use std::time::Duration;

use async_trait::async_trait;
use reqwest::header::HeaderMap;
use serde_json::json;

use crate::text::take_prefix_chars;
use crate::tools::traits::{Tool, ToolResult};

pub struct WebFetchTool {
    max_response_size: usize,
    timeout_secs: u64,
    user_agent: String,
}

impl WebFetchTool {
    pub fn new(max_response_size: usize, timeout_secs: u64) -> Self {
        Self {
            max_response_size,
            timeout_secs,
            user_agent: "Mozilla/5.0 (compatible; Picobot/1.0)".to_string(),
        }
    }

    fn validate_url(&self, url: &str) -> Result<String, String> {
        let url = url.trim();

        if url.is_empty() {
            return Err("URL cannot be empty".to_string());
        }

        if url.chars().any(char::is_whitespace) {
            return Err("URL cannot contain whitespace".to_string());
        }

        if !url.starts_with("http://") && !url.starts_with("https://") {
            return Err("Only http:// and https:// URLs are allowed".to_string());
        }

        let host = extract_host(url)?;

        if is_private_host(&host) {
            return Err(format!("Blocked local/private host: {}", host));
        }

        Ok(url.to_string())
    }

    fn truncate_response(&self, text: &str) -> String {
        if self.max_response_size == 0 {
            return text.to_string();
        }

        if text.chars().count() > self.max_response_size {
            format!(
                "{}\n\n... [Response truncated due to size limit] ...",
                take_prefix_chars(text, self.max_response_size)
            )
        } else {
            text.to_string()
        }
    }

    async fn fetch_content(&self, url: &str) -> Result<String, String> {
        let client = reqwest::Client::builder()
            .timeout(Duration::from_secs(self.timeout_secs))
            .build()
            .map_err(|e| format!("Failed to create HTTP client: {}", e))?;

        let mut headers = HeaderMap::new();
        headers.insert(
            reqwest::header::USER_AGENT,
            self.user_agent.parse().unwrap(),
        );

        let response = client
            .get(url)
            .headers(headers)
            .send()
            .await
            .map_err(|e| format!("Request failed: {}", e))?;

        let content_type = response
            .headers()
            .get(reqwest::header::CONTENT_TYPE)
            .and_then(|v| v.to_str().ok())
            .unwrap_or("");

        // Handle HTML content
        if content_type.contains("text/html") {
            let html = response
                .text()
                .await
                .map_err(|e| format!("Failed to read response: {}", e))?;
            return Ok(self.extract_text_from_html(&html));
        }

        // Handle JSON content
        if content_type.contains("application/json") {
            let text = response
                .text()
                .await
                .map_err(|e| format!("Failed to read response: {}", e))?;
            // Pretty print JSON
            if let Ok(parsed) = serde_json::from_str::<serde_json::Value>(&text) {
                return Ok(serde_json::to_string_pretty(&parsed).unwrap_or(text));
            }
            return Ok(text);
        }

        // For other content types, return raw text
        response
            .text()
            .await
            .map_err(|e| format!("Failed to read response: {}", e))
    }

    fn extract_text_from_html(&self, html: &str) -> String {
        let mut text = html.to_string();

        // Remove script and style tags with content using simple replacements
        text = strip_tag(&text, "script");
        text = strip_tag(&text, "style");

        // Remove all HTML tags
        text = strip_all_tags(&text);

        // Decode HTML entities
        text = self.decode_html_entities(&text);

        // Clean up whitespace
        let mut cleaned = String::new();
        let mut last_was_space = true;
        for c in text.chars() {
            if c.is_whitespace() {
                if !last_was_space {
                    cleaned.push(' ');
                    last_was_space = true;
                }
            } else {
                cleaned.push(c);
                last_was_space = false;
            }
        }

        cleaned.trim().to_string()
    }

    fn decode_html_entities(&self, text: &str) -> String {
        let entities = [
            ("&nbsp;", " "),
            ("&lt;", "<"),
            ("&gt;", ">"),
            ("&amp;", "&"),
            ("&quot;", "\""),
            ("&apos;", "'"),
            ("&mdash;", "—"),
            ("&ndash;", "–"),
            ("&copy;", "©"),
            ("&reg;", "®"),
            ("&trade;", "™"),
        ];

        let mut result = text.to_string();
        for (entity, replacement) in entities {
            result = result.replace(entity, replacement);
        }

        result
    }
}

fn strip_tag(s: &str, tag_name: &str) -> String {
    let open = format!("<{}>", tag_name);
    let close = format!("</{}>", tag_name);
    let mut result = s.to_string();

    // Keep removing until no more found (simple approach)
    while let Some(start) = result.to_lowercase().find(&open) {
        if let Some(end) = result.to_lowercase()[start..].find(&close) {
            let end_pos = start + end + close.len();
            result = format!("{}{}", &result[..start], &result[end_pos..]);
        } else {
            break;
        }
    }

    result
}

fn strip_all_tags(s: &str) -> String {
    let mut result = String::new();
    let mut in_tag = false;

    for c in s.chars() {
        if c == '<' {
            in_tag = true;
        } else if c == '>' {
            in_tag = false;
            result.push(' ');
        } else if !in_tag {
            result.push(c);
        }
    }

    result
}

fn extract_host(url: &str) -> Result<String, String> {
    let rest = url
        .strip_prefix("http://")
        .or_else(|| url.strip_prefix("https://"))
        .ok_or_else(|| "Only http:// and https:// URLs are allowed".to_string())?;

    let authority = rest
        .split(['/', '?', '#'])
        .next()
        .ok_or_else(|| "Invalid URL".to_string())?;

    if authority.is_empty() {
        return Err("URL must include a host".to_string());
    }

    let host = authority
        .split(':')
        .next()
        .unwrap_or_default()
        .trim()
        .to_lowercase();

    if host.is_empty() {
        return Err("URL must include a valid host".to_string());
    }

    Ok(host)
}

fn is_private_host(host: &str) -> bool {
    if host == "localhost" || host.ends_with(".localhost") {
        return true;
    }

    if host
        .rsplit('.')
        .next()
        .is_some_and(|label| label == "local")
    {
        return true;
    }

    if let Ok(ip) = host.parse::<std::net::IpAddr>() {
        return match ip {
            std::net::IpAddr::V4(v4) => {
                v4.is_loopback() || v4.is_private() || v4.is_link_local() || v4.is_unspecified()
            }
            std::net::IpAddr::V6(v6) => {
                v6.is_loopback() || v6.is_unspecified() || v6.is_multicast()
            }
        };
    }

    false
}

#[async_trait]
impl Tool for WebFetchTool {
    fn name(&self) -> &str {
        "web_fetch"
    }

    fn description(&self) -> &str {
        "Fetch a URL and extract readable text content. Supports HTML and JSON. Automatically extracts plain text from HTML, removes scripts and styles."
    }

    fn parameters_schema(&self) -> serde_json::Value {
        json!({
            "type": "object",
            "properties": {
                "url": {
                    "type": "string",
                    "description": "URL to fetch"
                }
            },
            "required": ["url"]
        })
    }

    fn read_only(&self) -> bool {
        true
    }

    async fn execute(&self, args: serde_json::Value) -> anyhow::Result<ToolResult> {
        let url = match args.get("url").and_then(|v| v.as_str()) {
            Some(u) => u,
            None => {
                return Ok(ToolResult {
                    success: false,
                    output: String::new(),
                    error: Some("Missing required parameter: url".to_string()),
                });
            }
        };

        let url = match self.validate_url(url) {
            Ok(u) => u,
            Err(e) => {
                return Ok(ToolResult {
                    success: false,
                    output: String::new(),
                    error: Some(e),
                });
            }
        };

        match self.fetch_content(&url).await {
            Ok(content) => Ok(ToolResult {
                success: true,
                output: self.truncate_response(&content),
                error: None,
            }),
            Err(e) => Ok(ToolResult {
                success: false,
                output: String::new(),
                error: Some(e),
            }),
        }
    }
}

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

    fn test_tool() -> WebFetchTool {
        WebFetchTool::new(50_000, 30)
    }

    #[tokio::test]
    async fn test_validate_url_success() {
        let tool = test_tool();
        let result = tool.validate_url("https://example.com");
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_validate_url_rejects_private() {
        let tool = test_tool();
        let result = tool.validate_url("https://localhost:8080");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("local/private"));
    }

    #[tokio::test]
    async fn test_validate_url_rejects_whitespace() {
        let tool = test_tool();
        let result = tool.validate_url("https://example.com/hello world");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("whitespace"));
    }

    #[tokio::test]
    async fn test_extract_text_simple() {
        let tool = test_tool();
        let html = "<html><body><p>Hello World</p></body></html>";
        let text = tool.extract_text_from_html(html);
        assert!(text.contains("Hello World"));
        assert!(!text.contains("<"));
    }

    #[tokio::test]
    async fn test_extract_text_removes_scripts() {
        let tool = test_tool();
        let html = "<html><body><script>alert('bad');</script><p>Good</p></body></html>";
        let text = tool.extract_text_from_html(html);
        assert!(text.contains("Good"));
        assert!(!text.contains("alert"));
    }

    #[tokio::test]
    async fn test_extract_text_removes_styles() {
        let tool = test_tool();
        let html = "<html><head><style>.x { color: red; }</style></head><body><p>Content</p></body></html>";
        let text = tool.extract_text_from_html(html);
        assert!(text.contains("Content"));
        assert!(!text.contains("color"));
    }

    #[tokio::test]
    async fn test_truncate_response_handles_multibyte_boundary() {
        let tool = WebFetchTool::new(3, 30);
        let text = "a\u{1F642}bc";
        let truncated = tool.truncate_response(text);
        assert_eq!(
            truncated,
            "a\u{1F642}b\n\n... [Response truncated due to size limit] ..."
        );
    }
}