/** Scope-aware name resolution over parsed Pascal units.
 *
 *  Covers hover/definition/completion/references/rename: same-file
 *  locals (innermost routine scope first, like `visibleAt`), record
 *  fields (`var.field`, `Type.field`, inline records), enumeration
 *  literals, and unit-qualified names (`Unit.Name`) via same-directory
 *  interface lookup. Best-effort: unknowable names yield null/empty,
 *  never diagnostics. Pascal is case-insensitive throughout.
 */

import * as fs from 'fs';
import * as path from 'path';
import { isIdent, lex, mask, parsePascal, parseUses, PasSymbol, PasUse, Tok } from './pascalSymbols';

export interface PasResolved {
  sym: PasSymbol;
  filePath: string;
}

const eq = (a: string, b: string) => a.toUpperCase() === b.toUpperCase();

/** Top-level symbols (unwrapping the program/unit module wrapper). */
function topLevel(symbols: PasSymbol[]): PasSymbol[] {
  const top: PasSymbol[] = [];
  for (const s of symbols) {
    if (s.kind === 'module') top.push(...s.children);
    else top.push(s);
  }
  return top;
}

/** True when (line, ch) lies within the symbol's scope, if known. */
function inScope(s: PasSymbol, line: number, ch: number): boolean {
  if (s.scopeEndLine === undefined) return true;
  if (line < s.line) return false;
  if (line > s.scopeEndLine) return false;
  if (line === s.scopeEndLine && s.scopeEndCh !== undefined && ch > s.scopeEndCh) return false;
  return true;
}

/** A name among scope children, including enumeration literals
 *  (constants declared inside a TYPE's `(A, B, ...)` list). Record
 *  fields never match bare: they need a qualifier. */
function findInScope(children: PasSymbol[], name: string): PasSymbol | null {
  const direct = children.find(c => c.name !== undefined && eq(c.name, name) && c.kind !== 'field');
  if (direct) return direct;
  for (const c of children) {
    if (c.kind === 'type') {
      const lit = c.children.find(g => g.kind === 'constant' && eq(g.name, name));
      if (lit) return lit;
    }
  }
  return null;
}

/** Resolve a same-file visible name to its declaration. */
export function resolveLocal(symbols: PasSymbol[], line: number, ch: number, name: string): PasSymbol | null {
  const top = topLevel(symbols);
  const routines = top
    .filter(s => (s.kind === 'procedure' || s.kind === 'function') && inScope(s, line, ch))
    .sort((a, b) => (b.line - a.line) || (b.ch - a.ch));
  for (const r of routines) {
    const found = findInScope(r.children, name);
    if (found) return found;
  }
  const globals = top.filter(s => s.kind === 'constant' || s.kind === 'type' || s.kind === 'variable');
  const g = findInScope(globals, name);
  if (g) return g;
  return top.find(s => (s.kind === 'procedure' || s.kind === 'function') && eq(s.name, name)) ?? null;
}

// ---- Cross-file unit cache ----

interface UnitEntry { mtimeMs: number; symbols: PasSymbol[]; uses: PasUse[]; }

const unitCache = new Map<string, UnitEntry>();
const dirCache = new Map<string, { mtimeMs: number; names: string[] }>();

/** Case-insensitive same-directory unit lookup (`Name.pas`/`.pp`/`.p`). */
function findUnitFile(dir: string, unitName: string): string | null {
  const exts = ['.pas', '.pp', '.p'];
  for (const ext of exts) {
    for (const cand of [`${unitName}${ext}`, `${unitName.toLowerCase()}${ext}`, `${unitName.toUpperCase()}${ext}`]) {
      try {
        if (fs.statSync(path.join(dir, cand)).isFile()) return path.join(dir, cand);
      } catch {
        // Try the next candidate.
      }
    }
  }
  try {
    const st = fs.statSync(dir);
    const hit = dirCache.get(dir);
    let names = hit?.names;
    if (!hit || hit.mtimeMs !== st.mtimeMs) {
      names = fs.readdirSync(dir);
      dirCache.set(dir, { mtimeMs: st.mtimeMs, names });
    }
    const want = unitName.toUpperCase();
    for (const ext of exts) {
      const hitName = names!.find(n => n.toUpperCase() === want + ext.toUpperCase());
      if (hitName) return path.join(dir, hitName);
    }
  } catch {
    // Unreadable directory: no unit found.
  }
  return null;
}

/** Parse a used unit's interface (whole file; callers only read top level). */
function loadUnit(dir: string, unitName: string): { symbols: PasSymbol[]; uses: PasUse[]; filePath: string } | null {
  const filePath = findUnitFile(dir, unitName);
  if (!filePath) return null;
  try {
    const st = fs.statSync(filePath);
    const hit = unitCache.get(filePath);
    if (hit && hit.mtimeMs === st.mtimeMs) return { ...hit, filePath };
    const text = fs.readFileSync(filePath, 'utf8');
    const entry: UnitEntry = { mtimeMs: st.mtimeMs, symbols: parsePascal(text), uses: parseUses(text) };
    unitCache.set(filePath, entry);
    return { ...entry, filePath };
  } catch {
    return null;
  }
}

/** Record fields of a named type: same file first, then used units. */
export function recordFieldsOf(
  symbols: PasSymbol[], uses: PasUse[], docDir: string, typeName: string,
): { fields: PasSymbol[]; filePath: string } | null {
  for (const s of topLevel(symbols)) {
    if (s.kind === 'type' && eq(s.name, typeName) && s.children.some(c => c.kind === 'field')) {
      return { fields: s.children.filter(c => c.kind === 'field'), filePath: '' };
    }
  }
  for (const u of uses) {
    const loaded = loadUnit(docDir, u.name);
    if (!loaded) continue;
    for (const s of topLevel(loaded.symbols)) {
      if (s.kind === 'type' && eq(s.name, typeName) && s.children.some(c => c.kind === 'field')) {
        return { fields: s.children.filter(c => c.kind === 'field'), filePath: loaded.filePath };
      }
    }
  }
  return null;
}

/** Exported top-level names of a unit (for `Unit.` completion). */
export function moduleExports(docDir: string, unitName: string): PasSymbol[] {
  const loaded = loadUnit(docDir, unitName);
  if (!loaded) return [];
  return topLevel(loaded.symbols).filter(s => s.kind !== 'module');
}

/** Resolve `name` or `Qualifier.name` at a document position. */
export function resolveAt(
  symbols: PasSymbol[], uses: PasUse[], filePath: string, docDir: string,
  line: number, ch: number, qualifier: string | null, name: string,
): PasResolved | null {
  if (qualifier) {
    // Record field on a local (`r.f`) or on a named type (`T.f`).
    const head = resolveLocal(symbols, line, ch, qualifier);
    if (head) {
      if (head.kind === 'type' && head.children.length > 0) {
        const f = head.children.find(c => c.kind === 'field' && eq(c.name, name));
        if (f) return { sym: f, filePath };
      }
      if (head.kind === 'variable' || head.kind === 'parameter' || head.kind === 'constant') {
        if (head.children.length > 0) {
          const f = head.children.find(c => c.kind === 'field' && eq(c.name, name));
          if (f) return { sym: f, filePath };
        }
        const typeMatch = /:\s*([A-Za-z_][A-Za-z0-9_]*)/.exec(head.detail);
        if (typeMatch) {
          const rec = recordFieldsOf(symbols, uses, docDir, typeMatch[1]);
          if (rec) {
            const f = rec.fields.find(c => eq(c.name, name));
            if (f) return { sym: f, filePath: rec.filePath || filePath };
          }
        }
      }
    }
    // Unit-qualified name: qualifier is a used unit (or any same-dir unit).
    const used = uses.find(u => eq(u.name, qualifier));
    const loaded = loadUnit(docDir, used ? used.name : qualifier);
    if (loaded) {
      const sym = findInScope(
        topLevel(loaded.symbols).filter(s => s.kind !== 'module'), name,
      ) ?? topLevel(loaded.symbols).find(s => (s.kind === 'procedure' || s.kind === 'function') && eq(s.name, name));
      if (sym) return { sym, filePath: loaded.filePath };
      return null;
    }
    return null;
  }
  const local = resolveLocal(symbols, line, ch, name);
  if (local) return { sym: local, filePath };
  // Bare name from a used unit's interface.
  for (const u of uses) {
    const loaded = loadUnit(docDir, u.name);
    if (!loaded) continue;
    const sym = findInScope(
      topLevel(loaded.symbols).filter(s => s.kind !== 'module'), name,
    ) ?? topLevel(loaded.symbols).find(s => (s.kind === 'procedure' || s.kind === 'function') && eq(s.name, name));
    if (sym) return { sym, filePath: loaded.filePath };
  }
  return null;
}

/** The unit name at a USES-clause position, for go-to-unit. */
export function unitAt(uses: PasUse[], docDir: string, line: number, ch: number): PasResolved | null {
  const hit = uses.find(u => u.line === line && ch >= u.ch && ch <= u.endCh);
  if (!hit) return null;
  const filePath = findUnitFile(docDir, hit.name);
  if (!filePath) return null;
  return {
    sym: {
      name: hit.name, kind: 'module', detail: `UNIT ${hit.name}`,
      line, ch: hit.ch, endLine: line, endCh: hit.endCh, children: [],
    },
    filePath,
  };
}

// ---- References & rename ----

export interface PasOccurrence {
  qualifier: string | null;
  name: string;
  line: number; ch: number; endLine: number; endCh: number;
}

export interface PasLocatedOccurrence extends PasOccurrence {
  filePath: string;
}

/** Every identifier token in masked-lexed text with its qualifier (`A` in `A.B`). */
export function identifierOccurrences(text: string): PasOccurrence[] {
  const toks = lex(mask(text));
  const out: PasOccurrence[] = [];
  for (let k = 0; k < toks.length; k++) {
    const t = toks[k];
    if (!isIdent(t)) continue;
    const qualifier =
      toks[k - 1]?.text === '.' && toks[k - 2] && isIdent(toks[k - 2]) ? toks[k - 2].text : null;
    out.push({ qualifier, name: t.text, line: t.line, ch: t.ch, endLine: t.endLine, endCh: t.endCh });
  }
  return out;
}

function flattenPositions(symbols: PasSymbol[], out: Set<string>): void {
  for (const s of symbols) {
    if (s.name) out.add(`${s.line}:${s.ch}`);
    flattenPositions(s.children, out);
  }
}

function sameDecl(a: PasResolved, b: PasResolved): boolean {
  if (a.sym === b.sym) return true;
  return a.filePath === b.filePath &&
    a.sym.line === b.sym.line && a.sym.ch === b.sym.ch &&
    a.sym.endLine === b.sym.endLine && a.sym.endCh === b.sym.endCh;
}

/** All occurrences in `text` that resolve to `decl`.
 *  The declaration occurrence itself is included iff `includeDeclaration`. */
export function findReferencesInText(
  text: string, filePath: string, docDir: string,
  decl: PasResolved, includeDeclaration = true,
): PasLocatedOccurrence[] {
  const symbols = parsePascal(text);
  const uses = parseUses(text);
  // Declaration sites belong to their own symbol: a shadowing
  // declaration must not count as a use of the symbol it shadows.
  const declared = new Set<string>();
  flattenPositions(symbols, declared);
  const declKey = `${decl.sym.line}:${decl.sym.ch}`;
  const out: PasLocatedOccurrence[] = [];
  for (const occ of identifierOccurrences(text)) {
    if (!eq(occ.name, decl.sym.name)) continue;
    const key = `${occ.line}:${occ.ch}`;
    if (filePath === decl.filePath && key === declKey) {
      if (includeDeclaration) out.push({ ...occ, filePath });
      continue;
    }
    if (declared.has(key)) continue;
    const resolved = resolveAt(symbols, uses, filePath, docDir, occ.line, occ.ch, occ.qualifier, occ.name);
    if (!resolved || !sameDecl(resolved, decl)) continue;
    out.push({ ...occ, filePath });
  }
  return out;
}

/** Extract `Qualifier.name` (or plain `name`) at a document offset.
 *  Runs on masked text (length-preserving, so offsets align) to skip
 *  comments and string literals. */
export function nameAtPosition(maskedText: string, offset: number): { qualifier: string | null; name: string } | null {
  let s = offset;
  while (s > 0 && /[A-Za-z0-9_]/.test(maskedText[s - 1] ?? '')) s--;
  let e = offset;
  while (e < maskedText.length && /[A-Za-z0-9_]/.test(maskedText[e] ?? '')) e++;
  if (s >= e) return null;
  const name = maskedText.slice(s, e);
  if (!/^[A-Za-z_]/.test(name)) return null;
  let k = s - 1;
  while (k >= 0 && (maskedText[k] === ' ' || maskedText[k] === '\t')) k--;
  if (maskedText[k] === '.') {
    let j = k - 1;
    while (j >= 0 && (maskedText[j] === ' ' || maskedText[j] === '\t')) j--;
    let h = j;
    while (h >= 0 && /[A-Za-z0-9_]/.test(maskedText[h] ?? '')) h--;
    const head = maskedText.slice(h + 1, j + 1);
    if (head && /^[A-Za-z_]/.test(head)) return { qualifier: head, name };
  }
  return { qualifier: null, name };
}

/** Identifier token covering a 0-based position, or null. */
export function tokenAtPosition(text: string, line: number, ch: number): Tok | null {
  for (const t of lex(mask(text))) {
    if (t.line === line && t.ch <= ch && ch <= t.endCh && isIdent(t)) return t;
  }
  return null;
}