//! Source location utilities.

pub use crate::span::Span;
#[cfg(feature = "deserialize")]
use granit_parser::Span as ParserSpan;
use serde_core::de::{self, IgnoredAny, MapAccess, Visitor};

/// Row/column location within the source YAML document (1-indexed, character-based).
///
/// This type is used for both:
/// - deserialization error reporting ([`crate::Error`])
/// - span-aware values ([`crate::Spanned`])
///
/// # Example
///
/// ```
/// # #[cfg(feature = "deserialize")]
/// # {
/// use serde::Deserialize;
///
/// #[derive(Deserialize, Debug)]
/// struct Doc {
///     val: String,
/// }
///
/// // 1. Parse invalid YAML (type mismatch: expected string, found sequence)
/// // Due emoji character and byte offsets are different.
/// let yaml = "val🔑: [1, 2]";
/// let err: Result<Doc, _> = serde_saphyr::from_str(yaml);
///
/// // 2. Obtain the error and its location
/// if let Err(e) = err {
///     if let Some(loc) = e.location() {
///         // 3. Print row, column, and byte offsets
///         // Output: Error at line 1, col 7. Byte offset: 9
///         println!("Error at line {}, col {}", loc.line(), loc.column());
///         if let Some(byte_off) = loc.span().byte_offset() {
///             println!("Byte offset: {}", byte_off);
///         }
///     }
/// }
/// # }
/// ```
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct Location {
    /// 1-indexed row number in the input stream.
    pub(crate) line: u32,
    /// 1-indexed column number in the input stream.
    pub(crate) column: u32,
    /// Character-based span within the document
    /// Byte offsets are available for string source but not from the reader.
    pub(crate) span: Span,
    /// Numeric id of the source where this location is from.
    pub(crate) source_id: u32,
}

// As we do not use serde here (serde core only), we need manual implementation.
impl<'de> serde_core::Deserialize<'de> for Location {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde_core::Deserializer<'de>,
    {
        enum Field {
            Line,
            Column,
            Span,
            SourceId,
            Ignore,
        }

        impl<'de> serde_core::Deserialize<'de> for Field {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: serde_core::Deserializer<'de>,
            {
                struct FieldVisitor;

                impl<'a> Visitor<'a> for FieldVisitor {
                    type Value = Field;

                    fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                        f.write_str("a Location field")
                    }

                    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
                    where
                        E: de::Error,
                    {
                        Ok(match value {
                            "line" => Field::Line,
                            "column" => Field::Column,
                            "span" => Field::Span,
                            "source_id" => Field::SourceId,
                            _ => Field::Ignore,
                        })
                    }
                }

                deserializer.deserialize_identifier(FieldVisitor)
            }
        }

        struct LocationVisitor;

        impl<'de> Visitor<'de> for LocationVisitor {
            type Value = Location;

            fn expecting(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                f.write_str("a source location")
            }

            fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
            where
                A: MapAccess<'de>,
            {
                let mut line = None;
                let mut column = None;
                let mut span = None;
                let mut source_id = None;

                while let Some(field) = map.next_key::<Field>()? {
                    match field {
                        Field::Line => {
                            if line.is_some() {
                                return Err(de::Error::duplicate_field("line"));
                            }
                            line = Some(map.next_value()?);
                        }
                        Field::Column => {
                            if column.is_some() {
                                return Err(de::Error::duplicate_field("column"));
                            }
                            column = Some(map.next_value()?);
                        }
                        Field::Span => {
                            if span.is_some() {
                                return Err(de::Error::duplicate_field("span"));
                            }
                            span = Some(map.next_value()?);
                        }
                        Field::SourceId => {
                            if source_id.is_some() {
                                return Err(de::Error::duplicate_field("source_id"));
                            }
                            source_id = Some(map.next_value()?);
                        }
                        Field::Ignore => {
                            let _ = map.next_value::<IgnoredAny>()?;
                        }
                    }
                }

                let line = line.ok_or_else(|| de::Error::missing_field("line"))?;
                let column = column.ok_or_else(|| de::Error::missing_field("column"))?;
                let span = span.unwrap_or_default();
                let source_id = source_id.unwrap_or_default();

                Ok(Location {
                    line,
                    column,
                    span,
                    source_id,
                })
            }
        }

        const FIELDS: &[&str] = &["line", "column", "span", "source_id"];
        deserializer.deserialize_struct("Location", FIELDS, LocationVisitor)
    }
}

impl Location {
    /// serde_yaml-compatible line information.
    #[inline]
    pub fn line(&self) -> u64 {
        self.line as u64
    }

    /// serde_yaml-compatible column information.
    #[inline]
    pub fn column(&self) -> u64 {
        self.column as u64
    }

    /// Character-based span within the source document.
    /// For string source, it also can provide byte offsets.
    #[inline]
    pub fn span(&self) -> Span {
        self.span
    }

    /// Numeric id of the source.
    #[inline]
    pub fn source_id(&self) -> u32 {
        self.source_id
    }
}

impl Location {
    /// Sentinel value meaning "location unknown".
    ///
    /// Used when a precise position is not yet available at error creation time.
    pub const UNKNOWN: Self = Self {
        line: 0,
        column: 0,
        span: Span::UNKNOWN,
        source_id: 0,
    };

    /// Create a new location record.
    ///
    /// Arguments:
    /// - `line`: 1-indexed line.
    /// - `column`: 1-indexed column.
    #[cfg(feature = "deserialize")]
    pub(crate) const fn new(line: usize, column: usize) -> Self {
        // 4 Gb is larger than any YAML document I can imagine, and also this is
        // error reporting only.
        Self {
            line: line as u32,
            column: column as u32,
            span: Span::UNKNOWN,
            source_id: 0,
        }
    }

    #[cfg(feature = "deserialize")]
    pub(crate) const fn with_span(mut self, span: Span) -> Self {
        self.span = span;
        self
    }

    #[cfg(feature = "deserialize")]
    pub(crate) const fn with_source_id(mut self, source_id: u32) -> Self {
        self.source_id = source_id;
        self
    }
}

/// Convert a `granit_parser::Span` to a 1-indexed [`Location`].
///
/// Called by:
/// - The live events adapter for each raw parser event.
///
/// The resulting [`Location::span`] carries character offsets/lengths (not bytes),
/// matching what the parser reports.
#[cfg(feature = "deserialize")]
pub(crate) fn location_from_span(span: &ParserSpan) -> Location {
    let start = &span.start;
    let end = &span.end;

    let mut out = Span::new(start.index() as u64, span.len() as u64);

    if let (Some(start_byte), Some(end_byte)) = (start.byte_offset(), end.byte_offset()) {
        let byte_len = end_byte.saturating_sub(start_byte);

        #[cfg(not(feature = "huge_documents"))]
        {
            // If byte offsets exceed 4 GiB on non-huge builds, mark byte info as unavailable.
            if start_byte <= (u32::MAX as usize) && byte_len <= (u32::MAX as usize) {
                out = out.with_byte_info(start_byte as u64, byte_len as u64);
            }
        }

        #[cfg(feature = "huge_documents")]
        {
            out = out.with_byte_info(start_byte as u64, byte_len as u64);
        }
    }

    Location::new(start.line(), start.col() + 1).with_span(out)
}

/// Pair of locations for values that may come indirectly from YAML anchors.
///
/// - `reference_location`: where the value is *used* (alias/merge site).
/// - `defined_location`: where the value is *defined* (anchor definition site).
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct Locations {
    pub reference_location: Location,
    pub defined_location: Location,
}

impl Locations {
    #[cfg_attr(not(any(feature = "garde", feature = "validator")), allow(dead_code))]
    pub(crate) const UNKNOWN: Locations = Locations {
        reference_location: Location::UNKNOWN,
        defined_location: Location::UNKNOWN,
    };

    #[inline]
    #[cfg(feature = "deserialize")]
    pub(crate) fn same(location: &Location) -> Option<Locations> {
        if location == &Location::UNKNOWN {
            None
        } else {
            Some(Locations {
                reference_location: *location,
                defined_location: *location,
            })
        }
    }

    #[inline]
    pub fn primary_location(self) -> Option<Location> {
        if self.reference_location != Location::UNKNOWN {
            Some(self.reference_location)
        } else if self.defined_location != Location::UNKNOWN {
            Some(self.defined_location)
        } else {
            None
        }
    }
}

#[cfg(all(test, feature = "deserialize"))]
mod tests {
    use super::*;
    use granit_parser::{Event, Parser};

    #[test]
    fn test_location_from_span() {
        let input = "foo";
        let mut parser = Parser::new_from_str(input);

        // StreamStart
        parser.next().unwrap().unwrap();
        // DocumentStart
        parser.next().unwrap().unwrap();

        // Scalar "foo"
        let (event, parser_span) = parser.next().unwrap().unwrap();
        assert!(matches!(event, Event::Scalar(..)));

        let loc = location_from_span(&parser_span);

        // "foo" starts at line 1, col 1
        assert_eq!(loc.line(), 1);
        assert_eq!(loc.column(), 1);

        let span = loc.span();
        assert_eq!(span.offset(), 0);
        assert_eq!(span.len(), 3);
        assert!(!span.is_empty());

        // "foo" is 3 bytes
        assert_eq!(span.byte_offset(), Some(0));
        assert_eq!(span.byte_len(), Some(3));
    }

    #[test]
    fn test_location_from_span_offset() {
        let input = "  bar";
        let mut parser = Parser::new_from_str(input);

        parser.next().unwrap().unwrap();
        parser.next().unwrap().unwrap();

        let (event, parser_span) = parser.next().unwrap().unwrap();
        assert!(matches!(event, Event::Scalar(..)));

        let loc = location_from_span(&parser_span);

        // "  bar" -> "bar" starts at line 1, col 3
        // Wait, does granit-parser count columns 0-indexed or 1-indexed?
        // location_from_span does `start.col() + 1`. So if parser is 0-indexed, loc is 1-indexed.
        // col 0: ' ', col 1: ' ', col 2: 'b'.
        // So start.col() should be 2. location.column() should be 3.
        assert_eq!(loc.line(), 1);
        assert_eq!(loc.column(), 3);

        let span = loc.span();
        assert_eq!(span.offset(), 2);
        assert_eq!(span.len(), 3);
    }

    #[test]
    fn test_span_methods() {
        let span = Span::new(10, 5).with_byte_info(20, 5);

        assert_eq!(span.offset(), 10);
        assert_eq!(span.len(), 5);
        assert!(!span.is_empty());
        assert_eq!(span.byte_offset(), Some(20));
        assert_eq!(span.byte_len(), Some(5));

        let empty_span = Span::new(10, 0).with_byte_info(20, 0);
        assert!(empty_span.is_empty());
    }

    #[test]
    fn test_location_methods() {
        let loc = Location::new(5, 10);
        assert_eq!(loc.line(), 5);
        assert_eq!(loc.column(), 10);
        assert!(loc.span().is_empty()); // initialized to Span::UNKNOWN which is usually 0,0,0

        let span = Span::new(100, 20).with_byte_info(100, 20);
        let loc_with_span = loc.with_span(span);

        assert_eq!(loc_with_span.line(), 5);
        assert_eq!(loc_with_span.column(), 10);
        assert_eq!(loc_with_span.span(), span);
    }

    #[test]
    fn deserialize_location_accepts_optional_and_unknown_fields() {
        let loc: Location = serde_json::from_str(
            r#"{
                "ignored": true,
                "line": 5,
                "column": 10,
                "span": { "offset": 20, "len": 3, "byte_info": [40, 3] },
                "source_id": 7
            }"#,
        )
        .unwrap();

        assert_eq!(loc.line(), 5);
        assert_eq!(loc.column(), 10);
        assert_eq!(loc.span().offset(), 20);
        assert_eq!(loc.span().len(), 3);
        assert_eq!(loc.span().byte_offset(), Some(40));
        assert_eq!(loc.span().byte_len(), Some(3));
        assert_eq!(loc.source_id(), 7);
    }

    #[test]
    fn deserialize_location_defaults_span_and_source_id() {
        let loc: Location = serde_json::from_str(r#"{ "line": 1, "column": 2 }"#).unwrap();

        assert_eq!(loc.line(), 1);
        assert_eq!(loc.column(), 2);
        assert_eq!(loc.span(), Span::default());
        assert_eq!(loc.source_id(), 0);
    }

    #[test]
    fn deserialize_location_rejects_duplicate_required_fields() {
        let err = serde_json::from_str::<Location>(r#"{ "line": 1, "line": 2, "column": 3 }"#)
            .unwrap_err();

        assert!(err.to_string().contains("duplicate field `line`"));
    }

    #[test]
    fn deserialize_location_rejects_duplicate_defaulted_fields() {
        let duplicate_span = serde_json::from_str::<Location>(
            r#"{
                "line": 1,
                "column": 2,
                "span": { "offset": 1, "len": 1, "byte_info": [0, 0] },
                "span": { "offset": 2, "len": 2, "byte_info": [0, 0] }
            }"#,
        )
        .unwrap_err();
        assert!(
            duplicate_span
                .to_string()
                .contains("duplicate field `span`")
        );

        let duplicate_source_id = serde_json::from_str::<Location>(
            r#"{ "line": 1, "column": 2, "source_id": 1, "source_id": 2 }"#,
        )
        .unwrap_err();
        assert!(
            duplicate_source_id
                .to_string()
                .contains("duplicate field `source_id`")
        );
    }

    #[test]
    fn deserialize_location_rejects_missing_required_fields() {
        let err = serde_json::from_str::<Location>(r#"{ "line": 1 }"#).unwrap_err();

        assert!(err.to_string().contains("missing field `column`"));
    }

    #[test]
    fn test_locations_methods() {
        let l1 = Location::new(1, 1);
        let locations = Locations::same(&l1).unwrap();
        assert_eq!(locations.reference_location, l1);
        assert_eq!(locations.defined_location, l1);

        assert_eq!(locations.primary_location(), Some(l1));

        let l2 = Location::new(2, 2);
        let locations_diff = Locations {
            reference_location: l1,
            defined_location: l2,
        };
        assert_eq!(locations_diff.primary_location(), Some(l1));

        let locations_unknown = Locations {
            reference_location: Location::UNKNOWN,
            defined_location: l2,
        };
        assert_eq!(locations_unknown.primary_location(), Some(l2));

        assert!(Locations::same(&Location::UNKNOWN).is_none());
    }
}
