"""
code_chunker.py — Split source files into semantically meaningful chunks.

Two strategies depending on file type:

1. AST chunking (Python only)
   Parse the file into an Abstract Syntax Tree. Extract each top-level
   function and class as its own chunk. Classes include all their methods.

   Why: A function is the natural unit of code — it has a name, inputs,
   outputs, and a single responsibility. Splitting mid-function loses context.

2. Character-window chunking (everything else)
   Split by character count with overlap — same approach used for prose.
   Works for markdown, YAML, config files, and languages without AST support.

   Why not AST for all languages? Python's `ast` module is in the stdlib.
   Multi-language AST (tree-sitter) adds complexity. For a learning project,
   Python AST + fallback covers 80% of cases cleanly.

Chunk shape (returned by both strategies):
  {
    "text":          str,        # the actual code/text content
    "language":      str,        # "python", "typescript", etc.
    "filepath":      str,        # "src/auth/middleware.py"
    "chunk_type":    str,        # "function", "class", "module", "text"
    "name":          str,        # function/class name (or "" for text chunks)
    "start_line":    int,        # 1-indexed line where chunk starts
    "end_line":      int,        # 1-indexed line where chunk ends
    "calls":         list[str],  # names called by this function (AST only)
    "imports":       list[str],  # imported module names (module chunks only; [] elsewhere)
    "base_classes":  list[str],  # base class names (class chunks only; [] elsewhere)
  }

The `calls` field is used to build the Code Knowledge Graph — an interactive
D3 visualization of how functions call each other across files. It's extracted
by the CallExtractor visitor which walks ast.Call nodes inside each function body.

The `imports` field enables file-level dependency edges in the Architecture diagram.
It records every module name imported at the top of the file (both "import X" and
"from X import Y" forms), extracted from the module-level chunk only.

The `base_classes` field enables real inheritance edges in the Class Hierarchy diagram.
It records the names of parent classes from "class Foo(Bar, Baz):" declarations,
extracted directly from each ClassDef node.
"""

import ast
import textwrap
from pathlib import Path


# ── Call extractor ────────────────────────────────────────────────────────────

class _CallExtractor(ast.NodeVisitor):
    """
    AST visitor that collects the names of all functions/methods called
    inside a function or class body.

    How ast.NodeVisitor works:
      - Subclass it and define visit_<NodeType> methods.
      - Call self.visit(node) to start traversal from any node.
      - self.generic_visit(node) continues the walk into child nodes.

    Two kinds of calls in Python's AST:
      ast.Name:      direct calls — foo(), bar()
                     → node.func is an ast.Name, name is node.func.id
      ast.Attribute: method/attr calls — self.foo(), obj.method()
                     → node.func is an ast.Attribute, name is node.func.attr

    We collect only the leaf name (not the full dotted path) because we match
    against function names in the index, not fully-qualified paths.
    """
    def __init__(self):
        self.calls: list[str] = []

    def visit_Call(self, node: ast.Call):
        if isinstance(node.func, ast.Attribute):
            self.calls.append(node.func.attr)          # self.embed() → "embed"
        elif isinstance(node.func, ast.Name):
            self.calls.append(node.func.id)            # embed() → "embed"
        self.generic_visit(node)                       # recurse into nested calls


def _extract_calls(node: ast.AST) -> list[str]:
    """Extract unique called names from an AST node (function or class)."""
    extractor = _CallExtractor()
    extractor.visit(node)
    # Deduplicate while preserving order; filter builtins that add noise
    _NOISE = {"print", "len", "range", "isinstance", "str", "int", "list",
               "dict", "set", "tuple", "super", "hasattr", "getattr", "setattr",
               "append", "extend", "format", "join", "split", "strip", "get",
               "items", "keys", "values", "zip", "enumerate", "map", "filter"}
    seen = set()
    result = []
    for name in extractor.calls:
        if name not in seen and name not in _NOISE:
            seen.add(name)
            result.append(name)
    return result


def _extract_imports(tree: ast.AST) -> list[str]:
    """
    Extract all imported module names from a parsed AST.
    Used to build file-level dependency edges for the Architecture diagram.

    Handles both forms:
      import os                  → ["os"]
      from micrograd.engine import Value → ["micrograd.engine"]
      from . import engine       → [".engine"] (relative, handled by caller)
    """
    imports = []
    for node in ast.walk(tree):
        if isinstance(node, ast.Import):
            for alias in node.names:
                imports.append(alias.name)
        elif isinstance(node, ast.ImportFrom):
            module = node.module or ""
            level  = node.level or 0   # number of dots for relative imports
            if level > 0:
                # Relative import — prefix with dots so caller can resolve them
                imports.append("." * level + module)
            elif module:
                imports.append(module)
    return list(dict.fromkeys(imports))  # deduplicate, preserve order


def _extract_base_classes(node: ast.ClassDef) -> list[str]:
    """
    Extract base class names from a ClassDef node.
    Used to build real inheritance edges for the Class Hierarchy diagram.

    Example: class MLP(Module): → ["Module"]
    Handles direct names (ast.Name) and dotted paths (ast.Attribute).
    """
    bases = []
    for base in node.bases:
        if isinstance(base, ast.Name):
            bases.append(base.id)
        elif isinstance(base, ast.Attribute):
            bases.append(base.attr)   # e.g. nn.Module → "Module"
    # Filter trivial bases that add noise
    return [b for b in bases if b not in ("object", "ABC", "Enum")]


# ── AST Chunking (Python) ─────────────────────────────────────────────────────

def chunk_python(content: str, filepath: str) -> list[dict]:
    """
    Parse Python source and extract functions and classes as individual chunks.

    Algorithm:
      1. Parse content into an AST with ast.parse()
      2. Walk top-level nodes looking for FunctionDef, AsyncFunctionDef, ClassDef
      3. For each, extract the source lines using node.lineno / node.end_lineno
      4. If a node is too large (>60 lines), split it further into sub-chunks

    What about module-level code (imports, constants, global statements)?
    We collect it as a single "module" chunk. It's useful context for
    understanding what a file imports and configures.
    """
    try:
        tree = ast.parse(content)
    except SyntaxError as e:
        # Fall back to character-window if the file can't be parsed
        # (e.g. Python 2 syntax, encoding issues)
        print(f"  [ast parse failed for {filepath}: {e}] → fallback chunking")
        return chunk_by_window(content, filepath, language="python")

    lines = content.splitlines()
    chunks = []

    # Collect line numbers of all top-level definitions
    definition_lines = set()
    for node in ast.walk(tree):
        if isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
            if hasattr(node, "lineno"):
                for ln in range(node.lineno, (node.end_lineno or node.lineno) + 1):
                    definition_lines.add(ln)

    # ── Module-level chunk ────────────────────────────────────────────────────
    # Lines not covered by any function/class (imports, constants, etc.)
    module_lines = [
        line for i, line in enumerate(lines, 1)
        if i not in definition_lines
    ]
    module_text = "\n".join(module_lines).strip()
    if module_text:
        chunks.append({
            "text":         f"# {filepath}\n{module_text}",
            "language":     "python",
            "filepath":     filepath,
            "chunk_type":   "module",
            "name":         "",
            "start_line":   1,
            "end_line":     len(lines),
            "calls":        [],
            "imports":      _extract_imports(tree),
            "base_classes": [],
        })

    # ── Function and class chunks ─────────────────────────────────────────────
    for node in tree.body:
        if not isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
            continue

        start = node.lineno
        end   = node.end_lineno or node.lineno
        node_lines = lines[start - 1 : end]
        node_text  = "\n".join(node_lines)

        chunk_type = "class" if isinstance(node, ast.ClassDef) else "function"
        name = node.name

        # If the chunk is large, split into sub-chunks by method (for classes)
        # or by logical blocks (for large functions)
        if len(node_lines) > 80 and chunk_type == "class":
            sub_chunks = _split_class(node, lines, filepath)
            chunks.extend(sub_chunks)
        else:
            chunks.append({
                "text":         f"# {filepath}\n{node_text}",
                "language":     "python",
                "filepath":     filepath,
                "chunk_type":   chunk_type,
                "name":         name,
                "start_line":   start,
                "end_line":     end,
                "calls":        _extract_calls(node),
                "imports":      [],
                "base_classes": _extract_base_classes(node) if isinstance(node, ast.ClassDef) else [],
            })

    return chunks if chunks else chunk_by_window(content, filepath, language="python")


def _split_class(class_node: ast.ClassDef, lines: list[str], filepath: str) -> list[dict]:
    """
    Split a large class into per-method chunks.

    Each method gets the class signature as a header so the LLM knows
    which class the method belongs to:

      class MyClass:
          def __init__(self): ...
          ↓
      Chunk: "class MyClass:\n    def __init__(self): ..."
    """
    chunks = []
    class_start = class_node.lineno
    class_header = lines[class_start - 1]   # "class MyClass(Base):"

    for node in class_node.body:
        if not isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef)):
            continue
        start = node.lineno
        end   = node.end_lineno or node.lineno
        method_lines = lines[start - 1 : end]
        # Indent method lines if not already indented (should be)
        method_text  = "\n".join(method_lines)

        chunks.append({
            "text":         f"# {filepath}\n{class_header}\n{method_text}",
            "language":     "python",
            "filepath":     filepath,
            "chunk_type":   "function",
            "name":         f"{class_node.name}.{node.name}",
            "start_line":   start,
            "end_line":     end,
            "calls":        _extract_calls(node),
            "imports":      [],
            "base_classes": [],
        })

    # Also include the class-level code (class variables, docstring)
    class_end = class_node.end_lineno or class_node.lineno
    class_text = "\n".join(lines[class_start - 1 : class_end])
    chunks.insert(0, {
        "text":         f"# {filepath}\n{class_text[:800]}",   # truncated overview
        "language":     "python",
        "filepath":     filepath,
        "chunk_type":   "class",
        "name":         class_node.name,
        "start_line":   class_start,
        "end_line":     class_end,
        "calls":        _extract_calls(class_node),
        "imports":      [],
        "base_classes": _extract_base_classes(class_node),
    })

    return chunks


# ── Character-window chunking (fallback) ──────────────────────────────────────

def chunk_by_window(
    content:   str,
    filepath:  str,
    language:  str = "text",
    chunk_size:  int = 1000,
    chunk_overlap: int = 200,
) -> list[dict]:
    """
    Split text into overlapping fixed-size character windows.

    Used for:
      - Markdown documentation (.md, .rst)
      - Config files (.yaml, .toml, .json)
      - Languages without AST support (TypeScript, Go, Rust, etc.)
      - Python files that failed to parse

    The overlap ensures that a concept spanning a chunk boundary isn't lost.
    With overlap=200, the last 200 chars of chunk N are the first 200 chars
    of chunk N+1.
    """
    if not content.strip():
        return []

    lines  = content.splitlines()
    chunks = []
    start  = 0

    while start < len(content):
        end  = min(start + chunk_size, len(content))
        text = content[start:end]

        # Find approximate start/end line numbers for this character range
        start_line = content[:start].count("\n") + 1
        end_line   = content[:end].count("\n") + 1

        chunks.append({
            "text":         f"# {filepath}\n{text}",
            "language":     language,
            "filepath":     filepath,
            "chunk_type":   "text",
            "name":         "",
            "start_line":   start_line,
            "end_line":     end_line,
            "calls":        [],
            "imports":      [],
            "base_classes": [],
        })

        if end == len(content):
            break
        start = end - chunk_overlap

    return chunks


# ── Main entry point ──────────────────────────────────────────────────────────

def chunk_file(file: dict) -> list[dict]:
    """
    Chunk a single file dict (as returned by repo_fetcher).

    Args:
        file: {"path": str, "content": str, "size": int, "repo": str}

    Returns:
        List of chunk dicts with text + metadata.
    """
    from ingestion.file_filter import language_from_path

    filepath = file.get("path") or file.get("filepath", "")
    content  = file["content"]
    language = language_from_path(filepath)
    repo     = file.get("repo", "")

    if language == "python":
        chunks = chunk_python(content, filepath)
    else:
        chunks = chunk_by_window(content, filepath, language=language)

    # Attach repo to every chunk
    for chunk in chunks:
        chunk["repo"] = repo

    return chunks


def chunk_files(files: list[dict]) -> list[dict]:
    """Chunk all files and return a flat list of all chunks."""
    all_chunks = []
    for file in files:
        file_chunks = chunk_file(file)
        all_chunks.extend(file_chunks)
        print(f"  {file.get('path') or file.get('filepath', '?')} → {len(file_chunks)} chunks")
    print(f"Total: {len(all_chunks)} chunks from {len(files)} files")
    return all_chunks