use std::io::{Seek, SeekFrom, Read, Result, Error, ErrorKind};
use byteorder::{ReadBytesExt, LE};
use genie_scx::Scenario;
use crate::{CPXVersion, CampaignHeader, ScenarioMeta};

pub fn read_fixed_str<R: Read>(input: &mut R, len: usize) -> Result<Option<String>> {
    let mut bytes = vec![0; len];
    input.read_exact(&mut bytes[0..len])?;

    if let Some(end) = bytes.iter().position(|&byte| byte == 0) {
        bytes.truncate(end);
    }
    if bytes.is_empty() {
        Ok(None)
    } else {
        String::from_utf8(bytes)
            .map(Some)
            .map_err(|_| Error::new(ErrorKind::Other, "invalid string"))
    }
}

fn read_campaign_header<R: Read>(input: &mut R) -> Result<CampaignHeader> {
    let mut version = [0; 4];
    input.read_exact(&mut version)?;
    let name = read_fixed_str(input, 256)?.expect("must have a name");
    let num_scenarios = input.read_i32::<LE>()? as usize;

    Ok(CampaignHeader {
        version,
        name,
        num_scenarios,
    })
}

fn read_scenario_meta<R: Read>(input: &mut R) -> Result<ScenarioMeta> {
    let size = input.read_i32::<LE>()? as usize;
    let offset = input.read_i32::<LE>()? as usize;
    let name = read_fixed_str(input, 255)?.expect("must have a name");
    let filename = read_fixed_str(input, 255)?.expect("must have a name");
    let mut padding = [0; 2];
    input.read_exact(&mut padding)?;

    Ok(ScenarioMeta {
        size,
        offset,
        name,
        filename,
    })
}

/// A campaign file containing scenario files.
#[derive(Debug, Clone)]
pub struct Campaign<R>
    where R: Read + Seek
{
    reader: R,
    header: CampaignHeader,
    entries: Vec<ScenarioMeta>,
}

impl<R> Campaign<R>
    where R: Read + Seek
{
    /// Create a campaign instance from a readable input.
    ///
    /// This immediately reads the campaign header and scenario metadata, but not the scenario
    /// files themselves.
    pub fn from(mut input: R) -> Result<Self> {
        let header = read_campaign_header(&mut input)?;
        let mut entries = vec![];
        for _ in 0..header.num_scenarios {
            entries.push(read_scenario_meta(&mut input)?);
        }

        Ok(Self {
            reader: input,
            header,
            entries,
        })
    }

    /// Consume this Campaign instance and get the reader.
    pub fn into_inner(self) -> R {
        self.reader
    }

    /// Get the campaign file version.
    pub fn version(&self) -> CPXVersion {
        self.header.version
    }

    pub fn name(&self) -> &str {
        &self.header.name
    }

    /// Iterate over the scenario metadata for this campaign.
    pub fn entries(&self) -> impl Iterator<Item = &ScenarioMeta> {
        self.entries.iter()
    }

    /// Get the number of scenarios in this campaign.
    pub fn len(&self) -> usize {
        self.entries.len()
    }

    pub fn is_empty(&self) -> bool {
        self.entries.is_empty()
    }

    pub fn get_name(&self, id: usize) -> Option<&str> {
        self.entries.get(id).map(|entry| entry.name.as_ref())
    }

    pub fn get_filename(&self, id: usize) -> Option<&str> {
        self.entries.get(id).map(|entry| entry.filename.as_ref())
    }

    fn get_id(&self, filename: &str) -> Option<usize> {
        self.entries.iter().position(|entry| entry.filename == filename)
    }

    /// Get a scenario by its file name.
    pub fn by_name(&mut self, filename: &str) -> Result<Scenario> {
        self.by_name_raw(filename)
            .map(std::io::Cursor::new)
            .and_then(|mut buf| Scenario::from(&mut buf))
    }

    /// Get a scenario by its campaign index.
    pub fn by_index(&mut self, index: usize) -> Result<Scenario> {
        self.by_index_raw(index)
            .map(std::io::Cursor::new)
            .and_then(|mut buf| Scenario::from(&mut buf))
    }

    /// Get a scenario file buffer by its file name.
    pub fn by_name_raw(&mut self, filename: &str) -> Result<Vec<u8>> {
        self.get_id(filename)
            .ok_or_else(|| std::io::Error::new(std::io::ErrorKind::NotFound, "scenario not found in campaign"))
            .and_then(|index| self.by_index_raw(index))
    }

    /// Get a scenario file buffer by its campaign index.
    pub fn by_index_raw(&mut self, index: usize) -> Result<Vec<u8>> {
        let entry = match self.entries.get(index) {
            Some(entry) => entry,
            None => return Err(std::io::Error::new(std::io::ErrorKind::NotFound, "scenario not found in campaign")),
        };

        let mut result = vec![];

        self.reader.seek(SeekFrom::Start(entry.offset as u64))?;
        self.reader.by_ref()
            .take(entry.size as u64)
            .read_to_end(&mut result)?;

        Ok(result)
    }
}

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

    /// Source: http://aoe.heavengames.com/dl-php/showfile.php?fileid=1678
    #[test]
    fn aoe1_trial_cpn() {
        let f = File::open("test/campaigns/Armies at War A Combat Showcase.cpn").unwrap();
        let mut c = Campaign::from(f).expect("could not read meta");

        assert_eq!(c.version(), *b"1.00");
        assert_eq!(c.name(), "Armies at War, A Combat Showcase");
        assert_eq!(c.len(), 1);
        let names: Vec<&String> = c.entries()
            .map(|e| &e.name)
            .collect();
        assert_eq!(names, vec!["Bronze Age Art of War"]);
        let filenames: Vec<&String> = c.entries()
            .map(|e| &e.filename)
            .collect();
        assert_eq!(filenames, vec!["Bronze Age Art of War.scn"]);

        c.by_index_raw(0).expect("could not read raw file");
        c.by_name_raw("Bronze Age Art of War.scn").expect("could not read raw file");
    }

    #[test]
    fn aoe1_beta_cpn() {
        let f = File::open("test/campaigns/Rise of Egypt Learning Campaign.cpn").unwrap();
        let c = Campaign::from(f).expect("could not read meta");

        assert_eq!(c.version(), *b"1.00");
        assert_eq!(c.name(), "Rise of Egypt Learning Campaign");
        assert_eq!(c.len(), 12);
        let filenames: Vec<&String> = c.entries()
            .map(|e| &e.filename)
            .collect();
        assert_eq!(filenames, vec![
            "HUNTING.scn",
            "FORAGING.scn",
            "Discoveries.scn",
            "Dawn of a New Age.scn",
            "SKIRMISH.scn",
            "Lands Unknown.scn",
            "FARMING.scn",
            "TRADE.scn",
            "CRUSADE.scn",
            "Establish a Second Colony.scn",
            "Naval Battle.scn",
            "Siege Battle.scn",
        ]);
    }
}