// title/content.rs from rustii-lib (c) 2025 NinjaCheetah & Contributors
// https://github.com/NinjaCheetah/rustii-lib
//
// Implements content parsing and editing.

use std::error::Error;
use std::fmt;
use std::io::{Cursor, Read, Seek, SeekFrom, Write};
use sha1::{Sha1, Digest};
use crate::title::tmd::ContentRecord;
use crate::title::crypto::decrypt_content;

#[derive(Debug)]
pub enum ContentError {
    IndexNotFound,
    CIDNotFound,
    BadHash,
}

impl fmt::Display for ContentError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let description = match *self {
            ContentError::IndexNotFound => "The specified content index does not exist.",
            ContentError::CIDNotFound => "The specified Content ID does not exist.",
            ContentError::BadHash => "The content hash does not match the expected hash.",
        };
        f.write_str(description)
    }
}

impl Error for ContentError {}

#[derive(Debug)]
pub struct ContentRegion {
    pub content_records: Vec<ContentRecord>,
    pub content_region_size: u32,
    pub num_contents: u16,
    pub content_start_offsets: Vec<u64>,
    pub contents: Vec<Vec<u8>>,
}

impl ContentRegion {
    pub fn from_bytes(data: &[u8], content_records: Vec<ContentRecord>) -> Result<Self, std::io::Error> {
        let content_region_size = data.len() as u32;
        let num_contents = content_records.len() as u16;
        // Calculate the starting offsets of each content.
        let content_start_offsets: Vec<u64> = std::iter::once(0)
            .chain(content_records.iter().scan(0, |offset, record| {
                *offset += record.content_size;
                if record.content_size % 64 != 0 {
                    *offset += 64 - (record.content_size % 64);
                }
                Some(*offset)
            })).take(content_records.len()).collect(); // Trims the extra final entry.
        let total_content_size: u64 = content_records.iter().map(|x| (x.content_size + 63) & !63).sum();
        // Parse the content blob and create a vector of vectors from it.
        // Check that the content blob matches the total size of all the contents in the records.
        if content_region_size != total_content_size as u32 {
            return Err(std::io::Error::new(std::io::ErrorKind::InvalidData, "Invalid content blob for content records"));
        }
        let mut contents: Vec<Vec<u8>> = Vec::with_capacity(num_contents as usize);
        let mut buf = Cursor::new(data);
        for i in 0..num_contents {
            buf.seek(SeekFrom::Start(content_start_offsets[i as usize]))?;
            let size = (content_records[i as usize].content_size + 15) & !15;
            let mut content = vec![0u8; size as usize];
            buf.read_exact(&mut content)?;
            contents.push(content);
        }
        Ok(ContentRegion {
            content_records,
            content_region_size,
            num_contents,
            content_start_offsets,
            contents,
        })
    }
    
    pub fn to_bytes(&self) -> Result<Vec<u8>, std::io::Error> {
        let mut buf: Vec<u8> = Vec::new();
        for i in 0..self.num_contents {
            let mut content = self.contents[i as usize].clone();
            // Round up size to nearest 64 to add appropriate padding.
            content.resize((content.len() + 63) & !63, 0);
            buf.write_all(&content)?;
        }
        Ok(buf)
    }
    
    pub fn get_enc_content_by_index(&self, index: usize) -> Result<Vec<u8>, ContentError> {
        let content = self.contents.get(index).ok_or(ContentError::IndexNotFound)?;
        Ok(content.clone())
    }

    pub fn get_content_by_index(&self, index: usize, title_key: [u8; 16]) -> Result<Vec<u8>, ContentError> {
        let content = self.get_enc_content_by_index(index)?;
        // Verify the hash of the decrypted content against its record.
        let content_dec = decrypt_content(&content, title_key, self.content_records[index].index);
        let mut hasher = Sha1::new();
        hasher.update(content_dec.clone());
        let result = hasher.finalize();
        if result[..] != self.content_records[index].content_hash {
            return Err(ContentError::BadHash);
        }
        Ok(content_dec)
    }

    pub fn get_enc_content_by_cid(&self, cid: u32) -> Result<Vec<u8>, ContentError> {
        let index = self.content_records.iter().position(|x| x.content_id == cid);
        if let Some(index) = index {
            let content = self.get_enc_content_by_index(index).map_err(|_| ContentError::CIDNotFound)?;
            Ok(content)
        } else {
            Err(ContentError::CIDNotFound)
        }
    }
    
    pub fn get_content_by_cid(&self, cid: u32, title_key: [u8; 16]) -> Result<Vec<u8>, ContentError> {
        let index = self.content_records.iter().position(|x| x.content_id == cid);
        if let Some(index) = index {
            let content_dec = self.get_content_by_index(index, title_key)?;
            Ok(content_dec)
        } else {
            Err(ContentError::CIDNotFound)
        }
    }
}