"""
AI-powered patch generation and application utilities.

This module ports the proven bash hook logic into Python so the orchestration
pipeline can be tested and extended more easily.
"""
from __future__ import annotations

import os
import re
import shutil
import subprocess
import tempfile
from dataclasses import dataclass
from pathlib import Path

from automation.config import RulesConfig


class PatchGenerationError(RuntimeError):
    pass


@dataclass
class ModelConfig:
    """Configuration for invoking the AI model command."""
    # The command to execute the AI model. Defaults to 'claude -p' or CDEV_AI_COMMAND env var.
    command: str = os.environ.get("CDEV_AI_COMMAND", "claude -p")


def generate_output(
    repo_root: Path,
    rules: RulesConfig,
    model: ModelConfig,
    source_rel: Path,
    output_rel: Path,
    instruction: str,
) -> None:
    """
    Generates or refreshes an output artifact using AI, based on staged changes
    and a given instruction. The process involves:
    1. Ensuring the output file is known to Git (for new files).
    2. Gathering relevant context (source diff, source content, existing output content).
    3. Building a prompt for the AI model.
    4. Calling the AI model to generate a unified diff.
    5. Extracting and sanitizing the generated patch.
    6. Applying the patch to the repository.

    Args:
        repo_root: The root directory of the Git repository.
        rules: The RulesConfig object for resolving template variables and paths.
        model: The ModelConfig object specifying the AI command.
        source_rel: The path to the source file relative to repo_root.
        output_rel: The path to the output file relative to repo_root.
        instruction: The instruction for the AI model.

    Raises:
        PatchGenerationError: If AI output is empty or patch application fails.
    """
    repo_root = repo_root.resolve()
    # Ensure paths are relative to the repository root for consistent Git operations.
    source_rel = source_rel
    output_rel = output_rel

    # Ensure the parent directory for the output file exists.
    (repo_root / output_rel).parent.mkdir(parents=True, exist_ok=True)

    # Ensure Git knows about the output file, especially if it's new.
    # This allows 'git apply --index' to work correctly for new files.
    ensure_intent_to_add(repo_root, output_rel)

    # Gather context for the AI prompt.
    source_diff = git_diff_cached(repo_root, source_rel)
    source_content = git_show_cached(repo_root, source_rel)
    # Get the current content of the output file (pre-image) and its Git hash.
    output_preimage, output_hash = read_output_preimage(repo_root, output_rel)

    # Build the comprehensive prompt for the AI model.
    prompt = build_prompt(
        source_rel=source_rel,
        output_rel=output_rel,
        source_diff=source_diff,
        source_content=source_content,
        output_content=output_preimage,
        instruction=instruction,
    )

    # Call the AI model and get its raw output.
    raw_patch = call_model(model, prompt, cwd=repo_root)

    # Use a temporary directory for storing intermediate patch files for debugging.
    with tempfile.TemporaryDirectory(prefix="cdev-patch-") as tmpdir_str:
        tmpdir = Path(tmpdir_str)
        raw_path = tmpdir / "raw.out"
        clean_path = tmpdir / "clean.diff"
        sanitized_path = tmpdir / "sanitized.diff"

        raw_path.write_text(raw_patch, encoding="utf-8")

        try:
            # Extract the actual diff content from the AI's raw output, using markers.
            extracted = extract_patch_with_markers(raw_path.read_text(encoding="utf-8"))
            clean_path.write_text(extracted, encoding="utf-8")
        except PatchGenerationError as e:
            # If extraction fails, save debug artifacts and re-raise the error.
            save_debug_artifacts(repo_root, output_rel, raw_path, None, None, None)
            raise

        # Sanitize the extracted patch to remove unwanted git metadata lines.
        sanitized = sanitize_unified_patch(clean_path.read_text(encoding="utf-8"))
        # Special handling for new files: ensure 'new file mode' is present if '--- /dev/null' is.
        if "--- /dev/null" in sanitized and "new file mode" not in sanitized:
            sanitized = sanitized.replace("--- /dev/null", "new file mode 100644\n--- /dev/null", 1)
        sanitized_path.write_text(sanitized, encoding="utf-8")

        # Determine the patch level. -p1 is common for diffs generated from repo root.
        patch_level = "-p1"
        final_patch_path = sanitized_path

        # Save all intermediate patch files for debugging purposes.
        save_debug_artifacts(repo_root, output_rel, raw_path, clean_path, sanitized_path, final_patch_path)

        # Check if the final patch is empty after sanitization.
        # This is normal when AI determines no changes are needed (e.g., gated outputs)
        if not final_patch_path.read_text(encoding="utf-8").strip():
            # Empty patch is not an error - AI decided not to make changes
            # Common cases:
            #   - implementation_gate_writer when status != READY_FOR_IMPLEMENTATION
            #   - AI determines output is already correct
            return  # Skip silently

        # Apply the generated patch to the Git repository.
        apply_patch(repo_root, final_patch_path, patch_level, output_rel)


def ensure_intent_to_add(repo_root: Path, rel_path: Path) -> None:
    """
    Ensures Git has an 'intent to add' for a new file, so 'git apply --index'
    can create it correctly. If the file is already tracked, do nothing.

    Args:
        repo_root: The root directory of the Git repository.
        rel_path: The path to the file relative to repo_root.
    """
    if git_ls_files(repo_root, rel_path):
        # File is already tracked by Git, no need for 'intent to add'.
        return
    # Use 'git add -N' to record the intent to add a new file without staging its content.
    run(["git", "add", "-N", "--", rel_path.as_posix()], cwd=repo_root, check=False)


def git_ls_files(repo_root: Path, rel_path: Path) -> bool:
    """
    Checks if a file is tracked by Git.

    Args:
        repo_root: The root directory of the Git repository.
        rel_path: The path to the file relative to repo_root.

    Returns:
        True if the file is tracked, False otherwise.
    """
    result = run(
        ["git", "ls-files", "--error-unmatch", "--", rel_path.as_posix()],
        cwd=repo_root,
        check=False,
    )
    return result.returncode == 0


def git_diff_cached(repo_root: Path, rel_path: Path) -> str:
    """
    Retrieves the cached diff (staged changes) for a specific file.

    Args:
        repo_root: The root directory of the Git repository.
        rel_path: The path to the file relative to repo_root.

    Returns:
        The unified diff string for the staged changes of the file.
    """
    result = run(
        ["git", "diff", "--cached", "--unified=2", "--", rel_path.as_posix()],
        cwd=repo_root,
        check=False,
    )
    return result.stdout


def git_show_cached(repo_root: Path, rel_path: Path) -> str:
    """
    Retrieves the content of a file as it exists in the Git index (staged version).
    If the file is not in the index, it attempts to read it from the working tree.

    Args:
        repo_root: The root directory of the Git repository.
        rel_path: The path to the file relative to repo_root.

    Returns:
        The content of the file as a string.
    """
    # Try to get content from the Git index.
    result = run(
        ["git", "show", f":{rel_path.as_posix()}"],
        cwd=repo_root,
        check=False,
    )
    if result.returncode == 0:
        return result.stdout
    # If not in index, try to read from the working tree (e.g., for new files not yet staged).
    file_path = repo_root / rel_path
    if file_path.exists():
        return file_path.read_text(encoding="utf-8")
    return ""


def read_output_preimage(repo_root: Path, rel_path: Path) -> tuple[str, str]:
    """
    Reads the current content and Git blob hash of the output file.
    This is used as the 'pre-image' for generating the AI patch.
    It first checks the Git index, then the working tree.

    Args:
        repo_root: The root directory of the Git repository.
        rel_path: The path to the output file relative to repo_root.

    Returns:
        A tuple containing (content_string, blob_hash_string).
        Returns empty string and default hash if the file does not exist.
    """
    # Check if the file is staged and get its blob hash.
    staged_hash_result = run(
        ["git", "ls-files", "--stage", "--", rel_path.as_posix()],
        cwd=repo_root,
        check=False,
    )
    blob_hash = "0" * 40  # Default hash if file is new or untracked.
    if staged_hash_result.returncode == 0 and staged_hash_result.stdout.strip():
        # If staged, get its content from the index.
        show_result = run(["git", "show", f":{rel_path.as_posix()}"], cwd=repo_root, check=False)
        content = show_result.stdout if show_result.returncode == 0 else ""
        # Extract the blob hash from 'git ls-files --stage' output.
        # The output format is: <mode> <hash> <stage>	<file>
        first_field = staged_hash_result.stdout.strip().split()[1]
        blob_hash = first_field
        return content, blob_hash

    # If not staged, try to read from the working tree.
    file_path = repo_root / rel_path
    if file_path.exists():
        content = file_path.read_text(encoding="utf-8")
        # Calculate blob hash for working tree file.
        blob_hash = run(
            ["git", "hash-object", file_path.as_posix()],
            cwd=repo_root,
            check=False,
        ).stdout.strip() or blob_hash
        return content, blob_hash

    # File does not exist.
    return "", blob_hash


# This template defines the structure and content of the prompt sent to the AI model.
# It includes context about the source file, current output, and specific instructions.
PROMPT_TEMPLATE = """You are assisting with automated artifact generation during a git commit.

SOURCE FILE: {source_path}
OUTPUT FILE: {output_path}

=== SOURCE FILE CHANGES (staged) ===
{source_diff}

=== SOURCE FILE CONTENT (staged) ===
{source_content}

=== CURRENT OUTPUT CONTENT (use this as the preimage) ===
{output_content}

=== GENERATION INSTRUCTIONS ===
{instruction}

=== OUTPUT FORMAT REQUIREMENTS ===
Wrap your unified diff with these exact markers:
<<<AI_DIFF_START>>>
[your diff here]
<<<AI_DIFF_END>>>

For NEW FILES, use these headers exactly:
--- /dev/null
+++ b/{output_path}

=== TASK ===
Create or update {output_path} according to the instructions above.

Output ONLY a unified diff patch in proper git format:
- Use format: diff --git a/{output_path} b/{output_path}
- (Optional) You may include an "index ..." line, but it will be ignored
- Include complete hunks with context lines
- No markdown fences, no explanations, just the patch

Start with: <<<AI_DIFF_START>>>
End with: <<<AI_DIFF_END>>>

Only include the diff between these markers.
If the output file doesn't exist, create it from scratch in the patch.
"""


def build_prompt(
    source_rel: Path,
    output_rel: Path,
    source_diff: str,
    source_content: str,
    output_content: str,
    instruction: str,
) -> str:
    """
    Constructs the full prompt string for the AI model by formatting the
    PROMPT_TEMPLATE with the provided context and instructions.

    Args:
        source_rel: Relative path to the source file.
        output_rel: Relative path to the output file.
        source_diff: Git diff of the staged source file.
        source_content: Content of the staged source file.
        output_content: Current content of the output file (pre-image).
        instruction: Specific instructions for the AI.

    Returns:
        The formatted prompt string.
    """
    return PROMPT_TEMPLATE.format(
        source_path=source_rel.as_posix(),
        output_path=output_rel.as_posix(),
        source_diff=source_diff.strip(),
        source_content=source_content.strip(),
        output_content=output_content.strip() or "(empty)", # Indicate if output content is empty.
        instruction=instruction.strip(),
    )


def call_model(model: ModelConfig, prompt: str, cwd: Path) -> str:
    """
    Invokes the AI model command with the given prompt and captures its output.

    Args:
        model: The ModelConfig object containing the AI command.
        prompt: The input prompt string for the AI model.
        cwd: The current working directory for executing the command.

    Returns:
        The raw string output from the AI model.

    Raises:
        PatchGenerationError: If the AI command fails or returns an API error.
    """
    command = model.command
    result = subprocess.run(
        command,
        input=prompt,
        text=True,
        capture_output=True,
        cwd=str(cwd),
        shell=True, # Use shell=True to allow command to be a string with arguments.
    )
    # The Claude CLI (and potentially others) might return a non-zero exit code
    # even on successful responses if there are warnings or specific API behaviors.
    # We prioritize stdout content over return code for initial check.
    if result.stdout.strip():
        # Check for specific API error messages in the output.
        if "API Error:" in result.stdout and "Overloaded" in result.stdout:
            raise PatchGenerationError("Claude API is overloaded (500 error) - please retry later")
        return result.stdout

    # If stdout is empty, then a non-zero return code indicates a true failure.
    if result.returncode != 0:
        raise PatchGenerationError(f"AI command failed ({result.returncode}): {result.stderr.strip()}")
    return result.stdout


def extract_patch_with_markers(raw_output: str) -> str:
    """
    Extracts the unified diff string from the AI model's raw output.
    It looks for specific start and end markers (<<<AI_DIFF_START>>> / <<<AI_DIFF_END>>>).
    If markers are not found, it attempts to find the first 'diff --git' line.

    Args:
        raw_output: The complete raw string output from the AI model.

    Returns:
        The extracted unified diff string.

    Raises:
        PatchGenerationError: If no valid diff markers or diff header are found.
    """
    start_marker = "<<<AI_DIFF_START>>>"
    end_marker = "<<<AI_DIFF_END>>>"
    if start_marker in raw_output:
        start_idx = raw_output.index(start_marker) + len(start_marker)
        end_idx = raw_output.find(end_marker, start_idx)
        if end_idx == -1:
            raise PatchGenerationError("AI output missing end marker")
        return raw_output[start_idx:end_idx].strip()

    # Fallback: if markers are not present, try to find a 'diff --git' header.
    match = re.search(r"^diff --git .*", raw_output, re.MULTILINE | re.DOTALL)
    if match:
        return raw_output[match.start() :].strip()
    raise PatchGenerationError("AI output did not contain a diff")


def sanitize_unified_patch(patch: str) -> str:
    """
    Cleans up a unified diff patch by removing specific Git metadata lines
    that can interfere with 'git apply'.

    Args:
        patch: The raw unified diff string.

    Returns:
        The sanitized diff string, or empty string if no diff header found.
        An empty result indicates the AI chose not to make changes (e.g., gated output).
    """
    lines = patch.replace("\r", "").splitlines()
    cleaned = []
    for line in lines:
        # Skip lines that are typically added by 'git diff' but not needed for 'git apply'.
        if line.startswith("index ") or line.startswith("similarity index ") or line.startswith("rename from ") or line.startswith("rename to "):
            continue
        cleaned.append(line)
    text = "\n".join(cleaned)

    # Look for the 'diff --git' header
    diff_start = text.find("diff --git")
    if diff_start == -1:
        # No diff header means AI chose not to generate a patch
        # This is normal for gated outputs or when AI determines no changes needed
        return ""
    return text[diff_start:] + "\n"


def rewrite_patch_for_p0(patch: str) -> str:
    """
    Rewrites a unified diff patch to be compatible with 'git apply -p0'.
    This adjusts file paths in the diff headers to remove the 'a/' and 'b/' prefixes.

    Args:
        patch: The unified diff string.

    Returns:
        The rewritten diff string.
    """
    rewritten_lines = []
    diff_header_re = re.compile(r"^diff --git a/(.+?) b/(.+)$")
    for line in patch.splitlines():
        if line.startswith("diff --git"):
            m = diff_header_re.match(line)
            if m:
                # Remove 'a/' and 'b/' prefixes for -p0.
                rewritten_lines.append(f"diff --git {m.group(1)} {m.group(2)}")
            else:
                rewritten_lines.append(line)
        elif line.startswith("+++ "):
            # Remove '+++ b/' prefix.
            rewritten_lines.append(line.replace("+++ b/", "+++ ", 1))
        elif line.startswith("--- "):
            # Remove '--- a/' prefix, unless it's '--- /dev/null' for new files.
            if line != "--- /dev/null":
                rewritten_lines.append(line.replace("--- a/", "--- ", 1))
            else:
                rewritten_lines.append(line)
        else:
            rewritten_lines.append(line)
    return "\n".join(rewritten_lines) + "\n"


def save_debug_artifacts(
    repo_root: Path,
    output_rel: Path,
    raw_path: Path | None,
    clean_path: Path | None,
    sanitized_path: Path | None,
    final_path: Path | None,
) -> None:
    """
    Saves various stages of the generated patch to a debug directory within .git.
    This is crucial for debugging AI model outputs and patch application issues.

    Args:
        repo_root: The root directory of the Git repository.
        output_rel: The relative path of the output file being processed.
        raw_path: Path to the raw AI output file.
        clean_path: Path to the extracted diff file.
        sanitized_path: Path to the sanitized diff file.
        final_path: Path to the final patch file that was attempted to be applied.
    """
    debug_dir = repo_root / ".git" / "ai-rules-debug"
    debug_dir.mkdir(parents=True, exist_ok=True)
    # Create a unique identifier for the debug artifacts.
    identifier = f"{output_rel.as_posix().replace('/', '_')}-{os.getpid()}"
    if raw_path and raw_path.exists():
        shutil.copy(raw_path, debug_dir / f"{identifier}.raw.out")
    if clean_path and clean_path.exists():
        shutil.copy(clean_path, debug_dir / f"{identifier}.clean.diff")
    if sanitized_path and sanitized_path.exists():
        shutil.copy(sanitized_path, debug_dir / f"{identifier}.sanitized.diff")
    if final_path and final_path.exists():
        shutil.copy(final_path, debug_dir / f"{identifier}.final.diff")


def apply_patch(repo_root: Path, patch_file: Path, patch_level: str, output_rel: Path) -> None:
    """
    Applies a generated patch to the Git repository, attempting a 3-way merge
    first and falling back to a strict apply if necessary.

    Args:
        repo_root: The root directory of the Git repository.
        patch_file: The path to the patch file to apply.
        patch_level: The patch level (e.g., '-p1').
        output_rel: The relative path of the file the patch is intended for.

    Raises:
        PatchGenerationError: If both 3-way and strict patch application fail.
    """
    absolute_patch = patch_file.resolve()
    
    # First, try a dry-run check with --check to see if the patch applies cleanly.
    check_args = ["git", "apply", patch_level, "--index", "--check", absolute_patch.as_posix()]
    if run(check_args, cwd=repo_root, check=False).returncode == 0:
        # If it applies cleanly, perform the actual apply.
        run(["git", "apply", patch_level, "--index", absolute_patch.as_posix()], cwd=repo_root)
        return

    # If direct apply --check fails, try 3-way merge with a check first.
    three_way_check_args = ["git", "apply", patch_level, "--index", "--3way", "--recount", "--whitespace=nowarn", absolute_patch.as_posix()]
    if run(three_way_check_args + ["--check"], cwd=repo_root, check=False).returncode == 0:
        # If 3-way check passes, perform the actual 3-way apply.
        run(three_way_check_args, cwd=repo_root)
        return
    
    # Special handling for new files: if the patch creates a new file ('--- /dev/null'),
    # a simple 'git apply' might work, followed by 'git add'.
    text = patch_file.read_text(encoding="utf-8")
    if "--- /dev/null" in text:
        # Try applying without --index and then explicitly add the file.
        if run(["git", "apply", patch_level, absolute_patch.as_posix()], cwd=repo_root, check=False).returncode == 0:
            run(["git", "add", "--", output_rel.as_posix()], cwd=repo_root)
            return

    # If all attempts fail, raise an error.
    raise PatchGenerationError("Failed to apply patch (strict and 3-way both failed)")


def run(args: list[str], cwd: Path, check: bool = True) -> subprocess.CompletedProcess[str]:
    result = subprocess.run(
        args,
        cwd=str(cwd),
        text=True,
        capture_output=True,
    )
    if check and result.returncode != 0:
        raise PatchGenerationError(f"Command {' '.join(args)} failed: {result.stderr.strip()}")
    return result