use reqwest::Client;
use serde::Deserialize;

#[derive(Debug, Clone)]
pub struct Api {
    client: Client,
    pub server_url: String,
    pub auth_token: String,
}

#[derive(Debug, Deserialize)]
struct StreamContents {
    items: Vec<Item>,
}

#[derive(Debug, Deserialize)]
struct Item {
    id: String,
    title: Option<String>,
    origin: Option<Origin>,
    canonical: Option<Vec<Link>>,
    published: Option<i64>,
    summary: Option<Summary>,
    author: Option<String>,
    categories: Option<Vec<String>>,
}

#[derive(Debug, Deserialize)]
struct Origin {
    title: Option<String>,
}

#[derive(Debug, Deserialize)]
struct Link {
    href: String,
}

#[derive(Debug, Deserialize)]
struct Summary {
    content: Option<String>,
}

use crate::model::Article;

/// Return the candidate base URLs to try in order.
/// Miniflux serves the Greader API at the server root;
/// FreshRSS serves it at /api/greader.php.
fn candidate_base_urls(server_url: &str) -> Vec<String> {
    let base = server_url.trim_end_matches('/');
    if base.ends_with("/api/greader.php") {
        vec![base.to_string()]
    } else {
        vec![
            base.to_string(),
            format!("{base}/api/greader.php"),
        ]
    }
}

impl Api {
    pub async fn login(
        server_url: &str,
        username: &str,
        password: &str,
    ) -> Result<Self, String> {
        let client = Client::new();
        let candidates = candidate_base_urls(server_url);
        let mut last_err = String::new();

        for base in candidates {
            let url = format!("{base}/accounts/ClientLogin");
            let resp = match client
                .post(&url)
                .form(&[("Email", username), ("Passwd", password)])
                .send()
                .await
            {
                Ok(r) => r,
                Err(e) => { last_err = e.to_string(); continue; }
            };

            let status = resp.status();
            let body = resp.text().await.map_err(|e| e.to_string())?;

            if !status.is_success() {
                last_err = format!("Login failed ({}): {}", status.as_u16(), human_error(&body, status.as_u16()));
                continue;
            }

            let auth_token = match body.lines().find_map(|l| l.strip_prefix("Auth=")) {
                Some(t) => t.to_string(),
                None => {
                    last_err = if looks_like_html(&body) {
                        format!(
                            "The server at {base} does not appear to be a \
                             Greader API endpoint. Check your server URL."
                        )
                    } else {
                        format!("Unexpected response from server: {}", body.trim())
                    };
                    continue;
                }
            };

            return Ok(Self { client, server_url: base, auth_token });
        }

        Err(last_err)
    }

    pub async fn fetch_write_token(&self) -> Result<String, String> {
        let url = format!("{}/reader/api/0/token", self.server_url);
        let resp = self
            .client
            .get(&url)
            .header("Authorization", format!("GoogleLogin auth={}", self.auth_token))
            .send()
            .await
            .map_err(|e| e.to_string())?;

        if !resp.status().is_success() {
            return Err(format!("Failed to fetch write token: {}", resp.status()));
        }

        resp.text().await.map_err(|e| e.to_string()).map(|s| s.trim().to_string())
    }

    pub async fn fetch_unread(&self) -> Result<Vec<Article>, String> {
        let url = format!(
            "{}/reader/api/0/stream/contents/reading-list\
             ?xt=user/-/state/com.google/read&n=200&output=json",
            self.server_url
        );
        let resp = self
            .client
            .get(&url)
            .header("Authorization", format!("GoogleLogin auth={}", self.auth_token))
            .send()
            .await
            .map_err(|e| e.to_string())?;

        if !resp.status().is_success() {
            return Err(format!("Failed to fetch articles: {}", resp.status()));
        }

        let stream: StreamContents = resp.json().await.map_err(|e| e.to_string())?;

        Ok(stream.items.into_iter().map(|item| {
            let unread = !item.categories.as_deref().unwrap_or_default()
                .iter()
                .any(|c| c == "user/-/state/com.google/read");
            let content = item.summary
                .as_ref()
                .and_then(|s| s.content.clone())
                .unwrap_or_default();
            let excerpt = plain_text_excerpt(&content, 150);
            Article {
                id: item.id,
                title: item.title.unwrap_or_default(),
                feed_title: item.origin.as_ref().and_then(|o| o.title.clone()).unwrap_or_default(),
                author: item.author.unwrap_or_default(),
                link: item.canonical.as_ref()
                    .and_then(|v| v.first())
                    .map(|l| l.href.clone())
                    .unwrap_or_default(),
                published: item.published.unwrap_or(0),
                content,
                excerpt,
                unread,
            }
        }).collect())
    }

    pub async fn mark_read(
        &self,
        write_token: &str,
        item_id: &str,
    ) -> Result<(), String> {
        self.edit_tag(write_token, item_id, "a", "user/-/state/com.google/read").await
    }

    pub async fn mark_unread(
        &self,
        write_token: &str,
        item_id: &str,
    ) -> Result<(), String> {
        self.edit_tag(write_token, item_id, "r", "user/-/state/com.google/read").await
    }

    async fn edit_tag(
        &self,
        write_token: &str,
        item_id: &str,
        action_key: &str,
        state: &str,
    ) -> Result<(), String> {
        let url = format!("{}/reader/api/0/edit-tag", self.server_url);
        let resp = self
            .client
            .post(&url)
            .header("Authorization", format!("GoogleLogin auth={}", self.auth_token))
            .form(&[("i", item_id), (action_key, state), ("T", write_token)])
            .send()
            .await
            .map_err(|e| e.to_string())?;

        if resp.status() == reqwest::StatusCode::UNAUTHORIZED {
            return Err("UNAUTHORIZED".to_string());
        }
        if !resp.status().is_success() {
            return Err(format!("edit-tag failed: {}", resp.status()));
        }
        Ok(())
    }
}

fn looks_like_html(body: &str) -> bool {
    let trimmed = body.trim_start();
    trimmed.starts_with("<!") || trimmed.to_ascii_lowercase().starts_with("<html")
}

fn human_error(body: &str, status: u16) -> String {
    if looks_like_html(body) {
        match status {
            401 | 403 => "Wrong username or password.".to_string(),
            404 => "API endpoint not found. Check your server URL.".to_string(),
            _ => format!("Server returned HTTP {status}. Check your server URL."),
        }
    } else {
        let trimmed = body.trim();
        if trimmed.is_empty() {
            format!("Server returned HTTP {status} with no message.")
        } else {
            trimmed.to_string()
        }
    }
}

fn plain_text_excerpt(html: &str, max_chars: usize) -> String {
    // Very simple HTML stripper — remove tags, collapse whitespace
    let mut out = String::with_capacity(html.len());
    let mut in_tag = false;
    for ch in html.chars() {
        match ch {
            '<' => in_tag = true,
            '>' => in_tag = false,
            c if !in_tag => out.push(c),
            _ => {}
        }
    }
    let collapsed: String = out.split_whitespace().collect::<Vec<_>>().join(" ");
    let decoded = decode_html_entities(&collapsed);
    if decoded.chars().count() <= max_chars {
        decoded
    } else {
        decoded.chars().take(max_chars).collect::<String>() + "…"
    }
}

fn decode_html_entities(s: &str) -> String {
    s.replace("&amp;", "&")
     .replace("&lt;", "<")
     .replace("&gt;", ">")
     .replace("&quot;", "\"")
     .replace("&apos;", "'")
     .replace("&#39;", "'")
     .replace("&nbsp;", " ")
}