use std::collections::HashMap;

use anyhow::{anyhow, Result};
use chrono::{format::ParseErrorKind, prelude::*};

use serde::{Deserialize, Serialize};
use ureq::Agent;
use url::Url;

use crate::tasks::Task;

use super::CALDAV_ICON;

#[derive(Serialize, Deserialize, Clone)]
#[serde(default)]
pub struct CalDavSource {
    #[serde(skip)]
    agent: ureq::Agent,
    pub calendar_name: String,
    pub username: String,
    pub password: String,
    pub base_url: String,
}

impl Default for CalDavSource {
    fn default() -> Self {
        Self {
            agent: Agent::new(),
            calendar_name: String::default(),
            username: String::default(),
            password: String::default(),
            base_url: String::default(),
        }
    }
}

const DATE_TIME_FORMAT: &str = "%Y%m%dT%H%M%S";
const DATE_ONLY_FORMAT: &str = "%Y%m%d";
const DATE_TIME_FORMAT_WITH_TZ: &str = "%Y%m%dT%H%M%S%#z";

fn parse_caldav_date(data: &str) -> Result<DateTime<Utc>> {
    match DateTime::parse_from_str(data, DATE_TIME_FORMAT_WITH_TZ) {
        Ok(result) => {
            let result_utc: DateTime<Utc> = DateTime::from(result);
            Ok(result_utc)
        }
        Err(e) => {
            if e.kind() == ParseErrorKind::TooShort {
                // Try without a timezone and intepret it as local
                let result_local =
                    NaiveDateTime::parse_from_str(data, DATE_TIME_FORMAT).or_else(|e| {
                        // This could be only a date without a time
                        if e.kind() == ParseErrorKind::TooShort {
                            let date = NaiveDate::parse_from_str(data, DATE_ONLY_FORMAT)?;
                            let end_of_day =
                                NaiveTime::from_hms_opt(23, 59, 59).unwrap_or_default();
                            Ok(date.and_time(end_of_day))
                        } else {
                            Err(e)
                        }
                    })?;
                match result_local.and_local_timezone(Local) {
                    chrono::offset::LocalResult::Single(result_local) => Ok(result_local.into()),

                    chrono::offset::LocalResult::Ambiguous(earliest, _) => Ok(earliest.into()),
                    chrono::offset::LocalResult::None => {
                        Err(anyhow!("The local time {:#?} does not exist", result_local))
                    }
                }
            } else {
                Err(anyhow::Error::from(e).context(format!("Could not parse CalDAV date '{data}'")))
            }
        }
    }
}

impl CalDavSource {
    pub fn query_tasks(&self) -> Result<Vec<Task>> {
        let base_url = Url::parse(&self.base_url)?;
        let credentials =
            minicaldav::Credentials::Basic(self.username.clone(), self.password.clone());
        let calendars = minicaldav::get_calendars(self.agent.clone(), &credentials, &base_url)?;
        let mut result = Vec::default();
        for c in calendars {
            if c.name().as_str() == self.calendar_name {
                let (todos, _errors) = minicaldav::get_todos(self.agent.clone(), &credentials, &c)?;
                for t in todos {
                    let props: HashMap<String, String> = t
                        .properties_todo()
                        .into_iter()
                        .map(|(k, v)| (k.to_string(), v.to_string()))
                        .collect();
                    let completed = props
                        .get("STATUS")
                        .filter(|s| s.as_str() == "COMPLETED")
                        .is_some()
                        || props.contains_key("COMPLETED");
                    // Check start due date if this task is ready to be started on
                    let start_due = props
                        .get("DTSTART")
                        .map(|raw| parse_caldav_date(raw))
                        .transpose()?;
                    let can_start = if let Some(start_due) = start_due {
                        let start_due: DateTime<Local> = DateTime::from(start_due);
                        Local::now().cmp(&start_due).is_ge()
                    } else {
                        true
                    };
                    if !completed && can_start {
                        if let Some(title) = props.get("SUMMARY") {
                            let title = unescape(title);
                            let description: String = props
                                .get("DESCRIPTION")
                                .map(|s| unescape(s))
                                .unwrap_or_default();
                            let due = props
                                .get("DUE")
                                .map(|raw| parse_caldav_date(raw))
                                .transpose()?;

                            let created = props
                                .get("CREATED")
                                .map(|raw| parse_caldav_date(raw))
                                .transpose()?;

                            let task = Task {
                                project: format!("{} {}", CALDAV_ICON, c.name()),
                                title: title.clone(),
                                description,
                                due: due.map(DateTime::<Utc>::from),
                                created: created.map(DateTime::<Utc>::from),
                                id: props.get("UID").cloned(),
                            };
                            result.push(task);
                        }
                    }
                }
            }
        }
        Ok(result)
    }
}

/// Unescape some known escaped characters in CalDAV.
/// This always allocates a new string.
fn unescape(val: &str) -> String {
    let mut chars = val.chars().peekable();
    let mut unescaped = String::new();

    loop {
        match chars.next() {
            None => break,
            Some(c) => {
                let escaped_char = if c == '\\' {
                    if let Some(escaped_char) = chars.peek() {
                        let escaped_char = *escaped_char;
                        match escaped_char {
                            _ if escaped_char == '\\'
                                || escaped_char == '"'
                                || escaped_char == '\''
                                || escaped_char == '`'
                                || escaped_char == '$'
                                || escaped_char == ',' =>
                            {
                                Some(escaped_char)
                            }
                            'n' => Some('\n'),
                            'r' => Some('\r'),
                            't' => Some('\t'),
                            _ => None,
                        }
                    } else {
                        None
                    }
                } else {
                    None
                };
                if let Some(escaped_char) = escaped_char {
                    unescaped.push(escaped_char);
                    // skip the escaped character instead of outputting it again
                    chars.next();
                } else {
                    unescaped.push(c);
                };
            }
        }
    }

    unescaped
}

#[cfg(test)]
mod tests;