package brain

import (
	"errors"
	"fmt"
	"io/fs"
	"log/slog"
	"path"
	"regexp"
	"sort"
	"strings"

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

// wikilinkRE matches [[target]] and [[target|Display Text]].
var wikilinkRE = regexp.MustCompile(`\[\[([^\]|]+)(?:\|([^\]]*))?\]\]`)

// fencedCodeRE and inlineCodeRE mark the regions where a [[...]] is a
// syntax example rather than a link. Same exclusion brain-gardener's audit
// applies on the read side, so the write gate and the audit agree on what
// counts as a link at all.
var (
	fencedCodeRE = regexp.MustCompile("(?s)```.*?```")
	inlineCodeRE = regexp.MustCompile("`[^`\n]*`")
)

// StripUnresolvedLinks unwraps every [[wikilink]] in content whose target
// resolves to no entry under knowledge/ or wiki/, leaving the link's display
// text (or its target) as plain prose. It returns the rewritten content and
// the sorted, de-duplicated targets it unwrapped.
//
// WHY UNWRAP RATHER THAN REJECT THE WRITE
// Agents write [[...]] around anything that feels related — a skill name, a
// repo, an agent-local memory file — and none of those are brain entries.
// Every one of those becomes a permanent [high] broken-link finding that no
// deterministic Fixer can repair, because there is no target to repoint to:
// the brain-audit digest grew from 19 to 63 high findings between 2026-08-26
// and 2026-09-16, and 53 of the 63 were exactly this. Rejecting the write
// instead would push the failure onto claudewatcher's unattended ingest path,
// where a refused write is a lost learning. Unwrapping keeps the author's
// words, keeps the write, and keeps the graph honest.
//
// An empty corpus (no knowledge/ or wiki/ yet, or a misconfigured brainDir)
// returns content unchanged: nothing resolving is a bootstrap state, not
// evidence that every target was invented.
func StripUnresolvedLinks(brainDir, content string) (string, []string, error) {
	index, err := entryIndex(brainDir)
	if err != nil {
		return "", nil, err
	}
	if len(index) == 0 {
		return content, nil, nil
	}

	code := codeSpans(content)
	stripped := map[string]struct{}{}

	var b strings.Builder
	last := 0
	for _, m := range wikilinkRE.FindAllStringSubmatchIndex(content, -1) {
		start, end := m[0], m[1]
		if overlaps(start, end, code) {
			continue
		}
		target := strings.TrimSpace(content[m[2]:m[3]])
		if _, ok := index[linkKey(target)]; ok {
			continue
		}
		display := target
		if m[4] >= 0 {
			if d := strings.TrimSpace(content[m[4]:m[5]]); d != "" {
				display = d
			}
		}
		b.WriteString(content[last:start])
		b.WriteString(display)
		last = end
		stripped[target] = struct{}{}
	}
	if last == 0 {
		return content, nil, nil
	}
	b.WriteString(content[last:])

	targets := make([]string, 0, len(stripped))
	for t := range stripped {
		targets = append(targets, t)
	}
	sort.Strings(targets)
	return b.String(), targets, nil
}

// linkedTrees are the two trees that hold linkable entries — the same pair
// package notes admits under ScopeNotes. Duplicated rather than imported
// because that list is unexported there and this is a read-only mirror.
var linkedTrees = []string{"knowledge", "wiki"}

// entryIndex maps every form a wikilink may name an entry by — its bare slug
// and its path form (wiki/<wing>/<hall>/<slug>.md -> wing/hall/slug) — to a
// present marker. Mirrors brain-gardener's resolver so an accepted link is
// one the audit will also resolve.
func entryIndex(brainDir string) (map[string]struct{}, error) {
	index := map[string]struct{}{}
	// Walked through the brain root (hyperguild#157): only regular files
	// count as entries, so a symlinked .md name cannot make a link resolve.
	bfs, err := brainfs.Open(brainDir)
	if err != nil {
		return nil, fmt.Errorf("open brain: %w", err)
	}
	defer func() { _ = bfs.Close() }()
	for _, dir := range linkedTrees {
		if _, err := bfs.Lstat(dir); errors.Is(err, fs.ErrNotExist) {
			continue
		}
		var walkErr error
		err := bfs.WalkRegular(dir, func(rel string) error {
			if !strings.HasSuffix(rel, ".md") {
				return nil
			}
			index[strings.TrimSuffix(path.Base(rel), ".md")] = struct{}{}
			index[strings.TrimPrefix(strings.TrimSuffix(rel, ".md"), "wiki/")] = struct{}{}
			return nil
		}, func(rel string, err error) {
			// A linked tree that is not a real directory (a symlink, a
			// file) is skipped, as filepath.WalkDir did: this runs before
			// every brain_write, and an error here loses the learning.
			if rel == dir && errors.Is(err, brainfs.ErrNotRegular) {
				slog.Warn("link check: skipping a linked tree that is not a real directory", "dir", dir)
				return
			}
			if walkErr == nil {
				walkErr = fmt.Errorf("%s: %w", rel, err)
			}
		})
		if err == nil {
			err = walkErr
		}
		if err != nil {
			return nil, fmt.Errorf("walk %s: %w", dir, err)
		}
	}
	return index, nil
}

// linkKey normalises a link target for index lookup: an exact path form is
// tried as written, and anything else falls back to its final segment.
func linkKey(target string) string {
	return strings.TrimSuffix(target, ".md")
}

// codeSpans returns the byte ranges of fenced blocks and inline code spans.
func codeSpans(content string) [][2]int {
	var spans [][2]int
	for _, m := range fencedCodeRE.FindAllStringIndex(content, -1) {
		spans = append(spans, [2]int{m[0], m[1]})
	}
	for _, m := range inlineCodeRE.FindAllStringIndex(content, -1) {
		spans = append(spans, [2]int{m[0], m[1]})
	}
	return spans
}

// overlaps reports whether [start,end) intersects any span.
func overlaps(start, end int, spans [][2]int) bool {
	for _, s := range spans {
		if start < s[1] && end > s[0] {
			return true
		}
	}
	return false
}