"""Parser for Prometheus text format metrics."""

import re
from typing import Dict, List, Any, Optional
from dataclasses import dataclass


@dataclass
class MetricSample:
    """A single metric sample with labels and value."""
    name: str
    labels: Dict[str, str]
    value: float
    timestamp: Optional[float] = None


def parse_prometheus_metrics(text: str) -> Dict[str, List[MetricSample]]:
    """
    Parse Prometheus text format into structured metrics.

    Args:
        text: Raw Prometheus metrics text

    Returns:
        Dictionary mapping metric names to lists of samples
    """
    metrics: Dict[str, List[MetricSample]] = {}

    for line in text.strip().split("\n"):
        line = line.strip()

        # Skip empty lines and comments
        if not line or line.startswith("#"):
            continue

        # Parse metric line
        sample = _parse_metric_line(line)
        if sample:
            if sample.name not in metrics:
                metrics[sample.name] = []
            metrics[sample.name].append(sample)

    return metrics


def _parse_metric_line(line: str) -> Optional[MetricSample]:
    """Parse a single Prometheus metric line."""
    # Pattern: metric_name{label1="value1",label2="value2"} value [timestamp]
    # Or: metric_name value [timestamp]

    # Match with labels
    match = re.match(
        r'^([a-zA-Z_:][a-zA-Z0-9_:]*)\{([^}]*)\}\s+([^\s]+)(?:\s+(\d+))?$',
        line
    )

    if match:
        name = match.group(1)
        labels_str = match.group(2)
        value_str = match.group(3)
        timestamp_str = match.group(4)

        labels = _parse_labels(labels_str)
        value = _parse_value(value_str)
        timestamp = float(timestamp_str) if timestamp_str else None

        return MetricSample(name=name, labels=labels, value=value, timestamp=timestamp)

    # Match without labels
    match = re.match(
        r'^([a-zA-Z_:][a-zA-Z0-9_:]*)\s+([^\s]+)(?:\s+(\d+))?$',
        line
    )

    if match:
        name = match.group(1)
        value_str = match.group(2)
        timestamp_str = match.group(3)

        value = _parse_value(value_str)
        timestamp = float(timestamp_str) if timestamp_str else None

        return MetricSample(name=name, labels={}, value=value, timestamp=timestamp)

    return None


def _parse_labels(labels_str: str) -> Dict[str, str]:
    """Parse label string into dictionary."""
    labels = {}

    # Pattern: key="value"
    for match in re.finditer(r'([a-zA-Z_][a-zA-Z0-9_]*)="([^"]*)"', labels_str):
        labels[match.group(1)] = match.group(2)

    return labels


def _parse_value(value_str: str) -> float:
    """Parse metric value, handling special cases."""
    if value_str.lower() == "nan":
        return float("nan")
    if value_str.lower() == "+inf":
        return float("inf")
    if value_str.lower() == "-inf":
        return float("-inf")
    return float(value_str)


def get_metric_value(
    metrics: Dict[str, List[MetricSample]],
    name: str,
    labels: Optional[Dict[str, str]] = None
) -> Optional[float]:
    """
    Get a specific metric value by name and optional labels.

    Args:
        metrics: Parsed metrics dictionary
        name: Metric name
        labels: Optional label filter

    Returns:
        Metric value or None if not found
    """
    if name not in metrics:
        return None

    for sample in metrics[name]:
        if labels is None:
            return sample.value

        # Check if all specified labels match
        if all(sample.labels.get(k) == v for k, v in labels.items()):
            return sample.value

    return None


def get_histogram_quantile(
    metrics: Dict[str, List[MetricSample]],
    name: str,
    quantile: float,
    labels: Optional[Dict[str, str]] = None
) -> Optional[float]:
    """
    Get histogram quantile value from Prometheus histogram.

    Args:
        metrics: Parsed metrics dictionary
        name: Base metric name (without _bucket suffix)
        quantile: Desired quantile (e.g., 0.95 for P95)
        labels: Optional label filter

    Returns:
        Approximate quantile value or None
    """
    bucket_name = f"{name}_bucket"
    if bucket_name not in metrics:
        return None

    # Get all buckets
    buckets = []
    for sample in metrics[bucket_name]:
        if labels and not all(sample.labels.get(k) == v for k, v in labels.items()):
            continue
        le = sample.labels.get("le")
        if le and le != "+Inf":
            buckets.append((float(le), sample.value))

    if not buckets:
        return None

    # Sort by bucket boundary
    buckets.sort(key=lambda x: x[0])

    # Get total count
    total = buckets[-1][1] if buckets else 0
    if total == 0:
        return None

    # Find bucket containing quantile
    target = quantile * total
    prev_bound = 0
    prev_count = 0

    for bound, count in buckets:
        if count >= target:
            # Linear interpolation within bucket
            fraction = (target - prev_count) / (count - prev_count) if count > prev_count else 0
            return prev_bound + fraction * (bound - prev_bound)
        prev_bound = bound
        prev_count = count

    return buckets[-1][0] if buckets else None