/**
 * Exact-text ("str_replace") edit application — vendored from the pi coding
 * agent.
 *
 * Source: `@earendil-works/pi-coding-agent` `dist/core/tools/edit-diff.ts`
 * (the `edit` tool's pure application core). Vendored rather than imported
 * because that package only exports its root index (the apply core is internal)
 * and pulling the `edit` tool drags in `@earendil-works/pi-tui` (a terminal UI)
 * plus a CLI/bash dependency tree unsuitable for the Next.js web bundle. The
 * `diff`-backed unified-patch/preview helpers are intentionally omitted — we only
 * need to APPLY edits. Keep this in sync with upstream if the matching algorithm
 * changes.
 *
 * Semantics: each `{ oldText, newText }` is matched against the ORIGINAL content
 * (not after earlier edits), exact match first then a fuzzy fallback (smart
 * quotes / Unicode dashes / trailing whitespace normalized). Each oldText must
 * be unique and non-overlapping; otherwise it throws with a model-actionable
 * message so the agent can retry with a longer anchor.
 */

export interface Edit {
  oldText: string;
  newText: string;
}

interface MatchedEdit {
  editIndex: number;
  matchIndex: number;
  matchLength: number;
  newText: string;
}

type TextReplacement = Pick<MatchedEdit, 'matchIndex' | 'matchLength' | 'newText'>;

interface FuzzyMatchResult {
  found: boolean;
  index: number;
  matchLength: number;
  usedFuzzyMatch: boolean;
  contentForReplacement: string;
}

export function detectLineEnding(content: string): '\r\n' | '\n' {
  const crlfIdx = content.indexOf('\r\n');
  const lfIdx = content.indexOf('\n');
  if (lfIdx === -1) return '\n';
  if (crlfIdx === -1) return '\n';
  return crlfIdx < lfIdx ? '\r\n' : '\n';
}

export function normalizeToLF(text: string): string {
  return text.replace(/\r\n/g, '\n').replace(/\r/g, '\n');
}

export function restoreLineEndings(text: string, ending: '\r\n' | '\n'): string {
  return ending === '\r\n' ? text.replace(/\n/g, '\r\n') : text;
}

/**
 * Normalize text for fuzzy matching: strip trailing whitespace per line,
 * normalize smart quotes / Unicode dashes / special spaces to ASCII.
 */
export function normalizeForFuzzyMatch(text: string): string {
  return (
    text
      .normalize('NFKC')
      // Strip trailing whitespace per line
      .split('\n')
      .map((line) => line.trimEnd())
      .join('\n')
      // Smart single quotes → '
      .replace(/[‘’‚‛]/g, "'")
      // Smart double quotes → "
      .replace(/[“”„‟]/g, '"')
      // Various dashes/hyphens → -
      .replace(/[‐‑‒–—―−]/g, '-')
      // Special spaces → regular space
      .replace(/[  -   　]/g, ' ')
  );
}

function splitLinesWithEndings(content: string): string[] {
  return content.match(/[^\n]*\n|[^\n]+/g) ?? [];
}

function getLineSpans(content: string): Array<{ start: number; end: number }> {
  let offset = 0;
  return splitLinesWithEndings(content).map((line) => {
    const span = { start: offset, end: offset + line.length };
    offset = span.end;
    return span;
  });
}

function getReplacementLineRange(
  lines: Array<{ start: number; end: number }>,
  replacement: TextReplacement,
): { startLine: number; endLine: number } {
  const replacementStart = replacement.matchIndex;
  const replacementEnd = replacement.matchIndex + replacement.matchLength;
  let startLine = -1;
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (replacementStart >= line.start && replacementStart < line.end) {
      startLine = i;
      break;
    }
  }
  if (startLine === -1) {
    throw new Error('Replacement range is outside the base content.');
  }
  let endLine = startLine;
  while (endLine < lines.length && lines[endLine].end < replacementEnd) {
    endLine++;
  }
  if (endLine >= lines.length) {
    throw new Error('Replacement range is outside the base content.');
  }
  return { startLine, endLine: endLine + 1 };
}

function applyReplacements(content: string, replacements: TextReplacement[], offset = 0): string {
  let result = content;
  for (let i = replacements.length - 1; i >= 0; i--) {
    const replacement = replacements[i];
    const matchIndex = replacement.matchIndex - offset;
    result =
      result.substring(0, matchIndex) +
      replacement.newText +
      result.substring(matchIndex + replacement.matchLength);
  }
  return result;
}

/**
 * Apply replacements matched against `baseContent` to `originalContent` while
 * preserving unchanged line blocks from the original.
 */
export function applyReplacementsPreservingUnchangedLines(
  originalContent: string,
  baseContent: string,
  replacements: TextReplacement[],
): string {
  const originalLines = splitLinesWithEndings(originalContent);
  const baseLines = getLineSpans(baseContent);
  if (originalLines.length !== baseLines.length) {
    throw new Error(
      'Cannot preserve unchanged lines because the base content has a different line count.',
    );
  }
  const groups: Array<{ startLine: number; endLine: number; replacements: TextReplacement[] }> = [];
  const sortedReplacements = [...replacements].sort((a, b) => a.matchIndex - b.matchIndex);
  for (const replacement of sortedReplacements) {
    const range = getReplacementLineRange(baseLines, replacement);
    const current = groups[groups.length - 1];
    if (current && range.startLine < current.endLine) {
      current.endLine = Math.max(current.endLine, range.endLine);
      current.replacements.push(replacement);
      continue;
    }
    groups.push({ ...range, replacements: [replacement] });
  }
  let originalLineIndex = 0;
  let result = '';
  for (const group of groups) {
    result += originalLines.slice(originalLineIndex, group.startLine).join('');
    const groupStartOffset = baseLines[group.startLine].start;
    const groupEndOffset = baseLines[group.endLine - 1].end;
    result += applyReplacements(
      baseContent.slice(groupStartOffset, groupEndOffset),
      group.replacements,
      groupStartOffset,
    );
    originalLineIndex = group.endLine;
  }
  result += originalLines.slice(originalLineIndex).join('');
  return result;
}

/** Find oldText in content, exact match first, then fuzzy match. */
export function fuzzyFindText(content: string, oldText: string): FuzzyMatchResult {
  const exactIndex = content.indexOf(oldText);
  if (exactIndex !== -1) {
    return {
      found: true,
      index: exactIndex,
      matchLength: oldText.length,
      usedFuzzyMatch: false,
      contentForReplacement: content,
    };
  }
  const fuzzyContent = normalizeForFuzzyMatch(content);
  const fuzzyOldText = normalizeForFuzzyMatch(oldText);
  const fuzzyIndex = fuzzyContent.indexOf(fuzzyOldText);
  if (fuzzyIndex === -1) {
    return {
      found: false,
      index: -1,
      matchLength: 0,
      usedFuzzyMatch: false,
      contentForReplacement: content,
    };
  }
  return {
    found: true,
    index: fuzzyIndex,
    matchLength: fuzzyOldText.length,
    usedFuzzyMatch: true,
    contentForReplacement: fuzzyContent,
  };
}

/** Strip a UTF-8 BOM if present, returning the BOM (if any) and the rest. */
export function stripBom(content: string): { bom: string; text: string } {
  return content.charCodeAt(0) === 0xfeff
    ? { bom: content[0], text: content.slice(1) }
    : { bom: '', text: content };
}

function countOccurrences(content: string, oldText: string): number {
  const fuzzyContent = normalizeForFuzzyMatch(content);
  const fuzzyOldText = normalizeForFuzzyMatch(oldText);
  return fuzzyContent.split(fuzzyOldText).length - 1;
}

function getNotFoundError(path: string, editIndex: number, totalEdits: number): Error {
  if (totalEdits === 1) {
    return new Error(
      `Could not find the exact text in ${path}. The old text must match exactly including all whitespace and newlines.`,
    );
  }
  return new Error(
    `Could not find edits[${editIndex}] in ${path}. The oldText must match exactly including all whitespace and newlines.`,
  );
}

function getDuplicateError(
  path: string,
  editIndex: number,
  totalEdits: number,
  occurrences: number,
): Error {
  if (totalEdits === 1) {
    return new Error(
      `Found ${occurrences} occurrences of the text in ${path}. The text must be unique. Please provide more context to make it unique.`,
    );
  }
  return new Error(
    `Found ${occurrences} occurrences of edits[${editIndex}] in ${path}. Each oldText must be unique. Please provide more context to make it unique.`,
  );
}

function getEmptyOldTextError(path: string, editIndex: number, totalEdits: number): Error {
  if (totalEdits === 1) {
    return new Error(`oldText must not be empty in ${path}.`);
  }
  return new Error(`edits[${editIndex}].oldText must not be empty in ${path}.`);
}

function getNoChangeError(path: string, totalEdits: number): Error {
  if (totalEdits === 1) {
    return new Error(
      `No changes made to ${path}. The replacement produced identical content. This might indicate an issue with special characters or the text not existing as expected.`,
    );
  }
  return new Error(`No changes made to ${path}. The replacements produced identical content.`);
}

/**
 * Apply one or more exact-text replacements to LF-normalized content. Throws a
 * model-actionable error on empty / not-found / ambiguous / overlapping /
 * no-op edits.
 */
export function applyEditsToNormalizedContent(
  normalizedContent: string,
  edits: Edit[],
  path: string,
): { baseContent: string; newContent: string } {
  const normalizedEdits = edits.map((edit) => ({
    oldText: normalizeToLF(edit.oldText),
    newText: normalizeToLF(edit.newText),
  }));
  for (let i = 0; i < normalizedEdits.length; i++) {
    if (normalizedEdits[i].oldText.length === 0) {
      throw getEmptyOldTextError(path, i, normalizedEdits.length);
    }
  }
  const initialMatches = normalizedEdits.map((edit) =>
    fuzzyFindText(normalizedContent, edit.oldText),
  );
  const usedFuzzyMatch = initialMatches.some((match) => match.usedFuzzyMatch);
  const replacementBaseContent = usedFuzzyMatch
    ? normalizeForFuzzyMatch(normalizedContent)
    : normalizedContent;
  const matchedEdits: MatchedEdit[] = [];
  for (let i = 0; i < normalizedEdits.length; i++) {
    const edit = normalizedEdits[i];
    const matchResult = fuzzyFindText(replacementBaseContent, edit.oldText);
    if (!matchResult.found) {
      throw getNotFoundError(path, i, normalizedEdits.length);
    }
    const occurrences = countOccurrences(replacementBaseContent, edit.oldText);
    if (occurrences > 1) {
      throw getDuplicateError(path, i, normalizedEdits.length, occurrences);
    }
    matchedEdits.push({
      editIndex: i,
      matchIndex: matchResult.index,
      matchLength: matchResult.matchLength,
      newText: edit.newText,
    });
  }
  matchedEdits.sort((a, b) => a.matchIndex - b.matchIndex);
  for (let i = 1; i < matchedEdits.length; i++) {
    const previous = matchedEdits[i - 1];
    const current = matchedEdits[i];
    if (previous.matchIndex + previous.matchLength > current.matchIndex) {
      throw new Error(
        `edits[${previous.editIndex}] and edits[${current.editIndex}] overlap in ${path}. Merge them into one edit or target disjoint regions.`,
      );
    }
  }
  const baseContent = normalizedContent;
  const newContent = usedFuzzyMatch
    ? applyReplacementsPreservingUnchangedLines(
        normalizedContent,
        replacementBaseContent,
        matchedEdits,
      )
    : applyReplacements(replacementBaseContent, matchedEdits);
  if (baseContent === newContent) {
    throw getNoChangeError(path, normalizedEdits.length);
  }
  return { baseContent, newContent };
}

/**
 * Convenience wrapper: apply str_replace edits to an HTML document, preserving
 * its BOM and line endings (mirrors the pi edit tool's file wrapping). Throws on
 * any unappliable edit. `label` is only used in error messages.
 */
export function applyHtmlEdits(html: string, edits: Edit[], label = 'the page'): string {
  const { bom, text } = stripBom(html);
  const ending = detectLineEnding(text);
  const normalized = normalizeToLF(text);
  const { newContent } = applyEditsToNormalizedContent(normalized, edits, label);
  return bom + restoreLineEndings(newContent, ending);
}