first commit

src/language/context.ts

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+import type { XmlAttribute, XmlDocument, XmlElement } from "./xmlParser";
+
+export type ContextKind =
+  | "element-name"
+  | "attribute-name"
+  | "attribute-value"
+  | "content"
+  | "none";
+
+export interface CompletionContext {
+  kind: ContextKind;
+  /** The element whose start tag the cursor is in (or whose content). */
+  element: XmlElement | null;
+  /** Set when the cursor is inside a closing tag name ("</..."). */
+  closing: boolean;
+  /** The attribute being edited (attribute-value context). */
+  attr: XmlAttribute | null;
+  /** Text between the opening quote and the cursor. */
+  valuePrefix: string;
+  /** Names of attributes already present on the element. */
+  existingAttrs: string[];
+}
+
+export function analyzeContext(
+  doc: XmlDocument,
+  text: string,
+  offset: number,
+): CompletionContext {
+  // Find the innermost element whose span contains the offset.
+  let container: XmlElement | null = null;
+  for (const el of doc.elements) {
+    if (el.end < 0) continue;
+    if (offset >= el.start && offset <= el.end) {
+      if (!container || el.depth > container.depth) container = el;
+    }
+  }
+
+  if (!container) return empty("none");
+
+  // Inside the start tag of the element.
+  if (offset >= container.start && offset <= container.startTagEnd) {
+    return analyzeStartTag(container, text, offset);
+  }
+
+  // Otherwise the cursor is in element content.
+  return {
+    kind: "content",
+    element: container,
+    closing: false,
+    attr: null,
+    valuePrefix: "",
+    existingAttrs: [],
+  };
+}
+
+function analyzeStartTag(
+  el: XmlElement,
+  text: string,
+  offset: number,
+): CompletionContext {
+  const closing = text.startsWith("</", el.start);
+  const nameStart = el.start + (closing ? 2 : 1);
+  const nameEnd = nameStart + el.name.length;
+  const existingAttrs = el.attrs.map((a) => a.name);
+
+  if (offset <= nameEnd) {
+    return {
+      kind: "element-name",
+      element: el,
+      closing,
+      attr: null,
+      valuePrefix: "",
+      existingAttrs,
+    };
+  }
+
+  // Inside an attribute value?
+  for (const attr of el.attrs) {
+    if (attr.hasValue && offset >= attr.quoteStart && offset <= attr.quoteEnd) {
+      const start = attr.valueStart;
+      const prefix = offset > start ? text.slice(start, offset) : "";
+      return {
+        kind: "attribute-value",
+        element: el,
+        closing: false,
+        attr,
+        valuePrefix: prefix,
+        existingAttrs,
+      };
+    }
+  }
+
+  // Right after "=" (no quotes yet) or between attributes.
+  const before = text.slice(el.start, offset);
+  const trimmed = before.replace(/\s+$/, "");
+  if (trimmed.endsWith("=")) {
+    return {
+      kind: "attribute-value",
+      element: el,
+      closing: false,
+      attr: lastAttrOf(el),
+      valuePrefix: "",
+      existingAttrs,
+    };
+  }
+
+  return {
+    kind: "attribute-name",
+    element: el,
+    closing: false,
+    attr: null,
+    valuePrefix: "",
+    existingAttrs,
+  };
+}
+
+function lastAttrOf(el: XmlElement): XmlAttribute | null {
+  return el.attrs.length ? el.attrs[el.attrs.length - 1] : null;
+}
+
+function empty(kind: ContextKind): CompletionContext {
+  return {
+    kind,
+    element: null,
+    closing: false,
+    attr: null,
+    valuePrefix: "",
+    existingAttrs: [],
+  };
+}