export type DiffLineType =
  | "file-header"
  | "hunk-header"
  | "added"
  | "removed"
  | "context"
  | "no-newline";

export interface ParsedDiffLine {
  type: DiffLineType;
  content: string;
  oldLineNumber: number | null;
  newLineNumber: number | null;
}

const FILE_HEADER_PREFIXES = [
  "diff ",
  "index ",
  "--- ",
  "+++ ",
  "new file",
  "deleted file",
  "old mode",
  "new mode",
  "rename ",
  "similarity ",
];

export function parseDiff(diffContent: string): ParsedDiffLine[] {
  const result: ParsedDiffLine[] = [];
  let oldLine = 0;
  let newLine = 0;

  for (const line of diffContent.split("\n")) {
    if (FILE_HEADER_PREFIXES.some((prefix) => line.startsWith(prefix))) {
      result.push({ type: "file-header", content: line, oldLineNumber: null, newLineNumber: null });
    } else if (line.startsWith("@@")) {
      const match = line.match(/@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@/);
      if (match) {
        oldLine = parseInt(match[1], 10);
        newLine = parseInt(match[2], 10);
      }
      result.push({ type: "hunk-header", content: line, oldLineNumber: null, newLineNumber: null });
    } else if (line.startsWith("+")) {
      result.push({
        type: "added",
        content: line.slice(1),
        oldLineNumber: null,
        newLineNumber: newLine++,
      });
    } else if (line.startsWith("-")) {
      result.push({
        type: "removed",
        content: line.slice(1),
        oldLineNumber: oldLine++,
        newLineNumber: null,
      });
    } else if (line.startsWith(" ")) {
      result.push({
        type: "context",
        content: line.slice(1),
        oldLineNumber: oldLine++,
        newLineNumber: newLine++,
      });
    } else if (line === "\\ No newline at end of file") {
      result.push({ type: "no-newline", content: line, oldLineNumber: null, newLineNumber: null });
    }
    // Skip empty trailing lines
  }

  return result;
}

const EXTENSION_MAP: Record<string, string> = {
  ts: "typescript",
  tsx: "typescript",
  js: "javascript",
  jsx: "javascript",
  rs: "rust",
  py: "python",
  svelte: "xml",
  css: "css",
  scss: "scss",
  less: "less",
  html: "html",
  json: "json",
  md: "markdown",
  toml: "ini",
  yaml: "yaml",
  yml: "yaml",
  sh: "bash",
  bash: "bash",
  go: "go",
  java: "java",
  cpp: "cpp",
  c: "c",
  rb: "ruby",
  php: "php",
  sql: "sql",
  kt: "kotlin",
  swift: "swift",
  cs: "csharp",
  r: "r",
  lua: "lua",
  xml: "xml",
};

export function detectLanguage(filePath: string): string {
  const ext = filePath.split(".").pop()?.toLowerCase() ?? "";
  return EXTENSION_MAP[ext] ?? "plaintext";
}