use std::cell::Cell;
use std::error::Error;
use std::io::{self, Cursor, Read};
use std::path::PathBuf;
use std::sync::atomic::{AtomicUsize, Ordering};

use frontend::{
    DiagnosticKind, EndorReader, EndorSourceProvider, ResolvedEndorSource, SourceOrigin,
    SourceReadErrorKind, lex_source, parse_source, parse_source_expression,
};

struct OneByte<R>(R);

impl<R: Read> Read for OneByte<R> {
    fn read(&mut self, buffer: &mut [u8]) -> io::Result<usize> {
        let count = buffer.len().min(1);
        self.0.read(&mut buffer[..count])
    }
}

#[test]
fn strings_and_split_utf8_streams_produce_the_same_ast_and_exact_text() {
    let text = "// 日本語\r\nfunction 表示(): String { return \"こんにちは🌸\" }\r\n";
    let memory = EndorReader::from_text("<editor>", text);
    let stream = EndorReader::from_stream("<pipe>", OneByte(Cursor::new(text.as_bytes()))).unwrap();
    assert_eq!(memory.text(), text);
    assert_eq!(stream.text(), text);
    assert_eq!(
        parse_source(&memory).unwrap(),
        parse_source(&stream).unwrap()
    );
    assert_eq!(
        memory.origin(),
        &SourceOrigin::Text {
            name: "<editor>".into()
        }
    );
    assert_eq!(
        stream.origin(),
        &SourceOrigin::Stream {
            name: "<pipe>".into()
        }
    );
    assert_eq!(lex_source(&memory).unwrap(), lex_source(&stream).unwrap());
    let empty = EndorReader::from_stream("<empty>", Cursor::new(b"")).unwrap();
    assert!(empty.text().is_empty());
    assert_eq!(
        parse_source(&empty).unwrap_err().diagnostic.kind,
        DiagnosticKind::Syntax
    );
    let bom = EndorReader::from_stream("<bom>", Cursor::new("\u{feff}1".as_bytes())).unwrap();
    assert_eq!(bom.text(), "\u{feff}1");
    let error = lex_source(&bom).unwrap_err();
    assert_eq!(error.diagnostic.kind, DiagnosticKind::Lexical);
    assert_eq!(error.diagnostic.span.end, 3);
}

#[test]
fn source_diagnostics_keep_session_names_unicode_locations_and_original_offsets() {
    let source = EndorReader::from_text("<session:one/input:2>", "\"日\" + )");
    let error = parse_source_expression(&source).unwrap_err();
    assert_eq!(error.location.line, 1);
    assert_eq!(error.location.column, 7);
    assert_eq!(
        &source.text()[error.diagnostic.span.start..error.diagnostic.span.end],
        ")"
    );
    assert_eq!(error.origin, source.origin().clone());
    drop(source);
    assert!(error.to_string().starts_with("<session:one/input:2>:1:7:"));
    assert!(error.source().is_some());

    let source = EndorReader::from_text("<editor>", "\r\n\"日\\q\"");
    let error = lex_source(&source).unwrap_err();
    assert_eq!(error.diagnostic.kind, DiagnosticKind::Lexical);
    assert_eq!(error.location.line, 2);
    assert_eq!(error.location.column, 3);
    assert!(error.to_string().contains("unsupported string escape"));
}

#[test]
fn incomplete_or_invalid_utf8_is_rejected_without_replacement_characters() {
    for bytes in [vec![0xff], vec![0xe6, 0x97], vec![b'a', 0xff]] {
        let error = EndorReader::from_stream("<bytes>", OneByte(Cursor::new(bytes))).unwrap_err();
        assert!(matches!(error.kind, SourceReadErrorKind::InvalidUtf8(_)));
        assert!(error.to_string().contains("<bytes>: invalid UTF-8 at byte"));
        assert!(error.source().is_some());
    }
}

struct FailingStream(bool);

impl Read for FailingStream {
    fn read(&mut self, buffer: &mut [u8]) -> io::Result<usize> {
        if buffer.is_empty() {
            return Ok(0);
        }
        if !self.0 {
            self.0 = true;
            buffer[0] = b'x';
            return Ok(1);
        }
        Err(io::Error::other("stream failure"))
    }
}

#[test]
fn a_failed_stream_never_returns_partially_read_source() {
    let error = EndorReader::from_stream("<failed>", FailingStream(false)).unwrap_err();
    assert!(matches!(error.kind, SourceReadErrorKind::Io(_)));
    assert!(error.to_string().contains("stream failure"));
}

static NEXT_FILE: AtomicUsize = AtomicUsize::new(0);

struct SourceFile(PathBuf);

impl SourceFile {
    fn new(bytes: &[u8]) -> Self {
        let path = std::env::temp_dir().join(format!(
            "aster-reader-{}-{}.endor",
            std::process::id(),
            NEXT_FILE.fetch_add(1, Ordering::Relaxed)
        ));
        std::fs::write(&path, bytes).unwrap();
        Self(path)
    }
}

impl Drop for SourceFile {
    fn drop(&mut self) {
        let _ = std::fs::remove_file(&self.0);
    }
}

#[test]
fn file_sources_preserve_the_path_and_read_errors_are_not_lexical_errors() {
    let file = SourceFile::new(b"function f(): Number { return 1 }\r\n");
    let source = EndorReader::from_file(&file.0).unwrap();
    assert_eq!(
        source.origin(),
        &SourceOrigin::File {
            path: file.0.clone()
        }
    );
    assert!(source.text().ends_with("\r\n"));
    assert!(parse_source(&source).is_ok());
    let invalid = SourceFile::new(&[0xff]);
    let error = EndorReader::from_file(&invalid.0).unwrap_err();
    assert!(matches!(error.kind, SourceReadErrorKind::InvalidUtf8(_)));
    assert!(error.to_string().contains(&invalid.0.display().to_string()));
    let missing = file.0.with_extension("missing");
    let error = EndorReader::from_file(&missing).unwrap_err();
    let SourceReadErrorKind::Io(error) = error.kind else {
        panic!("expected I/O error");
    };
    assert_eq!(error.kind(), io::ErrorKind::NotFound);
}

struct Provider {
    calls: Cell<usize>,
}

impl EndorSourceProvider for Provider {
    fn load(&self, uri: &str) -> io::Result<ResolvedEndorSource> {
        assert_eq!(uri, "endor:workspace/namespace/function");
        let version = self.calls.get() + 1;
        self.calls.set(version);
        Ok(ResolvedEndorSource {
            revision: format!("revision-{version}"),
            bytes: format!("function f(): Number {{ return {version} }}").into_bytes(),
        })
    }
}

#[test]
fn each_uri_read_resolves_once_and_old_snapshots_keep_their_original_revision() {
    let provider = Provider {
        calls: Cell::new(0),
    };
    let uri = "endor:workspace/namespace/function";
    let first = EndorReader::from_endor(uri, &provider).unwrap();
    let second = EndorReader::from_endor(uri, &provider).unwrap();
    assert_eq!(provider.calls.get(), 2);
    assert!(first.text().contains("return 1"));
    assert!(second.text().contains("return 2"));
    assert_eq!(
        first.origin(),
        &SourceOrigin::Endor {
            uri: uri.into(),
            revision: "revision-1".into()
        }
    );
    assert_eq!(
        second.origin(),
        &SourceOrigin::Endor {
            uri: uri.into(),
            revision: "revision-2".into()
        }
    );
    assert!(parse_source(&first).is_ok());
    assert!(parse_source(&second).is_ok());
    assert_eq!(provider.calls.get(), 2); // Parsing never resolves the URI again.
}

struct StaticProvider {
    revision: &'static str,
    bytes: &'static [u8],
}

impl EndorSourceProvider for StaticProvider {
    fn load(&self, _uri: &str) -> io::Result<ResolvedEndorSource> {
        Ok(ResolvedEndorSource {
            revision: self.revision.into(),
            bytes: self.bytes.into(),
        })
    }
}

#[test]
fn uri_snapshots_require_a_revision_and_preserve_it_in_source_diagnostics() {
    let uri = "endor:workspace/namespace/function";
    let provider = StaticProvider {
        revision: "rev-one",
        bytes: b"function f(): Number { return ) }",
    };
    let source = EndorReader::from_endor(uri, &provider).unwrap();
    let error = parse_source(&source).unwrap_err();
    assert_eq!(error.origin, source.origin().clone());
    assert!(error.to_string().contains("[revision rev-one]"));
    let missing = StaticProvider {
        revision: " \t",
        bytes: b"1",
    };
    assert!(matches!(
        EndorReader::from_endor(uri, &missing).unwrap_err().kind,
        SourceReadErrorKind::MissingRevision
    ));
    let invalid = StaticProvider {
        revision: "rev-two",
        bytes: &[0xff],
    };
    let error = EndorReader::from_endor(uri, &invalid).unwrap_err();
    assert!(matches!(error.kind, SourceReadErrorKind::InvalidUtf8(_)));
    assert!(error.to_string().contains("[revision rev-two]"));
}

struct DeniedProvider;

impl EndorSourceProvider for DeniedProvider {
    fn load(&self, _uri: &str) -> io::Result<ResolvedEndorSource> {
        Err(io::Error::new(
            io::ErrorKind::PermissionDenied,
            "host denied source access",
        ))
    }
}

#[test]
fn invalid_uris_do_not_call_the_provider_and_denials_do_not_fall_back_to_files() {
    let provider = Provider {
        calls: Cell::new(0),
    };
    for uri in [
        "",
        "endor:",
        "file:source",
        "https://example.com",
        "endor:space here",
        "endor:bad\nname",
    ] {
        assert!(matches!(
            EndorReader::from_endor(uri, &provider).unwrap_err().kind,
            SourceReadErrorKind::InvalidEndorUri
        ));
    }
    assert_eq!(provider.calls.get(), 0);
    let error = EndorReader::from_endor("endor:anywhere", &DeniedProvider).unwrap_err();
    let SourceReadErrorKind::Io(error) = error.kind else {
        panic!("expected provider error");
    };
    assert_eq!(error.kind(), io::ErrorKind::PermissionDenied);
}