package api

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"

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

// PendingNote describes a raw/ note awaiting human promotion to the wiki.
type PendingNote struct {
	Filename  string `json:"filename"`
	CreatedAt string `json:"created_at"`
	SizeBytes int64  `json:"size_bytes"`
	Excerpt   string `json:"excerpt"`
}

// datePrefix matches a leading YYYY-MM-DD- on a raw filename, stripped when
// deriving the default promoted slug.
var datePrefix = regexp.MustCompile(`^\d{4}-\d{2}-\d{2}-`)

// ListPending returns the notes in brain/raw/ awaiting review, oldest-first
// (natural review order). An absent raw/ dir yields an empty slice, not an
// error. Only .md files are listed; tunnel-candidate files are skipped.
func ListPending(brainDir string) ([]PendingNote, error) {
	dir := filepath.Join(brainDir, "raw")
	entries, err := os.ReadDir(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return []PendingNote{}, nil
		}
		return nil, fmt.Errorf("read raw dir: %w", err)
	}

	out := make([]PendingNote, 0, len(entries))
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".md") || strings.HasPrefix(e.Name(), "tunnel-candidates-") {
			continue
		}
		info, statErr := e.Info()
		if statErr != nil {
			continue
		}
		raw, readErr := os.ReadFile(filepath.Join(dir, e.Name()))
		if readErr != nil {
			continue
		}
		fm, body := parseFrontmatter(string(raw))
		created := fm.get("created_at")
		if created == "" {
			created = info.ModTime().UTC().Format(time.RFC3339)
		}
		out = append(out, PendingNote{
			Filename:  e.Name(),
			CreatedAt: created,
			SizeBytes: info.Size(),
			Excerpt:   excerpt(body, 200),
		})
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].CreatedAt < out[j].CreatedAt })
	return out, nil
}

// PromoteOptions identifies a raw note to promote and its wiki destination.
type PromoteOptions struct {
	Filename string // basename in brain/raw/
	Wing     string
	Hall     string
	Slug     string // optional; defaults to Filename minus date prefix + .md
}

// PromoteNote moves a note from brain/raw/ into the structured wiki: it
// rewrites frontmatter (sets wing/hall/promoted_at, preserves created_at and
// any custom fields), writes to brain/wiki/<wing>/<hall>/<slug>.md, deletes
// the source, then rebuilds the wing index and runs auto-tunnel detection.
//
// It is atomic from the caller's view: validation (hall, wing, slug,
// collision) happens before any filesystem change, and the source is deleted
// only after the destination write succeeds (write-then-delete, never move).
// Returns the promoted note's path relative to brainDir.
func PromoteNote(brainDir string, opts PromoteOptions) (string, error) {
	// Validate filename (basename only — no traversal) before touching fs.
	base := filepath.Base(opts.Filename)
	if base != opts.Filename || base == "." || base == ".." || strings.ContainsAny(opts.Filename, `/\`) {
		return "", fmt.Errorf("invalid filename %q", opts.Filename)
	}

	slug := opts.Slug
	if slug == "" {
		slug = datePrefix.ReplaceAllString(strings.TrimSuffix(base, ".md"), "")
	}
	// NotePath validates hall + wing + slug; do this before reading anything.
	dest, err := brain.NotePath(brainDir, opts.Wing, opts.Hall, slug)
	if err != nil {
		return "", err
	}

	src := filepath.Join(brainDir, "raw", base)
	raw, err := os.ReadFile(src)
	if err != nil {
		if os.IsNotExist(err) {
			return "", fmt.Errorf("pending note %q does not exist in raw/", base)
		}
		return "", fmt.Errorf("read source: %w", err)
	}

	// Collision: never silently overwrite an existing promoted note.
	if _, statErr := os.Stat(dest); statErr == nil {
		rel, _ := filepath.Rel(brainDir, dest)
		return "", fmt.Errorf("target %s already exists; choose a different slug", filepath.ToSlash(rel))
	}

	fm, body := parseFrontmatter(string(raw))
	now := time.Now().UTC().Format(time.RFC3339)
	fm.set("wing", brain.Sanitise(opts.Wing))
	fm.set("hall", opts.Hall)
	if fm.get("created_at") == "" {
		fm.set("created_at", now)
	}
	fm.set("promoted_at", now)

	if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
		return "", fmt.Errorf("create wing dir: %w", err)
	}
	// Write-then-delete: the source survives any write failure.
	if err := os.WriteFile(dest, []byte(fm.render()+body), 0o644); err != nil {
		return "", fmt.Errorf("write promoted note: %w", err)
	}
	if err := os.Remove(src); err != nil {
		return "", fmt.Errorf("promoted note written but source removal failed: %w", err)
	}

	rel, _ := filepath.Rel(brainDir, dest)
	relSlash := filepath.ToSlash(rel)

	// Best-effort wiki upkeep — the note is already promoted.
	_ = brain.BuildWingIndex(brainDir, opts.Wing)
	_ = brain.AutoTunnel(brainDir, relSlash, body)

	return relSlash, nil
}

// excerpt returns the first n runes of s, trimmed, single-spaced.
func excerpt(s string, n int) string {
	s = strings.TrimSpace(s)
	r := []rune(s)
	if len(r) > n {
		r = r[:n]
	}
	return strings.TrimSpace(string(r))
}