf reads `kind:` from a facts page's frontmatter.
func kindOf(bfs *brainfs.Brain, rel string) (PageType, bool) {
	content, err := bfs.ReadRegular(rel)
	if err != nil {
		return "", false
	}
	return KindFromContent(string(content))
}

// KindFromContent maps frontmatter `kind: concept|entity` to a PageType.
func KindFromContent(content string) (PageType, bool) {
	inFM := false
	for _, line := range strings.Split(content, "\n") {
		if strings.TrimSpace(line) == "---" {
			if inFM {
				break
			}
			inFM = true
			continue
		}
		if !inFM {
			continue
		}
		if key, val, ok := strings.Cut(line, ":"); ok && strings.TrimSpace(key) == "kind" {
			switch strings.Trim(strings.TrimSpace(val), `"'`) {
			case "concept":
				return PageTypeConcept, true
			case "entity":
				return PageTypeEntity, true
			}
		}
	}
	return "", false
}