use once_cell::sync::Lazy;
use regex::Regex;
use serde::{Deserialize, Serialize};

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PiiMatch {
    pub entity_type: String,
    pub original: String,
    pub placeholder: String,
    pub start: usize,
    pub end: usize,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RedactionResult {
    pub redacted_text: String,
    pub pii_map: Vec<PiiMatch>,
}

static PATTERNS: Lazy<Vec<(Regex, &'static str)>> = Lazy::new(compile_patterns);

fn compile_patterns() -> Vec<(Regex, &'static str)> {
    let mut patterns = Vec::new();
    for (pattern, label) in [
        (r"\b(?:Dr\.|Dr|Professor|Prof\.)\s+[A-Z][a-z]+\b", "PROVIDER_NAME"),
        (r"\b(?:Patient|Pt\.|Mr\.|Mrs\.|Ms\.)\s+[A-Z][a-z]+(?:\s+[A-Z][a-z]+)+\b", "PERSON_NAME"),
        (r"\b[A-Z][a-z]+(?:\s+[A-Z][a-z]+)+\b", "PERSON_NAME"),
        (r"\b\d{1,2}/\d{1,2}/\d{2,4}\b", "DATE"),
        (r"\b\d{4}-\d{2}-\d{2}\b", "DATE"),
        (r"\b\d{3}-\d{2}-\d{4}\b", "SSN"),
        (r"\bMRN[:\s-]*[A-Z0-9-]{3,}\b", "MRN"),
        (r"\b\d{10}\b", "PHONE"),
        (r"\b\+?\d[\d\s().-]{7,}\b", "PHONE"),
        (r"\b[A-Z]{2}\d{2}\s?\d{2}\s?\d{2}\s?\d\b", "NHS_NUMBER"),
        (r"\b\d{2,3}\s?(?:years?|yo|yrs?)\b", "AGE"),
        (r"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b", "EMAIL"),
        (r"\b(?:insurance|member|policy)\s*(?:id|number|#)?\s*[:=]?\s*[A-Z0-9-]{5,}\b", "INSURANCE_ID"),
        (r"\b(?:\d{1,3}\s)?[A-Za-z]+\s(?:Street|St\.|Road|Rd\.|Avenue|Ave\.|Boulevard|Blvd\.|Lane|Ln\.)\b", "ADDRESS"),
    ] {
        if let Ok(re) = Regex::new(pattern) {
            patterns.push((re, label));
        }
    }
    patterns
}

pub fn redact_pii(raw_text: &str) -> RedactionResult {
    let mut spans: Vec<(usize, usize, &'static str, String)> = Vec::new();

    for (re, label) in PATTERNS.iter() {
        for mat in re.find_iter(raw_text) {
            spans.push((mat.start(), mat.end(), *label, mat.as_str().to_string()));
        }
    }

    spans.sort_by(|a, b| a.0.cmp(&b.0).then_with(|| (b.1 - b.0).cmp(&(a.1 - a.0))));

    let mut selected: Vec<(usize, usize, &'static str, String)> = Vec::new();
    let mut cursor = 0usize;
    for span in spans {
        if span.0 >= cursor {
            cursor = span.1;
            selected.push(span);
        }
    }

    let mut counts = std::collections::HashMap::<&'static str, usize>::new();
    let mut redacted = String::with_capacity(raw_text.len() + 64);
    let mut pii_map = Vec::with_capacity(selected.len());
    let mut index = 0usize;

    for (start, end, label, original) in selected {
        if start > index {
            redacted.push_str(&raw_text[index..start]);
        }
        let count = counts.entry(label).or_insert(0);
        *count += 1;
        let placeholder = format!("[{}_{}]", label, count);
        redacted.push_str(&placeholder);
        pii_map.push(PiiMatch {
            entity_type: label.to_string(),
            original,
            placeholder,
            start,
            end,
        });
        index = end;
    }

    if index < raw_text.len() {
        redacted.push_str(&raw_text[index..]);
    }

    RedactionResult { redacted_text: redacted, pii_map }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn redaction_replaces_sensitive_text() {
        let input = "Patient John Smith, 45 yo, MRN 847291A, phone 5551234567, SSN 123-45-6789.";
        let result = redact_pii(input);
        assert!(!result.redacted_text.contains("John Smith"));
        assert!(!result.redacted_text.contains("5551234567"));
        assert!(result.redacted_text.contains("[PERSON_NAME_1]") || result.redacted_text.contains("[PERSON_NAME_2]"));
        assert!(result.redacted_text.contains("[PHONE_1]"));
        assert!(result.redacted_text.contains("[SSN_1]"));
    }
}