// Markdown Core module implements ir behavior.
import MarkdownIt from "markdown-it";
import { chunkText } from "./chunk-text.js";
import type { MarkdownTableMode } from "./types.js";

type ListState = {
  type: "bullet" | "ordered";
  index: number;
  openLevel: number;
};

type LinkState = {
  href: string;
  labelStart: number;
};

const OPEN_MARKDOWN_HTML_TAG_PATTERN = /<\/?[a-zA-Z][a-zA-Z0-9-]*\b[^<>]*$/;

type RenderEnv = {
  listStack: ListState[];
};

type MarkdownToken = {
  type: string;
  tag?: string;
  content?: string;
  info?: string;
  children?: MarkdownToken[];
  attrs?: [string, string][];
  attrGet?: (name: string) => string | null;
  hidden?: boolean;
  level?: number;
};

export type MarkdownStyle =
  | "bold"
  | "italic"
  | "strikethrough"
  | "code"
  | "code_block"
  | "spoiler"
  | "blockquote"
  | "heading_1"
  | "heading_2"
  | "heading_3"
  | "heading_4"
  | "heading_5"
  | "heading_6";

export type MarkdownStyleSpan = {
  start: number;
  end: number;
  style: MarkdownStyle;
  language?: string;
};

export type MarkdownLinkSpan = {
  start: number;
  end: number;
  href: string;
};

export type MarkdownIR = {
  text: string;
  styles: MarkdownStyleSpan[];
  links: MarkdownLinkSpan[];
};

function createStyleSpan(params: MarkdownStyleSpan): MarkdownStyleSpan {
  const span: MarkdownStyleSpan = {
    start: params.start,
    end: params.end,
    style: params.style,
  };
  if (params.language) {
    span.language = params.language;
  }
  return span;
}

type MarkdownTableAlignment = "left" | "center" | "right";

export type MarkdownTableData = {
  headers: string[];
  rows: string[][];
  aligns?: (MarkdownTableAlignment | undefined)[];
};

export type MarkdownTableCell = {
  text: string;
  styles: MarkdownStyleSpan[];
  links: MarkdownLinkSpan[];
};

export type MarkdownTableMeta = MarkdownTableData & {
  placeholderOffset: number;
  headerCells: MarkdownTableCell[];
  rowCells: MarkdownTableCell[][];
};

type OpenStyle = {
  style: MarkdownStyle;
  start: number;
};

type RenderTarget = {
  text: string;
  styles: MarkdownStyleSpan[];
  openStyles: OpenStyle[];
  links: MarkdownLinkSpan[];
  linkStack: LinkState[];
};

type TableCell = MarkdownTableCell;

type TableState = {
  headers: TableCell[];
  rows: TableCell[][];
  aligns: (MarkdownTableAlignment | undefined)[];
  currentRow: TableCell[];
  currentCell: RenderTarget | null;
  inHeader: boolean;
};

type RenderState = RenderTarget & {
  env: RenderEnv;
  headingStyle: "none" | "bold" | "rich";
  blockquotePrefix: string;
  enableSpoilers: boolean;
  tableMode: MarkdownTableMode;
  table: TableState | null;
  hasTables: boolean;
  collectedTables: MarkdownTableMeta[];
};

export type MarkdownParseOptions = {
  linkify?: boolean;
  enableSpoilers?: boolean;
  headingStyle?: "none" | "bold" | "rich";
  blockquotePrefix?: string;
  autolink?: boolean;
  /** How to render tables (off|bullets|code|block). Default: off. */
  tableMode?: MarkdownTableMode;
};

function createMarkdownIt(options: MarkdownParseOptions): MarkdownIt {
  const md = new MarkdownIt({
    html: false,
    linkify: options.linkify ?? true,
    breaks: false,
    typographer: false,
  });
  md.enable("strikethrough");
  if (options.tableMode && options.tableMode !== "off") {
    md.enable("table");
  } else {
    md.disable("table");
  }
  if (options.autolink === false) {
    md.disable("autolink");
  }
  return md;
}

function getAttr(token: MarkdownToken, name: string): string | null {
  if (token.attrGet) {
    return token.attrGet(name);
  }
  if (token.attrs) {
    for (const [key, value] of token.attrs) {
      if (key === name) {
        return value;
      }
    }
  }
  return null;
}

function markdownTableAlignmentFromToken(token: MarkdownToken): MarkdownTableAlignment | undefined {
  const value = getAttr(token, "style") ?? "";
  if (/text-align\s*:\s*left/i.test(value)) {
    return "left";
  }
  if (/text-align\s*:\s*center/i.test(value)) {
    return "center";
  }
  if (/text-align\s*:\s*right/i.test(value)) {
    return "right";
  }
  return undefined;
}

function createTextToken(base: MarkdownToken, content: string): MarkdownToken {
  return { ...base, type: "text", content, children: undefined };
}

function applySpoilerTokens(tokens: MarkdownToken[]): void {
  for (const token of tokens) {
    if (token.children && token.children.length > 0) {
      token.children = injectSpoilersIntoInline(token.children);
    }
  }
}

function injectSpoilersIntoInline(tokens: MarkdownToken[]): MarkdownToken[] {
  let totalDelims = 0;
  for (const token of tokens) {
    if (token.type !== "text") {
      continue;
    }
    const content = token.content ?? "";
    let i = 0;
    while (i < content.length) {
      const next = content.indexOf("||", i);
      if (next === -1) {
        break;
      }
      totalDelims += 1;
      i = next + 2;
    }
  }

  if (totalDelims < 2) {
    return tokens;
  }
  const usableDelims = totalDelims - (totalDelims % 2);

  const result: MarkdownToken[] = [];
  const state = { spoilerOpen: false };
  let consumedDelims = 0;

  for (const token of tokens) {
    if (token.type !== "text") {
      result.push(token);
      continue;
    }

    const content = token.content ?? "";
    if (!content.includes("||")) {
      result.push(token);
      continue;
    }

    let index = 0;
    while (index < content.length) {
      const next = content.indexOf("||", index);
      if (next === -1) {
        if (index < content.length) {
          result.push(createTextToken(token, content.slice(index)));
        }
        break;
      }
      if (consumedDelims >= usableDelims) {
        result.push(createTextToken(token, content.slice(index)));
        break;
      }
      if (next > index) {
        result.push(createTextToken(token, content.slice(index, next)));
      }
      consumedDelims += 1;
      state.spoilerOpen = !state.spoilerOpen;
      result.push({
        type: state.spoilerOpen ? "spoiler_open" : "spoiler_close",
      });
      index = next + 2;
    }
  }

  return result;
}

function initRenderTarget(): RenderTarget {
  return {
    text: "",
    styles: [],
    openStyles: [],
    links: [],
    linkStack: [],
  };
}

function resolveRenderTarget(state: RenderState): RenderTarget {
  return state.table?.currentCell ?? state;
}

function appendText(state: RenderState, value: string) {
  if (!value) {
    return;
  }
  const target = resolveRenderTarget(state);
  target.text += value;
}

function openStyle(state: RenderState, style: MarkdownStyle) {
  const target = resolveRenderTarget(state);
  target.openStyles.push({ style, start: target.text.length });
}

function closeStyle(
  state: RenderState,
  style: MarkdownStyle,
  options?: { trimTrailingParagraphSeparator?: boolean },
) {
  const target = resolveRenderTarget(state);
  for (let i = target.openStyles.length - 1; i >= 0; i -= 1) {
    if (target.openStyles[i]?.style === style) {
      const start = target.openStyles[i].start;
      target.openStyles.splice(i, 1);
      const end =
        options?.trimTrailingParagraphSeparator && target.text.endsWith("\n\n")
          ? target.text.length - 2
          : target.text.length;
      if (end > start) {
        target.styles.push({ start, end, style });
      }
      return;
    }
  }
}

function appendParagraphSeparator(state: RenderState, token?: MarkdownToken) {
  if (state.table) {
    return;
  } // Don't add paragraph separators inside tables
  if (state.env.listStack.length > 0) {
    const currentList = state.env.listStack[state.env.listStack.length - 1];
    const directListParagraphLevel = (currentList?.openLevel ?? 0) + 2;
    if (
      token?.type !== "paragraph_close" ||
      token.hidden ||
      token.level !== directListParagraphLevel
    ) {
      return;
    }
  }
  state.text += "\n\n";
}

function appendTopLevelListSeparator(state: RenderState) {
  const trailingNewlines = state.text.match(/\n*$/)?.[0].length ?? 0;
  if (trailingNewlines < 2) {
    state.text += "\n";
  }
}

function appendNestedListSeparator(state: RenderState) {
  if (!state.text.endsWith("\n")) {
    state.text += "\n";
  }
}

function appendListPrefix(state: RenderState) {
  const stack = state.env.listStack;
  const top = stack[stack.length - 1];
  if (!top) {
    return;
  }
  top.index += 1;
  const indent = "  ".repeat(Math.max(0, stack.length - 1));
  const prefix = top.type === "ordered" ? `${top.index}. ` : "• ";
  state.text += `${indent}${prefix}`;
}

function renderInlineCode(state: RenderState, content: string) {
  if (!content) {
    return;
  }
  const target = resolveRenderTarget(state);
  const start = target.text.length;
  target.text += content;
  target.styles.push({ start, end: start + content.length, style: "code" });
}

function resolveFenceLanguage(info: string | undefined): string | undefined {
  const language = info?.trim().split(/\s+/, 1)[0]?.trim();
  return language || undefined;
}

function renderCodeBlock(state: RenderState, content: string, info?: string) {
  let code = content ?? "";
  if (!code.endsWith("\n")) {
    code = `${code}\n`;
  }
  const target = resolveRenderTarget(state);
  const start = target.text.length;
  target.text += code;
  target.styles.push(
    createStyleSpan({
      start,
      end: start + code.length,
      style: "code_block",
      language: resolveFenceLanguage(info),
    }),
  );
  if (state.env.listStack.length === 0) {
    target.text += "\n";
  }
}

function handleLinkClose(state: RenderState) {
  const target = resolveRenderTarget(state);
  const link = target.linkStack.pop();
  if (!link?.href) {
    return;
  }
  const href = link.href.trim();
  if (!href) {
    return;
  }
  const start = link.labelStart;
  const end = target.text.length;
  if (end <= start) {
    target.links.push({ start, end, href });
    return;
  }
  target.links.push({ start, end, href });
}

function headingStyleFromToken(token: MarkdownToken): MarkdownStyle | null {
  switch (token.tag) {
    case "h1":
      return "heading_1";
    case "h2":
      return "heading_2";
    case "h3":
      return "heading_3";
    case "h4":
      return "heading_4";
    case "h5":
      return "heading_5";
    case "h6":
      return "heading_6";
    default:
      return null;
  }
}

function isInsideMarkdownHtmlTag(text: string): boolean {
  const openTagStart = text.lastIndexOf("<");
  if (openTagStart === -1) {
    return false;
  }
  return (
    text.lastIndexOf(">") < openTagStart &&
    OPEN_MARKDOWN_HTML_TAG_PATTERN.test(text.slice(openTagStart))
  );
}

function initTableState(): TableState {
  return {
    headers: [],
    rows: [],
    aligns: [],
    currentRow: [],
    currentCell: null,
    inHeader: false,
  };
}

function finishTableCell(cell: RenderTarget): TableCell {
  closeRemainingStyles(cell);
  return {
    text: cell.text,
    styles: cell.styles,
    links: cell.links,
  };
}

function trimCell(cell: TableCell): TableCell {
  const text = cell.text;
  let start = 0;
  let end = text.length;
  while (start < end && /\s/.test(text[start] ?? "")) {
    start += 1;
  }
  while (end > start && /\s/.test(text[end - 1] ?? "")) {
    end -= 1;
  }
  if (start === 0 && end === text.length) {
    return cell;
  }
  const trimmedText = text.slice(start, end);
  const trimmedLength = trimmedText.length;
  const trimmedStyles: MarkdownStyleSpan[] = [];
  for (const span of cell.styles) {
    const sliceStart = Math.max(0, span.start - start);
    const sliceEnd = Math.min(trimmedLength, span.end - start);
    if (sliceEnd > sliceStart) {
      trimmedStyles.push({ start: sliceStart, end: sliceEnd, style: span.style });
    }
  }
  const trimmedLinks: MarkdownLinkSpan[] = [];
  for (const span of cell.links) {
    const sliceStart = Math.max(0, span.start - start);
    const sliceEnd = Math.min(trimmedLength, span.end - start);
    if (sliceEnd > sliceStart) {
      trimmedLinks.push({ start: sliceStart, end: sliceEnd, href: span.href });
    }
  }
  return { text: trimmedText, styles: trimmedStyles, links: trimmedLinks };
}

function appendCell(state: RenderState, cell: TableCell) {
  if (!cell.text) {
    return;
  }
  const start = state.text.length;
  state.text += cell.text;
  for (const span of cell.styles) {
    state.styles.push({
      start: start + span.start,
      end: start + span.end,
      style: span.style,
    });
  }
  for (const link of cell.links) {
    state.links.push({
      start: start + link.start,
      end: start + link.end,
      href: link.href,
    });
  }
}

function appendCellTextOnly(state: RenderState, cell: TableCell) {
  if (!cell.text) {
    return;
  }
  state.text += cell.text;
  // Do not append styles - this is used for code blocks where inner styles would overlap
}

function collectTableBlock(state: RenderState) {
  if (!state.table) {
    return;
  }
  const headerCells = state.table.headers.map(trimCell);
  const rowCells = state.table.rows.map((row) => row.map(trimCell));
  const table = {
    headers: headerCells.map((cell) => cell.text),
    rows: rowCells.map((row) => row.map((cell) => cell.text)),
    headerCells,
    rowCells,
    placeholderOffset: state.text.length,
    ...(state.table.aligns.some(Boolean) ? { aligns: [...state.table.aligns] } : {}),
  };
  state.collectedTables.push(table);
}

function appendTableBulletValue(
  state: RenderState,
  params: {
    header?: TableCell;
    value?: TableCell;
    columnIndex: number;
    includeColumnFallback: boolean;
  },
) {
  const { header, value, columnIndex, includeColumnFallback } = params;
  if (!value?.text) {
    return;
  }
  state.text += "• ";
  if (header?.text) {
    appendCell(state, header);
    state.text += ": ";
  } else if (includeColumnFallback) {
    state.text += `Column ${columnIndex}: `;
  }
  appendCell(state, value);
  state.text += "\n";
}

function renderTableAsBullets(state: RenderState) {
  if (!state.table) {
    return;
  }
  const headers = state.table.headers.map(trimCell);
  const rows = state.table.rows.map((row) => row.map(trimCell));

  // If no headers or rows, skip
  if (headers.length === 0 && rows.length === 0) {
    return;
  }

  // Determine if first column should be used as row labels
  // (common pattern: first column is category/feature name)
  const useFirstColAsLabel = headers.length > 1 && rows.length > 0;

  if (useFirstColAsLabel) {
    // Format: each row becomes a section with header as row[0], then key:value pairs
    for (const row of rows) {
      if (row.length === 0) {
        continue;
      }

      const rowLabel = row[0];
      if (rowLabel?.text) {
        const labelStart = state.text.length;
        appendCell(state, rowLabel);
        const labelEnd = state.text.length;
        if (labelEnd > labelStart) {
          state.styles.push({ start: labelStart, end: labelEnd, style: "bold" });
        }
        state.text += "\n";
      }

      // Add each column as a bullet point
      for (let i = 1; i < row.length; i++) {
        appendTableBulletValue(state, {
          header: headers[i],
          value: row[i],
          columnIndex: i,
          includeColumnFallback: true,
        });
      }
      state.text += "\n";
    }
  } else {
    // Simple table: just list headers and values
    for (const row of rows) {
      for (let i = 0; i < row.length; i++) {
        appendTableBulletValue(state, {
          header: headers[i],
          value: row[i],
          columnIndex: i,
          includeColumnFallback: false,
        });
      }
      state.text += "\n";
    }
  }
}

function renderTableAsCode(state: RenderState) {
  if (!state.table) {
    return;
  }
  const headers = state.table.headers.map(trimCell);
  const rows = state.table.rows.map((row) => row.map(trimCell));

  const columnCount = Math.max(headers.length, ...rows.map((row) => row.length));
  if (columnCount === 0) {
    return;
  }

  const widths = Array.from({ length: columnCount }, () => 0);
  const updateWidths = (cells: TableCell[]) => {
    for (let i = 0; i < columnCount; i += 1) {
      const cell = cells[i];
      const width = cell?.text.length ?? 0;
      if (widths[i] < width) {
        widths[i] = width;
      }
    }
  };
  updateWidths(headers);
  for (const row of rows) {
    updateWidths(row);
  }

  const codeStart = state.text.length;

  const appendRow = (cells: TableCell[]) => {
    state.text += "|";
    for (let i = 0; i < columnCount; i += 1) {
      state.text += " ";
      const cell = cells[i];
      if (cell) {
        // Use text-only append to avoid overlapping styles with code_block
        appendCellTextOnly(state, cell);
      }
      const pad = widths[i] - (cell?.text.length ?? 0);
      if (pad > 0) {
        state.text += " ".repeat(pad);
      }
      state.text += " |";
    }
    state.text += "\n";
  };

  const appendDivider = () => {
    state.text += "|";
    for (let i = 0; i < columnCount; i += 1) {
      const dashCount = Math.max(3, widths[i]);
      state.text += ` ${"-".repeat(dashCount)} |`;
    }
    state.text += "\n";
  };

  appendRow(headers);
  appendDivider();
  for (const row of rows) {
    appendRow(row);
  }

  const codeEnd = state.text.length;
  if (codeEnd > codeStart) {
    state.styles.push({ start: codeStart, end: codeEnd, style: "code_block" });
  }
  if (state.env.listStack.length === 0) {
    state.text += "\n";
  }
}

function renderTokens(tokens: MarkdownToken[], state: RenderState): void {
  for (const token of tokens) {
    switch (token.type) {
      case "inline":
        if (token.children) {
          renderTokens(token.children, state);
        }
        break;
      case "text":
        appendText(state, token.content ?? "");
        break;
      case "em_open":
        openStyle(state, "italic");
        break;
      case "em_close":
        closeStyle(state, "italic");
        break;
      case "strong_open":
        openStyle(state, "bold");
        break;
      case "strong_close":
        closeStyle(state, "bold");
        break;
      case "s_open":
        openStyle(state, "strikethrough");
        break;
      case "s_close":
        closeStyle(state, "strikethrough");
        break;
      case "code_inline":
        renderInlineCode(state, token.content ?? "");
        break;
      case "spoiler_open":
        if (state.enableSpoilers) {
          openStyle(state, "spoiler");
        }
        break;
      case "spoiler_close":
        if (state.enableSpoilers) {
          closeStyle(state, "spoiler");
        }
        break;
      case "link_open": {
        const target = resolveRenderTarget(state);
        const href = isInsideMarkdownHtmlTag(target.text) ? "" : (getAttr(token, "href") ?? "");
        target.linkStack.push({ href, labelStart: target.text.length });
        break;
      }
      case "link_close":
        handleLinkClose(state);
        break;
      case "image":
        appendText(state, token.content ?? "");
        break;
      case "softbreak":
      case "hardbreak":
        appendText(state, "\n");
        break;
      case "paragraph_close":
        appendParagraphSeparator(state, token);
        break;
      case "heading_open":
        if (state.headingStyle === "bold") {
          openStyle(state, "bold");
        } else if (state.headingStyle === "rich") {
          const style = headingStyleFromToken(token);
          if (style) {
            openStyle(state, style);
          }
        }
        break;
      case "heading_close":
        if (state.headingStyle === "bold") {
          closeStyle(state, "bold");
        } else if (state.headingStyle === "rich") {
          const style = headingStyleFromToken(token);
          if (style) {
            closeStyle(state, style);
          }
        }
        appendParagraphSeparator(state);
        break;
      case "blockquote_open":
        if (state.blockquotePrefix) {
          state.text += state.blockquotePrefix;
        }
        openStyle(state, "blockquote");
        break;
      case "blockquote_close":
        closeStyle(state, "blockquote", { trimTrailingParagraphSeparator: true });
        break;
      case "bullet_list_open":
        // Add newline before nested list starts (so nested items appear on new line)
        if (state.env.listStack.length > 0) {
          appendNestedListSeparator(state);
        }
        state.env.listStack.push({ type: "bullet", index: 0, openLevel: token.level ?? 0 });
        break;
      case "bullet_list_close":
        state.env.listStack.pop();
        if (state.env.listStack.length === 0) {
          appendTopLevelListSeparator(state);
        }
        break;
      case "ordered_list_open": {
        // Add newline before nested list starts (so nested items appear on new line)
        if (state.env.listStack.length > 0) {
          appendNestedListSeparator(state);
        }
        const start = Number(getAttr(token, "start") ?? "1");
        state.env.listStack.push({
          type: "ordered",
          index: start - 1,
          openLevel: token.level ?? 0,
        });
        break;
      }
      case "ordered_list_close":
        state.env.listStack.pop();
        if (state.env.listStack.length === 0) {
          appendTopLevelListSeparator(state);
        }
        break;
      case "list_item_open":
        appendListPrefix(state);
        break;
      case "list_item_close":
        // Avoid double newlines (nested list's last item already added newline)
        if (!state.text.endsWith("\n")) {
          state.text += "\n";
        }
        break;
      case "code_block":
      case "fence":
        renderCodeBlock(state, token.content ?? "", token.info);
        break;
      case "html_block":
      case "html_inline":
        appendText(state, token.content ?? "");
        break;

      // Table handling
      case "table_open":
        if (state.tableMode !== "off") {
          state.table = initTableState();
          state.hasTables = true;
        }
        break;
      case "table_close":
        if (state.table) {
          if (state.tableMode === "bullets") {
            renderTableAsBullets(state);
          } else if (state.tableMode === "code") {
            renderTableAsCode(state);
          } else if (state.tableMode === "block") {
            collectTableBlock(state);
          }
        }
        state.table = null;
        break;
      case "thead_open":
        if (state.table) {
          state.table.inHeader = true;
        }
        break;
      case "thead_close":
        if (state.table) {
          state.table.inHeader = false;
        }
        break;
      case "tbody_open":
      case "tbody_close":
        break;
      case "tr_open":
        if (state.table) {
          state.table.currentRow = [];
        }
        break;
      case "tr_close":
        if (state.table) {
          if (state.table.inHeader) {
            state.table.headers = state.table.currentRow;
          } else {
            state.table.rows.push(state.table.currentRow);
          }
          state.table.currentRow = [];
        }
        break;
      case "th_open":
      case "td_open":
        if (state.table) {
          state.table.currentCell = initRenderTarget();
          if (token.type === "th_open" && state.table.inHeader) {
            state.table.aligns[state.table.currentRow.length] =
              markdownTableAlignmentFromToken(token);
          }
        }
        break;
      case "th_close":
      case "td_close":
        if (state.table?.currentCell) {
          state.table.currentRow.push(finishTableCell(state.table.currentCell));
          state.table.currentCell = null;
        }
        break;

      case "hr":
        // Render as a visual separator
        state.text += "───\n\n";
        break;
      default:
        if (token.children) {
          renderTokens(token.children, state);
        }
        break;
    }
  }
}

function closeRemainingStyles(target: RenderTarget) {
  for (let i = target.openStyles.length - 1; i >= 0; i -= 1) {
    const open = target.openStyles[i];
    const end = target.text.length;
    if (end > open.start) {
      target.styles.push({
        start: open.start,
        end,
        style: open.style,
      });
    }
  }
  target.openStyles = [];
}

function clampStyleSpans(spans: MarkdownStyleSpan[], maxLength: number): MarkdownStyleSpan[] {
  const clamped: MarkdownStyleSpan[] = [];
  for (const span of spans) {
    const start = Math.max(0, Math.min(span.start, maxLength));
    const end = Math.max(start, Math.min(span.end, maxLength));
    if (end > start) {
      clamped.push(createStyleSpan({ start, end, style: span.style, language: span.language }));
    }
  }
  return clamped;
}

function clampLinkSpans(spans: MarkdownLinkSpan[], maxLength: number): MarkdownLinkSpan[] {
  const clamped: MarkdownLinkSpan[] = [];
  for (const span of spans) {
    const start = Math.max(0, Math.min(span.start, maxLength));
    const end = Math.max(start, Math.min(span.end, maxLength));
    if (end > start) {
      clamped.push({ start, end, href: span.href });
    }
  }
  return clamped;
}

function mergeStyleSpans(spans: MarkdownStyleSpan[]): MarkdownStyleSpan[] {
  const sorted = [...spans].toSorted((a, b) => {
    if (a.start !== b.start) {
      return a.start - b.start;
    }
    if (a.end !== b.end) {
      return a.end - b.end;
    }
    return a.style.localeCompare(b.style);
  });

  const merged: MarkdownStyleSpan[] = [];
  for (const span of sorted) {
    const prev = merged[merged.length - 1];
    if (
      prev &&
      prev.style === span.style &&
      prev.language === span.language &&
      // Blockquotes are container blocks. Adjacent blockquote spans should not merge or
      // consecutive blockquotes can "style bleed" across the paragraph boundary.
      (span.start < prev.end || (span.start === prev.end && span.style !== "blockquote"))
    ) {
      prev.end = Math.max(prev.end, span.end);
      continue;
    }
    merged.push({ ...span });
  }
  return merged;
}

function resolveSliceBounds(
  span: { start: number; end: number },
  start: number,
  end: number,
): { start: number; end: number } | null {
  const sliceStart = Math.max(span.start, start);
  const sliceEnd = Math.min(span.end, end);
  if (sliceEnd <= sliceStart) {
    return null;
  }
  return { start: sliceStart, end: sliceEnd };
}

function sliceStyleSpans(
  spans: MarkdownStyleSpan[],
  start: number,
  end: number,
): MarkdownStyleSpan[] {
  if (spans.length === 0) {
    return [];
  }
  const sliced: MarkdownStyleSpan[] = [];
  for (const span of spans) {
    const bounds = resolveSliceBounds(span, start, end);
    if (!bounds) {
      continue;
    }
    sliced.push(
      createStyleSpan({
        start: bounds.start - start,
        end: bounds.end - start,
        style: span.style,
        language: span.language,
      }),
    );
  }
  return mergeStyleSpans(sliced);
}

function sliceLinkSpans(spans: MarkdownLinkSpan[], start: number, end: number): MarkdownLinkSpan[] {
  if (spans.length === 0) {
    return [];
  }
  const sliced: MarkdownLinkSpan[] = [];
  for (const span of spans) {
    const bounds = resolveSliceBounds(span, start, end);
    if (!bounds) {
      continue;
    }
    sliced.push({
      start: bounds.start - start,
      end: bounds.end - start,
      href: span.href,
    });
  }
  return sliced;
}

export function sliceMarkdownIR(ir: MarkdownIR, start: number, end: number): MarkdownIR {
  return {
    text: ir.text.slice(start, end),
    styles: sliceStyleSpans(ir.styles, start, end),
    links: sliceLinkSpans(ir.links, start, end),
  };
}

export function markdownToIR(markdown: string, options: MarkdownParseOptions = {}): MarkdownIR {
  return markdownToIRWithMeta(markdown, options).ir;
}

export function markdownToIRWithMeta(
  markdown: string,
  options: MarkdownParseOptions = {},
): { ir: MarkdownIR; hasTables: boolean; tables: MarkdownTableMeta[] } {
  const env: RenderEnv = { listStack: [] };
  const md = createMarkdownIt(options);
  const tokens = md.parse(markdown ?? "", env as unknown as object);
  if (options.enableSpoilers) {
    applySpoilerTokens(tokens as MarkdownToken[]);
  }

  const tableMode = options.tableMode ?? "off";

  const state: RenderState = {
    text: "",
    styles: [],
    openStyles: [],
    links: [],
    linkStack: [],
    env,
    headingStyle: options.headingStyle ?? "none",
    blockquotePrefix: options.blockquotePrefix ?? "",
    enableSpoilers: options.enableSpoilers ?? false,
    tableMode,
    table: null,
    hasTables: false,
    collectedTables: [],
  };

  renderTokens(tokens as MarkdownToken[], state);
  closeRemainingStyles(state);

  const trimmedText = state.text.trimEnd();
  const trimmedLength = trimmedText.length;
  let codeBlockEnd = 0;
  for (const span of state.styles) {
    if (span.style !== "code_block") {
      continue;
    }
    if (span.end > codeBlockEnd) {
      codeBlockEnd = span.end;
    }
  }
  const finalLength = Math.max(trimmedLength, codeBlockEnd);
  const finalText =
    finalLength === state.text.length ? state.text : state.text.slice(0, finalLength);

  return {
    ir: {
      text: finalText,
      styles: mergeStyleSpans(clampStyleSpans(state.styles, finalLength)),
      links: clampLinkSpans(state.links, finalLength),
    },
    hasTables: state.hasTables,
    tables: state.collectedTables.map((table) =>
      Object.assign({}, table, {
        placeholderOffset: Math.min(table.placeholderOffset, finalLength),
      }),
    ),
  };
}

export function chunkMarkdownIR(ir: MarkdownIR, limit: number): MarkdownIR[] {
  if (!ir.text) {
    return [];
  }
  if (limit <= 0 || ir.text.length <= limit) {
    return [ir];
  }

  const chunks = chunkText(ir.text, limit);
  const results: MarkdownIR[] = [];
  let cursor = 0;

  chunks.forEach((chunk, index) => {
    if (!chunk) {
      return;
    }
    if (index > 0) {
      while (cursor < ir.text.length && /\s/.test(ir.text[cursor] ?? "")) {
        cursor += 1;
      }
    }
    const start = cursor;
    const end = Math.min(ir.text.length, start + chunk.length);
    results.push({
      text: chunk,
      styles: sliceStyleSpans(ir.styles, start, end),
      links: sliceLinkSpans(ir.links, start, end),
    });
    cursor = end;
  });

  return results;
}
