// src/editor/extensions/image-embed-utils.ts
/**
 * Shared utilities for image embed parsing, used by both
 * image-embed-widget.ts (single images) and image-gallery-widget.ts (galleries).
 */
import type { EditorState, Text } from '@codemirror/state'
import { ImageResolver } from '../../services/image-resolver'
import {
  getFrontmatterRange,
  shouldSkipMarkdownEnhancement,
  isOffsetRangeInTableCell,
} from './markdown-context'

/**
 * Regex for Obsidian-style image embeds: `![[target|optional-alias]]`
 * Captures:
 *   1 = target (filename, no `]` or `|`)
 *   2 = optional alias (everything between `|` and `]]`)
 *
 * IMPORTANT: This regex has the `g` flag, so reset `lastIndex` before each use
 * OR create a fresh instance via `new RegExp(EMBED_RE.source, EMBED_RE.flags)`.
 */
export const EMBED_RE = /!\[\[([^\]|]+?)(?:\|([^\]]+?))?\]\]/g

const embedSyntaxPresence = new WeakMap<Text, boolean>()

/** Shared document-level prefilter for the image and gallery state fields. */
export function hasImageEmbedSyntax(doc: Text): boolean {
  const cached = embedSyntaxPresence.get(doc)
  if (cached !== undefined) return cached
  const present = doc.toString().includes('![[')
  embedSyntaxPresence.set(doc, present)
  return present
}

/**
 * Detect Obsidian image-sizing specs in the alias slot:
 *   - `100` → width only
 *   - `100x200` → width x height
 * Anything else (e.g., `caption`, `My alt text`) is treated as a real
 * alias and rendered into `<img alt="...">` or `<figcaption>`.
 */
export function isSizingSpec(alias: string): boolean {
  return /^\d+(?:x\d+)?$/.test(alias)
}

export interface GalleryImage {
  target: string
  alias: string | undefined
  from: number
  to: number
}

/**
 * Collect all valid image embeds on a line and determine whether the line
 * qualifies as a gallery (2+ image embeds with ONLY whitespace between them).
 *
 * Returns the collected images if the line is a gallery, or `null` if not.
 * This avoids the double-scan problem: callers that need both the boolean
 * check and the image list get them in one pass.
 *
 * A line qualifies as a gallery when:
 *   1. Every `![[...]]` embed on the line is an image target
 *   2. There's no non-embed, non-whitespace text on the line
 *   3. At least 2 image embeds pass the exclusion guards
 *
 * Examples:
 *   `![[a.png]] ![[b.png]]`           → gallery (2 images)
 *   `Here is ![[a.png]] ![[b.png]]`   → null (non-embed text)
 *   `![[note.md]] ![[a.png]]`         → null (non-image embed)
 *   `![[a.png]]`                      → null (only 1 image)
 */
export function collectGalleryImages(state: EditorState, lineNumber: number): GalleryImage[] | null {
  const doc = state.doc
  if (lineNumber < 1 || lineNumber > doc.lines) return null
  const line = doc.line(lineNumber)
  if (!line.text.includes('![[')) return null

  // Structural check: scan all embeds and verify that every embed on the
  // line is an image target. Also track the character ranges consumed by
  // embeds so we can verify nothing else remains.
  const re = new RegExp(EMBED_RE.source, EMBED_RE.flags)
  const frontmatter = getFrontmatterRange(state)
  const images: GalleryImage[] = []
  let consumed = 0 // total characters consumed by embed syntax
  let match: RegExpExecArray | null

  while ((match = re.exec(line.text)) !== null) {
    const target = match[1]
    consumed += match[0].length

    // If ANY embed on the line is not an image, the line has non-image
    // content and is not a gallery (e.g., `![[note.md]] ![[a.png]]`).
    if (!ImageResolver.isImageTarget(target)) return null

    const from = line.from + match.index
    const to = from + match[0].length

    if (shouldSkipMarkdownEnhancement(state, from, to, frontmatter)) continue
    if (isOffsetRangeInTableCell(state, from, to)) continue

    images.push({ target, alias: match[2], from, to })
  }

  // Check that the non-embed remainder is only whitespace.
  // (line.text.length - consumed) gives the characters NOT inside embeds.
  const remainderLength = line.text.length - consumed
  if (remainderLength > 0) {
    // Build remainder by stripping matched embed ranges
    const remainder = line.text.replace(new RegExp(EMBED_RE.source, EMBED_RE.flags), '').trim()
    if (remainder.length > 0) return null
  }

  return images.length >= 2 ? images : null
}

/**
 * Quick boolean check for whether a line is a gallery line.
 *
 * Used by image-embed-widget.ts to skip gallery lines. For callers that
 * also need the image list, use `collectGalleryImages()` directly.
 *
 * This function is in the shared utils module to prevent a circular
 * dependency between image-embed-widget and image-gallery-widget.
 */
export function isGalleryLine(state: EditorState, lineNumber: number): boolean {
  return collectGalleryImages(state, lineNumber) !== null
}